Is a first-degree atrioventricular (AV) block expected after left atrial ablation?

From the Guidelines

First degree AV block is not typically expected after left atrial ablation, though it can occur as a potential complication. Most patients undergoing left atrial ablation for conditions like atrial fibrillation do not develop first degree AV block as a direct result of the procedure. The ablation targets primarily involve the pulmonary veins and sometimes other left atrial structures, which are generally anatomically distant from the AV node. However, first degree AV block (characterized by PR interval prolongation >200 ms) may occasionally develop due to several factors: edema near the AV node following extensive ablation, particularly if ablation is performed near the septum or around the mitral annulus; effects of anesthesia or antiarrhythmic medications used during or after the procedure; or pre-existing conduction disease that becomes more apparent after ablation. According to the study by Tracy et al 1, the incidence of complications, including heart block, is low, with a reported rate of 1.3% in patients who underwent AV node modification. Most cases of procedure-related first degree AV block are transient and resolve within days as inflammation subsides. Patients should be monitored with ECGs following ablation to detect any conduction abnormalities, but specific treatment for isolated first degree AV block is typically not required unless it progresses to higher-degree blocks. Some key points to consider include:

• The risk of heart block is higher in patients who undergo AV node modification, with a reported rate of 4.7% in the 1996 study from the MERFS 1.
• The use of a slow pathway ablation approach may reduce the risk of heart block, as reported by Calkins et al from the Atakr Multicenter Ablation Investigators Group 1.
• Catheter ablation provides a safe and highly effective treatment for symptomatic patients with supraventricular tachycardia, with a low risk of serious complications 1.

From the Research

Expected Outcomes After Left Atrial Ablation

• First-degree atrioventricular (AV) block is not a typical expected outcome after left atrial ablation, as the procedure primarily targets the left atrium and not the AV node 2.
• However, iatrogenic AV block can occur in the context of cardiac electrophysiologic procedures, including catheter ablation of atrial fibrillation 2.
• The development of AV block after left atrial ablation may be related to the proximity of the ablation site to the AV node or the His bundle, and the risk of AV conduction system injury 2.
• Studies have shown that AV block can occur after catheter ablation of atrial fibrillation, but the incidence is relatively low 3, 4.

Relationship Between AV Block and Atrial Fibrillation

• First-degree AV block is more common in patients with atrial fibrillation and atrial flutter, and may be due to intra-atrial conduction delay 5.
• The presence of AV block may affect the outcome of cardiac resynchronization therapy in patients with atrial fibrillation, and may be a marker of more advanced heart disease 6.
• AV nodal ablation and pacemaker implantation can be an effective treatment for patients with drug-resistant atrial fibrillation, but may also be associated with a risk of AV block 3.

Clinical Implications

• The development of AV block after left atrial ablation may require pacemaker implantation, and may affect the patient's long-term outcome 6, 3.
• The risk of AV block should be considered when performing left atrial ablation, and measures should be taken to minimize this risk 2.
• Further studies are needed to determine the incidence and clinical significance of AV block after left atrial ablation, and to develop strategies to prevent and manage this complication 6, 5, 2, 4.