Longitudinal Changes in Wearable-Captured Physiology Before Sudden Cardiac Death

Consumer wearables provide continual physiological data, including multiple cardiovascular metrics, yet their use in detecting physiological changes that precede cardiac events remains limited.

A 76-year-old man with structural heart disease experienced sudden cardiac death minutes after high-intensity indoor cycling. Change-point analysis of wearable-captured physiology revealed a coordinated step-change, with most changes clustering 4-6 months before the sudden cardiac death: heart rate variability halved, resting and nocturnal heart rate rose, deep sleep and 6-minute walk distance fell. These coincided with a fatigue complaint and a murmur prompting echocardiography, which revealed severe left ventricular dilation with preserved ejection fraction (approximately 60%), severe mitral regurgitation, moderate aortic regurgitation, and trace tricuspid regurgitation, consistent with advanced structural heart disease.

The key signal was not any single abnormal value but a coordinated, sustained step-change from the patient's own baseline that preceded imaging. Data of this kind could complement the episodic measurements cardiovascular care now relies on, informing both when to re-evaluate patients with known heart disease and how wearable heart-rate kinetics might guide their exercise.

Embedding continuous digital physiology monitoring into traditional cardiology has the potential to aid clinicians in timely evaluation and intervention.