Altered cardiac repolarisation in highlanders with high-altitude pulmonary hypertension during wakefulness and sleep.

High-altitude pulmonary hypertension (HAPH) is an altitude-related illness associated with hypoxaemia that may promote sympathetic excitation and prolongation of the QT interval. The present case-control study tests whether QT intervals, markers of malignant cardiac arrhythmias, are prolonged in highlanders with HAPH (HAPH+) compared to healthy highlanders (HH) and healthy lowlanders (LL). The mean pulmonary artery pressure (mPAP) was measured by echocardiography in 18 HAPH+ (mPAP, 34 mmHg) and 18 HH (mPAP, 23 mmHg) at 3,250 m, and 18 LL (mPAP, 18 mmHg) at 760 m, Kyrgyzstan (p < .05 all mPAP comparisons). Groups were matched for age, sex and body mass index. Electrocardiography and pulse oximetry were continuously recorded during nocturnal polysomnography. The heart rate-adjusted QT interval, QTc, was averaged over consecutive 1-min periods. Overall, a total of 26,855 averaged 1-min beat-by-beat periods were semi-automatically analysed. In HAPH+, maximum nocturnal QTc was longer during sleep (median 456 ms) than wakefulness (432 ms, p < .05) and exceeded corresponding values in HH (437 and 419 ms) and LL (430 and 406 ms), p < .05, respectively. The duration of night-time QTc >440 ms was longer in HAPH+ (median 144 min) than HH and LL (46 and 14 min, p < .05, respectively). HAPH+ had higher night-time heart rate (median 78 beats/min) than HH and LL (66 and 65 beats/min, p < .05, respectively), lower mean nocturnal oxygen saturation than LL (88% versus 95%, p < .05) and more cyclic oxygen desaturations (median 24/hr) than HH and LL (13 and 3/hr, p < .05, respectively). In conclusion, HAPH was associated with higher night-time heart rate, hypoxaemia and longer QTc versus HH and LL, and may represent a substrate for increased risk of malignant cardiac arrhythmias.