ABSENCE OF PARASYMPATHETIC CONTROL OF HEART-RATE AFTER HUMAN ORTHOTOPIC CARDIAC TRANSPLANTATION

Background Partial reinnervation of cardiac sympathetic nerves has bee n observed after heart transplantation; we hypothesized that parasympa thetic control to the heart after transplantation may return as well. To test this hypothesis, we examined heart rate responses produced by two cardiovascular reflexes whose efferent limbs are subserved by vaga l fibers to the heart: (1) trigeminal reflex (simulated diving reflex) and (2) arterial baroreflex with phenylephrine Injection. Methods and Results An ''early'' group (n = 31, < 24 months after transplantation ) and a ''late group'' (n = 27, > 45 months after transplantation) wer e studied and compared with a control group with intact cardiac innerv ation (n = 32) and a renal transplant group with similar transplant im munosuppressive regimen (n = 11). For trigeminal reflex testing, respo nses of the donor sinus node (DSN) (sinus node controlling heart rate) and recipient sinus node (RSN) in the innervated remnant right atrium in cardiac transplant patients were compared with heart rate response s in the control groups. For arterial baroreflex testing, baroreflex g ains for the DSN and RSN in the cardiac transplant groups were compare d with those of the control group. With engagement of the trigeminal r eflex, the DSN rate of both transplant groups changed minimally (early . 1.2 +/- 1.2 bpm; late, 1.8 +/- 25 bpm) compared with the expected de crease in control subjects (-19.8 +/- 3.0 bpm) and renal transplant pa tients (-23.9 +/- 4.9 bpm) (P < .001 versus cardiac transplants). Chan ges in the RSN rate of both cardiac transplant groups (early, -13.0 +/ - 4.0 bpm; late, -10.0 +/- 3.7 bpm) were similar to the control groups . Arterial baroreflex gains for the DSN were also depressed (early, 0. 1 +/- 0.2 ms/mm Hg; late, 0.2 +/- 0.2 ms/mm Hg) compared with control (14.9 +/- 1.8 ms/mm Hg) and RSN (early, 9.9 +/- 1.3 ms/mm Hg; lace, 10 .9 +/- 1.3 ms/mm Hg; P < .001 versus DSN transplant). Conclusions Thes e data suggest that parasympathetic influences on donor heart rate are absent in the majority of patients up to 96 months after cardiac tran splantation.