"Routine invasive" versus "selective invasive" approaches to non–ST-segment elevation acute coronary syndromes management in the post-stent/platelet inhibition era
William E. Boden, MD, FACC*
,*,1
* Division of Cardiology and the Henry Low Heart Center at Hartford Hospital, Hartford, Connecticut, USA
Department of Medicine, University of Connecticut School of Medicine, Farmington, Connecticut, USA
Manuscript received May 31, 2002;
accepted December 11, 2002.
*
Reprint requests and correspondence: William E. Boden, Hartford Hospital, 80 Seymour St., Jefferson Building 722, Hartford, Connecticut 06102, USA.
wboden{at}harthosp.org
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Abstract
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Is a "routine invasive" or "selective invasive" strategy the best approach for patients with non–ST-segment elevation acute coronary syndrome (ACS)? A "selective invasive" strategy incorporates ischemia-guided use of aggressive medical therapy followed by angiography and revascularization for angina or stress-induced myocardial ischemia. The "routine invasive" strategy (cardiac catheterization followed by percutaneous coronary intervention within 24 to 48 h of symptom-onset) is frequently employed, but no randomized, controlled trials have demonstrated improved clinical outcomes. Recently, the second Fragmin and fast Revascularization during InStability in Coronary artery disease (FRISC-II) and the Treat angina with Aggrastat and determine Cost of Therapy with an Invasive or Conservative Strategy–Thrombolysis in Myocardial Infarction (TACTICS TIMI-18) trials found significant reductions in death, recurrent myocardial infarction, or hospitalization for biomarker-positive ACS. Also, the third Randomized Intervention Trial of unstable Angina (RITA-3) recently reported a halving of refractory angina and reduction in the use of antianginal medication with early intervention. Early trials failed to demonstrate the superiority of the "routine invasive" approach, presumably because of fewer revascularizations, unavailability of stents, and more recent use of glycoprotein IIb/IIIa inhibitors and low-molecular-weight heparins. The FRISC-II, TACTICS TIMI-18, and RITA-3 studies indicate that higher-risk patients benefit from early revascularization, but that aggressive antiplatelet, antithrombin, and anti-ischemic therapy are also important. While all three trials support an "early invasive" approach in intermediate- and high-risk patients, other trials support a more "conservative" approach in those without electrocardiographic changes or enzyme elevations. Optimal management should incorporate both strategies.
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Abbreviations and Acronyms
| | ACS | = acute coronary syndrome(s) | | CABG | = coronary artery bypass graft | | CK-MB | = creatine kinase-myocardial band | | GP | = glycoprotein | | LMWH | = low-molecular-weight heparin | | NSTEMI | = non–ST-segment elevation myocardial infarction | | PCI | = percutaneous coronary intervention | | RR | = risk ratio | | UA | = unstable angina | | UFH | = unfractionated heparin |
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Among patients who present with non–ST-segment elevation (NSTE) acute coronary syndromes (ACS), should risk stratification be anatomy-driven or ischemia-driven? The American College of Cardiology/American Heart Association Task Force on Practice Guidelines has published recommendations regarding diagnosis and treatment of patients with known or suspected unstable angina (UA)/NSTE myocardial infarction (NSTEMI) (1,2). The acute ischemia pathway presented in these guidelines encompasses both an early invasive strategy and an early conservative strategy (1) (Fig. 1). However, both the continued technical evolution of stents and the widespread availability and success of catheter-based revascularization have prompted many clinicians to question the need for noninvasive risk stratification of any kind. Accordingly, this discussion will address the following four key issues: 1) Which patients benefit from early percutaneous coronary intervention (PCI)? 2) When is the optimal time to intervene? 3) What are the relative roles of revascularization and adjunctive pharmacologic therapy? and 4) Why do patients benefit?
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Figure 1 Acute ischemia pathway. EF = ejection fraction; LV = left ventricular; Rx = treatment. Adapted from ACC/AHA Guidelines for the Management of Patients with Unstable Angina and Non-ST-Segment Elevation Myocardial Infarction. J Am Coll Cardiol 2000;36:970–1062. Copyright 2002 by the American College of Cardiology and American Heart Association, Inc. Permission granted for one-time use.
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During the past two decades, PCI has become a standard treatment option for many patients with coronary heart disease. With the widespread acceptance of PCI and the continued technical evolution of catheter-based procedures, notably intracoronary stents, an increasingly aggressive approach to primary angioplasty has been adopted. In particular, this approach is commonly chosen for patients presenting with ST-segment elevation MI (where the evidence of clinical benefit from urgent primary PCI is mounting rapidly) and for those with NSTEMI (where evidence for urgent PCI is less well defined).
The "routine early invasive strategy" is typically defined as cardiac catheterization followed by PCI in patients without a clinical contraindication within the first 24 to 48 h of presentation. Proponents of this strategy believe it is appropriate for all patients presenting with ACS, including those with NSTEMI and those who are biomarker-negative. Clinicians who favor the more invasive approach to treatment tend to argue that any form of risk stratification results in less definitive management. The rationale behind this concept is that once coronary angiography is performed, the cardiologist can tailor therapy more appropriately. However, no randomized clinical trial to date has evaluated this strategy in NSTE ACS patients who present within 24 h of symptom-onset.
By contrast, a "selective invasive strategy" involves aggressive medical therapy (intensive antiplatelet, antithrombotic, and anti-ischemic medications) combined with careful clinical assessment and provocative testing. Such testing may utilize exercise electrocardiography (the most commonly performed test), nuclear myocardial perfusion scintigraphy, dobutamine or dipyridamole stress echocardiography, pharmacologic vasodilator stress testing, or other evaluation methods, depending on availability, cost, and specific information sought. This is followed by the selective use of coronary angiography and, if necessary, revascularization for spontaneous angina or objective evidence of stress-induced myocardial ischemia. Whether improved clinical outcomes can be demonstrated with an aggressive early revascularization approach in all subsets of patients remains to be determined, however.
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Randomized studies comparing invasive versus conservative strategies
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The TIMI-IIIB trials.
The Thrombolysis in Myocardial Ischemia (TIMI-IIIB) trials included 1,473 patients with UA or non–Q-wave MI (3). This trial was a 2 x 2 factorial design comparing tissue plasminogen activator with placebo and an early invasive strategy (n = 740) versus a conservative strategy (n = 733) within 48 h of randomization. The invasive strategy involved cardiac catheterization, left ventricular angiography, and coronary arteriography 18 to 48 h after randomization. The PCI was performed in all lesions with >60% stenosis. Coronary artery bypass graft (CABG) surgery was performed in the presence of significant left main coronary artery obstruction, three-vessel disease, and depressed left ventricular function, or recurrent UA. The conservative strategy involved initial medical therapy, with intervention only after ischemia was detected on stress testing at six weeks. All patients were treated with bed rest, oxygen, anti-ischemic medications (beta-blockade, calcium channel blockade, and long-acting nitrates), aspirin, and heparin.
The primary outcome (combined death, nonfatal MI, or ischemia on stress testing) occurred in 18.1% of patients in the invasive-strategy group and in 16.2% of patients in the conservative-strategy group (a nonsignificant difference) (Table 1). Of the patients randomized to the conservative-strategy group, ST-segment depression on the qualifying electrocardiogram, prior aspirin use, and older age were independent predictors of primary outcome components (3).
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Table 1 Invasive Versus Conservative Strategies in Patients With Non–ST-Segment Elevation MI: Outcomes at Six Weeks in the TIMI-IIIB Trial
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VANQWISH.
The Veterans Affairs Non–Q-Wave Infarction Strategies in Hospital (VANQWISH) trial (4) compared early and late clinical outcomes (death or recurrent MI) in patients randomly assigned to either early invasive strategy or conservative treatment. This trial was the largest of its kind to test the efficacy of long-term management strategies in patients who sustained an acute non-Q-wave MI. As shown in Figure 2, patients treated with the early invasive strategy (heart catheterization followed by myocardial revascularization) had significantly worse clinical outcomes during the first year of follow-up than did those treated with a conservative strategy (intervention guided by rigorous ischemia management, noninvasive stress testing, and medical therapy). The number of patients who had one of the components of the primary end point was significantly higher in the invasive-strategy group at hospital discharge (36 vs. 15 events, p = 0.004), at one month (48 vs. 26 events, p = 0.012), and at one year (111 vs. 85 events, p = 0.05) (4).
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Figure 2 From the VANQWISH trial: Kaplan-Meier curves for the trial primary end points (death or MI) at one-year of follow-up. CHR = Cox hazard ratio; CI = confidence interval; MI = myocardial infarction; VANQWISH = Veterans Affairs Non–Q-Wave Infarction Strategies in Hospital. Adapted with permission from Boden WE, O’Rourke RA, Crawford MH, et al., for the Veterans Affairs Non–Q-Wave Infarction Strategies in Hospital (VANQWISH) trial investigators. Outcomes in patients with acute non-Q-wave myocardial infarction randomly assigned to an invasive as compared with a conservative management strategy. N Engl J Med 1998;338:1785–92. Copyright © 2002, Massachusetts Medical Society. All rights reserved.
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An overlooked feature of the VANQWISH trial is that patients who remained in the conservative treatment arm and did not cross over to cardiac catheterization in the 44 months of follow-up (52% of this arm) had a remarkably low cardiac event rate; two patients (1%) died, and three patients (1%) experienced a clinical event at 30-day follow-up (Table 2). This low rate of events occurred in patients with high clinical comorbidity and an almost 80% incidence of triple-vessel and left main coronary disease. There was no evidence of an interaction that supported improved outcomes in the patients with the invasive strategy (4). In contrast, the ischemia-guided strategy benefited 4 of 10 prespecified subsets of patients: those who underwent thrombolysis; those with no prior MI; patients without ST-segment depression; and those 
60 years).
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Table 2 Clinical Outcomes of Patients Who Underwent Coronary Angiography With Revascularization or No Coronary Angiography and No Revascularization: VANQWISH Trial
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Are these results relevant to the contemporary management of patients with NSTEMI, in light of the advances of the last two to three years? The use of stents, the rise of newer catheter-based techniques, and the use of glycoprotein (GP) IIb/IIIa receptor antagonists have expanded rapidly (5–8). The benefits of low-molecular-weight heparins (LMWHs), particularly enoxaparin, have been convincingly demonstrated (9–11). Evidence from the Organisation to Assess Strategies for Ischemic Syndromes (OASIS-2) trial revealed that hirudin (lepirudin), a direct thrombin inhibitor, may have benefit (12). The Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events (CAPRIE) (13) and the Clopidogrel in Unstable angina to prevent Recurrent ischemic Events (CURE) (14) trials showed that clopidogrel, a thienopyridine derivative similar to ticlopidine, is an important adjunctive treatment in the management of patients with ACS.
However, the TIMI-IIIB and VANQWISH trials are relevant to risk stratification because they reveal that both high- and low-risk subsets can be identified. In the VANQWISH trial, only 9% of patients were excluded during the first 48 to 72 h for symptoms of refractory angina, persistent ischemia, heart failure, or significant ventricular tachyarrhythmia or fibrillation. As discussed, the 30-day event rate of death and MI was remarkably low (1%) with the conservative strategy, despite the high prevalence of clinical comorbidity and angiographic morbidity.
FRISC-II
The Fragmin and Fast Revascularisation during InStability in Coronary artery disease (FRISC-II) invasive trial (15) showed, for the first time, a significant event rate reduction favoring the invasive over the noninvasive strategy at six months in a subset of patients with unstable angina and non–Q-wave infarction (Fig. 3). In the trial, 2,457 patients in 58 Scandinavian hospitals were assigned to early invasive or noninvasive treatment with placebo-controlled LMWH (dalteparin) for three months. In the invasive group, 96% of patients received angiography within 7 days; of those, 71% underwent revascularization within 10 days. For the noninvasive group, 10% received angiography within seven days; of those, 9% went on to undergo revascularization procedures. At six months, the rate of death, MI, or both was 9.4% in the invasive group and 12.1% in the noninvasive group (risk ratio [RR], 0.78; 95% confidence interval, 0.62 to 0.98; p = 0.031) (15).
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Figure 3 From the FRISC-II trial. Kaplan-Meier analysis of the probability of event-free survival according to strategy group during six months of follow-up for the trial primary end point of death or MI, showing significant benefit in clinical outcomes for the routine invasive strategy. CI = confidence interval; FRISC = Fragmin and fast Revascularization during InStability in Coronary artery disease; MI = myocardial infarction; RR = risk reduction. Adapted with permission from Elsevier Science (The Lancet 1999;354:708–15).
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The results favoring the invasive strategy were not uniformly shown among patient subsets in FRISC-II, however. In a substudy analysis of the influence of troponin levels, 42% of patients were found to be troponin-negative (<0.1 g/l) (16). The six-month rate of death or MI was 8.3% in patients assigned to an invasive strategy versus 10.3% in those assigned to a conservative strategy, a nonsignificant difference.
Similarly, in the evaluation of patients who had ST-segment deviations on the admission electrocardiogram in FRISC-II, 418 patients had no demonstrable ST-T wave changes (Table 3)
(17). The relative risk of an unfavorable outcome (death or MI at six months) was actually slightly higher for patients in the invasive group. No significant benefit was shown with the invasive strategy in patients who had isolated T-wave inversion only. The early invasive strategy was not shown to be beneficial in fully 52% of patients who had either no electrocardiogram changes or T-wave inversion only. The true benefit of early invasive treatment, when evaluated by electrocardiography, was derived from the subset of patients with ST-segment depression MI.
In summary, patients who were troponin-negative and those who had no ST-T-wave changes or only isolated T-wave inversions (>50% of all patients) did not benefit from an invasive strategy. Only observational data and registry data are available to show a reduction of death or MI, or refractory ischemia, in NSTEMI patients who underwent PCI within 24 h of presentation. Thus, much remains to be proven with regard to the overall benefit of applying an early aggressive invasive strategy in such patients.
TACTICS TIMI-18
The Treat angina with Aggrastat and determine Cost of Therapy with an Invasive or Conservative Strategy–TIMI-18 (TACTICS TIMI-18) trial included 2,220 patients with UA/NSTEMI (18). Inclusion criteria were an accelerating pattern, prolonged or recurrent anginal pain at rest or minimal effort within the previous 24 h, plus ischemia, electrocardiogram changes, elevated cardiac markers, or a history of prior coronary artery disease. Study subjects were immediately treated with aspirin, heparin, and the GP IIb/IIIa inhibitor tirofiban (administered for 48 to 108 h). Patients were then randomized to one of the following two groups: a) catheterization and subsequent PCI/CABG within 4 to 48 h; b) conservative strategy with catheterization performed only if objective evidence showed recurrent ischemia or there was a positive exercise stress test.
At six months, the primary outcome (death, MI, and rehospitalization for ACS) occurred in 15.9% of the invasive-strategy group and 19.4% of the conservative-strategy group (odds ratio [OR], 0.78; p = 0.025). The rate of death or MI was also significantly lower in the invasive-strategy group (7.3% vs. 9.5%; OR, 0.74; p < 0.05) (Fig. 4).
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Figure 4 From the TACTICS TIMI-18 trial. Kaplan-Meier analysis of the probability of event-free survival for the triple composite end point of death, MI, and biomarker-positive ACS during six months of follow-up, showing a significant benefit for the routine invasive strategy. CI = confidence interval; MI = myocardial infarction; OR = odds ratio; TACTICS TIMI = Treat angina with Aggrastat and determine Cost of Therapy with an Invasive or Conservative Strategy–Thrombolysis in Myocardial Infarction trial. Adapted with permission from Cannon CP, Weintraub WS, Demopoulos LA, et al., for the TACTICS–Thrombolysis in Myocardial Infarction-18 investigators. Comparison of early invasive and conservative strategies in patients with unstable coronary syndromes treated with the glycoprotein IIb/IIIa inhibitor tirofiban. N Engl J Med 2001;344:1879–87. Copyright © 2002, Massachusetts Medical Society. All rights reserved.
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Subgroup analysis according to troponin-T status on admission revealed that the difference between the two strategies was largely due to a reduction in the primary outcome among troponin-T-positive patients. In this subgroup, the invasive strategy was associated with a primary outcome rate of 14.3% compared with 24.2% for the conservative strategy (OR, 0.52; p < 0.001). The two strategies were comparable in their effects on the primary outcome in troponin-T-negative patients. Patients with an intermediate or high TIMI UA risk score also benefited from an invasive over a conservative strategy. In patients with a low TIMI UA score, the two strategies were comparable.
RITA-3
Results from the Randomized Intervention Trial of unstable Angina (RITA)-3 study, carried out by the British Heart Foundation, were recently published (19). The study compared early intervention (angiography followed by revascularization) with a conservative strategy (antianginal and antithrombotic medications) in 1,810 NSTE ACS patients in the United Kingdom (38% women). All patients were treated with optimal antianginal and antiplatelet treatment, including enoxaparin. For the primary end point of death, MI, or refractory angina at four months, there was a 9.6% risk in the intervention group compared to 14.5% in the conservative group (RR, 0.66; p = 0.001), mainly attributable to a halving of the incidence of refractory angina with the interventional strategy. (Refractory angina was defined as ischemic pain at rest or on minimum exertion, despite maximum medical treatment, associated with new cardiographic changes prompting revascularization within 24 h or readmission to hospital after discharge.) For the co-primary end point of rates of death or MI at one year, the results were similar for both groups, but refractory angina and use of antianginal medications were more significantly reduced in the early intervention group (p < 0.0006). This difference was also evident at four months (p = 0.0001) (Table 4).
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Table 4 Overview of Three Randomized Trials Comparing Early Invasive With Early Noninvasive Strategy in Unstable Coronary Artery Disease
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A subanalysis of RITA-3 and FRISC-II found significant reductions in the composite of death and MI in men, but that a trend to hazard was found for early intervention in women. Women tend to have more procedurerelated complications than men and, with equivalent clinical presentations to men, usually have less coronary artery disease, and therefore less to gain from an invasive procedure.
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Importance of adjunctive therapies
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In contrast to the negative results from the TIMI-IIIB and VANQWISH studies, the favorable results of FRISC-II, TACTICS TIMI-18, and RITA-3 may be explained, in part, by the fact that relative to the two earlier studies, patients in FRISC-II and RITA-3 were treated adjunctively with LMWH, whereas in the TACTICS TIMI-18 study, patients were nearly universally treated with tirofiban. Moreover, concomitant therapy with aspirin, unfractioned heparin (UFH), intravenous nitroglycerin, and beta-blockers was utilized for up to 96 h in TACTICS TIMI-18 or up to six days in FRISC-II. In RITA-3, aspirin, beta-blockade, and enoxaparin were administered, and GP IIb/IIIa inhibitors or other antiplatelet agents, nitrates, and antithrombotic drugs were provided when appropriate. This could have resulted in improved clinical outcomes due to the induction of a state of intracoronary "plaque passivation" from the combined effects of antiplatelet, antithrombin, and anti-ischemic therapy.
Furthermore, stents were utilized liberally among patients undergoing revascularization in both FRISC-II (65% of patients) and TACTICS TIMI-18 (84%), whereas neither of these advanced antithrombotic therapies nor stents were available at the time of TIMI-IIIB or VANQWISH. Unlike the FRISC-II study, no "early hazard" was noted among patients managed invasively in the TACTICS–TIMI-18 study. Tirofiban may have not only reduced the incidence of early recurrent ischemic events (20,21) but also may have attenuated myocardial necrosis resulting from incomplete or inadequate platelet inhibition occurring during attempts at percutaneous coronary revascularization (22–26).
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Clinical risk factors and response to therapy with GP IIb/IIIa receptor antagonists
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Careful assessment of patients with NSTE ACS should help to identify patients with high-risk clinical presentations (Table 5) and, in addition, contribute to therapeutic decision making. By using both clinical information (history, physical, electrocardiogram results) and biochemical methods (serum cardiac markers), risk-stratification for ischemic complications in NSTE ACS patients can be reliably established, including the likelihood of recurrent instability, progression to MI, or even death (27–30). This approach can also ensure the optimal selection of therapeutic interventions for NSTE ACS patients, predicting the benefits of intravenous platelet GP IIb/IIIa receptor antagonism, or routine early invasive strategies.
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Table 5 American College of Cardiology/American Heart Association Unstable Angina/Non–ST-Segment Elevation Myocardial Infarction Guidelines: Recommendations for Patients Who May Benefit From Early Aggressive Management
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The use of clinical risk scores to predict GP IIb/IIIa response was demonstrated in recently published data from two substudies of the Platelet Receptor Inhibition for Ischemic Syndrome Management in Patients Limited by Unstable Signs and symptoms (PRISM-PLUS) trial. Using an exploratory analysis of clinical factors associated with patients from PRISM-PLUS, Sabatine and colleagues (28) identified five clinical variables that could be used in an additive fashion to identify expected benefits to patients from the use of tirofiban. These variables were advanced age, prior aspirin use, prior beta-blocker use, prior CABG, or ST-segment depression on the presenting electrocardiogram. Patients with 0 to 1 risk factors accrued no benefit; those with 2 or 3 risk factors accrued intermediate benefit; patients with 4 or 5 risk factors gained the most benefit. Similarly, Morrow and colleagues (31) identified seven additive risk factors in developing the TIMI Risk Score: age 65 years, prior history of CAD, 3 coronary risk factors, ST-segment deviation, prior aspirin use within seven days, frequent angina, or elevated serum markers of myocardial necrosis. Using this Risk Score, they were able to predict the benefits of therapy with tirofiban in PRISM-PLUS, which were particularly strong in patients with scores 4.
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Serum markers and response totherapy with GP IIb/IIIa receptor antagonists
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Hamm and colleagues (32), in the Chimeric c7E3 AntiPlatelet Therapy in Unstable angina Refractory to standard treatment trial (CAPTURE) study, were the first to use serum markers of myocardial necrosis to identify patients who might benefit from treatment with GP IIb/IIIa receptor antagonists. Elevated serum troponin levels were later shown, in PRISM (33), Platelet IIb/IIIa Antagonism for the Reduction of Acute coronary syndrome events in a Global Organization Network (PARAGON B) (34), and PRISM-PLUS (6), to be associated with patients at particularly high risk for ischemic complications and who are likely to benefit most from intravenous GP IIb/IIIa receptor antagonism (Table 6). A notable exception to these data is the result from Global Use of Strategies To Open occluded arteries in Acute Coronary Syndrome (GUSTO IV-ACS) trial (35), in which the serum troponin results did not predict benefit from medical therapy with abciximab.
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Table 6 Summary Detailing the Benefits of Glycoprotein IIb/IIIa Receptor Antagonists Among Troponin-Positive Patients in Various Clinical Trials
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As noted earlier, the results of serum troponin testing generally identified those patients who benefited the most from invasive management in the TACTICS TIMI-18 study (18,20,36). These results echoed those from the FRISC-II study, which suggested that the benefits of early invasive management were particularly strong for those with elevated serum troponins (37,38).
The mechanism of GP IIb/IIIa benefit (with or without early invasive management) among patients with elevated troponins remains speculative. It may relate to the fact that patients with elevated serum troponins appear to have higher-risk coronary anatomy, including more extensive coronary artery disease, as well as a significantly higher prevalence of intracoronary thrombi and worse epicardial blood flow rates present at the time of angiography compared to those without elevated troponin levels (37,39). In these patients, the use of aggressive platelet receptor antagonism is thought to be accompanied by reductions in coronary thrombosis, improved plaque stability, and decreased amounts of distal "microembolism" of platelet-rich debris to the distal microvasculature (with consequent reductions in myocardial injury). The fact that angiographic substudies from CAPTURE and PRISM-PLUS both demonstrated significant reductions in intracoronary thrombi with abciximab or tirofiban treatment (with concomitant improvements in TIMI angiographic flow rates) lends credence to this hypothesis (40,41). Similarly, an analysis from PRISM-PLUS by Januzzi and colleagues (21) demonstrated significant reductions in serum troponin I release among ACS patients treated with tirofiban compared to those treated with heparin alone. The decrease in troponin levels correlated with reductions in intracoronary thrombi.
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Risk stratification
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High-risk patients.
High-risk patients with NSTE ACS (Fig. 5) who clearly warrant catheterization and early revascularization include those with rest angina with ST-segment depression and/or elevated serum concentrations of cardiac markers of ischemic injury (creatine kinase-myocardial band [CK-MB] isoenzyme, troponin, myoglobin). Those who have rest angina with hemodynamic instability, heart failure, or an ejection fraction <40%, and those with rest angina and prior revascularization (PCI or CABG) should be sent to the catheterization laboratory with revascularization as indicated.
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Figure 5 Flow diagram of a proposed risk-stratification algorithm for patients with non–ST-segment elevation acute coronary syndromes. ASA = aspirin; ECG = electrocardiogram; GP IIb/IIIa = glycoprotein platelet IIb/IIIa inhibitor; Hx = history; LMWH = low-molecular-weight heparin; PCI = percutaneous coronary intervention; PE = physical exam; STTWA = ST-T-wave abnormalities; TW = T-waves; UFH = unfractionated heparin. Derived from Boden WE, McKay R. Optimal treatment of acute coronary syndromes—an evolving strategy. N Engl J Med 2001;344:1939–42.
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Intermediate-risk patients
Patients with NSTE ACS at an intermediate level of risk are likely to benefit from catheterization and early revascularization. This subset includes patients with Canadian Cardiovascular Society class III or IV angina within the previous two weeks, those with diabetes mellitus, and those who have deep T-wave inversions in more than five leads and who have chest discomfort or pain.
Low-risk patients
Patients with NSTE ACS who are not likely to benefit from catheterization or early revascularization include those with Canadian Cardiovascular Society class I or II angina, normal or nonspecific electrocardiogram changes, T-wave inversion without ST-segment depression, and biochemical markers that are negative for CK-MB or troponin levels.
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Clinical implications
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The current data support the following conclusions and caveats:
Who benefits from early PCI?.
Tailoring treatment to the level of risk remains a sound and proven approach to management. The FRISC-II and TACTICS TIMI-18 studies support the utility of troponin T in risk stratification, although this is based on retrospective analysis. High-risk patients who are biomarker positive or have ST-segment depression are likely to benefit from a strategy of early revascularization. Low-risk patients are not likely to benefit from early revascularization, which accounts for 15% to 40% of all patients (3,4,15,18).
When is the optimal time to intervene?
The optimal timing of PCI in the setting of intensive medical therapy remains ill defined. The FRISC-II study supports an interval of four to six days, but this is impractical according to current North American practice standards. The TACTICS TIMI-18 trial provides data to support this approach between two to three days’ postevent. There are no data from within 24 h of symptom-onset.
What factors are at play?
Aggressive antiplatelet, antithrombin, and anti-ischemic therapy may be as important as revascularization. In FRISC-II, intervention was associated with early hazard, with the survival curves crossing over between months 1 and 6. This phenomenon was not observed in the TACTICS TIMI-18 study, prompting the hypothesis that early hazard might be a consequence of inadequate platelet inhibition. Indeed, pharmacotherapy with GP IIb/IIIa platelet inhibition and LMWH may reduce clinical events whether an early invasive or early conservative strategy is followed.
Why do patients benefit?
Plaque passivation may be pivotal to optimizing benefits of PCI and CABG. With the "routine invasive" strategy, late clinical benefit may negate early hazard, especially with more complete platelet and thrombin inhibition. The more widespread use of intracoronary stents, coupled with aggressive, multifaceted medical therapy that includes antiplatelet, antithrombin, and anti-ischemic therapy, is likely critical to achieving optimized clinical outcomes.
Conclusions
Risk stratification makes as much sense in 2003 as it did 30 years ago because NSTE ACS is heterogeneous, with a spectrum of risk ranging from low to high. The important findings of the FRISC-II, TACTICS TIMI-18, and RITA-3 trials demonstrate significantly improved clinical outcomes among intermediate- to high-risk patients, notably those with positive biomarker and/or ST-segment depression. For NSTE ACS patients who are clinically stable and do not exhibit these high-risk features, stress myocardial perfusion imaging, preferably symptom-limited exercise-induced imaging, should clearly delineate high- and intermediate-risk subgroups.
Aggressive pharmacologic therapy is indicated in all patients. This includes use of aspirin, UFH or LMWH (especially enoxaparin), and anti-ischemic therapy (intravenous nitroglycerin, beta-blockers and/or calcium antagonists), with appropriate secondary prevention (statins and angiotensin-converting enzyme inhibitors). The GP IIb/IIIa receptor antagonists should likely be reserved for the intermediate- to high-risk patient, with either abciximab or eptifibatide for patients who are undergoing a PCI, or tirofiban for patients who are first being stabilized clinically in the coronary care unit. Clopidogrel, coupled with aspirin, will now likely become standard therapy in all NSTE ACS patients, based on the results of the CURE Trial (14).
Finally, tailoring therapy to risk level is essential for optimizing efficacy and cost-effectiveness in this heterogeneous group of patients. Use of an interventional approach in intermediate- to high-risk patients and a noninvasive, ischemia-guided approach in initially low-risk patients is both rational and evidence-based.
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Footnotes
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Please refer to the Trial Appendix at the back of this supplement for the complete list of clinical trials.
1 Dr. Boden does not have any financial or commercial agreement with any organization insofar as it would be perceived as a real conflict of interest. 
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References
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- The TIMI-IIIB investigators. Effects of tissue plasminogen activator and a comparison of early invasive and conservative strategies in unstable angina and non–Q-wave myocardial infarction. Results of the TIMI-IIIB trial. Circulation. 1994;89:1545–1556
- Veterans Affairs Non-Q-Wave Infarction Strategies in Hospital (VANQWISH) trial investigatorsBoden WE, O’Rourke RA, Crawford MH, et al. Outcomes in patients with acute non-Q-wave myocardial infarction randomly assigned to an invasive as compared with a conservative management strategy. N Engl J Med. 1998;338:1785–1792
- The Platelet Receptor Inhibition in ischemic Syndrome Management (PRISM) study investigators. A comparison of aspirin plus tirofiban with aspirin plus heparin for unstable angina. N Engl J Med. 1998;338:1498–1505
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Abstract
Randomized studies comparing...
