Use of Invasive Cardiac Procedures in Unstable Angina
October 1, 1998 6 minutes read
Use of Invasive Cardiac Procedures in Unstable Angina
ABSTRACT & COMMENTARY
Synopsis: A routine invasive strategy may not be appropriate and suggests that catheterization for individuals for unstable angina or non-Q-wave myocardial infarction might be reserved only for individuals with recurrent ischemia or in subsets where revascularization is clearly beneficial.
Source: Yusuf S, et al. Lancet 1998;352:507-514.
In recent years, there has been an increasing dialogue and focus on how best to care for patients with coronary artery disease vis-à-vis medically conservative therapy or aggressive/invasive. This large registry database report adds additional information and some fuel to the controversy that variation in the use of angiography and revascularization does not necessarily account for differences in clinical outcome. Yusuf and the Oasis Trial (Organization to Assess Strategies for Ischemic Syndromes) Registry investigators examined seven-day and six-month morbidity and mortality in 8000 patients from six countries (Australia, Brazil, Canada, United States, Hungry, and Poland) who represented widely divergent use of cardiac catheterization and revascularization procedures. The goals of the study were to compare outcomes for patients with acute ischemic syndromes in countries with a more aggressive vs. more conservative approach, as well as to examine outcomes of patients admitted initially to facilities with and without cardiac catheterization laboratories. Ninety-five hospitals were involved, with consecutive eligible patients enrolled in 1995-1996. Major criteria for admission were an acute ischemic syndrome within 48 hours with ECG changes, or if without, prior documentation of coronary artery disease. Individuals with ST elevation were excluded. Primary end points included new myocardial infarction, refractory angina, stroke, and major bleeding. A sophisticated set of statistical analyses were used, in part to compensate for the marked variation in characteristics of the six countries. Baseline characteristics were roughly comparable among the countries; the United States had the lowest enrollment (918 patients), and Australia had the largest (1899 patients); 40% were women, and the large majority were admitted with the diagnosis of unstable angina. Approximately 90% had an abnormal ECG; 28-50% had a prior myocardial infarction. In-hospital drug treatment included heparin in the majority, aspirin in almost all, beta blockers in 50-70%, and nitrates in 80%. Approximately half the patients received a calcium antagonist. As expected, rates of angiography and revascularization were widely variable with Brazil and the United States having the greatest use of catheterization. Approximately 60% of enrollees from these countries underwent angiography, with 22% and 36% undergoing revascularization by one week, and another 27% and 12% having revascularization between seven days and six months, respectively. In the other countries, rates of angiography ranged from 2% in Poland to 35% in Canada, with revascularization rates substantially lower than in the United States and Brazil, both early and at six months. By six months, cumulative rates of angiography and revascularization remained approximately two-fold greater in Brazil and the United States than the other four countries, although major cardiovascular outcomes, such as death, MI, or stroke showed no correlation with the rates of cardiac catheterization. The overall rate of cardiovascular death or myocardial infarction within seven days was 4-5% in all countries and ranged between 6-7% between seven days and six months, without significant differences among the countries. However, stroke and major bleeding were slightly but significantly increased in the high angiography centers. Total revascularizations by six months were almost 50% in Brazil and the United States and ranged between 10-38% in the other six countries. Rates of refractory angina or readmission with unstable angina were substantially lower in the high angiography countries (P = 0.001).
When the data were examined by the availability of cardiac catheterization facilities, rates of catheterization and revascularization in the first week were much higher in hospitals with catheterization laboratories. At six months, the overall rate of catheterization and revascularization remained higher in these institutions. There were slightly lower rates of cardiovascular death or myocardial infarction both at seven days and in six months among patients admitted to hospitals without catheterization facilities (NS). Adjusted rates of refractory or unstable angina were greater in hospitals without catheterization facilities, although the overall rates of recombined outcome of death, myocardial infarction, stroke, or unstable angina were similar among both hospital categories. When patients were risk stratified by standard clinical parameters, rates of death, myocardial infarction, refractory angina, or stroke were no different among the three risk groups regardless of whether patients were treated in a hospital or cath without a cath lab. In fact, in the highest risk group, major clinical events were greater in hospitals with cath labs. The data demonstrate that revascularization procedures are directly linked to the proportion of individuals undergoing cardiac catheterization. On the other hand, major clinical events were slightly less in individuals who did not undergo cardiac catheterization, although significant angina was greater. Yusuf et al conclude that "there was no evidence of a better prognosis in countries with a more aggressive approach," and that "the availability of invasive facilities showed no evidence of a reduction in cardiovascular death or myocardial infarction." Furthermore, there is the interesting and unexpected observation that lower risk patients were more likely to undergo interventions. A tradeoff was noted with respect to refractory angina or readmission for unstable angina being less in catheterization patients but with some increase in excess of stroke and major bleeding. Yusuf et al discuss similarities of these data to several other important trials, such as TIMI-2, TIMI-3, RITA-2, and VANQWISH, as well as prior reports in the differences between procedure rates and outcomes after infarction in Canada and the United States. They conclude that a routine invasive strategy may not be appropriate and suggest that catheterization for individuals for unstable angina or non-Q-wave myocardial infarction might be reserved only for individuals with recurrent ischemia or in subsets where revascularization is clearly beneficial. Yusuf et al call for additional trials to address issues of appropriate patient selection, rates, and timing of angiography and unstable angina.
COMMENT BY JONATHAN ABRAMS, MD
These observations are of interest and add to the increasing clinical trial database that a routine angiographic approach is not necessarily best for patients. This is not to say that the intelligent use of angiography and revascularization is not a good strategy, but more that an "all comers" approach does not appear to be indicated in acute coronary syndromes. The clinical trial evidence from a variety of studies, including the recently published DANAFMI Trial, indicate that symptomatic or inducible ischemia are the key markers to pursue an aggressive approach, and that in the absence of ischemia in an individual who otherwise does not appear to be at high risk (e.g., multivessel disease, poor left ventricular function), careful clinical observation with appropriate risk stratification is adequate. Most studies that have compared an aggressive to a conservative approach have reached similar conclusions.
It should be noted that there is significant crossover to revascularization in many-if not most-of these trials, although not in the OASIS Registry Database. However, these data only extend to six months and do not necessarily predict the clinical status at one year or more. In fact, these patients do not appear to be at particularly high risk, with cardiovascular death or infarction rates at six months of 10-11%. In the high-risk group, the rate of death, MI, or stroke was substantially greater, although the intervention rate of angiography and revascularization was paradoxically less than in the low and intermediate risk groups. Topol, in an accompanying editorial comment, points out the problems of a registry database, with its insufficient patient characterization, and criticizes the admixture of unstable angina and non-Q-wave infarction. However, this is a common approach to clinical trials, and has been used by Topol. Furthermore, the total number of documented infarcts in the Oasis database was relatively modest (< 10%). Topol also stresses that stents and the new platelet IIbIII/a inhibitors were not used. It is unlikely that, even in the United States, there is yet widespread use of the new platelet inhibitors or ubiquitous stenting. Thus, the OASIS appear to represent the contemporary practices in a wide variety of countries and institutions.
In conclusion, it seems reasonable to demand clearcut clinical indications to proceed with angiography as opposed to a standard policy to catheterize all patients with unstable angina. In the United States, however, it appears that ischemia-driven decisions for catheterization are not the rule, and, as documented in Oasis and prior observations, lower risk rather than higher risk patients tend to get angiography and revascularization. The robust discussions that are now going on with respect to medical vs. aggressive therapy are useful. As good physicians are aware, this is somewhat of an artificial construct; excellent clinical practice integrates both approaches, with clinical decision making based on careful risk stratification.
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