Background Smartphone and wearable-based activity data provide an opportunity to remotely monitor functional capacity in patients. In this study, we assessed the ability of a home-based 6-minute walk test (6MWT) as well as passively collected activity data to supplement or even replace the in-clinic 6MWTs in patients with cardiovascular disease. Methods We enrolled 110 participants who were scheduled for vascular or cardiac procedures. Each participant was supplied with an iPhone and an Apple Watch running the VascTrac research app and was followed for 6 months. Supervised 6MWTs were performed during clinic visits at scheduled intervals. Weekly at-home 6MWTs were performed via the VascTrac app. The app passively collected activity data such as daily step counts. Logistic regression with forward feature selection was used to assess at-home 6MWT and passive data as predictors for “frailty” as measured by the gold-standard supervised 6MWT. Frailty was defined as walking <300m on an in-clinic 6MWT. Results Under a supervised in-clinic setting, the smartphone and Apple Watch with the VascTrac app were able to accurately assess ‘frailty’ with sensitivity of 90% and specificity of 85%. Outside the clinic in an unsupervised setting, the home-based 6MWT is 83% sensitive and 60% specific in assessing “frailty.” Passive data collected at home were nearly as accurate at predicting frailty on a clinic-based 6MWT as was a home-based 6MWT, with area under curve (AUC) of 0.643 and 0.704, respectively. Conclusions In this longitudinal observational study, passive activity data acquired by an iPhone and Apple Watch were an accurate predictor of in-clinic 6MWT performance. This finding suggests that frailty and functional capacity could be monitored and evaluated remotely in patients with cardiovascular disease, enabling safer and higher resolution monitoring of patients.
Background The 6-Mniute-Walk-Test (6MWT) is a validated proxy for frailty and a predictor of clinical outcomes, yet is not widely used due to implementation challenges. This comparative effectiveness study assesses the reliability and repeatability of a home-based 6MWT compared to in-clinic 6MWTs in patients with cardiovascular disease. Methods One hundred and ten (110) patients scheduled for cardiac or vascular surgery were enrolled during a study period from June 2018 to December 2019 at the Palo Alto VA Hospital. Subjects were provided with an Apple iPhone 7 and Apple Watch Series 3 loaded with the VascTrac research study application and performed a supervised in-clinic 6MWT during enrollment, at two weeks, one, three, and six months post-operatively. Subjects also received notifications to perform at-home smartphone-based 6MWTs once a week for a duration of six months. Test-retest reliability of in-clinic measurements and at-home measurements was assessed with an industry standard Cronbach’s alpha reliability test. Results Test-Retest Reliability for in-clinic ground truth 6MWT steps vs. in-clinic iPhone 6MWT steps was 0·99, showing high reliability between the two tested measurements. When comparing for in-clinic ground truth 6MWT steps vs. neighboring at-home iPhone 6MWT steps, reliability was 0·74. Conclusion Running the test-reliability test on both measurements shows that an iPhone 6MWT test is reliable compared to an in-clinic ground truth measurement in patients with cardiovascular disease.
Objective: Society guidelines recommend supervised exercise therapy as first-line therapy for patients with nondisabling claudication. Use is poor because of lack of programs as well as difficulty with travel to facilities. There is interest in evaluating home-based exercise programs, leveraging smartphones and wearables; however, there are few data on patient reception, engagement, or activation.Methods: As part of a 6-month clinical validation study, 65 patients scheduled for cardiovascular intervention (peripheral intervention, bypass, endarterectomy, coronary artery bypass graft, or transcatheter aortic valve replacement) were provided an iPhone and Apple Watch. They were prompted to perform an at-home weekly 6-minute walk test by receiving a mobile notification through a study application called VascTrac. In addition, patients are provided the opportunity to perform an "open walk" from within the VascTrac app whenever they desire. We report the weekly scheduled walk test compliance, the number of open walks performed, and the results of an end of study patient activation survey.Results: By the time of this evaluation, 758 at-home scheduled walk tests and 1023 open walks were completed by 63 patients enrolled (mean age, 68 years; 29 had never owned a smartphone). Six patients withdrew from the study. Seven patients had completed the 6-month study at the time of our analysis. Overall scheduled weekly 6-minute walk test compliance was 64.8% (standard deviation, 2.6%) for all patients. The range for compliance was between 13% and 100% and included patients with extended postoperative intensive care unit stays and hospitalizations. No significant association was noted between age and compliance. The pre-mobile intervention activation score for the seven patients who completed the study was 8 of 10, and the post-mobile intervention activation score was 9 of 10.Conclusions: Patients with cardiovascular disease undergoing interventions were responsive to mobile reminders to perform active walking tasks, even if smartphone naive. No significant correlation between compliance and the patient's characteristics could be identified. Noncompliance was affected by hospital admissions, extended postoperative intensive care unit stays, and occasional patient technical confusion. Improvement in patient activation was noted through participation in our study. Changes in total steps will be reported at completion of the study. There was an overall positive response to mobile engagement with a wide range of compliance. Deeper behavioral analysis will be required to uncover patients ideally suited for a mobile intervention.
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