Although stress testing is quite useful in preoperative cardiac risk stratification, it is a flawed modality.

There are several serious cardiac complications that can result from non-cardiac surgery. These include ischemic events, arrhythmias—both bradyand tachyarrhythmias—and heart failure. Although stress testing can give some insight into an individual’s propensity for arrhythmias and heart failure, its role is quite limited. By and large its main use is in the diagnosis of clinically significant coronary artery disease (CAD). Much attention has therefore been focused on stress testing, because the most catastrophic cardiac complication of surgery, myocardial infarction (MI), with the attendant permanent loss of cardiac muscle and thus function, is caused by CAD.

The sensitivity and specificity of exercise stress testing for diagnosing coronary disease varies with the severity of this disease. Table 68.1 gives average results for various severity subsets across studies.

As can be seen, the test is more useful in severe forms of CAD. It is in these patients that prior intervention (regardless of the proposed surgery) may improve survival. Remember that the greater the sensitivity of a test, the more useful it is for excluding a diagnosis when the test is negative. More specific tests help in establishing a diagnosis when the test is positive. The main utility of the stress test in the context of risk stratification for surgery is in excluding severe CAD in a patient with a negative test. To add to the confusion, many of these statistics are from specialized centers under controlled circumstances. Depending on the population studied, the accuracy of stress testing may be much poorer. In several community hospital studies in a general medical population, the sensitivity was substantially worse (<50%).

The posttest likelihood of CAD is highly dependent on the pretest likelihood. If the pretest probability of CAD is either very low or high, the test provides little additional information. A negative test in a 70-year-old hypertensive diabetic with typical anginal chest pain is not helpful for excluding the diagnosis of CAD. It can be argued that it decreases the statistical chance of severe three-vessel or left main disease, but recall that one of the causes
of a false-negative nuclear scan is global ischemia, usually caused by critical left main stenosis.