Chicago, IL—Cardiac resynchronization therapy (CRT) in the setting of atrial fibrillation (AF) and heart failure (HF) has clear challenges, and the evidence is mixed about its benefit.
Randomized clinical trial evidence is needed, including the use of atrioventricular junction (AVJ) ablation, according to Jonathan S. Steinberg, MD, FACC, Cardiologist and Professor of Medicine at Columbia University, College of Physicians and Surgeons of New York, and Director of the Arrhythmia Institute at Valley Health System in New York and New Jersey, at the 2012 American College of Cardiology meeting.
The prevalence of AF ranges from approximately 10% in patients with mild HF to 50% in patients with New York Heart Association (NYHA) class IV HF. AF markedly worsens the prognosis of HF and the clinical course in those with left ventricle dysfunction and those with an implantable cardioverter- defibrillator. AF also affects ventricular arrhythmias, increases the likelihood of ventricular tachycardia fibrillation, and causes hemodynamic deterioration.
The benefit of CRT may depend on ventricular rate control in patients with AF, independent of resynchronization, making it more complicated to assess the alternate effects of CRT in the population with AF.
Dr Steinberg noted that US Food and Drug Administration approval of CRT was based on clinical trials of patients with sinus rhythm, and the benefit of CRT may be mediated in part by optimizing atrioventricular timing in patients with sinus rhythm; however, this timing is not relevant if the patient is experiencing AF.
CRT is more challenging in patients with permanent AF than in those with sinus rhythm.
Biventricular Pacing Needed
Biventricular pacing is needed virtually all the time in patients with CRT to accrue the most benefit. Yet, this can be challenging in patients with AF and competing asynchronous rhythm. Pacing options are designed to try to maintain biventricular pacing when CRT is used in patients with AF, but no benefit has been proved. Medical therapy to slow the ventricular rate and block atrioventricular nodal conduction is often unsuccessful.
A challenge to achieving consistent biventricular capture is the need for a higher programmed pacing rate for a higher intrinsic heart rate. Frequent fusion and pseudofusion beats can occur and represent ineffective biventricular capture, “in which only a small amount of left-ventricular myo cardium is captured by the leftventricular pacing, negating the intended effects of CRT,” Dr Steinberg said. Inaccurate assessment of biventricular capture on device counters— the gold standard to assess proper delivery of CRT—can occur.
Benefit of CRT
In terms of left-ventricular ejection fraction (LVEF) and NYHA class, CRT showed benefit in some studies and equivalence in others in a meta-analysis. Dr Steinberg presented a prospective study in patients with permanent AF receiving CRT that showed that effective pacing improved NYHA class, reverse remodeling, and LVEF; however, effective pacing occurred in only 44% of the patients in that study.
This study also identified a high rate of inaccurate recording of the absolute percentage of biventricular pacing, as much as 40% of the >90% documented pacing.
AVJ ablation improved survival as was shown in a large observational study of CRT in patients with AF and sinus rhythm. Dr Steinberg noted that this is strong evidence for the need for AVJ ablation, which is the ultimate atrioventricular nodal blockade and forces completely effective ventricular capture, although this is an observational study. Similar results were shown in 2 subsequent observational studies.
Who Should Receive CRT?
Dr Steinberg said that appropriate patients for CRT are those with permanent AF meeting the clinical criteria for CRT, those who have mild HF and left bundle branch block only, and patients with advanced HF and left bundle branch blockage. Approximately 66% of patients with AF ultimately have AVJ ablation, which is a stepwise process based on clinical response and capture rates, according to Dr Steinberg.
Candidates for AVJ ablation are patients with moderately rapid ventricular rates that cannot be slowed and will not have pacing capture (performed with CRT implantation); those with pacing counters that do not reach ≥90% (subsequent AVJ ablation); and nonresponders whose electrocardiogram and Holter recordings show high percentages of ineffective capture. Patients with relatively slow rates who are pharmacologically controlled at the time of CRT implantation are followed.
Careful attention to rate control is required, and physicians should not rely solely on pacing counters to ensure effective CRT capture.—MM