From the Guidelines
Initial investigations for a patient with left posterior fascicular block (LPFB) should include a 12-lead ECG to confirm the diagnosis, laboratory tests such as cardiac enzymes, electrolytes, and renal function tests, and echocardiography to assess cardiac structure and function. The diagnosis of LPFB is based on specific ECG criteria, including a QRS duration <120 ms, frontal plane axis between 90 and 180 in adults, and specific patterns in leads I, aVL, III, and aVF 1. A comprehensive cardiac evaluation is necessary to identify underlying causes, as LPFB is rarely an isolated finding.
Some key points to consider in the initial investigation include:
- A detailed 12-lead ECG to confirm the diagnosis, looking for right axis deviation (typically +90° to +180°), small R waves in leads I and aVL, and prominent R waves in leads II, III, and aVF
- Laboratory tests, such as cardiac enzymes, electrolytes (particularly potassium, calcium, and magnesium), renal function tests, and complete blood count
- Echocardiography to assess cardiac structure and function, looking for cardiomyopathy, valvular disease, or evidence of ischemia
- Consideration of stress testing or coronary angiography if coronary artery disease is suspected
Management of LPFB focuses on treating the underlying cause rather than the conduction abnormality itself, and may include standard therapies such as antiplatelet agents, statins, beta-blockers, and possibly revascularization for cardiac ischemia, or heart failure medications such as ACE inhibitors, beta-blockers, and diuretics for cardiomyopathy 1. Regular follow-up with serial ECGs is important to monitor for progression to more complete heart block.
From the Research
Initial Investigations for Left Posterior Fascicular Block
The initial investigations for a patient with a left posterior fascicular block (LPFB) include:
- Electrocardiogram (ECG) to confirm the diagnosis of LPFB, as it is characterized by a specific pattern on the ECG 2, 3
- Vectorcardiography (VCG) to assess the QRS loop and confirm the diagnosis of LPFB 2
- Echocardiogram to rule out any structural heart disease, such as right ventricular hypertrophy (RVH) or extensive lateral myocardial infarction (MI) 2
- Treadmill test or stress echocardiogram to evaluate for coronary artery disease, as LPFB is often associated with inferior myocardial infarction (IMI) and severe coronary artery disease 3, 4
- Coronary angiography to assess for critical stenosis in the coronary arteries, particularly in patients with exercise-induced LPFB 4
Management of Left Posterior Fascicular Block
The management of LPFB depends on the underlying cause and associated conditions:
- In patients with LPFB and suspected coronary artery disease, invasive investigation and coronary angiography may be necessary to assess the extent of disease 3
- In patients with exercise-induced LPFB, a dobutamine stress echocardiogram or coronary angiography may be performed to evaluate for coronary artery disease 4
- In patients with LPFB and associated conditions such as right bundle branch block (RBBB) or acute inferior MI, close monitoring and management of the underlying condition is necessary 2