CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Cheuk-Man Yu, MD, FRCP*,
Qing Zhang, PhD and
Jeffrey Wing-Hong Fung, FRCP
* Division of Cardiology, Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, People’s Republic of China (Email: cmyu{at}cuhk.edu.hk).
We thank Dr. Breithardt for his comment on our study on cardiac resynchronization therapy (CRT) in patients with narrow QRS complexes and coexisting systolic asynchrony by echocardiography (1). Our report suggested the potential beneficial role of CRT for heart failure patients with narrow QRS complexes if they exhibited systolic asynchrony by tissue Doppler imaging. This included the improvement of exercise capacity, symptoms as well as echocardiographic findings of left ventricular (LV) reverse remodeling, and gain in systolic function. The findings are corroborated by the study of Bleeker et al. (2) in the same issue of the Journal and in 2 previous reports (2–4). Of note, the lack of control group was pointed out by Dr. Breithardt. We agree this is a potential limitation, although the data from the aforementioned studies support the design of a multicenter, randomized, controlled clinical trial, as stated in our study. In fact, we also provided additional information to illustrate the independent benefit of CRT in the narrow QRS group.
First, the study was designed with a pacing "off" period. During such a period, the benefits of pacing on cardiac function and LV reverse remodeling disappeared gradually. Second, those patients in the narrow QRS group who had significant systolic asynchrony responded more than did those with minimal asynchrony. Third, our study also included a group of wide QRS patients, and the magnitude of response was similar in both the narrow and wide QRS groups. Intriguingly, we have shown that for a similar level of systolic dyssynchrony, the magnitude of reverse remodeling response is nearly identical in both groups.
As similar to the wide QRS group, we optimized atrioventricular interval by the Ritter method for patients in the narrow QRS group. As previously mentioned, we did not find any difference in the optimized atrioventricular interval between the 2 groups. However, we ensured patients had successful biventricular capture by examination of a 12-lead electrocardiogram. Arguably, some patients might have fusion beats, though pacing by both ventricular leads remains present even in fusion beats; hence, pacing efficacy should not be affected.
In conclusion, our study does not suggest abandoning the electrocardiogram as a selection criterion for CRT, but recommended the need for multicenter trials for heart failure patients with a narrow QRS complex by using echocardiography for screening of systolic asynchrony. It is hoped that this may extend the benefit of CRT to more heart failure patients beyond the scope of using wide QRS complex as a surrogate marker for the presence of systolic asynchrony.
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References
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- Yu CM, Chan YS, Zhang Q, et al. Benefits of cardiac resynchronization therapy for heart failure patients with narrow QRS complexes and coexisting systolic asynchrony by echocardiography J Am Coll Cardiol 2006;48:2251-2257.[Abstract/Free Full Text]
- Bleeker GB, Schalij MJ, Molhoek SG, et al. Frequency of left ventricular dyssynchrony in patients with heart failure and a narrow QRS complex Am J Cardiol 2005;95:140-142.[CrossRef][ISI][Medline]
- Achilli A, Sassara M, Ficili S, et al. Long-term effectiveness of cardiac resynchronization therapy in patients with refractory heart failure and "narrow" QRS J Am Coll Cardiol 2003;42:2117-2124.[Abstract/Free Full Text]
- Turner MS, Bleasdale RA, Vinereanu D, et al. Electrical and mechanical components of dyssynchrony in heart failure patients with normal QRS duration and left bundle-branch block: impact of left and biventricular pacing Circulation 2004;109:2544-2549.[Abstract/Free Full Text]
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