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We report a 51-year-old man with severe ischemic cardiomyopathy and heart failure in whom incessant bigeminal ventricular ectopy failed to generate a detectable arterial pressure. This created a mechanical bradycardia despite an adequate electrical heart rate. Dual chamber pacing increased the effective heart rate and allowed discontinuation of an intraaortic balloon pump from which the patient could not otherwise be weaned. [ABSTRACT FROM AUTHOR]

Post-cardiac surgery atrial fibrillation (AF) places patients at risk for thromboembolism and stroke, while the surgery and cardiopulmonary bypass alter the multiple factors of coagulation and may increase the tendency to bleed. It is in the context of this complex clinical picture that the physician must make decisions regarding the risks and benefits of anticoagulation therapy to lower the risk for thromboembolism and stroke associated with postoperative AF. Physicians must also weigh the usually transient and self-limited duration of new-onset postoperative AF against the potential for postoperative bleeding if anticoagulation therapy is started. No randomized, controlled clinical trials are available that specifically address the problem of anticoagulation therapy for the postoperative AF. In that context, recommendations are based on the established therapy for nonsurgical situations modified by the potential risk of bleeding in the postoperative patient. [ABSTRACT FROM AUTHOR]

Background: Etripamil is a fast-acting, intranasally administered calcium-channel blocker in development for on-demand therapy outside a health-care setting for paroxysmal supraventricular tachycardia. We aimed to evaluate the efficacy and safety of etripamil 70 mg nasal spray using a symptom-prompted, repeat-dose regimen for acute conversion of atrioventricular-nodal-dependent paroxysmal supraventricular tachycardia to sinus rhythm within 30 min., Methods: RAPID was a multicentre, randomised, placebo-controlled, event-driven trial, conducted at 160 sites in North America and Europe as part 2 of the NODE-301 study. Eligible patients were aged at least 18 years and had a history of paroxysmal supraventricular tachycardia with sustained, symptomatic episodes (≥20 min) as documented by electrocardiogram. Patients were administered two test doses of intranasal etripamil (each 70 mg, 10 min apart) during sinus rhythm; those who tolerated the test doses were randomly assigned (1:1) using an interactive response technology system to receive either etripamil or placebo. Prompted by symptoms of paroxysmal supraventricular tachycardia, patients self-administered a first dose of intranasal 70 mg etripamil or placebo and, if symptoms persisted beyond 10 min, a repeat dose. Continuously recorded electrocardiographic data were adjudicated, by individuals masked to patient assignment, for the primary endpoint of time to conversion of paroxysmal supraventricular tachycardia to sinus rhythm for at least 30 s within 30 min after the first dose, which was measured in all patients who administered blinded study drug for a confirmed atrioventricular-nodal-dependent event. Safety outcomes were assessed in all patients who self-administered blinded study drug for an episode of perceived paroxysmal supraventricular tachycardia. This trial is registered at ClinicalTrials.gov, NCT03464019, and is complete., Findings: Between Oct 13, 2020, and July 20, 2022, among 692 patients randomly assigned, 184 (99 from the etripamil group and 85 from the placebo group) self-administered study drug for atrioventricular-nodal-dependent paroxysmal supraventricular tachycardia, with diagnosis and timing confirmed. Kaplan-Meier estimates of conversion rates by 30 min were 64% (63/99) with etripamil and 31% (26/85) with placebo (hazard ratio 2·62; 95% CI 1·66-4·15; p<0·0001). Median time to conversion was 17·2 min (95% CI 13·4-26·5) with the etripamil regimen versus 53·5 min (38·7-87·3) with placebo. Prespecified sensitivity analyses of the primary assessment were conducted to test robustness, yielding supporting results. Treatment-emergent adverse events occurred in 68 (50%) of 99 patients treated with etripamil and 12 (11%) of 85 patients in the placebo group, most of which were located at the administration site and were mild or moderate, and all of which were transient and resolved without intervention. Adverse events occurring in at least 5% of patients treated with etripamil were nasal discomfort (23%), nasal congestion (13%), and rhinorrhea (9%). No serious etripamil-related adverse events or deaths were reported., Interpretation: Using a symptom-prompted, self-administered, initial and optional-repeat-dosing regimen, intranasal etripamil was well tolerated, safe, and superior to placebo for the rapid conversion of atrioventricular-nodal-dependent paroxysmal supraventricular tachycardia to sinus rhythm. This approach could empower patients to treat paroxysmal supraventricular tachycardia themselves outside of a health-care setting, and has the potential to reduce the need for additional medical interventions, such as intravenous medications given in an acute-care setting., Funding: Milestone Pharmaceuticals., Competing Interests: Declaration of interests BSS, PTS, BM, MC, PRK, JPP, SDP, and AJC are consultants for Milestone Pharmaceuticals. AJC has received grants and personal fees from Boehringer Ingelheim, Bayer, Pfizer, Bristol-Myers Squibb, and Daiichi Sankyo; personal fees from Medtronic, Boston Scientific, Menarini, and Biotronik; and support from Anthos, Sanofi, Abbott, GlaxoSmithKline, and Johnson & Johnson. PRK has received personal fees from Acesion Pharma, Allergan, Astellas Pharma, AstraZeneca, AtriCure, Boehringer Ingelheim, Bristol-Myers Squibb, Chattem, Correvio, Daiichi Sankyo, GlaxoSmithKline, InCarda Therapeutics, Johnson & Johnson, Medtronic, Merck, Novartis, Pfizer, Roche, and Sanofi-Aventis; serves on a data safety monitoring board for Eli Lilly; and has equity in CardioNet. SDP has received personal fees from Medtronic, Boston Scientific, Pfizer, Bristol-Myers Squibb, Janssen Pharmaceuticals, Philips, Zoll, and Sanofi-Aventis and research grants from Boston Scientific, Gilead Sciences, Pfizer, Bristol-Myers Squibb, the US Food and Drug Administration, Janssen Pharmaceuticals, Philips, Medtronic, and Sanofi-Aventis. HH has received lecture and consultancy fees from Abbott, Biotronik, Daiichi Sankyo, Pfizer-BMS, Medscape, and Springer Healthcare and unconditional research grants through the University of Antwerp and/or the University of Hasselt from Abbott, Bayer, Biotronik, Biosense Webster, Boston Scientific, Boehringer Ingelheim, Daiichi Sankyo, Fibricheck/Qompium, Medtronic, and Pfizer-BMS, all outside of the scope of this work. JLM has received grants and personal fees from Medtronic, Microport, and Sanofi. JPP has received grants for clinical research from Abbott, the American Heart Association, the Association for the Advancement of Medical Instrumentation, Bayer, Boston Scientific, iRhythm, and Philips and serves as a consultant to Abbott, AbbVie, ARCA biopharma, Bayer, Boston Scientific, Bristol Myers Squibb (Myokardia), Element Science, Itamar Medical, LivaNova, Medtronic, ElectroPhysiology Frontiers, ReCor, Sanofi, Philips, and UpToDate. AV has received personal fees from MedLumics and Adagio Medical and research grants from Bayer, Biosense Webster, and Medtronic. JMW has received personal fees from Sanofi-Aventis, Bristol-Myers Squibb, and Janssen Pharmaceuticals and a research grant from Milestone Pharmaceuticals. PTS has equity in Milestone Pharmaceuticals. DBB, FP, and SS are employees of Milestone Pharmaceuticals. JEI, MA, BSS, PD, and AJC serve on the steering committee for Milestone Pharmaceuticals. JH declares no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved.)

Background Atrial tachyarrhythmias are common after atrial fibrillation ablation, so adjunctive antiarrhythmic drug therapy is often used. Data on the effectiveness and safety of dronedarone and sotalol after AF ablation are limited. Here, we compared health outcomes of ablated patients treated with dronedarone versus sotalol. Methods and Results A comparative analysis of propensity score-matched retrospective cohorts was performed using IBM MarketScan Research Databases. Patients treated with dronedarone after atrial fibrillation ablation were matched 1:1 to patients treated with sotalol between January 1, 2013 and March 31, 2018. Outcomes of interest included cardiovascular hospitalization, proarrhythmia, repeat ablation, and cardioversion. This study was exempt from institutional review board review. Among 30 696 patients who underwent atrial fibrillation ablation, 2086 were treated with dronedarone and 3665 with sotalol after ablation. Propensity-score matching resulted in 1815 patients receiving dronedarone matched 1:1 to patients receiving sotalol. Risk of cardiovascular hospitalization was lower with dronedarone versus sotalol at 3 months (adjusted hazard ratio [aHR], 0.77 [95% CI, 0.61-0.97]), 6 months (aHR, 0.76 [95% CI, 0.63-0.93]), and 12 months after ablation (aHR, 0.70 [95% CI, 0.66-0.93]). Risk of repeat ablation and cardioversion generally did not differ between the 2 groups. A lower risk of proarrhythmia was associated with dronedarone versus sotalol at 3 months (aHR, 0.76 [95% CI, 0.64-0.90]), 6 months (aHR, 0.80 [95% CI, 0.70-0.93]), and 12 months (aHR, 0.83 [95% CI, 0.73-0.94]) after ablation. Conclusions These data suggest that dronedarone may be a more effective and safer alternative after ablation than sotalol.

Introduction: Cor triatriatum sinister (CTS) is a rare congenital heart defect characterized by fibromuscular septation of the left atrium associated with atrial fibrillation (AF). The incidence of hemodynamically insignificant CTS in the AF ablation population and effect on ablation success are not known. Furthermore, little is known about the potential effect of CTS on arrhythmogenic substrate., Objective: We define the incidence of hemodynamically insignificant CTS in patients undergoing AF ablation with RF and cryoballoon ablation, the technical challenges created by the left atrial partitioning, and the potentially arrhythmogenic effects of the membrane. We also review the literature of CA in patients with CTS., Methods: First-time AF ablation cases at our institution over a 10-year period were screened to identify patients with CTS. Retrospective review was performed to obtain clinical characteristics and ablation data., Results: Of the 3953 consecutive patients undergoing initial AF ablation during the study period, four patients (0.10%) had CTS. Ablation was successful acutely in all patients. One patient had recurrent AF and required repeat ablation for a single procedure success rate of 75% and multi-procedure success rate of 100%. The CTS membrane was associated with low voltage zones in the two patients in whom it was measured and with substrate for macro-reentrant atrial tachycardia in one of these patients., Conclusion: The incidence of hemodynamically insignificant CTS in patients undergoing CA for AF is very low, but does not serve as a significant barrier to successful ablation as long as directed access to the superoposterior chamber is obtained., (© 2021 Wiley Periodicals LLC.)

Objective: The objective of this study was to correlate early recurrence of atrial fibrillation (AF) after ablation with noninvasive imaging using cardiac computed tomography (CT)., Methods: CT image data of 260 patients who had undergone wide area circumferential ablation (WACA) between October 2005 and August 2010 as well as from 30 subjects in sinus rhythm without a history of AF (control group) were retrospectively analyzed. To evaluate early outcome of AF ablation, all AF patients underwent follow-up with a 30-day event monitor 3 to 4 months after ablation. In addition, a cardiac CT was also performed 3 to 4 months after ablation to exclude pulmonary vein (PV) stenosis. The presence of early AF was correlated with anatomic and functional PV and left atrial parameters, as assessed by cardiac CT., Results: A total of 70 patients (26.9%) were found to have early recurrence of AF. However, we found no association between PV or left atrial anatomic or functional parameters derived from cardiac imaging with early AF recurrence. Furthermore, no correlation (P>0.05) between AF recurrence and coronary artery stenosis, anatomic origin of the sinoatrial, or atrioventricular nodal arteries was observed. Finally, PV contraction did not predict AF recurrence. However, when comparing PV contraction in WACA patients with the control group, a significant (P<0.05) reduction in left superior PV and right superior PV contractility was found in patients after radiofreqency ablation., Conclusions: In our relatively large cohort, cardiac CT did not yield any anatomic or functional markers for the prediction of early AF recurrence after undergoing WACA. However, our data may provide insights into functional changes that occur following ablation procedures.

Background: Atrial arrhythmias (AA), including atrial fibrillation (AF), have been reported in patients after cavotricuspid isthmus (CTI) ablation for typical atrial flutter (AFL). Several studies have examined the effect of performing concomitant pulmonary vein isolation (PVI) with CTI on recurrent AA. These studies were analyzed to determine the overall effect of this approach on recurrent AA., Methods: PubMed and Google Scholar were searched for randomized trials comparing the incidence of AA after CTI versus CTI + PVI until June 2018. Only patients without prior history of AF were included in the recurrent AA analysis. All patients were included in the analyses of other clinical outcomes., Results: Four randomized control trials were included in the meta-analysis. In the recurrent AA analysis, a total of 314 patients were randomized in the studies (n = 158 CTI, n = 156 CTI + PVI). Freedom from AA at 1 year was significantly higher in the CTI + PVI group versus CTI alone (odds ratio [OR] 0.25 [0.14, 0.44] 95% confidence interval [CI], P < 0.00001). A total of 550 patients (n = 336 CTI, n = 214 CTI + PVI) were included in analyses for procedure time, fluoroscopy time, and complications rates. Procedure time and fluoroscopy time were significantly longer in the CTI + PVI group (mean difference [MD]: 103.31 min [94.40, 112.23] 95% CI, P < 0.00001) and (MD: 16.47 min [14.89, 18.05] 95% CI, P < 0.00001), respectively. Total complications were statistically similar between groups., Conclusion: This meta-analysis shows addition of a prophylactic PVI during CTI ablation significantly reduces recurrent AA at 1 year without significantly increasing major complications., (© 2019 Wiley Periodicals, Inc.)

Sotalol is effective for treating atrial fibrillation (AF), ventricular tachycardia, premature ventricular contractions, and supraventricular tachycardia. Racemic (DL) sotalol inhibits the rapid component of the delayed rectifier potassium current. There is a near linear relationship between sotalol dosage and QT interval prolongation. However, in dose ranging trials in patients with AF, low-dose sotalol was not more effective than placebo. Orally administered sotalol has a bioavailability of nearly 100%. The only significant drug interactions are the need to avoid or limit use of concomitant drugs that cause QT prolongation, bradycardia, and/or hypotension., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Atrial fibrosis is considered to contribute to atrial fibrillation (AF) recurrence following cardioversion. This study tested the hypothesis that circulating levels of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) can predict AF recurrence postcardioversion. Precardioversion plasma samples (n = 82) were assayed for MMPs (eight types), TIMPs (all four types), N-terminus pro B-type natriuretic peptide, and high-sensitivity C-reactive protein levels. Patients were followed for AF recurrence postcardioversion. Despite 100 % restoration of sinus rhythm, 36 (44 %) reverted to AF within 3 months. Left atrial volume was increased in patients in whom AF recurred. Precardioversion MMP-9 was higher and TIMP-4 lower with AF recurrence. MMP-9, MMP-3, and TIMP-4 independently predicted AF recurrence. In multivariate analysis, combination of MMP-9, MMP-3, and TIMP-4 increased prediction of AF recurrence. Circulating levels of MMPs and TIMPs predict AF recurrence postcardioversion and may be used in a novel biomarker panel to guide AF stratification and therapy.

The perioperative bleeding risk associated with therapeutic anticoagulation at cardiac implantable electronic device implantation has previously been demonstrated to vary by the specific anticoagulant used. Although uninterrupted anticoagulation with warfarin appears to be safe, heparin products have been shown to increase the risk of perioperative bleeding. However, the risk associated with cardiac implantable electronic device implantation with anticoagulation using dabigatran, a novel oral direct thrombin inhibitor, is not known. We performed a prospective observational study of patients receiving dabigatran for anticoagulation who underwent cardiac implantable electronic device implantation from June 2011 through May 2012. The study end points included thromboembolic and bleeding complications within 30 days of surgery. Major bleeding complications were defined as bleeding requiring surgical intervention, prolongation of hospitalization, and discontinuation of the anticoagulant or transfusion of blood products within 30 days of surgery. Minor bleeding complications included the development of a hematoma not requiring additional intervention. The thrombotic end points included stroke, transient ischemic attack, myocardial infarction, pulmonary embolism, and deep vein thrombosis. A total of 25 patients were identified for inclusion. During the index hospitalization, no thromboembolic or bleeding complications developed. No major bleeding complications occurred within 30 days of surgery. One minor bleeding event (4%) occurred within 30 days of surgery in 1 patient who was also receiving dual antiplatelet therapy. In conclusion, although no thromboembolic or major bleeding events were observed, additional studies are required to define the optimal antithrombotic management in the perioperative period., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Background: Defibrillation threshold (DFT) testing is performed in part to ensure an adequate safety margin for the termination of spontaneous ventricular arrhythmias. Left ventricular mass is a predictor of high DFTs, so patients with hypertrophic cardiomyopathy (HCM) are often considered to be at risk for increased defibrillation energy requirements. However, there are little prospective data addressing this issue., Objective: To assess DFTs in patients with HCM and evaluate the clinical predictors of elevated DFTs., Methods: Eighty-nine consecutive patients with HCM and 600 control patients with ischemic or nonischemic cardiomyopathy underwent a uniform modified step-down DFT testing protocol. DFT was compared between the control and HCM populations. Predictors of elevated DFT were evaluated in the HCM group., Results: There was no difference in DFT between HCM and control groups (10.4 ± 5.8 J vs 11.2 ± 5.6 J, respectively). Among patients with HCM, clinical parameters such as left ventricular ejection fraction, interventricular septal thickness, left ventricular mass, and QRS duration were not predictive of an elevated DFT. Only 3 patients (3.4%) with HCM had a DFT >20 J., Conclusion: Patients with HCM do not have elevated DFTs as compared to more typical populations undergoing implantable cardioverter-defibrillator implant; high-energy devices or complex lead systems are not needed routinely in this population., (© 2010 Wiley Periodicals, Inc.)

Background: Implantable cardioverter-defibrillator (ICD) leads are traditionally placed in the right ventricular apex (RVA), in part because this is considered the preferred vector for minimizing defibrillation threshold (DFT). However, if adequate DFT safety margins are attainable, ICD leads placed in the right ventricular outflow tract (RVOT) might confer advantages if frequent ventricular pacing is anticipated., Objective: The purpose of this study was to compare RVA with RVOT transvenous ICD lead position on DFT., Methods: This was a prospective, randomized, crossover study of RVA versus RVOT DFT in 33 patients undergoing left pectoral ICD placement. A binary search algorithm was used to measure DFT, with initial lead position tested in randomized order. The relationship between RVOT position and DFT was assessed by evaluation of the distance between RVA and RVOT., Results: The study population had a mean age of 59 ± 12 years and ejection fraction of 33% ± 14%. Mean DFT in the RVA was 9.8 ± 7.3 J versus 10.8 ± 7.2 J in the RVOT (P = .53), with no correlation between RVOT location and DFT., Conclusion: The study found no evidence that ICD lead placement in the RVOT is associated with significantly higher DFT than lead placement in the RVA., (Copyright © 2010 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

External or internal shocks administered to terminate ventricular arrhythmias as a part of electrophysiology or implantable cardioverter-defibrillator testing, can inadvertently cardiovert atrial fibrillation (AF). Moreover, anticoagulation therapy is often withheld in these patients in anticipation of an invasive procedure. The risk of embolic events during these procedures has not been well described. Accordingly, the present study was a prospective evaluation of the incidence of left atrial (LA) thrombus and AF cardioversion among patients undergoing ventricular arrhythmia assessment. Transesophageal echocardiography was routinely performed on 44 consecutive patients in AF with subtherapeutic anticoagulation undergoing electrophysiology or implantable cardioverter-defibrillator testing. Arrhythmia induction was not performed when LA thrombus was present. The incidence and clinical predictors of thrombus, the inadvertent cardioversion of AF, and adverse events related to the procedure were assessed during the subsequent 4 to 6 weeks. Left atrial thrombus was observed in 12 patients (27%). Sinus rhythm was restored in 29 patients (91%), at least transiently, who underwent testing with a shock delivered. No adverse neurologic or hemorrhagic complications were observed. Univariate analysis identified no predictors of LA thrombus or cardioversion to sinus rhythm. In conclusion, LA thrombus and cardioversion to sinus rhythm are common among patients with AF undergoing an evaluation of ventricular arrhythmias. Transesophageal echocardiography performed before the procedure in patients with subtherapeutic anticoagulation is warranted to minimize embolic complications. This strategy appears to be a safe method to guide diagnostic testing in this patient population.

Introduction: High defibrillation threshold (DFT) with an inadequate defibrillation safety margin remains an infrequent but troubling problem associated with defibrillator implantation. Dofetilide is a selective class III antiarrhythmic drug that reduces DFTs in a canine model. We hypothesized that dofetilide would reduce DFTs in humans, obviating the need for complex lead systems., Methods and Results: Sixteen consecutive patients with DFTs > or =20 J delivered energy at implant-received dofetilide therapy and underwent follow-up DFT testing acutely following drug loading and/or chronically (128 +/- 94 days). Amiodarone was discontinued in four patients at implantation. With dofetilide, DFTs decreased from 28 +/- 4 J to 19 +/- 7 J (P < 0.0001), resulting in a safety margin of 15 +/- 8 J for the implanted devices. Five patients subsequently had spontaneous arrhythmias terminated successfully with shocks., Conclusion: Dofetilide reduces DFTs sufficiently to prevent the need for more complex lead systems. This strategy should be considered when an inadequate defibrillation safety margin is present.

Objectives: The purpose of this study was to examine the effects of alcohol septal ablation (ASA) on ventricular arrhythmias among patients with obstructive hypertrophic cardiomyopathy (HCM), as measured by appropriate implantable cardioverter-defibrillator (ICD) discharges., Background: Alcohol septal ablation is an effective therapy for patients with symptomatic HCM. However, concern has been raised that ASA may be proarrhythmic secondary to the iatrogenic scar created during the procedure. The impact of ASA on ventricular arrhythmias has not been well described., Methods: This prospective study included 123 consecutive patients with obstructive HCM who underwent ASA and had an ICD implanted for primary prevention of sudden cardiac death (SCD). The ICDs were implanted based on commonly accepted risk factors for SCD in the HCM population. Data from ICD interrogations during routine follow-up were collected., Results: Nine appropriate ICD shocks were recorded over a mean follow-up of 2.9 years in the cohort, which had a mean of 1.5 +/- 0.9 risk factors for SCD. Using Kaplan-Meier survival analysis, the estimated annual event rate was 2.8% over 3-year follow-up. There were no significant differences in the incidence of risk factors between patients who did and did not receive appropriate shocks., Conclusions: The annual rate of appropriate ICD discharges after ASA is low and less than that reported previously for primary prevention of SCD in HCM. This suggests that ASA is not proarrhythmic. Traditional SCD risk factors did not predict ICD shocks in this cohort.

Atrial fibrillation (AF) produces changes in atrial structure and extracellular matrix composition, which is regulated by matrix metalloproteinases (MMPs). Moreover, AF often occurs in the setting of congestive heart failure (CHF), which also affects MMPs. Whether changes in MMPs or the tissue inhibitors of metalloproteinases (TIMPs) within atrial and ventricular myocardium are differentially regulated with AF remains unclear. Myocardium from the walls of the right atrium, right ventricle, left atrium, and left ventricle was obtained from the explanted hearts of 43 patients with end-stage CHF. AF was present in 23 patients (duration 1 to 84 months). The remaining 20 patients served as non-AF controls. The groups were well matched clinically, but left atrial (LA) size was increased in the AF cohort (5.5 +/- 0.8 vs 4.9 +/- 0.7 cm, p <0.05). Myocardial collagen content and levels of MMP-1, -2, -8, -9, -13, and -14, and TIMP-1, -2, -3, and TIMP-4 were determined. With AF, collagen content was greater within the atrial myocardium but less in the ventricular myocardium. There were chamber-specific differences in MMPs and TIMPs with AF. For example, MMP-1 in the right atrium and MMP-9 in the left atrium were greater with AF. TIMP-3 levels were greater in the right ventricle, left atrium, and left ventricle. Although total LA collagen was positively correlated with AF duration (r = 0.49, p <0.03), there was an inverse relation between soluble collagen I and AF duration (n = 6, r = -0.84, p <0.04). In conclusion, AF is associated with chamber-specific alterations in myocardial collagen content and MMP and TIMP levels, indicative of differential remodeling and altered collagen metabolism. Differences in MMP and TIMP profiles may provide diagnostic and mechanistic insights into the pathogenesis of AF with CHF.

Background: The left superior vena cava (LSVC) is the embryological precursor of the ligament of Marshall, which has been implicated in the initiation and maintenance of atrial fibrillation (AF). Rarely, the LSVC may persist and has been associated with some organized arrhythmias, though not with AF. We report 5 patients in whom the LSVC was a source of ectopy, initiating AF., Methods and Results: In 5 patients (4 men; age, 46+/-11 years) with symptomatic drug-refractory AF, ectopy from the LSVC resulting in AF was observed after pulmonary vein isolation. The ectopics were spontaneous in 2 and induced by isoproterenol in the others and preceded P-wave onset by 67+/-13 ms. During multielectrode or electroanatomic mapping, venous potentials were recorded circumferentially at the proximal LSVC near its junction with the coronary sinus (CS), but at the mid-LSVC level, they were recorded only on part of the circumference. The LSVC was electrically connected to the lateral left atrium (LA) and through the CS to the right atrium, with 4.1+/-2.3 CS-LSVC and 1.6+/-0.5 LA-LSVC connections per patient. Catheter ablation in the LSVC targeting these connections resulted in electrical isolation in 4 of the 5 patients without complications. After 15+/-10 months, the 4 patients with successful isolation, including 1 who had successful reablation for LA flutter, remained in sinus rhythm without drugs., Conclusions: The LSVC can be the arrhythmogenic source of AF with connections to the CS and LA. Ablation of these connections resulted in electrical isolation.

Various approaches for catheter ablation of focal initiators of atrial fibrillation or the substrate for maintaining atrial fibrillation have evolved over the past 5 years. Despite these advances, there are still a large number of unresolved issues regarding the efficacy and safety of these procedures as well as optimal patient selection for the different approaches. These uncertainties raise questions about the applicability at the present time of atrial fibrillation as front-line therapy within the community.

Objectives: The purpose of this multicenter study was to evaluate the safety and efficacy of a radiofrequency (RF) catheter ablation system with internal saline irrigation., Background: Catheter ablation of ventricular tachycardia (VT) associated with structural heart disease is more difficult than ablation of idiopathic VT. The larger size of responsible reentrant circuits contributes to the difficulty in achieving an adequate ablation lesion with conventional techniques. Recently, cooling of the ablation electrode by saline irrigation has been shown to increase RF lesion size., Methods: The patient population included 146 patients who participated in the Cooled RF Ablation System clinical trial and underwent an attempt at ablation of VT occurring in the presence of structural heart disease. The duration of follow-up was 243 +/- 153 days., Results: Catheter ablation was acutely successful, as defined by elimination of all mappable VTs, in 106 patients (75%). In 59 patients (41%), no VT of any type was inducible after ablation. Twelve patients (8%) experienced a major complication. After catheter ablation, 66 patients (46%) developed one or more episodes of a sustained ventricular arrhythmia., Conclusions: The results of this study demonstrate that catheter ablation of all mappable forms of sustained VT can be performed with high initial success and a moderate incidence of major complications (8%).

Objectives: The purpose of this study was to determine the efficacy and risks of radiofrequency ablation of various forms of supraventricular tachycardia after Mustard and Senning operations for d-transposition of the great arteries., Background: In this patient group, the reported success rate of catheter ablation of intraatrial reentry tachycardia is about 70% with a negligible complication rate. There are no reports of the use of radiofrequency ablation to treat other types of supraventricular tachycardia., Methods: Standard diagnostic criteria were used to determine supraventricular tachycardia type. Appropriate sites for attempted ablation included 1) intraatrial reentry tachycardia: presence of concealed entrainment with a postpacing interval similar to tachycardia cycle length; 2) focal atrial tachycardia: a P-A interval < or =-20 ms; and 3) typical variety of atrioventricular (AV) node reentry tachycardia: combined electrographic and radiographic features., Results: Nine Mustard and two Senning patients underwent 13 studies to successfully ablate all supraventricular tachycardia substrates in eight (73%) patients. Eight of eleven (73%) patients having intraatrial reentry tachycardia, 3/3 having typical AV node reentry tachycardia, and 2/2 having focal atrial reentry tachycardia were successfully ablated. Among five patients having intraatrial reentry tachycardia (IART) and not having ventriculoatrial (V-A) conduction, two suffered high-grade AV block when ablation of the systemic venous portion of the medial tricuspid valve/inferior vena cava isthmus was attempted., Conclusions: Radiofrequency catheter ablation can be effectively and safely performed for certain supraventricular tachycardia types in addition to intraatrial reentry. A novel catheter course is required for slow pathway modification. High-grade AV block is a potential risk of lesions placed in the systemic venous medial isthmus.

Objectives: We compared the efficacy of a novel rectilinear biphasic waveform, consisting of a constant current first phase, with a damped sine wave monophasic waveform during transthoracic defibrillation., Background: Multiple studies have shown that for endocardial defibrillation, biphasic waveforms have a greater efficacy than monophasic waveforms. More recently, a 130-J truncated exponential biphasic waveform was shown to have equivalent efficacy to a 200-J damped sine wave monophasic waveform for transthoracic ventricular defibrillation. However, the optimal type of biphasic waveform is unknown., Methods: In this prospective, randomized, multicenter trial, 184 patients who underwent ventricular defibrillation were randomized to receive a 200-J damped sine wave monophasic or 120-J rectilinear biphasic shock., Results: First-shock efficacy of the biphasic waveform was significantly greater than that of the monophasic waveform (99% vs. 93%, p = 0.05) and was achieved with nearly 60% less delivered current (14 +/- 1 vs. 33 +/- 7 A, p < 0.0001). Although the efficacy of the biphasic and monophasic waveforms was comparable in patients with an impedance < 70 ohms (100% [biphasic] vs. 95% [monophasic], p = NS), the biphasic waveform was significantly more effective in patients with an impedance > or = 70 ohms (99% [biphasic] vs. 86% [monophasic], p = 0.02)., Conclusions: This study demonstrates a superior efficacy of rectilinear biphasic shocks as compared with monophasic shocks for transthoracic ventricular defibrillation, particularly in patients with a high transthoracic impedance. More important, biphasic shocks defibrillated with nearly 60% less current. The combination of increased efficacy and decreased current requirements suggests that biphasic shocks as compared with monophasic shocks are advantageous for transthoracic ventricular defibrillation.

Desmoplastic malignant melanoma (DMM) is an uncommon but potentially devastating malignancy that can be cured with early recognition and surgery. DMM has clinical as well as histological features that may be subtle and overlooked, or misdiagnosed as other benign or malignant lesions that would require less aggressive therapy for cure. We have reviewed the preliminary clinical diagnoses and histological features of 18 cases of desmoplastic malignant melanoma, defined as either an inapparent lesion clinically, or a papule or small nodule less than 0.7 cm, which proved histologically to be DMM. Nine of 18 cases (50%) were clinically pigmented. Histologically, early lesions were characterized by superficial tumor fascicles, and random diffuse hypercellularity in the upper dermis identified as elongated hyperchromatic pleomorphic spindle cells with stromal myxoid change. Neuroidal melanocytic structures, invasion of adventitial dermis, islands of inflammation, and epidermal lentiginous melanocytic hyperplasia were often present. The most reliable and characteristic features of an early lesion of DMM are aggregates of lymphocytes, tumor cell cytological atypia, stromal myxoid change, and poor circumscription of the dermal infiltrate. DMM is a disease best treated by complete excision at the time of initial surgery, but is also a lesion easily missed or misdiagnosed in the early stages. Features of early DMM are identified and illustrated to enable early diagnosis and cure of these lesions.

Unlabelled: Although changes in autonomic tone affect ventricular defibrillation, little is known about the effect of increased parasympathetic or sympathetic tone on the atrial defbrillation threshold., Methods: To evaluate the effect of reflexly increased parasympathetic and increase alpha- and beta-adrenergic tone on the atrial defibrillation threshold (ADFT), atrial fibrillation was induced in 14 patients. ADFTs, right atrial refractory period (RARP), and monophasic action potential duration (MAPD) were determined before and after autonomic intervention. ADFTs were determined with a step-up protocol using 3/3-ms biphasic shocks delivered through decapolar catheters in the right atrial appendage and coronary sinus. Two groups were studied. Group I (N = 8) had ADFTs determined at baseline, after receiving phenylephrine (PE), and with PE plus atropine (A). Group 2 (N = 6) had ADFTs determined at baseline and after receiving isoproterenol (ISO)., Results: Group I: PE significantly increased sinus cycle length (SR-CL) compared to baseline (742 +/- 123 to 922 +/- 233 ms) without significantly changing RARP, MAPD, or ADFT (2.3 +/- 1.3 J vs 2.3 +/- 0.8 J). With PE + A, SR-CL significantly decreased (529 +/- 100 ms vs 742 +/- 123 ms) and MAPD shortened (231 +/- 41 ms vs 279 +/- 49 ms) without altering RARP or ADFT (1.94 +/- 0.9 J vs 2.25 +/- 1.25 J). Group 2: ISO decreased SR-CL (486 +/- 77 ms vs 755 +/- 184 ms) and MAPD (169 +/- 37 ms vs 226 + 58 ms) but not RARP or ADFT (2.25 +/- 1.21 J vs 2.33 +/- 1.75 J)., Conclusions: Increasing parasympathetic, alpha-, or beta-adrenergic tone does not affect the ADFT despite causing significant electrophysiological changes in the atria.

A patient with repaired tetralogy of Fallot presented with recurrent syncope and had multiple haemodynamically unstable ventricular tachycardias unresponsive to antiarrhythmic medications. Ventricular tachycardias became haemodynamically tolerated with amiodarone, procainamide and dopamine, permitting activation and entrainment mapping. Radiofrequency ablation of three tachycardia circuits was performed. Ventricular tachycardia could not be induced 1 week, and 3 and 9 months later. Radiofrequency ablation is feasible for multiple, haemodynamically unstable ventricular tachycardias in repaired tetralogy of Fallot.

Although ventricular tachyarrhythmias usually occur in the setting of definable heart disease, up to 15% of ventricular tachycardias and 10% of ventricular fibrillation occur in patients without heart disease. Of the various clinical entities comprising these idiopathic ventricular tachyarrhythmias, a few well-defined clinical syndromes have been described, such as idiopathic right ventricular outflow tract tachycardia, idiopathic left posterior fascicular ventricular tachycardia, and the right bundle branch block and ST segment elevation syndrome of idiopathic ventricular fibrillation. Many advances have been made in the past few years in our understanding and treatment of idiopathic ventricular tachyarrhythmias, and these advances are the subject of this review.

During testing of a CPI model 1715 ICD, an apparent sensing abnormality was noted following shock delivery for VF. Close inspection of the recording prior to the defibrillation attempt revealed that the surface leads spontaneously lost 848 ms of data while the event marker was unaffected. Computer simulations revealed that an inadequate buffer size for the amplified (surface ECG) data was the likely source of data loss. It is important to recognize that a discordance between surface leads and event marker may represent an abnormality in the data acquisition system and simulate an ICD or lead malfunction.

Whether the presence of abnormal PR before selective slow pathway ablation for AV node reentrant tachycardia increased the risk of complete heart block remains controversial. We report our experience in seven patients with prolonged PR intervals undergoing catheter ablation for AV reentry tachycardia. Their mean age was 66 +/- 12 years; four patients were female and three were male. RF ablation was performed using an anatomically guided stepwise approach. In six patients, common type AV node reentry was induced and uncommon type was observed in the remaining patient. In all seven patients, successful selective slow pathway ablation was associated with no occurrence of complete heart block and was followed by shortening of the AH interval in five patients. In all seven patients, successful ablation was achieved at anterior sites (M1 in two patients and M2 in five patients). Despite AH shortening after ablation, the 1:1 AV conduction was prolonged after elimination of the slow pathway, excluding either sympathetic tone activation or parasympathetic denervation. In conclusion, selective slow pathway ablation can be performed safely in the majority of patients with prolonged PR interval before the procedure. Because successful ablation is achieved at anterior sites in most patients, careful selection and monitoring of catheter position is required.

This case describes ventricular proarrhythmia as a result of a synchronized internal atrial defibrillation shock in a 29-year-old man with Ebstein's anomaly referred for radiofrequency ablation of a right posterior accessory pathway. During the electrophysiologic study, atrial fibrillation was induced and 3/3 msec shocks of various strengths were delivered between two decapolar defibrillation catheters in the coronary sinus and right atrial appendage. A 2.0-J biphasic shock synchronized to an R wave after a short-long-short ventricular cycle length pattern with a preshock coupling interval of 245 msec induced ventricular fibrillation, which was externally defibrillated with 200 J. This observation has implications for the development of implantable atrial defibrillators.

Background: The optimal waveform for internal atrial defibrillation (IAD) in humans is unknown. This study tested the effect of waveform duration and phase duration on the efficacy of biphasic waveforms for IAD., Methods and Results: Electrodes were positioned in the right atrial appendage and coronary sinus in 13 patients. In part 1, the atrial defibrillation thresholds (ADFTs) for 5 monophasic waveforms (2, 4, 6, 10, and 20 ms) and 5 symmetrical biphasic waveforms (1/1, 2/2, 3/3, 5/5, and 10/10 ms) were compared in 6 patients. In part 2, the ADFTs for two asymmetrical biphasic waveforms (7.5/2.5 and 2.5/7.5 ms) were compared with those for a symmetrical biphasic waveform (5/5 ms) and a monophasic waveform (10 ms) in 7 patients. In part 1, biphasics with total durations of 4 to 20 ms had significantly lower ADFTs than monophasic waveforms of the same total duration. For a total duration of 2 ms, there was no significant difference in ADFTs between the biphasic and the monophasic waveforms. There was no difference between symmetrical biphasic waveforms of 4 to 20 ms. In part 2, the 7.5/2.5 ms asymmetrical biphasic had significantly lower ADFTs than the three other waveforms tested. Both the 7.5/2.5 ms asymmetrical and the 5/5 ms symmetrical biphasic waveform had significantly lower ADFTs than the 2.5/7.5 ms asymmetrical biphasic and the 10 ms monophasic waveforms., Conclusions: For IAD in humans, biphasic waveforms were more efficacious than monophasic waveforms. This improved efficacy is related to the total duration of the biphasic waveform and each individual phase duration of the biphasic waveform.

Limited information is available regarding potential adverse interactions between transvenous nonthoracotomy cardioverter defibrillators and pacemakers. We describe our experience with 37 patients who have undergone successful implantation of both a transvenous defibrillator and pacemaker. The patients' mean age was 64 +/- 12.9 years. Thirty-three were male and four were female. The mean LVEF was 30.8% +/- 11.8%. The indications for pacemaker implantation included sick sinus syndrome in 13 patients, complete heart block in 15 patients, sinus bradycardia secondary to medications in 8 patients, and neurocardiogenic syncope in 1 patient. The indications for insertion of a defibrillator included medically refractory VT in 27 patients and sudden cardiac death in 10 patients. Twenty-three patients received an Endotak lead and 14 patients received a Transvene lead. Eighteen patients had a pacemaker prior to an ICD, 14 patients had an ICD prior to a pacemaker, and 4 patients had both devices placed simultaneously. Interaction was evaluated at implant of the second device and 1-3 days after both devices were placed. Detection of VF/VT was analyzed during asynchronous pacing (DOO/VOO) with maximum pacing output. In addition, in six patients, DFT was determined before and after pacemaker implantation. In 14 patients (38%), device interactions that could not always be optimally corrected were observed. In five patients, the pacemaker was reset to the "noise reversion" mode after high energy ICD discharge. Oversensing of atrial pacemaker stimuli resulted in inappropriate ICD firings in four patients. This was observed only with a specific device and could not be prevented by atrial lead repositioning in two of them, but required reprogramming of the pacemaker to the VVI mode. An increase in DFT was observed in five patients who had a pacemaker implanted after an ICD. Compared with previously published studies, a greater frequency of transvenous ICD and pacemaker interactions were observed. Considering that almost 50% of the patients already have a pacemaker at the time of ICD implant, the availability of defibrillators with dual chamber pacing capability will not eliminate the potential for this problem.

Unlabelled: The presence of chronic indwelling leads in the area targeted for RF ablation may pose a technical challenge and reduce the chance of success of the ablation. In addition, application of lesions in close proximity to pacemaker leads or other permanent catheters could affect their function. Fourteen patients referred for RF ablation of atrial flutter/fibrillation and atrial tachycardia, who had a permanent dual chamber pacemaker (10 patients), ICD (1 patient), or both (3 patients) were studied to assess the safety, efficacy, and effects of the ablative procedure on device function. Lead impedance, R and P wave amplitude, and pacing threshold of the defibrillator and pacemaker were measured before and after ablation. The procedure was successful in all patients. In one patient who underwent both atrial flutter and atrial fibrillation ablation, the atrial pacing threshold increased from 1.0 preablation to 2.0 V postablation. No P wave was detectable after ablation. In another patient, the P wave amplitude went from 4.0 to 2.0 mV postablation. In both patients the device converted to the power reset mode. No changes were observed in the remaining patients. Postablation defibrillator testing showed no malfunction. Follow-up reinterrogation of the devices revealed no alterations., In Conclusion: (1) RF ablation of atrial flutter and/or tachycardia is feasible even in patients with multiple chronic atrial and ventricular indwelling catheters; and (2) RF applications in close proximity of defibrillator and pacing catheters does not appear to alter their function unless lesions are produced in the area surrounding the distal pacing electrode.

A 26-year-old man underwent an electrophysiological study for evaluation of a history of congenital heart disease, presyncope, and wide complex tachycardia. During the study the patient developed sustained atrial fibrillation with a rapid ventricular response. A 17-year-old man with a history of sick sinus syndrome developed sustained atrial fibrillation. Both patients failed four attempts at external cardioversion with a maximum delivered energy of 360 J. Low energy cardioversion was successful in both patients using biphasic waveforms and internal transvenous defibrillation electrodes. Internal cardioversion using a transvenous electrode system can be successful in patients with atrial fibrillation refractory to external cardioversion.

Third-generation implantable cardioverter defibrillators (ICD) are frequently implanted with nonthoracotomy systems and provide noninvasive methods for electrical stimulation and ventricular fibrillation induction. These modalities facilitate postoperative testing of the ICD. Rapid right ventricular burst pacing via the defibrillator is commonly used for initiation of ventricular tachyarrhythmias. However, with the available third-generation devices, ventricular fibrillation (VF) induction may be impossible in up to 19% of the patients. In these cases, transvenous placement of a right ventricular catheter has been required to generate VF and appropriately evaluate the device. We report a new technique of noninvasive induction of VF using a low energy external nonsynchronized shock delivered during ICD fibrillation induction pacing. In three patients, after all efforts to induce VF by the Ventritex Cadence V-100 had failed, a 20 J nonsynchronized shock was delivered during rapid RV pacing. This resulted in VF on the first attempt in all patients. This noninvasive technique of VF initiation may provide a useful clinical approach to ICD testing that eliminates the costs and risks of an invasive procedure.

This study examined the complex interaction between vagal enhancement and how a concealed atrial impulse alters atrioventricular (AV) nodal function. In theory, vagal augmentation could increase or decrease the effect that a premature atrial beat has on the subsequent beat. In 10 patients we established the AV nodal effective refractory period (ERP) without and with a conditioning atrial stimulus (Sc); the stimulation protocol was then repeated after enhancing reflex vagal tone with a continuous phenylephrine infusion. During phenylephrine infusion, the sinus cycle length prolonged from 827 +/- 99 to 1,029 +/- 223 ms (p < 0.001) and AV nodal ERP increased from 331 +/- 51 to 425 +/- 64 ms (p < 0.005). At control, AV nodal ERP in the presence of Sc prolonged to 536 +/- 69 ms (p < 0.001), and during phenylephrine infusion increased to 579 +/- 57 ms (p < 0.01), a change significantly less than during control (58 +/- 14% vs 31 +/- 14%, respectively, p < 0.01). Further experiments suggest that the effect of Sc was reduced because it occurred earlier relative to the vagally prolonged AV nodal ERP. In conclusion, this study demonstrates a complex relation between the timing of a premature atrial beat causing concealed conduction and the degree of vagal tone. The concealed beat, as related to the AV node ERP, has a substantial effect on subsequent AV nodal conduction. These data give insights into clinical AV nodal function.

In a study of 11 dogs, we assessed whether the defibrillation energy requirements of a single transvenous right ventricular electrode/defibrillator can system depended on the can size. We compared the defibrillation threshold obtained with 65% fixed-tilt biphasic shocks with 20, 40, and 80 ml surface area defibrillator cans. The energy was delivered between a right ventricular coil inserted through the jugular vein and the can placed in the subcutaneous tissue of the left superior chest wall. The testing order of each can size was randomly determined. Triplicate defibrillation thresholds were obtained with each can. Despite a higher impedance (20 ml 85 +/- 22 ohms vs 80 ml 71 +/- 16 ohms, p < 0.01), the 20 ml can resulted in a similar defibrillation threshold compared with the 80 ml (20 ml 7.6 +/- 2.8 J vs 80 ml 7.5 +/- 3.4 J) and the 40 ml cans (20 ml 7.6 +/- 2.8 J vs 7.5 +/- 3.4 J). In conclusion, with the unipolar lead system the can size does not appear to be a factor limiting defibrillation success. Even a can the size of a pacemaker does not appear to significantly affect the defibrillation efficacy of this lead system.

A case of bundle branch reentry tachycardia with an unusual induction pattern is presented. Unlike typical cases of this arrhythmia in which tachycardia is usually inducible with routine programmed ventricular stimulation and/or short-long sequences, tachycardia in this case was inducible only with atrial stimulation. It also arose spontaneously during atrial flutter and during isoproterenol administration. After ablation of the right bundle, possible interfascicular reentry tachycardia with a similar induction pattern was observed. This tachycardia was successfully ablated in the region of the posterior fascicle of the left bundle branch.

Introduction: The delivery of radiofrequency (RF) energy through conventional catheter electrodes is often associated with coagulation necrosis at the tissue-electrode interface, with resultant impedance rise and limited lesion size. This study was performed to examine the effects of catheter tip cooling during RF delivery, to test the hypothesis that such cooling would decrease the likelihood if impedance rise and allow the creation of larger endomyocardial lesions., Methods and Results: The experiments were performed in eight open chest, anesthetized sheep. RF lesions were created within both ventricular chambers of each animal through a catheter tip that could be cooled with a saline perfusate. Assignment of cooled versus noncooled RF delivery to either ventricle was alternated from one animal to the next. In each set of experiments, lesion volumes relative to the mode of RF delivery were compared. The mean power delivered via the cooled electrode (22.04 +/- 4.51 W) was significantly higher than that delivered via the noncooled electrode (6.10 +/- 2.47 W; P < 0.001). The mean duration of RF delivery was 42.7 +/- 11.2 sec for noncooled lesions versus 49.2 +/- 6.8 sec for cooled lesions (P < 0.01). Mean lesion volume was 436.07 +/- 177.00 mm3 for noncooled RF delivery versus 1247.78 +/- 520.51 mm3 for cooled RF delivery (P < 0.001). This significantly larger lesion size with cooled RF delivery was associated with no instance of impedance rise in 27 attempts versus 11 impedance rises in 28 attempts with noncooled RF (P < 0.001)., Conclusions: Delivery of RF energy through a cooled catheter tip allows the creation of larger endomyocardial lesions by limiting the occurrence of impedance rise despite the delivery of greater energy. These observations suggest that, under certain conditions, resistive tissue heating at a distance from the site of current delivery may play an important role in RF ablation therapy.

Due to the limited efficacy of antiarrhythmic drugs for atrial fibrillation, several nonpharmacologic therapeutic options have evolved. One of these is an implantable atrial defibrillator. Recent studies have shown that internal atrial defibrillation is feasible with relatively low energies. To date, the optimal electrode configuration involves large surface area catheters in the right atrium and coronary sinus. In humans, atrial defibrillation can generally be achieved with < 2 J using this electrode configuration and a biphasic shock waveform. For shocks < 5 J, there is no significant pathological damage to the atria or coronary sinus. Further investigation is needed to guarantee that atrial defibrillation shocks do not provoke ventricular arrhythmias. Preliminary data suggest that atrial defibrillation shocks synchronized to R waves that are not closely coupled are safe. In addition, the shocks are well tolerated if the shock energy is < 1.5 J. With additional studies to confirm the safety of implantable atrial defibrillators, further reduce shock energy, and improve patient tolerance, an implantable atrial defibrillator can become an acceptable therapy for patients with symptomatic, paroxysmal atrial fibrillation.

The differential diagnosis of VTs with LBBB morphology includes several well-defined syndromes. Although the majority of cases are attributable to acquired structural heart disease, including ischemia, prior infarction, or dilated cardiomyopathy, consideration of specific right ventricular processes is essential to proper evaluation and treatment. The approach to older patients or those with evidence for heart disease should begin with an evaluation for coronary artery disease and an assessment of biventricular function. Careful evaluation for bundle branch reentry should be performed during electrophysiological study, especially when there is underlying conduction system disease. Younger patients, those without overt heart disease, or those with isolated right ventricular disease, should receive a complete noninvasive evaluation of right and left ventricular size and function. An abnormal SAECG or identification of intracardiac late potentials suggest right ventricular dysplasia or cardiomyopathy, whereas responsiveness to adenosine and absence of detectable heart disease support the diagnosis of idiopathic right VT. Newer techniques, including MRI, show promise in identifying subtle right ventricular disease not otherwise detectable even in the setting of presumed idiopathic right VT. Following surgical repair of selected congenital heart defects, particularly tetralogy of Fallot, symptoms of recurrent palpitations, near syncope, syncope, or aborted sudden death may be attributable to recurrent VT, and diagnostic electrophysiological study should be considered for these patients. Finally, SVTs with LBBB morphology, particularly cases associated with right-sided or septal accessory pathways, should always be considered in this differential diagnosis.

Nearly 80% of patients with coronary artery disease who have map-directed surgery for control of ventricular tachycardias require no drug therapy to prevent recurrences, while fewer than 50% of patients undergoing catheter ablation have similar outcomes. Catheter ablation will fail if arrhythmogenic sites are incompletely ablated by lesions that are too small or too far away from the reentrant pathway or if all arrhythmogenic sites are not identified. The underlying assumptions used to guide site selection are that: (a) ventricular tachycardias arise from reentrant mechanisms; (b) monomorphic ventricular tachycardias with similar QRS morphologies arise from the same pathway; (c) the ventricular tachycardia initiated during the procedure represents the patient's spontaneous arrhythmia; (d) the endocardial site that should be ablated can be identified from cardiac activation maps produced during induced ventricular tachycardia or from ancillary techniques; and (e) the patient has only one or two reentrant pathways. Relying on incorrect assumptions may account for the difference in success rates. Patients may have similar appearing ventricular tachycardias that arise from different pathways, and the entire thin layer of viable tissue between the infarct and the endocardium may contain many reentrant pathways. Some ventricular tachycardias may arise from the myocardium away from the endocardium, while others may arise from the epicardium. Small lesions may not be large enough to eliminate all possible reentrant pathways. Catheter ablation may be less successful because the lesions are inadequate, the assumptions guiding the selection of arrhythmogenic tissue are incorrect, or all arrhythmogenic sites are not identified. The primary reason catheter ablation is less successful than surgery in the treatment of ventricular tachycardias is that catheter ablation does not ablate as much tissue as is removed by surgery. The success rate of catheter ablation probably can be improved if the amount of tissue ablated is increased.

In patients with Wolff-Parkinson-White syndrome and atrial fibrillation, digoxin may increase the ventricular rate by facilitating conduction over the accessory pathway either directly by enhancing accessory pathway conduction and/or indirectly as a consequence of its effect on atrioventricular nodal conduction. Two cases are presented in which the intravenous administration of magnesium sulfate reversed digoxin facilitation of the ventricular rate to atrial fibrillation in the Wolff-Parkinson-White syndrome.

Objectives: This study evaluates 1) the safety and efficacy of catheter delivery of radiofrequency current to eliminate sustained sinoatrial node reentrant tachycardia; 2) the incidence of sinoatrial node reentrant tachycardia in the current group of patients undergoing electrophysiologic study for paroxysmal supraventricular tachycardia; and 3) the association of sinoatrial node reentrant tachycardia with other tachyarrhythmias., Background: Sustained sinoatrial node reentrant tachycardia is an uncommon cause of paroxysmal supraventricular tachycardia that is reported to occur infrequently in conjunction with other arrhythmias. Although pharmacologic and surgical therapies are available, there is limited information with regard to catheter ablation of sinoatrial node reentrant tachycardia., Methods: Ten patients with sustained sinoatrial node reentrant tachycardia underwent electrophysiologic study and radiofrequency current ablation. Patients were followed up for 9.2 +/- 6.0 months., Results: Of 343 consecutive patients referred for electrophysiologic evaluation of paroxysmal supraventricular tachycardia, 11 (3.2%) were found to have inducible sustained sinoatrial node reentrant tachycardia. Nine of the 11 patients had other associated arrhythmias, including atrioventricular (AV) node reentrant tachycardia (6 patients), AV reciprocating tachycardia (2 patients), ectopic atrial tachycardia (2 patients) and bundle branch reentrant tachycardia (1 patient). In 10 patients, direct ablation of sinoatrial node reentrant tachycardia was attempted and was successful in all (confidence interval for failure 0-0.26). Sinoatrial node reentrant tachycardia was eliminated with a median of four radiofrequency current applications (range 1 to 10) at 20 to 30 W. Successful ablation site characteristics during sinoatrial node reentrant tachycardia included 1) atrial activation > or = 35 ms (mean 44 +/- 8 ms) before the onset of the surface P wave, 2) atrial activation > or = 20 ms (mean 28 +/- 6 ms) before the onset of high right atrial activation, and 3) significantly prolonged and fractionated electrograms (mean duration 87 +/- 21 ms). No complications were encountered, and there have been no recurrences of sinoatrial node reentrant tachycardia., Conclusions: Sinoatrial node reentrant tachycardia may be effectively and safely treated with radiofrequency current ablation at the site of earliest atrial activation.

Implantable cardioverter defibrillators reduce the risk of sudden cardiac death in patients with ventricular tachyarrhythmias. However, for the few patients with unacceptably high defibrillation thresholds at implantation the risk of sudden death may remain high. If a small number of defibrillation attempts are used to determine a defibrillation threshold, then a high defibrillation threshold may occur in some patients due to the probabilistic nature of defibrillation: a small percentage of shocks will fail even at optimal shock strengths. Basic investigations have suggested mechanisms for high defibrillation thresholds in other patients. The extracellular potential gradients produced by a shock correlate with ability to defibrillate and may be used to classify mechanisms for high defibrillation thresholds. Computerized mapping studies have demonstrated that extracellular potential gradient fields produced by defibrillation shocks are uneven with high gradient areas close to the electrodes and low gradient areas distant from the electrodes. A high defibrillation threshold may occur because: (1) a shock creates a subthreshold potential gradient in the low gradient areas; (2) a patient has a higher minimum potential gradient threshold than other patients; or (3) a shock leads to refibrillation in the high gradient areas. This article reviews experimental evidence to support each of these three possibilities then suggests experimental and clinical investigations that may clarify the causes of high defibrillation thresholds in patients.