The Effects of Ascent and Descent on Heart Rate and Rhythm at High Altitude

Abstract

Introduction: Previous studies have reported a variable burden of cardiac arrhythmias, particularly supraventricular (SVE) and ventricular extrasystoles (VES), during hypoxic exposure. The majority of studies have either used simulated altitude and/or subjects at rest with passive ascent (eg cable car). In this study the burden and type of cardiac arrhythmias were recorded during exercise on ascent and descent to Kala Patthar (5643 m) in the Himalayas. Methods: Ten healthy British Military servicemen aged 18-50 years were included. Health status was confirmed following a baseline history, clinical examination, electrocardiogram and transthoracic echocardiogram. Continuous ambulatory 3 lead ECG recordings (Spacelabs LifeCardTM) were made during trekking ascent to 5643 m at 2610-3840 m, 3450-3880 m, 4240-4940 m and during descent at 5140-4371 m and at 4371-3710 m. Results: The average age of subjects was 36.1 ± 10.3 years (50% women). All subjects completed the three ascent and two descent treks that were recorded. There was a decrease in the maximal heart rates (p<0.0001) and oxygen saturations (p=0.004) with increasing HA. VEs were observed in 9/10 subjects at 2610- 3440 m, 7/10 at 3440-3710 m, 6/10 at 4270-4910 m, 9/10 at 5150-4270 m and in 6/10 at 4270-3710 m (p=0.30). Overall VE burden was non-significantly higher over ascent (95.0 ± 258.6/hour) versus descent (58.5 ± 171.5/hour; p=0.58). There was no significant change in SVEs (4/10 subjects overall) across the 5 treks (p=0.24). VEs (80.4 ± 226.5/hour) were more common than SVEs (0.11 ± 0.4/hour; p<0.001). There were no sustained pathological tachyarrhythmias. Conclusion: In this study moderate intensity exercise to 5643 m did not lead to significant cardiac arrhythmia development in healthy subjects. VEs are common and much more prevalent than SVEs and consistently observed during both ascent and descent.