Will a patient with a combination of background Right Bundle Branch Block (RBBB) and First-Degree Atrioventricular Block (FD-AVB) with alternating Left Anterior Hemiblock (LAHB) and Left Posterior Hemiblock (LPHB) inevitably develop Complete Heart Block (CHB) and die without a pacemaker?

From the Guidelines

No, someone with a combination of right bundle branch block (RBBB) and first-degree atrioventricular block (FD-AVB) with alternating left anterior hemiblock (LAHB) and left posterior hemiblock (LPHB) will not always progress to complete heart block (CHB) and die without a pacemaker. According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1, the management of conduction disorders involves a step-wise approach considering symptoms, the presence of bundle branch block, and the risk of progression to complete heart block. Key considerations include:

• The presence of symptoms such as syncope or presyncope
• The type and severity of the conduction disorder
• The presence of underlying structural heart disease
• The results of additional testing such as electrophysiology studies The guideline recommends permanent pacing for patients with alternating bundle branch block (Class I) 1, but the decision to implant a pacemaker should be individualized based on the patient's specific clinical scenario. While the risk of progression to complete heart block is a concern, it is not inevitable, and some patients may remain stable for years without developing complete heart block. However, careful evaluation and monitoring by a cardiologist or electrophysiologist are necessary to assess the risk of progression and determine the best course of management. In general, the approach should prioritize minimizing morbidity, mortality, and improving quality of life, considering the individual patient's risk factors and clinical presentation.

From the Research

Combination of Background RBBB/FD-AVB with Alternating LAHB/LPHB

• The combination of background RBBB/FD-AVB with alternating LAHB/LPHB is a complex conduction abnormality that can increase the risk of complete heart block (CHB) and sudden cardiac death (SCD) 2.
• A study published in 1985 found that patients with this combination of conduction abnormalities had a higher incidence of CHB (22.7% vs 3.2%) and SCD (15.9% vs 3.9%) compared to those with only RBBB and left anterior or left posterior fascicle block 2.
• Another study published in 1991 classified trifascicular block into four groups, including acute transient, acute advanced, chronic, and chronic advanced, and found that patients with severe symptoms benefited from pacemaker implantation 3.
• However, not all studies suggest a poor prognosis for patients with this combination of conduction abnormalities. A study published in 1979 found that transient left anterior hemiblock obscuring the diagnosis of right bundle branch block in acute myocardial infarction had a benign clinical course with an in-hospital mortality of 6.7% 4.

Risk of Complete Heart Block and Sudden Cardiac Death

• The risk of CHB and SCD in patients with a combination of background RBBB/FD-AVB with alternating LAHB/LPHB is significant, with one study finding a 22.7% incidence of CHB and 15.9% incidence of SCD over a mean follow-up period of 1581 days 2.
• Another study found that baseline RBBB and first-degree AVB were independent predictors of 30-day permanent pacemaker implantation after transcatheter aortic valve replacement 5.
• A study published in 2021 found that RBBB in the setting of anterior wall ST-segment elevation myocardial infarction was associated with a higher risk of in-hospital mortality, acute heart failure, complete heart block, and permanent pacemaker implantation 6.

Pacemaker Implantation

• Pacemaker implantation may be beneficial for patients with a combination of background RBBB/FD-AVB with alternating LAHB/LPHB, particularly those with severe symptoms 3.
• A study published in 1985 suggested that prophylactic pacemaker implantation should be considered in patients with trifascicular block, including those with RBBB and left anterior or left posterior fascicle block, due to the high risk of CHB and SCD 2.
• However, not all patients with this combination of conduction abnormalities require pacemaker implantation, and the decision to implant a pacemaker should be made on a case-by-case basis 4.