VASOVAGAL REACTIONS MAY OCCUR AFTER ORTHOTOPIC HEART-TRANSPLANTATION

Objectives. This study evaluated the ability of patients to manifest vasovagal reactions after orthotopic heart transplantation. Background. Paradoxic stimulation of left ventricular baroreceptors may be the afferent limb of the vasovagal reflex in humans. Orthotopic heart transplantation causes surgical denervation of these receptors and would therefore be expected to abolish the vasovagal reflex. Methods. To attempt to confirm this hypothesis, 10 patients with orthotopic heart transplantation underwent both head-up tilt testing while resting on a saddle support and testing for parasympathetic innervation of the donor heart before and after atropine infusion. Native and donor heart sinus rates were monitored by using an esophageal pill electrode throughout tilting and during parasympathetic testing. Results. Unexpectedly, seven patients had vasovagal responses at saddle support tilt testing, during which native heart rate decreased by 25 +/- 7 beats/min and mean arterial blood pressure decreased by 55 +/- 9 mm Hg. In three of these patients, there was also a decrease in donor heart rate of 23 +/- 26 beats/min. Parasympathetic testing showed possible evidence of donor heart vagal reinnervation in these patients with donor heart bradycardia during tilt but not in those with vasovagal reactions to tilt without slowing of the donor heart rate. Conclusions. Vagal efferent reinnervation can occur after orthotopic heart transplantation in humans. However, the absence of such reinnervation in some patients with vasovagal responses to tilt calls into question the role of left ventricular receptors in inducing the vasovagal reaction.