Faculty Bibliography

OBJECTIVES: Our objective was to evaluate the short-term safety and efficacy of cardiac resynchronization therapy (CRT) in children. BACKGROUND: Cardiac resynchronization therapy has been beneficial for adult patients with poor left ventricular function and intraventricular conduction delay. The efficacy of this therapy in the young and in those with congenital heart disease (CHD) has not yet been established. METHODS: This is a multi-center, retrospective evaluation of CRT in 103 patients from 22 institutions. RESULTS: Median age at time of implantation was 12.8 years (3 months to 55.4 years). Median duration of follow-up was four months (22 days to 1 year). The diagnosis was CHD in 73 patients (71%), cardiomyopathy in 16 (16%), and congenital complete atrioventricular block in 14 (13%). The QRS duration before pacing was 166.1 +/- 33.3 ms, which decreased after CRT by 37.7 +/- 30.7 ms (p < 0.01). Pre-CRT systemic ventricular ejection fraction (EF) was 26.2 +/- 11.6%. The EF increased by 12.8 +/- 12.7 EF units with a mean EF after CRT of 39.9 +/- 14.8% (p < 0.05). Of 18 patients who underwent CRT while listed for heart transplantation, 3 improved sufficiently to allow removal from the transplant waiting list, 5 underwent transplant, 2 died, and 8 others are currently awaiting transplant. CONCLUSIONS: Cardiac resynchronization therapy appears to offer benefit in pediatric and CHD patients who differ substantially from the adult populations in whom this therapy has been most thoroughly evaluated to date. Further studies looking at the long-term benefit of this therapy in this population are needed.

OBJECTIVE: Optimal pacemaker lead choice in pediatric patients eligible for either epicardial or transvenous leads remains unclear. We compared performances of modern thin transvenous (TTV) and steroid-eluting epicardial (SEE) leads in patients followed at one pediatric center. METHODS: Retrospective review of patients with qualifying leads implanted from August 1997 to March 2004. Threshold energy (TE) at implant and follow-up, sensing thresholds, lead complications, and repeat pacing-related procedures were analyzed. Lead performances were compared using t-tests, Wilcoxon rank-sum tests and Cox regression. Survival curves were plotted using Kaplan-Meier analysis. RESULTS: A total of 370 implant procedures, 521 leads, and 1549 visits were evaluated. In all, 256 leads were SEE (49%, 184 implants) and 265 were TTV (51%, 186 implants). Median follow-up was 29 months (range 1-80 months). Patients with SEE systems were younger at implant (6 vs. 17 yrs, p < 0.001), and more had congenital heart defects (82% vs. 57%, p < 0.001). At follow-up, ventricular TEs were higher for SEE leads at implant (p < 0.001), 1 month (p < 0.001), and up to 4 years (p = 0.019). When compared across all follow-up durations combined, TTV TEs were significantly lower than SEE TEs for both atrial and ventricular leads (p < 0.001). A total of 70 repeat procedures were performed in 60 patients during the study period, which comprised 18% of SEE and 14% of TTV system patients (p = NS). In all, 18 TTV and 19 SEE leads failed (p = NS). Estimated freedom from lead failure at 1, 3, and 5 years was 97%, 88%, 85% for TTV leads and 96%, 92%, and 58% for SEE leads (log rank P = NS). CONCLUSIONS: Both SEE and TTV leads showed good mid-term performance and survival in our cohort. Higher TEs seen for SEE leads, especially ventricular and unipolar leads, may result in higher current drain and thus more generator replacements than TTV systems. Lead failure rates were comparable across lead types. TTV leads offer a promising alternative to SEE systems in terms of performance for young patients without intracardiac shunting who do not require open-chest surgery for another indication.

Automated external defibrillators (AEDs) are currently not recommended for use in children under 1 year of age. We report the first description of successful AED defibrillation in an infant using a 50 J shock and provide rationale for employing these life-saving devices in infants at risk for sudden cardiac death.

BACKGROUND: Ablation success rates reported for atrial tachycardia (AT) patients with congenital heart disease (CHD) is lower than the rates reported for other varieties of supraventricular tachycardia. Retrospective studies suggest these rates might be increased by the use of irrigated radiofrequency (RF) ablation. OBJECTIVES: The purpose of this study was to determine whether irrigated RF ablation increases ablation success rates in patients with CHD and AT. METHODS: Patients were studied in a prospective, randomized, nonblinded manner. The operator was limited to use of randomized therapy (standard or irrigated ablation) for the first 6 minutes of RF application to each targeted arrhythmia. Lesion characteristics were recorded, and acute ablation success was ascertained. Structured clinical follow-up was performed over a 6-month period. RESULTS: Forty-seven ATs were targeted in 26 patients; 72% of these ATs were ablated. Within the 6-minute randomization period, no difference in success rates of standard and irrigated catheters was noted. However, crossover from standard to irrigated ablation more likely was successful than vice versa (irrigated: 8 successes/8 attempts vs standard: 1 success/4 attempts, P = .018), and overall success was greater using irrigated catheters (66% vs 33%, P = .019). Mean delivered power was slightly higher in irrigated lesions (32.5 W vs 30.2 W, P = .025), and mean temperature was much lower (33.5 degrees C vs 59.3 degrees C, P < .001). A composite AT intensity score was significantly reduced compared with preablation values at 6-month follow-up of all patients. CONCLUSIONS: Ablation of ATs in patients with CHD results in symptomatic improvement over short-term follow-up. Irrigated ablation may result in higher acute success rates in these patients.

We report 4 cases of congenital and acquired coronary sinus ostial atresia incidentally found during electrophysiologic assessment for supraventricular arrhythmias. Congenital variants consisted of coronary sinus drainage predominantly via persistent left superior vena cavae and partial coronary sinus unroofing into the left atrium. The acquired variant was inadvertently produced during surgery for cor triatriatum. A variety of electrophysiologic substrates including right and left-sided accessory pathways and both typical and atypical AV nodal reciprocating tachycardia were identified. Approaches to imaging and accessing the coronary sinus when the os cannot be cannulated are discussed, including a search for right atrial accessory venous collaterals, venography to rule-out a persistent left superior vena cava, and coronary angiography.

INTRODUCTION: Recent studies have suggested that routine defibrillation threshold (DFT) testing of implantable cardioverter defibrillators (ICDs) in adults may not be necessary. The congenital heart disease and pediatric populations are a unique group of ICD recipients having a higher incidence of lead failure. We investigated the utility of follow-up DFT testing in this population. METHODS AND RESULTS: The records of 155 ICD recipients at one center were retrospectively reviewed, and patients having one or more follow-up DFT tests were analyzed. The patients were divided into two groups. The "routine" group consisted of 58 follow-up DFT procedures in 46 patients, without known changes in ICD parameters. The "prompted" group consisted of 21 follow-up DFT procedures in 18 patients, motivated by clinical concerns about changes in ICD lead status. Of 58 "routine" DFTs performed at a mean postimplant duration of 32 +/- 23 months (range 2-78), 7 (12%) had reprogramming, and 1 required a hardware change as a result of the testing. Of the 21 "prompted" DFTs performed, 7 required device reprogramming, and 3 required hardware upgrade. Overall, 19 (24%) of 79 procedures detected clinically significant changes, requiring reprogramming or ICD system revision. No complications were seen from follow-up DFT testing. CONCLUSION: A high rate of abnormalities was found at follow-up DFT testing in this population, especially in the group of patients with clinically prompted testing. Clinically indicated DFT testing, as expected, has a high yield of important information on device function in congenital heart disease and pediatric populations.

OBJECTIVE: To assess correlations between preoperative heart rate variability (a noninvasive measure of autonomic cardiac activity) and adverse respiratory events during anesthesia emergence in children. DESIGN: Case control study. SETTING: Tertiary care pediatric operating room. PATIENTS: Sixty-one children, aged 8 months to 13 yrs. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Heart rate power spectra were obtained from two 5-min immediate-preoperative electrocardiographs with an orthostatic posture change interposed and (n = 32) from a 24-hr preoperative Holter monitor. Observers recorded emergence from standardized anesthesia for coughing, laryngospasm, and desaturation. Low-frequency/high-frequency ratios (LF/HF) were derived from power spectra of heart rate variability. The orthostatic change in heart rate variability derived from brief preoperative recordings was significantly different if adverse events occurred during emergence from anesthesia (LF/HF standing/LF/HF supine = 1.3 vs. 2.8, p = .019). Holter-derived heart rate variability had no correlation with adverse events. Receiver operating characteristic analysis showed a sensitivity of 85% and specificity of 52% for predicting adverse events with preoperative recordings. CONCLUSIONS: This study provides new information regarding pathophysiology in children with upper respiratory infection. The magnitude of difference demonstrated is insufficient to propose this method as a preoperative screening test.

INTRODUCTION: Radiofrequency ablation of some right-sided accessory pathways continues to be challenging. The purpose of this study was to evaluate the efficacy of introducing a multielectrode microcatheter in the right coronary artery to localize accessory pathways when conventional mapping was unsuccessful. METHODS AND RESULTS: A retrospective study was conducted of all right-sided accessory pathway radiofrequency ablation procedures in which a multielectrode microcatheter as a reference in the right coronary artery was used to assist mapping. Between January 1998 and January 2002, 10 patients (5 males) underwent mapping of 11 accessory pathways with this technique at mean age of 12.3 +/- 3.8 years. Five patients had Ebstein's anomaly of the tricuspid valve. Accessory pathways were identified in the following locations: right anterior 3, right anterolateral 2, right lateral 1, right posterolateral 2, and right posterior 3. Mean procedure time was 285 +/- 70.3 minutes, and fluoroscopy time was 68.7 +/- 21 minutes. Average mapping duration prior to microcatheter insertion in the right coronary artery was 136 +/- 40 minutes. After microcatheter placement in the right coronary artery, the time to successful ablation of accessory pathways was 38 +/- 11 minutes. All 11 (100%) accessory pathways were successfully ablated. CONCLUSION: Mapping in the right coronary artery with a microcatheter is an effective method to improve localization and successful ablation of difficult right-sided accessory pathways.

OBJECTIVES: The aim of this study was to expand data on outcomes for radiofrequency catheter ablation (RFCA) of ventricular tachycardia (VT) in young patients and to identify obstacles to success. BACKGROUND: Ablation of VT is performed infrequently in young patients. Published experience has been limited to case reports and small descriptive series. METHODS: A retrospective review of 97 consecutive VT ablation procedures involving 62 patients at a single institution from 1990 to 2003 was undertaken. All intention-to-treat procedures were analyzed. RESULTS: Mean age was 13.9 +/- 9.4 years. Procedures were categorized according to VT mechanism as follows: idiopathic right ventricle (n = 37); idiopathic left ventricle (n = 24); congenital heart disease (n = 20); or other structural disease (n = 16). Acute success was achieved in 58 (60%) of 97 procedures. Of the 39 failures, 33 were aborted cases due to inability to induce sufficient ectopy for mapping in 12, high-risk location near the His bundle or coronary artery in 11, unstable VT in 7, and anatomic obstacles in 3. Recurrence rate after acutely successful RFCA was 34% (20/58 procedures) at a mean follow-up of 3.8 +/- 2.0 years. Ultimately, long-term success was achieved in 38 (61%) of 62 patients after a mean of 1.6 +/- 0.9 procedures, with the highest success rate (87%) for idiopathic left ventricular tachycardia. CONCLUSIONS: When analyzed on a strict intention-to-treat basis, a long-term success rate of 61% is observed with ablation of VT in young patients. Inability to induce stable VT for precision mapping and certain high-risk VT locations can be significant obstacles to success.

OBJECTIVES: To examine outcomes of children with pacemakers over a 22-year period and identify risk factors for lead failure. BACKGROUND: Small patient size, structural cardiac abnormalities, and growth may complicate pediatric pacemaker management. Better knowledge of risk factors for lead failure in these patients may help improve future outcomes. METHODS: All pacemaker patients followed at one pediatric center 1980-2002 were included. Lead failures were identified retrospectively as leads repaired, replaced, or abandoned due to fracture, insulation break, dislodgement, or abnormalities in pacing or sensing. Risk factors were identified using logistic regression and Cox analyses. RESULTS: A total of 1007 leads were implanted in 497 patients during the study period (5175 lead-years). Median age at implant was 9 years (0-55); 64% of patients had structural congenital heart disease. Median follow-up time was 6.2 years (0-22). Lead failure occurred in 155 leads (15%), and 115 patients (23%), with 28% of patients experiencing multiple failures. Significant independent correlates of lead failure included age <12 years at implant, history of structural congenital heart defects, and epicardial lead placement. Younger patients (<12 years) experienced significantly more lead fractures than older children (P = .005), while patients with congenital heart defects experienced more exit block. Epicardial leads were more likely to fail due to fracture or exit block, while transvenous leads failed more due to insulation breaks or dislodgements. CONCLUSIONS: Pediatric pacing patients have a high incidence lead failures. These occur most commonly in younger patients, structural congenital heart disease, and those with epicardial lead systems. Approaches to pacing system implantation and follow-up in these patients need to be individualized, with special attention to minimizing risk of lead failures. Our findings suggest that expanded utilization of transvenous systems in smaller patients seems justified when anatomy permits.