Objectives: The main objective of the study is to investigate the short-term efficacy of Acceptance and Commitment Therapy (ACT) on the simultaneous modification of biological indicators of risk and psychological well-being in patients with coronary heart disease attending cardiac rehabilitation (CR).

Design: This was a two-arm randomised controlled trial comparing a brief, manualised, ACT-based intervention with usual care (UC).

Setting: The study was conducted in an outpatient CR unit in Italy. Data collection took place from January 2016 to July 2017.

Participants: Ninety-two patients were enrolled and randomised, following an unbalanced randomisation ratio of 2:1 to the ACT group (n=59) and the control group (n=33). Eighty-five patients completed the ACT (n=54) and the UC (n=31) interventions and were analysed.

Interventions: The control group received UC, a 6 weeks multidisciplinary outpatient CR programme, encompassing exercise training, educational counselling and medical examinations. The experimental group, in addition to UC, participated in the Acceptance and Commitment Therapy on HEART disease (ACTonHEART) intervention encompassing three group sessions based on ACT.

Outcomes: The primary outcomes were Low Density Lipoproteins (LDL)cholesterol, resting systolic blood pressure, body mass index (BMI) and psychological well-being measured by the Psychological General Well-Being Index (PGWBI). Outcome measures were assessed at baseline and at the end of CR.

Results: Based on linear mixed models, no significant group × time interaction was observed for either the primary outcomes (β, 95% CI: PGWBI =-1.13, -6.40 to -4.14; LDL cholesterol =-2.13, -11.02 to -6.76; systolic blood pressure =-0.50, -10.76 to -9.76; diastolic blood pressure =-2.73, -10.12 to -4.65; BMI =-0.16, -1.83 to -1.51, all p values >0.05) or the secondary outcomes (all p values >0.05). A significant time effect was found for the PGWBI total (beta=4.72; p=0.03).

Conclusions: Although analyses revealed null findings, the results can inform the design of future ACT-based CR interventions and can help researchers to strike a balance between the idealised implementation of an ACT intervention and the structural limitations of existing CR programmes.

Trial registration number: NCT01909102.