1 Department of Psychology, Concordia University, 7141 Sherbrooke St. W, Montréal, H4B 1R6, Canada; Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal (CRIUGM), CIUSSS Centre-Sud-de-l'île-de-Montréal, 4565 Queen Mary Rd, Montréal, H3W 1W5, Canada. Electronic address: james.garneau@mail.concordia.ca.
2 School of Psychology, Université Laval, 2325 Rue des Bibliothèques, Québec, G1V 0A6, Canada; CHU de Québec-Université Laval Research Center, 2705 Bd Laurier, Québec, G1V 4G2, Canada; Université Laval Cancer Research Center, 9 Rue McMahon, Québec, G1R 3S3, Canada. Electronic address: josee.savard@psy.ulaval.ca.
3 Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal (CRIUGM), CIUSSS Centre-Sud-de-l'île-de-Montréal, 4565 Queen Mary Rd, Montréal, H3W 1W5, Canada; Department of Health, Kinesiology and Applied Physiology, Concordia University, 7141 Sherbrooke St. W, Montréal, H4B 1R6, Canada. Electronic address: tt.dangvu@concordia.ca.
4 Department of Psychology, Concordia University, 7141 Sherbrooke St. W, Montréal, H4B 1R6, Canada; Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal (CRIUGM), CIUSSS Centre-Sud-de-l'île-de-Montréal, 4565 Queen Mary Rd, Montréal, H3W 1W5, Canada. Electronic address: jp.gouin@concordia.ca.

Objective: This study examined whether high frequency heart-rate variability (HF-HRV) and HF-HRV reactivity to worry moderate response to cognitive behavioural therapy for insomnia (CBT-I) within both a standard and stepped-care framework among cancer patients with comorbid insomnia. Biomarkers such as HF-HRV may predict response to CBT-I, a finding which could potentially inform patient allocation to different treatment intensities within a stepped-care framework.

Methods: 177 participants (86.3 % female; M_age = 55.3, SD = 10.4) were randomized to receive either stepped-care or standard CBT-I. 145 participants had their HRV assessed at pre-treatment during a rest and worry period. Insomnia symptoms were assessed using the Insomnia Severity Index (ISI) and daily sleep diary across five timepoints from pre-treatment to a 12-month post-treatment follow-up.

Results: Resting HF-HRV was significantly associated with pre-treatment sleep efficiency and sleep onset latency but not ISI score. However, resting HF-HRV did not predict overall changes in insomnia across treatment and follow-up. Similarly, resting HF-HRV did not differentially predict changes in sleep diary parameters across standard or stepped-care groups. HRV reactivity was not related to any of the assessed outcome measures in both cross-sectional and longitudinal analyses.

Conclusion: Although resting HF-HRV was related to initial daily sleep parameters, HF-HRV measures did not significantly predict longitudinal responses to CBT-I. These findings suggest that HF-HRV does not predict treatment responsiveness to CBT-I interventions of different intensity in cancer patients.