Five years after orthotopic cardiac transplantation, the recipient is most likely at increased risk for which of the following?
There is no parasympathetic, sensory or sympathetic inner-vation in the transplanted heart. Long-term studies in humans have shown reinnervation to be absent or – at best – partial or incomplete.
The lack of vagal tone results in a resting heart rate slightly higher than normal. The lack of sympathetic innervation results in a loss of reflex tachycardia in response to various stimuli such as hypovolemia, severe pain, or direct laryngoscopy and intubation. Because the allograft does have normal cate-cholamine receptors, direct-acting agonists such as epinephrine, isoproterenol and dobutamine have predictable effects, and heart rate will gradually increase in response to rising systemic catecholamine levels (e.g., with exercise). The transplanted heart is preload-dependent, and increases in cardiac output are accomplished predominantly via Frank–Starling mechanisms.
Pharmacologic agents that have both direct and indirect...