Influence of opiate systems in pain transmission during angina pectoris.

The situation of absent pain with silent myocardial ischemia is highly difficult to define. There are probably several reasons for the lack of pain. Partly, nerve ways may be destroyed, partly, myocardial ischemia as peripheral pain stimulus may be to weak and beyond threshold, however, additionally, there are a lot of clues for the participation of endogenous pain modification systems therein. A certain amount of myocardial ischemia is a necessary, but not sufficient precondition for anginal pain. Myocardial ischemia is only felt painfully if the peripheral nociceptive impulse rate is high enough to pass the actual inhibitory pain threshold, and if the nerve ways are intact. It is generally accepted that the endogenous opiate system, to some extent, takes part in the endogenous analgesia system. A range of examinations in recent years hinted at the fact that endorphins are in relation to the absence of pain in silent ischemia. Patients with symptomatic and asymptomatic myocardial ischemia are significantly different in plasma beta-endorphin levels at rest and during physical exercise. A relation between peripheral endogenous opiates and suffering behavior can, at present, only be indicated correlatively. It is likely that the intensive overlaying of the cardiovascular and pain regulating systems is related to the absence of pain in silent myocardial ischemia.