Q: 54 year old male who is POD # 22 heart transplant is found to have symptomatic bradycardia with heart rate of 24. Resident administered 3 mg of Atropine without any effect. Your explanation?

Answer:  

Atropine is ineffective and should be avoided in heart transplant patients. The vagus nerve is not retransplanted after transplant and so Atropine would be useless in symptomatic bradycardia.

The transplanted heart is able to function in its new host through the capacity of its intact, intrinsic nervous system.The heart's nervous system contains around 40,000 neurons, called sensory neurites, which detect circulating hormones and neurochemicals and sense heart rate and pressure information. Hormonal, chemical, rate and pressure information is translated into neurological impulses by the heart's nervous system and sent from the heart to the medulla in brain through several afferent pathways. The signals have a regulatory role over many of the autonomic nervous system signals that flow out of the brain to the heart, blood vessels and other glands and organs.

Murphy D A, Thompson G W, et al (2000), The heart reinnervates after transplantation. Annals of Thoracic Surgery; 69(6): 1769-1781.