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Fetal arrhythmias occur commonly, but most are benign. Clinically significant arrhythmias should be distinguished and managed. Supraventricular tachycardia (SVT) and severe bradycardia from complete heart block (CHB) can progress to heart failure and hydrops fetalis. This retrospective review of 2042 fetal echocardiograms aims to characterize an institutional experience with fetal arrhythmias. 131 fetuses were referred for arrhythmia evaluation. Premature atrial contractions (PACs) were found in 67 (51%) of which a third had a prominent atrial septal aneurysm. 49 (37%) had sinus rhythm (no noted arrhythmia). 15 (11%) had hemodynamically significant arrhythmias, which included fetal tachycardias in 12 (9%) and CHB in 3 (2%). All fetuses with tachycardia had structurally normal hearts. 10 had fetal SVT (3 with hydrops and 7 without hydrops) and 2 had atrial flutter (1 with hydrops and 1 without hydrops). All fetuses in tachycardia were converted to sinus rhythm and 2 required antiarrhythmic treatment after birth. CHB was found in 3 fetuses. Major cardiac malformations and hydrops were noted in 2 of these fetuses, both resulting in fetal demise. The third fetus with CHB had a structurally normal heart, was associated with maternal systemic lupus erythematosus (positive SS-A, SS-B antibodies), and required a pacemaker after birth. PACs and sinus rhythm were the most common diagnosis in fetuses referred for arrhythmia evaluation. Despite the presence of hydrops, SVTs responded well to maternal administration of antiarrhythmic therapy and were successfully converted to sinus rhythm. CHB can be associated with maternal autoimmune disease and certain cardiac malformations. The prognosis of CHB in the presence of cardiac disease is poor.

Background: Although there is agreement of the importance of cardiac catheterization, especially interventional procedures, cardiac catheterization in postoperative critical care unit (CCU) period is often debated. The focus of this study was to explore the indications for and determinants of outcome after cardiac catheterization in this setting. Methods: Between March 2004 and October 2006, 49 children (2.8% of cardiac surgeries) underwent 62 catheterizations before discharge from the CCU. Morphological, surgical, and catheterization data were accrued and analyzed using parametric competing risks models and multivariable risk-hazard analysis. Results: Median age at surgery was 167 days (0–13.5 years) and time to catheterization was 8.5 (0–84) days following surgery. Catheterization procedures were either interventional (n = 35) or noninterventional (n = 27). Children who required a more urgent investigation following initial surgery more often had deployment of a stent at catheterization (P = 0.01) or subsequent surgical pulmonary artery augmentation (P < 0.01). Surgical reoperation was required following 23 (37%) catheterizations and was more common following index surgery involving a cavopulmonary shunt. Overall mortality was high (43%). Delayed invasive investigation beyond 2–3 weeks (P = 0.04) or a splinted sternum (P < 0.001) were risk factors for death. In addition, reoperation after a noninterventional catheterization predicted worse survival (P < 0.001). Conclusions: The need for invasive investigation in the immediate CCU period is associated with a poor outcome, especially when the investigation is delayed or an intervention is not possible. Identification of at-risk patients may improve outcomes. Best outcomes follow expedient catheterization with definitive management (often stent deployment or pulmonary artery augmentation). © 2009 Wiley-Liss, Inc.

Standardized guidelines for polysomnography (PSG) have not specified methods for acquiring or interpreting electrocardiographic (ECG) data. The practice of single lead ECG monitoring during PSG may allow identification of simple measures of cardiac rhythm but reduces the ability to detect myocardial ischemia and to define cardiac intervals. Although simple measures of cardiac rhythm such as heart rate and cardiac pauses are inherently reliable, there is limited data regarding outcome measures relative to sleep related heart rates and cardiac events during sleep. Several observational and cross-sectional studies demonstrate that average heart rate drops nearly 50% from infancy through young adulthood and that the average heart rate slows during sleep compared with wakefulness; the definitions of sinus bradycardia and sinus tachycardia should therefore be lower during sleep than wakefulness. Asystoles of up to 2 seconds are seen in normal populations during sleep. Although there may be an increased risk of certain arrhythmias at night, particularly in sleep disordered breathing, there is no evidence that supports different definitions for these arrhythmias during sleep compared with wakefulness. When the quality of tracings permits, the standard definitions of narrow- and wide-complex tachycardias and atrial fibrillation may be employed. In the future, expansion to multiple ECG leads and the use of alternative tools may provide better definition of heart rates and cardiac events during sleep.

Hematopoietic stem cell transplantation (HSCT) treats disorders affecting patients of all ages. We studied the rate-corrected cardiac QT interval (QTc) in 995 consecutive children and adults undergoing HSCT at the University of Minnesota. We sought to (1) describe QTc before and after HSCT; (2) describe the change in QTc after HSCT; (3) identify factors affecting QTc and its change; and (4) scrutinize an 'at risk' sub-cohort with a long QTc before HSCT. Pre HSCT: 952 (96%) patients had an evaluable electrocardiography (ECG); median QTc was 426 ms and depended upon disease necessitating transplant. Post HSCT: 506 (51%) patients had an evaluable ECG; median QTc was 441 ms. Intrapatient QTc change: 490 (49%) evaluable patients showed median QTc change (pre to post HSCT) of +16 ms (P

The development and structure of the cardiac conduction system, including the known molecular and cellular factors that regulate development of the conduction system are outlined. Part II includes the structure of the cardiac conduction system and its relationship to the working myocardium, including the influence of the autonomic nervous system. The final section outlines the impact of individual congenital heart defects on the anatomy and function of the conduction system.

Background: The anatomic substrate for protected isthmus conduction in the right atrium has been well defined. Little is known of similar substrates in the left atrium (LA). Methods: Patients (pts) with reentrant tachycardia (AVRT) supported by a single left-sided accessory pathway were studied retrospectively (n = 64) and prospectively (n = 31). Intracardiac electrograms were recorded from the His bundle position and coronary sinus (CS). The LA was mapped with a steerable catheter using the transseptal approach. LA anatomy was examined grossly and histologically in six cadaver hearts after removal of endocardium. Results: A distal-to-proximal CS activation sequence during AVRT was seen in all patients with a left lateral accessory pathway before ablation. After one to three radiofrequency (RF) energy deliveries that did not interrupt accessory pathway conduction, the CS activation sequence was reversed in three patients in the retrospective group and bidirectional conduction block in the posterior atrioventricular vestibule of the LA (PAVV) was demonstrated in nine patients in the prospective group. Four of the six cadaver hearts showed a distinct circumferential inferoposterior myocardial bundle that coursed parallel to the CS in the PAVV. Conclusions: We described evidence of bidirectional intraatrial block in the PAVV after application of RF energy during accessory pathway ablation. Such conduction block may mimic the presence of a second accessory pathway. Our data suggest that circumferential conduction in the PAVV may be poorly coupled to the rest of the LA and may be involved in the macro-reentrant circuit around the mitral annulus. The circumferential inferoposterior myocardial bundle may serve as the underlying anatomic substrate

Atriofascicular pathways supporting antidromic reentrant tachycardia are uncommon, and may be difficult to ablate. Traditional mapping can be associated with traumatic loss of atriofascicular conduction. Atriofascicular fibers can insert into the right bundle and will, therefore, first activate the right ventricle. In contrast to initial activation of the ventricle near the tricuspid annulus that can be seen in patients with right-sided decremental atrioventricular pathways. We used electroanatomic mapping to map and ablate the ventricular insertion of atriofascicular pathways in two patients during sinus rhythm and during atrial pacing. In our 2 cases an atriofascicular potential was recorded from below the tricuspid valve annulus and tagged. At this site, each pathway was ablated with one radiofrequency lesion. We describe 2 cases where electroanatomic mapping of the right ventricle was used to map and ablate atriofascicular pathways.

Since children have different activity patterns and exercise responses, uncertainty exists as to whether minute ventilation (MV) sensors designed for adults provide adequate chronotropic response in pediatrics. In particular, high respiratory rates (RR48 breaths/min), which are characteristic of the ventilatory response to exercise in children, cannot be sensed by MV rate responsive pacemakers. The purpose of this study was to evaluate the MV sensor rate response of the Medtronic Kappa 400 using exercise data from healthy children in a computer simulation of its rate response algorithm. Thirty-eight healthy children, ages 6-14, underwent a treadmill maximal exercise test. Subjects were divided based on body surface area (BSA) and MV rate response parameters were selected. Respiratory rates and tidal volumes were entered into the Kappa 400 rate response algorithm to calculate sensor-driven rates. Intrinsic heart rate (HR), oxygen uptake, and sensor-driven rates were normalized to HR reserve (HRR), metabolic reserve (MR), and sensor-driven reserve to compare across groups. Linear regression analysis among sensor-driven rate reserve, HRR, and MR was performed as described by Wilkoff. The mean slopes (+/- SD) of the relationships between the sensor-driven rate reserve and HRR were 1.06 +/- 0.34, 1.07 +/- 0.28, and 1.01 +/- 0.19 for children with BSA1.10 m2, 1.10BSA1.40 m2, and BSA1.40 m2, respectively. High correlations were found between sensor-drive rates and HR responses and between sensor-drive rates and MV throughout exercise. No significant differences were noted between sensor-drive rates and HR using the Wilkoff model. From this study the authors conclude that: (1) MV is a good physiological parameter to control heart rate and (2) simulated sensor-driven rates closely match intrinsic HRs during exercise in healthy children, which supports the appropriateness of clinical validation in pediatric pacemaker patients.

Background —We correlated the electrophysiologic (EP) effects of adenosine with tachycardia mechanisms in patients with supraventricular tachycardias (SVT). Methods and Results —Adenosine was administered to 229 patients with SVTs during EP study: atrioventricular (AV) reentry (AVRT; n=59), typical atrioventricular node reentry (AVNRT; n=82), atypical AVNRT (n=13), permanent junctional reciprocating tachycardia (PJRT; n=12), atrial tachycardia (AT; n=53), and inappropriate sinus tachycardia (IST; n=10). There was no difference in incidence of tachycardia termination at the AV node in AVRT (85%) versus AVNRT (86%) after adenosine, but patients with AVRT showed increases in the ventriculoatrial (VA) intervals (13%) compared with typical AVNRT (0%), P P P Conclusions —The EP response to adenosine proved of limited value to identify the location of AT or SVT mechanisms. Features favoring AT were the presence of AV block or marked shortening of atrial cycle length before tachycardia suppression. Atrial fibrillation was more common after adenosine in patients with AVRT, PJRT, or AT. Patients with IST showed increases in cycle length with little change in atrial activation sequence after adenosine.

ObjectiveThe purpose of this study is to review the clinical course of persistent junctional reciprocating tachycardia (PJRT) in 21 patients spanning a wide age range to examine the electrophysiologic characteristics of the conduction system in these patients with PJRT, particularly in regards to its incessant nature and to evaluate the long-term response to radiofrequency ablation.BackgroundPersistent junctional reciprocating tachycardia is uncommon, occurring in 1% of patients with supraventricular tachycardia. Its presentation, course and treatment are incompletely characterized.MethodsThe clinical, electrocardiographic, electrophysiologic and echocardiographic data of 21 patients with PJRT were reviewed.ResultsIn 9 of these 21 patients, the mean tachycardia cycle length increased significantly (p < 0.0001) as the patients grew, from a mean tachycardia cycle length of 308 ± 64 ms in the patients less than 2 years, 414 ± 57 ms in the patients between 2 years and 5 years, to 445 ± 57 ms in the patients greater than 5 years, primarily due to slowing of retrograde conduction in the accessory pathway. Persistent junctional reciprocating tachycardia was associated with impaired ventricular function in 11, improving spontaneously in 4 and, after successful ablation of the accessory pathway, in 7. All patients except one were uncontrolled on one or more medications. Ablation of the accessory pathway was successful in 19 of 21 patients.ConclusionsWe conclude that PJRT is characterized by an onset in early childhood and by an age-related prolongation of the tachycardia cycle length mediated primarily through conduction delay in the concealed, retrogradely conducting accessory pathway. Ablation of the accessory pathway provides definitive treatment for PJRT.

In patients with congenital heart disease who have undergone palliative surgical interventions postoperative arrhythmias frequently complicate the clinical course. Intraatrial reentrant tachycardias (IARTs) are one of the most common forms of postoperative arrhythmias in these patients and can lead to significant morbidity and even mortality. Drug therapy and/or antitachycardia pacing have been disappointing. Ablative therapy with radiofrequency energy offers a potential for cure for these patients but the conventional approach using multielectrode recordings and fluoroscopic guidance is technically difficult and provides limited success. Recent development of a novel nonfluoroscopic technology with electroanatomical mapping using the CARTO mapping/ablation system has shown promising results in defining the arrhythmia circuit, facilitating diagnosis, and guiding ablative therapy. Based on our preliminary experience, a systematic approach to postoperative IART using electroanatomical mapping is described. Further studies are needed to fully evaluate the impact of this new technology on the management and therapy of IART.

To review our experience with cases of narrow complex tachycardia with VA block, highlighting the difficulties in the differential diagnosis, and the therapeutic implications. Prior reports of patients with narrow complex tachycardia with VA block consist of isolated case reports. The differential diagnosis of this disorder includes: automatic junctional tachycardia, AV nodal reentry with final upper common pathway block, concealed nodofascicular (ventricular) pathway, and intra-Hissian reentry. Between June 1994 and January 1996, six patients with narrow complex tachycardia with episodes of ventriculoatrial block were referred for evaluation. All six patients underwent attempted radiofrequency ablation of the putative arrhythmic site. Three of six patients had evidence suggestive of a nodofascicular tract. Intermittent antegrade conduction over a left-sided nodofascicular tract was present in two patients and the diagnosis of a concealed nodofascicular was made in the third patient after ruling out other tachycardia mechanisms. Two patients had automatic junctional tachycardia, and one patient had atrioventricular nodal reentry with proximal common pathway block. Attempted ablation in the posterior and mid-septum was unsuccessful in patients with nodofascicular tachycardia. In contrast, those with atrioventricular nodal reentry and automatic junctional tachycardia readily responded to ablation. The presence of a nodofascicular tachycardia should be suspected if: (1) intermittent antegrade preexcitation is recorded, (2) the tachycardia can be initiated with a single atrial premature producing two ventricular complexes, and (3) a single ventricular extrastimulus initiates SVT without a retrograde His deflection. The presence of a nodofascicular pathway is common in patients with narrow complex tachycardia and VA block. Unlike AV nodal reentry and automatic junctional tachycardia, the response to ablation is poor.

Adenosine, when given as an intravenous bolus, has been shown to produce atrioventricular nodal block in humans. To examine the effect of adenosine on conduction across both accessory pathways and the atrioventricular node in children, we reviewed our experience with adenosine administered during both atrial and ventricular pacing in 42 patients with atrioventricular resting tachycardia and in eight patients with atrioventricular nodal reentry tachycardia. Adenosine was administered as a mean bolus of 195 μg/kg/dose during both atrial and ventricular pacing, examining antegrade and retrograde conduction before and after radiofrequency ablation. In those patients with persistent or intermittent pre-excitation, anomalous ventricular activation was either unchanged (n=8) or increased (n=11). Retrograde conduction (either through the accessory pathway alone in three, or across both the accessory pathway and the atrioventricular node in 19) persisted in 92% of the 24 patients studied. Adenosine produced either first or third degree antegrade heart block in all patients studied without pre-excitation (those with either dual atrioventricular nodal pathways or concealed accessory pathways). Adenosine produced retrograde block in all of the eight patients with dual atrioventricular nodal pathways. In contrast, retrograde conduction persisted in 82% (14/17) of patients with concealed accessory pathways (p=0.001). When used to examine retrograde conduction, adenosine was a sensitive (82%) and highly specific (producing retrograde atrioventricular block in all patients with dual atrioventricular nodal pathways) predictor of tachycardia supported by a concealed accessory pathway. Adenosine yielded a sensitivity and specificity of 96% and a positive predictive value of 99.5% for the success of ablation of accessory pathways. These data indicate that the pattern of adenosine-induced changes in either antegrade or retrograde atrioventricular conduction, or conduction in both directions, in young patients with supraventricular tachycardia is related to the mechanism of the tachycardia. Adenosine, therefore, is a useful adjunct in the electrophysiologic evaluation of supraventricular tachycardia in children.

In a canine puppy model, pulmonary artery stenosis was created by banding the left pulmonary artery to 30-40% of its original diameter. Animals underwent right heart catheterization and angiography 1-2 mo later, and Palmaz P308 stents were implanted. Stent redilation was performed 3-5 mo later. One mo postredilation, the animals were restudied and sacrificed. Coarctations of the aorta were created by transverse aortic incision and longitudinal repair. P308 stent implantation was performed 2-3 mo later. Stent redilation was performed after 6-10 mo, and the animals were restudied and sacrificed 1-2 mo later. Stent implantation was performed in 6 puppies with pulmonary artery stenosis, as 2 animals developed postoperative pulmonary arterial hypoplasia, precluding stenting. The stenosis diameter increased from 4.8 +/- 0.5 mm to 7.4 +/- 0.6 mm (mean +/- SE) following stenting (P = 0.005), and increased further to 9.2 +/- 0.7 mm following redilation (P < 0.001). There were no significant vessel tears or ruptures. Coarctation stenting was performed in 8 animals. The coarctation was dilated from 5.8 +/- 0.9 mm to 9.8 +/- 0.6 mm (P < 0.001), and to 13.5 +/- 0.5 mm at redilation (P = 0.002). Redilation could not be performed in 1 animal. Aortic rupture and death occurred in 2 of 7 animals at redilation. Stent implantation and redilation in experimental pulmonary artery stenosis appears safe and effective. Though stent implantation for coarctation of the aorta appears safe, there was a 28% aortic rupture rate at stent redilation in this model.

The Senning and Mustard procedures are often associated with the development of atrial tachyarrhythmias, which may be a cause of sudden death. We hypothesized that atrial surgery creates barriers to impulse propagation, establishing potential routes for atrial reentry, and that mapping combined with knowledge of the surgical anatomy could identify zones that are critical to the tachycardia to be targeted for radiofrequency catheter ablation. Patients underwent mapping to identify early sites of atrial activation that were related to anatomic or surgically created obstacles, with confirmation by pacing to demonstrate concealed entrainment. Radiofrequency lesions were placed to connect these obstacles, while observing for tachycardia termination. Thirteen tachycardias were attempted in 10 patients, 10 successfully. Three patients had 2 distinct tachycardias. Successful sites were in right atrial tissue, although in many, a retrograde approach to the pulmonary venous atrium was necessary. Ablation of the clinically documented tachycardia was successful in 9 of 10 patients. The most common successful site was the region of the coronary sinus mouth, approached antegrade or retrograde. Ablation of intraatrial reentrant tachycardias after the Senning or Mustard procedure is feasible using concealed entrainment mapping techniques, but requires a detailed knowledge of the individual surgical anatomy and the ability to approach the pulmonary venous atrium. Radiofrequency ablation offers significant advantages over other management modalities in this patient group.

Cardiac arrhythmias in children in the pediatric cardiovascular intensive care unit are a function of the interaction between the intrinsic disease, complications of successful palliation and treatment, and the moment-to-moment homeostatic state of the patient (autonomic tone, electrolyte balance, hemodynamic status, therapeutic agents). Knowledge regarding all three factors are critical for the successful management of arrhythmias in patients in the pediatric cardiovascular intensive care unit. Continuous electrocardiographic monitoring with an archival system is essential for instantaneous and accurate detection of potentially life-threatening tachy and bradyarrhythmias. Intensivists, cardiologists and intensive care nursing personnel must constantly process data that lead to rapid diagnosis and definitive management of an abnormal cardiac rhythm in these highly vulnerable children.

Percutaneous catheter mapping and radiofrequency ablation of the AV node-His bundle system (with subsequent transvenous endocardial ventricular pacing) were performed on an 18-year-old woman with transposition of the great arteries and intact ventricular septum and chronic arrhythmias 15 years following a Mustard operation. Exclusion of the AV conduction tissue from the systemic venous circulation by the complex anatomy and the Mustard repair was circumvented by a retrograde approach across the aortic valve to the morphological right ventricle yielding access to the AV node-His bundle system.

Between January 1990 and February 1993, 73 patients underwent first-stage reconstruction for hypoplastic left heart syndrome at the University of Michigan Medical Center. During this period, surgical reconstruction remained essentially constant and consisted of a pulmonary artery–to–aorta anastomosis with allograft augmentation of the ascending, transverse, and proximal descending aorta, restriction of pulmonary blood flow with a polytetrafluoroethylene shunt from the innominate artery to the central pulmonary artery confluence, and atrial septectomy. Hospital survival was 62 of 73 patients, 85% (70% confidence limits: 80% to 89%). These results stand in marked contrast to those obtained during the earlier years of our experience from 1986 to 1989 when only 21 of 50 patients (42%, 70% confidence limits: 35% to 49%) survived ( p = 0.001). Among the most recent group of patients, only 2 of 7 patients older than 1 month of age at operation survived, whereas 60 of 66 (91%, 70% confidence limits: 87% to 94%) patients younger than 1 month of age survived ( p = 0.0001). Anatomic subtype and ascending aortic diameter were not predictive of survival. Actuarial survivals for those patients younger than 1 month of age at the first-stage operation, including hospital deaths and subsequent operative procedures, were 81%, 74%, and 74% at 6 months, 1 year, and 2 years, respectively. These results indicate that survival for patients after first-stage reconstruction for hypoplastic left heart syndrome has significantly improved in recent years. Older age was a strong risk factor, with a hospital survival of 91% for those patients undergoing first-stage palliation within the first month of life. These data have important implications for the type of operative intervention and its timing. (J THORAC CARDIOVASC SURG 1994;107:934-40)

Persistent junctional reciprocating tachycardia is an arrhythmia that usually presents in infancy or childhood but may not be recognized until adulthood. In older patients, the heart rate may not be sufficiently fast to result in enough symptoms to provoke further examination or evaluation by a physician. Age-related changes in both the rate and the intermittent nature of the tachycardia may mask the diagnosis. Thus, the diagnosis may be delayed until tachycardia-related symptoms or palpitations become more apparent. Presentation with heart failure is more common in younger patients. Since the heart rates associated with PJRT will most likely slow with age, radiofrequency ablation may usually be deferred in small children with this tachycardia. Because the tachycardia has a possible spontaneous or intermittent resolution, as well as variable expression of impaired ventricular function, and since it may be effectively and safely treated with ablation, this definitive therapy, whether radiofrequency current or cryotherapy, should be considered only in patients of suitable size and when there are symptoms related to the tachycardia.

A stable rhythm of very short cycle length (CL) in the left atrium (LA) can cause fibrillatory conduction, particularly in the right atrium (RA). Fast Fourier transform (FFT) analysis reliably identifies LA to RA conduction path(s) during atrial fibrillation (AF). We tested the hypotheses that FFT analysis of atrial electrograms (AEGs) during AF simulation will reliably identify the critical LA driver CL that causes RA fibrillatory conduction (i.e., the critical conduction breakdown CL) and that a longer critical conduction breakdown CL is found in atria of abnormal (sterile pericarditis) compared to normal dogs. We paced from Bachmann's bundle and the posterior-inferior LA at rapid rates to mimic an LA driver. During pacing, 4 sec of FFT analysis of 203 bipolar AEGs was performed and showed: 1) a single dominant frequency peak at the pacing CL in both atria when the atria followed the pacing in a 1:1 manner; 2) multiple and broad frequency peaks on the RA and parts of the LA at the conduction breakdown CL; and 3) the conduction breakdown CL is longer in pericarditis than normal dogs. FFT analysis allowed reliable detection of the critical CL of an LA driver that induces RA fibrillatory conduction.

Automatic atrial tachycardia (AAT) is a rare supraventricular tachyarrhythmia (

In anisotropic tissue (e.g., right atrium), nonuniform conduction may cause conduction block/delay, or form a functional line of block, thus, providing a substrate for the initiation/maintenance of atrial arrhythmias. We tested the hypothesis that the activation patterns generated by bipolar, linear, triple site stimulation create more uniform propagation compared to single site stimulation, thereby, minimizing or eliminating potential substrates for initiation/maintenance of reentrant atrial arrhythmias. The canine sterile pericarditis model and normal dogs were studied. A plunge wire electrode pair was placed at the superior aspect of the crista terminalis (CT) for single site pacing. For triple site pacing, three bipolar pairs were placed perpendicular and parallel to the superior aspect of the CT in a linear fashion. Rapid pacing using different electrode configurations was performed at 200 ms and 300 ms cycle lengths up to 6 sec. During pacing, 404 unipolar atrial electrograms were recorded simultaneously from electrode arrays placed on the atria. The data demonstrate that linear triple site pacing creates more uniform linear propagation with less or no conduction delay/block, in contrast to single site pacing which creates elliptical impulse propagation. These findings may help develop alternative pacing techniques for termination and/or prevention of atrial arrhythmias.

Atriofascicular pathways supporting antidromic reentrant tachycardia are uncommon, and may be difficult to ablate. Traditional mapping can be associated with traumatic loss of atriofascicular conduction. Atriofascicular fibers can insert into the right bundle and will, therefore, first activate the right ventricle. In contrast to initial activation of the ventricle near the tricuspid annulus that can be seen in patients with right-sided decremental atrioventricular pathways. We used electroanatomic mapping to map and ablate the ventricular insertion of atriofascicular pathways in two patients during sinus rhythm and during atrial pacing. In our 2 cases an atriofascicular potential was recorded from below the tricuspid valve annulus and tagged. At this site, each pathway was ablated with one radiofrequency lesion. We describe 2 cases where electroanatomic mapping of the right ventricle was used to map and ablate atriofascicular pathways.

This article summarizes delayed interruption in anomalous conduction through accessory connections following radiofrequency ablation attempts in three patients. The time course of the delayed interruption in accessory connection conduction suggests that such an effect is unlikely to occur after the first week following unsuccessful radiofrequency ablation.

Background Atrial fibrillation (AF) may cause life-threatening ventricular arrhythmias in patients with Wolff-Parkinson-White syndrome. We prospectively evaluated the effects of ibutilide on the conduction system in patients with accessory pathways (AP). Methods and Results In part I, we gave ibutilide to 22 patients (18 men, 31±13 years of age) who had AF during electrophysiology study, including 6 pediatric patients ≤18 years of age. Ibutilide terminated AF in 21 of 22 patients (95%) during or 8±5 minutes after infusion and prolonged the shortest preexcited R-R interval during AF. Successful ablation was performed in all patients. In part II, ibutilide was given to 18 patients (14 men, 28±21 years) to assess its effects on the AP and conduction system. Ibutilide prolonged the antegrade atrioventricular node effective refractory period (ERP) (from 252±60 to 303±70 ms; P P Conclusions We report the use of ibutilide in terminating AP-mediated AF, including the first report in the pediatric population. Ibutilide prolonged refractoriness of the atrioventricular node, His-Purkinje system, and AP.

Changes in the retrograde conduction time (ventriculoatrial [VA]) interval during functional bundle branch block (BBB) have been used to separate septal from free wall accessory pathways (APs), but different values of the VA interval prolongation (deltaVA) have been described in different reports. A total of 95 patients with single nondecremental APs who developed BBB during atrioventricular reentrant tachycardia were studied. Free wall APs were found in 60 patients, and 35 had septal APs. For patients with free wall APs, complete and incomplete BBB ipsilateral to the atrial insertion site of APs were observed in 39 of 60 patients (65%) and 31 of 60 patients (52%), respectively. For patients who had both complete (QRSor = 120 ms) and incomplete (QRS120 ms) BBB during atrioventricular reentrant tachycardia, deltaVA for patients with complete BBB was significantly greater than in those with incomplete BBB, 59 +/- 19 ms versus 30 +/- 11 ms, p0.001. For patients with septal APs and complete and incomplete BBB during tachycardia, the mean deltaVA for those with complete BBB was 31 +/- 20 ms and was significantly longer than in patients with incomplete BBB (14 +/- 6 ms), p0.001. There was no significant difference in deltaVA between those with free wall APs and incomplete BBB compared with those with septal APs and complete BBB. The criteria of QRSor = 120 ms associated with deltaVAor =40 ms served to best separate free wall from septal APs with a sensitivity of 88% and a specificity of 89%. Left anterior fascicular block was associated with marked lengthening of deltaVA for those with left free wall APs, whereas a left posterior fascicular block pattern resulted in a marked increase in the deltaVA for patients with posteroseptal APs. In the absence of fascicular block patterns, a deltaVAor =40 ms provides strong evidence of a free wall AP, with a sensitivity of 95% and a specificity of 100%. The left posterior fascicle appears to provide predominant innervation of the posterior septum.

Background —The long-QT syndrome is associated with sudden cardiac death. Combination of β-blocker and pacing therapy has been proposed for treatment of drug-resistant patients. The purpose of this study was to summarize our long-term experience with combined therapy in patients with long-QT syndrome. Methods and Results —A total of 37 patients with idiopathic long-QT syndrome were treated with combined therapy consisting of continuous cardiac pacing and maximally tolerated β-blocker therapy and followed up for 6.3±4.6 years (mean±SD). The group consisted of 32 female and 5 male patients with a mean age of 31.6 years. The mean paced rate was 82±7 bpm (range, 60 to 100 bpm). On follow-up, recurrent symptoms caused by pacemaker malfunction were documented in 3 patients. Four patients died during the follow-up period: 2 adolescents stopped β-blocker therapy, 1 patient died suddenly while treated with combined therapy, and 1 patient died of unrelated causes. In addition, 3 patients had resuscitated cardiac arrest while on combined therapy, and 1 patient had repeated, appropriate implantable cardioverter-defibrillator discharges on follow-up. Conclusions —Because 28 of 37 patients remain without symptoms with β-blocker therapy and continuous pacing, combined therapy appears to provide reasonable, long-term control for this high-risk group. However, the incidence of sudden death and aborted sudden death (24% in all patients and 17% in compliant patients) strongly suggests the use of a “back-up” defibrillator, particularly in noncompliant adolescent patients. Implantable cardioverter-defibrillator therapy, however, may be associated with recurrent shocks in susceptible patients.

Intraatrial reentrant tachycardia, which occurs frequently in patients who have undergone corrective surgery for congenital heart disease, presents a challenge to successful management. Because the surgical repair sites are invariably critical to the development and maintenance of reentrant atrial tachycardia, we use the term "incisional reentry" to describe these arrhythmias. An understanding of the electrophysiology of such "incisional reentry," and techniques to identify a critical isthmus, are essential for successful ablation of these circuits. A critical isthmus may be identified by the presence of entrainment with concealed fusion. Confirmation that the site is critical to the tachycardia circuit is obtained by an analysis of the relationship between the postpacing interval and the tachycardia cycle length. Advances in mapping from multiple simultaneous sites, along with the ability to create larger, deeper lesions will be needed in order to cure a larger number of these patients. Ultimately, in some cases one must consider each procedure palliative rather than curative, as the disease progresses and substrate evolves and more tachycardia circuits become active.

We describe a technique for ablation of junctional tachycardia focus by means of examining the earliest atrial activation sequence during tachycardia. The procedure was successful in 7 of 9 patients, and 1 developed complete atrioventricular block.

Electrograms observed prior to successful and unsuccessful ablation trials in 33 patients (362 attempts) with manifest pathways and 18 patients (194 attempts) with concealed pathways were compared to identify the electrogram patterns that are associated with successful radiofrequency ablation of accessory atrioventricular connections in young patients (mean age 12.7 years; range 4-22 years). Success was defined as permanent or transient interruption of conduction in the accessory connection. Predictors of success in patients with manifest pathways were local ventricular preexcitation (pequals 0.0001), left-sidedness (43 or 174) of the accessory connection compared (pequals 0.04) to right-sidedness (27 of 172), a probable Kent bundle potential (29 of 84 versus 39 of 256; pequals 0.0001), and short antegrade atrioventricular conduction intervals (53.1 +/- 31.9 ms versus 64.6 +/- 32.0 ms; pequals 0.02). Predictors of success in patients with concealed pathways were short ventriculoatrial conduction times (103.3 +/- 35.8 ms versus 117.9 +/- 34.8 ms; pequals 0.01), and left-sided (42 of 125) pathways (pequals 0.03; versus right-sided, 11 of 60). The presence of a Kent bundle potential was not significant. We conclude that specific electrogram patterns can predict successful ablation of either manifest or concealed accessory pathways. Use of these criteria may reduce the delivery of unnecessary energy to young myocardium.

Comprehensive electrophysiologic study with radiofrequency ablation requires a number of intracardiac catheters. To reduce the number of catheters placed in children, the authors evaluated a series of customized catheters that combined the functions of two catheters. The customized 6F catheter contains eight electrodes placed in pairs at 4, 5, 6, 7, or 8 cm from the tip for recording the His electrogram and at the tip for right ventricular pacing. The amplitude of the bundle of His potential recorded through the His right ventricular apex (RVA) catheter (n = 63) and the ventricular pacing threshold (in mA) (n = 48) were measured and compared to the maximal bundle of His potential recorded with a 6F hexapolar catheter in 24 and 13 other patients, respectively. The relationship between the distance from the distal electrode pair at the tip and the third electrode from the tip (the His/RVA distance) and patient size was analyzed in 42 patients. Following the initial study in the 90 patients, the selection of the optimal His/RVA catheter for 19 patients was determined by examining the regression plots derived from the first group of 90 patients. The measured His/RVA distance was then determined by noting the His/RVA distance of the catheter used. Regression analysis was then used to evaluate the fit between the predicted His/RVA distance based on weight, height, or body surface area (BSA) and the observed His/RVA distance. The maximal bundle of His electrogram measured in the two groups using the His/RVA catheter was compared. To evaluate catheter stability during the study, the amplitude of the maximal His potential was measured in the 19 patients at the onset, midpoint, and end of the study. The maximal His potential recorded through the octapolar catheter (0.21 mV) was significantly (P < .04) greater than that recorded through the hexapolar catheter (0.10 mV). The mean ventricular threshold measured through the octapolar catheter (0.44 mA) was significantly (P < .001) less than that measured through the hexapolar catheter (1.13 mA). There was a significant (P < .0001) correlation between BSA, weight, and height and the His/RVA distance. There was no significant difference in the mean maximal amplitude of the His potential (0.21 +/- 0.31 mV vs 0.15 +/- 0.12 mV) recorded through the His/RVA catheter between the two groups. The His/RVA distance estimated by weight, when plotted against the measured distance, demonstrated a good correlation (r = .84) between the expected His/RVA distance based on the subject's weight and that actually observed. In 18 of 19 subjects, the first catheter based on the patient's weight (in kilograms) predicted the appropriate and only catheter used. There was no significant difference in the mean maximal bundle of His electrogram recorded at the beginning of the study (0.15 +/- 0.12 mV), midway into the study (0.15 +/- 0.11 mV), and at the end (0.13 +/- 0.13 mV); however, there was extensive variation within individuals and over time. These data support the recording of a stable, high-quality bundle of His electrogram and RVA pacing through a single catheter system and, hence, have important, practical implications for invasive electrophysiologic studies in children.

Abstract 1967 Introduction: The cardiac QT interval (QT) has gained deserved scrutiny among electrophysiologists. Reflecting the duration of the ventricular myocardial depolarization/repolarization cycle, the QT depends upon ion exchange across cardiomyocyte membranes. Ion flux perturbations (due to abnormalities of membrane-bound ion channel number, structure or function) can predispose to QT prolongation that, in turn, is associated with linearly increasing risks of ventricular tachy-arrhythmias and sudden death. As both polypharmacy and dys-electrolytemia have been reported to affect QT, we studied the interval's behavior in the potentially at-risk population of children and adults undergoing hematopoietic cell transplantation (HCT). Methods: We retrospectively reviewed over 2600 cardiologist-evaluated electrocardiograms (ECG) and transplant-related data for 995 consecutive children and adults undergoing HCT between 2006 and 2010, inclusive. Patients underwent routine pre-HCT ECG screening; repeat studies were obtained for various clinical indications. Corrected QT intervals (QTc) were noted; any study demonstrating non-sinus rhythm was disregarded. Multivariate regression models tested the association between QTc and other patient or transplant-related covariates (including age, gender, primary diagnosis, intensity of conditioning, and donor relatedness/graft-versus host disease prophylaxis for allograft recipients); reference groups representing fixed covariate characteristics were defined among the cohort for comparison. Student's t-test was used to determine the significance of aggregate intra-patient change in QTc from pre- to post-HCT. Results: Pre-HCT: 952 patients had an evaluable pre-HCT maximum QTc observed at a median Day −22. Median QTc was 428 ms (range, 330 to 569; interquartile range [IQR], 409 to 447). Statistically significant QTc variability with age was observed and reflected widely accepted age-dependent phenomena in the population-at-large. Factors predicting shorter QTc included male gender (-11 ms compared to reference group [CRG], p < 0.01) and inherited metabolic disorder (IMD) as HCT indication (-10 ms CRG, p = 0.03). Factors predicting longer QTc were myeloproliferative disorder (+22 ms CRG, p = 0.01) and acute myeloid leukemia (+7 ms CRG, p = 0.02) as HCT indications. Post-HCT: 578 patients had an evaluable post-HCT maximum QTc observed at a median Day +69. Median QTc was 454 ms (range, 367 to 619; IQR, 433 to 476). Age was not significantly predictive of maximum QTc post-HCT. Factors predicting shorter QTc were male gender (-7 ms CRG, p = 0.05) and no exposure to mycophenolate mofetil (MMF) for graft-versus-host disease (GvHD) prophylaxis (-11 ms CRG; p = 0.05). Patients diagnosed with acute lymphoblastic leukemia (ALL) demonstrated longer QTc (+17 ms CRG, p = 0.03). δQTc: 559 patients had at least one evaluable pre- and one evaluable post-HCT ECG. The median δQTc (defined per patient as [mean post-HCT QTc] - [mean pre-HCT QTc]) was 15.7 ms (range, −72 to 142; IQR, −2 to 32). A highly significant difference between post-HCT and pre-HCT QTc per patient was observed in this cohort (p < 0.01). Very Long QTc: 92 (15%) males demonstrated QTc ≥ 480 ms and 39 (10%) females demonstrated QTc ≥ 500 ms on any ECG. Of patients with ≥ 2 evaluable ECGs, 306 (50%) demonstrated prolongation ≥ 40 ms. Factors significantly predicting extreme prolongation included age < 1 year (+39 ms CRG, p < 0.01) and diagnosis of ALL (+15 ms CRG, p = 0.04); a trend toward more extreme prolongation was seen in patients with myelodysplastic syndrome (+14 ms CRG, p = 0.05). The factor protecting from extreme QTc prolongation was treatment with a related allograft (-9 ms CRG, p = 0.03); trends toward less extreme prolongation were also seen in autologous HCT and those not receiving MMF for GvHD prophylaxis. Conclusion: Prolonged QTc is associated with life-threatening ventricular tachy-arrhythmias. This retrospective analysis of a large, diverse HCT cohort shows statistically significant prolongation during transplantation. Too, we identify sub-populations demonstrating very-long QTc and/or experiencing marked QT prolongation during HCT. Further analysis regarding pharmacologic, electrolytic and HCT-related predictors as well as outcomes for the cohort is underway. Disclosures: No relevant conflicts of interest to declare.