Management of Left Posterior Fascicular Block (LPFB)
LPFB itself requires no specific treatment in asymptomatic patients, but mandates evaluation for underlying structural heart disease and monitoring for progression to higher-grade conduction abnormalities. 1
Initial Diagnostic Evaluation
When LPFB is detected on ECG, the following workup is essential:
Transthoracic echocardiography is recommended to exclude structural heart disease (cardiomyopathies and conduction tissue disease are common causes). 1
In symptomatic patients where atrioventricular block is suspected, ambulatory ECG monitoring is useful to detect progression to higher-grade blocks. 1
Consider that LPFB may indicate severe coronary artery disease, particularly when associated with inferior myocardial infarction—one study found 5.5% of inferior MI patients had LPFB, with 89% having three-vessel disease. 2
Management Based on Clinical Presentation
Asymptomatic LPFB Without Structural Heart Disease
No specific treatment is required—LPFB itself rarely causes symptoms. 1
Monitor for progression to more advanced conduction disorders, particularly if associated with other conduction abnormalities (increased risk of clinically significant AV block). 3
Permanent pacing is not indicated for isolated fascicular block, even with first-degree AV block, in the absence of symptoms. 3
LPFB with Symptomatic Fascicular Ventricular Tachycardia
When LPFB is associated with verapamil-sensitive idiopathic left ventricular tachycardia (left posterior fascicular VT):
First-line treatment:
Catheter ablation is recommended as first-line therapy in experienced centers, particularly for young patients who would otherwise require lifelong drug therapy. 4, 1
Acute success rates exceed 90% with recurrence rates of 0-20%. 4
The target is typically the distal insertion of the anterograde limb of the Purkinje system along the inferior LV septum near the left posterior fascicle junction. 4
Alternative medical management:
Beta-blockers, verapamil, or sodium channel blockers (class IC agents) are recommended when catheter ablation is not available, not desired, or has failed. 4, 1, 5
Intravenous verapamil is recommended for acute VT termination in hemodynamically stable patients. 4
Chronic oral verapamil can be useful for preventing recurrences, though it may not be effective long-term in all patients. 4
LPFB in Acute Myocardial Infarction
More vigilant monitoring is warranted due to potential progression to higher-grade AV block and association with more severe coronary disease. 3
Permanent pacing may be considered for persistent second-degree AV block in the His-Purkinje system with alternating bundle-branch block or third-degree AV block after ST-elevation MI. 3
Permanent pacing is recommended for persistent and symptomatic second- or third-degree AV block. 3
Common Pitfalls to Avoid
Do not diagnose LPFB in the presence of right ventricular hypertrophy (COPD/emphysema), extensive lateral MI, or extremely vertical heart—these conditions can mimic the ECG pattern. 6
In children, apply diagnostic criteria cautiously due to their normally more rightward axis until age 16; only diagnose when a distinct rightward axis change is documented. 1
Recognize that intermittent LPFB is never a complete block (transient or second-degree LPFB), and even permanent forms may not be complete. 6
When LPFB is associated with right bundle branch block and acute inferior MI, PR interval prolongation is very frequent—monitor closely for progression. 6