Differentiating Sensor Changes in a Composite Heart Failure ICD Monitoring Index: Clinical Correlates and Implications

Background The HeartLogic algorithm integrates data from implantable defibrillator(ICD) sensors to predict heart failure(HF) decompensation: first(S1) and third(S3) heart sounds, intrathoracic impedance, respiration rate, ratio of respiration rate to tidal volume(RSBI), and night heart rate. Objective This study assessed the relative changes in ICD sensors at the onset of HeartLogic alerts, their association with patient characteristics, and outcomes. Methods The study included 568 HF patients carrying ICDs(CRT-D,n=410) across 26 centers, with a median follow-up of 26 months. HeartLogic alerts triggered patient contact and potential treatment. Results A total of 1200 HeartLogic alerts were recorded in 370 patients. The sensor with the highest change at the alert’s onset was S3 in 27% of alerts, followed by S3/S1(25%). Patients with atrial fibrillation(AF) and chronic kidney disease(CKD) at implantation had higher alert prevalence(AF,84% vs. no-AF,58%; CKD,72% vs. no-CKD,59%; p <0.05) and rate (AF,1.51/patient-year vs. no-AF,0.88/patient-year; CKD,1.30/patient-year vs. no-CKD,0.89/patient-year; p<0.05). During follow-up, 247 patients experienced more than one alert; in 85%, the sensor with the highest change varied between successive alerts. Of the 88(7%) alerts associated with HF hospitalization or death, respiration rate or RSBI(11%, p=0.007 vs. S3/S1) and night heart rate(11%, p=0.031 vs. S3/S1) were more commonly the sensors showing the highest change. Clinical events were more common with the first alert(12.6%) than subsequent alerts(5.2%,p <0.001). Conclusion HeartLogic alerts are mostly triggered by changes in heart sounds, but clinical events are more linked to respiration rate, RSBI, and night heart rate. Recurrent alerts often involve different sensors, indicating diverse mechanisms of HF progression.