David S. Spar

Utility of ambulatory monitoring in patients with congenital heart disease.

Patients with congenital heart disease (CHD) are at increased risk of cardiac arrhythmias. The utility of ambulatory (Holter) monitoring in predicting these arrhythmias remains unclear. We sought to evaluate the clinical utility and cost effectiveness of Holter monitoring in patients with CHD. A retrospective study of patients with CHD who had undergone Holter monitoring was performed. The Holter data from patients with tetralogy of Fallot (TOF), d-transposition of the great arteries (d-TGA) after an atrial switch operation, and patients with a single ventricle after Fontan palliation were reviewed. The Holter indication included evaluation of clinical symptoms or as a part of routine screening. The Holter results were deemed clinically significant if they resulted in a change in patient treatment. Sudden cardiac events included death or aborted sudden death and appropriate defibrillator therapies. A total of 589 Holter studies were performed in 189 patients (100 with TOF, 38 with d-TGA, and 51 with Fontan). The results of Holter monitoring performed for clinical symptoms had a low positive predictive value (0.08) for clinically significant changes in management. On routine monitoring, the sensitivity was low (0.40) but the negative predictive value was high (0.96) for future clinically significant arrhythmias. The frequency of clinically significant findings and associated cost-effectiveness improved with older patient age and Fontan and d-TGA CHD type. Nonsustained ventricular tachycardia was associated with sudden cardiac events in patients with TOF but not in those with d-TGA or Fontan palliation. In conclusion, Holter monitoring is generally inefficient for symptomatic evaluation; however, within specific age and CHD type subgroups, such as patients with repaired TOF >25 years old, it could be useful in clinical management and risk assessment as a part of routine care.

Usefulness of combined history, physical examination, electrocardiogram, and limited echocardiogram in screening adolescent athletes for risk for sudden cardiac death.

Sudden cardiac death in the young (SCDY) is the leading cause of death in young athletes during sport. Screening young athletes for high-risk cardiac defects is controversial. The purpose of this study was to assess the utility and feasibility of a comprehensive cardiac screening protocol in an adolescent population. Adolescent athletes were recruited from local schools and/or sports teams. Each subject underwent a history and/or physical examination, an electrocardiography (ECG), and a limited echocardiography (ECHO). The primary outcome measure was identification of cardiac abnormalities associated with an elevated risk for sudden death. We secondarily identified cardiac abnormalities not typically associated with a short-term risk of sudden death. A total of 659 adolescent athletes were evaluated; 64% men. Five subjects had cardiac findings associated with an elevated risk for sudden death: prolonged QTc >500 ms (n = 2) and type I Brugada pattern (n = 1), identified with ECG; dilated cardiomyopathy (n = 1) and significant aortic root dilation; and z-score = +5.5 (n = 1). History and physical examination alone identified 76 (11.5%) subjects with any cardiac findings. ECG identified 76 (11.5%) subjects in which a follow-up ECHO or cardiology visit was recommended. Left ventricular mass was normal by ECHO in all but 1 patient with LVH on ECG. ECHO identified 34 (5.1%) subjects in whom a follow-up ECHO or cardiology visit was recommended. In conclusion, physical examination alone was ineffective in identification of subjects at elevated risk for SCDY. Screening ECHO identified patients with underlying cardiac disease not associated with immediate risk for SCDY. Cost of comprehensive cardiac screening is high.

Ambulatory Monitoring and Arrhythmic Outcomes in Pediatric and Adolescent Patients With Duchenne Muscular Dystrophy

Background Patients with Duchenne Muscular Dystrophy (DMD) develop cardiac fibrosis and dilated cardiomyopathy. We described the frequency of significant Holter findings in DMD, the relationship between cardiac function and arrhythmia burden, and the impact of these findings on clinical management. Methods and Results A retrospective review was done of patients with DMD who received a Holter from 2010 to 2014. Clinical and arrhythmic outcomes were analyzed. Patients were classified based on left ventricular ejection fraction (LVEF): ≥55%, 35% to 54% and <35%. Significant Holter findings included atrial tachycardia, ventricular tachycardia and atrial fibrillation/flutter. Logistic regression was used to assess predictors of significant Holter findings and change in care. The study included 442 Holters in 235 patients. Mean age was 14±4 years. Patients with cardiac dysfunction were older, and had increased late gadolinium enhancement and left ventricular dilation (P<0.01). There were 3 deaths (1%), all with normal function and none cardiac. Patients with LVEF <35% had more arrhythmias including nonsustained atrial tachycardia (P=0.01), frequent premature ventricular contractions, ventricular couplets/triplets, and nonsustained ventricular tachycardia (P<0.001) compared to the other groups. LVEF <35% (P<0.001) was the only predictor of clinically significant Holter finding. Four patients (40%) had change in medication in the LVEF <35% group compared to 9 (3%) in the ≥55% and 4 (4%) in the 35% to 54% groups (P<0.001). Conclusions Sudden cardiac events are rare in DMD patients with an LVEF >35%. Significant Holter findings are rare in patients with DMD who have an LVEF >35%, and cardiac dysfunction appears to predict significant Holter findings. Holter monitoring is highest yield among DMD patients with cardiac dysfunction.

Short QT Interval Prevalence and Clinical Outcomes in a Pediatric Population

Background—Risk associated with short QT interval has recently received recognition. European studies suggest a prevalence of 0.02% to 0.1% in the adult population, but similar studies in pediatric patients are limited. We sought to determine the prevalence of short QT interval in a pediatric population and associated clinical characteristics and outcomes. Methods and Results—Retrospective review of an ECG database at a single pediatric institution. The database was queried for ECGs on patients ⩽21 years with electronically measured QTc of 140 to 340 ms. Patients with QTc of 140 to 340 ms confirmed by a pediatric electrophysiologist were identified for chart review for associated clinical characteristics, symptoms, and outcome. Patients with and without symptoms were compared in an attempt to identify variables associated with outcome. The query included 272 504 ECGs on 99 380 unique patients. Forty-five patients (35 men, 76%) had QTc ⩽340 ms, for a prevalence of 0.05%. Median age was 15 years (interquartile range, 2–17), median QT 330 ms (interquartile range, 280–360), and median QTc 323 ms (IQR, 313–332). Women had significantly shorter QTc compared with men (312 versus 323 ms; P=0.03). Two deaths were noted in chart review—one from respiratory failure and the second of unknown pathogenesis in a patient with dilated cardiomyopathy. Conclusions—Short QT interval was a rare finding in this pediatric population, with a prevalence of 0.05%. Male predominance was identified, although the median QT interval was significantly shorter in women. There seem to be no unifying clinical characteristics for this pediatric patient cohort with short QT interval.

Consequence of Use of Lower Dose Flat Plate Fluoroscopy in Pediatric Patients Undergoing Ablation for Supraventricular Tachycardia

Traditional imaging for ablation of supraventricular tachycardia has been fluoroscopy, although 3-dimensional electroanatomic mapping (3D) has been demonstrated to reduce radiation exposure. This study compares a technique for the reduction of radiation, low-dose fluoroscopy (LD), with standard-dose fluoroscopy (SD) and 3D with SD (3D-SD). This was a single institutional retrospective cohort study. All patients undergoing initial ablation for atrioventricular reentrant tachycardia (AVRT) or atrioventricular nodal reentrant tachycardia (AVNRT) from 2009 to 2012 were reviewed and divided into 3 groups: (1) SD, (2) 3D (CARTO or NavX) with SD, or (3) LD. LD uses the same equipment as SD but includes customized changes to the manufacturers lowest settings by decreasing the requested dose to the detector. Primary outcomes were fluoroscopy time and dose area product exposure. One hundred eighty-one patients were included. The median age was 15.0 years (3.3-20.8); 59% had AVRT, 35% had AVNRT, and 6% had both AVRT and AVNRT. LD decreased the dose area product (DAP) compared with SD (637.0 vs 960.1 cGy*cm², p = 0.01) with no difference in fluoroscopy time. 3D-SD decreased fluoroscopy time compared with SD (9.9 vs 18.3 minutes, p <0.001) with DAP of 570.1.0 versus 960.1 cGy*cm² (p = 0.16). LD and 3D-SD had comparable DAP (637.0 vs 570.1 cGy*cm², p = 0.67), even though LD had significantly longer fluoroscopy time (19.9 vs 9.9 minutes, p <0.001). In conclusion, LD during catheter ablation of AVRT and AVNRT significantly reduced the DAP compared with SD and had similar radiation exposure compared with 3D with SD.

Usefulness of Ventricular Premature Complexes in Asymptomatic Patients ≤21 Years as Predictors of Poor Left Ventricular Function

Although ventricular premature complexes (VPCs) have been shown to correlate with decreased cardiac function in adults, the correlation of left ventricular (LV) function to VPCs in asymptomatic children remains unclear. The aim of this study was to determine the correlation of VPC burden with LV function in asymptomatic pediatric patients with structurally normal hearts. This was a retrospective analysis of patients aged ≤21 years with echocardiograms and 24-hour Holter monitors with ≥0.5% VPCs completed within 60 days of each other. LV fractional shortening (FS) was compared with VPC burden and VPC characteristics. Normal LV function was defined as FS ≥28%. Correlation between VPC burden and LV function was determined by regression analysis. Wilcoxons rank-sum test was used to compare LV function with VPC characteristics. This study included 123 patients (77 male [63%]). The median age was 11.6 years (interquartile range 5.8 to 14.3). The median VPC burden was 11.2% (interquartile range 4.8% to 18.9%), and median FS was 36% (interquartile range 33% to 38%). There was no significant correlation between VPC burden and LV FS (p = 0.50). The presence of uniform versus multiform VPCs (p = 0.29), ventricular couplets (p = 0.37), or runs of ventricular ectopy (p = 0.19) were not associated with a decrease in LV FS. Twenty-two patients (18%) had VPC burden >24%, none of which had decreased LV FS. In conclusion, there was no significant relation between VPC burden or VPC characteristics and LV systolic function in this pediatric population with structurally normal hearts.

Outcomes, Arrhythmic Burden and Ambulatory Monitoring of Pediatric Patients With Left Ventricular Non-Compaction and Preserved Left Ventricular Function

Pediatric patients with left ventricular noncompaction (LVNC) and severe ventricular dysfunction are at risk for sudden death. The aims of this study were to (1) evaluate outcomes, (2) describe arrhythmic burden on Holter monitoring, and (3) analyze the utility of Holter monitoring and its impact on care in pediatric patients with LVNC and preserved or mild ventricular dysfunction. This was a retrospective study including patients <21 years of age with LVNC and ejection fractions ≥45%. Demographic and outcome data were analyzed. Individual and cumulative Holter data were evaluated for all patients. Arrhythmias, conduction system disease, and symptoms were analyzed for each Holter recording. The incidence of significant findings and the impact on care were determined for each study. Outcome and Holter data were compared between patients on the basis of the ejection fraction (≥55% [normal] or ≥45% to <55% [mild]). This study included 72 patients, 65 with normal function and 7 with mild dysfunction (mean age 13 years). There was a single death in the cohort, which was sudden in nature. Simple ventricular ectopy was common on Holter monitoring and more common in patients with mild dysfunction (86% vs 27%, p = 0.005). Significant Holter findings (4% vs 6%) and changes to patient care (2% vs 4%) improved with cumulative Holter monitoring. In conclusion, in contrast to patients with severe dysfunction, pediatric patients with LVNC and normal or mild dysfunction have significantly better outcomes. However, worsening LV systolic function was correlated with increasing ventricular ectopy. The role of Holter monitoring is unknown, but it may have utility in patient care if used as part of ongoing screening.

Risk factors for complications in the implantation of epicardial pacemakers in neonates and infants

BACKGROUND Complications related to epicardial pacemakers in infants have been reported, though limited data are available on their incidence and associated risk factors. OBJECTIVE The hypothesis of the study is that younger, smaller patients and larger devices would be associated with complications in neonates and infants. METHODS This is a retrospective study of all patients at a single center receiving an epicardial pacemaker at ≤12 months of age (1996-2015). Patient and device characteristics were obtained. Characteristics of patients with and without complications were compared. RESULTS There were 86 patients with a median age of 73 days (interquartile range 13-166 days), of whom 12 (14%) had a complication. Eight (9%) needed surgical intervention, of whom 5 (6%) required explantation. Younger age (9 days vs 89 days; P = .01) and lower weight (2.91 kg vs 4.44 kg; P = .004) at implantation were associated with complications. Device characteristics were not statistically different. Patients ≤3 kg in weight and/or <5 days of age had an odds ratio of 18.1 (3.6-91.2; P < .001) for developing a complication with a negative predictive value (NPV) of 97%. Regardless of weight, patients aged >21 days were found to be at lower risk with an NPV of 96%; and regardless of age, patients weighing >4 kg had an NPV of 98%. CONCLUSION Young age and low weight at the time of implantation are risk factors for complications, while device characteristics appear to play a minor role. Reserving pacemaker implantation for patients >3 kg in weight and 5 days of age may predict patients at low risk of developing complications.

Long QT genetics manifesting as atrial fibrillation

fetal bradycardia of unknown etiology. The pregnancy was Introduction Congenital long QT syndrome (LQTS) is a familial channelopathy with variable penetrance of genetic mutations that lead to QT prolongation. The most common type of familial LQTS is type 1 (LQT1) due to loss of function mutations in the KCNQ1 gene. The majority of KCNQ1mutations involve the alpha subunit of the rapid or slow (IKs) currents of the potassium ion channel. The KCNQ1 gene codes for KvLQT1, a voltage-gated potassium channel protein that mediates IKs. Defects in IKs result in lack of QT shortening with increase in heart rate, which can result in an R on T phenomenon and progression to life-threatening ventricular arrhythmia. Contrarily, gain of function mutation of the KCNQ1 gene has been associated with sinus bradycardia, short QT syndrome, and familial atrial fibrillation. Classically considered a potassium channelopathy, familial atrial fibrillation has recently been associated with various ion channel genes including KCNQ1, SCN5A, and KCNJ2. The potassium channel mutations result in a shortened atrial action potential, while the sodium channel mutations lead to prolonged atrial repolarization, which create an environment susceptible to reentrant pathways. These alterations in atrial excitability may play a role in the frequency of atrial arrhythmias in patients with LQTS. Atrial arrhythmias have been reported in 2%–30% of the population with LQTS, manifesting as polymorphic atrial tachycardia and atrial fibrillation. In this report, we describe one family with a KCNQ1 gene mutation that has been previously reported in LQT1 but whose phenotype in this case is that of atrial fibrillation with no evidence of prolonged QT on electrocardiogram (ECG).

The US Experience of the Wearable Cardioverter-Defibrillator in Pediatric Patients

Background: Certain pediatric patients are at risk for sudden cardiac death. The wearable cardioverter-defibrillator (WCD) can be used in clinical situations in which implantable cardioverter-defibrillator placement is not ideal. The objectives of the study are to examine the effectiveness, safety, and compliance of the WCD in the identification and treatment of life-threatening ventricular arrhythmias in pediatric patients. Methods: All United States pediatric patients <18 years who wore a WCD, from 2009 to 2016 were retrospectively reviewed. Results: In total, 455 patients were identified. The median age was 15 (3–17) years, median duration of WCD use was 33 (1–999) days and median patient wear time was 20.6 (0.3–23.8) hours per day. The population was divided into 2 groups: (1) patients with implantable cardioverter-defibrillator problem, n=63 and (2) patients with nonimplantable cardioverter-defibrillator problem, n=392. Wear time per day was >20 hours in both groups. Wear duration was shorter in the implantable cardioverter-defibrillator problem group, 26 days versus 35 days, P<0.05. There were 7 deaths (1.5%); all not wearing WCD at time of death. Eight patients (1.8%) received at least 1 WCD shock treatment. Of the 6 patients (1.3%) who had appropriate therapy, there were 7 episodes of either polymorphic ventricular tachycardia or ventricular fibrillation with a total of 13 treatments delivered. All episodes were successfully converted and the patients survived. Conclusions: The WCD has overall adequate compliance with appropriate wear times and wear durations in pediatric patients. The WCD is safe and effective in treating ventricular arrhythmias that can lead to sudden cardiac death in pediatric patients.