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Background: Sinus rhythm activation time is useful to assess infarct border zone substrate., Objective: We sought to further investigate sinus activation in ventricular tachycardia (VT)., Methods: Canine postinfarction data were analyzed retrospectively. In each experiment, an infarct was created in the left ventricular wall by left anterior descending coronary artery ligation. At 3 to 5 days after ligation, 196-312 bipolar electrograms were recorded from the anterior left ventricular epicardium overlapping the infarct border zone. Sustained monomorphic VT was induced by premature electrical stimulation in 50 experiments and was noninducible in 43 experiments. Acquired sinus rhythm and VT electrograms were marked for electrical activation time, and activation maps of representative sinus rhythm and VT cycles were constructed. The sinus rhythm activation signature was defined as the cumulative number of multielectrode recording sites that had activated per time epoch, and its derivative was used to predict VT inducibility and to define the sinus rhythm slow/late activation sequence., Results: Plotting mean activation signature derivative, a best cutoff value was useful to separate experiments with reentrant VT inducibility (sensitivity, 42/50) vs noninducibility (specificity, 39/43), with an accuracy of 81 of 93. For the 50 experiments with inducible VT, recording sites overlying a segment of isochrone encompassing the sinus rhythm slow/late activation sequence spanned the VT isthmus location in 32 cases (64%), partially spanned it in 15 cases (30%), but did not span it in 3 cases (6%)., Conclusion: The sinus rhythm activation signature derivative is assistive to differentiate substrate supporting reentrant VT inducibility vs noninducibility and to identify slow/late activation for targeting isthmus location., Competing Interests: Disclosures The authors have no conflicts of interest to disclose., (Copyright © 2024 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Where activation wavefront curvature is convexly shaped, functional conduction block can occur., Objective: The purpose of this study was to determine whether left ventricular (LV) wall thickness determined from contrast-enhanced computed tomography (CT) is useful in localizing such areas in clinical postinfarction reentrant ventricular tachycardia (VT)., Methods: We evaluated data from 6 patients who underwent catheter ablation for postinfarction VT. CT imaging with inHEART processing was conducted 1-3 days before electrophysiological (EP) study to determine LV wall thickness (T). Activation wavefront curvature was approximated as ΔT/T, where ΔT represents wall thickness change. During EP study, bipolar LV VT electrograms were acquired using a high-density mapping catheter, and activation times were determined. Maps of T, ΔT/T, and VT activation were subsequently compared using statistical analyses., Results: Two of 6 cases exhibited dual circuit morphologies, resulting in a total of 8 VT morphologies analyzed. The LV wall near the VT isthmus location tended to be thin, on the order of a few hundred micrometers. Regions of largest ΔT/T partially coincided with the lateral isthmus boundaries where electrical conduction block occurred during VT. ΔT/T at the boundaries, measured from imaging, was significantly larger compared to values at the isthmus midline and to the global LV mean value (P <.001)., Conclusion: Wavefront curvature measured by ΔT/T and caused by source-sink mismatch is dependent on ventricular wall thickness. Areas of high wavefront curvature partly coincide with and may be helpful in locating the VT isthmus in infarct border zones using preprocedural imaging analysis., Competing Interests: Disclosures The authors have no conflicts of interest to disclose., (Copyright © 2024 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Previous observations have reported that the number of pacing stimuli required to entrain a tachycardia varies on the basis of arrhythmia type and location, but a quantitative formulation of the number needed to entrain (NNE) that unifies these observations has not been characterized., Objective: We sought to investigate the relationship between the number of pacing stimulations, the tachycardia cycle length (TCL), the overdrive pacing cycle length (PCL), and the postpacing interval (PPI) to accurately estimate the timing of tachycardia entrainment., Methods: First, we detailed a mathematical derivation unifying electrophysiological parameters with empirical confirmation in 2 patients undergoing catheter ablation of typical atrial flutter. Second, we validated our formula in 44 patients who underwent various catheter ablation procedures. For accuracy, we corrected for rate-related changes in conduction velocity., Results: We derived the equations NNE = |(PPI - TCL)/(TCL - PCL)| + 1 and Tachycardia advancement = (NNE - 1) × (TCL - PCL) - (PPI - TCL), which state that the NNE and the amount of tachycardia advancement on the first resetting stimulation are determined using regularly measured intracardiac parameters. In the retrospective cohort, the observed PPI - TCL highly correlated with the predicted PPI - TCL (mean difference 5.8 ms; r = 0.97; P < .001), calculated as PPI - TCL = (NNE - 1) × (TCL - PCL) - tachycardia advancement., Conclusion: The number of pacing stimulations required to entrain a reentrant tachycardia is predictable at any PCL after correcting for cycle length-dependent changes in conduction velocity. This relationship unifies established empirically derived diagnostic and mapping criteria for supraventricular tachycardia and ventricular tachycardia. This relationship may help elucidate when antitachycardia pacing episodes are ineffective or proarrhythmic and could potentially serve as a theoretical basis to customize antitachycardia pacing settings for improved safety and effectiveness., (Copyright © 2016 Heart Rhythm Society. All rights reserved.)

Background: Right bundle branch block (RBBB) with superior axis electrocardiographic (ECG) morphology is common in patients with idiopathic ventricular arrhythmia (VA) originating from the left posterior fascicle (LPF), from the left ventricular (LV) posterior papillary muscles (PPM), and rarely from the cardiac apical crux., Objective: The purpose of this study was to describe the ECG and clinical characteristics of idiopathic VA presenting with RBBB and superior axis., Methods: We studied 40 patients who underwent successful catheter ablation of idiopathic VAs originating from the LPF (n = 18), LV PPM (n = 15), and apical crux (n = 7). We investigated clinical and ECG characteristics, including maximum deflection index and QRS morphology in leads aVR and V6., Results: Syncope was more frequently seen in apical crux VA compared with other VAs (57% vs 6%, P < .001). Patients with apical crux VA more frequently had an maximum deflection index ≥0.55 compared with LPF VA and PPM VA (P = .02). A monophasic R wave in aVR and QS or r/S ratio <0.15 in V6 (P < .001) could distinguish apical crux VA from other VAs with high accuracy. All patients with VA underwent attempted ablation in the endocardium (success rate: LPF 89%, PPM 80%, crux 14%). Only 1 of 7 patients with apical crux VA had acute success with ablation in the middle cardiac vein. In 2 of apical crux patients, epicardial ablation using subxiphoid approach was performed successfully., Conclusion: We could distinguish LPF VA, PPM VA, and apical crux VA using a combination of clinical and ECG characteristics. These findings might be useful for counseling patients and planning an ablation strategy., (Copyright © 2015. Published by Elsevier Inc.)

Background: Ventricular arrhythmias (VAs) originating from the aortic root are common. Coronary angiography is typically recommended before catheter ablation to document proximity of the ablation catheter to the coronary ostia., Objective: To investigate how often catheter ablation in the aortic root could be guided by phased-array intracardiac echocardiography (ICE) and electroanatomic mapping without requiring aortography or coronary angiography., Methods: We reviewed consecutive patients referred for aortic root VAs to operators experienced in the use of ICE at a single center. An ICE catheter and a 3.5-mm irrigated ablation catheter were used in all cases, and the need for angiography before ablation was documented. Acute success and acute and 30-day complications were noted., Results: Thirty-five patients (age 58 ± 13 years; 74% men) were referred for the ablation of VAs; 32 of 35 (91%) underwent ablation using ICE and 3-dimensional mapping without the need for coronary angiography. Successful acute ablation was achieved in 29 of 35 (83%) patients. In all cases, the catheter tip was directly visualized with ICE >1 cm from the coronary ostia. The site of origin of the earliest VA was the left cusp (17 of 35 [49%]), right cusp (9 of 35 [26%]), right-left cusp junction (8 of 35 [23%]), or right-noncoronary cusp junction (1 of 35 [3%]). There were no cases of coronary injury, embolic stroke, aortic root perforation, worsening of aortic regurgitation, or death acutely or at 30 days., Conclusion: Radiofrequency ablation of VAs originating from the aortic root may be safely performed using ICE and electroanatomic mapping in the majority of cases without the need for coronary angiography., (Copyright © 2014 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Catheter ablation of ventricular arrhythmias (VAs) with cryoenergy has not been widely reported., Objective: The purpose of this study was to assess the feasibility and safety of cryoablation for VA., Methods: Cases where cryoablation of VA was attempted as the initial strategy or was considered to prevent potential damage to other structures such as the coronary arteries, phrenic nerve, and His bundle were collected. Thirty-three patients with either normal heart or structural heart disease undergoing VA ablation using cryoenergy at six different institutions were enrolled in the study. Epicardial access was obtained when appropriate., Results: Fifteen patients (7 men) underwent endocardial ablation, 13 (9 men) epicardial ablation (from the coronary sinus in 7), and 5 (2 men) aortic cusp ablation. Mean age was 54 ± 8 years, and ejection fraction was 45% ± 5%. In 15 (45%) patients, VAs were successfully ablated, whereas cryoablation was unsuccessful in the remaining 18 (55%) patients. Cryoablation was successful in all parahisian cases (100%). In three patients, epicardial cryoablation was successful after several failed attempts with open irrigated catheter. An aortic dissection occurred during catheter placement in the aortic cusp. At follow-up of 24 ± 5 months, all patients with acute success were free from clinical VA., Conclusion: Use of cryoenergy for ablation of VA has excellent success for arrhythmias near the His bundle; however, success rates at other sites appear less favorable. Cryoablation may be considered as an alternative approach for reducing complications during ablation of VAs originating from sites close to other relevant cardiac structures (conduction system, coronary arteries, phrenic nerve) and, in rare cases, could be used epicardially when radiofrequency energy applications have failed., (Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: The biventricular implantable cardioverter-defibrillator (ICD) is an important therapy for select patients with severe heart failure. Given reported risk factors for elevated defibrillation thresholds (DFTs), patients undergoing biventricular ICD placement would be suspected of having a higher incidence of elevated DFT., Objectives: The purpose of this study was to examine the clinical predictors and mortality risk of elevated DFTs in patients receiving a biventricular ICD., Methods: Characteristics of patients undergoing biventricular ICD placement with an elevated DFT were compared to those without an elevated DFT., Results: An elevated DFT was found in 14 (12%) of 121 patients. Mean QRS duration was 210 +/- 50 ms in the elevated DFT group and 171 +/- 36 ms in the normal DFT group (P = .01). Patients with a QRS duration >or=200 ms were more likely to have an elevated DFT than those with a duration <200 ms (odds ratio 13.4, 95% confidence interval 3.1-66.7, P <.01). No other clinical characteristics were associated with an elevated DFT. More than 90% of patients with an elevated DFT achieved an adequate safety margin through system modification or manipulation of their drug regimen. An elevated DFT did not have an impact on 2-year mortality., Conclusion: Patients with a biventricular ICD had a 12% incidence of elevated DFT in our sequential patient cohort. QRS duration prior to biventricular ICD placement is the most powerful predictor of patients at risk for an elevated DFT. An elevated DFT does not have an impact on mortality, perhaps because of successful implementation of system modifications to ensure an adequate defibrillation safety margin.

Background: Despite improvements in cardiac resynchronization therapy (CRT) implantation techniques, a significant minority of CRT attempts are unsuccessful. Inability to cannulate the coronary sinus (CS) because of difficult anatomy is a major reason for unsuccessful CRT implantation. Direct visualization of intracardiac structures during the implant may facilitate access into the CS. The present study describes CRT implantation with the aid of an endocardial visualization catheter (EVC)., Methods: Fifty-eight consecutive patients (mean age 72 +/- 12 years; ejection fraction 26.2% +/- 7.0%; New York Heart Association [NYHA] class 2.9) underwent CRT implantation using a steerable fiberoptic EVC (Acumen Medical, Inc., Sunnyvale, CA)., Results: The EVC was able to visualize the CS ostium in all cases. The CS was successfully cannulated in 57 (98.3%) of 58 patients. The time from vascular access to CS visualization was 6 +/- 5 minutes, and the total time to CS access was 8 +/- 6 minutes. Successful left ventricle (LV) lead implantation was accomplished in 55 (94.8%) of 58 patients. Three patients who had a previous history of failed LV lead implantation were successfully implanted using the EVC., Conclusion: Fiberoptic imaging of intracardiac structures during CRT implantation may be performed rapidly in a wide range of patients with an EVC. The ability to visualize right atrial anatomy may aid CS access and LV lead implantation.

Background: Detailed anatomic characterization of endocardial substrate of ventricular tachycardia (VT) is limited., Objectives: The purpose of this study was to determine the endocardial dimensions and local electrogram voltage characteristics of the reentrant circuit. VT-related conducting channels corresponding to zones of slow conduction may be identified., Methods: Electroanatomic mapping was performed in 26 patients with uniform VT. Entrainment mapping was performed in 53 VTs, of which 19 entrance, 37 isthmus, 48 exit, and 32 outer loop sites were identified. The color display of voltage maps was adjusted to identify conducting channels associated with VT circuits. A conducting channel was defined as a path of multiple orthodromically activated sites within the VT circuit that demonstrated an electrogram amplitude higher than that of surrounding areas as evidenced by voltage color differences., Results: Forty-seven (84%) of 56 entrance or isthmus sites were located within dense scar (<0.5 mV). Nearly all exits (92%) were located in abnormal endocardium (<1.5 mV), with more than half (54%) located in the border zone (0.5-1.5 mV). VT-related conducting channels was identified in 18 of 32 VTs with detailed mapping (average length 32 +/- 22 mm). The voltage threshold in the conducting channels ranges from 0.1 to 0.7 mV (mean 0.33 +/- 0.15 mV)., Conclusion: (1) Most entrance and isthmus sites of hemodynamically stable VT are located in dense scar, whereas exits are located in the border zone. (2) VT-related conducting channels may be identified by careful voltage threshold adjustment. These findings have important implications regarding strategies for substrate-based VT ablation.

Background: Idiopathic "fascicular" left ventricular tachycardia (IFLVT) is frequently not inducible or nonsustained at the time of planned catheter ablation. The mechanism of the arrhythmia has been suggested to be reentry involving a sizable area of the LV inferior septum extending from base toward the apex., Objective: We tested the ability of a series of radiofrequency lesions delivered in a linear fashion to the inferior-mid septum to control ventricular tachycardia not amenable to standard mapping ablation strategies., Methods: Programmed stimulation both at baseline state and with isoproterenol after heart rate was increased by at least 25% was performed in all patients. The patients included in the study were either non-inducible or only had brief nonsustained VT not amenable to "traditional" mapping. A detailed electroanatomic map of the LV was performed in sinus rhythm. The location of the linear lesion along the inferior septum was guided by the presence of Purkinje potentials, with pacemapping as an additional guide. A linear lesion was placed perpendicular to the long axis of the ventricle approximately midway from the base to the apex in the region of the mid to mid-inferior septum. Radiofrequency lesions were delivered using a 4mm tip catheter at 50 Watts and 52 degrees for 60-90 seconds., Results: Of 122 consecutive patients who underwent ablation of idiopathic VT from 1999 to 2003, 15 had IFLVT based on standard diagnostic criteria. Six of the 15 patients (40%) had nonsustained or no inducible VT in the EP lab. The number of RF lesions ranged from 7 to 15 (mean 9). The length of the effective linear lesion ranged from 1.2 to 2.2 cm (mean 1.7 cm). Development of left posterior fascicular block was noted in two of the six patients. However, despite the absence of development of left posterior fascicular block in the other four patients, no VT or premature ventricular beats could be induced after ablation using the same provocation maneuvers as performed in the baseline state. No spontaneous arrhythmias occurred during follow-up to 16 +/- 8 months (range 6 to 30 months)., Conclusion: In patients with difficult to induce or nonsustained VT with the typical right bundle branch block pattern and a superiorly directed axis on 12-lead ECG, RF energy ablation delivered in a linear fashion approximately midway to two thirds toward the apex along the mid to inferior septum and perpendicular to the plane of the septum is safe and effective for VT control.

Background: Idiopathic ventricular tachycardias (IVTs) can originate from the basal left ventricle (LV)., Objective: To determine if using magnetic electroanatomic mapping (MEAM) for accurate localization (1) unique ECG morphologies on pace maps from medial and lateral sites in basal LV could be identified and (2) this ECG information would facilitate VT localization., Methods: In 12 patients with structurally normal hearts undergoing ablation for IVT, detailed MEAM of LV was constructed in sinus rhythm and pace-mapping was done from the septal-parahisian (S-P) region, aortomitral continuity (AMC), and superior, superolateral, and lateral mitral annular (MA) locations. Pace maps were analyzed for ECG morphologies in limb leads and transition patterns in precordial leads., Results: Medial pacing sites (S-P and AMC) compared with lateral sites (superolateral and lateral MA) demonstrated narrower QRS complexes (134 +/- 24 msec vs. 182 +/- 18 msec; P < .05) with initial negative forces in lead V1 and predominantly positive forces in lead I (amplitude 0.59 +/- 0.27 mV vs. 0.16 +/- 0.34 mV; P < .05). The ratio of QRS complexes in leads II and III was >1 for all (12 of 12) S-P pace maps and 11 of 12 lateral MA pace maps but remained < or =1 for pace maps from 10 of 12 AMC locations, 11 of 12 superior MA locations, and 10 of 11 superolateral MA locations. Using these ECG criteria, a blinded reviewer was able to accurately localize the site of origin (SOO) of clinical arrhythmia (successful ablation site on MEAM) in 10 of 12 cases (83%) of IVT originating from basal LV., Conclusion: Pace maps from basal LV endocardium manifest site-dependent ECG morphologies that can help differentiate medial from lateral locations and can predict the SOO of clinical arrhythmias from this region.

Objectives: The purpose of this study was to (1) determine how often implantable cardioverter-defibrillator (ICD) system modifications were needed to obtain an adequate safety margin for defibrillation, (2) identify how often and for what indications defibrillation threshold (DFT) testing was not performed, and (3) identify factors predicting the need for modification., Background: Ventricular fibrillation (VF) typically is induced at the time of ICD insertion. Although DFT testing often is minimized, a safety margin of 10 J has been utilized as a standard of care. However, current devices offer technology such as biphasic waveforms and high outputs, and the need for testing has been questioned., Methods: We reviewed the records of the last 1,139 patients undergoing initial ICD placement, generator replacement, or revision., Results: Seventy-one patients (6.2%) were identified as having an unacceptably high DFT (<10 J safety margin) requiring intervention, and some required >1 modification. Use of a high-output device alone was not enough to obtain an adequate DFT in 48% (34/71) of patients who required modifications (3% of the total population). No arrhythmia inductions were performed in 54 patients (4.7%) because of well-defined clinical conditions. Patients who required system modification had a lower ejection fraction, were younger, were less likely to have coronary artery disease, were more likely to be undergoing upgrade/generator replacement, and were more likely to be taking amiodarone. Long-term mortality was not different between the group of patients who required modification compared with those who did not (17% vs 20%, P = NS)., Conclusions: Routine VF induction and documentation of effective defibrillation still remains a reasonable part of ICD placement because an inadequate safety margin may occur in >6% of patients. The incidence of patients who were inappropriate for testing based on well-defined clinical conditions is small (<5%) in this unselected large series. Although some clinical features may predict the need for system modification, additional studies are needed to better define "acceptable efficacy" of ICDs in preventing sudden death prior to altering these standards in selected patients.