Prediction of heart failure hospitalizations based on the direct measurement of intrathoracic impedance

New models for heart failure care delivery

Heart failure (HF) is a common disease with increasing prevalence around the world. There is high morbidity and mortality associated with poorly controlled HF along with increasing costs and strain on healthcare systems due to a high rate of rehospitalization and resource utilization. Despite the establishment of clear evidence-based guideline directed medical therapies (GDMT) proven to improve HF morbidity and mortality, there remains significant clinical inertia to optimizing HF patients on GDMT. Only a minority of HF patients are prescribed on all four classes of GDMT. To bridge the gap between the vulnerable population of HF patients and lifesaving GDMT, HF implementation is of increasing importance. HF implementation involves strategies and techniques to improve GDMT optimization along with other modalities to improve HF management. HF implementation meets patients where they are, including at the time of acute decompensation in the inpatient setting, at the vulnerable discharge stage, and at the chronic management stage in the outpatient setting. Inpatient HF implementation strategies include protocolized rapid titration of GDMT, site-level audit-and-feedback, virtual GDMT optimization teams, and electronic health record notifications and alerts. Discharge HF implementation strategies include education at patient and provider levels, discharge summaries, and HF transitional programs. Outpatient HF implementation strategies include digital innovations such as electronic health record utilization and mobile applications, population level strategies such as registries and clinical dashboards), changes in HF team structure and member roles, remote monitoring with implanted devices and telemonitoring, and hospital at home care model. With a growing population of HF patients, there is an increasing need for novel and creative HF implementation and monitoring methods.

INTERVENE-HF: feasibility study of individualized, risk stratification-based, medication intervention in patients with heart failure with reduced ejection fraction

Aims

Determine the feasibility of implementing a heart failure (HF) management strategy that (i) uses a device‐based, remote, dynamic, multimetric risk stratification model to predict the risk of HF events and (ii) uses a standardized, centrally administered, ambulatory medication intervention protocol to reproducibly and safely decrease elevated risk scores.

Methods and results

Prospective, non‐randomized, single‐arm, multicenter feasibility study (Intervene‐HF) was conducted in HF patients implanted with a cardiac resynchronization therapy with implantable cardio defibrillator (CRT‐D) with TriageHF risk score feature. Certified HF nurses (CHFN) in the Medtronic Care Management Services Program implemented an ambulatory medication intervention strategy by following a standardized guided action pathway triggered by risk‐based alert. When CHFN received notification of increased risk score (HF care alert), they implemented a 3 day course of diuretic up‐titration (PRN) previously prescribed by a physician. Safety was monitored daily. Recovery after PRN was defined as ≥70% recovery of impedance toward baseline levels. Sixty‐six patients followed for 8.2 ± 3.9 months had 49 HF care alerts. Twenty‐three of 49 alerts did not receive PRN due to protocol‐mandated criteria. Twenty‐six of 49 alerts received PRN, 22 were completed, and 19 led to impedance recovery. Four interventions were stopped for safety without leading to an adverse event (AE). One of 26 PRNs was followed by a HF event. Eighty‐five per cent (22/26) of PRNs were completed without an AE; 69% (18/26) met the recovery criteria.

Conclusions

The Intervene‐HF study supports the feasibility of testing, in a large randomized clinical trial, an ambulatory medication intervention strategy that is physician‐directed, CHFN‐implemented, and based on individualized device risk stratification.

Prediction of heart failure hospitalizations based on the direct measurement of intrathoracic impedance

Aims

OptiVol fluid index was developed as a transthoracic impedance‐based indicator of short‐term risk for heart failure hospitalization (HFH). OptiVol is calculated as the accumulating difference between daily impedance (measured impedance) and long‐term average impedance (reference impedance). Measured impedance alone was thought to have limited prognostic utility; however, measured impedance has the advantage of being simple, direct, and possibly additive to OptiVol fluid index in establishing long‐term HFH risk. We tested the hypothesis that directly measured impedance has independent prognostic value in predicting long‐term HFH risk and that changes in measured impedance result in a change in predicted long‐term HFH risk.

Methods and results

A retrospective analysis of 1719 patients studied in PARTNERS‐HF, FAST, and RAFT studies was performed. Baseline measured impedance was determined using daily values averaged over 1 month, from Month 6 to 7 post implant; change in measured impedance was determined from values averaged over 1 month, from Month 7 to 8 post implant compared with baseline. The predictive value of baseline measured impedance for HFHs was assessed beginning 7 months post implant. The predictive value of a change in measured impedance for a change in HFHs was assessed beginning 8 months post implant. Baseline measured impedance successfully predicted HFHs. For example, 3 year HFH rate for low baseline impedance < 70 Ω was 23%; for high baseline impedance ≥ 70 Ω was 15% (P < 0.001). Changes in measured impedance resulted in changes in predicted HFHs. For example, when a baseline impedance of ≥70 fell during follow‐up to <70 Ω, the subsequent HFHs were 15% compared with 4% in patients with measured impedance that remained >70 Ω (P = 0.004). In addition, when baseline measured impedance fell during follow‐up by >1%, 2%, or 3%, subsequent HFHs increased to 13%, 17%, or 18%, respectively. Finally, the prognostic value of measured impedance was additive to the prognostic value of the OptiVol fluid index.

Conclusions

Direct measurements of intrathoracic impedance using an implanted device can be used to stratify patients at varying risk of long‐term HFH. These direct measurements of impedance have practical clinical appeal because they are simple, continuous, and ambulatory.