Sleep Related Cardiovascular Risk

Although 20% of myocardial infarctions (MIs) and 15% of sudden cardiac deaths (SCD) occur between midnight and 6:00 A.M., nocturnal cardiac death remains an underappreciated and poorly understood phenomenon. The risk of nocturnal SCD may be‐especially high in patients with coronary disease confounded by apnea, heart failure, recent Ml, pause‐dependent Torsade de Pointes, and near miss victims of sudden infant death syndrome (SIDS) or siblings of SIDS vistims. During rapid eye movement (REM) sleep and dreaming, significant bursts in sympathetic nervous system activity may compromise coronary flow and trigger life‐threatening arrhythmia in susceptible individuals. In non‐REM or slow wave sleep, hypotension may lead to malperfusion of the heart and brain as a result of a lowered pressure gradient through stenosed vessels. Obstructive sleep apnea, which afflicts 1.5 million Americans, can generate reductions in arterial oxygen saturation, which may lead to hypertension and greatly increased risk of myocardial infarction. Cardiac medications which cross the blood‐brain barrier have the potential to alter sleep structure and provoke nightmares with severe cardiac autonomic discharge. Recently, new streamlined technology has been developed for tracking of sleep state. Among the most promising is the Nightcap, an unobtrusive, low cost device which accurately detects sleep state from eyelid and head movement with algorithms which could be incorporated into the circuity of ambulatory ECG recorders. Sleep states present unique autonomic, hemodynamic, and respiratory challenges to the diseased myocardium which cannot be replicated by daytime diagnostic tests. Because of the magnitude of the problem of nocturnal death and the availability of new practical technology for combined monitoring of sleep state and ECG, more widespread nighttime monitoring of the cardiac patient seems warranted.