Exercise stress testing is limited in some patients who cannot exercise because of musculoskeletal disease, pulmonary disease, or severe cardiac disease. Dipyridamole-thallium scanning may be used to overcome the limitations of exercise stress testing. This study has a high degree of sensitivity and specificity but a low positive predictive value (179,183). It relies on the ability of dipyridamole to dilate normal coronary arteries but not stenotic vessels. Normally perfused myocardium readily takes up thallium when it is given intravenously. Conversely, hypoperfused myocardium does not show good uptake of thallium when scanned 5 minutes after injection. Reperfusion and uptake of thallium 3 hours after injection identify viable but high-risk myocardium. Old infarctions are identified as areas without uptake. Several studies show an increasing risk of perioperative myocardial infarction dependent on the extent of reperfusion of thallium, or reversible defect, ranging from 3% to 49% (184,185). The dipyridamole-thallium scan is applicable to clinically high-risk patients who are unable to exercise because it uses a medically induced “stress.”
Dobutamine stress echocardiography is another test to evaluate cardiac risk in patients who are unable to exercise. This method identifies regional cardiac wall motion abnormalities after dobutamine infusion to identify patients at high risk for cardiac events. Positive and negative predictive values are similar to those of dipyridamole-thallium testing for a perioperative event (186,187). Dipyridamole-thallium testing is preferred for patients with known cardiac arrhythmias, and dobutamine is preferred for patients with bronchospastic lung disease and in those with severe cardiac stenosis (188). Coronary angiography should be considered only in patients who have an indication for angiography independent of the planned surgery, such as patients with acute coronary syndromes, unstable angina, angina refractory to medical therapy, or high-risk results on noninvasive testing.
Preoperative testing should be used discriminately in intermediate-risk patients. Controversy exists regarding the accuracy of these tests to provide prognostic information beyond what is obtained from clinical risk stratification for nonvascular procedures. Diagnostic testing should not lead to unnecessary additional testing or harmful delays in surgery. The American College of Cardiology and the American Heart Association present an updated detailed algorithm that incorporates risk-factor stratification to guide clinicians to proceed directly to surgery, to delay surgery and obtain preoperative noninvasive testing, or to attempt risk factor modification (179).
It is rare for patients who are younger than 50 years and who do not have diabetes, hypertension, hypercholesterolemia, or coronary artery disease to suffer a perioperative myocardial infarction. In contrast, patients with coronary artery disease are at increased risk of myocardial infarction in the postoperative period. Prevention, early recognition, and treatment are important because myocardial infarctions that occur in the postoperative period have mortality rates of up to 25% and are associated with increased rates of cardiovascular death in the 6 months following surgery (189).