Localization of coronary artery disease with exercise electrocardiography: correlation with thallium-201 myocardial perfusion scanning

In 61 patients with single vessel coronary artery disease (70 percent or greater obstruction of luminal diameter in only one vessel) and no previous myocardial infarction, the sites of ischemic changes on 12 lead exercise electrocardiography and on thallium-201 myocardial perfusion scanning were related to the obstructed coronary artery. The site of exercise-induced S-T segment depression did not identify which coronary artery was obstructed. In the 37 patients with left anterior descending coronary artery disease S-T depression was most often seen in the inferior leads and leads V₄ to V₆, and in the 18 patients with right coronary artery disease and in the 6 patients with left circumflex artery disease S-T depression was most often seen in leads V₅ and V₆. Although S-T segment elevation was uncommon in most leads, it occurred in lead V₁ or aVL, or both, in 51 percent of the patients with left anterior descending coronary artery disease. A reversible anterior defect on exercise thallium scanning correlated with left anterior descending coronary artery disease (probability [p] < 0.0001) and a reversible inferior thallium defect correlated with right coronary or left circumflex artery disease (p < 0.0001).In patients with single vessel disease, the site of S-T segment depression does not identify the obstructed coronary artery; S-T segment elevation in lead V₁ or aVL, or both, identifies left anterior descending coronary artery disease; and the site of reversible perfusion defect on thallium scanning identifies the site of myocardial ischemia and the obstructed coronary artery.     

Is the treadmill exercise test useful for evaluating coronary artery disease in patients with complete left bundle branch block?

To aid in the study of coronary artery disease, 57 patients with complete left bundle branch block underwent clinical evaluation, treadmill exercise testing and cardiac catheterization. The patients were classified into two groups according to coronary anglographic findings: 30 patients with significant stenosis (70 percent or greater luminal narrowing) of at least one major vessel and 27 with no significant coronary artery disease. There was no difference in age, presenting symptoms or previous medical treatment between the two groups. There were more men in the group with coronary artery disease. Exercise-induced S-T changes were similar in the two groups; the sensitivity and specificity of these changes for the diagnosis of coronary artery disease were unacceptable irrespective of the criterion chosen. With additional S-T depression of either 1 or 2 mm below the baseline value, the predictive accuracy was only 53 percent. Combined exertional chest pain and 1 mm S-T depression increased the predictive accuracy of exercise testing to 71 percent. These data indicate that exercise-induced electrocardiographic changes do not facilitate detection of coronary artery disease in patients with complete left bundle branch block.     

Correlation of computer-quantitated treadmill exercise electrocardiogram with arteriographic location of coronary artery disease

Graded treadmill exercise testing and coronary cinearteriographic studies were carried out on 86 patients with angina pectoris. At rest, all patients demonstrated a normal S-T segment on the modified bipolar lead V₅ recording used. The computer-quantitated S-T segment response to exercise was correlated with the location and extent of obstructive coronary artery disease. The coronary cineartertograms were reviewed by 3 physicians and stenosis of 75 percent or greater was considered significant. All patients showed at least this degree of stenosis in 1 or more major coronary arteries, and 83 of 86 exhibited 90 percent or greater stenosis in at least 1 artery. Thirty-one patients had stenosis in a single artery, 43 had stenosis in 2 arteries and 12 had significant lesions in all 3 major arteries. In 70 of the 86 (82 percent) patients, a positive S-T segment response developed during or immediately after exercise. In 12 of the 16 with a negative response, disease was limited to a single artery. In 11 of the 12 the disease was restricted to the right coronary or left circumflex arteries. Of the 12 patients with an isolated stenosis of the left anterior descending artery, 11 (92 percent) had a positive S-T segment response. Of 55 patients with 2- or 3-vessel disease, 51 (93 percent) demonstrated a positive S-T response. Graded treadmill exercise testing in 80 patients with chest pain, normal coronary art eriograms and normal left ventricular function revealed 4 (5 percent) with a false positive S-T segment response.     

Superior QRS axis of ventricular premature complexes: An additional criterion to enhance the sensitivity of exercise stress testing

The presence or frequency of ventricular premature complexes during exercise is not highly predictive for identifying patients with coronary artery disease. To determine whether the morphologic features or axis of exercise-induced ventricular premature complexes may increase this predictability, a study was made of 63 symptomatic patients with coronary artery disease (electrocardiographic evidence of infarction or occlusive lesions seen on coronary angiography, or both) and 10 control patients with normal coronary arteriograms. In 48 of the 63 patients with coronary artery disease the exercise-induced ventricular premature complexes had a superior frontal plane QRS axis between ?30 ° and ?120 °; in 12 the axis was between ?30 ° and +150 °, and in 2 the axis was indeterminate, between +150 ° and ?120 °. In all 10 control subjects without coronary artery disease the QRS axis of the exercise-induced ventricular premature complexes was in the normal range, between ?30 ° and +150 °. If the standard criterion of 1 mm S-T segment depression were used to predict coronary artery disease during exercise stress testing, 25 of the 63 patients with coronary artery disease would have had a normal or borderline exercise test. However, in 21 of these 25 patients the exercise-induced ventricular premature complexes had a superior axis, a criterion that would enhance the predictive sensitivity of the exercise test from 60 to 94 percent. A left bundle branch block pattern of ventricular premature complexes was not helpful in detecting patients with coronary artery disease, although a right bundle branch block pattern was infrequent in the control subjects. The occurrence of ventricular premature complexes with a superior axis during exercise testing can enhance the exercise test's sensitivity for detecting the presence of coronary artery disease, particularly when this criterion is used in patients with a nondiagnostic S-T segment response to exercise.     

Comparison of S-T segment changes on exercise testing with angiographic findings in patients with prior myocardial infarction

Ninety-seven patients with a prior transmural myocardial infarction who underwent coronary angiography and treadmill stress testing were studied retrospectively to assess the reliability of the exercise electrocardiogram in detecting additional disease in patients with a prior infarction. In patients with a previous inferior wall infarction, the S-T response to the treadmill stress test had a high degree of sensitivity (87 percent) and specificity (90 percent) in detecting additional significant coronary artery disease. However, in patients with a previous anteroseptal wall Infarction, the S-T response had much less sensitivity (52 percent), but the degree of specificity remained high (90 percent). In this group a positive test suggested the presence of ischemia in the lateral or inferoposterior region of the myocardium, or both. A negative S-T response was of little value In distingulshing among groups of patients with single or multiple vessel coronary artery disease. The presence of an anterior ventricular aneurysm is most likely responsible for this low sensitivity rate because it generates an opposing force to the ischemic vector, thereby cancelling the S-T segment changes and producing a false negative treadmill stress test. The resting surface electrocardiogram proved useful in predicting a false negative exercise test. The presence of Q waves in the precordial leads extending to lead V₄ or beyond decreased the sensltivity rate of treadmill stress testing to 33 percent.     

Exercise electrocardiography: recognition of the ischemic response, false positive and negative patterns

The ischemic electrocardiographic response is characterized by S-T segment depression in the left ventricular leads. When this response is elicited by exercise and is accompanied by anginal discomfort, it constitutes powerful diagnostic evidence of the presence of coronary arterial obstructive disease. The amount of exercise required to elicit the response is closely related to the extent of the obstruction. S-T segment elevation provoked by exercise rarely occurs with proximal severe stenosis in the left anterior descending coronary artery or in leads exploring the region of healed myocardial infarcts. Depression of the J point may be an ischemic manifestation reversible by administration of nitroglycerin.The ischemic electrocardiographic response may be obscured by conduction defects as in bundle branch block and healed myocardial infarcts. False positive ischemic responses may be encountered in patients taking digitalis glycosides or potassium-depleting drugs, or in patients with hyperadrenergic states, pectus excavatum or short P-R Intervals.     

Idiopathic hypertrophic subaortic stenosis: evaluation of anginal symptoms with thallium-201 myocardial imaging.

The evaluation of angina pectoris in patients with idiopathic hypertrophic subaortic stenosis is difficult in those in the age group prone to coronary artery disease. Ten patients with angina pectoris, normal coronary angiograms and idiopathic hypertrophic subaortic stenosis were studied with thallium-201 myocardial imaging performed in conjunction with submaximal treadmill exercise testing. The resting electrocardiogram demonstrated left ventricular hypertrophy with S-T segment abnormalities in seven patients, thereby vitiating the further increase in S-T segment abnormalities that developed in these patients during exercise or in the postexercise period. Of the three patients with a normal resting electrocardiogram, one had significant exercise-induced S-T segment depression. Thallium-201 myocardial imaging revealed no significant perfusion defects in 9 of the 10 patients (90 percent). In one patient with severe left ventricular hypertrophy significant perfusion defects developed after exercise that were not present at rest. Stress thallium-201 myocardial perfusion imaging is a useful noninvasive technique that assists in ruling out the presence of significant coronary artery disease in patients with idiopathic hypertrophic subaortic stenosis.     

Exercise-Induced S-T segment elevation in variant angina

Five patients with known ischemic heart disease had an unusual pattern of S-T segment depression during treadmill exercise testing followed by S-T segment elevation and chest pain in the postexercise period. Thallium-201 scintigraphy revealed reversible exercise-induced myocardial ischemia, in areas supplied by severely narrowed coronary arteries as documented by coronary arteriography. Ambulatory electrocardiographic recording for S-T segment shift using a frequency-modulated system showed S-T segment depressions and elevations at rest in the same leads that showed similar shifts during exercise tests. Three of the five patients had a myocardial infarction within 8 weeks of diagnosis, and two died. This syndrome may be associated with severe coronary artery disease and may have a very poor prognosis.     

The influence of early repolarization variant on the exercise electrocardiogram: a correlation with coronary arteriograms

Sixteen adult patients with S-T segment elevation in their resting electrocardiograms characteristic of early repolarization variant (ERV) and chest pain syndromes of possible myocardial ischemia were evaluated with both treadmill exercise electrocardiography and coronary arteriography. Of 14 patients with normal coronary arteriograms, 13 had their resting S-T elevation return (“normalize”) to the isoelectric baseline with physical exercise, while one patient with normal arteriograms and normal left ventricular contractility but moderately elevated left ventricular end-diastolic pressure of unknown etiology developed significant S-T depression with exercise. Two patients with significant coronary atherosclerotic occlusive lesions developed “ischemic” S-T depression during treadmill testing. Symptoms developed during treadmill exercise did not distinguish patients with coronary artery disease from those without. Thus, while ERV at rest may be “normalized” by graded physical exercise in the absence of significant coronary atherosclerosis, the presence of ERV does not prevent the usual electrocardiographic manifestations of exercise-induced myocardial ischemia.     

Treadmill exercise test in aortic stenosis and mitral stenosis.

The incidence of positive submaximal treadmill exercise tests was evaluated in patients with mitral stenosis and aortic stenosis, no electrocardiographic evidence of left ventricular hypertrophy, and normal coronary arteries on angiography. Seven of 19 patients (37 percent) with aortic stenosis (53 to 80 mm Hg gradient across the aortic valve) had greater than or equal to 1.0 mm of ischemic S-T segment depression during or after a submaximal treadmill test. Three of 15 patients (20 percent) with mitral stenosis (11 to 22 mm Hg mean gradient across the mitral valve) had greater than or equal to 1.0 mm of ischemic S-T segment depression during or after a submaximal treadmill exercise test. Patients with significant valvular disease, no electrocardiographic evidence of left ventricular hypertrophy, and normal coronary arteries may have a positive submaximal treadmill exercise test due to an unfavorable balance between myocardial oxygen supply and myocardial oxygen demand.     

Detection of critical coronary lesions with treadmill exercise testing: Fact or fiction?

This study was designed to determine whether treadmill exercise testing could identify patients with critical coronary lesions. Critical lesions were defined as obstruction of the left main coronary artery or concomitant narrowing of the left anterior descending and circumflex coronary arteries proximal to any major branches. The time of onset and degree of S-T segment depression were evaluated in 25 patients with critical lesions and in 50 patients with other types of lesions. S-T segment depression of 2 mm or more was present in 82 percent of patients with left main coronary disease and in 71 percent of patients with left main coronary equivalent lesions (both P < 0.02 when compared with 36 percent of patients with other lesions). However, half of the 37 patients with this degree of S-T segment depression had noncritical lesions. Ischemic changes appearing in the first 3 minutes of exercise were seen in 63 percent of patients with left main coronary disease and 35 percent of the patients with left main coronary equivalent lesions (P < 0.001 and P < 0.002, respectively, when compared with only 6 percent of patients with other lesions). The incidence of triple vessel disease was significantly greater in patients with critical lesions (55 percent in patients with left main coronary disease and 71 percent in those with left main coronary equivalent lesions versus 10 percent in those with other lesions) (P < 0.01). S-T segment depression of 2 mm or more is not a good indicator of critical coronary lesions because it has a low level of specificity. Consideration of the time of onset of ischemic changes adds to its usefulness, but it does not permit a definitive diagnosis in individual patients.     

Application of body surface mapping to exercise testing: S-T80 isoarea maps in patients with coronary artery disease

Body surface electrocardiographic maps were recorded before and after exercise in 25 men with angiographically documented coronary disease. Torso potential distributions at 192 locations were derived from a 32 lead electrode array using methods previously described in our laboratory. The S-T segment was characterized by the spatial distribution of the integral of S-T segment voltage over 80 ms (S-T₈₀). Body surface regions where the S-T₈₀ areas were —8 mV·ms or greater were identified in 18 of 25 patients. The most negative S-T₈₀ site on the map was called the “S-T₈₀ minimum.” The S-T₈₀ minima were located 1 or 2 electrode rows away from the standard V₄–V₆ electrode positions in 6 of 10 patients who developed S-T₈₀ areas of —8 mV·ms or greater. Our data suggest that standard electrocardiographic leads may not be optimal for identifying S-T segment depression in all patients with coronary disease. Furthermore, body surface mapping during exercise provides a more quantitative and qualitative method for characterizing the ischémic response to exercise.     

Variations in normal electrocardiographic response to treadmill testing

Forty healthy young men at low risk for coronary artery disease underwent progressive maximal treadmill testing. Four bipolar electrocardiographic leads including CM₅, CC₅, inferior-superior Y, anterior-posterior Z, and a standard V₅ were recorded and later computer-processed. Measurements included amplitudes of the Q, R, S, J junction and T wave, R-T and Q-S intervals and S-T segment slope. These variables are presented as the 10th, 50th (median) and 90th percentiles throughout the testing procedure to define reference values for the electrocardiographic response to maximal treadmill testing. The medians are presented graphically so that the exercise-induced changes can be visualized. In addition, the percent change of R wave amplitude in V₅ compared with the supine pretest value is displayed for each subject during and after testing.     

Predictive accuracy of Q-X/Q-T ratio, Q-Tc interval, S-T depression and R wave amplitude during stress testing.

The sensitivity, specificity and predictive value for $\text{Q-X}\text{Q-T}$ ratio, Q-Tc interval, S-T segment depression, R wave change and various combinations of these criteria were compared in 50 healthy, normal persons and 50 persons with angiographic coronary artery disease defined as 70 percent or greater stenosis of one or more major coronary vessels. Use of a positive S-T segment response and an increase or no change in R wave amplitude as criteria for coronary artery disease resulted in 84 percent sensitivity and 96 percent specificity levels and a 95 percent predictive value. The $\text{Q-X}\text{Q-T}$ and Q-Tc criteria offered no improvement in sensitivity, specificity or predictive value over S-T segment depression.When the study group was limited to 74 persons, 36 without and 38 with angiographically significant coronary artery disease, a Q-Tc interval of 1.08 or more in combination with either slowly or rapidly upsloping S-T depression after exercise predicted coronary disease at a sensitivity level of 76 percent compared with 50 percent with use of the S-T segment alone (P < 0.05). Specificity was not significantly reduced (89 percent for the S-T segment alone, 79 percent with the addition of the Q-Tc interval) (P > 0.05).Use of the R wave response with the presence of upsloping S-T segment depression of 1.5 mm or more 80 msec from the J point improved the sensitivity level from 50 percent for S-T depression alone to 76 percent (P < 0.05); specificity and predictive value were not significantly reduced (81 percent for each [P > 0.05]). The $\text{Q-X}\text{Q-T}$ ratio could be measured in only 55 patients (74 percent) and offered no improvement over S-T segment depression.Upsloping S-T segment depression of 1.5 mm or more 80 msec from the J point in the immediate postexercise period is most likely a positive test for ischemia. An increase or no change in R wave amplitude in response to exercise in these patients regardless of the degree of S-T segment depression is probably indicative of coronary artery disease. In patients with upsloping S-T segment depression, a Q-Tc interval of 1.08 or more in the immediate postexercise period is a useful measurement in predicting coronary artery disease.     

Comparison of the two-step and maximal exercise tests in patients with coronary artery disease

This study has investigated the claim that the electrocardiographic response to the maximal exercise test provides a more accurate method of assessing the presence and severity of coronary artery disease than the electrocardiographic response to the two-step test. One hundred and one men with a chest pain syndrome underwent the two-step test, maximal exercise test and coronary angiography during the same admission. There was a preponderance of men who performed the maximal exercise test as a result of a negative two-step test. A positive two-step test was defined as horizontal or downsloping S-T segment depression of 0.5 mm or more, whereas a positive maximal exercise test was defined as similar S-T segment depression of 1.0 mm or more. Of the 17 men with no or insignificant coronary artery disease, 5 had a positive two-step test and 6 a positive maximal exercise test. Of the 84 men with coronary artery disease, 33 had a positive two-step test and 38 a positive maximal exercise test. Thus, the specificity of the two-step test for coronary artery disease was 87 percent and that of the maximal exercise test was 86 percent; the respective sensitivity rates were 39 and 45 percent. The percentage of positive results of both exercise tests increased similarly with the severity of coronary artery disease.Nine patients, eight of whom had coronary artery disease, had a positive maximal exercise test but a negative two-step test; in these patients the maximal heart rate was significantly higher during the maximal exercise test than during the two-step test. Five patients, all with coronary artery disease, had a positive two-step test but a negative maximal exercise test. One patient manifested 0.5 mm S-T segment depression in both tests and was thus judged to have a positive two-step test and a negative maximal exercise test. In another patient results were positive in lead V₄ of the two-step test, a lead not recorded in the maximal exercise test. The other three patients had had positive results in a second maximal exercise test recorded in the supine position, thus demonstrating that in certain cases the effects of augmented venous return in the supine position may be as important a factor in eliciting ischemia as the achieved heart rate.     

Abnormal electrocardiographic responses to exercise in patients referred for noninvasive evaluation of occlusive peripheral arterial disease.

Fifty consecutive patients were referred to the noninvasive laboratory for evaluation of suspected peripheral vascular disease. There were 30 men and 20 women aged 27 to 88 years (mean 63). Measurement of cardiovascular risk factors revealed the following distributions: cigarette smoking 90 percent, hypertension 28 percent, diabetes mellitus 22 percent and hyperlipidemia 6 percent. Eight patients had a history of angina pectoris, 7 a prior myocardial infarction, 5 a cerebrovascular accident and 11 prior peripheral arterial revascularizatlon surgery. Evaluation detected 32 patients (64 percent) with occlusive arterial disease of the lower limbs. Lead II of the electrocardiogram was monitored during and 1, 2, 3, 4, and 5 minutes after treadmill exercise with a limiting grade of 10 percent at 2.5 miles/hour. The mean resting and maximal heart rates for the study group were, respectively, 78 and 106 beats/min. The average treadmill speed attained was 1.9 miles/hour at a mean duration of 3.8 minutes. Thirty-seven subjects (74 percent) had normal electrocardiographic responses to exercise. Of 13 patients (26 percent) with an abnormal exercise electrocardiogram, 7 had possible ischemic S-T segment responses. Six subjects manifested frequent premature ventricular complexes during exercise. Four other patients had abnormal S-T segments in the resting electrocardiogram (two had a pattern of left bundle branch block, and two a pattern of left ventricular hypertrophy and strain).A survey of 60 peripheral vascular laboratories in the United States revealed that only 29 percent of the responding 34 centers routinely performed electrocardiographic monitoring during exercise testing. It is concluded that (1) electrocardiographic monitoring during exercise in the peripheral vascular laboratory can provide useful information regarding S-T segment responses, (2) abnormal S-T segment responses in patients with suspected peripheral vascular disease are frequently manifested at low levels of work load, and (3) such routine monitoring should be performed for patient safety.     

The predictive value of a strongly positive stress test in patients with minimal symptoms

The ability of a strongly positive stress test to predict left main coronary artery disease in people with suspected coronary artery disease but with minimal or no angina was investigated in 40 such patients. Nine had a history of myocardial infarction but no angina. Thirty-one had mild angina or a history of mild angina. The stress electrocardiograms were analyzed according to criteria known to be associated with left main coronary artery disease in moderately or severely symptomatic patients; (1) early S-T segment changes (stage I or II of exercise), (2) 2 mm or more S-T segment depression, (3) downsloping S-T segments, (4) associated exercise-induced hypotension, (5) prolonged S-T segment changes after the test (≥8 minutes) and (6) anterior and inferior S-T segment depression. The prevalence of left main coronary artery disease was 35 percent and that of any severe coronary artery disease 75 percent. The criterion of anterior and inferior electrocardiographic changes with exercise was most predictive of left main coronary artery disease (P < 0.01 by χ²). Exercise electrocardiography is useful in the prediction of left main or other severe coronary artery disease even when performed in patients who have minimal angina or in those who are asymptomatic after myocardial infarction.     

Epidemiologic study of asymptomatic men screened by maximal treadmill testing for latent coronary artery disease

A group of 1,390 asymptomatic men screened for latent coronary artery disease by maximal treadmill testing and double Master two-step test were followed up for a mean of 6.3 years. Angina, sudden death or acute myocardial infarction was used as the end point for coronary heart disease. There were differences in testing sensitivity and specificity among age and subject groups, but maximal treadmill testing out-performed the double Master test as a screening technique. Maximal treadmill testing demonstrated a 60.9 percent sensitivity, 92 percent specificity and a 20 percent probability that coronary artery disease would develop in a subject with an abnormal response. A risk ratio of 14.3 was obtained and demonstrated that maximal treadmill testing was a valuable screening technique for latent coronary artery disease. However, limitations of the sensitivity and specificity of the functional S-T segment response were apparent. The abnormal S-T segment response to exercise testing did not absolutely predict the future presentation of coronary artery disease, and a normal response to maximal treadmill testing did not rule out this possibility. Because premature ventricular contractions demonstrated a very low sensitivity, predictive value and risk ratio they were not a practical indicator of increased risk for latent coronary artery disease except when associated with an abnormal S-T segment response.     

Value of treadmill exercise testing in patients with complete bundle branch block.

Exercise electrocardiography and selective coronary arteriography was performed in 24 consecutive patients with complete bundle branch block. The criteria for a positive exercise electrocardiogram (E-ECG) were a 1 mm depression or elevation in the J point from the control state, as well as in the ST-segment measured at 0.04 seconds from the J point. Eleven of 12 patients with complete left bundle branch block had a positive E-ECG. Nine of them had normal coronary arteriograms, except one with less than 50% lesions in two arteries. Two patients had severe three-vessel disease. Only one patient had a true negative exercise test. No patient had a false negative test. Nine of 12 patients with complete right bundle branch block had a positive E-ECG. One of these 9 had minimal nonobstructive disease, while the other 8 had severe two- or three-vessel coronary artery disease. Three of the 12 right bundle branch block patients had a negative E-ECG. Two of them had a true negative exercise test, and one a false negative test. Because of a high incidence of probably false positive results, E-ECG appears to be unreliable in detecting coronary artery disease in patients with complete left bundle branch block. But it can provide useful information in the noninvasive evaluation of coronary artery disease in patients with complete right bundle branch block.     

Septal Q wave in exercise testing: Angiographic correlation

A study of septal Q wave response in lead CM₅ was carried out to evaluate its usefulness in predicting coronary artery disease. Q wave amplitude was measured in 50 patients with coronary artery disease and 50 normal subjects before and immediately after exercise. In the 100 patients evaluated with coronary angiography, the septal Q wave in lead CM₅ was smaller in patients with coronary artery disease than in normal subjects at rest (probability [p]<0.001) and immediately after exercise (p<0.001). An embryonic (0.5 mm) or absent Q wave in lead CM₅ was significantly more frequent in patients with coronary artery disease than in normal subjects both at rest (76 versus 48 percent) and after exercise (82 versus 16 percent).The sensitivity for S-T depression was 52 percent, the specificity 74 percent and the predictive value 70 percent. The respective values for the Q wave were 82,88 and 87 percent. These differences were not significant (p <0.05). When either a positive S-T or Q wave response was used, the sensitivity increased to 92 percent (p <0.05), and the specificity and predictive values remained unchanged (p <0.01). An Increase in Q wave amplitude with exercise identified a false positive S-T segment response to stress in 75 percent of cases. Absence of the Q wave in lead CM₅ with S-T depression after exercise identified a true positive response in 100 percent of cases.These findings suggest that low Q wave voltage and its failure to increase after exercise imply abnormal septal activation, reflecting loss of contraction associated with ischemia. This finding may be a useful marker for ischemia; the increase in the septal Q wave with exercise may be of value in identifying a false positive S-T segment response.