Effective and rapid reperfusion is crucial in patients with acute ST-segment elevation myocardial infarction (MI). The preferred strategy for reperfusion—when it can be performed in a timely fashion at an experienced facility—is primary percutaneous coronary intervention (PCI), which produces outcomes superior to those of pharmacologic thrombolysis. 1
Unfortunately, in the United States about half of patients present to hospitals that do not have PCI capability, 2 and in one analysis, 91% of transferred patients had a door-to-balloon time greater than the recommended 90 minutes, with a mean of 152 minutes. 3 (In this case, the door-to-balloon time was the time that elapsed between entry into the first hospital and inflation of the PCI balloon at the second hospital.)
In situations such as these, a combined approach may be appropriate, with thrombolysis delivered by paramedics or at a local facility, followed by transfer to a PCI facility and performance of PCI within a few hours. However, this is feasible only if standardized community-based or regional protocols for prompt transfer and reperfusion are in place.
In this paper we discuss the rationale and the clinical data behind several approaches to combined reperfusion, as well as experiences with community-based care protocols.
WITHIN 3 HOURS OF SYMPTOM ONSET, THROMBOLYSIS IS AS GOOD AS PCI
The PRAGUE-2 Trial
In the randomized PRAGUE-2 trial, 4 patients with ST-elevation MI who presented to a non-PCI facility had better outcomes if they were transferred promptly for PCI (median door-to-balloon time 97 minutes), as opposed to receiving local therapy with streptokinase. However, for patients presenting within 3 hours of symptom onset, the mortality rates were comparable with either strategy. 4
See the glossary of clinical trial names below
The CAPTIM trial
In the CAPTIM trial, 5 patients who presented within 2 hours of symptom onset and who were randomized to receive prehospital thrombolysis had outcomes similar to those of patients treated with primary PCI, despite a short door-to-balloon time (82 minutes).
The Vienna STEMI Registry
In the Vienna STEMI Registry, 6 the mortality rates with primary PCI and with thrombolysis were similar when patients presented within 2 hours of symptom onset. However, as the time from symptom onset increased, primary PCI appeared to offer an increasing survival benefit compared with thrombolysis.
Comments: Thrombolysis is effective mostly in the first 2 to 3 hours, with some benefit up to 12 hours
Previous studies have shown that the sooner thrombolysis is given after symptom onset, the more effective it is. If it is given within an hour of symptom onset, the relative reduction in the mortality rate is 50% and the absolute reduction is 6.5% compared with no reperfusion therapy. If it is started in the second hour, the absolute reduction in the mortality rate drops to 4%, and a lesser benefit extends to patients presenting up to 12 hours after symptom onset. 7 This time-dependent benefit is due to the fact that very early reperfusion of the occluded coronary artery may lead to full recovery of ischemic tissue and thus prevent necrosis. In addition, thrombolysis in the first 2 hours is highly efficacious in lysing a fresh thrombus.