ST elevation is less common, but more ominous than ST depression, as it indicates transmural ischemia.1 This finding most often indicates high-grade left anterior descending (LAD) or left main CAD. It is most often seen in the anterior leads, and the location of ST changes correlates with the area of ischemia. Bear in mind, however, that the correlation between ST elevation and transmural ischemia is true only if the patient has no history of MI. ST elevation in leads in which Q waves are present at rest usually indicates ventricular dyskinesia or aneurysm and not ischemia.1
Premenopausal women and women who are taking estrogen supplements, in particular, are more likely than men to have false-positive ST changes, most likely because of a poorly understood effect of estrogen. The molecules of estrogen and of digitalis glycosides have some regions of structural similarity, and it is thought that both molecules can cause ST changes.10
And what about arrhythmias? Arrhythmias are often seen at rest and with exertion. Supraventricular arrhythmias, including supraventricular tachycardia, are not associated with CAD. Premature ventricular contractions (PVCs) are common at peak exertion. PVCs are probably related to catecholamine release and do not indicate ischemia. (See “A look at the stress test report”)
Ventricular tachycardia, however—defined as 3 or more consecutive PVCs—has a 90% correlation with significant coronary artery stenosis, as shown on angiography.1
Rate-dependent conduction disturbances, including 2-to-1 atrioventricular block and bundle-branch blocks, may also be seen. These may be associated with ischemia, but are not highly predictive of coronary artery stenosis. Further testing may be indicated to determine whether stenosis is present.1
A look at the stress test report
The report from the physician who performs or reads the stress test should contain the following elements:
Heart rate achieved, including both the rate itself and the percentage of the patient’s age-predicted maximum that the heart rate represents. Failure to reach 85% of the maximum may be related to underlying cardiac or pulmonary disease, the use of beta-blockers, musculoskeletal disorders, or general deconditioning. However, it is obviously noteworthy if the patient develops chest pain or significant ST changes at a lower heart rate.
BP at peak exertion. There are no established levels for systolic BP at various ages. But failure of the systolic pressure to rise, or a drop in systolic pressure with exercise, indicates a lack of ventricular reserve and is a poor prognostic sign.
Functional capacity (METS). In addition to documenting the METS level itself, the report should compare it to the expected functional capacity based on the patient’s age and sex.
Chest pain (or its absence). In addition to noting whether or not chest pain developed, the report should detail the character and intensity of any pain that the patient experienced, the time into the test and the heart rate at which it developed, and the response to rest or nitroglycerine.
ST changes. Unless something in the patient’s condition changes, the workload required to produce symptoms or ST changes should be reproducible from test to test. The workload at which angina or ST changes occur is key to assessing disease severity.
Arrhythmias. Whether they’re seen at rest or develop with exertion, arrhythmias should be noted, as well.
The final report should also indicate whether the test is negative, positive, or nondiagnostic for findings consistent with CAD. Whenever possible, it should include a validated treadmill score, as well.
CORRESPONDENCE Mark A. Knox, MD, UPMC Shadyside Family Medicine Residency Program, 5230 Centre Avenue, Pittsburgh, PA 15232; knoxma@upmc.edu