Postinfarction Management

Twenty percent of patients with acute myocardial infarction die before they reach the hospital. Mortality rates in hospitalized patients range from 5% to 15% and are determined chiefly by the size of the infarction and the age and general condition of the patient. Patients developing heart failure or hypotension have high early mortality rates. Several classification criteria have been developed to estimate early prognosis for survival. The most accurate is hemodynamic subsetting (Table 10-3). The prognosis after discharge is determined by three major factors: the degree of left ventricular dysfunction, the extent of residual ischemic myocardium, and the presence of ventricular arrhythmias. The mortality rate in the first year after discharge is approximately 6-8%, with over half of deaths occurring in the first 3 months, chiefly in patients with postinfarction heart failure. Subsequently, the mortality rate averages 4% per year.

A. Risk Stratification

A number of findings indicate increased risk after infarction. These include: (1) postinfarction angina; (2) non-Q wave infarction; (3) heart failure; (4) left ventricular ejection fraction less than 40%; (5) stress-induced ischemia, diagnosed by electrocardiography, scintigraphy, or echocardiography; and (6) ventricular ectopy (> 10 VPB/h).

Patients with postinfarction angina should undergo coronary arteriography. Authorities differ about which tests should be performed routinely in other patients, but in most a noninvasive assessment of left ventricular function and residual ischemia is appropriate. Significant left ventricular dysfunction is most likely with anterior infarction or multiple infarctions. In such patients, noninvasive assessment of left ventricular function by echocardiography or scintigraphy will help assess prognosis and facilitate medical management. If the ejection fraction is less than 40%, coronary angiography may be indicated, as this is a high-risk subset in which revascularization may improve prognosis. ACE inhibitor therapy is also indicated in patients with reduced ejection fractions. Submaximal exercise or pharmacologic stress testing before discharge or a maximal test after 3-6 weeks (the latter being more sensitive for ischemia) helps patients and physicians plan the return to normal activity. Imaging in conjunction with stress testing adds additional sensitivity for ischemia and provides localizing information. Both exercise and pharmacologic stress imaging have successfully predicted subsequent outcome. One of these tests should usually be employed prior to discharge in patients who have received thrombolytic therapy as a means of selecting appropriate candidates for coronary angiography.

Ambulatory electrocardiographic monitoring for arrhythmias is of less clear value; though it has some prognostic value beyond measurements of left ventricular function, no benefit from antiarrhythmic therapy for asymptomatic patients has been demonstrated. Ischemia detected during ambulatory monitoring is an indicator of poor prognosis, but it is unclear how much additional information is obtained in patients who have also undergone exercise testing or scintigraphic studies. The role of other procedures such as assessment of heart rate variability or baroreceptor testing is uncertain.