Kuniyoshi FHS et al. (2008) Day night variation of acute myocardial infarction in obstructive sleep apnea. J Am Coll Cardiol 52: 343–346

In the general population, sudden cardiac death occurs most frequently in the morning, between 6am and noon; by contrast, sudden cardiac death in patients with obstructive sleep apnea (OSA) usually occurs at night. Researchers have hypothesized that OSA might trigger myocardial infarction (MI), as MI can cause sudden cardiac death and patients with a history of MI are more likely to have OSA than the general population.

Kuniyoshi et al. prospectively studied 92 patients admitted to hospital with incident MI. Onset of MI between midnight and 6am occurred significantly more often in patients with OSA than in patients without OSA, irrespective of whether OSA was defined as ≥ 5 or ≥ 10 apnea–hypopnea events per hour (32% versus 7%, P = 0.01, and 33% versus 14%, P = 0.03, respectively). Patients who experienced an MI between midnight and 6am were six times more likely to have OSA than those who experienced MI at other times (P = 0.01); overall, 91% of patients who had an MI during this time period had OSA.

The authors of this study conclude that OSA might be a trigger for MI and suggest that patients with nocturnal onset of MI should be tested for this disorder. Given that the pathophysiology of OSA might increase the risk of MI at night, the potential for OSA therapy to prevent night-time cardiac events should be evaluated.