Electrocardiographic changes with corresponding oxygensaturation levels between 10 pm and 9 am. Oxygen saturation was reduced progressively between midnight and 4 am, and a corresponding increase in heart rate and prolongation ofthe QTc interval was observed during this time. capnoea) during the night. 2 The findings of Dr McNicholas and Professor Fitzgerald could be explained by nocturnal hypoxaemia and consequent cardiac damage. They found the highest death rate among patients with type 2 respiratory failure between 11 pm and 7 am. Some time during this period most of these patients are in rapid eve movement sleep, and they hypoventilate and develop hypercapnoea. 3 Patients with type 2 respiratory failure are often overweight, 4 and they develop hypoxaemia, hypoventilation, and sometimes sleep apnoea. 3 s

We have noticed these changes more often between 1 and 5 am. 2 During this time patients develop several electrocardiographic changes such as prolonged QTc interval (figure), tachycardia, ST-T depression, heart block, and various arrhythmias. 2 Prolonged QTc interval associated with hypoxaemia was found in most of these patients. 2 5 Schwartz et al reported that a prolonged QTc interval is arrhythmogenic and also a predictor of sudden death in patients with myocardial infarction. 6 Severe hypoxaemia, hypercapnoea, hypoventilation, and acidosis probably insult the myocardium and result in widespread electrocardiographic changes, 2 5 and these changes may predispose to nocturnal death among these patients. V G TIRLAPUR