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In this large, diverse cohort of healthy children, most ECG intervals and amplitudes varied by sex and race. These differences have important implications for interpreting pediatric ECGs in the modern era when used for diagnosis or screening, including thresholds for left ventricular hypertrophy.

Objectives The study objective was to determine the predictors of new-onset arrhythmia among infants with single-ventricle anomalies during the post-Norwood hospitalization and the association of those arrhythmias with postoperative outcomes (ventilator time and length of stay) and interstage mortality. Methods After excluding patients with preoperative arrhythmias, we used data from the Pediatric Heart Network Single Ventricle Reconstruction Trial to identify risk factors for tachyarrhythmias (atrial fibrillation, atrial flutter, supraventricular tachycardia, junctional ectopic tachycardia, and ventricular tachycardia) and atrioventricular block (second or third degree) among 544 eligible patients. We then determined the association of arrhythmia with outcomes during the post-Norwood hospitalization and interstage period, adjusting for identified risk factors and previously published factors. Results Tachyarrhythmias were noted in 20% of subjects, and atrioventricular block was noted in 4% of subjects. Potentially significant risk factors for tachyarrhythmia included the presence of modified Blalock–Taussig shunt (P = .08) and age at Norwood (P = .07, with risk decreasing each day at age 8–20 days); the only significant risk factor for atrioventricular block was undergoing a concomitant procedure at the time of the Norwood (P = .001), with the greatest risk being in those undergoing a tricuspid valve procedure. Both tachyarrhythmias and atrioventricular block were associated with longer ventilation time and length of stay (P<.001 for all analyses). Tachyarrhythmias were not associated with interstage mortality; atrioventricular block was associated with mortality among those without a pacemaker in the unadjusted analysis (hazard ratio, 2.3; P = .02), but not after adding covariates. Conclusions Tachyarrhythmias are common after the Norwood procedure, but atrioventricular block may portend a greater risk for interstage mortality.

Endomyocardial biopsy (EMB), the gold standard for diagnosis of acute cellular rejection (ACR), poses unique risks in children. Limited cross- sectional data has associated left ventricular myocardial performance index (LVMPI) with ACR. We hypothesize that a relative change in MPI from baseline without ACR to the time of ACR will better detect ACR than an absolute threshold LVMPI value. We identified 40 children with ACR ≥60 days post-transplant matching them by age and time from transplantation to 40 children without ACR. There was a significant increase in LVMPI at time of ACR vs. baseline (0.59±0.17 vs. 0.41±0.11; p<0.001). There was no difference in LVMPI between baseline and follow-up (0.41±0.11 vs. 0.42±0.11; p=0.65). An absolute increase in LVMPI of ≥0.47 had 82.5% sensitivity and 85% specificity for ACR whereas an increase in LVMPI from baseline of ≥20.4% was 90% sensitive and 100% specific. Serial measurement of LVMPI appears to be a sensitive and specific marker of ACR. LV MPI shows good inter-observer agreement and increases at the time of EMB proven ACR with subsequent resolution to baseline measurements upon EMB proven resolution of ACR. Future studies in larger, prospective cohorts should be undertaken to validate these findings.