Importance of generalized defective perception of painful stimuli as a cause of silent myocardial ischemia in chronic stable angina pectoris.

Growing evidence indicates that most patients with coronary artery disease frequently have episodes of painless myocardial ischemia. Previous studies from our institution show that the severity and duration of myocardial ischemia are necessary but not sufficient factors to explain the occurrence of anginal pain. The responses to a battery of painful stimuli were studied in 12 patients with predominantly painless (group A) and in 15 patients with predominantly painful (group B) ischemic episodes. The severity of myocardial ischemia as assessed by the measurement of ST-segment depression during exercise stress testing and during ambulatory electrocardiographic monitoring was comparable in the 2 groups. Patients in group A had a significantly higher threshold and tolerance for forearm ischemia (+32%, p less than 0.05; +120%, p less than 0.001), cold (+100%, p less than 0.05; +180%, p less than 0.01) and electrical skin stimulation (+145%, p less than 0.01; +109%, p less than 0.01), but the overlap between the 2 groups was often appreciable. In the 6 patients with the longest tolerance times for forearm ischemic pain (all in group A) and in the 5 having the shortest tolerance times (all in group B), plasma levels of beta endorphin, met-enkephalin, noradrenaline and adrenaline were similar during both the basal state and the induction of forearm ischemic pain. Thus, a generalized defective perception of painful stimuli plays an important role in many patients with predominantly painless myocardial ischemia. Other mechanisms, however, may also be important, particularly in patients whose threshold and tolerance values overlap with those of patients who have predominantly painful myocardial ischemia.