Hypoxia and cardiac arrhythmias in breath-hold divers during voluntary immersed breath-holds

The incidence and nature of cardiac arrhythmias during static apnea were studied by monitoring the electrocardiogram (ECG) and oxygen saturation (SaO₂) of 16 recreational breath-hold divers. All subjects completed a maximal apnea with a mean (±SD) breath-hold duration of 281 (±73) s without clinical complications. Both heart rate (HR) and SaO₂ decreased significantly with breath-hold duration. The decline in SaO₂ was inversely related to the decline in HR (r = −0.55, P < 0.05). Cardiac arrhythmias (supraventricular and ventricular premature complexes, right bundle branch block) occurred in 12/16 (77%) subjects and were related to breath-hold duration. Subjects with atrial premature complexes (n = 9) had a reduced BMI (P = 0.016) and a higher decline of the terminal SaO₂ (P = 0.01). In conclusion, ectopic arrhythmias were common during maximal static apneas for training purposes. The results indicate that the occurrence of ectopic beats is associated with individual factors such as the tolerable SaO₂ decrease.