Cardiac asystole during an hypoxic drive study in a normal subject

A healthy 31-year-old man who had previously sojourned to an altitude of 5,000 meters with no detrimental effect developed sudden cardiac asystole during a progressive hypoxic ventilatory response ( HVR ) test. At the moment of asystole, his alveolar PO2 (PAO2) was 41 mm Hg and his arterial oxygen saturation (SaO2) was 81 percent. Cardiopulmonary resuscitation was initiated, and after 20 seconds of asystole and apnea, he recovered normal sinus rhythm and spontaneous respiration. A subsequent ECG and cardiac enzyme levels were normal. During testing, he demonstrated depressed ventilation in response to hypoxia and a slowing of the heart rate. Careful observation of heart rate and breath-by-breath ventilation during HVR tests may predict this potentially fatal complication.