Morbidity and mortality from myocardial infarction are significantly reduced if patients and bystanders recognize symptoms early, activate the emergency medical service (EMS) system, and thereby shorten the time to definitive treatment. Trained prehospital personnel can provide life-saving interventions if the patient develops cardiac arrest. The key to improved survival is the availability of early defibrillation. Approximately 1 in every 300 patients with chest pain transported to the ED by private vehicle goes into cardiac arrest en route. Several studies have confirmed that patients with STEMI usually do not call 911; in one study, only 23% of patients with a confirmed coronary event used EMS.
The first goal for healthcare professionals is to diagnose in a very rapid manner whether the patient is having an STEMI or NSTEMI because therapy differs between the 2 types of myocardial infarction. Particular considerations and differences involve the urgency of therapy and degree of evidence regarding different pharmacological options. As a general rule, initial therapy for acute myocardial infarction is directed toward restoration of perfusion as soon as possible to salvage as much of the jeopardized myocardium as possible. This may be accomplished through medical or mechanical means, such as PCI or CABG.
Further treatment is based on the following:
Restoration of the balance between the oxygen supply and demand to prevent further ischemia
Pain relief
Prevention and treatment of any complications that may arise
Coronary collateral circulation
The coronary collateral circulation is an important factor in terms of the amount of damage to the myocardium that results from coronary occlusion. Well-developed collaterals may greatly limit or even completely eliminate myocardial infarction despite complete occlusion of a coronary artery. Reports vary as to the number of patients who have collaterals at the time of a myocardial infarction; many patients develop collaterals in the hours and days after an occlusion occurs.[46] When the patient is at rest, blood flow through collaterals is normal, a fact that accounts for the absence of resting ischemia. However, blood flow through collaterals does not increase with exercise; this inability accounts for the occurrence of ischemia during periods of stress.[47]