Nighttime acute coronary syndrome (ACS) is significantly more prevalent in patients with visceral fat accumulation and sleep-disordered breathing, according to a new study.

Researchers at Osaka University (Japan) conducted a study involving 109 consecutive patients (mean age 66) who had revascularization procedures for ACS and subsequent overnight cardiorespiratory monitoring before discharge. The study population consisted of patients with ST-segment elevation myocardial infarction (STEMI), 27 with non-ST elevation MI (NSTEMI), and 16 with high-risk angina. The patients had a mean body mass index (BMI) of 23.8, total fat area of 239 cm², visceral fat area of 127 cm², and an apnea-hypopnea index that averaged 11 events per hour. Adiponectin levels were measured shortly before sleep onset and after waking. Onset of chest pain from midnight to 7 am was considered nighttime ACS, and onset any other time was considered daytime ACS.

The researchers found that ACS had a nighttime onset in 25 patients, and daytime onset in 84. Sleep monitoring results showed that 63 (58%) of the patients had sleep-disordered breathing, and 64 (59%) had visceral fat accumulation of over 100 cm². Among patients with nighttime onset of ACS, 12 of 17 with excess visceral fat also had sleep-disordered breathing, as compared with two of eight patients who had visceral fat accumulation less than 100 cm². In patients with daytime ACS, the prevalence of sleep-disordered breathing did not differ between patients with and without excess visceral fat.

Among patients with daytime ACS, those with excess visceral fat had mean adiponectin levels of 6.8 µg/mL and 6.7 µg/mL before and after sleep, versus 11.6 µg/mL and 11.7 µg/mL for patients with less than 100 cm² visceral fat accumulation. Excess visceral fat was associated with a significantly higher apnea-hypopnea index in patients with nighttime ACS, but not in the group with daytime ACS. The study was published ahead of print on August 12, 2011, in the American Journal of Cardiology.

“These results suggest that an association of sleep-disordered breathing and excess visceral fat with nocturnal dysregulation of adiponectin may play some role in the development of nighttime-onset ACS,” said lead author Ken Kishida, MD, PhD. “Sleep-disordered breathing and excess visceral fat are treatable risk factors. Decrease of excess visceral fat and treatment of sleep-disordered breathing could be beneficial in preventing nocturnal cardiac events.”

ACS is usually one of three diseases involving the coronary arteries - STEMI (30%), NSTEMI (25%), or unstable angina (38%). These types are named according to the graphical appearance of the electrocardiogram (ECG) wave. ACS should be distinguished from stable angina, which develops during exertion and resolves at rest. In contrast with stable angina, unstable angina occurs suddenly, often at rest or with minimal exertion, or at lesser degrees of exertion than the individual's previous angina.

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