Since seminal experiments performed nearly 4 decades ago showing that ST-segment elevation was a powerful “atraumatic method for assessing alterations in the extent of myocardial ischemic injury” after coronary artery occlusion in dogs, its clinical utility in risk stratification after ST elevation myocardial infarction has proved to be robust. ST resolution (STR) provides an “electrocardiographic window” of epicardial and cellular reperfusion, correlating powerfully with intermediate and long-term cardiovascular outcomes. In the current era of primary percutaneous coronary intervention (PCI), driven by the paradigm of “shifting the open artery hypothesis downstream,” many advancements have occurred to reduce microvascular injury. With thienopyridines, glycoprotein inhibitors, and more recently thrombus aspiration devices, the likelihood of early epicardial and myocycte reperfusion appears higher than ever achievable by thrombolytic therapy, thus explaining why most patients who undergo primary PCI enjoy a favorable prognosis. Therefore, the challenge lies in the refinement of algorithms that identify high-risk patients early after primary PCI such that appropriate therapeutic interventions can be initiated promptly. STR assessment at earlier time points is one such strategy. We found that the immediate post-PCI time point offered the best opportunity to identify high-risk patients (STR <70%) compared to the 90-minute benchmark set in the lytic era, at which time point the prognostic capability of STR analysis was not as strong. When applying more complex algorithms (categorization of single-lead STR into absent (≤30%), incomplete (30% to 69%), or complete (≥70%), or even simpler assessment on the basis of residual ST elevation (<1, 1 to ≤2, or ≥2 mm), as suggested by Hallén et al in their comment, we found that assessment at the immediate time point remained superior in the partitioning of the risk for mortality and adverse cardiovascular outcomes in our study population ( Figure 1 ). Mechanical reperfusion allows the operator to identify the precise moment of epicardial reperfusion; and with recent advances in thrombus aspiration and prehospital and intracoronary pharmacotherapy, the assessment of STR immediately after primary PCI makes physiologic sense and allows a more timely assessment of reperfusion efficacy than at 90 minutes. However, we agree with the observations of Hallén et al that the optimal time point for electrocardiographically guided identification of high-risk patients may indeed lie somewhere between 0 and 90 minutes, although as therapies for reducing microvascular injury improve, it is hoped that it lies closer to the 0-minute mark. Although continuous ST-segment monitoring would provide the most accurate physiologic assessment of reperfusion, the simplicity, reproducibility, and time efficiency of static STR assessment at rigorously determined time points appears to be the most clinically applicable strategy for risk stratification after ST elevation myocardial infarction. Until a comprehensive assessment of other time points within this 90-minute interval is carried out, our results suggest that immediate STR is far superior to STR at 90 minutes and should be the contemporary goal of reperfusion with primary PCI.
