How should paroxysmal atrial fibrillation be considered in CRT studies?
It is with great interest that we read the contribution by Kayvan and colleagues (1) on the long-term effects of cardiac resynchronization therapy (CRT) in patients with atrial fibrillation (AF), not treated with atrio-ventricular junction (AVJ) ablation. Somewhat surprising is the extremely high proportion of AF patients in this cohort : 86/295 patients (29%), probably the highest incidence ever reported in CRT. At a more careful analysis, it can be noted that 20/86 (23%) of AF patients presented only paroxysmal AF (PAF). PAF patients, even before CRT, spend more than 90% of the time in sinus rhythm (SR), and it is well known that CRT significantly reduces AF burden during follow-up (2). This means that PAF patients, after CRT, are paced in DDD modality for about 90-95% of the time. Would these 20 PAF patients be considered in the SR group, then the proportion of AF patients would approach that of other larger series (3, 4). Placing PAF patients as part of the AF group may have introduced 2 important biases in the Kayvan study: 1) patients with PAF, usually present higher mean biventricular pacing percentages (BVP%) compared to patients with permanent AF (explaining the 87% BVP% in this AF group); 2) PAF behave “clinically” like SR patients, and drag, within the AF group, the positive effects conferred by CRT in SR. Mixing these 20 “clinically”, SR-like patients into the AF group, may confound any outcome result. The high BVP% reported into the AF group is even more astonishing considering the low use of chronotropic-negative drugs and the lack of use of ventricular rate regularization (VRR) feature, extremely important to ensure biventricular capture in case of fast irregular rhythm. Conversely, in our experience (3), after 2 months of CRT, only 30% (48/162) of AF patients presented BVP% >85% despite implementation of a rigorous rate-control protocol (rate-lowering drugs plus VRR and trigger mode). Another explanation accounting for the high BVP% in the Kayvan series may be that several AF patients presented very low-rate AF at baseline, with a possible coexisting pacing indication, thus rendering futile recourse to AVJ ablation: unfortunately this hypothesis cannot be ruled out as mean baseline heart rate was not presented.
1) Kayvan K, Foley PW, Chalil S et al.
Long-term effects of cardiac resynchronization therapy in patients with atrial fibrillation.
Heart Online First, January 2008.
2) Hugl B, Bruns HJ, Unterberger-Buchwald C et al.
Atrial fibrillation burden during the post-implant period period after crt using device-based diagnostics.
J Cardiovasc Electrophysiol 2006; 17: 813-7.
3) Gasparini M, Auricchio A, Regoli F et al.
Four-year efficacy of cardiac resynchronisation therapy on exercise tolerance and disease progression: the importance of performing atrioventricular junction ablation in patients with atrial fibrillation.
J Am Coll Cardiol. 2006 Aug 15;48(4):734-43.
4) Auricchio A, Metra M, Gasparini M et al.
Long-term survival of patients with heart failure and ventricular conduction delay treated with cardiac resynchronization therapy.
Am J Cardiol. 2007;99:232-8.
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