Cardiac fatigue following high altitude competitive running: No evidence for cumulative effect in the medium long term

The aim of this study was to assess the effects of prolonged, repetitive, competitive high altitude running on left ventricular performance. We studied 11 world-class athletes (8 males, 3 females, mean age 30 ± 3 years) in 2 consecutive years (1994-1995) before and after two high altitude races performed in Italy. On both occasions we recorded the 12-lead ECG as well as mono, two-dimensional and Doppler echocardiograms, 24 hours before, within 30 min and 24 hours after the end of the race. Measurements included heart rate, blood pressure, ejection fraction, early (E) and late (A) transmitral inflow velocities, their ratio (E/A) and percent atrial contribution (AC). Similar studies were obtained in 11 age and sex matched control subjects at baseline and following a maximal exercise testing. Blood pressure in athletes was not modified after both races, while heart rate immediately after the end of the race was significantly increased (p <0.001 in 1994, p <0.002 in 1995). Ejection fraction remained stable in both races (pre 61 ± 4%, post 60 ± 5% in 1994; pre 62 ± 5%, post 63 ± 4% in 1995). Conversely, Doppler E/A ratio significantly decreased early after the race from 1.9 ± 0.1 to 1.3 ± 0.1 (p <0.05) in 1994 and from 1.7 ± 0.1 to 1.4 ± 0.1 (p <0.05) in 1995. The decrease was mainly due to a reduction in E (p<0.05), since A was not modified. As a result, AC increased from 20 ± 3 to 28 ± 5% (p <0.05) and from 21 ± 3 to 26 ± 6% (p <0.05) respectively. All parameters returned to baseline at the 24-hour controls. No differences were found between pre-race measurements in 1994 and 1995. Compared to controls, all athletes had significantly higher resting E and A velocities and lower E/A ratio and AC to ventricular filling. However, soon after exercise E/A and AC were similar between the two groups and returned to baseline levels at the 24-hour control. As shown by the transient reduction in ventricular filling parameters, our findings are consistent with previous studies reporting transient cardiac fatigue following strenuous exercise. However, the functional effects of these changes do not seem to interfere with cardiac function and athletic performance both in the short and medium long term, since all subjects continued successful racing and did not show left ventricular deterioration at 1-year follow-up. Perhaps, repetitive episodes of cardiac fatigue may assume clinical importance over many years. Therefore, the indication to long term echocardiographic follow-up of such extreme endurance athletes may be discussed.