Changes in Intrathoracic Impedance During Sacubitril/Valsartan Treatment: CHILISALT Study

Background Cardiac implantable electronic devices (CIEDs) that are improving clinical outcomes in selected heart failure with reduced ejection fraction (HFrEF) patients also collect valuable diagnostic information from continuous monitoring of several physiological variables such as intrathoracic electrical impedance. Intrathoracic electrical impedance monitoring has been used as a tool to evaluate pulmonary congestion. Intrathoracic impedance is inversely correlated to pulmonary volume expansion and has been linked to cardiac filling pressures. Decreasing in intrathoracic impedance and -derived fluid indices such as OptiVol Fluid Index, has been shown to predict heart failure hospitalizations and all-cause mortality in patients with HFrEF. Furthermore, studies also have shown the usefulness of monitoring impedance to initiate timely interventions preventing decompensation.

In patients with symptomatic HFrEF, the PARADIGM-HF trial demonstrated that sacubitril/valsartan significantly reduced the primary endpoint of cardiovascular mortality and heart failure hospitalization, compared with enalapril. The rate of all-cause mortality was also significantly reduced. Subsequently, Sacubitril/Valsartan is recommended by current guidelines as foundational therapy for many patients with symptomatic HFrEF.

However as a natriuretic agent, effects of Sacubitril/Valsartan treatment on intrathoracic impedance and fluid index remains unclear.

Objective The CHILISALT Study aimed to explore the effect of angiotensin-neprilysin inhibition on intrathoracic impedance and fluid index values in HFrEF patients who were implanted with a device for cardiac resynchronization therapy and/or an implantable cardioverter-defibrillator (ICD; Medtronic Inc., Minneapolis, MN) allowing continuous measurement of intrathoracic impedance and OptiVol Fluid Index. Main outcome parameters are the change in intrathoracic impedanceand OptiVol Index values between baseline (before Sacubutril/Valsartan treatment) and, 14th and 28th days of Sacubutril/Valsartan treatment.

Material and Methods CHILISALT Study will designed as national, multicentre, non-interventional, observational, single arm cohort study. Study population will identified from dedicated CIED Clinics from participating centres. Patients will eligible if they had already taking Sacubitril/Valsartan for ≥2 weeks and had been implanted with CIED for ≥3 months. Additionally, eligible patients must have a CIED before Sacubitril/Valsartan prescription date. Due to descriptive (proof of mechanism) design of the CHILISALT Study a formal population volume calculation will not be made. However, after minimum 24 patients included an interim analysis will be done in terms of changes in impedance values and other related parameters between baseline and after Sacubitril/Valsartan treatment. An independent data monitoring committee will decide to enrol or to finalize the study according to main outcome variable distribution. Main outcome parameters are the change in intrathoracic impedance and OptiVol Fluid index values between baseline (before Sacubutril/Valsartan treatment) and, 14th and 28th days of Sacubutril/Valsartan treatment. As a tool to evaluate pulmonary fluid status, intrathoracic impedance measuring quantifies impedance changes. CIEDs measured intrathoracic impedance (ohms) using the RV-coil to can vector. Impedance-derived fluid index will obtained using a cumulative sum mathematical model that calculates the differences between impedance measured in ohms (measured impedance) and a reference impedance. OptiVol Fluid index will be expressed in ohm-days. It was demonstrated that the index value exceeded 60 ohm-days, the crossing of this threshold value predicted both increased morbidity and mortality. Other possible confounders such as change in body weight (kilogram), current diuretic dose (miligram per day), requirement of intravenous diuretic therapy (yes/no), and the change from baseline to 28th day of the treatment in the clinical summary score on the Kansas City Cardiomyopathy Questionnaire (KCCQ; on a scale from 0 to 100, with higher scores indicating fewer symptoms and physical limitations associated with heart failure) is selected as secondary outcomes.