[An unusual cause of oxygen desaturation: isorhythmic atrioventricular dissociation]

A 69-year-old man, with a history of angina pectoris treated with verapamil, was admitted in the intensive care unit after a right liver resection. On admission, the chest X ray and the arterial blood gases (PaO2/FlO2 = 320) were normal. There after, the patient exhibited brief decreases of SpO2 (at 82%) which were spontaneously reversible. The ECG showed an isorhythmic atrioventricular dissociation associated with SpO2 falls. The SpO2 returned to normal values when cardiac rhythm became sinusal again. This case shows that in case of an important and brief decrease in SpO2, unexplained by a respiratory cause, a decrease of arterial pressure due to rhythmic disease should be considered.