# Effect of high-intensity interval training on peak oxygen uptake, quality of life, and ventricular arrhythmias in patients with an implantable cardioverter defibrillator: a randomized controlled trial PMID: 42004906 Journal: European heart journal open Published: 2026-04-13 Authors: Nyman M, Mjølstad OC, Dale AC, Amundsen BH, Rossvoll O, Wisløff U, Loennechen JP ## Question Does a supervised 12-week HIIT programme improve exercise capacity and quality of life, and how does it affect ventricular arrhythmia burden, in selected ICD/CRT-D patients with coronary artery disease or non-ischaemic dilated cardiomyopathy? ## Summary In a single-centre randomized trial, 56 adults with an implantable cardioverter defibrillator or cardiac resynchronization therapy defibrillator because of coronary artery disease or non-ischaemic dilated cardiomyopathy were assigned to 12 weeks of supervised treadmill HIIT or usual activity. The HIIT protocol used 4 x 4 minute intervals at 85-95% of maximum heart rate, three times per week. HIIT improved VO2peak by about 7% compared with no change in controls and improved the SF-36 health change quality-of-life domain after multiple-comparison correction. Arrhythmia findings were inconclusive: sustained ventricular tachycardia incidence was statistically lower in the HIIT group, but events were few and unevenly distributed, and two HIIT participants had sustained ventricular tachycardia during training. ## Population - Selected adults with ICD or CRT-D for coronary artery disease or non-ischaemic dilated cardiomyopathy. - Sample size: 56 - Age: Mean 68.2 +/- 8.5 years. - Sex: 82% men. - Fitness level: Baseline VO2peak about 24.4 mL/kg/min; excluded if already doing HIIT-equivalent training at least twice weekly. - Health status: Clinical cardiac population with ICD/CRT-D and high ventricular arrhythmia risk; mostly NYHA class I-II. ## Methodology - Single-centre, parallel-group randomized controlled trial with stratification by coronary artery disease versus dilated cardiomyopathy and 1:1 allocation to supervised HIIT or usual activity control. - 12 weeks, with ventricular arrhythmia monitoring divided into pre-intervention, intervention, and 2-month post-intervention periods. - NextMove Core facility of the Cardiac Exercise Research Group at St Olavs Hospital, Trondheim, Norway; supervised group treadmill sessions. - Randomized and controlled study design. ## Protocol - Supervised 4 x 4 minute HIIT. - Modality: Uphill treadmill walking/running. - Work intervals: 4 minutes at 85-95% HRmax and/or Borg RPE 15-17. - Recovery: 3 minutes active recovery at 60-70% HRmax and/or Borg RPE 11-13. - Sets or repetitions: 4 intervals. - Intensity: Prescribed 85-95% HRmax/RPE 15-17 during intervals. - Session duration: 40 minutes. - Frequency: 3 sessions/week. - Program length: 12 weeks. - Progression: Speed or inclination increased to maintain relative intensity as exercise capacity improved. - Usual activity control. - Modality: Usual activity. - Intensity: Maintain usual activity and avoid starting new exercise programmes including HIIT. - Program length: 12 weeks. ## Outcomes ### VO2peak Status: improved HIIT increased VO2peak by 1.6 +/- 2.1 mL/kg/min (7.0%) from 24.4 to 26.1 mL/kg/min, while controls had no change. Between-group difference 1.7 mL/kg/min, 95% CI 0.7 to 2.6; P < 0.001. ### SF-36 health change Status: improved The SF-36 health change subscale improved in the HIIT group and declined in controls. +14.8 +/- 22.2 points after HIIT versus -7.1 +/- 23.4 in controls; 95% CI 9.6 to 34.3; P < 0.001 after Bonferroni correction. ### Other SF-36 domains Status: mixed Most other quality-of-life domains showed favourable numerical trends but did not remain statistically significant after correction. Bonferroni-adjusted alpha was 0.006 across nine subscales. ### Sustained ventricular tachycardia incidence Status: mixed Sustained VT incidence decreased in HIIT and increased in controls from baseline to follow-up, but events were few and unevenly distributed. Group difference -1.8 events per patient-year at follow-up; P = 0.037. ### Exercise-related adverse events Status: worse/safety concern Two HIIT participants had sustained VT during training, including one ICD shock after VT accelerated to ventricular fibrillation with loss of consciousness; one participant had a knee injury during training. ## Practical Insights - A classic 4 x 4 minute HIIT structure can improve VO2peak in selected cardiac rehabilitation patients when supervised and intensity-monitored. - In high-risk ICD populations, HIIT programming must be tied to clinical screening, emergency readiness, and individualized risk evaluation. - RPE can complement heart-rate targets when beta-blockers and device settings affect heart-rate interpretation. - Consumer-facing HIIT guidance should avoid implying that ICD patients can perform high-intensity intervals without medical clearance. ## Limitations - Single-centre study. - Small sample and under-recruitment relative to planned sample size. - Short intervention duration. - Not powered for safety outcomes. - Low inclusion rate and possible selection/volunteer bias. - Women underrepresented. - Baseline imbalances may have affected clinical and arrhythmia outcomes. - Participants and exercise staff could not be blinded to exercise intervention. - Control group activity was not actively monitored and some control contamination occurred. - Excluded important ICD subgroups and patients with exercise-induced arrhythmia at baseline. ## Safety And Adherence - Clinically relevant ventricular arrhythmias occurred in two patients during baseline CPET and two patients during HIIT. - Two sustained VT events occurred during HIIT; one required ICD shock and one was treated with ATP. - One knee injury during training led to withdrawal. - Several adverse events unrelated to exercise were reported, including ICD lead issues, angina/revascularization in control, gastrointestinal bleeding in control, subdural haemorrhage after a fall, and atrial flutter hospitalization. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/42004906/) (pubmed) - [DOI](https://doi.org/10.1093/ehjopen/oeag058) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13089605/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.