Background ST elevation acute myocardial infarction (STEMI) is frequently associated with reciprocal ST depression in the contralateral ECG leads. The ECG remains a primary diagnostic factor in the hyperacute treatment of myocardial infarction. There has been longstanding debate over the relevance of reciprocal ECG changes in STEMI. CMR can retrospectively determine myocardial area at risk (AAR), namely, the area of myocardium that is susceptible to infarction prior to opening the infarct-related artery. T2-weighted (T2w) imaging can be combined with measures of infarction by late gadolinium enhanced (LGE) imaging to derive myocardial salvage, a measure with established prognostic relevance. We hypothesised that reciprocal ECG change reflects larger AAR as defined by CMR.
Methods Patients after primary percutaneous coronary intervention for first STEMI underwent CMR at 1.5 T within 3 days of reperfusion. Presenting ECGs were assessed for presence or absence of reciprocal change, defined as ≥1 mm ST depression in ≥2 inferior leads for anterior STEMI, or ≥2 anterior leads for inferior STEMI. Patients with posterior ECG changes were excluded from analysis. Infarcted tissue was defined as hyperenhancement ≥2 SDs above remote myocardium on LGE imaging. AAR was defined on T2w images, defined as the mass of myocardium with signal intensity ≥2 SD above remote, normalised to LV myocardial mass (figure 1). Myocardial salvage was calculated as (AAR mass—infarct mass), and myocardial salvage index as (myocardial salvage/AAR mass).
Results Thirty-five patients had ECGs and images suitable for analysis. There were no significant differences in patient demographics (table 1). Patients with reciprocal ECG changes had significantly higher AAR than those without (42.3% vs 23.6%, p<0.001), myocardial salvage (17 g vs 2 g, p<0.001) and myocardial salvage index (40% vs 7%, p<0.001). Infarct size was not significantly different between patients with and without reciprocal ECG changes (25.6 g vs 27.4 g, p=0.8), nor was ejection fraction (43% vs 45%, p=0.5) or LV end diastolic volume (173 ml vs 174 ml, p=0.9).
Conclusions Patients with STEMI presenting with reciprocal ECG changes have significantly larger AAR, and significantly higher myocardial salvage and salvage index than those without. Reciprocal ECG changes may be a marker of larger volumes of myocardium at risk, and may also denote patients with larger potential for salvage with revascularization. There was no relationship to infarct size, presumably as other factors, such as time to revascularization and TIMI flow post-procedure will influence the degree of myocardium infarcted.
Data are shown as mean±SEM or n (%). There were no significant differences between the groups (p≥0.1 for all).