Electrocardiographic stress tolerance tests

Computer applications in the interpretation of the exercise electrocardiogram

The exercise electrocardiogram remains the noninvasive diagnostic test of first choice in patients with coronary artery disease. While new technology offers novel diagnostic possibilities and the ability to assess patients unsuitable for exercise testing, no other investigation has to this point furnished the quality of functional information and value-for-predictive accuracy of exercise electrocardiography. In this article, we describe how this central position in the work up of the cardiac patient has been secured through the evolution of the microprocessor. Particularly important has been its ability to harness and present large volumes of raw data, to derive and manipulate multivariate equations for diagnostic prediction, and to run 'expert' systems which can pool demographic and exercise test data, calculate risk scores, and prompt the nonexpert with advice on current management. These key features explain the pivotal role of the exercise test in the diagnostic, and increasingly prognostic, armoury of the cardiovascular clinician.

Observations on serum and red blood cell magnesium changes in treadmill exercise-induced cardiac ischemia

To evaluate changes in magnesium levels with treadmill exercise-induced coronary insufficiency, 59 consecutive patients were studied. In addition to electrocardiographic monitoring, hematocrit, total protein, whole blood, serum and red blood cell magnesium determinations were made before and after exercise testing. Fifteen patients had positive exercise test, 18 did not complete, and 26 had negative exercise test. There was no significant difference in the serum and red blood cell magnesium on the basis of stress test results for ischemia. Although whole blood magnesium, hematocrit, and total proteins increased (P less than .05) in both groups, we did not find a significant change in magnesium homeostasis.

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 18 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 ischemic response to exercise.

The cardiovascular effects of acute hypoxemia as a diagnostic aid

Acute hypoxemia produces opposite effects on the pulmonary and systemic vascular resistance. To assess the influence of acute hypoxemia on cardiac murmurs, 36 patients with a single valvular or congenital heart lesion were studied. As expected from these hemodynamic effects, right-sided regurgitant type murmurs increased in intensity during acute hypoxemia, while stenotic type murmurs were reduced. In contrast, left-sided murmurs remained constant or changed in opposite direction to their equivalent type from the right side. Additionally, acute hypoxemia produced a marked reduction of the murmurs due to left-to-right shunts and allowed an adequate differentiation of the murmurs due to ventricular septal defect from those due to mitral incompetence.

Chronotropic incompetence in exercise testing

Patients with chronotropic incompetence, defined as a failure of the heart rate response to exercise to rise to within two standard deviations of the expected increase with exercise, where studied and compared to patients with known coronary disease by angiogram with and without ST segment depression. 72% of the patients with chronotropic incompetence but without ST depression had significant coronary heart disease. The demonstration of chronotropic incompetence in exercise testing has important predictive implications and should be looked upon as carefully as ST segment changes. There was no evidence of SA node ischemia in these patients. Intrinsic heart rate measurements done in this study suggest autonomic dysfunction as a possible pathophysiologic mechanism for chronotropic incompetence. The heart rate response to exercise may be a useful predictor of the presence and severity of coronary disease. Therefore, a predicted heart rate response with standard deviation for age and sex should be included as part of the stress test protocol.

Echocardiographic assessment of a normal adult aging population

Echocardiograms were performed on 105 male participants in the National Institutes on Aging's volunteer Longitudinal Study Program. All subjects (25--84 years of age) were physically active and had no evidence of hypertension or cardiovascular disease. Measurements were made of the initial diastolic (E-F) slope of the anterior mitral valve leaflet, the aortic and left ventricular cavity dimensions, and the thickness of the posterior left ventricular wall. Fractional shortening of the minor semi-axis of the left ventricle and the velocity of circumferential fiber shortening were also determined. It was found that increasing age correlated with a decrease mitral valve E-F slope and increased aortic root diameter and left ventricular wall thickness. Aging did not affect left ventricular cavity dimension, fractional shortening of the minor semi-axis, and velocity of circumferential fiber shortening. These findings suggest that aging in the normal male is associated with altered left ventricular diastolic filling, increased aortic root diameter and left ventricle hypertrophy but little change in contractile ability in the resting state.

Systolic time intervals before and after maximal exercise treadmill testing for evaluation of chest pain

The change in systolic time intervals from before exercise to three to four minutes following a maximal-exercise treadmill test was measured to eveluate chest pain in 110 fasting supine subjects. Forty-six (85 percent) of 54 patients with chest pain and with abnormal findings on coronary arteriograms were found to have at least a 10-msec prolongation in the left ventricular ejection time index (LVETI), whereas only two (8 percent) of 25 subjects without heart disease and 5 (16 percent) of 31 subjects with chest pain but with normal findings on coronary arteriograms had 10 msec or more of prolongation of the LVETI after exercise. The change in the other systolic time intervals (total electromechanical systole, preejection phase [PEP], and PEP/LVET) were less reliable in detecting the presence or absence of coronary disease. We conclude that determination of LVETI before and after maximal-exercise treadmill testing is a clinically useful noninvasive disgnostic test for obstructive coronary disease in patients with chest pain.

The response of healthy men to treadmill exercise

Heart rates, blood pressures, and functional responses to submaximal, maximal and postexertional treadmill testing are presented for a group of 704 healthy, asymptomatic aircrewmen referred to the USAF School of Aerospace Medicine. The indicated measurements are individually described by the use of percentiles. These data provide the practicing clinician with an accurate and complete description of the response of healthy men to treadmill exercise.

Exercise testing in young asymptomatic diabetic patients

The cardiovascular response to submaximal bicycle exercise was studied in a group of 19 asymptomatic diabetic patients aged 18 to 39, including 11 males and 8 females and 18 control subjects (9 males and 9 females, aged 20 to 34 years). The maximum heart rate achieved by the control subjects (group I), 175.9 +/- 8.9 beats/min, was greater than that achieved by the diabetic patients (group II), 159.4 +/- 17.8 beats/min, (P less than 0.01). The work load at which the maximum heart rate was reached was lower in diabetic males, 681 +/- 155.4 kg m/min, than in healthy males, 866.7 +/- 139.9 kg m/min, (P less than 0.02). Although systolic blood pressure elevations were comparable during exercise and the postexercise period, the increase in diastolic blood pressure during exercise in the diabetic patients was greater than in control subjects (P less than 0.001). This difference, however, was only observed in the males and not in the females. The difference in diastolic blood pressure was again noted between the groups in the postexercise period; that of group II was higher than that of group I (P less than 0.01). This was particularly notable in the older diabetics (aged 31 to 40 years). One patient in group II developed ischemic ST segment changes, and 1 subject in each group was found to have J junction depression of 1.0 mm or more. The implications of these findings are discussed in relation to the possible pathophysiology of the diabetic patients.

Value of exercise testing for screening asymptomatic men for latent coronary artery disease

Treadmill exercise testing identifies a group of men at high risk for coronary atherosclerotic heart disease. However, the predictive value and sensitivity limitations are obvious. An abnormal electrocardiographic response does not absolutely predict the presence of coronary atherosclerotic heart disease, and a normal response does not rule out this possibility. Thus in appropriate instances when the minimal risk of coronary angiography is justified this procedure can be used to determine the anatomic correlation of exercise-induced functional ST-segment changes.

Comparison of ventricular ectopic activity during 24-hour monitoring and exercise testing in patients with coronary heart disease

The exposure of ventricular ectopic activity (VEA) by maximal exercise testing and 24-hour ambulatory monitoring was compared in 100 unselected patients with coronary heart disease. The arrhythmia was noted with exercise in 56 patients and with monitoring in 88. Repetitive forms such as couplets and ventricular tachycardia were found to be twice as frequent (40 vs. 20) with monitoring than with exercise. Patients with prior myocardial infarction had more frequent ventricular ectopic activity of a more advanced grade with both exercise and monitoring than patients with angina pectoris. Exercise exposed the grades of ectopic activity that recurred during two or more hours of the monitoring session. Of seven patients with ventricular tachycardia on exercise only four exhibited this grade with monitoring. It may be that these two methods divulge different information regarding the electrophysiologic state of the myocardium.

Maximum treadmill exercise electrocardiography in female patients

Exercise testing has become standardized for the diagnostic and functional evaluation of male patients but little data is available regarding its specificity and sensitivity in the female. Therefore, maximum treadmill exercise (Bruce protocol) was performed on 98 consecutive females and compared to coronary arteriography. Using 50% obstruction as indicating coronary artery disease and 1 mm ST-segment depression (horizontal or downsloping) as positive for ischemia, 24 patients had coronary artery disease with seven false-negative results (sensitivity = 71%) and 74 patients had no coronary artery disease with 16 false-positive responses (specificity = 78%).

Five of seven false-negative tests were in patients with single-vessel disease. Eleven of 16 false-positive responses were in patients on digitalis, diazepam, or methyldopa. In 39 patients on no drug therapy except for nitroglycerin there were no false negatives and only four false-positive tests. There were no false negatives and only two false-positive tests in 34 patients with normal resting electrocardiograms. Only one of 18 patients with both normal resting electrocardiograms and on no drug therapy had a false-positive test result. Eleven false-positive and seven false-negative results occurred in 40 patients with both an abnormal resting electrocardiogram and associated drug therapy.

The exercise electrocardiographic response in female patients is similar to the male when patients with resting electrocardiographic abnormalities and concomitant drug therapy are eliminated.

Early detection of silent ischaemic heart disease by 24-hour electrocardiographic monitoring of active subjects

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Maximum treadmill exercise test in patients with abnormal control electrocardiograms

To determine the validity and safety of exercise induced ST changes (1 mm ischemic depression or further depression in ECG lead V 5 ) as an indication of coronary artery disease (CAD) in patients with abnormal control electrocardiograms (ECG), 121 such patients were compared to 57 patients with a normal control ECG. All underwent a maximum graded treadmill exercise test and coronary arteriography. Among those patients with normal control ECGs, there were no false positives and five false negatives (sensitivity-85%, specificity-100%). In 61 patients with abnormal ECG (no drug therapy except nitrates) there were four false positives and nine false negatives (sensitivity-76%, specificity-79%). In this group of patients T waves reverted from negative to positive in four patients with CAD and 10 patients with no CAD, but T inversion during exercise only occurred in those with CAD (6 patients). Three of 12 patients (25%) with ECG evidence of old infarction and four of eight with single vessel disease had false negative tests. In 60 patients with abnormal ECG on drug therapy there were 10 false positives (17%) and 15 false negatives (sensitivity-55%, specificity-63%). Not helpful in differentiation were resting T vs ST changes, induction of arrhythmias or exercise induced chest pain.

The validity of exercise induced ST changes in differentiating CAD is excellent when the control ECG is normal and is only slightly reduced with control ST-T wave abnormalities. When the latter occur in association with cardiovascular drug therapy, other than nitrates, the exercise ECG is of no use in differential diagnosis although still valid and safe for the determination of exercise tolerance.

Use of exercise testing for diagnostic and functional evaluation of patients with arteriosclerotic heart disease

Myocardial oxygen demand generally increases with increasing levels of energy expenditure, but several factors which modify this relation must be considered, both in the design of the test methods and in interpretation of results of exercise tests in patients with arteriosclerotic heart disease (ASHD).

A wide variety of exercise test methods are currently used. Master's test is simple to perform and requires no elaborate equipment. It has been more widely employed than any other test and much clinicopathologic and correlative data are available. However, Master's test provides little information on the patient's physical work capacity. Multistage tests, carried to a symptom-limited or maximal/near-maximal workload level, provide quantitative data on physical performance capacity and also result in fewer false-negative ECG responses among patients with ASHD.

Follow-up studies of asymptomatic subjects have demonstrated that a horizontal S-T depression during or after exercise is associated with a high risk of developing clinical ASHD. The prognostic significance of the exercise test appears to be independent of other known risk factors.

Studies correlating the ECG response to exercise with findings at coronary angiography have demonstrated an abnormal ECG response in 0-30% of patients with no demonstrable arterial disease. The number of patients with significant coronary artery disease and negative ECG response tends to be higher.

Evaluation of physical performance capacity is the primary indication for exercise testing in patients with known ASHD. The results of the test form a basis for recommendations on occupational and recreational physical activity. Serial tests may be used to evaluate objectively the effect of medical and surgical therapy.