Nocturnal ischemic events in patients with obstructive sleep apnea syndrome and ischemic heart disease - Effects of continuous positive air pressure treatment

OBJECTIVES To investigate the occurrence of nocturnal ischemic events in pa tients with obstructive sleep apnea syndrome (OSAS) and ischemic heart dise ase (IHD). BACKGROUND Although previous reports documented nocturnal cardiac ischemic events among OSAS patients, the exact association between obstructive apnea s and ischemia is not yet clear. It is also not known what differentiates b etween patients showing nocturnal ischemia and those that do not. METHODS Fifty-one sleep apnea patients (age 61.3 +/- 8.3) with IHD particip ated in the study (after withdrawal of beta-adrenergic blocking agents and anti-anginotic treatment). All patients underwent whole-night polysomnograp hy including ambulatory blood pressure recordings (30 min interval) and con tinuous Holter monitoring during sleep. A control group of 17 OSAS patients free from IHD were also similarly studied. Fifteen of the 51 patients were also recorded under continuous positive airway pressure (CPAP). RESULTS Nocturnal ST segment depression occurred in 10 patients (a total of 15 events, 182 min), of whom six also had morning ischemia (06-08 am). Fiv e additional patients had only morning ischemia. No ischemic events occurre d in the control group. Age, sleep efficiency, oxygen desaturation, IHD sev erity and nocturnal-double product (DP) values were the main variables that significantly differentiated between patients who had ischemic events duri ng sleep and those who did not. Nocturnal ischemia predominantly occurred d uring the rebreathing phase of the obstructive apneas, and it is characteri zed by increased heart rate (HR) and DP values. Treatment with continuous p ositive airway pressure significantly ameliorated the nocturnal ST depressi on time from 78 min to 33 min (p < 0.001) as well as the maximal DP values (14,137 +/- 2,827 vs. 12,083 +/- 2,933, p < 0.001). CONCLUSIONS Exacerbation of ischemic events during sleep in OSAS may be exp lained by the combination of increased myocardial oxygen consumption as ind icated by increased DP values and decreased oxygen supply due to oxygen des aturation with peak hemodynamic changes during the rebreathing phase of the obstructive apnea. Treatment with CPAP ameliorated the nocturnal ischemia. (C) 1999 by the American College of Cardiology.