| Analysis_set | N |
|---|---|
| YCA enrolled | 51 |
| YCA paired 6MWD (primary analysis) | 48 |
| YCA paired 6MWD without rhythm/medication changes (sensitivity) | 39 |
| GMV paired 6MWD | 28 |
YouControl-AFib: Digital Health Intervention to Promote Physical Activity in Persons With Atrial Fibrillation
1 Study and analysis overview
YouControl-AFib (YCA) was a single-arm prospective digital health intervention designed to support physical activity among persons with atrial fibrillation. The primary analysis evaluates change in 6-minute walk distance (6MWD) from baseline to post-intervention assessment. Group Medical Visits (GMV) provides a nonrandomized contextual comparator cohort.
The primary continuous outcome is the change in 6MWD, calculated as
\[ \Delta \mathrm{6MWD} = \mathrm{6MWD}_{\mathrm{post}} - \mathrm{6MWD}_{\mathrm{baseline}}, \]
in meters. A clinically meaningful improvement is defined as ( ) meters.
2 Data preparation
3 Statistical analysis
Baseline characteristics will be summarized with counts and percentages for categorical variables and mean (SD) or median (IQR) for continuous variables. The primary within-YCA analysis will estimate the mean paired change in 6MWD, with a 95% confidence interval and paired t-test. The proportion with a clinically meaningful improvement of at least 30 m will be reported with an exact 95% confidence interval.
The analysis excluding participants with a rhythm or relevant medication change will be presented as a sensitivity analysis. YCA-versus-GMV comparisons are observational and will be presented as contextual, not causal, comparisons. Predictor, adherence, residence subgroup, and composite-score analyses will be described as exploratory.
4 Results
4.1 Cohort characteristics
The YCA cohort included 51 enrolled participants, of whom 48 completed both 6MWD assessments. The following tables describe the paired-6MWD analysis population. Because the urban/non-urban and YCA/GMV comparisons are exploratory and sample sizes are modest, the tables are descriptive; no baseline hypothesis tests are presented.
Table 2 compares baseline characteristics and 6MWD change between urban and non-urban YCA participants. Table 3 compares the YCA and GMV cohorts.
| Characteristic | Non-urban N = 281 |
Urban N = 231 |
Overall N = 511 |
|---|---|---|---|
| Age, years | 64 (7) | 62 (12) | 63 (10) |
| Gender | |||
| Female | 15 (54%) | 11 (48%) | 26 (51%) |
| Male | 13 (46%) | 12 (52%) | 25 (49%) |
| Body mass index, kg/m² | 39.8 (5.0) | 39.9 (6.2) | 39.9 (5.5) |
| Hypertension | 23 (82%) | 19 (83%) | 42 (82%) |
| Diabetes mellitus | 8 (29%) | 10 (43%) | 18 (35%) |
| Heart failure history | 10 (36%) | 8 (35%) | 18 (35%) |
| Prior ablations | 0.75 (0.70) | 0.70 (0.82) | 0.73 (0.75) |
| Prior cardioversions | 0.82 (1.19) | 1.13 (1.69) | 0.96 (1.43) |
| Rate-control agent at baseline | 21 (75%) | 17 (74%) | 38 (75%) |
| Rhythm-control agent at baseline | 11 (39%) | 8 (35%) | 19 (37%) |
| Rhythm at baseline | |||
| A-Paced | 0 (0%) | 1 (4.3%) | 1 (2.0%) |
| AFib | 2 (7.1%) | 1 (4.3%) | 3 (5.9%) |
| Sinus | 26 (93%) | 21 (91%) | 47 (92%) |
| Any rhythm or medication change | 3 (11%) | 7 (30%) | 10 (20%) |
| Left atrial enlargement | |||
| Normal | 8 (30%) | 13 (57%) | 21 (42%) |
| Dilated | 19 (70%) | 10 (43%) | 29 (58%) |
| Mitral regurgitation | |||
| None/trace/trivial | 17 (65%) | 16 (73%) | 33 (69%) |
| Mild or greater | 9 (35%) | 6 (27%) | 15 (31%) |
| LE8 BMI score | 12 (21) | 14 (22) | 13 (21) |
| LE8 blood-pressure score | 44 (31) | 50 (27) | 47 (29) |
| LE8 blood-glucose score | 58 (33) | 50 (28) | 55 (31) |
| LE8 cholesterol score | 49 (33) | 49 (32) | 49 (33) |
| LE8 nicotine score | 90 (13) | 87 (21) | 89 (17) |
| Change in 6-minute walk distance, m | 39 (45) | 17 (67) | 29 (56) |
| 1 Mean (SD); n (%) | |||
| Change in 6-minute walk distance was available for 48 of 51 enrolled participants. | |||
| Characteristic | Group Medical Visits N = 281 |
YouControl-AFib N = 511 |
Overall N = 791 |
|---|---|---|---|
| Age, years | 67 (10) | 63 (10) | 64 (10) |
| Gender | |||
| Female | 15 (54%) | 26 (51%) | 41 (52%) |
| Male | 13 (46%) | 25 (49%) | 38 (48%) |
| Body mass index, kg/m² | 35 (7) | 40 (6) | 38 (6) |
| Hypertension | 22 (79%) | 42 (82%) | 64 (81%) |
| Diabetes mellitus | 4 (14%) | 18 (35%) | 22 (28%) |
| Heart failure history | 11 (39%) | 18 (35%) | 29 (37%) |
| Prior ablations | 0.64 (0.78) | 0.73 (0.75) | 0.70 (0.76) |
| Prior cardioversions | 1.54 (1.71) | 0.96 (1.43) | 1.16 (1.55) |
| Rate-control agent at baseline | 27 (96%) | 38 (75%) | 65 (82%) |
| Rhythm-control agent at baseline | 10 (36%) | 19 (37%) | 29 (37%) |
| Rhythm at baseline | |||
| A-paced | 2 (7.1%) | 0 (0%) | 2 (2.5%) |
| A-Paced | 0 (0%) | 1 (2.0%) | 1 (1.3%) |
| AFib | 3 (11%) | 3 (5.9%) | 6 (7.6%) |
| Sinus | 23 (82%) | 47 (92%) | 70 (89%) |
| Any rhythm or medication change | 5 (18%) | 10 (20%) | 15 (19%) |
| Left atrial enlargement | |||
| Normal | 11 (41%) | 21 (42%) | 32 (42%) |
| Dilated | 16 (59%) | 29 (58%) | 45 (58%) |
| Mitral regurgitation | |||
| None/trace/trivial | 19 (73%) | 33 (69%) | 52 (70%) |
| Mild or greater | 7 (27%) | 15 (31%) | 22 (30%) |
| LE8 BMI score | 31 (31) | 13 (21) | 19 (26) |
| LE8 blood-pressure score | 59 (30) | 47 (29) | 51 (30) |
| LE8 blood-glucose score | 79 (26) | 55 (31) | 63 (31) |
| LE8 cholesterol score | 74 (19) | 49 (33) | 57 (31) |
| LE8 nicotine score | 89 (13) | 89 (17) | 89 (16) |
| Change in 6-minute walk distance, m | 19 (49) | 29 (56) | 25 (54) |
| 1 Mean (SD); n (%) | |||
| Change in 6-minute walk distance was available for 48 of 51 YouControl-AFib participants and all 28 Group Medical Visit participants. | |||
4.2 Primary 6MWD analysis
The primary analysis included the 48 YCA participants with both baseline and post-intervention 6MWD assessments. The mean paired change in 6MWD was 29.2 m (95% CI: 12.8 to 45.5 m; paired t-test <0.001). A clinically meaningful improvement of at least 30 m was observed in 24 of 48 participants (50%).
The sensitivity analysis excluding participants with a rhythm or relevant medication change included 39 participants. Results are shown alongside the primary analysis in Table 4.
Table 5 summarizes the distribution of 6MWD changes in the primary paired-analysis population.
| Analysis set | N | Baseline 6MWD, mean (SD) | Post-intervention 6MWD, mean (SD) | Mean change, m (95% CI) | Paired t-test p-value | Improvement ≥30 m, n (%) | Responder proportion, 95% CI |
|---|---|---|---|---|---|---|---|
| Primary analysis | 48 | 423.7 (99.1) | 452.9 (100.7) | 29.2 (12.8, 45.5) | <0.001 | 24 (50%) | (35%, 65%) |
| Sensitivity analysis: no rhythm or medication change | 39 | 421.2 (94.5) | 450.0 (95.0) | 28.8 (11.2, 46.5) | 0.002 | 20 (51%) | (35%, 68%) |
Figure 1 displays individual and overall changes in 6-minute walk distance among YCA participants with paired assessments.
| Change in 6-minute walk distance | n (%) |
|---|---|
| Decreased or no improvement (≤0 m) | 14 (29%) |
| Modest improvement (1 to <30 m) | 10 (21%) |
| Clinically meaningful improvement (≥30 m) | 24 (50%) |
4.3 Patient-reported outcomes
Changes in patient-reported outcomes from baseline to post-intervention are summarized in ?@tbl-patient-reported-outcomes. These analyses are exploratory; p-values are unadjusted for multiple comparisons.
For PHQ-9 and AFSS, negative changes indicate improvement. For AFKAT, AFEQT, and SF-12 scores, positive changes indicate improvement.
| Outcome | N | Baseline, mean (SD) | Post-intervention, mean (SD) | Mean change, post minus baseline (95% CI) | Paired t-test p-value |
|---|---|---|---|---|---|
| PHQ-9 score | 46 | 4.8 (3.3) | 3.9 (3.5) | -0.9 (-1.7, -0.1) | 0.022 |
| AFSS score | 46 | 6.9 (5.7) | 6.1 (5.5) | -0.9 (-2.2, 0.5) | 0.208 |
| AF knowledge assessment score (%) | 49 | 91.3 (5.8) | 92.2 (5.5) | 0.9 (-0.7, 2.4) | 0.267 |
| AFEQT score | 46 | 78.6 (15.6) | 83.7 (14.6) | 5.1 (1.1, 9.1) | 0.013 |
| SF-12 physical component score | 44 | 40.4 (4.1) | 41.8 (5.3) | 1.5 (0.2, 2.8) | 0.025 |
| SF-12 mental component score | 44 | 48.1 (5.6) | 48.0 (5.1) | -0.1 (-2.1, 1.8) | 0.887 |
| AFKAT scores are displayed as percentages. P-values are exploratory and unadjusted for multiple comparisons. | |||||
Figure 2 displays the distributions of the patient-reported outcomes at baseline and post-intervention. Lines connect paired observations from the same participant.
4.4 Contextual comparison with GMV
The GMV cohort is a nonrandomized contextual comparator. Accordingly, the following comparisons describe differences between the two cohorts and should not be interpreted as estimates of a causal intervention effect.
Table 6 summarizes 6MWD outcomes by cohort. Figure 3 displays paired baseline and post-intervention measurements in each cohort. The adjusted model controls for baseline 6MWD only.
| Cohort | N | Baseline 6MWD, mean (SD) | Post-intervention 6MWD, mean (SD) | Change in 6MWD, mean (SD) | Improvement ≥30 m, n (%) | Responder proportion, 95% CI |
|---|---|---|---|---|---|---|
| Group Medical Visits | 28 | 382.9 (102.1) | 402.0 (119.2) | 19.1 (48.7) | 12 (43%) | (24%, 63%) |
| YouControl-AFib | 48 | 423.7 (99.1) | 452.9 (100.7) | 29.2 (56.3) | 24 (50%) | (35%, 65%) |
| GMV is a nonrandomized contextual comparator. | ||||||
In an unadjusted comparison, the mean difference in change in 6MWD between YCA and GMV was 29.2, 19.1 m (95% CI: -14.4 to 34.6 m; 0.414).
After adjustment for baseline 6MWD, the estimated difference in post-intervention 6MWD for YCA versus GMV was 12.7 m (95% CI: -13.2 to 38.6 m; 0.331). These comparisons are contextual and not causal.
4.5 Exploratory predictors and composite score
The following analysis evaluates an exploratory composite score based on rural residence, LE8 blood-pressure score above the cohort median, and LE8 physical activity score above the cohort median. Because the components and cut points were selected using the present dataset, this analysis is hypothesis-generating and does not constitute validation of a prediction model.
The blood-pressure and physical-activity score medians were 50 and 40, respectively. Table 7 summarizes 6MWD change and clinically meaningful response by composite score.
| Composite score | N | Change in 6MWD, mean (SD) | Improvement ≥30 m, n (%) | Responder proportion, 95% CI |
|---|---|---|---|---|
| 0 | 6 | -9.6 (28.5) | 0 (0%) | (0%, 46%) |
| 1 | 16 | 19.9 (53.6) | 6 (38%) | (15%, 65%) |
| 2 | 21 | 42.1 (61.3) | 14 (67%) | (43%, 85%) |
| 3 | 5 | 50.8 (51.4) | 4 (80%) | (28%, 99%) |
| Composite score = rural residence + LE8 blood-pressure score above the paired-YCA median + LE8 physical-activity score above the paired-YCA median. | ||||
Figure 4 displays the relationship of the composite score with continuous 6MWD change and the proportion of participants achieving a clinically meaningful improvement.
4.6 Fitbit adherence and longitudinal activity
Weekly Fitbit step-count and activity-minute data were used to characterize intervention-period activity and post-intervention Fitbit continuation. Continued Fitbit use was defined as any weekly step count greater than zero after the participant’s intervention end date.
Table 8 summarizes post-intervention Fitbit continuation overall and its exploratory association with clinically meaningful improvement in 6MWD.
| Group | N | Post-trial Fitbit continuation, n (%) | Improvement ≥30 m, n (%) |
|---|---|---|---|
| All enrolled YCA participants | 51 | 47 (92%) | NA |
| Continued Fitbit use | 45 | NA | 23 (51%) |
| No post-trial Fitbit use | 3 | NA | 1 (33%) |
| Among participants with paired 6MWD assessments, the exploratory association between post-trial Fitbit continuation and clinically meaningful improvement was evaluated using Fisher's exact test (p = >0.999). | |||
The weekly Fitbit data contain complete study-week observations for all 51 YCA participants. Because the supplied data are indexed as study weeks 1 through 12, activity is summarized at Weeks 1, 6, and 12 rather than labeling Week 1 as Week 0.
| Measure | Study week | 6MWD response group | N | Mean (SD) |
|---|---|---|---|---|
| Weekly activity minutes | 1 | No clinically meaningful improvement (<30 m) | 24 | 258 (315) |
| Weekly activity minutes | 1 | Clinically meaningful improvement (≥30 m) | 24 | 185 (202) |
| Weekly activity minutes | 6 | No clinically meaningful improvement (<30 m) | 24 | 315 (348) |
| Weekly activity minutes | 6 | Clinically meaningful improvement (≥30 m) | 24 | 220 (223) |
| Weekly activity minutes | 12 | No clinically meaningful improvement (<30 m) | 24 | 273 (372) |
| Weekly activity minutes | 12 | Clinically meaningful improvement (≥30 m) | 24 | 168 (130) |
| Weekly step count | 1 | No clinically meaningful improvement (<30 m) | 24 | 42 394 (21 401) |
| Weekly step count | 1 | Clinically meaningful improvement (≥30 m) | 24 | 35 478 (20 330) |
| Weekly step count | 6 | No clinically meaningful improvement (<30 m) | 24 | 44 016 (23 690) |
| Weekly step count | 6 | Clinically meaningful improvement (≥30 m) | 24 | 41 605 (17 536) |
| Weekly step count | 12 | No clinically meaningful improvement (<30 m) | 24 | 41 565 (31 393) |
| Weekly step count | 12 | Clinically meaningful improvement (≥30 m) | 24 | 42 659 (20 370) |
Figure 5 displays the distributions of weekly step counts and activity minutes at Weeks 1, 6, and 12 by 6MWD response group.
