Myocardial ischemia can occur without overt symptoms. In fact, asymptomatic (or silent) ST-segment depression during ambulatory electrocardiogram monitoring occurs more often than symptomatic ST-segment depression in patients with
coronary artery disease. Initial studies documented that silent
ischemia provided independent prediction of adverse outcomes in patients with known and unknown
coronary artery disease. The ACIP (Asymptomatic Cardiac
Ischemia Pilot Study) enrolled patients in the 1990s and found that revascularization was better than medical
therapy in reducing silent ischemic episodes and possibly cardiovascular (CV) events. However, the more recent COURAGE (Clinical Outcomes Utilizing Revascularization and Aggressive
Drug Evaluation) trial found similar CV event rates between patients treated with optimal medical
therapy alone and those treated with optimal medical
therapy plus percutaneous revascularization. Therefore, in the current era, medical
therapy appears to be as effective as revascularization in suppressing symptomatic
ischemia and preventing CV events. COURAGE was not designed to evaluate changes in the frequency of silent
ischemia. Therefore, silent
ischemia may persist despite current-era treatment and might still identify patients with increased risk of CV events. Also, silent
ischemia is likely to occur frequently in heart transplant patients with denervated hearts and coronary allograft vasculopathy, and future study aimed at improving the management of silent
ischemia in this population is warranted. Additionally, future research is warranted to study the effect of newer medical
therapies such as
ranolazine or selected use of revascularization (for example, guided by fractional flow reserve) in those patients with persistent silent
ischemia despite optimal current-era medical
therapy.