Multifactor evaluation of the determinants of ischemic electrocardiographic response to maximal treadmill testing in coronary disease

Correlation between exercise-induced ischemic ST-segment depression and myocardial blood flow quantified by positron emission tomography

BACKGROUND

Ischemic ST-segment depression (horizontal or downsloping) is the most common manifestation of exercise-induced myocardial ischemia. The mechanisms responsible for these types of ST-segment depression are largely unknown. We investigated the relation of these 2 types of exercise-induced ST-segment depression to changes in regional myocardial blood flow (RMBF) by using exercise positron emission tomography (PET).

METHODS AND RESULTS

The RMBF was measured with nitrogen-13 ammonia PET both at rest and during low-level supine bicycle exercise in 27 patients with angiographically proven coronary artery disease and in 6 healthy volunteers. ST-segment depression was measured from the isoelectric PR segment 80 ms after the J point. Exercise-induced horizontal ST-segment depression > or =0.1 mV was observed in 9 patients and downsloping depression > or =0.1 mV was observed in 18 patients. Multivessel disease was more frequent and areas of exercise-induced ischemia were larger in patients with downsloping depression than in patients with horizontal depression (P < .02, P < .05). In patients with horizontal ST-segment depression, RMBF in ischemic areas and in surrounding areas increased by a similar amount (31%+/-29% and 32%+/-16%) with exercise. In patients with downsloping ST-segment depression, RMBF was unchanged or decreased in ischemic areas (10%+/-24%) but increased in surrounding areas (46%+/-27%) with exercise. In healthy volunteers, RMBF increased in all areas (56%+/-30%) with exercise.

CONCLUSIONS

Compared with horizontal changes in ST-segment morphology, downsloping changes may better indicate severe ischemia and greater differences in the increase of blood flow with exercise in the ischemic myocardium and in the surrounding areas.

Determinants of exercise-induced ST segment depression in patients with coronary artery disease: a multivariate approach

The purpose of this study was to delineate among the usually gathered parameters in an electrocardiographic exercise test the determinants of its positive outcome (delta ST decreases > or = 1 mm measured at 80 msec from the J point). The authors studied 832 patients investigated with Bruce's exercise testing and with diagnostic coronary arteriography, all of whom were shown to have significant coronary artery disease (diameter stenosis > or = 50%). Twenty-five demographic, clinical, electrocardiographic, exercise, and anatomic/hemodynamic parameters were analyzed. The stepwise forward logistic regression analysis retained seven among them as significant independent predictors: four as positive contributors: (1) three-vessel and/or left main disease (P = 0.0000), (2) Gensini's angio-graphic score for disease extent (P = 0.0025), (3) anginal pain during the test (P = 0.0000), and (4) age (P = 0.0031) and three as negative contributors: (1) resting heart rate (P = 0.0004), (2) history of old myocardial infarction (P = 0.0019), and (3) pathological Q waves at the resting ECG (P = 0.0018). These findings establish standards that permit the prediction of the positive electrocardiographic exercise outcome in patients with significant coronary disease.

Hemodynamic characteristics of patients with coronary artery disease presenting false-negative exercise stress test

The present study was designed to clarify the characteristics of left ventricular hemodynamics and coronary arteries in patients with coronary artery disease presenting false-negative response to the Master's two-step stress test. Eighty-eight consecutive patients performed the Master's two-step stress test and had coronary angiography for evaluation of suspected or known coronary artery disease. The frequency of false-negative and true-positive responses in the Master's two-step stress test was 20% and 45%, respectively. Elevated left ventricular end-diastolic pressure, reduced ejection fraction, and low cardiac output characterized the left ventricular hemodynamics in patients with false-negative responses, as compared with those with true-positive response. The severity and extent of coronary artery disease, as well as prior myocardial infarction, did not affect the frequency of false-negative response. This study indicates that the false-negative response to the Master's two-step test is unexpectedly frequent in coronary artery disease with severe left ventricular dysfunction. Thus, one should be careful in judging the results of the Master's two-step test in symptomatic patients with severe left ventricular dysfunction.

Clinical and pathophysiologic correlates of ST-T-wave abnormalities in coronary artery disease

Clinical, hemodynamic and coronary angiographic data from 9,801 patients were evaluated to determine the correlates of ST-segment depression, with or without T-wave inversion, on the resting routine electrocardiogram. The relative risk (RR) of having a measured clinical or angiographic variable was computed whether or not ST-T-wave abnormalities were observed. ST-segment depression was seen significantly more often in subjects greater than 55 years of age (RR = 1.4) who were women (RR = 1.3) or nonwhite (RR = 1.5), were hypertensive (RR = 1.8), had diabetes mellitus (RR = 1.6) or who smoked cigarettes (RR = 1.5). Angiographic findings related to presence of ST-T-wave abnormalities included severe coronary obstruction (less than 70%), higher number of diseased vessels, and the presence of obstruction in the left anterior descending coronary artery. In a multivariate model, the most significant correlates of ST-T-wave abnormalities were presence of left ventricular contraction abnormality, followed by age, gender, presence of left anterior descending coronary artery disease, elevated end-systolic volume index, and a diagnosis of hypertension. Thus, electrocardiographic ST-T abnormalities has specific and significant clinical and pathophysiologic correlates.

Silent versus symptomatic myocardial ischemia during exercise testing: a comparison with coronary angiographic findings

Two-hundred-and-eighty individuals with anginal complaints, without prior myocardial infarction and with a positive exercise stress test were divided into a group (n = 67) with exercise-induced silent myocardial ischemia and another group (n = 213) with exercise-induced angina pectoris. Both underwent coronary angiography and were compared with each other with respect to various exercise and angiographic parameters. Patients with exercise-induced silent ischemia attained a longer mean exercise duration (P less than 0.001), a higher peak exercise heart rate (P less than 0.0001) and a higher peak exercise rate pressure product (P less than 0.001) than patients with exercise-induced angina pectoris. In the latter group, more patients showed exercise-induced ST-segment depression greater than 2 mm (P less than 0.05). The group of patients with silent ischemia encompassed more individuals with normal coronary arteries (P less than 0.0001). More patients with exercise-induced angina pectoris had three-vessel disease (P less than 0.0001). The exclusion of patients with normal coronary arteries (23% in those with silent ischemia group and 6% in those with exercise-induced angina had no influence on the level of significance for peak heart rate, mean exercise duration and exercise duration greater than 10 min. Thus, in this population, exercise-induced silent myocardial ischemia is associated with better exercise performance and less extensive coronary arterial pathology than in exercise-induced angina pectoris.

Exercise-induced ST segment depression in the diagnosis of multivessel coronary disease: a meta analysis

To evaluate the variability in the reported accuracy of the exercise electrocardiogram (ECG) for predicting severe coronary disease, meta analysis was applied to 60 consecutively published reports comparing exercise-induced ST depression with coronary angiographic findings. The 60 reports included 62 distinct study groups comprising 12,030 patients who underwent both tests. Both technical and methodologic factors were analyzed. Wide variability in sensitivity and specificity was found (mean sensitivity 81% [range 40% to 100%, SD 12%]; mean specificity 66% [range 17% to 100%, SD 16%]). All three variables found to be significantly and independently related to sensitivity were methodologic (the exclusion of patients with right bundle branch block, the comparison with another exercise test thought to be superior in accuracy and the exclusion of patients taking digitalis). Exclusion of patients with right bundle branch block and comparison with a "better" exercise test were both significantly associated with sensitivity for the prediction of triple vessel or left main coronary artery disease. Adjustment of exercise-induced ECG changes for changes in heart rate was strongly associated with the specificity for critical disease (partial R2 = 0.436, p = 0.0001).

Alterations in transmural blood flow and body surface ST segment abnormalities produced by ischemia in the circumflex and left anterior descending coronary arterial beds of the dog

Previous studies have documented a quantitative relation between alterations in transmural myocardial blood flow and body surface electrocardiographic distributions during rapid atrial pacing after chronic occlusion of the left circumflex coronary artery (LCx). Because other studies have described functional differences between the left anterior descending (LAD) and the LCx perfusion beds, we tested the hypothesis that these two territories exhibit quantitative differences in their responses to demand-dependent myocardial ischemia. To do so, 25 sedated dogs were studied 3 weeks after implantation of an ameroid constrictor around the proximal LCx (15 dogs, group I) or the LAD (group II). Oxygen demand was increased by rapid atrial pacing at rates of 90 to 210 beats/min, myocardial blood flow was measured by serial injections of radiolabeled microspheres, and the electrocardiographic consequences were evaluated by isopotential body surface mapping. Endocardial flows and the endocardial/epicardial flow ratio fell to significantly lower levels during atrial pacing in the ischemic LAD bed than in the LCx perfusion zone. Electrocardiographic patterns indicative of subendocardial ischemia also developed with lesser abnormalities in endocardial/epicardial ratios as determined by logistic regression models, in the LAD than in the LCx bed. Thus the LAD bed is more susceptible to ischemia than the LCx region because of differences in collateral blood flow patterns. In addition, the intensity of the surface electrocardiographic potentials during ischemia was significantly greater, as measured by linear regression, after LAD than after LCx obstruction. These data thus demonstrate significant differences between the two cardiac regions as electrocardiographic potential sources during ischemia.

Studies on ergometer exercise testing. II. Effect of previous myocardial infarction, digoxin, and beta-blockade on exercise electrocardiography

The results of exercise electrocardiography were studied in a random sample of 317 subjects with clinical suspicion of coronary artery disease. In 278 patients with coronary artery disease the rate of false negative tests was 18% with and 12% without previous myocardial infarction. If ST elevation was considered a negative response, the corresponding values were 25% and 13%, respectively, p less than 0.01. The greatest prevalence of negative tests was seen after anterior myocardial infarction: 27% or 42% when ST elevation was not included into positive responses. The sensitivity of exercise-induced ST depression for the presence of multivessel disease was lower after anterior infarction (67%) than in other patients with previous infarction (86%), p less than 0.01. The corresponding specificities were 71% and 22%, respectively, p less than 0.005. If ST elevation was included into positive responses these differences were abolished. In subjects without myocardial infarction the sensitivity was 89% and specificity 43%. Digitalized patients had somewhat higher sensitivity in the exercise electrocardiogram than those without digoxin, 90% vs. 81% (p less than 0.05), but the difference was not seen with exclusion of ST elevation. The specificity was not influenced by digitalis. beta-blockade had no effect on the sensitivity or specificity, but the prevalence of postexercise ST evolution was lower with (11%) than without (30%) beta-blockade. The prevalence of slowly ascending ST depression was reduced by three factors: the presence of digitalis in patients without previous myocardial infarction, infarction itself, and the extent of coronary artery disease. We conclude that exercise electrocardiography has only a limited value in prediction of multivessel disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Symptomatic and silent myocardial ischemia during exercise testing in coronary artery disease

During exercise by patients with coronary artery disease (CAD), electrocardiographic evidence of myocardial ischemia may precede the onset of angina or may be unassociated with angina, even at peak levels of stress. However, neither the precise incidence of silent versus symptomatic ischemic episodes nor their interrelation in this setting has been clearly defined. The prevalence of silent and symptomatic myocardial ischemia during treadmill exercise testing was determined in 92 patients with angiographically documented CAD. The study group comprised 77 men (84%) and 15 women (16%) of mean age 57 years (range 32 to 79). Exercise testing resulted in ischemic ST-segment depression (greater than or equal to 1 mm for greater than or equal to 80 ms) only or in association with delayed (greater than or equal to 1 minute) angina in 39 patients (42%); angina only or in association with delayed ST-segment depression occurred in 42 patients (46%); and simultaneous occurrence of angina and ST-segment depression was noted in 11 patients (12%). Analysis of clinical, exercise and angiographic factors (age, sex, history of myocardial infarction, heart rate, maximal ST-segment depression, extent of CAD and left ventricular ejection fraction) revealed no significant correlation with the frequency of symptomatic and silent myocardial ischemia during exercise. Asymptomatic myocardial ischemia occurred commonly during exercise in patients with CAD, but there were no differences in the characteristics of patients with symptomatic and asymptomatic episodes.

Studies on ergometer exercise testing. I. Significance of the type of ST-segment response, sex, and chest pain

Ergometer exercise electrocardiographic (EECG) data were surveyed in a series of 328 patients (277 men and 51 women) subjected to coronary arteriography. The sensitivity and specificity of EECG for coronary artery disease (CAD) were 84% and 54%, respectively. The predictive accuracy of a positive test for CAD was 95% in men and 81% in women. The predictive accuracy of a negative test was 25% in men and 62% in women. When slowly ascending ST depression was considered insignificant, the sensitivity of EECG declined to 71%, with an increase in specificity to 64%. CAD was present in 89% of the patients with slowly ascending ST depression and 65% of them had a multivessel disease. Seventy-two subjects had postexercise ST-segment elevation. The predictive value of this sign for CAD was 94%. Exercise-induced chest pain had quite a similar diagnostic significance as EECG. The prevalence of CAD in patients with a history of typical angina was 94% in both sexes. Atypical chest pain was associated with normal coronary arteriography in 59% of males and 100% of females.

R wave amplitude: a new determinant of failure of patients with coronary heart disease to manifest ST segment depression during exercise

Patients with coronary artery disease may not manifest ST segment depression during exercise. Inadequate stress, mild coronary artery disease and severe left ventricular dysfunction have been postulated as mechanisms. The purpose of this study was to determine the influence of exercise R wave amplitude on ST segment depression in 81 patients with coronary artery disease (50% or greater diameter narrowing of one or more vessels). All patients underwent symptom-limited treadmill exercise testing and 71 patients (88%) had concomitant thallium-201 imaging. In 26 patients, the exercise R wave amplitude in electrocardiographic lead V5 was less than 11 mm (Group I), and in 55 patients it was 11 mm or greater (Group II). The two groups were similar with regard to age, sex, propranolol administration and left ventricular function. There was a significant difference in the incidence of positive exercise electrocardiograms in the two groups (2 patients [8%] in Group I and 27 patients [49%] in Group II; p = 0.002), despite similar exercise heart rate and extent of coronary artery disease. Myocardial ischemia, manifested by exercise-induced angina or exercise-induced thallium-201 perfusion defects, was similar in both groups. Thallium-201 imaging showed perfusion defects in 73% of patients in Group I and in 76% of patients in Group II (p = not significant). Thus, R wave amplitude is a new determinant of failure to develop ST depression during exercise. A low R wave amplitude (less than 11 mm) is rarely associated with ST depression, even in patients with multivessel coronary artery disease. Exercise thallium-201 imaging is a valuable diagnostic tool in patients with low R wave amplitude.

Discriminant value of clinical and exercise variables in detecting significant coronary artery disease in asymptomatic men

To determine whether clinical or exercise test variables could reliably detect coronary disease in asymptomatic men, several variables were compared with angiographic findings in 225 asymptomatic men. None of the individual clinical or rest electrocardiographic variables were able to detect coronary artery disease. The three individual exercise variables with a high likelihood ratio were: 1) at least 0.3 mV ST depression, 2) persistence of ST depression 6 minutes after exercise, and 3) total duration of exercise of less than 10 minutes. However, because of low sensitivity and predictive value, these single variables were not helpful in identifying individual patients with coronary disease. The combination of any single clinical risk factor and any two of these exercise risk predictors was highly predictive (89%) but relatively insensitive (37%) for detecting any coronary disease. These criteria have a sensitivity of 55% and a predictive value of 84% for the detection of two and three vessel coronary disease. The effectiveness of exercise testing for detecting asymptomatic coronary disease is improved when the group is first screened for the presence of risk factors and additional exercise variables other than ST segment criteria are evaluated.

Enhanced evaluation of treadmill tests by means of scoring based on multivariate analysis and its clinical application: a study of 608 patients

Six hundred eight patients being evaluated for chest pain who did not have valvular disease, cardiomyopathy, left ventricular hypertrophy or bundle branch block, and were not receiving digitalis, had treadmill tests and coronary angiograms. In 351, various exercise variables were correlated by multivariate analysis to coronary artery disease (CAD). In men, significant variables were: (1) maximal heart rate achieved less than 80% of maximal predicted heart rate (Mx PHR), (2) ST-T change greater than or equal to 1 mm, (3) age greater than or equal to 55 years and (4) treadmill time (TT) less than 8 minutes. These variables rated diagnostic scores of 9, 6, 5, and 3, respectively. A score of greater than or equal to 7 was considered diagnostic of CAD. In a test group of 192 men in which ST-T change was compared with treadmill score, sensitivity was 65 versus 85%, specificity 79 versus 74% and accuracy 69 versus 83%. In women, maximal heart rate less than 90% of Mx PHR and TT of less than 6 minutes were significant, with an accuracy of 75%. Moreover, 89% of incomplete tests and 70% of tests in patients with previous myocardial infarction were also correctly diagnosed. This method allows convenient use of significant exercise variables for clinical purposes with improved results.

Differential electrocardiographic effects of myocardial ischemia induced by atrial pacing in dogs with various locations of coronary stenosis

The spatial distribution of abnormal repolarization potentials caused by regional myocardial ischemia was determined in 45 dogs. Ameroid constrictors were placed around the left circumflex artery in 10, the left anterior descending artery in 10, and the right coronary artery in 10. Ten dogs without constrictors served as controls. Electrocardiographic events were determined from body surface isopotential distributions, which were computed from potentials sensed by 84 torso electrodes. In control dogs, pacing to heart rates of 230 to 250 beats/min increased the intensity of positive and negative surface extrema during the ST segment without altering their spatial features. Two weeks after placement of the ameroid constrictors, tachycardia induced abnormal negative potentials during the ST segment. Localization of these ischemic forces varied with the placement of the constrictor in a manner consistent with the affected perfusion territories. However, much of the torso surface was involved by all lesions, and only small zones of ST segment depression unique to specific lesions could be identified. In five additional dogs a constrictor was placed on the right coronary artery 3 months after implantation of a device on the circumflex vessel. ST segment patterns during pacing in dogs with two lesions were consistent with the sum of the two individual lesions. Thus, the regional nature of myocardial ischemia is detectable in the body surface isopotential distributions, but the degree of spatial overlap may limit the value of such techniques in extending the usefulness of clinical exercise-stress electrocardiography.

Implications of normal exercise electrocardiographic results in patients with angiographically documented coronary artery disease. Correlation with left ventricular function and myocardial perfusion

The purpose of this study was to examine the incidence and implications of false-negative exercise electrocardiographic results among 216 consecutive patients with angiographically documented coronary artery disease (50 percent diameter narrowing or greater of one or more vessels). Exercise electrocardiography gave negative (false-negative) results in 23 patients and positive (true-positive) results in 102 patients, and were nondiagnostic in the rest. Exercise thallium-201 imaging was performed in 88 patients. The extent of coronary artery disease was quantitated by a scoring system that takes into consideration the degree and site of narrowing in the major vessels and their branches. The exercise heart rate was higher in patients with false-negative than in patients with true-positive exercise electrocardiographic results (161 +/- 18 versus 133 +/- 24 beats per minute, mean +/- SD; p less than 0.0001). Q-wave infarction was present in two patients (9 percent) with false-negative and 20 patients (20 percent) with true-positive exercise electrocardiographic results (p = NS); left ventricular asynergy at rest was observed in 13 patients (57 percent) with false-negative and in 74 patients (74 percent) with true-positive results (p = NS). Patients with false-negative results had less extensive coronary disease than did patients with true-positive results (score 5.8 +/- 3.6 versus 9.2 +/- 5.0; p = 0.0025). Angina during exercise was less frequent in patients with false-negative results (p less than 0.01). Abnormal exercise thallium-201 images were seen in 15 of 20 patients (75 percent) with false-negative results and in 56 of 68 patients (82 percent) with true-positive results (p = NS). It is concluded that (1) false-negative exercise electrocardiographic results are infrequent (10 percent) among patients with coronary artery disease and are associated with less extensive coronary artery disease; (2) the frequency of Q-wave infarction and left ventricular asynergy is the same in patients with false-negative results as in patients with true-positive exercise electrocardiographic results; (3) exercise thallium images can identify 75 percent of patients with coronary disease and false-negative results of exercise electrocardiography.

Improving diagnostic accuracy of the exercise test by combining R-wave changes with duration of ST segment depression in a simplified index

To enhance the reliability of the exercise test in diagnosing both overall coronary artery disease and multivessel coronary artery disease, a discriminant function was obtained by means of stepwise linear discriminant analysis. Both electrocardiographic and nonelectrocardiographic factors were used to derive the discriminant function in a retrospective group of 231 patients, 168 of whom had angiographically defined coronary artery disease. The discriminant function converted into a simple exercise index or score was then applied to a retrospective group of 120 patients, 98 of whom had coronary artery disease. This index, combining R-wave changes with duration of ST segment depression and patient's sex, proved highly accurate in diagnosing coronary artery disease in male patients and in diagnosing the absence of coronary artery disease in female patients. When compared to standard ST segment criteria, the sensitivity and predictive value of the exercise index was significantly higher.

Incremental value of the exercise test for diagnosing the presence or absence of coronary artery disease

To determine the incremental value of the exercise test (ETT) for diagnosing coronary artery disease (CAD), we derived a multivariate logistic regression model for the pre-ETT prediction of CAD using data from 3840 patients at Duke University. We then applied the model to 324 patients at the Brigham and Women's Hospital. Using seven clinical factors, the multivariate model had an 84% overall predictive accuracy on both the training (Duke) and the validation (Brigham) sets of patients. Three ETT factors (ST-segment change in patients not taking digitalis, absence of ST-segment change in patients taking digitalis, ETT stopped because of ECG or blood pressure changes) had incremental, significant predictive power, but overall predictive accuracy based on both clinical and ETT factors improved only to 87%. When the ETT result was important enough to move the probability of CAD across a potential therapeutic threshold, the direction of the change in probability was correct only two-thirds of the time. Thus, the ETT was of limited value in predicting the presence or absence of CAD after other easily obtainable clinical data were taken into account.

Clinical significance of upsloping ST segments in exercise electrocardiography

Conventional exercise electrocardiographic criteria usually involve patterns with a horizontal or downsloping ST segment. In the present study we present criteria based on upsloping ST segments and compared these criteria with the conventional criteria. Using upsloping ST-segment criteria, the amount of ST-segment depression at 80 msec after the end of the QRS complex is used as a parameter (ST criterion E, with a depression of 100 mV, and ST criterion F, with a depression of 200 mV). In the graded exercise test a bicycle ergometer was used. The ECG leads were CM5 and CC5. The results of exercise electrocardiography were compared with the findings from coronary arteriography. In 623 selected patients (565 males and 58 females), application of conventional ST criteria gave a sensitivity of 56% and a specificity of 94%; with application of the ST criteria E or F, sensitivity was 75% and specificity 90%. In the 58 females use of these new criteria resulted in a sensitivity of 76% and specificity of 88%. Ninety-three patients (15%) could be classified as positive exercise responders by the sole presence of an upsloping ST segment (type E or F). Sixty-eight percent of the patients with type E and 75% with type F had two- or three-vessel disease (coronary obstructions greater their or equal to 50%). We conclude that ST criteria based on upsloping ST segments significantly increase the diagnostic yield of the exercise ECG.

Factors influencing the diagnostic sensitivity of the exercise test in coronary artery disease

A continuous multistage bicycle ergometer test was performed on 50 patients with coronary artery disease. Selective cinecoronary angiography and left ventriculography were performed within a week of the test in all patients. Overall, 62% had a positive ischemic response, defined as 1 mm or greater depression of the ST segment. Patients with 75% or greater stenosis in any vessel and those with triple-vessel involvement had a higher incidence of positive tests. Those with low systolic ejection fractions and areas of asynergy had fewer positive tests than patients with normal ejection fractions and normal or minimal segmental wall motion abnormalities. The level of exercise, location of arterial disease and the presence of collateral blood supply to the diseased vessels did not appear to influence the sensitivity of the exercise stress test.

A multivariate approach for interpreting treadmill exercise tests in coronary artery disease

To determine the value of a multivariate approach for the analysis of the treadmill exercise tolerance test (ETT), 237 patients referred for evaluation of chest pain who underwent a standard Bruce protocol ETT and coronary arteriography were studied. Predictive value of a positive ETT was 0.78 (43/55) using 1.0--1.9 mm ST segment depression criterion, 0.97 (59/61) using greater than or equal to 2.0 mm ST segment depression. When the 1.0--1.9 mm ST criterion was combined with peak systolic blood pressure-heart rate product (double product) less than or smaller than 23,000, exercise duration less than 6 minutes, and ST depression for greater than 3 minutes into recovery, predictive value improved to 0.89 in 18 patients with any two of the above. Predictive value for multivessel disease was also improved using non-ST criteria. Predictive value of a negative ETT for absence of coronary artery disease was 0.60 (29/48), and was 0.86 (12/14) if double product was greater than or equal to 30,000. Presence of chest pain during ETT did not improve predictive value of any type of test. Digitalis ingestion in 33 patients was not associated with decreased predictive value of a positive test. These data suggest that the predictive value of both positive and negative ETT in a symptomatic population can be improved with a multivariate approach.

The "false negative" treadmill exercise test and left ventricular dysfunction

One hundred and fifteen consecutive symptomatic patients undergoing graded exercise testing, selective coronary angiography and left ventriculography were retrospectively evaluated. The sensitivity, specificity, and false negative response rates of the exercise tests were 79%, 81%, and 21%, respectively. Although the magnitude of a positive ST-segment response was related to more extensive vascular disease, the frequency of false negative responses was nearly identical in patients with single, double, or triple vessel disease (22%, 21%, 19%). Analysis of the false negative group demonstrated significant ventriculographic and hemodynamic abnormalities when compared to the true positive responders. Five out of six patients with the most serious motion disorders in the study fell into the false negative group. There were no significant differences in the extent, distribution and severity of vascular involvement, or in the development of collateral circulation in the two groups. However, occluded vessels supplied abnormal ventricular segments more frequently in the false negative group (88% vs 38%); the absence of an "ischemic response" and the presence of segments of abnormal myocardium may be related. Left ventricular dysfunction appears to be an important reason for a false negative response to exercise.

Effects of digitalis on the exercise electrocardiogram in normal adult subjects

Controversy continues regarding the effects of administration of digitalis upon the exercise electrocardiogram. Thus, maximal treadmill exercise tests were performed before and two weeks after administration of 0.25 mg of digoxin daily in 15 normal subjects (documented by cardiac catheterization and coronary arteriographic studies). Administration of digitalis induced abnormal findings on exercise tests in all 14 subjects with serum levels of digoxin greater than or equal to 0.5 ng/ml; however, at workloads greater than 75 to 90 percent of maximal predicted heart rate, the changes in the ST segment reverted to a normal configuration in all subjects, thereby providing differentiation of digitalis-induced ST-segment alterations from those due to myocardial ischemia at maximal treadmill stress.