Electrocardiographic Changes During Exercise in Acute Hypoxia and Susceptibility to Severe High Altitude Illnesses
Background—To compare ECG at moderate exercise in normoxia and hypoxia at the same heart rate, to evidence independent predictors of hypoxia-induced ECG changes and evaluate electrocardiographic risk factors of severe high altitude illnesses (SHAI).
Methods and Results—456 subjects performed a 20-minute hypoxia exercise test with continuous recording of ECG and physiological measurements, before a sojourn above 4,000m. Hypoxia did not induce any conduction disorder, arrhythmias or change in QRS axis. The amplitude of P wave in V1 was lower in hypoxia than in normoxia. Amplitudes of S, R, and T wave as well as Sokolow index decreased in hypoxia. Under hypoxia, the amplitude of ST segment decreased in II and V6 and increased in V1; ST slope rose in V5 and V6 while J point was lower in II, V5 and V6. Multivariate regression of hypoxic/normoxic ratios of electrophysiological parameters and clinical characteristics showed a correlation between the decrease in Sokolow index, T wave amplitude in V5 with desaturation at exercise. Trained status and low body mass index were associated with a smaller decrease in T wave amplitude in V5 and V6. Comparison of ECG between subjects suffering or not from SHAI failed to show any difference.
Conclusions—During a hypoxia exercise test, a dose-dependent hypoxia-induced decrease in the amplitude of P/QRS/T waves was observed. No standard ECG characteristic predicted the risk of developing SHAI. Further studies are required to clarify the cause of these electrical changes and their potential predictive role of cardiac events.
- High altitute illnesses
- High altitude cerebral edema
- High altitude pulmonary edema
- exercise test
- Received September 5, 2014.
- Revision received December 14, 2014.
- Accepted December 29, 2014.