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

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 pro-vide an estimate of the anchor-based minimum clini-cally 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 car-diac defibrillators (ICDs). Mean daily activity was calculated for a two week period prior to both a base-line and follow-up routine clinical visit. Clinical cha-racteristics 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 labora-tory and cardiographic tests for determining the MCID. Results: There was a moderate correlation be-tween 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 de-cline 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 cli-nical 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.