Modern Invasive Therapy vs. Thrombolysis in Acute MI
September 1, 2000 4 minutes read
Modern Invasive Therapy vs. Thrombolysis in Acute MI
Abstract & Commentary
Synopsis: In patients with acute MI, immediate stenting plus platelet glycoprotein IIb/IIIa inhibitors results in better myocardial salvage and improved clinical outcomes as compared to thrombolytic therapy plus heparin.
Source: Schomig A, et al. N Engl J Med 2000;343: 385-391.
Controversy remains regarding whether primary angioplasty or thrombolysis is the best therapy for acute myocardial infarction (MI) when both are available. Thus, the report of the Stenting vs. Thrombolysis for Occluded Coronary Arteries in Patients with Acute Myocardial Infarction (STOPAMI) is of interest. Schomig and colleagues randomized 140 patients to stent plus abciximab vs. intravenous alteplase plus heparin within 12 hours of the onset of symptoms. All patients received 500 mg aspirin, a 5000 U intravenous heparin bolus, and 27 mCi of Tc 99m sestamibi. Radionuclide scintigrams of the heart were performed within eight hours and at 10 days. The alteplase patients received intravenous heparin for 48 hours and 100 mg aspirin b.i.d. indefinitely. The percutaneous intervention group received aspirin indefinitely and ticlopidine 250 mg b.i.d. for four weeks. The primary end point of the study was the myocardial salvage index, calculated as the percent of the left ventricle salvaged on repeat scintigraphy divided by the percent compromised on the initial scan. The secondary end point was the composite of death, reinfarction, or stroke within six months. In the stent group, the median infarct size was 14% of the LV vs. 19% in the thrombolysis group (P = 0.02). Accordingly, the salvage index was 0.57 in the stent group vs. 0.26 in the thrombolysis group (P < 0.001). The composite of death, reinfarction, or stroke at six months was lower in the stent group as compared to the thrombolysis group (23%; P = 0.02; relative risk [RR] 0.34, 95% CI = 0.13-0.88). Schomig et al conclude that in patients with acute MI, immediate stenting plus platelet glycoprotein IIb/IIIa inhibitors results in better myocardial salvage and improved clinical outcomes as compared to thrombolytic therapy plus heparin.
Comment by Michael H. Crawford, MD
The evidence for the superiority of an initial invasive approach to acute MI patients is growing. This study is important because it used modern interventional techniques (i.e., stents plus abciximab plus ticlopidine). Also, more than 80% of both groups were on ACE inhibitors, beta blockers, and statins. Although the study was only powered for the myocardial salvage end point, the composite clinical end point was significantly improved at six months with a RR of 0.34 in favor of an invasive approach.
The primary end point of scintigraphic myocardial salvage is a strength and a weakness of the study. It is a strength because it provides objective evidence of a biologically plausible mechanism for the clinical outcomes. Also, since the thrombolytic group did not undergo routine catheterization, we don’t know their infarct vessel patency status, so the salvage data provides a common mechanistic end point. Unfortunately, we have no long-term mortality prediction data for salvage index, whereas we do for infarct vessel patency. In addition, the logistics and cost of obtaining the scintigraphic data necessarily reduces the size of the study population. In general, the more end points you have and the more complex and costly they are, the smaller the population size of a trial. Hence, most of the mega trials largely evaluate mortality. In this study, 88% of the patients had initial and follow-up scans, despite this being the primary end point.
The importance of abciximab in the study is difficult to determine. It did not seem to increase complications, as major bleeding episodes were the same between the two groups and there were no strokes during follow-up. Also, this study was started before the results of TIMI 14 were released, which showed that abciximab plus thrombolytic therapy resulted in better infarct vessel patency than thrombolysis alone. Again, clinical practice is a moving target; perhaps if both groups had gotten abciximab in this trial, there would have been no difference in outcomes and the controversy would continue.
The issue of the availability of interventional procedures, especially performed by high-volume operators, is a problem. In this study, there was no statistically significant difference in mortality between the two groups, although at six months, there was a trend in favor of the invasive groups (4 vs 13 patients). At 30 days, the difference was less (4 vs 7 patients). Thus, perhaps a strategy of early thrombolysis followed by later revascularization would provide similar long-term results for the hospitals without catheterization laboratories, but with tertiary centers regionally available.
The STOPAMI study, the FRISC II study discussed above, and other recent studies seem to be tipping the scales toward an early invasive strategy for appropriate high-risk patients with acute coronary syndromes.
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