Silent myocardial ischemia (SMI) is a condition which is characterized by an imbalance between the heart's requirement for oxygen (demand) and the supply of oxygen. When transient, this imbalance between supply and demand results in chest pain or angina but is often silent (SMI). Episodes of SMI can be detected by continuous electrocardiographic monitoring of the ST segment using Holter monitoring. Some reports have suggested that presence of SMI on Holter identifies a high risk subgroup of patients with coronary artery disease. We investigated 80 patients with mild coronary artery disease who were not candidates for bypass surgery. Approximately half had SMI during normal daily activities but there was no increase in the frequency of heart attacks, death or unstable angina in these patients compared with those with absence of SMI indicating then the presence of SMI does not necessarily increase the risk in patients who are otherwise in the low risk category. Several techniques are currently available for detecting transient myocardial ischemia. These include treadmill exercise testing, exercise thallium scintigraphy, exercise radionuclide ventriculography , and ambulatory ST monitoring for SMI. To investigate the relationship between SMI detected by Holter monitoring and other techniques, we performed a multivariate analysis in 100 patients who had all tests including cardiac catheterization. The independent predictors of SMI during daily life were the 1) treadmill exercise time to onset of ischemia, 2) the heart rate during treadmill test at the onset of ischemia, and 3) the R wave height in lead V5 of the resting electrocardiogram. The lack of predictability with nuclear techniques can largely be explained by the poor detection of SMI during ambulatory monitoring in patients with previous heart attack.
