LAUSR

Type of funding sources: Public Institution(s). Main funding source(s): the Innovations Fund of the Alternate Funding Plan for the Academic Health Sciences Centre of the Ministry of Ontario. Lower cardiorespiratory fitness (CRF) in atrial fibrillation (AF) is associated with higher risk of mortality. Moderate-to-vigorous intensity continuous training (MICT) increases CRF; however, growing evidence indicates that high-intensity interval training (HIIT) elicits similar or greater improvements in CRF in people with cardiovascular disease. The purposes of this study were to: (1) compare the effects of HIIT and MICT on CRF in patients with persistent and permanent AF; and, (2) assess the proportion of participants who achieved a clinically meaningful increase in CRF (i.e., 3.5 mL/kg/min, associated with significant reduction in mortality in AF). This was a subanalysis of an RCT to examine the effects of HIIT and MICT on functional capacity. Participants completed cardiopulmonary exercise test (CPET) and were randomly assigned to 12-week, twice weekly supervised HIIT or MICT. Each HIIT session was 23 min in duration, completed on a stationary bike, and consisted of: (1) a 2-min warm up; (2) two blocks of 8 x 30-sec high-intensity work periods at 80-100% peak power output interspersed with 30-sec active recovery periods, with 4 min active recovery between the blocks; and, a 1-min cooldown. Each MICT session consisted of (1) a 15-min warm up; (2) 30-min of continuous aerobic exercise; and, (3) a 15-min cooldown. A subset of willing participants completed follow-up CPET. Repeated measures ANOVA was used to compare the changes in CRF between HIIT and MICT. Descriptive statistics was used to assess the proportion of patients meeting the clinically meaningful increase in CRF. Of 94 patients consented, 13 in HIIT (67±4 years old, 26% females) and 10 in MICT (71±9 years old, 40% females) completed pre and post CPET. Exercise adherence (i.e., % of sessions attended) was 91% for HIIT and 85% for MICT, respectively, and did not differ between the groups. At week 12, 76% of participants in HIIT and 80% in MICT achieved the prescribed exercise intensity targets. Our per-protocol analysis showed no overall change in CRF (pre: 19.0±5.1 vs. post: 19.4±4.6 mL/kg/min, p=0.461). No significant differences in changes in CRF were observed between HIIT (pre: 20.1±5.3 vs. post: 20.3±4.5 mL/kg/min) and MICT (pre: 17.6±4.8 vs. post: 18.4±4.7 mL/kg/min, interaction effect p=0.681). Two participants in HIIT (15.4%) and two in MICT (20.0%) achieved clinically meaningful increases. Twice weekly HIIT or MICT for 12 weeks did not improve CRF in patients with persistent and permanent AF who completed CPET. Further, a small proportion of these patients (≤ 20%) achieved clinically meaningful increase in CRF. Considering a greater increase in CRF (3.2±2.5 mL/kg/min) in patients with non-permanent AF following high-volume HIIT (a total of 16 min at high intensity per session, three times per week) in a previous RCT, a larger exercise volume may be required to improve the CRF of patients with persistent and permanent AF.