Estimating stride length in liver transplant (lt) candidates: A novel way to remotely track frailty with the 6-minute walk test (6mwt) using personal activity trackers (pat)

Background: The COVID pandemic has limited LT candidates access to clinics disrupting frailty assessment. Telehealth methods to assess frailty are needed. The liver frailty index (LFI) and 6MWT can objectively assess frailty. We aimed to develop a method to estimate the stride length of LT candidates, which would permit remote 6MWT calculation via a PAT. Methods: A physical therapist obtained LFI and 6MWT;patients wore a PAT (Fitbit) linked to EL-FIT (Exercise & Liver FITness app). Stride length was obtained by dividing the distance strolled by the steps during the 6MWT. In the first 10 patients we measured the stride length while performing the 6MWT and compared it to the PAT-calculated stride. Using multivariable linear regression models, we identified the clinical parameters better explaining stride length variability and developed formulas to estimate the stride length. We then multiplied the estimated stride length by steps taken during the test (from PAT) to obtain PAT-calculated 6MWT strolled distance and compared it to the observed distance. Investigators were masked to measured stride length and 6MWT distance. Results: We included 116 consecutive patients (age 57±12, male 53%, MELDNa 14±7). There was excellent agreement between measured and PAT-calculated stride (54±15 vs. 56±11 cm, p=0.5). LFI, height, albumin, and recurrent paracentesis were the best parameters predicting stride length (R2=0.58). An alternative model excluding LFI identified age, height, albumin, hemoglobin, and recurrent paracentesis (R2=0.45). There was a very strong correlation between observed and PAT-calculated 6MWT distance, as shown in Figure. Using 6MWT<250 m to define frailty, 16%, 14% and 12% of patients were frail according to measured distance, with and without LFI PAT-calculated methods, respectively. There was 91% agreement between each PATcalculated method and measured 6MWT distance (p=0.5 and p=0.2). Conclusion: We were able to accurately estimate the stride length of LT candidates using routine clinical parameters. This is the limiting factor precluding implementation of telemedicine frailty testing via PAT-calculated 6MWT. To fully assess patients remotely, excluding the in-office parameter LFI, we provided an alternate estimate with similar reliability. Future research should focus on validating telemedicineobtained PAT-calculated 6MWT against clinical outcomes and incorporating this novel method to existing telerehabilitation apps (i.e., EL-FIT).