ICD-measured heart sounds and their correlation with echocardiographic indexes of systolic and diastolic function

Novel implantable defibrillators (ICDs) allow first (S1) and third (S3) heart sounds to be measured by means of an embedded accelerometer. ICD-measured S1 and S3 have been shown to significantly correlate with hemodynamic changes in acute animal models. The HeartLogic algorithm (Boston Scientific) measures and combines multiple parameters, including S3 and S1, into a single index to predict impending heart failure decompensation. We evaluated the echocardiographic correlates of ICD-measured S1 and S3 in patients with ICD and cardiac resynchronization therapy ICD.

The HeartLogic feature was activated in 104 patients. During in-office visits, patients underwent echocardiographic evaluation, and parameters of systolic and diastolic function were correlated with S3 and S1 amplitude measured on the same day as the visit.

S3 amplitude inversely correlated with deceleration time of the E-wave (r = -0.32; 95% CI -0.46 - -0.17; P < 0.001), and S1 amplitude significantly correlated with left ventricular ejection fraction (r = 0.17; 95% CI 0.03-0.30; P = 0.021). S3 > 0.9 mG detected a restrictive filling pattern with 85% (95% CI 72%-93%) sensitivity and 82% (95% CI 75%-88%) specificity, while S1 < 1.5 mG detected ejection fraction < 35% with 28% (95% CI 19%-40%) sensitivity and 88% (95% CI 80%-93%) specificity.

ICD-measured heart sound parameters are significantly correlated with echocardiographic indexes of systolic and diastolic function. This confirms their utility for remote patient monitoring when used as single sensors and their potential relevance when considered in combination with other physiological ICD sensors that evaluate various aspects of heart failure physiology.