Medical Management

Tak W. Kwan, M.D.
(presented at the CAMS 1997 Semiannual Scientific Meeting)

Once coronary artery atherosclerosis has developed, patients may present with chronic stable angina or one of the features of acute ischemic syndromes such as unstable angina, non-Q wave myocardial infarction or Q wave myocardial infarction. In recent years, there is major break-through in terms of understanding the common pathophysiologic mechanism precipitating these events; it is the de-stabilization of an atherosclerotic plaque. As a result, coronary thrombosis of varying degree is developed. In the case of unstable angina and non-Q wave myocardial infarction, a subtotal occlusion is seen and in complete thrombotic occlusion, Q-wave myocardial infarction will be developed.

Patients usually present with a worsening pattern or prolonged episode of chest pain at rest. Based on the electrocardiogram, we can divide it into those without persistent ST elevation (unstable or non-Q wave myocardial infarction), and those with persistent ST segment elevation (Q wave myocardial infarction). The former group is difficult to differentiate because of their similar clinical presentation and treatment strategy.
The treatment for Q wave myocardial infarction is to restore the coronary blood flow and maintain the patency of the infarct-related artery. Also, an effort should be made to limit infarct size and to prevent complications. Patients with unstable angina or non-Q wave myocardial infarction are at increased risk for recurrent myocardial ischemia and infarction. Efforts should be made to stabilize the atherosclerotic plaque and to inhibit coronary thrombosis. Preventing recurrent myocardial damage and/or sudden death and promoting regression of atherosclero-sis are the primary goal in treating patients wit acute ischemic syndromes.

In summary, for patients with Q-wave myocardial infarction, intravenous thrombolysis is the main stay of therapy. The door-to-needle time is the most significant factor for survival. Although primary PTCA has shown to improve survival when compared to intravenous thrombolysis, there is still a limitation for this approach. The availability of the cardiac catheterization laboratory team and experiences of the interventionist are the most important factors. Intravenous thrombolysis is associated with a higher instances of complication in patients with non-Q wave myocardial infarction or unstable angina. Aspirin, heparin and a new glycoprotein IIb IIIa platelet inhibitors are extremely useful in these patients especially when they are undergoing PTCA. Angiotensin converting enzyme inhibitors should be given in all patients with myocardial infarction and low ejection fraction. There is some evidence that it is also advantageous in patients with myocardial infarction and normal ejection fraction. Nitroglycerin is one of the most important therapy of angina. However, in patients with myocardial infarction, the improvement of survival has not been shown. -blocker should be given to all patients post-myocardial infarction because of its beneficial effect shown in several large controlled trials. Calcium channel blockers should be avoided in all patients with Q-wave myocardial infarction especially with low ejection fraction. It should not be given even to patients with unstable angina. In non-Q wave myocardial infarction, the benefit of calcium channel blockers is very small. Anti-arrhythmic agents, particularly the type I drugs, should be totally avoided in all patients post myocardial infarction as it increases mortality. Amiodarone is the only agent that can be given in this group of patients but it has not been shown to improve survival. Alternative strategies such as electrophysiological guided therapy with AICD will be needed. In addition, cholesterol lowering agents has been demonstrated to improve survival in patients with myocardial infarction and unstable angina. Every effort should be made to lower the cholesterol as much as possible. Aggressive follow up and appropriate intervention are recommended for all patients with myocardial infarction and unstable angina.