BACKGROUND: The wearable defibrillator (WCD) is a useful device to prevent sudden cardiac death (SCD) due to fatal arrhythmias in patients in which an implantable cardioverter defibrillator (ICD) is not currently indicated. Measurement of mean daily heart rate and related variability (HRV) has proved to be useful in identifying patients at increased arrhythmic risk of SCD and in patients with chronic heart failure (CHF), although the specificity and predictive accuracy of fatal arrhythmic events is still relatively limited. We analyzed the mean HR of patients with WCD to determine their impact on the incidence of fatal and non-fatal arrhythmic events.
METHODS: We enrolled 7 patients with WCD and optimal medical therapy by monitoring daily HR and variability over a 30- 90 day follow-up. Monitoring was performed remotely, analyzing both trends acquired by the devices, daily ECG recordings, and telephone surveillance.
RESULTS: Men constituted 71.4% of the population, with a mean age of 69.1±10.3 yrs, and an ejection fraction of 30.7%±8.7. The devices were worn for 36±24 days, with a daily adherence of 23.8±0.23 hrs. The trend in mean HR showed a progressive, although non-significant reduction (77.5±10.2 bpm vs 66.5±11.9 bpm p=0.08). No fatal arrhythmic events were recorded during monitoring. Two non-fatal arrhythmic events were recorded from patient discharge.
CONCLUSIONS: Mean daily HR is a predictor of cardiac death, independent of other risk factors in patients with cardiovascular disease. Although the small sample size doesn't provide a convincing correlation, it is conceivable that reducing mean HR may contribute to a decrease in fatal cardiac arrhythmias. Further studies are needed to confirm these insights.