CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Hung-Fat Tse, MD, FACC* and
Chu-Pak Lau, MD, FACC
* Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong, China (Email: hftse{at}hkucc.hku.hk).
We thank Drs. Witte and Clark for their interest in our study (1). We agree with their comment that there is no established diagnostic criterion for chronotropic incompetence (CI) for patients with heart failure (HF). The commonly used definition of the age-predicted heart rate (HR) to diagnose CI is traditionally employed for patients with ischemic heart disease. Despite the wide application of rate-adaptive pacing, there is also no established definition of CI for pacemaker patients (2). From a pacing standpoint, the detection of CI is clinically relevant only when there is a functional improvement associated with rate-adaptive pacing. Prior studies have shown that HF patients with CI have lower peak oxygen consumption as compared with those without CI (3). Our data demonstrate that the conventional definition of CI is not applicable to patients with HF implanted with cardiac resynchronization therapy (CRT). Indeed, rate-adaptive pacing was found to be beneficial only in those patients with severe CI who failed to achieve >70% of age-predicted HR, and potentially harmful to patients with mild CI based on the conventional definition. Furthermore, the incidence of CI in HF patients implanted with CRT appears to be higher than for those reported in the general HF population (4). We have evaluated a total of 28 patients and have enrolled 20 patients (71%) with age-predicted HR <85% for this study. This is likely because the current CRT patients have more severe HF (class III to IV) and advanced conduction system abnormalities as compared with the general HF population.
As mentioned by Drs. Witte and Clark, a lower HR at rest predicts better outcome in patients treated with a beta-blocker. The use of rate-adaptive pacing only increases HR during exercise, but not the resting HR, and the increase in 24-h HR due to rate-adaptive pacing is minimal. In fact, the use of rate-adaptive pacing can alleviate the CI to allow more aggressive use of beta-blockers. Consistent with the findings in their recent studies (4), we have shown that the percentage of HR changes during exercise positively correlated with peak oxygen consumption (1). We believe that our data have demonstrated that rate-adaptive pacing is complementary to the use of CRT and optimal medical therapy, including beta-blocker, to improve exercise capacity in HF patients, and appropriate rate-adaptive pacing should be considered in patients in whom CRT response is suboptimal owing to concurrent CI.
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References
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1. Tse HF, Siu CW, Lee KL, et al. The incremental benefit of rate-adaptive pacing on exercise performance during cardiac resynchronization therapy J Am Coll Cardiol 2005;46:2292-2297.[Abstract/Free Full Text]2. Lau CP. Normal exercise cardiopulmonary physiology and chronotropic incompetenceIn: Lau CP, editor. Rate Adaptive Cardiac Pacing. Single and Dual Chamber. Mount Kisco, NY: Futura Publishing; 1993. pp. 7-23. 3. Fei L, Keeling PJ, Sadoul N, et al. Decreased heart rate variability in patients with congestive heart failure and chronotropic incompetence Pacing Clin Electrophysiol 1996;19:477-483.[CrossRef][Medline] 4. Witte KK, Cleland JG, Clark AL. Chronic heart failure, chronotropic incompetence, and the effects of beta-blockade Heart 2006;92:481-486.[Abstract/Free Full Text]
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