Worsening thoracic impedance as a ventricular tachyarrhythmia risk

The use of heart failure classification to identify patients with systolic dysfunction who are at risk for ventricular tachyarrhythmias (VAs), sudden cardiac death, and shocks from implantable cardioverter defibrillators (ICDs) is limited by its subjectivity. Measurement of thoracic impedance offers a more objective tool for assessing worsening of heart failure. We sought to look at the correlation between ventricular arrhythmia and heart failure as assessed objectively by thoracic impedance. We reviewed device interrogation data on thoracic impedance from ICD with Medtronic's OptiVol® feature (Medtronic Inc., Minneapolis, MN) at two medical centers. Data from the last two interrogations of the same device separated by at least 2 months were included. An OptiVol fluid index threshold of 60 represented early heart failure prior to appearance of symptoms. VAs included were ventricular fibrillation and/or ventricular tachycardia lasting more than 16 beats. Chi square distribution test was used in statistical data analysis. There were 24 VAs identified among the 322 interrogations reviewed (7.5%). Elevated OptiVol fluid index was seen in 71% (17/24), whereas normal OptiVol index was seen in the remaining 29% (7/24) of these interrogations with VA (P < .05). Our review shows that heart failure patients who have VA are approximately 2.5 times as likely to have worsening thoracic impedance as assessed objectively by the OptiVol fluid index. Careful monitoring of the OptiVol fluid index may identify a population at high risk of VA that merits more intense attention.