Mechanisms of painless myocardial ischaemia.

The mechanisms responsible for the frequent absence of pain during episodes of acute myocardial ischaemia are poorly understood. The severity and duration of ischaemia are inadequate predictors of painless ischaemia, and thus it appears likely that important additional mechanisms must be involved. One such mechanism that may be operating in some patients is a generally deficient perception of painful stimuli. Destruction of afferent nerve fibres subserving cardiac nociception is a relevant consideration in some patients with diabetes mellitus and silent ischaemia. Psychological factors may also, in some patients, be important in modulating the ischaemic stimulus. The role of endorphins in the perception of cardiac ischaemic pain is uncertain. It is unlikely that the mechanisms responsible for painless myocardial ischaemia vary from patient to patient and even within the same patient from week to week or from day to day.