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.
Idriss
Salim F
SF
Pediatric Cardiology, Duke University Medical Center, Durham, NC 27710, USA. salim.idriss@duke.edu
Bell
Jamie A
JA
D000375:Aging; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000175:diagnosis* / Q000503:physiopathology*; D006329:Heart Conduction System / Q000503:physiopathology*; D011817:Rabbits