Arterial baroreflex modulation of heart rate in patients early after hearttransplantation: Lack of parasympathetic reinnervation

Background: Orthotopic heart transplantation results in cardiac denervation . The presence of cardiac parasympathetic reinnervation in humans has been widely debated based on the application of differing indirect measures of a utonomic control. However no attempt has been made to analyse the reflex he art rate response to baroreceptor stimulation whose occurrence is generally considered a reliable marker of the ability to activate cardiac vagal refl exes. This study tested the hypothesis that the presence of donor heart RR interval lengthening following phenylephrine induced blood pressure increas e would be an index of parasympathetic reinnervation. Methods: Baroreflex s ensitivity (BRS) was assessed in 30 patients (mean age 51 +/- 12 years) 1-2 4 months after heart transplantation carried out by the standard LowerShumw ay technique. In 6 patients the recipient atrium rate response (P-P interva l) to baroreceptor stimulation by phenylephrine was also simultaneously det ermined by transesophageal recording. Results: None of the 30 patients show ed prolongation of RR intervals in the donor heart. The average BRS value w as -0.28 +/- 0.54 ms/mmHg (range -1.3-0.7 ms/mmHg). In the 6 patients in wh om BRS was obtained at both the recipient atrium (P-P) and donor heart (R-R ) the changes were 7.6 +/- 5.7 ms/mmHg and -0.38 +/- 0.58 ms/mmHg respectiv ely (p = 0.02), thus confirming that the absent RR interval lengthening in the donor heart is the consequence of efferent vagal fiber interruption. Co nclusions: The absence of any RR interval prolongation following phenylephr ine induced baroreceptor stimulation demonstrates that vagal efferent reinn ervation of the donor heart does not occur up to 24 months in patients oper ated via the standard Lower-Shumway procedure. It is also suggested that an alysis of baroreceptor reflexes is a more specific method in the examinatio n of cardiac parasympathetic reinnervation. J Heart Lung Transplant 1999;18 :399-406.