ESSENTIALS OF DIAGNOSIS
Sudden but not instantaneous development of prolonged (greater than 30 minutes) anterior chest discomfort (sometimes felt as “gas” or pressure).
Sometimes painless, masquerading as acute HF, syncope, stroke, or shock.
ECG: ST-segment elevation or left bundle branch block.
Immediate reperfusion treatment is warranted.
Primary PCI within 90 minutes of first medical contact is the goal and is superior to fibrinolytic therapy.
Fibrinolytic therapy within 30 minutes of hospital presentation is the goal and reduces mortality if given within 12 hours of onset of symptoms.
STEMI results, in most cases, from an occlusive coronary thrombus at the site of a preexisting (though not necessarily severe) atherosclerotic plaque. More rarely, infarction may result from prolonged vasospasm, inadequate myocardial blood flow (eg, hypotension), or excessive metabolic demand. Very rarely, MI may be caused by embolic occlusion, vasculitis, aortic root or coronary artery dissection, or aortitis. Cocaine, a cause of infarction, should be considered in young individuals without risk factors. A condition that may mimic STEMI is stress cardiomyopathy (also referred to as tako-tsubo or apical ballooning syndrome). ST elevation connotes an acute coronary occlusion and warrants immediate reperfusion therapy with activation of emergency services.
There is usually a worsening in the pattern of angina preceding the onset of symptoms of MI; classically the onset of angina occurs with minimal exertion or at rest.
Unlike anginal episodes, most infarctions occur at rest, and more commonly in the early morning. The pain is similar to angina in location and radiation but it may be more severe, and it builds up rapidly or in waves to maximum intensity over a few minutes or longer. Nitroglycerin has little effect; even opioids may not relieve the pain.
Patients may break out in a cold sweat, feel weak and apprehensive, and move about, seeking a position of comfort. They prefer not to lie quietly. Light-headedness, syncope, dyspnea, orthopnea, cough, wheezing, nausea and vomiting, or abdominal bloating may be present singly or in any combination.
One-third of patients with acute MI present without chest pain, and these patients tend to be undertreated and have poor outcomes. Older patients, women, and patients with diabetes mellitus are more likely to present without chest pain. As many as 25% of infarctions are detected on routine ECG without any recallable acute episode.
5. Sudden death and early arrhythmias
Of all deaths from MI, about half occur before the patients arrive at the hospital, with death presumably caused by ventricular fibrillation.