Heart Block: Which Patients Should Get an LV Lead?

Dear Readers,    For several years there was debate regarding whether or not a patient with complete atrioventricular (AV) block should undergo implantation of a dual chamber AV sequential pacemaker or simply a single chamber right ventricular (RV) pacemaker.There is now data to support implantation of a dual chamber device to provide AV synchrony, and it has become common practice to implant two leads. Now, the debate has become whether or not a patient with heart block and preserved ventricular function should receive an additional left ventricular lead to allow for cardiac resynchronization therapy (CRT) rather than a standard pacemaker.The argument is that biventricular pacing mitigates the mechanical dyssynchrony caused by RV pacing alone, and that the patient is less likely to develop ventricular dysfunction and heart failure down the road. However, there are certainly some additional risks and costs associated with adding a coronary sinus lead.    An ongoing trial, BLOCK HF, was designed to address this issue. BLOCK HF is a multi-center, randomized, controlled trial designed to determine whether patients with AV block, left ventricular dysfunction (EF ≤ 50%), and mild to moderate heart failure (NYHA I-III), and who require pacing, benefit from CRT compared with RV pacing alone.¹ Until this trial is complete, it is difficult to make a case that CRT should be the standard of care for patients with complete heart block, especially those patients who are older and have preserved ventricular function.    There are data from studies that show that in patients who have undergone AV node ablation, CRT is superior to standard RV pacing alone.There are also data to support CRT in patients with congenital heart block; this comes from the long-term follow-up of patients with congenital AV block who were paced for several years. It has long been known that children of women who have circulating antinuclear antibodies (ANA+) are at risk of being born with congenital heart block.A very interesting observation regarding the impact of ANA positivity in the patients born with AV block was recently made by a group of investigators from the Mayo Clinic and published in Circulation in April.² They assessed the effect of RV pacing in 103 patients who underwent pacemaker implantation for isolated congenital AV block between 1964 and 2005, and found that patients who were ANA+ were 23 times more likely to die or develop heart failure during long-term follow-up compared to those who were ANA-. Heart failure occurred in 67% of patients who were antibody positive, compared to 2% of patients who were antibody negative and 2% of a matched population. The ejection fraction fell from 52% to 38% in the patients who were ANA+, but remained stable in the ANA- patients. The authors concluded that long-term RV pacing alone does not appear to be associated with the development of heart failure, deterioration in ventricular function, or reduced survival in ANA- patients with isolated congenital AV block. Although the sample size was small, this is a powerful predictor of outcomes. When was the last time a variable was found in cardiology to be associated with a hazard ratio that high?    Like much of what we do in the field of device therapy, it is important to identify which patients are most likely to benefit from our therapies.There is currently not sufficient data to support implantation of a CRT device in every patient with heart block.This new observation by the group from the Mayo Clinic regarding the deleterious effects of ANA positivity in patients who are being paced for congenital AV block suggests that there might be ways to better identify which patients with complete heart block and no heart failure might do just fine with RV pacing alone.

Sincerely,

Bradley P. Knight, MD, FACC, FHRS Editor-in-Chief, EP Lab Digest