Background and Objective Intrathoracic impedance monitoring system had emerged as a new promising technique for detection impending heart failure (HF). Most commonly reported sensitivity in trials ranging between 76% and 83%. As all these researches carried out in patients with left ventricular malfunction, it is unknown the practical value of this system involving patients with preserved or regained left ventricular function. The aim of this study is to investigate the incidence of OptiVol alert episodes in real world clinical practise.
Methods 43 patients (mean age 57 ± 15 years, LVEF 33 ± 14%) undertook ICD or CRT-D implantation with feature of intrathoracic impedance monitoring system (Medtronic Inc, Minneapolis, MN, US) in our single centre from Sep 2010 to Oct 2012. All patients required in-office follow-up regularly and routinely in month 3, 6, 12 and every 12 months after that. Once alert events occurred and reported, unscheduled follow-up arranged. History taking, device interrogation, NT-proBNP measurement and echocardiogram were collected during each clinic interview. Worsening HF was defined as hospitalisation or presentation of symptoms or signs of HF.
Results 54 alert events and 14 adjudicated worsening HF detected within 288 ± 163 days follow-up duration. 11 (20.4%) alert episodes associated with acute decompensation in 9 patients with a positive predictive value of 78.6%. 43 audible alerts showed no connexion to worsening HF. The unexplained alerts rate was 79.6% and 1.27 per person-year. 37 alarm alerts detected in patients with EF 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 versus 2/17, p = 0.47).
Conclusions Patients with normal or nearly normal left ventricular systolic function also exhibited considerable alert events. OptiVol fluid index predicted cardiac worsening events with high unexplained detection rate and any alert need to be analysed with great caution. Efforts to improve the specificity of this monitoring system represent a significant aspect in future study.