Changes in Intrathoracic Impedance from a Pneumothorax: Insights from an Implanted Monitoring System

OptiVol fluid index predicts acute decompensation of heart failure with a high rate of unexplained events

Background

Intrathoracic impedance monitoring has emerged as a promising new technique for the detection of impending heart failure (HF). Although false positive episodes have been reported in case reports and clinical trials, the efficacy and false positive rate in real-world practice remain unclear.

Objective

The aim of this study is to investigate the utility and reliability of the OptiVol alert feature in clinical practice.

Methods

We continuously recruited patients who underwent implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy with defibrillator (CRT-D) implantation with feature of intrathoracic impedance monitoring system in our center from Sep. 2010 to Oct. 2012. Regular in-office follow-up were required of all patients and the following information was collected at each visit: medical history, device interrogation, N-terminal pro-brain natriuretic peptide (NT-proBNP) measurement and an echocardiogram. Worsening HF was defined as hospitalization or the presentation of signs or symptoms of HF.

Results

Forty three patients (male: 76.7%, mean age: 57 ± 15 years, left ventricular ejection fraction (LVEF): 33% ± 14%) were included in this observational study. Fifty four alert events and 14 adjudicated worsening HF were detected within 288 ±163 days follow-up. Eleven (20.4%) alert episodes were associated with acute cardiac decompensation in 9 patients with a positive predictive value of 78.6%. Forty three audible alerts showed no connection to worsening HF. The unexplained alerts rate was 79.6% and 1.27 per person-year. Thirty seven alarm alerts were detected in patients with EF < 45%, among which 9 accompanied with HF, 17 alerts detected in patients with LVEF ≥ 45% and 2 associated with HF. There was no significant difference between the two groups (9/37 vs. 2/17; P = 0.47).

Conclusions

Patients with normal or nearly normal left ventricular systolic function also exhibited considerable alert events. The OptiVol fluid index predicted worsening cardiac events with a high unexplained detection rate, and any alert must therefore be analyzed with great caution. Efforts to improve the specificity of this monitoring system represent a significant aspect of future studies.

Key lessons from cases worldwide

Since OptiVol fluid status monitoring (Medtronic, Inc., Minneapolis, MN) was released to the market in 2004, the manufacturer has been working together with clinicians to better understand the operation and utility of OptiVol in a clinical setting. This has been done through completed and ongoing clinical studies and through evaluation of case studies submitted by clinicians. In the process, much has been learned about some interesting aspects of OptiVol fluid status monitoring and its use with patients with heart failure.