Abstract Body (Do not enter title and authors here): Background
Patients with heart failure (HF) who are discharged after an acute hospitalization are at high risk for 30 day readmission. Mobile Integrated Health (MIH), a program that combines nurse triage, care coordination, community paramedic home visits, and telehealth physician consultations, has emerged as one strategy to mitigate this risk; however, its effectiveness across levels of frailty is unknown.

Hypothesis
MIH would preferentially lower 30 day all cause readmission in severely frail patients compared with less frail patients.

Methods
We performed a secondary analysis of the pragmatic MIGHTy Heart randomized trial, which compared MIH (n=1,006) with a Transitions of Care Coordinator (TOCC; n=997) intervention in 2,003 adults discharged with HF from 11 New York hospitals. Frailty was quantified during the index admission with a 34 item Rockwood deficit accumulation index (range 0 to 1) constructed from patient reported outcomes (physical function, social support, mental health) and EHR derived ICD 10 codes (comorbidities); the frailty index (FI) was dichotomized at >0.45 (severely frail) versus <0.45. The primary outcome was time to first all cause readmission ≤30 days. Weighted, robust Cox models included an FI × treatment interaction and demographic/clinical covariates.

Results
Among 1,784 analyzed participants (mean age 67.6 [SD 13.7]; 52% female) there were 357 readmissions (20%) within 30 days. The distribution of the index was: mean 0.48 (IQR 0.37, 0.62; min 0.00, max 0.88); 1,136 patients (63 %) were classified as severely frail. In the weighted, covariate adjusted Cox model, severe frailty (FI > 0.45) was independently associated with a 34% higher hazard of readmission (HR 1.33, 95% CI 1.02, 1.76; p=0.04). MIH alone was not statistically significant (HR 1.28, 95% CI 0.94, 1.74; p=0.12). The interaction term between MIH and frailty suggested differential effectiveness by frailty status (HR 0.69, 95% CI 0.48, 1.00; p=0.051). Among severely frail patients, MIH was associated with a 12% relative reduction in readmission (adjusted HR 0.88) versus TOCC; no benefit was observed in less frail patients.

Conclusion
A 34 item deficit accumulation frailty index was a strong predictor of 30 day readmission after HF discharge. While MIH did not reduce readmissions overall, evidence of benefit in the most frail patients suggests that targeting MIH to this subgroup and stratifying by frailty in future studies may optimize resource allocation.