EFFECTS OF HIGH INTENSITY INTERVAL TRAINING ON HEART RATE RECOVERY, HEART RATE VARIABILITY AND ARRHYTHMIAS IN PATIENTS POST-ACUTE CORONARY SYNDROME

Abstract

Heart rate recovery (HRR) and heart rate variability (HRV) are important predictors of mortality in patients post-acute coronary syndrome (PACS). High intensity interval exercise (HIIE) decreases the prevalence of arrhythmias and increases HRV in heart failure patients. However, the effects of high intensity interval training (HIIT) on HRR, HRV and arrhythmias in PACS patients are not documented. Our aims were to compare the effects of 12-weeks of HIIT vs. moderate intensity continuous exercise training (MICET) on HRR, HRV and arrhythmias in PACS patients. Thirty-one PACS patients from the Montréal Heart Institute (MHI) were randomly assigned to either HIIT (n=13) or isocaloric MICET (n=18) program on cycle ergometer. Cardiometabolic risk factors, maximal cardiopulmonary exercise test (CPET) and 24h-holter ECG monitoring were performed before and after the intervention. The MICET protocol consisted of 5 min warm-up at 30% maximal aerobic power (MAP) followed by 37 min at 60% of MAP, followed by 5 min cool down at 30% of MAP. The HIIT protocol included 2 to 3 blocks of 10 minutes of repeated phases of 15 sec at 100% of MAP alternating with 15 sec of passive recovery. A four-minute passive recovery was allowed between HIIT blocks. Warm up and cool down consisted of 5-minute cycling periods at 30% MAP. Maximal aerobic power was determined during CPET on cycle ergometer. During training sessions, continuous ECG monitoring was performed while BP was measured every 2 minutes. Heart rate recovery (HRR: Δ bpm) was measured during 5 min of recovery and was averaged every 5 sec. Heart rate variability was measured using 24h-holter monitoring. For HRV, time domain and spectral parameters were assessed. Heart rate recovery was not improved in the MICET group after the training. In the HIIT group, HRR was significantly improved (p<0.05) for the following recovery times: 5, 10, 80s, between 165 and 180s, between 205 and 255s, and between 265 and 275s for the HIIT group. Heart rate variability was unchanged in both groups. No significant atrial or ventricular arrhythmias occurred in either group during or after training sessions. Our results suggest that HIIT improves HRR in PACS patients and may result in higher parasympathetic reactivation during the 5-min recovery period although no long-term effects of HIIT on autonomic regulation of cardiovascular function were observed. In PACS patients, HIIT appears safe and does not increase ventricular arrhythmias.