Treatment strategies for daily life silent myocardial ischemia: A correlation with potential pathogenic mechanisms

[Significance of silent myocardial ischemia for identification and optimal therapy of patients with latent coronary heart disease. Is there a marker for prognostic indication for PTCA?]

Although percutaneous transluminal coronary angioplasty (PTCA) improves the symptomatic status and exercise capacity of patients with coronary artery disease and stale or unstable angina pectoris, a beneficial effect on long-term prognosis has not been convincingly demonstrated so far. In totally asymptomatic patients with coronary artery disease, however, decision to undertake PTCA is greatly influenced by prognostic considerations. Usually, detection of silent myocardial ischemia in non-invasive examinations (exercise stress testing, ambulatory electrocardiographic monitoring) precedes the angiographic diagnosis of coronary artery disease in these patients.

Improving care for unstable angina patients in a multiple hospital project sponsored by a federally designated quality improvement organization

In 1992, the Health Care Financing Administration (HCFA) implemented a major change in the methodology of the quality of care oversight activities conducted by Medicare Peer Review Organizations. The Health Care Quality Improvement Program (HCQIP) represented a shift in oversight activity direction from identifying and dealing with individual clinical errors to helping providers improve mainstream care. The change in the oversight activities of Peer Review Organizations has been so substantial that the organizations are now commonly referred to as Quality Improvement Organizations (QIOs). Since its introduction, the HCQIP has developed multiple cooperative projects between QIOs and participating hospitals to examine specific processes of care and to ultimately improve the quality of care provided to Medicare patients. This report describes one project in North Carolina focusing on inpatient treatment of patients with a principal diagnosis of unstable angina, one of the most frequent causes of hospital admissions for Medicare patients. Based on the guidelines for treating unstable angina issued by the Agency for Health Care Policy and Research, 5 measures of good medical care for these patients were selected as quality of care indicators. A total of 16 hospitals in North Carolina each provided medical records of approximately 50 Medicare patients discharged with a principal diagnosis of unstable angina. Our findings indicated that guidelines-recommended standard of care were met in only a minority of patients. These indicators of care--including ordering an electrocardiogram within the first hour of admission and admitting high-risk patients to the intensive care unit--all occurred in <50% of the patients. Moreover, use of drugs that improve outcomes in patients with unstable angina was lower than expected. Only 17% of eligible patients with unstable angina were discharged on a lipid-lowering medication. Although there was variation in compliance with the guidelines between types of hospitals, all hospitals had an opportunity to improve in at least one quality of care indicator. The data demonstrate that significant variances exist between published guidelines and actual practices. Given the high rates of readmission for patients with coronary disease, there is opportunity to improve compliance with recommended guidelines of good care. The new oversight activity direction taken by Medicare should ultimately improve care for more patients than could ever be achieved through individual case review.

Comparison of subgroups assigned to medical regimens used to suppress cardiac ischemia (the Asymptomatic Cardiac Ischemia Pilot [ACIP] Study)

This report focuses on the subset of 235 patients from the Asymptomatic Cardiac Ischemia Pilot (ACIP) study receiving randomly assigned medical therapy to treat angina and suppress ischemia detected on ambulatory electrocardiography: 121 patients received the sequence of atenolol and nifedipine, and 114 diltiazem and isosorbide dinitrate. After 12 weeks of therapy, the primary end point (absence of ambulatory electrocardiographic (ECG) ischemia and no clinical events) was reached in 47% of atenolol/nifedipine- versus 31% of diltiazem/isosorbide dinitrate-treated patients (adjusted p = 0.03). A trend to increased exercise time to ST depression was seen in the atenolol and nifedipine versus diltiazem and isosorbide dinitrate regimens (median treadmill duration 5.8 vs 4.8 minutes; p = 0.04). However, when adjusted for baseline imbalances in ambulatory ECG ischemia, the 2 medical combinations were similar in suppression of ambulatory ECG ischemia. In both medication regimens, an association between mean heart rate and ischemia on ambulatory electrocardiography after 12 weeks of treatment was observed so that patients on either regimen with a mean heart rate > 80 beats/min had ischemia detectable almost twice as often as those with a mean heart rate < 70 beats/min (p < 0.001).

Persistent transient myocardial ischemia despite beta-adrenergic blockade predicts a higher risk of adverse cardiac events in patients with coronary artery disease

OBJECTIVES

We evaluated the prevalence and prognostic significance of transient myocardial ischemia despite beta-adrenergic blockade in patients with coronary artery disease.

BACKGROUND

Persistence of transient ischemia despite therapy may correspond to a subset of high risk patients with coronary disease. The impact of beta-blocker withdrawal in these patients remains unknown.

METHODS

Patients (n = 313) with documented coronary artery disease and beta-blocker therapy, with (group I, n = 84) or without (group II, n = 229) transient ischemia on ambulatory electrocardiographic monitoring, were followed up during 21 +/- 9 months for cardiac events (death, myocardial infarction, percutaneous transluminal coronary angioplasty, coronary artery bypass surgery and worsening angina). Occurrence of events was compared by log-rank test.

RESULTS

The number of coronary stenoses did not differ significantly between groups I and II. Beta-blocker therapy was discontinued more frequently during follow-up in group II (25% vs. 14% in group I, p = 0.04). Cumulative percentage of death or myocardial infarction, or both, tended to be higher in group I a 30 months (17% vs. 5% in group II, p = 0.09). Coronary angioplasty and bypass surgery were significantly more frequent in group I (p = 0.01 and 0.0008, respectively). Transient ischemia was associated with a higher cumulative probability of adverse events (p = 0.004). The number of coronary stenoses, presence of transient ischemia and beta-blocker withdrawal were the only significant prognostic factors of cardiac events in the Cox model. In group I patients, the relative hazard of cardiac events was increased threefold when beta-blocker therapy was interrupted.

CONCLUSIONS

These data suggest that 1) the occurrence of transient ischemia despite beta-blocker therapy identifies a subset of high risk patients with coronary artery disease, and 2) the interruption of beta-blocker therapy increases the risk of adverse cardiac events.

Treatment of silent ischemia in unstable angina: a randomized comparison of sustained-release verapamil versus metoprolol

Silent ischemia is a frequent finding in patients with unstable angina and portends a poor prognosis. We compared the efficacy of sustained-release (SR) verapamil and metoprolol in reducing silent ischemia in patients with unstable angina and assessed whether detection of silent ischemia was related to unfavorable outcomes in the contemporary setting of concurrent therapy with heparin and aspirin. Holter monitoring (leads a VF, V2, V5) for the first 72 h was used to assess the frequency and duration of ST-shift episodes. There were 37 patients in the verapamil-SR group and 40 patients in the metoprolol group, with both groups having similar baseline characteristics. There were more episodes of angina in the verampamil-SR group (29 vs. 12, p = 0.05). There was no difference between the two groups in the frequency (51 vs. 49 episodes, p = 0.9) or duration (23 +/- 48 vs. 18 +/- 50 min, p = 0.6) of ST-shift episodes. There were 20 unfavorable in-hospital outcomes distributed equally between the two groups (p = 0.9). Patients with unfavorable outcomes had ST shift more often (50 vs. 28%, p = 0.07) and for a longer duration (40 +/- 69 vs. 13 +/- 38 min, p = 0.03). Patients with ST shift > or = 60 min had a 60% probability of unfavorable outcome compared with 33% for ST shift of 1-59 min duration and 20% for no ST shift (p = 0.04). We conclude that metoprolol appears to reduce symptoms better than verapamil-SR, but no difference in silent ischemia or unfavorable outcomes was seen. Silent ischemia remains a common occurrence in these patients despite heparin and aspirin therapy and its detection continues to have prognostic value.

Asymptomatic Cardiac Ischemia Pilot (ACIP) study: effects of coronary angioplasty and coronary artery bypass graft surgery on recurrent angina and ischemia. The ACIP investigators

OBJECTIVES

The Asymptomatic Cardiac Ischemia Pilot (ACIP) study showed that revascularization is more effective than medical therapy in suppressing cardiac ischemia at 12 weeks. This report compares the relative efficacy of coronary angioplasty or coronary artery bypass graft surgery in suppressing ambulatory electrocardiographic (ECG) and treadmill exercise cardiac ischemia between 2 and 3 months after revascularization in the ACIP study.

BACKGROUND

Previous studies have shown that coronary angioplasty and bypass surgery relieve angina early after the procedure in a high proportion of selected patients. However, alleviation of ischemia on the ambulatory ECG and treadmill exercise test have not been adequately studied prospectively after revascularization.

METHODS

In patients randomly assigned to revascularization in the ACIP study, the choice of coronary angioplasty or bypass surgery was made by the clinical unit staff and the patient.

RESULTS

Patients assigned to bypass surgery (n = 78) had more severe coronary disease (p = 0.001) and more ischemic episodes (p = 0.01) at baseline than those assigned to angioplasty (n = 92). Ambulatory ECG ischemia was no longer present 8 weeks after revascularization (12 weeks after enrollment) in 70% of the bypass surgery group versus 46% of the angioplasty group (p = 0.002). ST segment depression on the exercise ECG was no longer present in 46% of the bypass surgery group versus 23% of the angioplasty group (p = 0.005). Total exercise time in minutes on the treadmill exercise test increased by 2.4 min after bypass surgery and by 1.4 min after angioplasty (p = 0.02). Only 10% of the bypass surgery group versus 32% of the angioplasty group still reported angina in the 4 weeks before the 12-week visit (p = 0.001).

CONCLUSIONS

Angina and ambulatory ECG ischemia are relieved in a high proportion of patients early after revascularization. However, ischemia can still be induced on the treadmill exercise test, albeit at higher levels of exercise, in many patients. Bypass surgery was superior to coronary angioplasty in suppressing cardiac ischemia despite the finding that patients who underwent bypass surgery had more severe coronary artery disease.

Nitrates in silent ischemia

In recent years it has become clear that episodes of transient myocardial ischemia commonly occur in patients with coronary artery disease in the absence of chest pain or angina equivalent. These episodes of "silent myocardial ischemia" are particularly well documented during continuous ambulatory electrocardiographic monitoring in daily life. Evidence suggests that these episodes represent true ischemia, and appear to be a marker of unfavorable outcome. While the pathophysiology is not completely understood, it appears as though the mechanisms of angina and silent ischemia are the same. Both forms of ischemia respond to conventional antianginal medication. While long-acting nitrates are effective in reducing or preventing myocardial ischemia, because of their propensity to cause tolerance they should be used intermittently and in association with either beta-blockers or calcium antagonists. Nitrates are safe and comparatively inexpensive, and will continue to play an important role in the treatment and prevention of angina. However, in the light of current knowledge, there is no specific indication for the treatment of silent ischemia by nitrates.

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.

Effect of metoprolol and diltiazem on the total ischaemic burden in patients with chronic stable angina: a randomized controlled trial

We conducted a randomised controlled trial to study the effects of metoprolol and diltiazem on the total ischaemic burden--sum of symptomatic and silent myocardial ischaemia, in 146 patients with stable angina pectoris. One-hundred thirty-four completed the study protocol. Sixty-eight patients received metoprolol (100 mg twice daily, n = 52, 50 mg twice daily, n = 16) while 66 received diltiazem (90 mg three times daily, n = 50, 60 mg three times daily, n = 16). The drugs were given for 4 weeks. The primary outcome variables were frequency and duration of total ischaemic burden, silent and symptomatic myocardial ischaemia. These were measured on 48 h of Holter monitoring. The reductions in duration and frequency of total ischaemic burden by metoprolol, 76% and 40%, respectively, were significantly higher than by diltiazem, 43% and 24%, respectively (P < 0.01 and P < 0.02). The frequency and duration of silent myocardial ischaemia, which constituted more than 80% of the total ischaemic burden in the two groups showed similar results. However, the reduction in frequency of symptomatic myocardial ischaemia only was significantly greater by metoprolol (63% than diltiazem (24%) as the difference in reduction of duration of symptomatic ischaemia was insignificant (85% vs. 75%; P > 0.05). Whether a greater reduction of total ischaemic burden by metoprolol as compared to diltiazem has any implications for prognosis in patients with chronic stable angina remains to be established.

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.