Safety of maximal cardiopulmonary exercise testing in individuals with sickle cell disease: a systematic review.

OBJECTIVE: We evaluated the safety of maximal cardiopulmonary exercise testing (CPET) in individuals with sickle cell disease (SCD). Maximal CPET using gas exchange analysis is the gold standard for measuring cardiopulmonary fitness in the laboratory, yet its safety in the SCD population is unclear. DESIGN: Systematic review. DATA SOURCES: Systematic search of Medline (PubMed), EMBASE, Cochrane, ClinicalTrials.gov and professional society websites for all published studies and abstracts through December 2020. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Two reviewers independently extracted data of interest from studies that assessed safety outcomes of maximal CPET in children and adults with SCD. A modified version of the Newcastle-Ottawa Scale was used to assess for risk of bias in studies included. RESULTS: In total, 24 studies met inclusion/exclusion criteria. Adverse events were reported separately or as part of study results in 36 (3.8%) of 939 participants with SCD undergoing maximal CPET in studies included. Most adverse events were related to transient ischaemic changes on ECG monitoring or oxygen desaturation during testing, which did not result in arrhythmias or other complications. Only 4 (0.43%) of 939 participants experienced pain events due to maximal CPET. CONCLUSION: Maximal CPET appears to be a safe testing modality in children and adults with SCD and can be used to better understand the physiological basis of reduced exercise capacity and guide exercise prescription in this population. Some studies did not focus on reporting adverse events related to exercise testing or failed to mention safety monitoring, which contributed to risk of bias.

Cryoablation therapy for atrioventricular nodal reentrant tachycardia in children: a multicenter experience of efficacy.

Atrioventricular nodal reentrant tachycardia (AVNRT), a common tachycardia in children, is routinely treated by catheter ablation using radiofrequency or cryothermal energy. Acute success rates of 95-97 % are reported for cryoablation, similar to those achieved with radiofrequency ablation (RFA). However, early studies reported higher recurrence rates after cryoablation for treatment of AVNRT than those reported for RFA. This study evaluated the success and recurrence rates for cryoablation in a current cohort of pediatric patients across several institutions. Patients 21 years old or younger with AVNRT who underwent cryoablation at five participating centers between 2004 and 2009 were retrospectively reviewed. Patient demographics and procedural data were extracted from patient records and analyzed. A total of 434 patients with AVNRT who underwent cryoablation were identified. Cryoablation was used as the exclusive ablation method for 379 patients. For 97 % (368/379) of these patients, cryoablation was acutely successful. A higher acute success rate was found with the 6-mm-tip catheter (99 %) than with the 4-mm-tip catheter (91 %) (p < 0.01). Recurrence was experienced by 7.3 % of the patients. Recurrence was more likely for those treated with the 4-mm-tip catheter (6/42, 14 %) than for those who had the larger catheters (12/204, 6 %) No patient experienced permanent heart block. Success and recurrence rates for this cohort of patients were similar to those reported for RFA used to treat AVNRT in pediatric patients. The findings show a higher success rate and a lower recurrence rate after cryoablation with a 6-mm-tip catheter than after use of the 4-mm-tip catheter, with an associated excellent safety profile.

IV Sotalol Use in Pediatric and Congenital Heart Patients: A Multicenter Registry Study.

Background There is limited information regarding the clinical use and effectiveness of IV sotalol in pediatric patients and patients with congenital heart disease, including those with severe myocardial dysfunction. A multicenter registry study was designed to evaluate the safety, efficacy, and dosing of IV sotalol. Methods and Results A total of 85 patients (age 1 day-36 years) received IV sotalol, of whom 45 (53%) had additional congenital cardiac diagnoses and 4 (5%) were greater than 18 years of age. In 79 patients (93%), IV sotalol was used to treat supraventricular tachycardia and 4 (5%) received it to treat ventricular arrhythmias. Severely decreased cardiac function by echocardiography was seen before IV sotalol in 7 (9%). The average dose was 1 mg/kg (range 0.5-1.8 mg/kg/dose) over a median of 60 minutes (range 30-300 minutes). Successful arrhythmia termination occurred in 31 patients (49%, 95% CI [37%-62%]) with improvement in rhythm control defined as rate reduction permitting overdrive pacing in an additional 18 patients (30%, 95% CI [19%-41%]). Eleven patients (16%) had significant QTc prolongation to >465 milliseconds after the infusion, with 3 (4%) to >500 milliseconds. There were 2 patients (2%) for whom the infusion was terminated early. Conclusions IV sotalol was safe and effective for termination or improvement of tachyarrhythmias in 79% of pediatric patients and patients with congenital heart disease, including those with severely depressed cardiac function. The most common dose, for both acute and maintenance dosing, was 1 mg/kg over ~60 minutes with rare serious complications.

Multicenter study of the effectiveness of implantable cardioverter defibrillators in children and young adults with heart disease.

Implantable cardioverter defibrillators (ICDs) are being used with increasing frequency in children and young adults. Our aim was to examine the appropriateness and frequency of ICD discharges in children and young adults, to compare the effectiveness of ICDs when placed for primary or secondary prevention, and to provide time-dependent analysis of ICD discharges. Data were collected from seven institutions on 210 patients <30 years of age who underwent ICD implantation from October 1992 to January 2007. Median age at implant was 15.4 years with a follow-up average of 3.3 years. Heart disease was categorized as electrical (n = 90, 42%), cardiomyopathic (n = 62, 30%), or congenital heart disease (n = 58, 28%). ICDs are increasingly placed for primary prevention. There are increased appropriate ICD discharges for ICDs placed for secondary prevention (52%) versus primary prevention (14%) at 5 years. There is no difference in the risk of inappropriate discharges between primary and secondary prevention indications. There is an increased risk for inappropriate therapy in the congenital heart disease population. An increasing number of ICDs are being placed for primary prevention in young patients, a marked shift in practice during the last two decades. The benefits of ICDs remain greater in secondary than in primary-prevention patients. In both groups, approximately 25% of patients received inappropriate discharges within 5 years of implant. Patients with congenital heart disease are the most affected by inappropriate discharges.

Inappropriate ICD discharges in single-chamber versus dual-chamber devices in the pediatric and young adult population.

BACKGROUND: Implantable cardioverter defibrillator (ICD) use is increasing in young patients and is frequently complicated by inappropriate device discharges (IDs), leading to discomfort, anxiety and, potentially, proarrhythmia. Dual-chamber (DC) ICDs may decrease IDs by improving rhythm discrimination, but are associated with increased size, expense, and implant complications. We examined whether the frequency of IDs was the same in dual- and single-chamber (SC) ICDs in young patients. METHODS: A multicenter review of patients

Short QT syndrome in a pediatric patient.

Short QT syndrome (SQTS) is a recently described genetic syndrome characterized by abnormally brisk ventricular repolarization. Similar to long QT syndrome, SQTS might result in ventricular arrhythmias, syncope, and sudden death. The clinical diagnosis of SQTS is supported by the finding of an abnormally short QT interval on the resting electrocardiogram in combination with a suggestive clinical or family history. To date, few pediatric cases have been reported and the ideal therapy is unknown. We report a teenage boy who suffered a witnessed ventricular fibrillation arrest and was subsequently diagnosed with SQTS. Additional data from nine other pediatric patients diagnosed with SQTS are presented.

Safety of Sports for Young Patients With Implantable Cardioverter-Defibrillators: Long-Term Results of the Multinational ICD Sports Registry.

BACKGROUND: Despite safety concerns, many young patients with implantable cardioverter-defibrillators (ICDs) participate in sports. We undertook a prospective, multinational registry to determine the incidence of serious adverse events because of sports participation. The primary end points were death or resuscitated arrest during sports or injury during sports because of arrhythmia or shock. Secondary end points included system malfunction and incidence of ventricular arrhythmias requiring multiple shocks for termination. METHODS: Athletes with ICDs aged ≤21 years were included in this post hoc subanalysis of the ICD Sports Registry. Data on sports and clinical outcomes were obtained by phone interview and medical records review. ICD shocks and clinical details of lead malfunction were classified by 2 electrophysiologists. RESULTS: A total of 129 young athletes participating in competitive (n=117) or dangerous (n=12) sports were enrolled. The mean age was 16 years (range, 10-21; 40% female; 92% white). The most common diagnoses were long QT syndrome (n=49), hypertrophic cardiomyopathy (n=30), and congenital heart disease (n=16). The most common sports were basketball and soccer, including 79 varsity/junior varsity high school and college athletes. During a median follow-up of 42 months, 35 athletes (27%) received 38 shocks. There were no occurrences of death, arrest, or injury related to arrhythmia, during sports. There was 1 ventricular tachycardia/ventricular fibrillation storm during competition. Freedom from lead malfunction was 92.3% at 5 years and 79.6% at 10 years. CONCLUSIONS: Although shocks related to competition/practice are not uncommon, there were no serious adverse sequelae. Lead malfunction rates were similar to previously reported in unselected pediatric ICD populations. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov . Unique identifier: NCT00637754.

Impact of a computer assisted navigation system on radiation exposure during pediatric ablation procedures.

BACKGROUND: During catheter ablation procedures, non-radiologic navigation systems may reduce fluoroscopic exposure and energy applications, as well as improve procedural success rates. OBJECTIVE: To examine the impact of a non-radiologic navigation system on ablation procedures in pediatric patients, the procedural characteristics and success rates prior to and following incorporation of the LocaLisa (LL) navigation system into a pediatric electrophysiology laboratory were compared. METHODS: Between January 2000 and April 2005, 246 consecutive patients underwent catheter ablation for either Atrioventricular Reentry Tachycardia AVRT (168) or Atrioventricular Nodal Reentry Tachycardia AVNRT (78). Ablation procedures performed prior to LL (108) were compared to ablation procedures performed using LL (113). The first 25 patients using LL were censored to remove the bias of a learning curve. RESULTS: There was no difference in demographic features between the two groups. Statistically significant decreases were found in the diagnostic (11.4 +/- 6.1 min v 18.8 +/- 9.8 min w/o LL), ablation (5.7 +/- 10.3 vs 18.5 +/- 20.1 min w/o LL) and total (17.2 +/- 12.6 vs 37.3 +/- 21.3 min w/o LL) fluoroscopy times for the LL group, as well as in the total number of energy applications (9.0 +/- 8.5 vs 12.3 +/- 12.2 w/o LL). Success rates were 99.1% w/ LL v 97.2% w/o LL (p = NS). No major complications were observed in either group. CONCLUSIONS: The use of a computer assisted navigation system significantly decreased the diagnostic, ablation, and total fluoroscopy times, as well as the number of energy applications, without affecting procedural success or complication rates. Non-radiologic navigation systems reduce radiation exposure during transcatheter electrophysiologic procedures and thus lower the lifetime radiation cumulative risk, a goal particularly important in children.

Facilitation of cardiac vagal activity by CRF-R1 antagonists during swim stress in rats.

Exposure to stressors that elicit fear and feelings of hopelessness can cause severe vagal activation leading to bradycardia, syncope, and sudden death. These phenomena though documented, are difficult to diagnose, treat clinically, and prevent. Therefore, an animal model incorporating these cardiovascular conditions could be useful. The present study examined 'sinking' during a 2-h swim stress, a phenomenon that occurs in 50% of rats during 25 degrees C water exposure. Concurrent measurements of body temperature, immobility, heart rate (HR), and PR interval (a measure of vagal activity) were made. Neither decreases in immobility nor variations in hypothermia during swim were correlated with sinking. Bradycardia was more severe in sinking rats (average minimum HR+/-SEM; 143+/-13 vs 247+/-14; p<0.01), and PR interval was elevated (p<0.0001). To examine potential modulation of vagal activity during stress, corticotropin-relasing factor (CRF) receptor antagonists (antalarmin, R121919 and astressin B), a glucocorticoid receptor antagonist (RU486), and a peripherally acting cholinergic antagonist (methylatropine nitrate) were administered. The centrally acting CRF antagonist, antalarmin (32 mg/kg), produced elongation of the PR interval (p<0.0001), robust bradycardia (135+/-18; p<0.001), and increased sinking (92%; p<0.05), and methylatropine nitrate (3.2 mg/kg) blocked these effects. Corroborating these data, two different CRF antagonists, R121919 (30 mg/kg) and astressin B (intracerebroventricular (i.c.v.), 0.03 mug/rat) increased sinking to 100%. RU486 (20 mg/kg) blocked HPA axis negative feedback and decreased percent sinking to 25%. From these studies, we concluded that sinking during a 2-h water exposure was a result of extreme vagal hyperactivity. Furthermore, stress-induced CRF release may serve to protect against elevated cardiac vagal activity.

Transcatheter cryothermal ablation of junctional ectopic tachycardia in the normal heart.

BACKGROUND: Junctional ectopic tachycardia in the normal heart is rare and often is resistant to pharmacologic management. Transcatheter ablation using radiofrequency energy places the AV node at risk. OBJECTIVES: The purpose of this study was to report our experience with transcatheter cryothermal ablation using three-dimensional mapping in six patients with junctional ectopic tachycardia. METHODS: A review of clinical and electrophysiologic data was performed on all patients with structurally normal hearts who underwent cryothermal ablation for treatment of junctional ectopic tachycardia at two institutions. RESULTS: Six patients (age 7.7-36.5 years) underwent attempted transcatheter cryothermal ablation using three-dimensional mapping. Only one patient had achieved arrhythmia suppression on medical management. Cryothermal mapping (-30 degrees C) localized the junctional focus while normal conduction was monitored. The junctional focus was high in the triangle of Koch in four patients and was low in one patient. The sixth patient had only one run of junctional ectopic tachycardia during the procedure and therefore received an empiric cryoablation (-70 degrees C) lesion. Subsequent cryoablation lesions were delivered at and around the junctional focus. In one patient, cryomapping eliminated the junctional focus but resulted in transient complete AV block; therefore, cryoablation was not performed. All patients who received the cryoablation lesions had elimination of their junctional ectopic tachycardia at 6-week follow-up. The patient who did not receive a cryoablation lesion remained in a slower junctional rhythm at follow-up. CONCLUSION: Cryoablation of junctional ectopic tachycardia is safe and effective. Nonetheless, proximity to the His-Purkinje system may preclude success. Empiric cryoablation can be effective; cryotherapy may not yield immediate success, but a delayed salutary effect can follow.

Transcatheter cryotherapy for the treatment of supraventricular tachyarrhythmias in children: a single center experience.

INTRODUCTION: Transcatheter cryotherapy is an emerging technology for the treatment of children with supraventricular tachyarrhythmias. Limited data exist regarding the use of cryoablation therapy in children. We report a single center's experience with transcatheter cryoablation in the pediatric population. METHODS AND RESULTS: A retrospective review of demographic, procedural and outcome data was performed for patients undergoing cryoablation for treatment of supraventricular tachycardia (SVT). A historical control group was taken from the 3 years preceding the introduction of cryoablation. Between August 2003 and November 2005, 83 cryoablation procedures were performed in 81 patients (age: 4 to 21 years, mean: 13.4 years) for AV nodal reentrant tachycardia (AVNRT--53), AV reentrant tachycardia (AVRT--20), ectopic atrial tachycardia (EAT--9), and junctional ectopic tachycardia (JET--1). The acute success rate for all procedures was 88% (AVNRT: 96%, AVRT: 85%, EAT: 55%, and JET: 100%). Of 72 patients that underwent successful cryoablation, nine experienced recurrence of SVT (12.5%). The control group consisted of 73 patients (AVNRT--60, AVRT--13). There were no differences in demographic data between the two groups. The overall success rate for the RFA group (96%) was identical to that for patients with AVNRT and AVRT undergoing cryoablation. The recurrence rate for RFA (10%) was less but not significantly different than that for cryoablation (12%). There were no complications in either group. CONCLUSIONS: Cryoablation is a safe and effective alternative for the treatment of SVT in children.

Syncope Best Practices: A Syncope Clinical Practice Guideline to Improve Quality.

OBJECTIVE: To determine whether implementation of a standardized clinical practice guideline (CPG) for the evaluation of syncope would decrease practice variability and resource utilization. DESIGN: A retrospective review of medical records of patients presenting to our practice for outpatient evaluation of syncope before and after implementation of the CPG. The guideline included elements of history, physical exam, electrocardiogram, and "red flags" for further testing. SETTING: Outpatient pediatric cardiology offices of a large pediatric cardiology practice. PATIENTS: All new patients between 3 and 21 years old, who presented to cardiology clinic with a chief complaint of syncope. INTERVENTIONS: The CPG for the evaluation of pediatric syncope was presented to the providers. OUTCOME MEASURES: Resource utilization was determined by the tests ordered by individual physicians before and after initiation of the CPG. Patient final diagnoses were recorded and the medical records were subsequently reviewed to determine if any patients, who presented again to the system, were ultimately diagnosed with cardiac disease. RESULTS: Of the 1496 patients with an initial visit for syncope, there was no significant difference in the diagnosis of cardiac disease before or after initiation of the CPG: (0.6% vs. 0.4%, P = .55). Electrocardiography provides the highest yield in the evaluation of pediatric syncope. Despite high compliance (86.9%), there were no overall changes in costs ($346.31 vs. $348.53, P = .85) or in resource utilization. There was, however, a decrease in the variability of ordering of echocardiograms among physicians, particularly among those at the extremes of utilization. CONCLUSIONS: Although the CPG did not decrease already low costs, it did decrease the wide variability in echo utilization. Evaluation beyond detailed history, physical exam, and electrocardiography provides no additional benefit in the evaluations of pediatric patients presenting with syncope.

A human pluripotent stem cell model of catecholaminergic polymorphic ventricular tachycardia recapitulates patient-specific drug responses.

Although ß-blockers can be used to eliminate stress-induced ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), this treatment is unsuccessful in ∼25% of cases. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) generated from these patients have potential for use in investigating the phenomenon, but it remains unknown whether they can recapitulate patient-specific drug responses to ß-blockers. This study assessed whether the inadequacy of ß-blocker therapy in an individual can be observed in vitro using patient-derived CPVT iPSC-CMs. An individual with CPVT harboring a novel mutation in the type 2 cardiac ryanodine receptor (RyR2) was identified whose persistent ventricular arrhythmias during ß-blockade with nadolol were abolished during flecainide treatment. iPSC-CMs generated from this patient and two control individuals expressed comparable levels of excitation-contraction genes, but assessment of the sarcoplasmic reticulum Ca(2+) leak and load relationship revealed intracellular Ca(2+) homeostasis was altered in the CPVT iPSC-CMs. ß-adrenergic stimulation potentiated spontaneous Ca(2+) waves and unduly frequent, large and prolonged Ca(2+) sparks in CPVT compared with control iPSC-CMs, validating the disease phenotype. Pursuant to the patient's in vivo responses, nadolol treatment during ß-adrenergic stimulation achieved negligible reduction of Ca(2+) wave frequency and failed to rescue Ca(2+) spark defects in CPVT iPSC-CMs. In contrast, flecainide reduced both frequency and amplitude of Ca(2+) waves and restored the frequency, width and duration of Ca(2+) sparks to baseline levels. By recapitulating the improved response of an individual with CPVT to flecainide compared with ß-blocker therapy in vitro, these data provide new evidence that iPSC-CMs can capture basic components of patient-specific drug responses.

Transient atrioventricular conduction block with cryoablation following normal cryomapping.

OBJECTIVES: The purpose of this study was to demonstrate that adverse but reversible effects on AV conduction may be observed during cryoablation despite no evidence of deleterious effects evident during cryomapping. BACKGROUND: Transcatheter cryoablation has recently been introduced for treatment of supraventricular tachycardia. Potential advantages compared with radiofrequency ablation include decreased risk of thromboembolism and perforation, less patient discomfort, more sharply demarcated lesions, and decreased risk of inadvertent damage to adjacent structures due to the ability to observe the electrophysiologic effects of lesion generation prior to permanent tissue damage. Occasionally, however, adverse electrophysiologic effects may be observed during cryoablation when prior cryomapping suggests a safe location. METHODS: We reviewed the experience with our first 32 consecutive patients who underwent cryoablation for supraventricular tachycardia. Patients who experienced transient heart block during cryoablation following uneventful cryomapping were identified. RESULTS: Five patients in whom cryomapping was performed with no evidence for deleterious effects on AV conduction were identified. However, application of cryoablation at these mapped sites resulted in transient complete heart block. This experience demonstrates that the cryolesion created during cryoablation may expand relative to that suggested by cryomapping. CONCLUSIONS: It is important to maintain vigilance in monitoring for AV nodal conduction abnormalities during cryoablation, even when cryomapping suggests a safe location for cryoablation.

Prospective assessment after pediatric cardiac ablation: recurrence at 1 year after initially successful ablation of supraventricular tachycardia.

OBJECTIVES: A multicenter prospective study was performed to assess the results and risks associated with radiofrequency ablation in children. This report focuses on recurrences following initially successful ablation. METHODS: Patients recruited for the study were aged 0 to 16 years and had supraventricular tachycardia due to accessory pathways or atrioventricular nodal reentrant tachycardia (AVNRT), excluding patients with more than trivial congenital heart disease. A total of 481 patients were recruited into the prospective cohort and were followed at 2, 6, and 12 months following ablation. RESULTS: There were 517 successfully ablated substrates out of 540 attempted (95.7%). Loss to follow-up for individual substrates was 3.3%, 10.6%, and 21.2% at 2, 6, and 12 months, respectively. Recurrence was observed in 7.0%, 9.2%, and 10.7% of these substrates at 2, 6, and 12 months, respectively (adjusted for loss to follow-up as an independent source of data censoring). Recurrence rate varied by substrate location (24.6% for right septal, 15.8% for right free wall, 9.3% for left free wall, and 4.8% for left septal), as well as for AVNRT versus all others (4.8% vs 12.9%) at 12 months. The recurrence rate was higher for substrates ablated using power control but was not a function of whether isoproterenol was used for postablation testing. CONCLUSIONS: Recurrence after initially successful ablation occurs commonly in children. It is least common after AVNRT ablation and most common following ablation of right-sided pathways. These results serve as a benchmark for the time course of recurrence following initially successful ablation of supraventricular tachycardia in children.

Implantable cardioverter defibrillator therapy for life-threatening arrhythmias in young patients.

OBJECTIVES: This study examined the indications, efficacy and outcomes of implantable cardioverter defibrillator (ICD) use in the pediatric population. BACKGROUND: ICDs are first-line therapy for adults resuscitated from sudden cardiac death (SCD) or at high risk for life-threatening ventricular arrhythmias. Use of ICDs in children and young adults is infrequent and there are few data regarding this group. METHODS: We abstracted and analyzed data for all patients in whom ICDs were implanted. RESULTS: A total of 38 devices were implanted in 27 patients. Age ranged from 6 to 26 years (mean, 14) and weight ranged from 16 to 124 kg (mean, 47). Diagnoses included long QT syndrome (9), hypertrophic cardiomyopathy [6], repaired congenital heart disease [5];, and idiopathic ventricular tachycardia/fibrillation [4]. Indications comprised resuscitated SCD [15], syncope [9], and life-threatening ventricular arrhythmia [3]. Initial device placement was infraclavicular in 13, abdominal in 13 and intrathoracic in 1. Epicardial leads were used with 5 systems. A single coil lead was used in 17. Seven patients, all previously resuscitated from SCD, experienced 88 appropriate successful discharges. There were 6 inappropriate discharges in 3 patients. Mean time to device replacement was 3.1 years (n = 11). Complications included 2 infected systems, 2 lead dislodgments, 2 lead fractures, 1 post-pericardiotomy syndrome, 1 adverse event with defibrillation threshold (DFT); testing, and 1 patient with psychiatric sequelae. No deaths occurred with implanted ICDs. CONCLUSIONS: These data demonstrate that ICDs provide safe and effective therapy in young patients. The indications for ICDs as primary preventive therapy remain uncertain.

Early and delayed atrioventricular conduction block after routine surgery for congenital heart disease.

OBJECTIVES: Patients undergoing surgical closure of ventricular septal defects are at risk for immediate or delayed atrioventricular conduction block. Our goal was to better define the incidence of delayed atrioventricular conduction block. METHODS: A retrospective review was conducted of hospital records and pacemaker database for ventricular septal defect, atrioventricular canal, and tetralogy of Fallot repairs between 1999 and 2004. A total of 922 patients were identified (atrioventricular canal in 197, tetralogy of Fallot in 222, and ventricular septal defect in 503). Median follow-up was 4.1 years. RESULTS: There were 472 male and 450 female patients, median age 6 months (0-444 months) and median weight 5.8 kg (1.3-116 kg) at surgery. Postoperative atrioventricular conduction block developed in 21 (2.3%) of the 922, being transient, with return of conduction 3 days (1-14 days) after surgery, in 13 (1.4%) and permanent, with pacemakers implanted 10 days (6-20 days) after surgery, in 8 (0.9%). Of the 905 patients at risk for delayed atrioventricular conduction block, 3 (0.3%) had second- or third-degree block at 2, 8, and 16 months after surgery. Two of these 3 had transient postoperative block. For isolated ventricular septal defects, the incidence was 1 (0.2%) of 496. There were 8 late deaths at 31 months (7-45 months) after surgery. Five had normal conduction at death, but for 3 patients the conduction status at death could not be determined. Including these 3 patients as possible cases of delayed atrioventricular block yields an incidence of 0.3% to 0.7%. CONCLUSIONS: The incidence of early atrioventricular conduction block requiring a pacemaker was 0.9% and that of delayed atrioventricular conduction block was 0.3% to 0.7%. Transient atrioventricular conduction block may be a marker for increased risk of delayed block. These data may be useful for evaluation of new techniques.

Natural history and current therapy for complete heart block in children and patients with congenital heart disease.

Complete heart block, either congenital or acquired, in children and patients with congenital heart disease is a relatively frequent occurrence requiring therapy. The natural history of this condition has been distorted by the advent of new diagnostic and therapeutic modalities. The therapy of complete heart block is evolving with new data suggesting that traditional treatment strategies utilizing right ventricular apical pacing may have inadvertent deleterious effects on cardiac function. In the following manuscript, the natural history of complete heart block is reviewed and the current therapy examined.