Speaking at the 46th Annual Scientific Session of the American College of Cardiology, Dr. George W. Vetrovec provided a brief, but comprehensive overview of the different long-term treatment options for myocardial infarction (MI), emphasizing the need for physicians to be more proactive in converting new knowledge into behaviour.
Aspirin
The prophylactic long-term use of aspirin is aimed at trying to prevent rethrombosis of the associated coronary artery. Its use in patients subsequent to a first MI has resulted in 10% to 15% reductions in mortality and a 20% to 30% decreased risk of reinfarction. Although the combination of aspirin with warfarin has failed to demonstrate any significant difference in outcome, a slight trend has been shown towards an increased risk of stroke with low-dose warfarin.
ß-blockers
ß-blockers should be started within 12 hours in eligible patients and should be used long-term based on tolerability and the risk profile of the patient. Greatest benefits are seen in patients with large, particularly anterior MI, and the benefits are most striking when the drug is initiated early.
Angiotensin Converting Enzyme (ACE) Inhibitors
Provided MI patients are hemodynamically stable, treatment with an ACE inhibitor should be initiated within the first 24 hours and maintained for a six-week period. Thereafter, the physician may decide to continue treatment over the long term based on the individual patient's risk profile. As with ß-blockers, there is a risk stratification factor for ACE inhibitors. Studies have shown that for patients with <40% ejection fraction, anterior MI, or early congestive heart failure (CHF), the reduction in mortality can range from 19% to 27% with the use of ACE inhibitors. Patients at high risk of CHF are likely to require these agents lifelong. Although ACE inhibitors do not have intrinsic anti-ischemic properties, the Studies of Left Ventricular Dysfunction (SOLVD) trial has shown that the risk of subsequent MI, unstable angina, and death due to either of these ischemic events was significantly lower in patients being treated with them. It is postulated that this benefit may accrue from changes in acute catecholamines or, perhaps chronically, to some change in the behaviour of the plaque or proliferation at the plaque site.
Calcium Channel Blockers (CCB)
The advantage of long-term CCB use by MI patients is less clear. If needed, usually for ischemia that cannot be treated any other way, Dr. Vetrovec recommends using a rate-lowering agent, verapamil predominantly. Diltiazem is acceptable only if the patient has good ventricular function. And, if dihydropyridines are warranted, he recommends using a long-acting one to avoid the acute effects which often accompany those, like nifedipine, that are short acting.
Dietary Management
In general, dietary management of MI patients has not been aggressive enough. Targeting lipid reduction and risk modification in patients with MI is critical since their greatest impact has been realized in terms of secondary prevention: 50% of infarcts and 70% of deaths due to coronary artery disease occur in patients who have had a previous MI. Cholesterol levels should be obtained during the acute event and, if significantly elevated, lipid-lowering treatment should be initiated immediately.
Angiography
Patients must be stratified according to risk to determine their eligibility for angiography. It tends to be used in low-risk patients according to convenience and availability and avoided in high-risk patients who might, in fact, be the ones most likely to benefit from it. The GUSTO-I trial showed that in the U.S., angiography was used three times as often while intervention or revascularization was used twice as often as in Canada. While both countries had the same one-year mortality rates, patients in the U.S. had significantly fewer symptoms. The major driving factors behind determining patients who ought to undergo angiography are ongoing or early provocative ischemia, poor left ventricular function, or heart failure.
Using a composite of primary agents is often critical to reduce the risk of adverse events. Other risk factors should also be minimized wherever possible. For example, the significant risk inherent in smoking decreases to nearly control levels within about three years of cessation. In closing, Dr. Vetrovec mentioned that according to 1992 statistics, there was a 12% lower risk of mortality in patients managed by cardiologists as opposed to primary care physicians. Cardiologists used significantly more therapies, including ß-blockers, thrombolytics and cardiac procedures, so cost containment issues may be significant. With risk stratification, optimal care with minimal cost should be achievable. Pharmacological treatment should be used intensively early on and then reduced and targeted to patients with the highest risk. The use of angiography should be determined by risk, and lifestyle modification, such as lipid lowering, should be routine and risk-based.
