Changes in Phasic Heart Rate Variability Predict Clinical Outcomes Following Emotion Regulation Therapy for Generalized Anxiety Disorder and Comorbid Depression.

Generalized anxiety disorder (GAD) and major depressive disorder (MDD) frequently co-occur and are marked by greater chronicity, severity, and poorer treatment response. Perseverative negative thinking (e.g., worry, rumination) is a transdiagnostic mechanism implicated in both disorders and linked to disruptions in large-scale neural networks, threat and reward processing, and vagal modulation. Heart rate variability (HRV)-particularly phasic HRV (vagal reactivity/recovery)-is a peripheral marker of autonomic flexibility and dynamic emotion regulation that may be sensitive to therapeutic change. Yet few studies have tested whether evidence-based treatments modify phasic HRV and whether such changes predict clinical outcomes. Twenty-four adults with GAD ± MDD completed 20 sessions of Emotion Regulation Therapy. At pre- and midtreatment, participants completed laboratory emotion inductions (baseline, fear, sadness, recovery) while cardiac activity was recorded; community controls (n = 28) completed the same paradigm once. Patients self-reported anxiety, depression, worry, rumination, functional impairment, and quality of life at pre-, mid-, and posttreatment. Relative to controls, patients exhibited lower tonic HRV and marginally blunted phasic HRV during a sadness induction. During fear, patients showed decreased HRV from fear to recovery, whereas controls remained stable. From pre- to midtreatment, patients demonstrated improved vagal fear recovery, and greater improvements predicted lower posttreatment GAD severity, worry, and functional impairment, accounting for 12-29% of the variance. These findings preliminarily support vagal fear recovery as a modifiable, objective marker of treatment response in patients with GAD ± MDD. Limitations include small, demographically homogeneous samples and the absence of a midtreatment control group. Future work should incorporate ambulatory physiological monitoring to assess whether these effects generalize to daily life.