The drug trinitrin is widely used to treat angina and it may even help in the diagnosis.
These tablets are placed in the mouth and sucked or chewed but not swallowed. The drug is absorbed through the mucous membrane of the mouth directly into the blood stream and works immediately. Should a clot form on an atheromatous plaque in one of the coronary arteries, it will block the artery. This is a coronary occlusion.
If the heart muscle supplied by that artery is deprived totally of its blood supply, death of the muscle will occur — a myocardial infarct.
Ischaema is the term given to impaired blood supply of any tissue. Myocardial ischaema may be temporary, as in angina, or prolonged, as in coronary occlusion.
The pain from an occlusion is of the same type as angina but is not produced by exertion and is unrelieved by rest. The pain may persist for hours and only be relieved by giving strong pain-relieving drugs like morphine and its derivatives.