Increased dispersion of ventricular repolarization during head-up tilt test late after orthotopic heart transplantation in humans

Sympathetic reinnervation after heart transplantation may be regionally heterogeneous. It remains undetermined if such heterogeneous reinnervation will result in increased ventricular repolarization dispersion. To determine the changes of ventricular repolarization after transplantation, a 15-minute, 80-degree head-up tilt test was prospectively performed with isoproterenol provocation in 30 patients who were studied within 5 months after transplantation (early group) and 30 patients who were studied greater than or equal to12 months (late group). Holter monitor was initiated to evaluate heart rate variability, which was a surrogate of cardiac reinnervation. IT dispersion was defined as the difference between maximal and minimal IT interval measurements occurring among any of the 12 leads on a standard electrocardiogram. No subject had fewer than nine measurable leads. Compared with patients in the early group, the patients in the late group had higher low frequency activity, indicating partial sympathetic reinnervation. Analysis of the electrocardiogram showed that there were significant differences in the corrected IT dispersion in the late group compared with the early group and controls (74 +/- 18 vs 56 +/- 15 and 55 +/- 14 ms, both P <0.05) during isoproterenol infusion. Head-up tilt test is a useful tool to unmask the increased dispersion of ventricular repolarization, particularly during states of isoproterenol infusion. Early after cardiac transplantation, neither postural changes nor isoproterenol infusion caused a significant increase of corrected IT dispersion. Late after transplantation, heterogeneous sympathetic reinnervation may result in increased corrected IT dispersion. However, whether increased dispersion of ventricular repolarization is related to cardiac death late after operation warrants further investigation in a large and long-term trial.