Mechanism of sudden cardiac death in obstructive sleep apnea, revisited

Abstract

Obstructive sleep apnea (OSA) raises the risk of sudden cardiac death (SCD) by 300–400% depending on the severity of OSA. However published reports raised the association between OSA and SCD but not the mechanism of SCD. It is known that OSA exerts profound oxidative stress in the cardiovascular system. Repetitive nocturnal hypoxemia and arousals lead to ischemia reperfusion, cellular degeneration, and apoptosis, cardiac remodeling such as diastolic and systolic dysfunctions; which provide fertile environment for reentrant arrhythmias. Increase temporal dispersion in myocardial depolarization has been shown to enhance the genesis of malignant arrhythmias that in turn raise sudden death risk. We postulated that OSA leads to higher incidence of SCD due to reentrant arrhythmias initiated by ventricular extrasystoles that excite myocardial fibers at the height of its vulnerable period, reentrant beats trigger runs of ventricular tachycardia and ventricular fibrillation. We deployed microvolt T-wave alternans (MTWA) as a tool to measure myocardial vulnerability. We attempted to determine if OSA leads to higher incidence of positive microvolt T-wave alternan (MTWA+); thus higher risk for arrhythmic death; and correlated MTWA result with severity of OSA as measured by apnea hypopnea index (AHI). 201 (M/F 1.1/1) patients with OSA of varying severity underwent MTWA in a random manner. We segmented the patients into MTWA positive (MTWA+), MTWA Indeterminate (MTWAI), MTWA negative (MTWA-). We then analyzed the MTWA result in relation to AHI. It has been shown that MTWA+ and MTWAI patients have higher risk of SCD usually from ischemia and cardiomyopathy. There was a higher incidence of MTWA+ ( p -value < 0.004) and MTWAI ( p -value < 0.001) in severe OSA “AHI 30–50” and unusually severe OSA “AHI > 50” MTWA+ ( p -value < 0.003), MTWAI ( p -value < 0.001 respectively). These two subgroups of OSA could be at higher risk for arrhythmic deaths since MTWA+ and MTWAI patients have higher mortality rate from malignant arrhythmias than MTWA−. sp020The severity of OSA is directly proportional to the incidence of MTWA positive (MTWA+) and MTWA indeterminate test (MTWAI). Severe and unusually severe OSA patients could be at higher risk of arrhythmic death than milder OSA as measured by MTWA. Cambridge Heart sold the equipment and supplies to Chanwell Clinic in the performance of MTWA test.