The Sleep Heart Health Study  found that obstructive sleep apnea (OSA) with excessive daytime sleepiness triples the chance of heart failure and doubles the risk of a cardiovascular event.
The study evaluated data from over 1200 patients with OSA and an apnea-hypopnea index (AHI) of 15 or more events per hour.
Important symptom subtypes noted were as follows:
Disturbed Sleep (12.2%)
Minimally Symptomatic (32.6%)
Excessively Sleepy (16.7%)
Moderately Sleepy (38.5%)
Excessively Sleepy subtype was associated with over 3 times increased risk of prevalent heart failure. The same subtype was associated with increased risk of incident cardiovascular disease with hazard ratio 1.7-2.4. Compared to those without OSA (AHI less than 5), significantly increased risk of both prevalent and incident cardiovascular events were noted mostly in the Excessively Sleepy subtype.