Determinants of cardiorespiratory fitness after successfully reperfused ST-elevation myocardial infarction

Modern treatment of ST-elevation myocardial infarction (STEMI), emphasizing prompt reperfusion, has improved clinical outcomes by preserving cardiac function. Despite this, cardiorespiratory fitness remains impaired. The purpose of this study was to assess determinants of cardiorespiratory fitness in patients with reperfused STEMI and preserved cardiac function.

We prospectively collected data from two patient cohorts with reperfused STEMI who underwent cardiopulmonary exercise testing on either a semi-supine cycle ergometer (Cohort 1) or treadmill (Cohort 2). Peak oxygen consumption (VO₂) was measured as mL·kg^-1·min^-1 and as percent-predicted. Cardiac reserve was measured with Doppler echocardiography using heart rate (HR), stroke volume (SV), and cardiac output (CO) before and at peak exercise. Arterial-venous oxygen difference (a-v O₂diff) was calculated using the Fick equation.

We included ninety-five patients (58 [51-65] years, 34% female) tested 41 [37-45] days after STEMI (Cohort 1: n = 39; Cohort 2: n = 56). Resting LVEF was 55 [50-59] %, with 2 (2%) having <40%. E' velocity was 8.8 [7.3-10.5] and E/e' was 7.6 [6.5-9.2]. Peak VO₂ was 20.0 [16.3-22.9] mL·kg^-1·min^-1, and 74 (78%) and 24 (25%) patients had reduced peak VO₂ at <80% and <60% of predicted, respectively. A significant positive correlation was observed between peak VO₂ and peak CO (R = 0.42, p = 0.0001), SV (R = 0.24, p = 0.02), HR (R = 0.36, p = 0.006), and a-v O₂diff (R = 0.49, p < 0.0001). Peak HR and SV were each independent predictors of peak VO₂ using multivariate analyses (all p < 0.01).

Cardiorespiratory fitness remains impaired after successfully reperfused recent STEMI, despite rather preserved resting cardiac function. Cardiac and peripheral reserve partially explain the impairments, and preserving these may improve fitness after STEMI.