Cardiac Syndrome X

To the Editor: There may be an alternative explanation for the observations made by Panting et al. (June 20 issue) 1 in their elegant study of patients with cardiac syndrome X. Although the heart-rate response to adenosine infusion is not given, the occurrence of “adenosine-induced tachycardia” is mentioned. Huang et al. 2 , 3 showed that cardiac sensory-nerve endings in the canine heart possess specific adenosine receptors that can be activated by endogenous adenosine released from the heart. Exogenous adenosine administered to ventricular sensory-nerve endings greatly stimulates cardiac sensory neurons in the upper thoracic dorsal-root ganglia that project cardiac nociceptive input to the . . .