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Abstract
Acute myocardial infarction in a leading cause of death in Australia and worldwide. Early identification of high risk patients provides valuable prognostic information to help stratify medical and invasive strategies. Left ventricular (LV) function, measured by LV ejection fraction (LVEF) has traditionally been the most widely accepted prognostic marker in patients after acute ST elevation myocardial infarction (STEMI). Current risk stratification, based primarily on evaluation of LVEF, does not take into account modern imaging or multimodality diagnostics. Advanced imaging techniques, including cardiac magnetic resonance imaging (CMRI) have become the gold standard in non-invasive assessment of left ventricular myocardial damage and subsequent prognosis; however CMRI is expensive and has limited availability. The research aims were to identify early prognostic markers, using multiple non-invasive techniques (serum biomarkers and noninvasive imaging modalities), to identify high risk patients for major adverse cardiovascular events (MACE).
High-sensitivity troponin T (hs-TnT) levels are routinely available for clinical evaluation of acute coronary syndrome, and correlate with clinical outcomes after STEMI. Hs-TnT show a biphasic release profile with “plateau” phase blood levels, occurring between days 2 to 6 after STEMI, which may provide a stable sampling window. The first study aims were to determine the sampling period that would best predict CMRI measured infarct scar characteristics and LV function. First presentation STEMI patients were prospectively studied. Serial hs-TnT levels were performed at admission, peak, 24 hour, 48 hour and 72 hours after STEMI. Levels of hs-TnT at 48 and 72 hours, during the plateau phase post STEMI, predicted infarct scar size (ORs 3.08 and 3.53 respectively, both p<0.001), poor myocardial salvage (OR 1.39 [p=0.031] and OR 1.55 [p=0.009]), and reduced LVEF <40% (OR 1.47 [p=0.018] and OR 1.43 [p=0.026]).
The second study assessed the prognostic significance of hs-TnT during the plateau phase after STEMI. After a median of 602 days follow-up, measurement of hs-TnT at 48 and 72 hours, were associated with MACE (Log rank p=0.002, and p=0.012 respectively). Furthermore, a 48 and 72 hour hs-TnT levels were both independent predictors for MACE (HR=1.20, p=0.002, and HR=1.21, p=0.035 respectively).
Severe diastolic dysfunction (restrictive filing) has been an established prognostic marker after myocardial infarction. However this has been evaluated prior to the era of percutaneous revascularization, and indentifies a small subgroup of patients. The third study sought to evaluate adverse diastolic remodelling (i.e. worsening diastolic grade or persistent restrictive filling) by transthoracic echocardiography and its prognostic value after all reperfused STEMI presentations. Follow-up infarct scar size predicted adverse diastolic remodelling and persistent restrictive filling alone (area under curve 0.86 and 0.89 respectively). During a mean follow-up of 710 days, adverse diastolic remodelling was an independent predictor of MACE (HR=3.79, p<0.001) when adjusted for clinical risk factors (Thrombolysis In Myocardial Infarction (TIMI) risk score), infarct scar size, microvascular obstruction and LVEF. Furthermore, adverse diastolic remodelling identified a larger group of ‘at-risk’ patients than persistent restrictive filling alone.
Measurement of hs-TnT during the plateau phase after STEMI can provide an inexpensive method of prognostic risk assessment, and correlates well with CMRI derived infarct scar size and characteristics. Furthermore, adverse diastolic remodelling is a powerful prognostic marker, and emphasises the importance of serial early monitoring after STEMI. Given the limitations on healthcare resources and availability of some advanced imaging modalities, the current research has shown the utility of routinely accessible parameters for post STEMI risk stratification.