Does recovery from submaximal exercise predict response to cardiac resynchronisation therapy?

BACKGROUND: Exercise parameters are not routinely incorporated in decision making for cardiac resynchronisation therapy (CRT). Submaximal exercise parameters better reflect daily functional capacity of heart failure patients than parameters measured at maximal exertion, and may therefore better predict response to CRT. We compared various exercise parameters, and sought to establish which best predict CRT response.

METHODS: In 31 patients with chronic heart failure (61% male; age 68±7 years), submaximal and maximal cycling testing was performed before and 3 months after CRT. Submaximal oxygen onset (τVO2 onset) and recovery kinetics (τVO2 recovery), peak oxygen uptake (VO2 peak) and oxygen uptake efficiency slope (OUES) where measured. Response was defined as ≥15% relative reduction in end-systolic volume.

RESULTS: After controlling for age, New York Heart Association and VO2 peak, fast submaximal VO2 kinetics were significantly associated with response to CRT, measured either during onset or recovery of submaximal exercise (area under the curve, AUC=0.719 for both; p<0.05). By contrast, VO2 peak (AUC=0.632; p=0.199) and OUES (AUC=0.577; p=0.469) were not associated with response. Among patients with fast onset and recovery kinetics, below 60 s, a significantly higher percentage of responders was observed (91% and 92% vs 43% and 40%, respectively).

CONCLUSIONS: Impaired VO2 kinetics may serve as an objective marker of submaximal exercise capacity that is age-independently associated with non-response following CRT, whereas maximal exercise parameters are not. Assessment of VO2 kinetics is feasible and easy to perform, but larger studies should confirm their clinical utility.