Low Forward Flow and Early Mortality Despite Preserved Left Ventricular Ejection Fraction After Acute Myocardial Infarction: A MIMIC‐IV‐Echo Cohort Study

Purpose Left ventricular ejection fraction (LVEF) guides risk assessment after acute myocardial infarction (AMI), but preserved LVEF does not ensure preserved forward flow. We examined stroke volume index (SVI) and 30‐day mortality after AMI with preserved LVEF. Methods Adults with a first AMI‐coded hospitalization and echocardiography from 24 h before through 48 h after admission were identified in MIMIC‐IV and MIMIC‐IV‐Echo. Documented type 2 myocardial infarction was excluded. SVI was calculated from left ventricular outflow tract (LVOT) diameter, velocity‐time integral (VTI), and body surface area (BSA). Preserved LVEF was ≥50%; low flow was SVI <35 mL/m 2 . Modified Poisson regression estimated risk ratios (RRs); splines assessed nonlinearity. Results Among 4,307 patients, 2,142 had preserved LVEF; 864 (40.3%) had low flow. Thirty‐day mortality was 7.5% (65/864) with low flow and 4.7% (60/1,278) with normal flow. The adjusted RR was 1.65 (95% confidence interval, 1.19–2.29), but joint adjustment for shock and pre‐echocardiography support yielded RR 1.31 (0.95–1.82). The association was nonlinear ( P < 0.001). Spline‐modeled SVI increased the C‐statistic by 0.0147 (bootstrap 95% CI, 0.0051–0.0290) beyond clinical variables and LVEF; after adding shock, cardiac arrest, and support to the base model, the increase was 0.0024 (−0.0012–0.0097). Conclusion Low Doppler‐derived SVI identified a higher‐risk preserved‐LVEF phenotype, but its incremental discrimination was minimal after acute‐severity information was included. The finding supports descriptive hemodynamic phenotyping rather than an AMI treatment threshold and requires external validation against Killip class and established risk scores.