Cardiac repolarization instability during normal postnatal development.

Long QT syndrome is a disease characterized by abnormal lengthening of the QT interval and by sudden cardiac death. It is a disease of development, with the incidence of a sudden event increasing during childhood. Repolarization instability during postnatal development could make the substrate susceptible to a fatal arrhythmia. Dynamic changes in repolarization that occur on a beat-to-beat basis, known as alternans, are a hallmark of electrical instability. T-wave alternans (TWA) in the electrocardiogram correlates with arrhythmia risk and long-term survival in adults. We determined TWA properties longitudinally in vivo in 7 propofol-sedated New Zealand white rabbits using transesophageal pacing weekly from 2 to 10 weeks of age. Furthermore, TWA induction after the onset of rapid pacing was characterized in vitro in 6 infant (2 weeks) and 6 adolescent (7 weeks) isolated, arterially perfused rabbit hearts. In vivo, TWA amplitude was maximum at 2 weeks and declined with age. Isoproterenol increased TWA at 8 weeks (adolescence). In vitro, large-amplitude TWA was induced with rapid pacing in both infant and adolescents but decreased to low, steady-state levels in infants. We conclude that TWA properties are age dependent in rabbit. Significant TWA is induced in rabbit at the onset of rapid pacing.

Duke Scholars

Author Salim Farouk Idriss Pediatrics, Cardiology