Baseline predictors of final infarct size in patients with ST elevation myocardial infarction undergoing primary PCI

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Abstract Background In patients with coronary artery disease, the presence and extent of myocardial scar determined from cardiac magnetic resonance (CMR) imaging have recognized associations with major adverse cardiac events. Therefore, in patients presenting with ST elevation myocardial infarction (STEMI), early prediction of final infarct size (IS) has important prognostic and therapeutic implications. Purpose We sought to determine the predictors of final IS from baseline clinical, laboratory, and CMR imaging variables in patients presenting with STEMI and undergoing successful primary PCI (pPCI). Methods After successful pPCI, 76 STEMI patients underwent baseline (within 48-hours) and 3-months follow-up CMR imaging. The baseline CMR study was used to measure left ventricular (LV) volumes, ejection fraction (EF), and global longitudinal strain (GLS), the latter calculated using feature tracking from cine images. Final IS was measured in the 3-months follow up study using signal intensity quantification by the full width at half maximum method from late gadolinium enhancement images and expressed as a percentage of the total LV mass. Serum ST2 was drawn within 48 hours of STEMI presentation. Maximum values of ECG ST elevation prior to pPCI and serum Troponin I during index hospitalization were measured. Non-collinear baseline variables deemed significantly associated with the final IS on univariable linear regression and captured in all patients were entered into a multivariable model, adjusting for age and sex. Results Mean age was 54.1±10.9 years, 64 patients (78%) being males. Mean LV EF was 43.5±9.8%. Univariable predictors of final IS included hypertension, baseline maximum troponin, ST2, maximum ST elevation, LV volumes and EF, GLS, total angiographic procedure time, the presence of multi-vessel CAD, use of thrombectomy, TIMI flow and myocardial blush grades at baseline and after wiring, and prescription of loop diuretics and potassium-sparing diuretics on discharge (Table 1). A final multivariable linear model was constructed including age, sex, maximum troponin, maximum ST elevation, ST2, LV EF and GLS. In this model, baseline LV EF, maximum troponin, and maximum ST elevation remained independently associated with the final IS. Respective beta coefficients [95% CI] were -0.63 [-1- (-0.26)], 0.22 [0.11-0.33], and 0.90 [0.22-1.58]; p=0.001, <0.001, and 0.01) (Table 2; adjusted R2=0.6, p<0.001). ST2 and GLS were no longer associated with the IS. Conclusion After successful pPCI, baseline LV EF, maximum troponin I, and maximum ST elevation were independent predictors of final IS. These simple markers can identify patients at high risk of final IS who might benefit from advanced therapeutics. Future studies are warranted to confirm the prognostic value of risk scores incorporating these markers. Advanced laboratory (ST2) and imaging (strain) markers were not independently associated with IS.