Relation between exertional ischemia and prognosis in mildly symptomatic patients with single or double vessel coronary artery disease and left ventricular dysfunction at rest

Stress echocardiography in the diagnosis of coronary artery disease

Stress echocardiography (SE) is currently a widely accepted method for the diagnostic and prognostic assessment of coronary artery disease. This article reviews new concepts in SE, such as new stress techniques, new methods of endocardial border detection, strain, tissue Doppler velocities, and others. Although some of these techniques are in their infancy, we believe that they will become widely accepted.

[Nuclear cardiology: technical bases and clinical applications]

Although the role of nuclear cardiology is currently well consolidated, the addition of new radiotracers and modern techniques makes it necessary to continuously update the requirements, equipment and clinical applications of these isotopic tests. The characteristics of the radioisotopic drugs and examinations presently used are explained in the first part of this text. In the second, the indications of them in diagnostic and prognostic evaluation of the different coronary diseases are presented.

Prognostic implications of myocardial contractile reserve in patients with coronary artery disease and left ventricular dysfunction

OBJECTIVES

This study was performed to assess the prognostic implications of myocardial contractile reserve (MCR) in patients with coronary artery disease (CAD) and left ventricular (LV) dysfunction.

BACKGROUND

MCR during dobutamine stress echocardiography (DSE) identifies viable myocardium that may improve in function after revascularization. Whether revascularization influences prognosis of patients with MCR has not been determined.

METHODS

We performed DSE in 80 patients with CAD and LV dysfunction (ejection fraction < or =40%). Viable myocardium was defined in dysfunctional myocardial segments as enhanced thickening and contraction during low-dose dobutamine (5 to 10 mcg/kg/min). Serial prospective follow-up was obtained in all patients (mean follow-up 2.2 +/- 1.1 years).

RESULTS

Among 52 patients treated medically, there were 20 cardiac deaths. By multivariate analysis, the number of dysfunctional segments demonstrating MCR was the strongest predictor of survival (p < 0.03). Patients with MCR had better initial survival during medical therapy than did those without MCR, but this survival advantage was not maintained beyond three years. In contrast, survival was excellent in patients with MCR who underwent myocardial revascularization. Among 58 patients with MCR in > or =5 myocardial segments, survival at three years was 93 +/- 6% in the 24 patients who were revascularized but only 49 +/- 15% in the 34 treated medically (p < 0.02).

CONCLUSIONS

Myocardial contractile reserve is a significant predictor of survival in patients with CAD and LV dysfunction undergoing medical therapy. Although patients with MCR have an initial survival advantage, this advantage is lost over the course of three years. In contrast, survival in patients with significant MCR is enhanced by revascularization.

Prognostication in 3-vessel coronary artery disease based on left ventricular ejection fraction during exercise : influence of coronary artery bypass grafting

BACKGROUND

Previous data indicate that left ventricular ejection fraction (LVEF) provides prognostic information among patients with coronary artery disease (CAD), but the value of such testing specifically for defining benefits of coronary artery bypass grafting (CABG) may relate to severity of exercise-inducible ischemia measured noninvasively before surgery.

METHODS AND RESULTS

To determine the independent prognostic importance of preoperative ischemia severity for predicting outcomes of CABG among patients with extensive CAD, we monitored 167 stable patients with angiographically documented 3-vessel CAD (average follow-up of 9 years in event-free patients) who previously had undergone rest and exercise radionuclide cineangiography. Their course was correlated with data obtained during initial radionuclide testing, coronary arteriography, and clinical evaluation at study entry. Fifty-two patients received medical treatment only, and 115 underwent CABG (44 early [</=1 month after initial study]). Multivariate Cox model analysis indicated that change (Delta) in LVEF from rest to exercise during radionuclide study was the strongest independent predictor of major cardiac events (P=0.003) before surgery and also predicted magnitude of CABG benefit (P=0.04). Patients with DeltaLVEF -8% or less derived significant survival-prolonging and event-reducing benefit from CABG performed </=1 month after initial testing (P<0.02 for cardiac death and P=0.008 for cardiac events], early CABG versus medical-treatment-only patients); similar benefits were absent among patients with DeltaLVEF more than -8%, and among those in whom CABG was deferred.

CONCLUSIONS

Assessment of ischemia severity based on LVEF response to exercise enables effective prognostication among patients with 3-vessel CAD and defines the likelihood of life-prolonging and event-reducing benefits from CABG.

Transesophageal echocardiography with stress for the evaluation of patients with coronary artery disease

Echocardiography permits a comprehensive assessment of resting regional and global left ventricular function, the presence and extent of inducible myocardial ischemia, and the identification of myocardial viability. Accordingly, stress echocardiography has become a valuable tool for the evaluation of patient with known or suspected coronary artery disease. In some patients however, a suboptimal transthoracic echocardiogram may limit the performance of interpretation of the test. Transesophageal echocardiography in combination with stress has been recently used for the evaluation of patients with coronary artery disease. This technique is semi-invasive, more time-consuming, and requires a greater degree of expertise on the part of the personnel assisting with the test. In general, complications and side-effects are self-limited and rarely affect the diagnostic accuracy of the test. Based on its ability to provide high quality images, transesophageal stress echocardiography should be considered in patients who have suboptimal transthoracic ultrasound window for the quantitative assessment of myocardial wall-thickening in clinical investigations of ischemic heart disease.

Value of pharmacologic stress echocardiography in risk stratification of patients with single-vessel disease: a report from the Echo-Persantine and Echo-Dobutamine International Cooperative Studies

OBJECTIVES

This study sought to verify the effectiveness of pharmacologic stress echocardiography in risk stratification of patients with single-vessel disease.

BACKGROUND

Noninvasive prognostic assessment of single-vessel disease is an unresolved issue to date.

METHODS

The study evaluated prospectively collected data from 754 patients with angiographic single-vessel disease who underwent either dipyridamole (n = 576) or dobutamine (n = 178) stress echocardiography. Invasive treatment (coronary revascularization within 3 months of stress testing) was performed in 260 patients and medical treatment in 494.

RESULTS

Echocardiographic positivity was observed in 421 patients (56%). Patients treated invasively had a higher incidence of stress test positivity (69% vs. 49%, p < 0.001) and left anterior descending coronary artery involvement (60% vs. 46%, p < 0.001) than patients maintained with medical therapy. During a mean follow-up of 37 months, 54 hard cardiac events occurred (14 deaths, 40 nonfatal infarctions): 37 in medically and 17 in invasively treated patients (7.5% vs. 6.5%, p = NS). On Cox analysis, a positive result on stress testing was the only independent prognostic predictor in medically treated patients (relative risk 2.92, 95% confidence interval 1.29 to 6.59). The 4-year infarction-free survival rate was higher for a negative than a positive stress test result in medically (93.9% vs. 87.3%, p = 0.009) but not invasively treated patients (92.7% vs. 97.1%, p = 0.545). Moreover, a significantly higher 4-year infarction-free survival rate was found in invasively versus medically treated patients with a positive (p = 0.012), but not in those with a negative, stress test result (p = 0.853).

CONCLUSIONS

Pharmacologic stress echocardiography is effective in risk stratification of single-vessel disease and can accurately discriminate patients in whom coronary revascularization can have the maximal beneficial effect. These findings have a potential favorable impact on the cost-effectiveness of invasive procedures.

Worsening left ventricular performance on serial exercise radionuclide angiography does not identify high-risk patients

OBJECTIVE

To determine whether worsening exercise performance on serial exercise radionuclide angiography identifies patients at increased risk of future cardiac events.

MATERIAL AND METHODS

One hundred nine medically treated patients with previous Q-wave myocardial infarction underwent two exercise radionuclide angiographic studies at least 6 months apart (median, 16 months) without an intervening clinical event. Worsening exercise performance between the two studies was defined by five criteria: (1) lower (5% or more) peak exercise ejection fraction; (2) worsening peak exercise wall motion score; (3) combination of criteria 1 and 2; (4) worsening serial delta (exercise - rest) ejection fraction; or (5) increasing exercise ST-segment depression of 1 mm or more. Patients were followed up for a median duration of 3.9 years after the second exercise study.

RESULTS

Five cardiac deaths and 10 nonfatal myocardial infarctions occurred during follow-up. A Cox proportional hazards analysis failed to show an association between any of the aforementioned variables and cardiac events. Of the 15 patients with cardiac events, 4 (27%) had a lower (5% or more) exercise ejection fraction and 2 (13%) had a worsening exercise wall motion score. Of the 94 patients without cardiac events, 37 (39%) had a lower (5% or more) exercise ejection fraction and 28 (30%) had a worsening serial exercise wall motion score (not a statistically significant difference).

CONCLUSION

Worsening exercise performance on serial exercise radionuclide angiography does not identify patients at increased risk of future cardiac events.

Risk stratification in coronary artery disease and special populations

In patients with coronary artery disease (CAD), left ventricular (LV) function, the number of diseased vessels, and the severity of myocardial ischemia are important determinants of survival. These factors can be used to identify subsets of high-risk patients who are candidates for aggressive intervention. Among patients with LV dysfunction, those with left main CAD, three-vessel disease, and one- or two-vessel disease with inducible ischemia are at highest risk. High-risk subsets among those with preserved LV function include patients with left main CAD and those with inducible ischemia and either three-vessel disease or two-vessel disease with involvement of the proximal left anterior descending coronary artery. Thus, exercise testing, assessment of ventricular function and, in selected patients, coronary angiography to determine coronary anatomy are valuable tools in risk stratification. In the primary-care setting, patient characteristics such as gender, race, age, and concomitant medical conditions may also be most useful in identifying high-risk patients. Although women in general have some primary protection against premature CAD, especially prior to the menopause, coronary risk in women who have experienced a cardiovascular event is similar to that in men. Coronary mortality is increased in minority populations, and the presence of other risk factors, such as diabetes and hyperlipidemia, can further increase this risk. Up to 80% of diabetic patients die of cardiovascular disease, 75% of which is CAD. The risk in this population is exacerbated by the abnormalities in lipid metabolism associated with the diabetic state. CAD mortality increases with aging, but it is recommended that elderly patients with CAD also receive risk factor intervention, such as cholesterol-lowering therapy. Consideration of the impact of such therapy on quality of life is especially important in initiating such interventions in the older population.

Gender-related differences in exercise ventricular function among healthy subjects and patients

Increasing numbers of women are undergoing noninvasive stress testing for coronary artery disease evaluation. Limited information is available regarding the presence, magnitude, and importance of gender-related differences in exercise ventriculography among the heterogeneous population of patients referred for noninvasive stress testing. Patients referred for exercise radionuclide ventriculography between 1979 and 1986 were evaluated, including 175 patients with a likelihood of coronary artery disease, 59 patients with angiographically normal coronary arteries, and 419 patients with coronary artery disease. Overall, women demonstrated higher resting left ventricular ejection fraction and lower delta left ventricular ejection fraction response to exercise compared with men. Although left ventricular response to exercise correlated with the underlying severity of coronary artery disease in both women and men, fewer women demonstrated a delta left ventricular ejection fraction >5 percent despite a lower prevalence of multivessel coronary artery disease compared with men. We conclude that gender-related differences in left ventricular response to exercise are present in a wide range of patients referred for testing.

The limited efficacy of exercise radionuclide ventriculography in assessing prognosis of women with coronary artery disease

Increasing numbers of women are undergoing stress testing for coronary artery disease evaluation. Limited study is available as to its efficacy in women. Four hundred nineteen patients with coronary artery disease (74 women and 345 men) referred for exercise radionuclide ventriculography between 1979 and 1986 were evaluated in a prospective cohort evaluation with 5-year follow-up. Exercise radionuclide ventriculographic variables were analyzed and compared between women and men. The prognostic efficacy of exercise radionuclide ventriculography was assessed separately for women and men among patients with coronary artery disease by Kaplan-Meier cumulative survival curves, univariate Cox regression analyses, and hierarchical stepwise Cox regression analyses. Overall, women demonstrated higher resting and peak left ventricular ejection fraction response to exercise than men. Ninety-six of 419 patients (23%) had cardiac events at 5-year follow-up. Although left ventricular response to exercise conveyed prognostic information in the combined and male populations (multivariate hierarchical analyses chi-square 11, p = 0.001 for delta left ventricular ejection fraction and chi-square 10, p = 0.002 for worsening exercise wall motion score), these variables were not found to be prognostically useful in women. Women with coronary artery disease demonstrated a worsened functional status, evidenced by greater compromise of exercise capacity, despite having less extensive anatomic disease than their male counterparts. We conclude that sex-related differences in left ventricular response to exercise limit the prognostic utility of exercise ventriculography in women with coronary artery disease.

Relation between ischemic threshold measured during dobutamine stress echocardiography and known indices of poor prognosis in patients with coronary artery disease

BACKGROUND

Stress echocardiography has become an accepted methodology for the evaluation of coronary artery disease. One potential advantage of dobutamine over other stressors used with echocardiography is the possibility of assessing the ischemic threshold. However, whether this measurement correlates with indices associated with adverse outcome has not been established.

METHODS AND RESULTS

One hundred four patients (91 men and 13 women; age, 61 +/- 9 years) with coronary artery disease were studied with transesophageal echocardiography during infusion of dobutamine 2.5 to 40 microgram/kg per minute. When regional dyssnergy developed, the dobutamine ischemic threshold (the dose of dobutamine at which induced regional wall motion abnormalities were first detected) was identified. The dobutamine stress echocardiogram was abnormal in 90 patients (sensitivity, 87%). The dobutamine ischemic threshold was 25.4 +/- 11.2 micrograms/kg per minute in patients with single-vessel disease, 14.4 +/- 7.9 in patients with two-vessel disease, and 9.1 +/- 7.9 in patients with three-vessel disease (P < .0001). The dobutamine ischemic threshold correlated with the ejection fraction response to exercise measured by radionuclide angiography: Patients with low ischemic threshold had a mean fall in ejection fraction, and patients with high ischemic threshold or normal tests had a mean increase in ejection fraction.

CONCLUSIONS

In patients with coronary artery disease, the ischemic threshold measured during dobutamine stress echocardiography correlates with both the number of stenosed vessels and the left ventricular ejection fraction response to exercise. Because these variables are associated with poor prognosis, these findings provide further support regarding the utility of dobutamine stress echocardiography in the clinical evaluation of patients with chronic coronary artery disease.

Risk stratification of patients with coronary artery disease and left ventricular dysfunction by exercise radionuclide angiography and exercise electrocardiography

BACKGROUND

The results of multicenter trials indicate that patients with left ventricular dysfunction and either three-vessel or left main coronary artery disease have improved prognosis when treated surgically.

OBJECTIVE

As part of a larger evaluation and follow-up study of coronary artery disease, the objective of this investigation was to determine whether exercise radionuclide angiography can be used, in patients with mild symptoms of coronary artery disease and left ventricular dysfunction at rest, to identify patients with three-vessel or left main coronary artery disease.

METHODS AND RESULTS

Eighty-four consecutive patients were studied with angiographically defined coronary artery disease in whom left ventricular ejection fraction at rest ranged from 20% to 40%. Patients underwent exercise electrocardiography, rest and exercise radionuclide angiography, and 24-hour electrocardiographic monitoring. There were 22 patients with one-vessel, 31 with two-vessel, 27 with three-vessel, and four with left main coronary artery disease. All but four patients had a documented history of myocardial infarction. By univariate analysis, the following parameters were related to the anatomic severity of coronary artery disease: magnitude of ST segment depression with exercise (p < 0.001), magnitude of change in ejection fraction with exercise (p < 0.005), and occurrence of angina during exercise (p < 0.005). However, because of the extensive overlap among anatomic subgroups, no single factor had both a satisfactory sensitivity and a satisfactory specificity in identifying patients with three-vessel and left main coronary artery disease. Multivariate stepwise regression analysis also failed to predict three-vessel or left main coronary artery disease satisfactorily (sensitivity 73% and specificity 73%; positive predictive accuracy 59% and negative predictive accuracy 83%). Nonetheless, this multivariate analysis provided important prognostic information. During medical therapy (mean follow-up 56 months), the patients with a high likelihood of three-vessel or left main coronary artery disease had a greater risk of death or reinfarction than had patients with a low likelihood (p < 0.05). These functional data were better than coronary anatomy alone in providing risk stratification. Four of six patients with two-vessel disease who died were classified incorrectly by the multivariate analysis in the high-likelihood group for three-vessel or left main coronary artery disease, but classified correctly as being at high risk; whereas none of the patients with three-vessel disease who were misclassified in the low-likelihood group died during medical therapy.

CONCLUSION

Although exercise radionuclide angiography in patients with minimal symptoms of coronary artery disease and left ventricular dysfunction is not precise in predicting three-vessel or left main coronary artery disease, it provides important functional information regarding subsequent prognosis during medical therapy.

Role of nuclear cardiology for determining management of patients with stable coronary artery disease

Both radionuclide angiography and myocardial perfusion imaging provide important insights that determine the management of patients with stable coronary artery disease. Both nuclear cardiology procedures have clearly demonstrated use in the noninvasvie identification of severe (left main or three-vessel) coronary artery disease and the noninvasive assessment of prognosis and thereby determine which patients should be sent to coronary angiography. Both radionuclide angiography and myocardial perfusion imaging provide prognostic information that is independent of resting left ventricular function and coronary anatomy and thereby influence the decision regarding which patients should be sent to coronary revascularization. This review considers the evidence supporting the uses of these nuclear cardiology procedures and provides suggestions regarding their cost-effective application.

Impaired left ventricular function, one- or two-vessel coronary artery disease, and severe ischemia: outcome with medical therapy versus revascularization

OBJECTIVE

To determine whether patients with impaired left ventricular function and one- or two-vessel coronary artery disease who manifest severe ischemia during exercise radionuclide angiography have a lower rate of subsequent cardiac events when initial management is revascularization rather than medical therapy.

DESIGN

During a median follow-up of 100 months, we compared the outcome between 37 patients who underwent a revascularization procedure and 22 who received medical therapy at the Mayo Clinic between September 1980 and December 1985.

MATERIAL AND METHODS

The revascularization therapy consisted of coronary artery bypass grafting in 31 patients and coronary angioplasty in 6. Overall survival and survival free of initial cardiac events were compared statistically for the medically and surgically treated patients.

RESULTS

Eleven deaths occurred in the patients who received medical therapy and 9 in the revascularization group. Five-year overall survival was 58% in the medically treated patients versus 84% in the revascularization group. A significant association was noted between type of treatment and overall survival (adjusted chi 2 = 6.20; P = 0.013). Twenty patients had initial cardiac events--7 in the medically treated group (3 cardiac deaths and 4 nonfatal myocardial infarctions) and 13 in the revascularization group (3 cardiac deaths, 3 out-of-hospital cardiac arrests, and 7 nonfatal myocardial infarctions). Survival free of cardiac events at 5 years was 72% in the medically treated patients and 66% in those who underwent revascularization. No association was detected between type of treatment and survival free of cardiac events.

CONCLUSION

These nonrandomized data suggest that overall survival for patients with one- or two-vessel coronary artery disease, impaired left ventricular function, and severe exercise-induced ischemia may be improved by revascularization, but the subsequent cardiac event rates are not.

Prognostic assessment in coronary artery disease: role of radionuclide angiography

Left ventricular function is one of the most important determinants, if not the most important determinant, of outcome in patients with coronary artery disease. The ability of radionuclide angiography to assess resting and exercise ejection fraction accurately and reproducibly has been shown to be a critical determinant of survival in large-scale studies of survivors of myocardial infarction, as well as patients with chronic stable angina. In addition, several centers have demonstrated that the exercise ejection fraction is an extremely valuable (and perhaps the most valuable) noninvasive parameter in predicting survival among patients with coronary artery disease. The prognostic insights gained from the exercise ejection fraction add incremental predictive information to the coronary anatomic information obtained from coronary arteriography, especially in patients with multivessel disease and those with left ventricular dysfunction at rest.

Assessment of left ventricular dysfunction by nuclear cardiology

Nuclear cardiology techniques may be of help in evaluating the patient with symptoms of congestive heart failure and ventricular dysfunction in two respects: quantification of functional parameters by radionuclide angiography, and differentiation of viable from nonviable myocardium by perfusion and metabolic imaging. Left ventricular ejection fraction and volumes can be accurately assessed by equilibrium radionuclide angiography with a count-based method without any geometric assumptions. Indeed, because of its high reproducibility, this method is particularly suited for making sequential measurements in the same patient. The distinction between viable or reversible and scarred or irreversible dysfunctional myocardium can be made on the basis of myocardial perfusion, cell membrane integrity, and metabolic activity. Thallium myocardial imaging is used clinically to assess the first two parameters based on experimental data. Two clinical methods may be applied to the detection of viability: stress-redistribution-reinjection imaging or rest-redistribution imaging. In both of these, the severity of the reduction in thallium activity should be assessed to discriminate viable from nonviable myocardium. Stress-redistribution-reinjection thallium imaging should be the first approach, if possible, because inducible ischemia is a much more significant clinical variable in a patient with ventricular dysfunction in terms of management and risk assessment than is knowledge of myocardial viability. Positron emission tomography (PET) provides enhanced image resolution and correction for body attenuation, thereby overcoming the two major limitations of thallium imaging. In addition, it provides the capacity to quantitate regional blood flow and to assess regional metabolic activity independent of flow. Overall, the accuracies of thallium imaging (around 70%) and PET imaging (around 82%) are similar for the prediction of segmental changes after revascularization. However, in patients with poor global left ventricular function, the accuracy of PET seems to be better. Further studies are needed in a large number of patients evaluated for regional and global function to establish algorithms using thallium and PET imaging in dysfunctional myocardium. Dobutamine echocardiography should also be evaluated in these algorithms.

Severe exercise-induced ischemia does not identify high risk patients with normal left ventricular function and one- or two-vessel coronary artery disease

OBJECTIVES

This study was conducted to determine whether severe exercise-induced ischemia identifies high risk patients with a normal left ventricular ejection fraction and one- or two-vessel coronary artery disease.

BACKGROUND

Severe ischemia during exercise radionuclide angiography has been shown to identify high risk patients among certain other patient subsets.

METHODS

Four hundred twenty patients with left ventricular ejection fraction > or = 50% and one- or two-vessel disease underwent exercise radionuclide angiography within 3 months of coronary angiography. Patients were treated initially with revascularization (n = 140) or medical therapy (n = 280) at the discretion of their physicians. Patients treated with revascularization were more likely to have angina by history, a positive exercise electrocardiogram, a lower exercise ejection fraction, two-vessel disease and proximal left anterior descending coronary artery disease. Two hundred sixty-four of the 280 patients given medical therapy who had complete follow-up data formed the study group. Outcome was compared between patients with (n = 56) and without (n = 208) severe exercise-induced ischemia, defined by previously published criteria (work load < or = 600 kg-m/min, ST segment depression > or = 1 mm and decrease in ejection fraction with exercise).

RESULTS

During follow-up, there were 30 initial cardiac events (12 cardiac deaths and 18 nonfatal myocardial infarctions). There was no difference in the 5-year event-free survival rate: 91% in patients with and 87% in patients without severe ischemia (p = 0.89). There was no association between event-free survival and severe ischemia (chi 2 = 1.41, p = 0.24). The study had approximately 80% power at alpha = 0.05 to detect a 25% decrease in event-free survival in the group with severe ischemia. In addition, there was no association between severe ischemia and outcome if late revascularization was included as an event or if the total mortality rate (overall survival) was analyzed.

CONCLUSIONS

Severe exercise-induced ischemia fails to identify a high risk subgroup among patients with normal left ventricular function and one- or two-vessel disease who are treated initially with medical therapy.

Radionuclide angiography for risk stratification of patients with coronary artery disease

Radionuclide angiography has become an accepted diagnostic method that is relied upon for its rapid, accurate and quantitative capabilities to characterize LV function. This method will continue to be used extensively in the future for the evaluation of patients with CAD. In addition to its common use to measure LV function at rest, the application of radionuclide angiography to assess LV function during exercise has proven prognostic potential that can be used in the clinical decision-making process in patients with known or suspected CAD.

Silent myocardial ischemia

The documentation of abnormalities related to myocardial ischemia, whether symptomatic or silent, is of central importance. Whenever this information is available, it should be used in the overall assessment of the patient at risk for adverse outcome. The level of concern for treatment of CAD should be based on the risk implications associated with the ischemia-related abnormalities detected during objective testing rather than on the presence or absence of pain. The exercise stress test is still the single most useful test to begin the evaluation of a patient with an analyzable ST segment. In persons suspected of having CAD, the detection of ischemic-type ST-segment depression, at a low workload (e.g., < 120 beats/min or < 6.5 METS) of > 2 mm magnitude or persisting for more than 6 min implies high risk for adverse outcome. Asymptomatic ischemia during everyday activities, detected by Holter monitoring, in the high-risk patient, most probably adds additional risk beyond the risk of an abnormal stress test alone. Left ventricular imaging by two-dimensional echocardiography, RNA, angiogram, vest, etc, showing an ejection fraction > or = 40%, reversible wall motion abnormalities in multiple regions and redistribution defects or a failure to increase ejection fraction during exercise even if the patient remains asymptomatic, also imply high risk. The presence of any of these abnormal findings, regardless of symptoms, should therefore prompt as high a degree of concern as with ischemia-related signals associated with pain. Thus any therapy chosen should be directed toward elimination of transient ischemia, not just relief of symptoms that may or may not be ischemia related. If this course is chosen, the efficacy of the therapeutic regimen and possible progression of CAD should be assessed with follow-up testing for ischemia. We believe that risk factor modification and aspirin should be considered for most, if not all, patients in whom ischemia, silent or symptomatic, is suspected or detected. If symptoms or ischemia suggesting low risk is present, anti-ischemic medical therapy may be considered, but follow-up is advised. If a high-risk ischemic signal, even without symptoms, is detected, medical therapy should be used to attempt to modify the signal. If the ischemic signal suggesting high risk persists despite medical therapy, revascularization should be considered. Until additional data from large clinical trials are available, this approach appears to have the greatest likelihood of modifying the adverse outcome of CAD.

Prognostic implications of myocardial ischemia during daily life in low risk patients with coronary artery disease

OBJECTIVES

The purpose of this study was to determine the incidence and prognostic importance of myocardial ischemia detected by ambulatory monitoring in low risk, medically managed patients with coronary artery disease.

BACKGROUND

Previous studies have demonstrated that certain high risk subsets of patients with coronary artery disease have improved survival with revascularization. The remaining low risk medically managed patients may still have episodes of silent ischemia during daily living, but the frequency and prognostic implications of such episodes in this group are unknown.

METHODS

We prospectively studied the incidence and prognostic significance of ST segment changes recorded during daily activities in 116 asymptomatic or mildly symptomatic low risk patients with native coronary artery disease who were followed up for 29 +/- 13 months. Low risk patients were selected after excluding patients with 1) left main disease; 2) three-vessel coronary artery disease and left ventricular dysfunction at rest; 3) three-vessel disease and inducible ischemia during exercise; and 4) two-vessel disease, left ventricular dysfunction and inducible ischemia.

RESULTS

Forty-five patients (39%) had transient episodes of ST segment depression during 48-h electrocardiographic (ECG) monitoring (total 217 episodes, lasting 7,223 min, 82% of episodes silent). There were eight acute cardiac events (seven myocardial infarctions, one episode of unstable angina) and nine patients underwent elective revascularization. Seven of the eight acute events occurred in patients without silent ischemia during monitoring. Kaplan-Meier survival analysis revealed no significant differences in event-free survival from either acute or total events in subgroups with or without silent ischemia during ambulatory ECG monitoring. None of the clinical, treadmill exercise, radionuclide ventriculographic or cardiac catheterization variables were predictive of outcome by Cox multivariate proportional hazard function analysis. Analysis of coronary arteriograms before and after acute cardiac events revealed that in five of the six patients studied, acute occlusion occurred in a coronary artery different from the artery with the severest stenosis on initial angiography.

CONCLUSIONS

In patients categorized as at low risk on the basis of the results of cardiac catheterization and stress testing, silent myocardial ischemia during daily life was not uncommon, and its presence failed to predict future coronary events.

Relation between left ventricular function at rest and with exercise and silent myocardial ischemia

The prognostic value of radionuclide measures of left ventricular function at rest and exercise is well established. Some studies have suggested that the frequency and duration of silent ischemia during ambulatory monitoring provide similar prognostic information; however, studies comparing these two techniques have not been performed. This study examines the relation between left ventricular function at rest and exercise-induced ischemia assessed by radionuclide ventriculography with myocardial ischemia during ambulatory electrocardiographic (ECG) monitoring. Of the 155 patients with coronary artery disease studied, 88% had left ventricular dysfunction with exercise, defined as failure of the ejection fraction to increase by greater than 4% with exercise, and 33% of patients had left ventricular dysfunction at rest (ejection fraction less than 45%); 52% had transient episodes of ST segment depression during 48-h ambulatory ECG monitoring. Exercise-induced left ventricular dysfunction during radionuclide ventriculography was extremely sensitive (94%) in detecting patients with ischemic episodes during ambulatory ECG monitoring; however, only 55% of patients with exercise-induced left ventricular dysfunction had ST segment depression during ambulatory monitoring. Moreover, patients with left ventricular dysfunction at rest had a lower prevalence of transient episodes of ST segment depression (31%) than did patients with normal left ventricular function at rest (62%) (p = 0.008). The relation between prognostically important variables during exercise radionuclide ventriculography and the number and duration of transient episodes of ST depression was examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Silent myocardial ischemia after acute myocardial infarction

Silent ischemia after myocardial infarction has definite prognostic significance but should be interpreted within the context of other prognostic indicators. The rationale for therapeutic intervention is based on the prognostic implications of silent ischemia and the potentially deleterious effect of repeated episodes of ischemia on the integrity of the left ventricle. We measured parameters of ischemia in 20 patients who showed asymptomatic ischemic ST-T changes on exercise testing in the early phase after myocardial infarction. After diltiazem administration, a reduction of exercise-induced ST-T depression from 2.3 +/- 0.8 to 0.7 +/- 0.6 mm (p less than 0.01) occurred, and regional wall-motion score at exercise, determined by radionuclide angiography, improved significantly (p less than 0.02). These and other observations warrant further studies in which the duration, severity and frequency of the ischemic episodes should be quantified and correlated with prognosis after myocardial infarction.

Long-term variation in myocardial ischemia during daily life in patients with stable coronary artery disease: its relation to changes in the ischemic threshold

Long-term variation in the frequency of myocardial ischemia during daily activity in patients with coronary artery disease who do not experience symptomatic changes has not been documented. Because at one point in time, the magnitude of such ischemia is strongly related to the ischemic threshold measured during exercise testing, this study was undertaken to determine whether patients with stable coronary artery disease show long-term variations in the frequency and duration of myocardial ischemia and to establish whether such variability is related to parallel changes in the ischemic threshold during exercise testing. Forty consecutive patients (mean age 61 +/- 8 years) who showed a stable clinical course over greater than or equal to 12 months were studied with a repeat exercise treadmill test and ambulatory electrocardiographic (ECG) monitoring after withdrawal of antianginal medications. The ischemic threshold was determined as the exercise time at 1 mm of ST segment depression. The mean interval to both follow-up evaluations was 15 +/- 3 months. Among the 23 patients with myocardial ischemia on ambulatory ECG monitoring at initial evaluation, the number and duration of ischemic episodes at follow-up were increased in 5 patients (mean increase 3.6 +/- 2 episodes and 123 +/- 98 min), unchanged in 1 patient and decreased in 17 patients (mean decrease 2.6 +/- 2 episodes and 98 +/- 72 min). Of the 17 patients without ischemic episodes at initial evaluation, 3 had evidence of ischemia on follow-up ambulatory ECG monitoring.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of myocardium at risk by technetium-99m sestamibi: correlation with coronary angiography

Previous studies have shown that tomographic perfusion imaging with technetium-99m sestamibi (RP-30A) can accurately measure the myocardium at risk during acute myocardial infarction. The ability of coronary angiography to predict the wide variability in myocardium at risk was studied in 21 patients with their first acute myocardial infarction. In blinded fashion, two experienced angiographers provided an overall "best estimate" of the percent of left ventricular myocardium at risk considering multiple angiographic variables--infarct-related artery, location of stenosis (proximal or nonproximal), vessel diameter, length, territory and the number and size of proximal branches and collateral vessels. Many of these individual variables showed a significant association with myocardium at risk. The most important angiographic variable was the mean best estimate of the two angiographers (r = 0.89, p less than 0.0001). However, the SEE was large (8.6% of the left ventricle) and angiography significantly (p less than 0.002) overestimated myocardium at risk. When patients with an anterior or an inferior infarct were considered separately, the angiographic best estimate had a weaker correlation with myocardium at risk measured by technetium-99m sestamibi in patients in both groups (anterior infarction r = 0.65, p = 0.04; inferior infarction r = 0.65, p = 0.04. Seven patients with an inferior infarct and myocardium at risk ranging from 7% to 32% of the left ventricle had identical angiographic best estimates. Although angiographic estimates correlate closely with measurements of myocardium at risk in groups of patients, their ability to predict the myocardium at risk in individual patients is limited.

Capabilities of supine exercise electrocardiography versus exercise radionuclide angiography in predicting coronary events

The ability of supine exercise electrocardiography and exercise radionuclide angiography to predict time to subsequent cardiac events (cardiac death, nonfatal myocardial infarction or late coronary bypass grafting or angioplasty) were compared in 265 patients with normal resting electrocardiograms who were not taking digoxin. All patients had undergone coronary catheterization and were initially treated medically. Follow-up study was performed at a median of 51 months. Separate logistic regression models, which had been previously developed to predict 3-vessel or left main coronary artery disease (CAD), were compared using a Cox regression analysis to predict time to a subsequent cardiac event. The exercise electrocardiography model, consisting of the magnitude of ST depression, exercise heart rate and patient gender, was a powerful predictor (chi-square = 30.8, p less than 0.0001) of subsequent events. The exercise radionuclide angiography model, which included the exercise response of the pressure-volume ratio in addition to the exercise electrocardiography variables, had similar prognostic power (chi-square = 31.8, p less than 0.0001). In a separate analysis considering only cardiac death and nonfatal myocardial infarction, the exercise electrocardiography model remained a significant predictor of events (chi-square = 12.2, p less than 0.001). None of the radionuclide angiography variables added significantly to the prognostic power of the exercise electrocardiography model. Thus, in patients with a normal resting electrocardiogram who are not taking digoxin, the supine exercise electrocardiography model that predicts 3-vessel or left main CAD also predicts future cardiac events. Exercise radionuclide angiography does not provide any additional prognostic information in such patients.

Comparison of exercise performance in left main and three-vessel coronary artery disease

From a consecutive series of patients who underwent rest and exercise radionuclide angiography over several years, we retrospectively identified 34 patients with left main coronary artery disease and 103 patients with three-vessel coronary artery disease who did not have significant left main disease. The results of gated equilibrium radionuclide angiography were compared in these 2 groups. Multiple exercise hemodynamic, exercise electrocardiographic, and exercise radionuclide angiographic parameters were considered in an attempt to separate the 2 groups. The only parameter that was significantly different between the 2 groups was exercise heart rate. However, no value of the exercise heart rate could meaningfully separate the 2 groups. Despite their known difference in prognosis, patients with left main and three-vessel disease had very similar exercise performance and could not be distinguished from one another by exercise electrocardiography or exercise radionuclide angiography. The inability to distinguish these two groups is a clear limitation of noninvasive exercise modalities.

Risk stratification of single or double vessel coronary artery disease and impaired left ventricular function using exercise radionuclide angiography

Patients with 3-vessel coronary artery disease (CAD) and normal left ventricular (LV) function have a worse prognosis if they manifest ischemia during exercise testing. The present study determines if exercise radionuclide angiography can aid in the risk stratification of patients with 1- or 2-vessel CAD and impaired LV function (ejection fraction less than 50%). Sixty-five consecutive patients with these findings were followed for a median duration of 24 months (range 12 to 49). Eleven of the 65 patients (17%) had severely ischemic exercise radionuclide angiograms, defined as: a decrease in ejection fraction with exercise; greater than or equal to 1.0 mm of ST-segment depression; and peak exercise workload less than or equal to 600 kg-m/min. During follow-up 11 patients had initial significant cardiac events: 4 cardiac deaths, 1 cardiac arrest, 4 myocardial infarctions and 2 bypass or angioplasty procedures for unstable angina greater than or equal to 3 months after the exercise study. Four of 11 patients (36%) with severely ischemic exercise radionuclide angiograms had events, compared to 7 of 54 patients (13%) without ischemic radionuclide angiograms. Event-free survival at 18 months was 73% for patients with severe exercise ischemia versus 92% for those without ischemia (p less than 0.05). Univariate analysis showed that severe ischemia on radionuclide angiography was the only variable of several tested that significantly predicted future cardiac events (chi-square = 8.16, p less than 0.005). Among patients with 1- or 2-vessel CAD and impaired resting LV function, severe ischemia on exercise radionuclide angiography identifies a subgroup at high risk for future cardiac events.