Analysis of daily activity data from implanted cardiac defibrillators: The minimum clinically important difference and relationship to mortality/life expectancy

Michael J. Shoemaker, Amy B. Curtis, Eric Vangsnes, Michael G. Dickinson, Rajib Paul

Department of Statistics, Western Michigan University, Kalamazoo, USA.
Interdisciplinary Health Sciences PhD Program, Western Michigan University, Kalamazoo, USA.
Physician Assistant Program, Western Michigan University, Kalamazoo, USA.
Spectrum Health Frederik Meijer Heart and Vascular Institute, Grand Rapids, USA.

DOI: 10.4236/wjcd.2012.23021                

Abstract

Background: Daily activity is a potentially important measure for assessing prognosis in individuals with chronic heart failure (CHF), and few studies have investigated the prognostic value of daily activity measurement. The present study sought to determine whether there is an association between daily activity and mortality/mean life expectancy as predicted by the Seattle Heart Failure Model (SHFM), and to provide an estimate of the anchor-based minimum clinically important difference (MCID) for daily activity measured by single-axis accelerometers in implanted cardiac defibrillators. Methods: This study utilized a retrospective chart review of 102 medical records of patients with CHF and Medtronic? implanted cardiac defibrillators (ICDs). Mean daily activity was calculated for a two week period prior to both a baseline and follow-up routine clinical visit. Clinical characteristics from the baseline clinic visit were used for calculating SHFM estimates of mean life expectancy, 1-year mortality, and 5-year mortality. A five-point global rating scale was scored based on documented clinician impression, patient self-report, and laboratory and cardiographic tests for determining the MCID. Results: There was a moderate correlation between baseline daily activity and each of the SHFM prognostic indicators: 1-year mortality (r = 0.36, p < 0.001, 5-year mortality (r = 0.40, p < 0.001), and life expectancy (r = 0.43, p < 0.001). The MCID for a decline in daily activity was approximately 0.5 hours and was approximately 1.0 hours for improvement in daily activity. Conclusions: Although previous re- search has established the short-term predictive value of ICD-measured daily activity for CHF-related clinical events, no prior study has examined the longer-term prognostic value of ICD-based daily activity. The results of the present study suggest that low daily activity, as recorded by ICDs in patients with CHF, should prompt a more formal evaluation of prognosis using the SHFM. Furthermore, changes of 0.5 to 1.0 hours of activity per day appear to be clinically mean- ingful.

Keywords

Heart Failure; Daily Activity; Prognosis; Cardiac Defibrillator

Conflicts of Interest

The authors declare no conflicts of interest.

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