T wave alternans threshold in normal children

Introduction: Sustained microvolt-level T wave alternans (TWA) during exerc ise is a predictor of ventricular arrhythmia propensity in adult population s. TWA occurs in normal adults, but it is rare at < 70% of predicted maximu m heart rate. An onset heart rate <less than or equal to>110 is believed to be significant. The aim of this study was to examine the feasibility of pe rforming the test in children and to determine the normal heart rate thresh old for sustained TWA in children. Methods and Results: Alternans was evaluated during bicycle exercise in 100 normal volunteers aged 8 to 17 years. Adequate resting data were obtained in 76 of 100 children and was negative in all. Exercise data from 16 of 100 was excluded due to excessive noise. Median maximum heart rate was 192 (ra nge 140 to 214), Sustained alternans was absent in 75 (89%) of 84, In the n ine children with sustained alternans, median onset heart rate was 138 (ran ge 120 to 158), and 7 of 9 had an onset heart rate greater than or equal to 135. Median heart rate threshold as a percentage of predicted maximum hear t rate (220 - age) was 67% (range 58% to 76%), Only 1 subject (1.2%) had an onset heart rate <60% of predicted maximum. There was no significant diffe rence between age, gender, endurance, maximum heart rate, QRS duration, QT interval, or QTc in those with and those without sustained TWA, Conclusion: Noninvasive assessment of TWA is feasible at <greater than or e qual to>8 years of age, Sustained TWA was present in 11% of normal children , but was absent at heart rates below 120 and rare (1.2%) below 60% of pred icted maximum heart rate.