REINNERVATION OF THE TRANSPLANTED HUMAN HEART AS EVIDENCED FROM HEART-RATE-VARIABILITY STUDIES

This study evaluated heart rate variability (HRV) after cardiac transp lantation in humans in an attempt to test the hypothesis that cardiac reinnervation occurs in the post-transplant period. HRV was measured u sing 24-hour Holter recordings performed on 37 ambulant patients 1 to 122 months after cardiac transplantation. All patients were free of hi stologic rejection and were taking no medication likely to influence H RV. Time and frequency domain were analyzed and circadian rhythm of ho urly average heart rate was calculated. HRV increased with time after the transplant. Compared with patients in the early post-transplant pe riod, patients >36 months after transplant had lower 24-hour heart rat es (86 vs 93 beats/min), an increased average of all 5-minute SDs of N N intervals (17.6 vs 11.3), and higher low- and high-frequency power. Ten of the 27 patients >3 years after transplantation had evidence of functional cardiac reinnervation. Compared with patients who had no re innervation, these patients had increased circadian variability with l ower nocturnal heart rates (76 vs 91 beats/min) and greater sympatheti c activity during both daytime (natural logarithm sympathetic power -0 .36 vs -1.45) and nighttime (natural logarithm sympathetic power -0.43 vs -1.98). Despite lower nocturnal heart rates, there was no HRV evid ence for an increase in parasympathetic activity. Thus, patients late after cardiac transplantation have HRV evidence for an increase in sym pathetic control of the heart.