Different mechanisms for the relief of angina after coronary bypass surgery. Physiological versus anatomical assessment

Thallium scintigraphy in prediction of occlusion of bypass grafts in asymptomatic and symptomatic patients

To evaluate thallium scintigraphy in predicting coronary artery bypass graft patency, exercise thallium scintigraphy and selective graft and native vessel angiograms were performed in 22 asymptomatic and 29 symptomatic consecutive patients three months after coronary artery bypass grafting (CABG). Twelve out of 22 asymptomatic patients (55%) had reversible thallium defects on postoperative images; in 10 patients the postoperative scans were normal. The graft patency was significantly lower in asymptomatic patients with abnormal thallium perfusion compared to those with normal perfusion after CABG (68% vs. 91%, p less than 0.05). The rate of graft patency in symptomatic patients was 66/87 (76%). Thallium scintigraphy was 77% sensitive and 78% specific in detecting one or more stenosed or occluded bypass grafts in patients without angina (accuracy 77%). When data from exercise electrocardiography were combined with scintigraphy, all but one patient with incomplete revascularization could be detected (positive predictive accuracy 92%). In symptomatic patients, thallium scintigraphy accurately predicted the presence or absence of graft occlusion in 24/29 (83%) cases. Thus, abnormal myocardial perfusion due to stenosis or occlusion of bypass grafts is common in both asymptomatic and symptomatic patients after CABG. Thallium scintigraphy together with exercise electrocardiography appear to be useful non-invasive methods in detecting painless myocardial ischemia and in predicting bypass graft occlusion after CABG.

Myocardial Ischemia after Coronary Bypass: Comparison of Trimetazidine and Diltiazem

The aim of this prospective randomized study was to evaluate the effect of trimetazidine and diltiazem on persistent myocardial ischemia, mostly silent myocardial ischemia, after coronary artery bypass graft surgery. Sixty patients were divided into three groups of 20 each and followed up for 12 months. Patients in all 3 groups received acetylsalicylic acid 100 mg per day, those in group 1 also had trimetazidine 60 mg per day, and those in group 2 had diltiazem 90 mg per day. Each patient had coronary angiography during the first 3 weeks after surgery, 24-hour ambulatory monitoring every month, and cardiac scintigraphy at 3 weeks, 6 months, and 12 months. Ischemic episodes had resolved at 27 weeks in group 1, at 35 weeks in group 2 and at 51 weeks in group 3 (p < 0.05). Perfusion defects had resolved in the trimetazidine group at 6 months. At 12 months, perfusion defects had resolved in the diltiazem group but not in the group receiving only acetylsalicylic acid (p < 0.05). At these doses, trimetazidine and diltiazem were effective in decreasing silent myocardial ischemia following coronary artery bypass grafting. Trimetazidine appeared to be superior to diltiazem at 6 months on 24-hour ambulatory electrocardiogram monitoring and myocardial scintigraphy.

Effects of treatment strategies to suppress ischemia in patients with coronary artery disease: 12-week results of the Asymptomatic Cardiac Ischemia Pilot (ACIP) study

OBJECTIVES

The Asymptomatic Cardiac Ischemia Pilot (ACIP) study was initiated to determine the feasibility of a large trial in evaluating the effects of treatment of ischemia on outcome (mortality and myocardial infarction). The study was designed to examine the effects of medical treatment to control angina compared with treatment strategies guided by ambulatory electrocardiographic (ECG) ischemia or coronary anatomy.

BACKGROUND

Treatments to suppress ischemia (asymptomatic and symptomatic) have not been evaluated in a large prospective, randomized trial. Before undertaking such a trial, issues about recruitment and treatment strategies must be addressed.

METHODS

The 618 enrolled patients had coronary artery disease suitable for revascularization, ischemia on stress test and asymptomatic ischemia on ambulatory ECG. Patients were assigned randomly to one of three treatment strategies: 1) angina-guided medical strategy with titration of anti-ischemic medication to relieve angina (angina-guided strategy); 2) angina-guided plus ambulatory ECG ischemia-guided medical strategy with titration of anti-ischemic medication to eliminate both angina and ambulatory ECG ischemia (ischemia-guided strategy); and 3) revascularization by angioplasty or bypass surgery (revascularization strategy).

RESULTS

Ambulatory ECG ischemia was no longer present at the week 12 visit in 39% of patients assigned to the angina-guided strategy, 41% of patients assigned to the ischemia-guided strategy and 55% of patients assigned to the revascularization strategy. All strategies reduced the median number of episodes and total duration of ST segment depression during follow-up ambulatory ECG monitoring. Revascularization was the most effective strategy. Treadmill test results were concordant with those of ambulatory ECG monitoring. For most patients in the two medical strategies, angina was controlled with low to moderate doses of anti-ischemic medication, and the majority of patients (65%) in the revascularization strategy did not require medication for angina.

CONCLUSIONS

This pilot study demonstrated that cardiac ischemia can be suppressed in 40% to 55% of patients with either low or moderate doses of medication or revascularization and that a large trial is feasible.

Asymptomatic and electrically silent myocardial ischemia during upright leg cycle ergometry and treadmill exercise (clandestine myocardial ischemia)

The frequency of "clandestine" (electrically silent and asymptomatic, but scintigraphically evident) myocardial ischemia during treadmill and upright leg cycle ergometric studies was compared in 38 patients with coronary artery disease and reversible ischemia on both thallium-201 scintigraphy and exercise radionuclide angiography. A similar peak double product was attained in both studies. Angina pectoris was significantly more frequent with treadmill exercise than with leg cycling (29 vs 5%, p = 0.0079). An interpretable and positive exercise electrocardiogram occurred in 53% of treadmill tests, but in only 19% of leg cycle tests (p = 0.0025); in a group of 22 patients without scintigraphic ischemia, leg cycle testing had greater specificity (95 vs 64%, p = 0.0248). Ischemia was manifest by symptoms or an abnormal electrocardiogram in 59% of treadmill tests, but in only 18% of leg cycle tests (p = 0.0003). There were no differences between the exercise variables or the degree of scintigraphic abnormalities of the 22 patients with manifest ischemia and the 16 with clandestine ischemia. However, patients with previous coronary artery bypass surgery experienced clandestine ischemia more frequently than did those without bypass surgery (80 vs 33%, p = 0.0103). Thus, clandestine ischemia occurs more frequently during symptom-limited upright leg cycle ergometry (82%) than during treadmill exercise (42%). The symptomatic and electrical manifestations of exercise-induced ischemia have a critical dependence on the type of exercise used.

Digital dipyridamole stress echocardiography in silent ischemia after coronary artery bypass grafting and/or after healing of acute myocardial infarction

This study evaluates dipyridamole stress echocardiography in silent ischemia. Fourteen patients with previous coronary artery bypass grafting (group A) and 16 patients with healed myocardial infarction (group B) were studied. All had > or = 1 mm ST depression without chest pain during bicycle exercise testing. Left ventricular wall motion was analyzed using a computerized display of digital systolic cineloops with a high frame rate. Test results were compared with coronary angiography. Dipyridamole echocardiography accurately identified patients with significant coronary artery stenosis in both groups (3 of 4 in group A, 11 of 14 in group B). Retrograde flow to the occluded native artery was associated with positive results on dipyridamole testing in 6 of 7 patients in group A and all 3 in group B. Sensitivity, specificity and diagnostic accuracy for detecting significant coronary stenosis or occlusions with retrograde flow was 78, 100 and 83%, respectively. Patients with angiographic multivessel disease had a significantly larger increase in wall motion score index during dipyridamole stress than patients with 0- or 1-vessel disease, 0.18 +/- 0.11 versus 0.05 +/- 0.18 (p < 0.05). Two patients developed symptomatic bradycardia and hypotension during dipyridamole infusion. It is concluded that dipyridamole echocardiography accurately identifies myocardial regions with restricted coronary flow. Stress echocardiography is a valuable tool for assessing coronary flow in silent ischemia.

Total ischemic burden in patients with coronary artery disease

In patients with coronary artery disease, angina pectoris provides an unreliable underestimation of disease activity and risk. Unheralded myocardial infarction and sudden death are common clinical presentations. Furthermore, objective testing, in hospital and more recently during the patient's normal daily activities, has demonstrated frequent and asymptomatic episodes of ischemia, as indicated by transient ST-segment depression. Since the underlying pathophysiologic disturbances of myocardial perfusion appear to be similar in painful and painless episodes, it seems appropriate to consider them together as the "total ischemic burden" on the myocardium. Research into this functional expression of coronary disease has indicated that active ischemia is associated with an increased risk of morbid events in all clinical subgroups of patients, including those with stable angina, unstable angina, peripheral vascular disease and following myocardial infarction. If this is confirmed in prospective trials, the assessment of total ischemic burden is likely to become part of the clinical investigation of patients with coronary disease. Clinical trials testing the efficacy of interventions will need to examine the effect on ischemic activity during normal daily life, in addition to symptoms and exercise tolerance. Evidence is still required to demonstrate whether therapy aimed at reducing the total ischemic burden will prolong life. The total ischemic burden provides a marker to follow the dynamic changes of the atherosclerotic lesion. Future research may have to concentrate on treatment aimed at altering the natural history of obstructive coronary atherosclerosis in order to affect the long-term outlook for patients with coronary artery disease.

Relation of silent myocardial ischemia after coronary artery bypass grafting to angiographic completeness of revascularization and long-term prognosis

The prevalence and characteristics of silent myocardial ischemia as detected by 24-hour ambulatory electrocardiography ST-segment depression were prospectively assessed in 94 patients examined early (1 to 3 months) and 184 patients examined late (12 months) after coronary artery bypass grafting (CABG), and followed for a mean of 48 +/- 11 (range 4 to 62) months. The relation of ambulatory electrocardiographic silent ischemia to evidence of completeness of revascularization as defined by cardiac angiography performed 1 and 12 months after CABG, and to prognosis by follow-up of adverse clinical events was analyzed. Silent ischemia was detected early in 20% (19 of 94) and late in 27% (50 of 184) of patients, and showed a mean frequency of episodes ranging from 6 to 10 episodes/24 hours with a mean duration ranging from 15 to 23 minutes. The circadian distribution of episodes disclosed a significant peak of ischemic activity during the period of 6 A.M. to noon and a secondary peak between 6 P.M. and midnight (p less than 0.01 and p less than 0.001, respectively). Silent ischemia was not found by univariate analysis to be associated with graft or anastomotic site occlusions, low graft flow rates, grafted arteries with significant distal residual stenoses or ungrafted stenotic native coronary arteries. Kaplan-Meier analysis of time to cardiac event showed that silent ischemia was not predictive of an adverse clinical event in the early years after CABG. Cox regression analysis of 30 covariates only disclosed age (relative risk 1.06 [95% confidence interval, 1.01 to 2.94]) as having an effect on time to adverse clinical event.(ABSTRACT TRUNCATED AT 250 WORDS)

Planar positron imaging of rubidium-82 for myocardial infarction: a comparison with thallium-201 and regional wall motion

Rubidium-82 (Rb-82) is a generator-produced, short half-life (76 seconds) positron emitting potassium analog. Using a mobile gamma camera equipped with a rotating tungsten collimator and high-energy shielding, we examined the use of Rb-82 in the coronary care unit and clinical laboratory for detection of perfusion defects due to myocardial infarction. We studied 31 subjects, 10 patients with acute myocardial infarction, 12 with remote myocardial infarction, and nine controls. Rb-82 images were compared with Tl-201 and regional wall motion for detection of infarct-related arteries. Of the 22 patients with myocardial infarction, 16 were identified with Rb-82 and Tl-201. In nine control subjects, eight were normal with each method. Correlation between Rb-82 and Tl-201 defect scores was excellent. Sensitivity and specificity for infarct-related arteries were similar for Rb-82, Tl-201, and wall motion imaging. Thus planar Rb-82 imaging can detect MI reliably in the coronary care unit and in the clinical laboratory.

Ambulatory (Holter) electrocardiography and myocardial ischemia

Ambulatory (Holter) electrocardiography has evolved over the past two decades to allow accurate assessment of the cardiac rhythm, and more recently, accurate detection and measurement of ST segment changes. These ambulatory ECG ST segment changes that occur with and without symptoms, although thought to be of questionable clinical value for many years, have recently been clearly documented in coronary artery disease patients to represent true myocardial ischemia. Concurrent with these technologic developments has been an evolution of the pathophysiologic understanding of myocardial ischemia, and the relative role and sequential nature that ECG ST segment changes have in its development. This review examines from a clinical perspective the current understanding of the pathophysiologic sequence of development of myocardial ischemia, emphasizes the ECG diagnostic methods that detect this sequential change, examines the criteria that define ambulatory ECG myocardial ischemia, and discusses those nonischemic factors that affect the ECG ST segment and its interpretation. Moreover, an ever increasing number of ambulatory ECG studies of coronary artery disease and normal patients have defined unique characteristics of the ambulatory ECG ST segment changes observed with regard to its diagnostic, prognostic, and therapeutic assessment value in the study of myocardial ischemia.

Asymptomatic myocardial ischemia as a predictor of cardiac events after coronary artery bypass grafting for stable angina pectoris

Thirty-six patients with chronic stable angina were studied before and after coronary artery bypass grafting (CABG) to assess the prevalence and prognostic implications of asymptomatic myocardial ischemia obtained by ambulatory monitoring. Ambulatory monitoring performed during medical therapy before CABG detected 66 episodes of transient ischemia, 54 (82%) being asymptomatic. All patients were asymptomatic or with minimal symptoms 3 months after CABG. Additional ambulatory monitoring was performed for 36 hours. There were 39 episodes of silent ischemia detected in the 12 patients of group 1, whereas no episodes of ST-segment shift occurred in the 24 patients of group 2. Coronary artery bypass grafting reduced the frequency of transient ischemia by 41% (p less than 0.05) compared with medical therapy, whereas the number of ischemic episodes in group 1 increased from 23 during medical therapy to 39 episodes after CABG (41%, p less than 0.05). During a follow-up of 9 months, 8 cardiac events occurred: 6 in group 1 comprising sudden death (1), revascularization (2), and angina (3) and 2 in group 2, including revascularization (1) and angina (1) (p = 0.005). Kaplan-Meier analysis demonstrated that asymptomatic myocardial ischemia was correlated with a significant cumulative probability of cardiac events (p less than 0.025) and multivariate analysis of 11 variables showed that silent ischemia was the most powerful predictor of cardiac events (p less than 0.005). Silent ischemia was a forerunner for angina pectoris in some patients, whereas angina did not occur during the follow-up period in others. This study does not reveal whether or not these patients are at higher risk for cardiac events during long-term follow-up.

The efficacy of cardiovascular nuclear medicine exercise studies

Radionuclide stress tests were initially introduced into medicine as new diagnostic tests for coronary artery disease (CAD). These tests are very effective for this purpose when applied to populations with an intermediate pre-test probability of coronary artery disease. Radionuclide stress tests, however, also are used now in guiding many management decisions in patients with established CAD, based on the ability of these tests to assess the extent and severity of myocardial ischemia, the functional significance of coronary stenoses, and myocardial viability. Specific uses beyond diagnosis include decisions regarding whom to catheterize, send to coronary bypass surgery, or angioplasty; risk stratification following myocardial infarction or before noncardiac surgery; and evaluation of the results of therapy. This article reviews both the diagnostic efficacy of radionuclide stress tests and their efficacy in guiding management decisions in patients with known coronary artery disease.

Holter monitoring in assessment of angina pectoris

Holter monitoring of ST-segment changes is a unique method of studying the character of transient myocardial ischemia that occurs during ordinary daily life. The electrocardiographic signal is a reliable marker of ischemia in defined populations of patients with angina and coronary disease, but should be interpreted with caution outside of these groups. Detailed studies in patients with chronic stable angina have shown that transient ischemia is frequently silent and prolonged, and may occur without evidence of physical exertion. Analysis of underlying changes in regional myocardial perfusion using rubidium-82 and positron tomography has shown that a decrease in myocardial perfusion (supply) is involved in the genesis of many episodes of ischemia during daily life. Clinical trials have shown that drugs that affect demand and supply are efficacious against both painful and painless ischemia and that combinations of agents can provide useful benefits. There is, however, marked natural variability in disease activity despite "stable" symptoms, which must be taken into account in individual patient assessment and the rational design of clinical trials. Ambulatory monitoring permits quantitation of previously unrecognized myocardial ischemia, and treatment can thus be assessed in terms of ischemic activity during everyday life rather than on data obtained during brief hospital visits. An active approach to the detection and monitoring of transient ischemia with and without pain will be necessary if prospective clinical research shows that treatment of silent myocardial ischemia can prevent myocardial damage and improve prognosis.

Clinical significance of exercise-induced silent myocardial ischemia in patients with coronary artery disease

Exercise-induced silent myocardial ischemia is a frequent feature in patients with coronary artery disease. The purpose of this study was to compare the clinical and angiographic characteristics of 269 patients who complained of chest pain during an exercise test (group I) with those of 204 who developed exercise-induced silent myocardial ischemia (group II). Group I patients more frequently had anginal symptoms of class III and IV of the Canadian Cardiovascular Society than did group II patients, who had milder symptoms (p less than 0.001). The only angiographic difference observed between the two groups was a slightly but significantly higher left ventricular end-diastolic pressure in group II patients (p less than 0.05), who also showed a longer exercise duration (p less than 0.01) with a higher heart rate-systolic pressure product (p less than 0.01) and more pronounced ST segment depression at peak exercise (p less than 0.001). Moreover, ventricular ectopic beats during exercise were more frequently observed in group II patients (p less than 0.05). Coronary bypass surgery was performed in 45% of patients of group I and in 24% of patients of group II (p less than 0.05). Survival curves of medically treated patients did not show any statistically significant difference between the two groups. Thus, although patients with a defective anginal warning system may have more pronounced signs of myocardial ischemia and a greater incidence of ventricular arrhythmias during exercise, their long-term prognosis is not different from that of patients who are stopped by angina from the activity that is inducing myocardial ischemia.

Character of transient ischemia in angina pectoris

There is growing interest in the possible therapeutic and prognostic significance of silent myocardial ischemia in coronary artery disease (CAD) and its detection by ambulatory electrocardiographic (ECG) monitoring. In 100 apparently healthy normal subjects (20 with angiographically normal coronary arteries), Holter monitoring revealed significant ST-segment depression in only 2 (both over 40 years, one with positive treadmill test, the other with risk factor for CAD). No significant ECG changes were found in those with normal coronary vessels. In 30 patients with documented CAD, significant ST-segment depression during 1,934 episodes over 446 days of monitoring over 18 months was found. Only 24% of the episodes were associated with angina. Asymptomatic and symptomatic episodes were associated with comparable changes in perfusion detected by positron emission tomography. Heart rate increases greater than 10 beats/min preceding the onset of the ST-segment changes occurred in only 23% of the episodes. There was considerable variability in the ST-segment changes in the same patient monitored serially over long periods of time. The data indicate that it is extremely uncommon for patients without CAD to exhibit silent myocardial ischemia, whereas patients with stable angina exhibit frequent, variable and often asymptomatic ECG evidence of myocardial ischemia rarely triggered by increases in heart rate. These findings are likely to be of therapeutic and prognostic significance.

Dynamic 123I-HDA myocardial scintigraphy after aortocoronary bypass grafting

In an attempt to evaluate the dynamics of fatty acid metabolism after aortocoronary bypass grafting (ACBG), ten patients were investigated after ACBG by 123I-HDA myocardial scintigraphy. Tracer kinetics were followed for 90 min and compared to those of 36 nongrafted patients with different underlying heart diseases, including healthy volunteers. Regional analysis and monoexponential curve fitting were used to evaluate t1/2 (half-life of the early period of tracer elimination); biexponential curve analysis was used to calculate Ca/Cb, the ratio of a fast and a slow component of tracer elimination. Rest and stress MUGA-RNV served as discriminating parameters to discern between patient groups with normal and abnormal ventricular function. Group I (normal controls) encompassed ten patients with normal ventricular function, including three after ACBG, and group II seven patients after ACBG and with abnormal ventricular function. Group III had coronary artery disease (CAD) documented by angiography, and group IV by prior myocardial infarction (MI). Group V included patients with cardiomyopathy (CMP). Regional analysis of group II revealed no significant differences to control regions (Gr I) for t1/2 or Ca/Cb, but showed for Ca/Cb a nonsignificant shift toward group III values. However, group II differed significantly from group III and V. Three patients with normal ventricular function after ACBG showed elimination values that were all well within the range of completely normal individuals. Thus our data support the assumption that a normal function is indicative of a normal metabolism. Following myocardial fatty acid metabolism during rest might be a helpful noninvasive tool for etiologic differentiation of disturbed ventricular function.