Cardiac magnetic resonance (CMR) imaging provides useful prognostic information in revascularized ST-segment elevation (STEMI) patients, according to a recent study published in June 2018, in the Journal of the American College of Cardiology.
Microvascular obstruction (MVO) which occurs in approximately 50% of successfully revascularized STEMI patients may lead to myocardial injury and is an independent predictor of adverse outcomes. It is associated with larger myocardial infarction (MI) size, adverse left ventricular (LV) remodeling, and poor prognosis.
The current American Heart Association/American College of Cardiology and European Society of Cardiology guidelines for STEMI recommend quantification of left ventricular (LV) ejection fraction (EF) for decision-making and risk stratification in all STEMI patients. However, this parameter is considerably influenced by post-infarction stunning and compensatory hyperkinesis of the non-infarcted myocardium which limits the accuracy of it being used as a prognostic marker. Therefore, the quantification of irreversible ischemic damage after STEMI seems to be more accurate to predict clinical outcomes.
CMR has the potential to become the preferred imaging modality in STEMI patients because of its accurate and comprehensive evaluation of left ventricular structure and function using quantitative multi-parametric characterization of infarcted myocardium. However, previous CMR studies in STEMI patients have been limited by a single-center design, small sample sizes, and short-term follow-up.
In this study, 810 STEMI patients from 6 European centres treated with primary percutaneous coronary intervention (PPCI) were analyzed, led by Rolf Symons from the University Hospital Gashuisberg in Leuven, over a 12-year period for the long-term incremental prognostic value of CMR as compared to clinical predictors. CMR was performed a median of 4 days after PPCI and patients were followed up over an average period of 5.5 years. The primary endpoint was a total of decompensated heart failure (HF) and all-cause mortality.
The results indicated that early post-infarction cardiac MR-based microvascular obstruction (MVO) has a strong independent prognostic value in reperfused STEMI patients at long-term follow-up. In addition, patients with the extent of MVO ≥ 2.6 percent of LV had an approximately 3 fold higher likelihood of experiencing the primary endpoint when compared to those with MVO extent < 2.6% of LV. Moreover, the extent of MVO ≥ 2.6 percent of the left ventricle was the strongest independent predictor of all death and HF hospitalization (HR:2.05 (95% CI), p:0.029; HR: 5.99 (95% CI), p<0.001 respectively). Finally, this cut-off value of MVO extent also provided incremental prognostic value in addition to traditional outcome predictors, improving long-term risk stratification of STEMI patients.
The authors reinforce the importance of future research, stating that ‘Experimental and clinical studies are warranted to better understand the pathophysiology of MVO in STEMI and to design strategies for counteracting this detrimental phenomenon’.