The
calcium antagonists provide a unique tool to reduce myocardial
oxygen demand and prevent increases in coronary vasomotor tone. For patients with
Prinzmetal's variant angina,
diltiazem,
nifedipine and
verapamil are extremely effective in preventing episodes of
coronary vasospasm and symptoms of
ischemia.
Unstable angina pectoris is a more complex pathophysiologic syndrome with episodes of
ischemia due to increases in coronary vasomotor tone, intermittent platelet aggregation or alterations in the underlying
atherosclerotic plaque. Each of the
calcium antagonists is effective as monotherapy in decreasing the frequency of
angina at rest.
Nifedipine is the only
calcium antagonist that has been studied in a combination regimen with beta blockers and
nitrates for patients with
unstable angina, and control of angina is better with the combination regimen than with either form of
therapy alone. Although symptoms of
myocardial ischemia in
unstable angina are reduced by
calcium antagonists, these agents do not seem to decrease the incidence of adverse outcomes. Antiplatelet
therapy appears to improve morbidity and mortality in patients with
unstable angina, suggesting that
thrombus formation may play a central role in that disorder. Episodes of silent or asymptomatic
myocardial ischemia, identified by ST-segment monitoring, occur in a variety of disorders of
coronary disease. Among patients with
Prinzmetal's variant angina and
unstable angina, episodes of silent
ischemia appear to be as frequent as episodes of angina and the
calcium antagonists are effective in decreasing episodes of
ischemia regardless of the presence or absence of symptoms. Persisting episodes of silent
ischemia among patients with
unstable angina despite maximal medical
therapy identify patients at high risk for an early unfavorable outcome. Among patients with stable exertional angina, episodes of silent
ischemia may be up to 5 times as frequent as episodes of angina, and may be due to increases in coronary vasomotor tone, transient platelet aggregation or increases in myocardial
oxygen demand. Preliminary experience suggests that
calcium antagonists and beta blockers are effective in decreasing episodes of silent
ischemia in patients with stable exertional angina and that a combination regimen may be more effective than either form of
therapy alone.