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

Piercarlo Ballo

Cardiology Operative Unit
S. Andrea Hospital
Via Vittorio Veneto 197
19100 La Spezia
Italy
Tel: +39 0187533299
Fax: +39 0187533456
E-mail address: pcballo{at}tin.it

Sandra Badolati

Cardiology Operative Unit
S. Andrea Hospital
Via Vittorio Veneto 197
19100 La Spezia
Italy

Daniele Bernabò

Cardiology Operative Unit
S. Andrea Hospital
Via Vittorio Veneto 197
19100 La Spezia
Italy

Sergio Antonio Faraguti

Cardiology Operative Unit
S. Andrea Hospital
Via Vittorio Veneto 197
19100 La Spezia
Italy

We read the recent article by Melenovsky et al.1 concerning functional impact of ventricular response irregularity in patients with atrial fibrillation (AF) and heart failure and found it interesting. The authors found that irregular biventricular pacing produced an impairment in left ventricular (LV) function in comparison with regular pacing when the mean rate was 120 b.p.m., but not when the mean rate was 80 b.p.m. The results of the study highlight that rate control rather than regularization should be the primary aim in these patients.

We would like to point out an important aspect in the interpretation of these findings. A correct evaluation of the effect of heart rate on differences in LV performance between regular and irregular pacing requires algorithms of irregular stimulation to produce comparable degrees of RR interval variability and/or irregularity at different mean rates. This condition is a major issue for such an analysis, as it allows us to rule out the hypothesis that the detrimental changes in cardiac function observed during irregular vs. regular pacing at high rates, but not at normal rates, may derive from different RR variability or irregularity indices, and not from the increase in mean ventricular rate itself. Unfortunately, a comparison of such parameters between the ventricular cycle series used to stimulate irregularly at 80 and 120 b.p.m. was not reported in the text. The authors used computer-generated irregular sequences of RR intervals that followed the discrete Poisson distribution—a well-known probability function that accurately describes the probabilistic behaviour of the ventricular response to AF. However, a Poisson-distributed series of ventricular cycles may be characterized by consistently different degrees of RR interval variability, depending on the mean cycle length, the histogram bar width, and the minimal RR interval under which the probability reduces to zero, i.e. the absolute refractory period of the atrioventricular node. Beat-to-beat variability and RR irregularity indices may also vary significantly, even in distributions with similar mean values and standard deviations.

These considerations raise the problem of defining the concept of ‘comparable’ degrees of variability and/or irregularity at different mean rates, as several indices have been previously proposed to analyse the dynamics of ventricular response to AF.24 Moreover, it should be taken into account that in patients with AF most of these indices show a positive association with mean ventricular cycle length.2 From this point of view, in order to better analyse the effect of heart rate on the differences in cardiac function between regular and irregular ventricular pacing, it may be appropriate to generate sequences of RR intervals with different mean rate but similar rate-adjusted parameters of both variability and irregularity. However, it might also be interesting to evaluate the haemodynamic effect of sequences characterized by variable degrees of RR variability and irregularity, in order to explore the relative role of each index, and its interaction with mean heart rate, in affecting cardiac function. We believe that future analyses investigating these issues may further reinforce the message of this study, and clarify intriguing aspects of LV haemodynamic response to AF.

References

  1. Melenovsky V, Hay I, Fetics BJ, Borlaug BA, Kramer A, Pastore JM, Berger R, Kass DA. Functional impact of rate irregularity in patients with heart failure and atrial fibrillation receiving cardiac resynchronization therapy. Eur Heart J 2005;26:705–711.[Abstract/Free Full Text]
  2. Yamada A, Hayano J, Sakata S, Okada A, Mukai S, Ohte N, Kimura G. Reduced ventricular response irregularity is associated with increased mortality in patients with chronic atrial fibrillation. Circulation 2000;102:300–306.[Abstract/Free Full Text]
  3. Hogue CW Jr, Domitrovich PP, Stein PK, Despotis GD, Re L, Schuessler RB, Kleiger RE, Rottman JN. RR interval dynamics before atrial fibrillation in patients after coronary artery bypass graft surgery. Circulation 1998;98:429–434.[Abstract/Free Full Text]
  4. Pincus S. Approximate entropy as a measure of system complexity. Proc Natl Acad Sci USA 1991;88:2297–2301.[Abstract/Free Full Text]




This Article
Full Text (PDF)
All Versions of this Article:
26/16/1689-a    most recent
ehi371v1
Alert me when this article is cited
Alert me if a correction is posted
Services
Email this article to a friend
Similar articles in this journal
Similar articles in ISI Web of Science
Similar articles in PubMed
Alert me to new issues of the journal
Add to My Personal Archive
Download to citation manager
Request Permissions
Google Scholar
Articles by Ballo, P.
Articles by Faraguti, S. A.
PubMed
PubMed Citation
Articles by Ballo, P.
Articles by Faraguti, S. A.