Clinical Drug Experience Knowledgebase

BACKGROUND:

Asymptomatic cardiac ischemia, frequently designated as silent myocardial ischemia, refers to episodes of objectively demonstrable transient ischemia in the absence of symptoms. Annually, more than one million patients suffer acute myocardial infarction. Of the approximately 700,000 who are discharged alive from the hospital, as many as 180,000 will be asymptomatic but have evidence of myocardial ischemia on a pre-discharge exercise test. Asymptomatic ischemia has been linked with sudden death or myocardial infarction. It is estimated that in the United States over six million patients have chronic, symptomatic coronary heart disease and up to three million of these may exhibit transient asymptomatic myocardial ischemia. Asymptomatic ischemia is thought to be present in the majority of coronary heart disease patients with stable angina pectoris, over 70 percent of all ischemic episodes being asymptomatic. Asymptomatic ischemia following myocardial infarction or in the presence of chronic stable angina may be associated with substantially increased morbidity and mortality

Traditionally, treatment of patients with coronary heart disease has been given for and guided by patients' symptoms. There was a growing trend toward recognizing asymptomatic cardiac ischemia and according it importance equal to that of symptomatic ischemia. Many physicians believed that suppression of asymptomatic ischemia in patients with coronary heart disease would reduce morbidity and mortality. This was leading to rapidly increasing and widespread applications of both medical and revascularization therapies.

In 1989, there was a lack of knowledge as to the relative efficacy of different treatment strategies to control asymptomatic cardiac ischemia. Given the estimated high prevalence of asymptomatic cardiac ischemia in patients with coronary heart disease and evidence of increased risk of untoward outcome, the public health problem was of sufficient magnitude to warrant a pilot study to determine to what extent asymptomatic ischemia could be controlled. If the pilot study demonstrated feasibility, a full-scale clinical trial would then be considered to evaluate the impact of effective treatment of asymptomatic ischemia on survival and cardiovascular morbidity in patients with coronary heart disease.

DESIGN NARRATIVE:

A total of 1,959 patients were screened by AECG monitoring; 49 percent had asymptomatic ischemia, and 65 percent were enrolled in the study. The 618 patients were randomized to one of the three treatment strategies: 202 to angina-guided medical strategy with titration of anti-ischemic medication to relieve angina; 202 to angina-guided plus AECG ischemia-guided medical strategy with titration of anti-ischemic medication to eliminate both angina and AECG ischemia; and 212 to revascularization by angioplasty or bypass surgery. Patients able to take either beta-adrenergic blocking agents or calcium antagonists were also randomized to receive one of two medical combination regimens: atenolol plus nifedipine or diltiazem plus isosorbide dinitrate. Those who could be treated with only one regimen, such as asthmatic patients, were assigned to the appropriate regimen. The primary outcome was the absence of ischemia at twelve weeks. Recruitment ended in January 1993. Clinical based follow-up was completed for 18 months and survival status free of MI was completed for 24 months