Purpose Both prolonged exercise and acute high-altitude exposure are known to induce cardiac changes. We sought to describe the cardiac responses to speed climbing at high-altitude, including left ventricular (LV) performance assessment using the myocardial work index (MWI), a new index derived from 2D speckle tracking echocardiography (STE). Methods Eleven elite alpinists (9 males, age: 26 ± 4 years) were evaluated before and immediately after a speed ascent of the Mont-Blanc (4808 m) by echocardiography using conventional measurements as well as STE and MWI computation with derivate parameters as global work efficiency (GWE) or global wasted work (GWW). Results Athletes performed a long-duration (8 h 58 min ± 60 min) and intense (78 ± 4% of maximal heart rate) ascent under gradual hypoxic conditions (minimal SpO2 at 4808 m: 71 ± 4%). Hypoxic exercise-induced cardiac fatigue was observed post-ascent with a change in right ventricular (RV) and LV systolic function (RV fractional area change: - 20 ± 23%, p = 0.01; LV global longitudinal strain change: - 8 ± 9%, p = 0.02), as well as LV geometry and RV-LV interaction alterations with emergence of a D-shape septum in 5/11 (46%) participants associated with RV pressure overload (mean pulmonary arterial pressure change: + 55 ± 20%, p < 0.001). Both MWI and GWE were reduced post-ascent (- 21 ± 16%, p = 0.004 and - 4 ± 4%, p = 0.007, respectively). Relative decrease in MWI and GWE were inversely correlated with increase in GWW (r = - 0.86, p = 0.003 and r = -0.97, p < 0.001, respectively). Conclusions Prolonged high-altitude speed climbing in elite climbers is associated with RV and LV function changes with a major interaction alteration. MWI, assessing the myocardial performance, could be a new tool for evaluating LV exercise-induced cardiac fatigue.
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