ST elevation myocardial infarction (STEMI), also known as “current of injury”, is defined by the occurrence of new or presumed new ST elevation in two or more contiguous leads that is
0.2 mV in leads V1, V2, and V3 and > 0.1 mV in other leads or the occurrence of new onset left bundle branch block.2
These patients usually have ongoing occlusion of an epicardial coronary artery and require consideration for immediate reperfusion therapy.
An ECG not only helps in establishing the diagnosis of STEMI but also provides valuable information on infarct location, success or failure of reperfusion, as well as prognosis.3
Arterial occlusion at particular anatomical sites is associated with specific ECG patterns and imparts correspondingly varying degrees of short or long term mortality hazard.4
The majority of patients with ST elevation MI have ST depression in reciprocal leads. This finding appears to be associated with an increased hazard of adverse long term outcome, at least in some series.5,6
While the utility of ECG in screening for epicardial coronary arterial occlusion has been long recognised, the ECG provides accretive information on the integrity of the microcirculation, the significance of which has been only recently recognised.
Impaired myocardial microperfusion has been shown to be a major predictor of adverse outcome in patients undergoing reperfusion therapy.7
Complete resolution of ST changes has emerged as a simple yet robust marker of microvascular perfusion with the degree of ST resolution being strongly correlated with myocardial blush grade on angiography.8
Numerous groups have demonstrated a poor short and long term outcome in patients that have persistent ST elevation despite successful restoration of TIMI (thrombolysis in myocardial infarction) grade 3 flow in the infarct related artery by mechanical or pharmacological means.9–14
Cura and colleagues recently reported the results of RESTART (resolution of ST segment after reperfusion therapy), a substudy of the GUSTO (global use of strategies to open occluded coronary arteries) V trial.15
In this prospective study of 1764 patients randomised to full dose reteplase or half dose reteplase and abciximab, patients with > 70% ST resolution at 60 minutes had a 30 day mortality of 2.1%, those with partial resolution (30–70%) 5.2%, those with no ST resolution 5.5%, while those with worsening ST elevation had a mortality of 8.1%. Persistent ST segment elevation may be a more sensitive marker of impaired microcirculation with at least one study demonstrating worst outcome in those with both poor myocardial blush and persistent ST elevation, the best outcome in those with resolution of both, and an intermediate outcome in those with normal blush but persistent ST elevation.16
Furthermore, compared with myocardial blush, normalisation of ST segment is a better predictor of early recovery of left ventricular function. Indeed, in a small study, failure to resolve ST segment was closely related to defects on myocardial contrast echocardiography.10
The demographic factors that predispose to persistent ST segment elevation remain somewhat ambiguous, but include older age and low systolic blood pressure at presentation,17
anterior myocardial infarction,15
as well as prolonged time to reperfusion.18
Given its universal availability, simplicity and proven superiority to angiographic measures, the ECG continues to be the platinum standard for assessing adequacy of myocardial reperfusion in STEMI.