Pathophysiological mechanisms of noncardiac syncope in athletes

The investigation of the differences in orthostatic responses of individuals with a history of noncardiac syncope(NCS) between athletes and nonathletes.

A passive tilt test for 30min was performed in 133 athletes (54 with NCS, 79 without NCS) and 48 nonathletes (15 with NCS, 33 without NCS). We performed measurement of haemodynamic, heart rate variability and baroreflex sensitivity parameters. All comparisons were adjusted for age, gender and body mass index(BMI).

Athletes with NCS had increased heart rate(HR) (90±11 vs 81±10bpm, p=0.001) and decreased total peripheral resistance index(TPRI) (2227±408 vs 2918±733dynesm²/cm⁵, p=0.039) and baroreflex effectiveness index(BEI) [70.16(37.42-89.71) vs 72.19(48.49-91.35)%, p=0.016] compared with athletes without NCS. After applying backward stepwise logistic regression analysis to predict history of NCS in athletes, the final model included age, gender, BMI, HR and TPRI. Nonathletes with NCS had increased HR (95±24 vs 83±11bpm, p=0.024) and TPRI (3744±1606 vs 2937±880dynesm²/cm⁵, p=0.030) and decreased stroke index(SI) (25.4±7.6 vs 33.0±7.5mL/m², p=0.003) compared with nonathletes without NCS. After applying backward stepwise logistic regression analysis to predict history of NCS in nonathletes, the final model included SI and HR. Among individuals with NCS, athletes had increased SI and BEI and decreased HR and TPRI compared with nonathletes. Among individuals without NCS, a positive result of tilt test was less frequent in athletes compared with nonathletes (p=0.031).

The possible main underlying mechanism for NCS during upright standing in athletes is the decreased TPRI, while the inadequate preservation of SI in nonathletes.