Cardiac Arrhythmias at Extreme Altitude

Background: Several physiological changes at high altitude give rise to a pro-arrhythmic milieu. A fall in atmospheric pressure at high altitude decreases the partial pressure of oxygen (PaO2) and causes arterial hypoxemia. Respiratory alkalosis secondary to hyperventilation causes hypokalemia and hypocalcemia. Both factors facilitate the occurrence of rhythm disturbances, and may be further exacerbated in an adrenergic state with increased epinephrin levels. Objectives: The primary objective is to investigate the incidence of supraventricular and ventricular tachyarrhythmias, and the incidence of bradyarrhythmias in climbers during the ascent of Mount Everest. The secondary objective is to investigate clinical, electrocardiographic and echocardiographic predictors of cardiac arrhythmias at extreme altitude. Methods: This is a prospective cohort study of healthy volunteers climbing Mount Everest. Subjects will be evaluated for eligibility by electrocardiography and echocardiography. All participants will undergo a stress test in order to rule out pre-existing rhythm disturbances during exercise. Study participants will undergo ambulatory rhythm monitoring in their home environment within 12 weeks of the climb. Subsequently, subjects will repeat ambulatory rhythm monitoring during the ascent from basecamp to the summit of Mount Everest. The subjects will act as their own controls.