Cardiac Reserve And Cardiorespiratory Fitness After Reperfused ST-elevation Myocardial Infarction

PURPOSE: Myocardial damage in ST-elevation myocardial infarction (STEMI) reduces cardiac function, which may impair cardiorespiratory fitness (CRF - assessed by exercise capacity and ventilatory efficiency). The relationship of cardiac reserve with CRF in patients with reperfused STEMI has not been well characterized. METHODS: We assessed cardiac reserve and CRF in patients with reperfused STEMI using a symptom-limited cardiopulmonary exercise test 41 [39-43] days after the index STEMI. Patients were excluded if they had a prior STEMI or heart failure, and included only those with a respiratory exchange ratio (RER) > 1.0. Cardiac reserve was measured with Doppler echocardiography using left ventricular ejection fraction (LVEF), stroke volume (SV), and cardiac output (CO) before and after peak exercise. We assessed CRF by measuring VO2peak, oxygen uptake efficiency slope (OUES), and minute ventilation/carbon dioxide production slope [VE/VCO2]. Wasserman formula was used to calculate predicted VO2peak. Correlations were tested with Spearman’s rank test. Data are expressed as median [interquartile range]. RESULTS: We included fifty-six patients (median age 58 years, 38% female, median BMI: 30.2 kg/m2). After STEMI, LVEF was 55 [49-58] %. Peak RER was 1.14 [1.06-1.22] and peak heart rate was 137 [123-151] bpm. VO2peak was 19.8 [16.5-23.2] ml·kg-1·min-1, and 71 [63-78] % of predicted. VE/VCO2 slope was 32 [29-37] and OUES was 2.0 [1.5-2.6]. Exercise SV was 79 [70-94] mL and exercise CO was 11.3 [9.0-13.1] L/min. There was a significant correlation between both cardiac reserve, such as exercise SV, and CO, and measures of CRF such as VO2peak (Figure1A and 1B), VE/VCO2 slope (Figure 1C and 1D), and OUES (Figure 1E and 1F). CONCLUSIONS: Cardiac reserve with exercise correlates with CRF in patients with reperfused STEMI early after the index event. Strategies aimed at preserving or restoring cardiac reserve may also improve CRF in patients with STEMI. Supported by: 5R01AG076360-03