Tse HF, Siu CW, Lee KLF, Fan K, Chan HW, Tang MO, Tsang V, Lee SWL, Lau CP

J Am Coll Cardiol. 2005;46(12):2292-2297.

Background:

Chronotropic incompetence is common among patients with heart failure and contributes to the impairment of exercise capacity. Appropriate rate adaptation using a rate-responsive pacemaker may improve exercise capacity in these patients. Cardiac resynchronization therapy (CRT) has been shown to improve functional class, exercise capacity, and quality of life in patients with heart failure. However, the potential incremental benefits of using optimal rate-adaptive pacing and atrioventricular interval (AVI) adaptation with CRT during exercise have not been studied.

Objective:

The aim of this study is to investigate the effect of using rate-adaptive pacing and AVI adaptation algorithm on exercise performance in patients with chronotropic incompetence who receive CRT.

Methods:

Twenty patients with New York Heart Association functional class III or IV heart failure, with chronotropic incompetence (defined as <85% age-predicted heart rate and <80% heart rate reserve), and who received CRT were included in the study. Thirteen (65%) had idiopathic dilated cardiomyopathy, whereas 7 (35%) had ischemic cardiomyopathy. Medical therapy was stable for 3 months or more. Six months after the implantation of the CRT device, all patients underwent cardiopulmonary exercise treadmill test, with their CRT devices programmed to (1) DDD mode with fixed AVI (DDD-OFF); (2) DDD mode with adaptive AVI algorithm (DDD-ON); and (3) DDDR mode with adaptive AVI algorithm (DDDR-ON). The following exercise variables were measured: exercise workload as measured by metabolic equivalents (METs), peak heart rate (HR), minute oxygen consumption (VO₂), minute carbon dioxide production (VCO₂), peak oxygen consumption (VO₂ max), and peak respiratory exchange ratio (peak VCO₂/peak VO₂) as an index of effort adequacy.

Results:

During the DDD-OFF mode, all patients failed to reach 85% of the age-predicted HR during exercise, and 55% had less than 70% age-predicted HR. In patients with less than 70% age-predicted HR, DDDR-ON mode increased peak exercise HR, exercise time, METs achieved, and VO₂ max compared with the DDD-OFF and DDD-ON modes (P < .05). There were no significant differences in these exercise parameters between the DDD-OFF and DDD-ON modes. There were also no significant differences in peak exercise HR, exercise time, METs achieved, and VO₂ max among the three pacing modes in patients with greater than 70% age-predicted HR. In patients with improvement in exercise performance during rate-adaptive pacing, VO₂ max increased by 2.5 +/- 0.5 ml kg^-1 min^-1 (range 0.8-5.3 ml kg^-1 min^-1). The percentage HR change during exercise positively correlated with exercise time, METs achieved, and VO₂ max.

Discussion:

Rate-adaptive pacing during CRT increased peak exercise HR and exercise time in patients with heart failure and chronotropic incompetence but did not have an incremental benefit on exercise capacity. However, in patients with more severe chronotropic incompetence (< 70% age-predicted HR achieved during exercise), rate-adaptive pacing during CRT significantly increased peak exercise HR, exercise time, and METs achieved. In most of these patients, this improvement in HR response to exercise is associated with a 20% increase in VO₂ max compared with without rate-adaptive pacing. The results of this study suggest that appropriate rate adaptation with CRT provides an incremental benefit to patients with heart failure and severe chronotropic incompetence during exercise. Hence, after stabilization of medical therapy, patients with heart failure implanted with CRT should undergo exercise testing to assess their HR response to exercise and be considered for rate-adaptive pacing.

Comment:

Optimization of pacemaker settings (AV and VV delays) has been demonstrated to further improve benefit from CRT. This is the first study to examine the impact of optimal programming of CRT devices during exercise in patients with heart failure. It should be noted that not all patients with heart failure and CRT benefited from the use of rate-adaptive pacing. In fact, in patients without improvement in exercise performance during rate-adaptive pacing, VO₂ max during the DDDR-ON mode actually decreased by 1.4 +/- 0.4 ml kg^-1 min^-1 compared with the DDD-OFF mode. Clearly, optimization of pacemaker settings appears to require individualized patient evaluation, with collaboration between heart failure, exercise rehabilitation, and electrophysiology specialists.

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