We are not at the end of the road but we can see it from here

DOI: 10.19102/icrm.2011.021206

Ulrika Birgersdotter-Green, MD, FACC, FHRS

Editor-in-Chief

Despite continuous advancements in the field of Cardiac Resynchronization Therapy (CRT) for patients with Heart Failure, treatment remains at times challenging. Early trials documented functional and clinical benefits in a defined patient population which laid the foundation for the ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities establishing CRT as a Class I indication for patients in Normal Sinus Rhythm (NSR), NYHA III-IV, EF≤35% and QRS≥120 ms. We have also learned that CRT in this patient population can positively impact morbidity and mortality. More recent trials have investigated the role of CRT in patients with less symptomatic HF, NYHA Class I and II with results suggesting that this therapy may be of significant benefit in this patient population as well. However, patient selection for CRT remains challenging as we know much less about the impact of CRT in sub groups of patients such as those with Right Bundle Branch Block (RBBB) and in patients with Atrial Fibrillation (AF). Patients with AF present a particular challenge as this arrhythmia is the most common arrhythmia in HF patients and is present in many patients with an indication for CRT.

The paper by Drs Lo and Obel provide a very timely review of the background and current body of knowledge of AF in CRT as well as discussion of optimal management of AF in CRT patients. Evidence is emerging that patients in AF may not derive the same potential benefits from CFT due to AV desynchronization from AF and competition between delivery of continuous biventricular (BiV) pacing and native ventricular conduction. In light of these concerns it becomes all the more important to analyze the circumstances by which AF may worsen response to CRT and how to then apply this knowledge, as Drs Lo and Obel state, to maximizing cardiac resynchronization therapy in patients with atrial fibrillation.

Drs Lo and Obel detail the issues with achieving maximum percentage BiV pacing in a comprehensive overview. They make a clear case for monitoring patients for rapidly conducting AF but also wisely caution against using the percentage BiV pacing counters from device interrogations without an actual review of the findings. Falsely high BiV pacing may be reported due to fused and pseudo-fused beats and although sophisticated device algorithms now exist to promote BiV pacing in AF turning them ON without evaluating effectiveness will not be sufficient.

Improved rate control can clearly be achieved through pharmacologic therapy but the most effective means of rate control remains AV node ablation ensuring that CRT is delivered without fusion or pseudo-fusion beats despite short R-R intervals. A recent meta analysis (Wilton et al Heart Rhythm 2011;8:1088-1094) compared outcomes between patients with HF, QRS>120 ms and either AF or NSR. AVN ablation, used in several of the studies included in the meta-analysis, appeared to reduce the risk of clinical nonresponse by 60% compared with otherwise similar AF patients with some studies also showing improved survival in this group. This assessment is corroborated in the present review making the case for considering an AVN ablation in patients with AF and CRT to meet the goal of maximized BiV pacing.

Lastly, it is not unreasonable to consider rhythm control through AF ablation for a subset of patients with AF undergoing CRT. These patients may not be ideal candidates for an AF ablation but there is potential for the procedure to significantly improve CRT response in selected patients as is discussed in this review.

Patient selection for CRT remains challenging as we navigate through clinical trials, expanding indications and patients with more comorbidity. Managing patients with HF and AF will only continue to grow in complexity. It will be very important to have a clear understanding of the role of CRT in these patients and how we can best apply this knowledge to improve response and outcome for our patients.

Ulrika Birgersdotter-Green, MD, FACC, FHRS
ubgreen@mail.ucsd.edu
Professor of Medicine
Director of Pacemaker and ICD Clinic
University of California -San Diego
San Diego, CA