Silent myocardial ischemia.

Myocardial ischemia can manifest itself as strictly silent or a combination of symptomatic and silent episodes. We have demonstrated that most asymptomatic patients have a higher threshold for pain than did symptomatic patients. Low sensitivity to pain in patients with silent ischemia may be related to both a neural pain inhibitory system and the release of endogenous opiates, the endorphins. beta-Endorphin release occurs during and after exercise; patients with asymptomatic ischemia had higher plasma beta-endorphin levels than did patients with symptomatic ischemia, especially during exercise. With naloxone treatment, the pain threshold of patients with silent myocardial ischemia (SMI) can be reduced to the same values as those of symptomatic patients. This supports the possibility of a role for endorphins in SMI. Patients who experience both asymptomatic and symptomatic ischemic episodes do so because their pain threshold and endorphin regulatory system varies throughout the day and because severity and duration of ischemic episodes are different. Although there is controversy over the appropriate therapy for SMI, it is more likely that this should simply be treated in the same way as painful ischemia.