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CLINICAL RESEARCH: PACING SCHEMES AND RESYNCHRONIZATION

The Incremental Benefit of Rate-Adaptive Pacing on Exercise Performance During Cardiac Resynchronization Therapy

Hung-Fat Tse, MD, FACC^_*, Chung-Wah Siu, MBBS^_*, Kathy L.F. Lee, MBBS^_*, Katherine Fan, MBBS, Hon-Wah Chan, MBBS^_*, Man-Oi Tang, MD^_*, Vella Tsang, RN^_*, Stephen W.L. Lee, MBBS, FACC^_* and Chu-Pak Lau, MD, FACC^_*,_*

^_* Cardiology Division, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, China
Cardiac Medical Unit, Grantham Hospital, Hong Kong, China

Manuscript received December 31, 2004; revised manuscript received February 14, 2005, accepted February 22, 2005.

^_* Reprint requests and correspondence: Dr. Chu-Pak Lau, Division of Cardiology, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, China (Email: cplau{at}hkucc.hku.hk).

OBJECTIVES: The purpose of this research was to investigate the effect of using rate-adaptive pacing and atrioventricular interval (AVI) adaptation on exercise performance during cardiac resynchronization therapy (CRT).

BACKGROUND: The potential incremental benefits of using rate-adaptive pacing and AVI adaptation with CRT during exercise have not been studied.

METHODS: We studied 20 patients with heart failure, chronotropic incompetence (<85% age-predicted heart rate [AP-HR] and <80% HR reserve), and implanted with CRT. All patients underwent a cardiopulmonary exercise treadmill test using DDD mode with fixed AVI (DDD-OFF), DDD mode with adaptive AVI on (DDD-ON), and DDDR mode with adaptive AVI on (DDDR-ON) to measure metabolic equivalents (METs) and peak oxygen consumption (VO₂max).

RESULTS: During DDD-OFF mode, not all patients reached 85% AP-HR during exercise, and 55% of patients had <70% AP-HR. Compared to patients with >70% AP-HR, patients with <70% AP-HR had significantly lower baseline HR (66 ± 3 beats/min vs. 80 ± 5 beats/min, p = 0.015) and percentage HR reserve (27 ± 5% vs. 48 ± 6%, p = 0.006). In patients with <70% AP-HR, DDDR-ON mode increased peak exercise HR, exercise time, METs, and VO₂max compared with DDD-OFF and DDD-ON modes (p < 0.05), without a significant difference between DDD-OFF and DDD-ON modes. In contrast, there were no significant differences in peak exercise HR, exercise time, METs, and VO₂max among the three pacing modes in patients with >70% AP-HR. The percentage HR changes during exercise positively correlated with exercise time (r = 0.67, p < 0.001), METs (r = 0.56, p < 0.001), and VO₂max (r = 0.55, p < 0.001).

CONCLUSIONS: In heart failure patients with severe chronotropic incompetence as defined by failure to achieve >70% AP-HR, appropriate use of rate-adaptive pacing with CRT provides incremental benefit on exercise capacity during exercise.

Abbreviations and Acronyms   AP-HR = age-predicted heart rate   AVI = atrioventricular interval   CRT = cardiac resynchronization therapy   HR = heart rate   METs = metabolic equivalents   LV = left ventricle/ventricular   peak VCO2/peak VO2 = peak respiratory exchange ratio   VCO2 = minute carbon dioxide production   VO2 = minute oxygen consumption   VO2max = peak oxygen consumption

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