Low-activity alerts as a prognostic marker in ICD/CRT
I Almeida, M Camara Farinha, I Coutinho Dos Santos, V Pereira Ferreira, M I Barradas, F Duarte, L Oliveira, C Machado, M PachecoAbstract
Introduction
Remote monitoring of ICD/CRT devices allows continuous quantification of daily physical activity. Sustained reductions in activity ("low burden activity") have been associated with worse outcomes, but national evidence remains scarce.
Objective
To evaluate the associaon between low activity and a composite endpoint (urgent HF visit, HF hospitalization, stroke, ACS, and all-cause mortality) in ICD/CRT patients under remote monitoring.
Methods
We conducted a single-center cohort retrospective study of 130 patients. Low activity was defined as <1 hour/day of physical activity; patients were divided into Group 1 (low-activity alerts) and Group 2 (no alerts). Proportional hazards were evaluated using a Cox model adjusted for age, sex, chronic kidney disease (CKD), and device type (reference: transvenous ICD; comparators: CRTP, CRT-D, and subcutaneous ICD). Due to missing data in some covariates, the multivariable analysis followed a complete-case approach (N=95). The mean follow-up was 8 years.
Results
A total of 130 ICD/CRT patients were included, 63 with low-activity alerts and 64 controls. Most baseline characteristics were similar between groups, with no significant differences in sex, atrial fibrillation, coronary disease, hypertension, dyslipidemia, obesity, sleep apnea, psychiatric disease, malignancy, or smoking. Low-activity patients were older (72 vs. 62 years; p<0.01) and had a higher prevalence of chronic kidney disease (30% vs. 10%; p<0.01). Diabetes and prior malignancy were more common in this group but did not reach significance (both p≈0.07). Device type differed between groups (p=0.04), with more CRT-P/CRT-D devices among lowactivity patients and more transvenous ICDs in controls. NYHA class, LVEF, and other comorbidities were similar. Low activity was associated with a higher cumulative incidence of events (log-rank p=0.043). In the adjusted Cox model, low activity remained independently associated with the endpoint (HR 3.20; 95%CI 1.61–6.35; p=0.001). Female sex showed a borderline protective effect (HR 0.44; 95%CI 0.19–1.00; p=0.050). Among device types, CRT-D was independently protective (HR 0.33; 95%CI 0.15–0.72; p=0.006), while CRT-P and subcutaneous ICD were not significant. The overall model was significant (LRT χ²=28.3; df=7; p<0.001), with a concordance statistic of 0.696.
Conclusion
A device-derived measure of <1 hour/day of physical activity identifies ICD/CRT patients at higher risk of major cardiovascular events, even aIer multivariable adjustment. Remote monitoring may serve as an effective tool for early risk stratification and more targeted follow-up.