CARDIOPULMONARY AND HEMODYNAMIC EFFECTS OF HIGH-VOLUME ENDURANCE RACE TRAINING IN HFrEF

INTRODUCTION: The rising participation in endurance sports among populations with a high prevalence of premature ischemic Heart Failure with Reduced Ejection Fraction (HFrEF) creates a clinical dilemma. The physiological limits and cardiorenal effects of high-volume, race-oriented training in this patient population are undefined. This study prospectively documents the cardiopulmonary, hemodynamic, and renal adaptations to a supervised, high-volume endurance program in a patient with severe ischemic HFrEF. CASE PRESENTATION: The patient is a 61-year-old male endurance athlete with severe ischemic HFrEF (baseline Left Ventricular Ejection Fraction [LVEF] 32%). His condition resulted from an anterior wall myocardial infarction, which was complicated by a cardioembolic stroke and recurrent ventricular arrhythmias, necessitating the implantation of an Automatic Implantable Cardioverter-Defibrillator (AICD) for secondary prevention. MANAGEMENT or OUTCOME: Over a 20-month period, the patient was managed with quadruple guideline-directed medical therapy (GDMT) and a supervised, hybrid exercise regimen averaging >300 minutes/week, with training guided by serial cardiopulmonary exercise testing (CPET). Longitudinal assessment demonstrated profound positive cardiac remodeling: LVEF improved from 32% to 42% (a 31% relative increase), resting cardiac output increased by 34% (3.8 to 5.1 L/min), and peak oxygen consumption (VO2 max) rose by 35% (14.2 to 19.1 mL/kg/min). Renal function remained stable throughout the study (baseline estimated Glomerular Filtration Rate [eGFR] 79 vs. 76 mL/min/1.73m² at follow-up). The patient successfully completed over 20 endurance events. However, an Ironman 70.3 event precipitated an episode of acute respiratory distress, highlighting a critical adverse event. DISCUSSION: In a highly selected HFrEF patient, a meticulously monitored, high-volume exercise program can drive profound improvements in cardiac function and aerobic capacity without compromising renal function. However, this intervention operates within a narrow therapeutic window, as evidenced by the acute decompensation during maximal exertion. This case demonstrates that while exceptional cardiorespiratory adaptations are possible, they demand a sophisticated, technology-enabled, and cardiorenal-conscious management strategy to mitigate the substantial risks.