Electrocardiographic repolarization abnormalities and increased risk of life-threatening arrhythmias in children with dilated cardiomyopathy.

BACKGROUND: Life-threatening arrhythmia events (LTEs) occur in ~5% of children with dilated cardiomyopathy (DCM). While prolonged QRS duration has been shown to be associated with LTEs, electrocardiographic (ECG) repolarization findings have not been examined. OBJECTIVE: We sought to determine the associations between ECG repolarization abnormalities and LTEs in children with DCM. METHODS: A single-center retrospective review of children with DCM was performed. LTEs were defined as documented ventricular tachycardia or fibrillation requiring medical intervention. Three pediatric cardiologists, blinded to clinical events, evaluated ECGs obtained at the time of initial referral. Kaplan-Meier survival and Cox proportional hazards analyses were used to evaluate time to LTEs. RESULTS: A total of 137 patients (mean age 7.8 ± 6.7 years; 75(55%) male patients) with DCM (mean ejection fraction 35% ± 16%) were included; 67 patients (49%) had a corrected JT (JTc) interval of ≥340 ms, 72 (53%) had a corrected QT (QTc) interval of ≥450 ms, and 41 (30%) had abnormal T waves. LTEs occurred in 15 patients at a median of 12 months (interquartile range 3-36 months) after the initial ECG. Patients with LTEs had a longer JTc interval (371 ± 77 ms vs 342 ± 41 ms; P = .02) and a longer QTc interval (488 ± 96 ms vs 453 ± 44 ms; P = .01). In survival analysis, a JTc interval of ≥390 ms (hazard ratio [HR] 4.07; 95% confidence interval [CI] 1.12-14.83; P = .03), a QTc interval of ≥510 ms (HR 6.95; 95% CI 1.53-31.49; P = .01), abnormal T-wave inversion (HR 11.62; 95% CI 2.75-49.00; P = .001), and ST-segment depression (HR 6.91; 95% CI 1.25-38.27; P = .03) were associated with an increased risk of LTEs, even after adjusting for QRS duration and amiodarone use. CONCLUSION: Repolarization abnormalities are common in children with DCM. Certain ECG repolarization abnormalities, such as significantly prolonged JTc and QTc intervals, may be useful in identifying patients at risk of LTEs.

Acute effects of single-site pacing from the left and right ventricle on ventricular function and ventricular-ventricular interactions in children with normal hearts.

OBJECTIVE: We studied, as a physiological benchmark, acute effects of right ventricular (RV) apical, RV outflow, and left ventricular (LV) pacing in children with normal cardiac function on LV and RV function and ventricular-ventricular interactions. DESIGN: The design of the study was a prospective, acute intervention. SETTING: The study was conducted in a tertiary care electrophysiology laboratory. Population and Methods. Seven children (mean +/- SD, 12 +/- 4 years) were paced after accessory pathway ablation, at baseline (AOO), and with atrioventricular pacing (DOO) from the RV apex, RV outflow, and left ventricle. OUTCOME MEASURES: Right ventricular dP/dT(max) and RV dP/dT(neg) (high-fidelity transducer-tipped catheters, Millar Instruments, Houston, TX, USA), cardiac index (Fick), blood pressure, and QRS duration were measured at each pacing condition. Intra- and interventricular mechanical dyssynchrony, systolic- and diastolic peak tissue velocities, and isovolumic acceleration were recorded by tissue Doppler imaging at the lateral mitral, septal, and tricuspid annuli at each condition. Results at each pacing condition were compared by repeated-measures analysis of variance. Results. Pacing prolonged QRS duration, causing electrical dyssynchrony (86 +/- 19 ms [baseline], 141 +/- 44 ms [RV apex], 121 +/- 18 ms [RV outflow], and 136 +/- 34 ms [LV], P < .01). Right ventricular outflow pacing caused LV intraventricular delay (63 +/- 52 vs. 12 +/- 7 ms, P < .05). Right ventricular apical pacing caused interventricular delay (61 +/- 29 vs. 25 +/- 18 ms, P < .05). There were no significant changes in blood pressure, cardiac index, RV dp/dT(max), RV dP/dT(neg), regional tissue velocities, or isovolumic acceleration during any of the pacing conditions, indicating preserved ventricular function and hemodynamics. No important ventricular-ventricular interactions were seen. CONCLUSIONS: In children with normal cardiac anatomy and function, single-site RV apical, RV outflow, and LV pacing induce electromechanical dyssynchrony without significantly changing ventricular function or hemodynamics, or adversely affecting ventricular-ventricular interactions.