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Use of Risk Stratification to Identify Patients with Unstable Angina Likeliest to Benefit from an Invasive Versus Conservative Management Strategy Solomon DH, Stone PH, Glynn RJ, et
al. J Am Coll Cardiol 2001; 38:969-76
Background: There is an ongoing debate on how to best treat patients presenting with unstable angina or non-Q-wave myocardial infarction (NQMI). The VANQWISH (Veterans Affairs Non-Q-Wave Infarction Strategies in Hospital) trial suggested that an early invasive approach might be harmful (Boden WE et al. N Engl J Med 1998; 338:1785-92). On the other hand, the FRISC-II (Fast Revascularization during Instability in Coronary Artery Disease) (Lancet 1999; 354:708-15) and TIMI-18 trials (Cannon CP et al. N Engl J Med 2001; 344:1879-87) came to the opposite conclusions. With the debate unsettled, the American College of Cardiology/American Heart Association guidelines for management of acute coronary syndromes allow wide latitude in determining who may be appropriate for an early invasive therapy (Braunwald E et al. Circulation 2000; 102:1193-209). The authors of the current study hypothesized that the reason for the inconsistent results of the large clinical trials might be that not all patients with acute coronary syndrome are at equal risk for cardiac events and clinical factors at initial presentation may help categorize such patients and help determine the optimal management for each patient. Methods: The authors performed a retrospective analysis of data collected during the Thrombolysis In Myocardial Infarction (TIMI) IIIB trial. The TIMI-IIIB trial was a randomized, prospective trial of patients with unstable angina or NQMI, comparing early invasive management and conservative medical management in improving cardiac outcome. Whereas patients in the invasive arm of the study underwent cardiac catheterization and other interventions within 48 hours of enrollment, patients in the conservative arm had cardiac catheterization and revascularization only if there was evidence of ongoing ischemia despite maximal medical therapy, consisting of bed rest, oxygen, beta-adrenergic blockade, a calcium channel blocking agent, a nitrate, heparin, and aspirin. The trial enrolled 1,473 patients, mostly white, middle-aged, and male. Using MI or death within 42 days as the primary outcome, various clinical factors on presentation were examined for their predictive value. Predictive factors with P values < 0.2 on the initial analysis were then entered into a multivariate analysis and those variables with P values > 0.2 in the multivariate analysis were removed. Variables with odds ratios (OR) > 1 in the multivariate analysis were assigned risk scores: 1 point for OR of 1.01 to 1.5, 2 points for OR of 1.51 to 2.0, etc. The risk scores were then summed up to create five categories of risk-stratification from very low to very high. All patients were stratified according to their risk categories and treatment assignment (invasive vs. conservative) and the 42-day and 365-day MI or death rate in each group was examined. Results: The final multivariate model included advanced age (1 point for age 51-59, 3 points for 60-69, and 5 points for ³ 70), ST segment depression ³ 0.1 mV in at least two contiguous leads (2 points), creatine kinase MB fraction ³ 5 IU/ml (1 point) and a history of complicated angina within 2 months (2 points). Complicated angina was defined as rest, nocturnal, accelerated, or prolonged (> 20 min) episodes of angina. Within each treatment arm, higher risk scores predicted higher 42-day and 365-day cardiac event rates. For patients with risk scores ³ 7, the early invasive strategy led to significantly lower cardiac event rates than the conservative strategy. On the other hand, for patients with risk scores < 7, there was no significant difference between the different treatment arms. Comments: As the authors themselves point out, there were several limitations to the study. First, the study was a retrospective analysis of a trial previously carried out and the subgroups in the study were defined post hoc. Second, the TIMI-IIIB trial took place from 1989 to 1992, when the medical regimen did not include the use of glycoprotein IIb/IIIa inhibitors or low molecular-weight heparin and coronary stenting was not used in those who underwent cardiac catheterization. Inclusion of these modalities might affect the relative benefit of the medical vs. invasive treatment strategies. Despite these limitations, this study helps explain the conflicting results of the recent trials. The VANQWISH trial, which did not find an advantage with early invasive therapy, enrolled patients up to 72 hours after presentation, so that those patients with the most severe acute coronary syndrome, who would have been most likely to benefit from an early invasive intervention, might not have entered into the trial. On the other hand, the FRISC-II trial enrolled only patients with ST segment depression or elevated CK-MB, i.e., high-risk patients who are most likely to benefit from an early invasive management. Not surprisingly, they found a benefit from an early cardiac catheterization. In addition, this study provided a paradigm for stratifying patients with acute coronary syndromes. An application of the paradigm may be in stratifying patients with unstable angina or uncorrected coronary artery disease presenting for major noncardiac surgery. It is apparent that not all of these patients with uncorrected CAD will benefit from a cardiac catheterization and/or revascularization, prior to undergoing the proposed major noncardiac surgery. Correctly identifying those patients who will benefit from revascularization is important, since the immediate post-revascularization period may represent a high-risk period for subsequent noncardiac surgery (Kaluza GL et al. J Am Coll Cardiol 2000; 35:1288-94) and the noncardiac surgery may need to be delayed for a month or longer. A scheme for risk stratification may be developed and applied in order for the practitioner to selectively catheterize and revascularize a subgroup of patients with uncorrected CAD, while sending the rest directly to the noncardiac surgery. Table of Contents
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