Relation between the electrocardiographic stress test and degree and location of myocardial ischemia.

Factors that influence frequency and location of stress-induced electrocardiographic (ECG) ST depression and the development of chest pain are incompletely understood. We studied 331 patients with ischemic myocardial nuclear defects in response to routine clinical treadmill testing with simultaneous ECG recording. Nuclear defects were analyzed for location and extent of myocardium involved. Exercise-induced ischemic ST changes were demonstrated in 59% of patients (196 of 331). Subjects with stress-induced ECG changes and/or chest pain had more extensive nuclear perfusion defects. Diabetic patients were significantly less likely to experience chest pain (24%) versus nondiabetics (41%) during testing (p = 0.04). Larger perfusion defects were associated with greater magnitude, lead distribution, and incidence of ECG changes. The number of ECG lead zones (anterior, lateral, and inferior) responding positively were related to both magnitude of ST depression and severity of ischemia, but not to location of ischemic defects. Regardless of location of ischemia, ST depression occurred with similar frequency. Thus, exercise-induced ECG ST depression remains a valuable indicator of the severity of myocardial ischemia. Greater ST depression involving multiple leads usually signified extensive myocardial ischemia, but provided no information regarding its location. Anginal-type chest pain induced by exercise testing also denoted more extensive ischemia.

The treadmill test--where to stop and what does it mean?

The prognostic utility of an exercise ECG test depends upon having an adequate workload to stress the cardiac system. A negative stress test, in which there are no adverse clinical or ECG findings, and in which an adequate workload is achieved, stratifies patients into a low-risk group. The 1997 American Heart Association guidelines imply that any index of workload--heart rate, rate-pressure product, or exercise duration in multiples of resting O2 consumption (METS)--could be used to indicate that adequate stress was achieved. However, while there is considerable evidence supporting the use of METS as a strong independent prognostic variable, there is less support for the use of rate-pressure product or heart rate. Indeed, there is evidence that a high heart rate at a low workload carries an adverse prognosis. Further research is needed to identify the number of METS achieved that would define an adequate workload. In the meantime, a review of the literature suggests that 7 to 10 METS is a reasonable ballpark figure of the minimum workload in patients with a negative stress test that would imply a favorable outcome.

The appearance of gallop rhythm after exercise stress testing.

BACKGROUND AND HYPOTHESIS: Although it is generally assumed that the appearance of an early diastolic gallop, or third heart sound, appearing immediately after exercise during treadmill stress testing, indicates the presence of serious myocardial disease, no systemically collected data are available to test this hypothesis. METHODS: The author performed auscultation on 3,679 patients undergoing routine treadmill testing together with thallium-201 perfusion scans. Exercise-induced diastolic sounds were related to the available clinical information and electrocardiographic and nuclear test results. These findings were compared with those of 665 randomly selected patients undergoing stress testing in whom such sounds were absent. RESULTS: A total of 165 patients had audible third heart sounds (Group 1). In comparison with those patients lacking such sounds (Group 2), there was a considerably greater prevalence of myocardial scarring (68.5 vs. 26.9%), abnormal lung uptake of thallium (40 vs. 12.8%), diabetes mellitus (20.6 vs. 6.2%), and left bundle-branch block on the resting electrocardiogram (ECG) (15.1 vs. 1.2%). In addition, 65 patients (39.3%) had dilatation of the left ventricle after exercise; 31 (18.8%) of these were also dilated at rest, but only 2 (1.2%) had a drop in blood pressure during stress. In those individuals also subjected to nuclear ventriculography, the average resting ejection fraction was 35%. Estimated exercise capacity was generally reduced in Group 1 (average peak of 6.6 METs), but 29 (17.6%) exceeded 9 METs. Sensitivity and specificity of electrocardiographic ST depression were relatively poor in the detection of perfusion defects within this group (36 and 62%, respectively). Of the 39 patients in Group 1 with a normal resting ECG, 19 (48.7%) had scar (usually posterior or lateral) on nuclear scans. In an additional 10 of this group, nuclear evidence of ischemia (often extensive) was found. CONCLUSIONS: An early or mid-diastolic gallop sound developing after exercise virtually always signifies myocardial disease with reduced myocardial function. Common associated findings are prior infarction (with or without associated ischemia), diabetes, and left bundle-branch block. When found in the presence of a normal resting ECG, this sound commonly signals the presence an occult left ventricular scar and, less commonly, extensive myocardial ischemia. In those patients manifesting such sounds, electrocardiographic ST changes in response to exercise appear limited in the detection of coronary ischemia.