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
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.
Methodology
- Selected adults with ICD or CRT-D for coronary artery disease or non-ischaemic dilated cardiomyopathy.
- 56 participants.
- 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.
- Intensity: Prescribed 85-95% HRmax/RPE 15-17 during intervals.
- 40 minutes.
- 3 sessions/week.
- 12 weeks.
- 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.
- VO2peak, Quality of life, Ventricular arrhythmia burden, and Premature ventricular contractions and VT by Holter were tracked.
Outcomes
VO2peak
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
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
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
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
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.
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
- 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.