Can myocardial ischemia be recognized by the exercise electrocardiogram in coronary disease patients with abnormal resting Q waves?

Detection of coronary artery disease in the presence of left ventricular atrophy

To evaluate the accuracy of exercise echocardiography for the recognition of coronary artery disease in the presence of left ventricular hypertrophy 70 patients were studied. Significant coronary artery disease was present in 25 patients and left ventricular hypertrophy had 29 patients. All patients underwent an exercise ECG and echocardiographic test during which cine-loop digitized echocardiography was obtained. Wall motion was analyzed and a regional wall motion score index was calculated. The overall sensitivities of exercise ECG and echocardiography for detecting coronary artery disease were 60% and 64%, respectively, and the specificities were 49% and 78%, respectively. In patients with left ventricular hypertrophy the specificity of exercise echocardiography was higher (71%) compared to exercise ECG (21%) while in patients without hypertrophy the sensitivity was higher (70% vs. 40%, respectively). Of the 19 patients with a non-diagnostic stress ECG, echocardiography correctly identified 100% of those with coronary artery disease but only 53% of those without disease. It is concluded that exercise digital echocardiography represents a good diagnostic alternative to the exercise ECG for identifying coronary artery disease in the presence of left ventricular hypertrophy and should be useful in patients with a non-diagnostic exercise ECG.

Exercise echocardiography after coronary artery bypass surgery: correlation with coronary angiography

OBJECTIVES

Our aim was to assess, in patients after coronary artery bypass surgery, how well exercise echocardiography predicts the presence of vascular compromise on angiography.

BACKGROUND

Because late graft failure frequently occurs after bypass surgery, a reliable noninvasive technique is needed to identify those patients who would benefit from angiographic study.

METHODS

In 182 patients, a total of 213 symptom-limited treadmill exercise electrocardiograms (ECGs) and exercise echocardiograms were performed in association with coronary and bypass angiography 2 weeks to 21 years after bypass surgery.

RESULTS

There were more inconclusive exercise ECGs (28%) than exercise echocardiograms (9%). The positive predictive value was 85% for the exercise echocardiogram versus 62% for the exercise ECG; the corresponding negative predictive values were 81% versus 52%. The accuracy of the exercise echocardiogram was linked to the degree of underlying vascular compromise. After excluding cases with nondiagnostic results, due to either submaximal stress or poor image quality, the exercise echocardiogram detected 46 of the 60 cases with vascular compromise in one region (sensitivity 77%) and 47 of the 49 cases with compromise in two or three regions (sensitivity 96%). Similarly, an abnormal exercise echocardiogram had a positive predictive value of 71% for vascular compromise in one region and 98% for compromise in two or three regions. Most false negative exercise echocardiographic results were associated with posterolateral single-region vascular compromise on angiography.

CONCLUSIONS

This study confirms a high positive and negative predictive value of exercise echocardiography in the detection of vascular compromise in patients after bypass surgery. It is clearly superior to exercise electrocardiography in predicting which patients will have angiographically significant graft or arterial lesions, and it can be used to obtain a better selection of patients for angiographic study.

Technetium-99m sestamibi tomographic evaluation of residual ischemia after anterior myocardial infarction

OBJECTIVES

This study investigated the value of sestamibi scintigraphy in assessing residual ischemia after anterior myocardial infarction.

BACKGROUND

Serial imaging with sestamibi, the uptake and retention of which correlate with regional myocardial blood flow and viability, has been used to estimate salvaged myocardium and risk area after acute infarction. We recently documented that recovery of perfusion and contraction in the infarcted area may continue well after the subacute phase, suggesting myocardial hibernation. Some underestimation of viability in the setting of hibernating myocardium by sestamibi imaging has been reported.

METHODS

We studied 58 patients in stable condition after Q wave anterior infarction. Regional perfusion and function were quantitatively assessed by sestamibi tomography and two-dimensional echocardiography at 4 to 6 weeks and at 7 months after infarction. In sestamibi polar maps, abnormal areas with tracer uptake > 2.5 SD below our reference values were computed at rest and after symptom-limited exercise. On two-dimensional echocardiography the ejection fraction and extent of rest wall motion abnormalities were assessed by a computerized system. All patients had coronary angiography between the two studies.

RESULTS

At 7 months the extent of rest sestamibi defect was significantly reduced in 40 patients (69%, group 1) and unchanged in 18 (31%, group 2). Rest wall motion abnormalities and ventricular ejection fraction significantly improved in group 1 but not in group 2. Underlying coronary disease, patency of the infarct-related vessel and rest sestamibi defect extent at 5 weeks were comparable between the two groups. At 7 months, an increase in the reversible (stress-rest defect) tracer defect was observed in group 1 (p < 0.05) despite a smaller stress-induced hypoperfusion (p < 0.05). Reversible sestamibi defects and stress hypoperfusion were unchanged in group 2. In 38 (95%) of 40 group 1 patients, the area showing reversible sestamibi defects at 7 months matched the area showing fixed hypoperfusion at 5 weeks.

CONCLUSIONS

The reduction in the rest tracer uptake defect that can occur late after infarction may affect the assessment of ischemic burden by sestamibi imaging early after anterior myocardial infarction.

Comparison of symptom-limited and low level exercise tolerance tests early after myocardial infarction

OBJECTIVES

This study was conducted to determine the diagnostic yield and risks of a symptom-limited treadmill exercise test before hospital discharge.

BACKGROUND

Currently, predischarge low level and 6-week symptom-limited exercise treadmill tests are recommended for risk stratification after myocardial infarction. However, few data exist on the safety and value of a predischarge symptom-limited exercise test.

METHODS

We utilized a modified Bruce protocol starting at 1.7 mph and 0 grade with 3-min stages in 150 consecutive patients 6.4 +/- 3.1 days after myocardial infarction. Each exercise test was interpreted for duration, symptoms and ST segment changes at the low level (70% of predicted heart rate) and symptom-limited end point.

RESULTS

There were no complications related to the symptom-limited exercise tests. The test results were positive in only 23% of the patients at the low level end point, but were positive in 40% of the patients at the later symptom-limited end point (p < 0.001). During a mean follow-up period of 15 +/- 5 months in 138 patients (92%), 50 patients (36%) had a cardiac event. Of the patients with a cardiac event, significantly more (p < 0.001) had a positive exercise test at the symptom-limited end point (31 vs. 16 patients). Five patients with a negative and 14 patients with a nondiagnostic symptom-limited exercise test had an event.

CONCLUSIONS

In patients with uncomplicated myocardial infarction, we demonstrated the safety of an early symptom-limited treadmill exercise test. Symptom-limited exercise tests will identify more patients with inducible ischemia who are at risk of future cardiac events and who may benefit from early intervention.

Exercise-provoked ST-segment depression and prognosis in patients recovering from acute myocardial infarction. Significance and pitfalls

The importance of maximal versus submaximal exercise testing and the significance of heart failure on the prognostic value of exercise-provoked ST-segment depression > or = 0.1 mV was studied in 143 patients recovering from acute myocardial infarction. Patients were exercise tested prior to discharge and follow up lasted for up to 18 months (mean 17 months). End-point was first major event (i.e. first non-fatal reinfarction or death). A symptom-limited exercise test was superior to a heart-rate-limited test in detecting ST-segment depressions (27% vs. 20%: P < 0.5), and patients with ST-segment depression at lower heart rates did not have an increased risk of subsequent events compared with patients with ST-segment depression at higher heart rates (14% vs. 27%; NS). Heart failure surpassed ST-segment depression as a risk predictor (34% vs. 18%). Based on a meta-analysis including 13 studies (1987 patients) exercise-provoked ST-segment depression possessed an increased risk of subsequent major events (P < 0.0001; risk ratio = 1.90; 95% confidence limits 1.43,2.51). Thus, ST-segment depression provoked by a symptom-limited test selects patients with an increased risk of subsequent major events. In patients with a history of heart failure exercise-provoked ST-segment depression is of limited value.

Cardiac imaging after acute myocardial infarction. Identification of patients at continued risk

Diagnostic imaging performed early in the course of acute myocardial infarction provides anatomic and functional information that is useful in assessing patients at risk for future cardiac events and premature death. Early identification of left ventricular dysfunction or complications of myocardial infarction allows appropriate and timely management of high-risk patients and early transfer of stable patients from the intensive care environment. Noninvasive predischarge functional imaging to unmask patients with jeopardized myocardium identifies high-risk patients who may need invasive studies and surgical or interventional treatment. Postdischarge risk stratification with diagnostic imaging provides vital prognostic information in high- and low-risk patients, allowing for appropriate allocation of medical resources.

Exercise echocardiography after coronary artery bypass grafting

Exercise echocardiography was used to assess the adequacy of regional myocardial perfusion in 125 patients who had undergone coronary artery bypass grafting. There were 108 men and 17 women (mean age 65 years) evaluated from 6 weeks to 16 years (mean 7 years) after surgery. Resting parasternal long- and short-axis and apical 4- and 2-chamber echocardiograms were recorded, digitized and stored. Maximal, symptom-limited upright treadmill exercise was then performed with continuous electrocardiographic monitoring. Repeat echocardiographic imaging and digitization were repeated within 1 minute of exercise termination. Resting and postexercise digitized echocardiograms were compared. A normal regional wall motion response to exercise consisted of improved segmental contraction and was used to predict uncompromised regional vascular supply. Unimproved or worsened segmental contraction after exercise was abnormal and was used as a predictor of regional vascular insufficiency. All patients underwent cardiac catheterization within 1 month after exercise testing. Regional coronary insufficiency was considered to exist when a segment's major vascular conduit exhibited greater than or equal to 50% luminal diameter reduction. Compared with the simultaneously acquired stress electrocardiogram, exercise echocardiography had superior sensitivity (98 vs 41%), specificity (92 vs 67%), positive predictive value (99 vs 91%), and negative predictive value (86 vs 12%) (p less than 0.001, 0.1, 0.01 and less than 0.001, respectively). In addition, exercise echocardiography correlated closely with the extent and regional distribution of compromised vascular supply. Exercise echocardiography is a highly sensitive, specific and accurate screening test for abnormal global and regional myocardial vascular supply in patients who have undergone coronary artery bypass grafting.

Post-myocardial infarction exercise testing. Non-Q wave versus Q wave correlation with coronary angiography and long-term prognosis

BACKGROUND

The presence or absence of baseline diagnostic Q waves has been believed to compromise the accuracy of standard exercise electrocardiography in identifying severe coronary artery disease (three-vessel and/or left main disease); therefore, a retrospective analysis was performed using a personal computer data base of exercise test responses and cardiac catheterization results to evaluate this premise, and follow-up was performed to observe how Q waves and/or severe coronary disease impacted on survival.

METHODS AND RESULTS

Two hundred fifty-three male patients who had survived a myocardial infarction were studied. Patients on digitalis, those with left bundle branch block or left ventricular hypertrophy on their baseline electrocardiogram, those with previous revascularization procedures, and those with significant valvular or congenital heart disease were excluded. All patients performed either a low-level predischarge or a sign/symptom limited exercise test and underwent diagnostic coronary angiography within 32 days of each test (range, 0-90 days). Long-term follow-up on patients was performed for an average of 45 months (+/- 17 months). Group NQMI comprised 103 post-myocardial infarction patients lacking Q waves at the time of exercise testing and group QMI comprised 150 patients who developed Q waves with their myocardial infarction. The cut points of greater than or equal to 1 mm (chi 2 = 14.39, p less than 0.001) and greater than or equal to 2 mm (chi 2 = 26.11, p less than 0.001) of exercise-induced ST segment depression were reliable markers of severe coronary disease in Q wave infarct survivors. This was also true for non-Q wave infarct survivors as greater than or equal to 1 mm (chi 2 = 6.02, p = 0.01) and greater than or equal to 2 mm (chi 2 = 4.37, p = 0.04) of ST segment depression were reliable markers of severe coronary disease. Receiver operating characteristic curve analysis revealed that exercise-induced ST segment depression had discriminating power for the identification of severe coronary artery disease in both the Q wave myocardial infarction patients (area = 0.735, z = 4.47, p less than 0.001) and the non-Q wave infarct patients (area = 0.700, z = 3.20, p less than 0.001). After 4.4 years of cumulative follow-up, patients with severe coronary disease had an infarct-free survival rate of 72% (95%, CI, 50.0-86.0%), whereas those without severe disease had an 86% (95% CI, 76.5-91.5%) infarct-free survival rate (Cox chi 2 = 4.00, p = 0.045). Non-Q wave patients had an infarct-free survival rate of 81% (95% CI, 66.0-89.5%), whereas those with Q waves had an infarct-free survival rate of 85% (95% CI, 73.9-91.3%) (Cox chi 2 = 0.0005, p = NS).

CONCLUSIONS

The presence or absence of diagnostic Q waves has no significant effect on the ability of the exercise electrocardiogram to identify severe coronary artery disease in survivors of myocardial infarction. Long-term infarct-free survival of patients with myocardial infarction is more related to the presence of severe coronary disease rather than if they suffered a non-Q wave or Q wave infarction.

Asymptomatic myocardial ischemia during percutaneous transluminal coronary angioplasty and importance of prior Q-wave infarction and diabetes mellitus

Eighty-eight patients undergoing percutaneous transluminal coronary angioplasty (PTCA) of 100 stenoses were studied for the presence of factors deemed significant in the etiology of silent myocardial ischemia. Thirty-two patients were asymptomatic during balloon dilations of 36 arteries, and 56 patients had angina during PTCA of 64 arteries. There were no differences in age, sex, prior anginal history, antianginal regimen, extent of coronary artery disease and number or duration of inflations between the 2 study groups. Previous infarction (33 vs 12%, p less than 0.02), Q waves in the target area (31 vs 7%, p less than 0.005) and diabetes mellitus (36 vs 17%, p less than 0.05) were present more often in the asymptomatic group. Sixty-four% of all asymptomatic patients had either diabetes or previous infarction in the target territory. Collateral circulation was more frequent in asymptomatic patients, probably reflecting the ability of collateral arteries to ameliorate ischemia. During 2-vessel PTCA, patients without angina during dilation of only 1 of the 2 treated arteries (discordant responders) had previous infarction in that artery's territory (5 of 5, 100%), whereas patients without previous infarction were either symptomatic or asymptomatic (concordant responders) during PTCA of both arteries. This study shows that asymptomatic ischemia occurs frequently during PTCA in patients with symptomatic coronary disease. Prior Q-wave infarction and diabetes mellitus are important, independent factors associated with painless ischemia. It is suggested that infarction produces a localized dysfunction of afferent cardiac pain fibers, whereas diabetes can cause a global cardiac sensory neuropathy.

Exercise echocardiography as a screening test for coronary artery disease and correlation with coronary arteriography

We evaluated exercise echocardiography as a screening test for coronary artery disease in 228 patients, all of whom underwent subsequent coronary angiography. After an echocardiogram at rest was obtained, each patient performed maximal, symptom-limited, upright treadmill exercise, immediately after which repeat imaging was performed. The exercise echocardiogram was abnormal if any segment failed to become hypercontractile with exercise, and these regional wall motion abnormalities were used to predict the extent and distribution of coronary disease. At subsequent angiography, coronary stenosis was defined as significant if luminal diameter was reduced greater than or equal to 50%. Compared with electrocardiography, exercise echocardiography was more sensitive (97 vs 51%) and specific (64 vs 62%), and had higher positive (90 vs 82%) and negative (87 vs 28%) predictive accuracies. Exercise echocardiography was also highly predictive of the extent (no, 1-, 2- or 3-vessel disease) and distribution (which vessel) of coronary stenoses. It is concluded that exercise echocardiography is an excellent screening test for the presence, extent and distribution of coronary artery disease.

Prognostic value of an exercise test one year after myocardial infarction

An exercise test was performed in 306 patients who had had acute myocardial infarction one year previously. The five year cumulative coronary heart disease mortality was 40.0%, when the test had to be discontinued because of ventricular arrhythmias but only 13.0% if discontinued because of fatigue (P less than 0.05). If the maximum work load was less than 80 W the mortality was 30.7% compared with 16.6% in patients who exercised at least 80 W (P less than 0.01). If maximum systolic blood pressure was less than or equal to 150 mmHg mortality was 40.3% compared with 8.5% in patients with greater than 200 mgHg (P less than 0.001). The mortality was 38.2% in patients having single monoform ventricular ectopic beats at a rate of three or more per minute or multiform, paired or early cycle ventricular ectopic beats or ventricular tachycardias: this compared with 14.1% (P less than 0.001) in patients having no or only single monoform ventricular ectopic beats at a rate of less than three per minute. ST-segment depression in univariate testing had no prognostic value. When both exercise test and clinical variables were used in survival analysis (Cox's regression) the most important variable was heart volume and after that ventricular arrhythmias. In multivariate regression analysis ST segment depression also had additional prognostic value. Thus ventricular arrhythmias turned out to be the most important prognostic factor measured during exercise test.

Coronary heart disease morbidity and mortality in hypercholesterolemic men predicted from an exercise test: the Lipid Research Clinics Coronary Primary Prevention Trial

A positive exercise electrocardiogram (ECG) has been proved to predict cardiovascular events in asymptomatic normolipidemic men. To study whether it is also predictive for hypercholesterolemic men, data from 3,806 asymptomatic hypercholesterolemic men in the Lipid Research Clinics Coronary Primary Prevention Trial were analyzed. All the men had performed a submaximal treadmill exercise test at baseline, before they were assigned to the cholestyramine or placebo treatment group. Because of missing or inconclusive data, 31 men were excluded from the analyses. A test was positive if the ST segment was displaced by greater than or equal to 1 mm (visual code) or there was greater than or equal to 10 microV-s change in the ST integral (computer code), or both. The prevalence of a positive test was 8.3%. During the 7 to 10 year (mean 7.4) follow-up period, the mortality rate from coronary heart disease was 6.7% (21 of 315) in men with a positive test and 1.3% (46 of 3,460) in men with a negative test (placebo and cholestyramine groups combined). The age-adjusted rate ratio for a positive test, compared with a negative test, was 6.7 in the placebo group and 4.8 in the cholestyramine group. With use of Cox's proportional hazards models, it was found that the risk of death from coronary heart disease associated with a positive test was 5.7 times higher in the placebo group and 4.9 times higher in the cholestyramine group after adjustment for age, smoking history, systolic blood pressure, high density lipoprotein cholesterol and low density lipoprotein cholesterol. A positive test was not significantly associated with nonfatal myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Does the rest electrocardiogram after myocardial infarction determine the predictive value of exercise-induced ST depression? A 2 year follow-up study in a veteran population

The failure of exercise-induced ST segment depression to consistently predict prognosis in patients after myocardial infarction could be a result of population differences and the rest electrocardiogram (ECG). These hypotheses were tested by studying 198 veterans who survived a myocardial infarction, underwent a submaximal predischarge treadmill exercise test and were followed up for cardiac events for 2 years. During the 2 years, 29 deaths, 19 reinfarctions and 28 revascularization procedures were documented. The prevalence of death or reinfarction was two times higher in patients who had exercise-induced ST depression than in patients who did not. However, in the 55 patients without Q waves, the risk increased to 11 times for an abnormal ST response. These findings suggest that exercise-induced ST depression only predicts high risk in patients after myocardial infarction whose ECG at rest does not exhibit Q waves and that differences in the prevalence of rest ECG patterns are the most likely explanation for the failure of agreement among prior studies.

Infarct vessel status after intravenous tissue plasminogen activator and acute coronary angioplasty: prediction of clinical outcome

To determine the risk of arterial reocclusion or recurrent ischemia after acute intervention in myocardial infarction, we analyzed the results of coronary arteriography performed acutely and at 1 week in 50 consecutive patients who received acute intervention. Successful recanalization of the infarct vessel was achieved in 46 (92%) patients after therapy with intravenous tissue plasminogen activator, percutaneous coronary angioplasty, or both. Follow-up angiography in 44 showed early reocclusion in 10 patients (23%). Intermittent patency during acute arteriography was always associated with reocclusion; suboptimal (Thrombolysis in Myocardial Infarction [TIMI] class 2) flow was associated with a 50% rate of reocclusion. Although residual stenosis of greater than 50% alone was not predictive of rethrombosis, 90% of all reocclusions were associated with either stenosis greater than 50%, TIMI 2 flow, or intermittent patency. Absence of these angiographic risk factors predicted a 95% patency rate at follow-up. In-hospital cardiac complications occurred in 17 of 23 (74%) patients with residual stenosis of greater than 50% (death in four, ischemia in 13), and late revascularization was required in 53% of survivors. Only 15% of the group with less than 50% stenosis had an in-hospital ischemic event (p less than 0.001). Thus, after acute intervention, an infarct vessel with intermittent patency or suboptimal flow is associated with a high rate of reocclusion. Residual stenosis greater than or equal to 50% appears to predict a high incidence of negative in-hospital clinical outcomes and the need for subsequent revascularization.

Application of meta-analysis using an electronic spread sheet to exercise testing in patients after myocardial infarction

Decision analysis is being applied to medical practice in order to achieve cost efficacy in health care delivery. Critical to this process is establishing the diagnostic and prognostic accuracy of medical tests and the effectiveness of interventions. Meta-analysis is an approach that applies statistical methods to groups of studies in order to extract consensus results. Electronic spreadsheets facilitate meta-analysis with their ability to store, sort, graph, and mathematically manipulate both the methodologic approaches and clinical findings of seemingly disparate studies. As an example, this application is demonstrated with an analysis of studies that were performed to evaluate the prognostic value of exercise testing in patients recovering from a myocardial infarction. The following conclusions were reached: (1) patients excluded from exercise testing have the highest mortality; (2) only subsets of patients have been tested resulting in highly selected patient samples that make findings difficult to generalize; (3) of the five exercise test responses, only an abnormal systolic blood pressure response and a poor exercise capacity predicted risk more frequently than by chance; (4) submaximal or predischarge testing has greater predictive power than postdischarge or maximal testing; and (5) exercise-induced ST segment depression only appears to be predictive of increased risk in patients with inferior-posterior myocardial infarctions. This approach to combining studies is important since even careful analysis of a single study cannot elucidate all of the complex interactions and selective biases that have occurred. However, comparison of many heterogeneous studies is at best an arduous and time-consuming task. This approach to using electronic spreadsheets to collate and analyze multiple studies facilitates recognition of the population characteristics, clinical factors, and methodologic considerations that affect outcome and allows the quick inclusion of additional studies for re-analysis and interpretation.

How many electrocardiographic leads are required for exercise treadmill tests?

Forty-four consecutive patients who had perfusion defects on thallium-201 scanning and positive exercise treadmill tests were prospectively studied. Thirty-eight (86%) subjects had diagnostic ST segment changes in lead V5, 37 (84%) in lead V4, and 44 (100%) in either lead V4, V5 or both. Thirty patients had ST segment changes in the inferior leads, 20 in lead aVR, and only four in lead I and/or aVL. All of these latter subjects had diagnostic ST segments in lead V4 and/or V5. It is concluded that: combined electrocardiographic leads V4 and V5 detect the vast majority of ischemic changes during exercise treadmill testing, regardless of the site of perfusion defects detected by thallium-201 scanning; and monitoring the inferior and lateral leads rarely provides more diagnostic information.