To date, no studies have evaluated the safety or efficiency (improvement of maximal oxygen uptake [VO2peak]) of a high-intensity interval training (HIIT) program in post-acute coronary syndrome (post-ACS) patients. Heart rate variability (HRV) and recovery (HRR), QT dispersion (QTd) and ventricular arrhythmias are all indices associated with an increased risk of cardiac death. HIIT has been shown to improve these risk markers and be safe in coronary heart disease patients but not yet in post-ACS patients which are considered more at risks.

The aim of this study was to compare a HIIT program to a moderate-intensity continuous exercise training (MICET) program on HRV, HRR, QTd parameters and occurrence of ventricular arrhythmias in post-ACS patients.

Inclusion Criteria:

• Males or females aged ≥ 18 years
• Acute coronary syndrome within 6 weeks (unstable angina, or non-ST elevation myocardial infarction (NSTEMI), or ST elevation myocardial infarction (STEMI with the presence of 2/3 criteria (i.e. typical chest pain, electrocardiographic ischemic change or elevated troponin T
• Complete revascularization defined as no major epicardial coronary artery or bypass graft with a residual diameter stenosis >50% and no residual left main stenosis ≥40%
• Left ventricular ejection fraction >40%
• Stable doses of medication during the 4 weeks prior to enrolment (STEMI patients must be on a stable dose of beta-blocker)
• Able to perform a maximal cardiopulmonary exercise test, 7) capacity and willingness to sign informed consent.

Exclusion Criteria:

• Recent coronary bypass surgery (<6 months)
• Incomplete revascularisation, left ventricular ejection fraction <40%
• Significant valvular disease (mitral stenosis, moderate to severe mitral insufficiency, aortic stenosis, or aortic insufficiency)
• Uncontrolled hypertension (systolic blood pressure/diastolic blood pressure >180/110 mmHg)
• Significant resting electrocardiogram abnormalities (left bundle branch block, non-specific intraventricular conduction delay, left ventricular hypertrophy, resting ST-segment depression)
• Chronic atrial fibrillation
• Pacemaker or implantable cardioverter defibrillator
• Low functional capacity (<5 basal Metabolic Equivalent of Task [METs])
• Change of cardiac medications within 4 weeks of enrolment and any contraindication to exercise testing or exercise training.