Long-duration human spaceflight induces atrophy in the left ventricular papillary muscles

Microgravity exposure induces cardiac deconditioning, primarily due to hypovolemia and inactivity. Animal models suggest microgravity may cause left ventricular (LV) papillary muscle atrophy, but this has not been studied in humans. This study used MRI to assess LV papillary muscle mass and LV morphology and function in nine male cosmonauts before and 6 ± 2 days after long-duration spaceflight (247 ± 90 days). Spaceflight did not affect LV volumes, ejection fraction, and strain parameters, but increased heart rate (P < 0.001) and cardiac output (P = 0.03). LV papillary muscle mass decreased by 14% (P = 0.017), while LV mass tended to increase (P = 0.083), mitral annular diameter increased (P = 0.004) without mitral leakage, and LV sphericity increased (P = 0.02). These findings suggest LV adapts to space with geometric changes, but microgravity-induced papillary muscle atrophy requires further study for long-term implications.