BACKGROUND: The wearable cardioverter defibrillator (WCD) records electrocardiograms and cardiohemic vibrations that can be algorithmically combined to provide cardiac acoustic biomarkers (CABs). We characterized CAB variability, diurnal variations, and changes over time among heart failure patients.
METHODS: Wearable cardioverter defibrillator heart failure patients who had CAB recordings from March 2015 to July 2017 were included. CAB parameters included: electromechanical activation time (EMAT), EMATc (EMAT/RR interval), left ventricular systolic time (LVST), LVSTc (LVST/RR interval), S3 and S4 strengths, and systolic dysfunction index (SDI). Descriptive statistics, correlation analysis, and analysis of variance were used to report temporal and clinical associations.
RESULTS: One thousand and sixty-six WCD patients met the study criteria. Diastolic CAB parameters showed significantly greater intra-subject variability than systolic CAB parameters (>29% vs. <15%, p < .01). CAB parameters varied very little with age, gender, and ejection fraction (R(2) = 0.004 to 0.06) in this heart failure population. Similarly, all CABs except SDI (R(2) = 0.58) were independent of QRS duration, (R(2 ) = -0.01 to 0.58). Heart rate had a more of significant influence on the systolic CABs than the diastolic CABs (p < .05). CABs were significantly different when measured at daytime versus nighttime (p < .01) and were significantly lower at the end of WCD wear compared with the beginning of wear (p < .05).
CONCLUSIONS: Noninvasive CABs offer the possibility to assess parameters associated with LV function, clinical status, and other aspects of cardiovascular physiology that differ between normal and heart failure states. The present study provides critical information about typical values in heart failure patients, intra-subject variability, circadian rhythms, and changes over time of these parameters.