Faculty Bibliography

BACKGROUND: Transposition of the great arteries with intra-atrial baffle repair is among the congenital heart defects at highest risk of sudden death. Little is known about mechanisms of sudden death and the role of implantable cardioverter defibrillators. METHODS AND RESULTS: We conducted a multicenter cohort study in patients with transposition of the great arteries to determine actuarial rates of implantable cardioverter defibrillator shocks, identify risk factors, assess underlying arrhythmias, and characterize complications. Overall, 37 patients (age, 28.0+/-7.6 years; 89.2% male) were enrolled from 7 sites. Implantable cardioverter defibrillators were implanted for primary prevention in 23 (62.1%) patients and secondary prevention in 14 patients (37.8%). Annual rates of appropriate shocks were 0.5% and 6.0% in primary and secondary prevention, respectively (P=0.0366). Independent predictors were a secondary prevention indication (hazard ratio, 18.0; P=0.0341) and lack of beta-blockers (hazard ratio, 16.7; P=0.0301). In patients with appropriate shocks, intracardiac electrograms documented supraventricular tachycardia preceding or coexisting with ventricular tachycardia in 50%. No patient with inducible ventricular tachycardia received an appropriate shock in comparison with 37.5% of noninducible patients (P=0.0429). Inappropriate shocks occurred in 6.6% per year, more so in patients of lesser weight (hazard ratio, 0.91 per kg; P=0.0168). Additionally, 14 patients (37.8%) experienced complications: 5 (13.5%) acute, 1 (2.7%) late generator related, and 12 (32.4%) late lead related. CONCLUSIONS: In patients with transposition of the great arteries, high rates of appropriate shocks are noted in secondary but not primary prevention. Supraventricular arrhythmias may be implicated in the etiology of ventricular tachyarrhythmias; beta-blockers seem protective, and inducible ventricular tachycardia does not seem to predict future events. Inappropriate shocks and late lead-related complications are common.

BACKGROUND: Episodic 2:1 block occurs in 9% of adults with atrioventricular nodal reentry tachycardia (AVNRT), but developmental differences in conduction physiology among children could influence this phenomenon. OBJECTIVE: This study sought to characterize the frequency and mechanism of 2:1 block during AVNRT in the pediatric population. METHODS: Records of 179 patients (mean age 13.5 +/- 3.4 years) undergoing ablation for AVNRT were reviewed. RESULTS: Periods of 2:1 AVNRT were observed in 31 cases (17%). A His potential was visible on the blocked beats of 13, absent in 17, and undetermined in 1. Compared with 148 patients with exclusive 1:1 conduction, those with 2:1 AVNRT had: (1) longer baseline slow pathway refractory period (351 +/- 71 msec vs. 278 +/- 65 msec, P =.04), (2) shorter atrial cycle length during AVNRT (303 +/- 54 msec vs. 333 +/- 62 msec, P =.01), and (3) a higher incidence of bundle-branch aberration (35% vs. 18%, P =.03). Long-short oscillations in atrial cycle length were observed in 55% of patients during 2:1 AVNRT, but not during 1:1 AVNRT. CONCLUSION: A pattern of 2:1 block occurs in 17% of pediatric patients with AVNRT undergoing ablation. Although this incidence is higher than in older patients, the mechanism appears identical. These data provide further evidence that functional block within or below the His bundle is the mechanism of 2:1 AVNRT, regardless of the presence of a His potential. Oscillations in atrial cycle length are common during 2:1 AVNRT in children and may contribute to the block pattern, but are not a requisite.

OBJECTIVES: We sought to determine the implications of implantable cardioverter-defibrillator (ICD) placement in children and patients with congenital heart disease (CHD). BACKGROUND: There is increasing frequency of ICD use in pediatric and CHD patients. Until recently, prospective registry enrollment of ICD patients was not available, and children and CHD patients account for only a small percentage of ICD recipients. Therefore, we retrospectively obtained collaborative data from 4 pediatric centers, aiming to identify implant characteristics, shock frequency, and complications in this unique population. METHODS: Databases from 4 centers were collated in a blinded fashion. Demographic information, implant electrical parameters, appropriate and inappropriate shock data, and complications were recorded for all implants from 1992 to 2004. RESULTS: A total of 443 patients were included, with a median age of 16 years (range 0 to 54 years) and median weight of 61 kg (range 2 to 130 kg), with 69% having structural heart disease. The most common diagnoses were tetralogy of Fallot (19%) and hypertrophic cardiomyopathy (14%). Implant indication was primary prevention in 52%. Shock data were available on 409 patients, of whom 105 (26%) received appropriate shocks (mean 4 shocks/patient, range 1 to 29 shocks/patient). Inappropriate shocks occurred in 87 of 409 patients (21%), with a mean of 6 per patient (range 1 to 60), mainly attributable to lead failure (14%), sinus or atrial tachycardias (9%), and/or oversensing (4%). CONCLUSIONS: Children and CHD ICD recipients have significant appropriate and inappropriate shock frequencies. Optimizing programming, medical management, and compliance may diminish inappropriate shocks. Despite concerns regarding generator recalls, lead failure remains the major cause of inappropriate shocks, complications, and system malfunction in children. Prospective assessment of ICD usage in this population may identify additional important factors in pediatric and CHD patients.

BACKGROUND: Use of implantable cardiac defibrillators (ICDs) in children and patients with congenital heart disease is complicated by body size and anatomy. A variety of creative implantation techniques has been used empirically in these groups on an ad hoc basis. OBJECTIVE: To rationalize ICD placement in special populations, we used subject-specific, image-based finite element models (FEMs) to compare electric fields and expected defibrillation thresholds (DFTs) using standard and novel electrode configurations. METHODS: FEMs were created by segmenting normal torso computed tomography scans of subjects ages 2, 10, and 29 years and 1 adult with congenital heart disease into tissue compartments, meshing, and assigning tissue conductivities. The FEMs were modified by interactive placement of ICD electrode models in clinically relevant electrode configurations, and metrics of relative defibrillation safety and efficacy were calculated. RESULTS: Predicted DFTs for standard transvenous configurations were comparable with published results. Although transvenous systems generally predicted lower DFTs, a variety of extracardiac orientations were also predicted to be comparably effective in children and adults. Significant trend effects on DFTs were associated with body size and electrode length. In many situations, small alterations in electrode placement and patient anatomy resulted in significant variation of predicted DFT. We also show patient-specific use of this technique for optimization of electrode placement. CONCLUSION: Image-based FEMs allow predictive modeling of defibrillation scenarios and predict large changes in DFTs with clinically relevant variations of electrode placement. Extracardiac ICDs are predicted to be effective in both children and adults. This approach may aid both ICD development and patient-specific optimization of electrode placement. Further development and validation are needed for clinical or industrial utilization.

BACKGROUND: Concern exists regarding the potential electromagnetic interaction between pacemakers, implantable cardioverter-defibrillators (ICDs) and digital music players (DMPs). A preliminary study reported interference in 50% of patients whose devices were interrogated near Apple iPods. OBJECTIVE: Given the high prevalence of DMP use among young patients, we sought to define the nature of interference from iPods and evaluate other DMPs. METHODS: Four DMPs (Apple Nano, Apple Video, SanDisk Sansa and Microsoft Zune) were evaluated against pacemakers and ICDs (PM/ICD). Along with continuous monitoring, we recorded a baseline ECG strip, sensing parameters and lead impedance at baseline and for each device. RESULTS: Among 51 patients evaluated (age 6 to 60 years, median 22), there was no interference with intrinsic device function. Interference with the programmer occurred in 41% of the patients. All four DMPs caused programmer interference, including disabled communication between the PM/ICD and programmer, noise in the ECG channel, and lost marker channel indicators. Sensing parameters and lead impedances exhibited no more than baseline variability. When the DMPs were removed six inches, there were no further programmer telemetry interactions. CONCLUSIONS: Contrary to a prior report, we did not identify any evidence for electromagnetic interference between a selection of DMPs and intrinsic function of PM/ICDs. The DMPs did sometimes interfere with device-programmer communication, but not in a way that compromised device function. Therefore, we recommend that DMPs not be used during device interrogation, but suggest that there is reassuring counterevidence to mitigate the current high level of concern for interactions between DMPs and implantable cardiac rhythm devices.

Although long-term survival after craniopharyngioma treatment is excellent in childhood and early adulthood, sudden deaths in two craniopharyngioma survivors with cardiac findings suggest a need to determine whether treated patients exhibit potential substrates for sudden cardiac death. We present a retrospective review of two index patients with cardiac mortality. This motivated a prospective cardiac screening of 12 survivors that identified nearly a third with significant QTc prolongation. QTc-prolonging medication and stimulants should be used with caution in this population, and routine electrocardiogram screening may identify those at highest risk.

INTRODUCTION: An insertable loop recorder (ILR) in patients with infrequent syncope or palpitations may be useful to decide management strategies, including clinical observation, medical therapy, pacemaker, or implantable cardioverter defibrillator (ICD). We sought to determine the diagnostic utility of the Reveal ILR (Medtronic, Inc., Minneapolis, MN, USA) in pediatric patients. METHODS: Retrospective review of clinical data, indications, findings, and therapeutic decision in 27 consecutive patients who underwent ILR implantation from 1998-2007. RESULTS: The median age was 14.8 years (2-25 years). Indications were syncope in 24 patients and recurrent palpitations in three. Overall, eight patients had structural heart disease (six congenital heart disease, one hypertrophic cardiomyopathy, one Kawasaki), five had previous documented ventricular arrhythmias with negative evaluation including electrophysiology study, and three patients had QT prolongation. Tilt testing was performed in 10 patients, of which five had neurocardiogenic syncope but recurrent episodes despite medical therapy. After median three months (1-20 months), 17 patients presented with symptoms and the ILR memory was analyzed in 16 (no episode stored in one due to full device memory), showing asystole or transient atrioventricular (AV) block (2), sinus bradycardia (6), or normal sinus rhythm (8). Among asymptomatic patients, 3/10 had intermittent AV block or long pauses, automatically detected and stored by the ILR. In 19 of 20 patients, ILR was diagnostic (95%) and five subsequently underwent pacemaker implantation, while seven patients remained asymptomatic without ILR events. Notably, no life-threatening events were detected. The ILR was explanted in 22 patients after a median of 22 months, two due to pocket infection, 12 for battery depletion and eight after clear documentation of nonmalignant arrhythmia. CONCLUSIONS: The ILR in pediatrics is a useful adjunct to other diagnostic studies. Patient selection is critical as the ILR should not be utilized for malignant arrhythmias. A diagnosis is attained in the majority of symptomatic patients, predominantly bradyarrhythmias including pauses and intermittent AV block.

BACKGROUND: Tetralogy of Fallot is the most common form of congenital heart disease in implantable cardioverter-defibrillator (ICD) recipients, yet little is known about the value of ICDs in this patient population. METHODS AND RESULTS: We conducted a multicenter cohort study in high-risk patients with Tetralogy of Fallot to determine actuarial rates of ICD discharges, identify risk factors, and characterize ICD-related complications. A total of 121 patients (median age 33.3 years; 59.5% male) were enrolled from 11 sites and followed up for a median of 3.7 years. ICDs were implanted for primary prevention in 68 patients (56.2%) and for secondary prevention in 53 (43.8%), defined by clinical sustained ventricular tachyarrhythmia or resuscitated sudden death. Overall, 37 patients (30.6%) received at least 1 appropriate and effective ICD discharge, with a median ventricular tachyarrhythmia rate of 213 bpm. Annual actuarial rates of appropriate ICD shocks were 7.7% and 9.8% in primary and secondary prevention, respectively (P=0.11). A higher left ventricular end-diastolic pressure (hazard ratio 1.3 per mm Hg, P=0.004) and nonsustained ventricular tachycardia (hazard ratio 3.7, P=0.023) independently predicted appropriate ICD shocks in primary prevention. Inappropriate shocks occurred in 5.8% of patients yearly. Additionally, 36 patients (29.8%) experienced complications, of which 6 (5.0%) were acute, 25 (20.7%) were late lead-related, and 7 (5.8%) were late generator-related complications. Nine patients died during follow-up, which corresponds to an actuarial annual mortality rate of 2.2%, which did not differ between the primary and secondary prevention groups. CONCLUSIONS: Patients with tetralogy of Fallot and ICDs for primary and secondary prevention experience high rates of appropriate and effective shocks; however, inappropriate shocks and late lead-related complications are common.

INTRODUCTION: Transvenous ventricular pacing leads across the tricuspid valve may cause or exacerbate tricuspid regurgitation (TR). The literature in adults is inconclusive and no studies have investigated the association between pacing leads and TR in children or congenital heart disease patients. METHODS AND RESULTS: A retrospective chart review was conducted at a large children's hospital, yielding 123 patients with initial placement of a transvenous lead across their tricuspid valve that had adequate echocardiographic data for review. The median age was 16 years (range 2-52) at time of lead placement. The pre-procedure echo was compared both to the first echo after lead placement and the most recent echo. Median time was 242 days from implant to first echo, and 827 days to most recent echo. There was no difference in TR between the pre-procedure echo and first follow-up echo (p = NS). However, TR was more likely to progress mildly between the pre-procedure echo and the most recent echo (p < 0.02) with a mean increase from 1.54 to 1.69 on a 0 to 4 ordinal scale. There were 76 pts (62%) with CHD. Mean pre-procedure TR was 1.82 in right-sided valvular CHD (e.g., tetralogy of Fallot, repaired AV canal) vs. 1.43 without right-sided CHD (p < 0.01). CONCLUSIONS: In patients with transvenous ventricular leads across the tricuspid valve, echocardiography demonstrates a small, but statistically significant change in TR. The detected change is minimal, suggesting that there is little impact of transvenous leads on TR, even in growing children or patients with right-sided structural heart disease.