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European Heart Journal Advance Access originally published online on June 21, 2005
European Heart Journal 2005 26(16):1690; doi:10.1093/eurheartj/ehi372
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© The European Society of Cardiology 2005. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org

Impact of ventricular response irregularity in patients with atrial fibrillation and heart failure: reply

Vojtech Melenovsky

Division of Cardiology
Department of Medicine
Johns Hopkins Medical Institutions
Ross 835
720 Rutland Avenue
Baltimore
MD 21205
USA

Ronald Berger

Division of Cardiology
Department of Medicine
Johns Hopkins Medical Institutions
Ross 835
720 Rutland Avenue
Baltimore
MD 21205
USA

David A. Kass

Division of Cardiology
Department of Medicine
Johns Hopkins Medical Institutions
Ross 835
720 Rutland Avenue
Baltimore
MD 21205
USA
E-mail address: dkass{at}jhmi.edu

We appreciate the interest of Ballo et al. in our study and their thoughtful comments. Their major concern was that the observed haemodynamic differences between regular and irregular pacing at two different levels of heart rate might have been confounded by differences in R–R interval variability at the two rates. We appreciate how this concern might arise given the lack of full details regarding the pacing sequence we used to simulate atrial fibrillation. However, as explained in detail here, we believe this concern is not warranted.

We used a random number generator to derive an R–R interval sequence at a mean rate of 80, which yielded an event histogram following a Poisson distribution. As noted, this is typical of R–R interval histograms that approximate naturally occurring atrial fibrillation.1 For studies at the faster rate, we used the identical random sequence of R–R intervals, but shortened each interval by one-third, taking into account dependency of heart-rate variability on prevailing mean heart rate.2,3 Thus, the coefficient of variation (COV=SD/meanx100), was identical at both mean rates (25.6%). This mirrors measured data from patients with atrial fibrillation in whom adrenergic or anticholinergic medications were used to vary heart rate (48, 60, and 90 b.p.m.), yet the COV of the R–R intervals remained essentially constant at ~23% for each rate.2 In addition, we used the identical ‘random’ time-sequence of R–R intervals at both rates, so the temporal course of intervals was reproduced in each patient at each rate. We regret that these details were not provided in the manuscript.

We agree that it would be interesting to investigate the haemodynamic consequences of different degrees of R–R variability and irregularity (entropy), particularly in the setting of an animal model. However, in an invasive study of severely ill human subjects, we limited our efforts to the most contrasting conditions—the categorical comparison between completely regular and irregular pacing sequences with a distribution that resembles real-life atrial fibrillation.

References

  1. Goldstein RE, Barnett GO. A statistical study of the ventricular irregularity of atrial fibrillation. Comput Biomed Res 1967;1:146–161.[Medline]
  2. van den Berg MP, Haaksma J, Brouwer J, Tieleman RG, Mulder G, Crijns HJ. Heart rate variability in patients with atrial fibrillation is related to vagal tone. Circulation 1997;96:1209–1216.[Abstract/Free Full Text]
  3. Friedman HS. Heart rate variability in atrial fibrillation related to left atrial size. Am J Cardiol 2004;93:705–709.[CrossRef][Web of Science][Medline]

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This Article
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