A transient decrease in night-to-night variability of REM sleep before myocardial infarction

A first myocardial infarction in adults using Fitbit sleep data is preceded by a transient decrease in REM-sleep night-to-night variability at days 30–16, returning by days 15–1.

• Why it matters: Time to treatment and pre-event fatigue or sleep disturbance are clinically important, but whether wearable-measured sleep variability changes within individuals before MI—and whether it is MI-specific—was unknown.
• What they did: In the All of Us Research Program, 45 first-MI cases with ≥180 valid Fitbit sleep nights in the prior 360 days were matched to up to 10 controls; REM-fraction variability (SD, RMSSD, CV) was tested against 10,000 randomly placed index dates (max-T).
• The result: The decrease-then-return pattern was rarely matched at 10,000 index dates (max-T p<0.001), driven by SD decreasing at days 30–16 (Cliffs {delta} -0.30, p=0.004; max-T p=0.0034) and RMSSD returning over days 15–1 (Cliffs {delta} +0.36, p<0.001; max-T p=0.0035), and the SD decrease was not seen before pneumonia, fracture/appendicitis, or any-cause admissions.