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Insights
Left bundle branch hemiblocks occur when one division of the left bundle branch is blocked, impacting impulse travel to the left ventricle. Diagnosis involves specific ECG criteria for left anterior or posterior hemiblock, often associated with heart disease.
Area of Science:
- Cardiology
- Electrophysiology
- Diagnostic Electrocardiography
Background:
- The left bundle branch divides into anterior and posterior divisions, crucial for left ventricular impulse conduction.
- Blockage in one of these divisions results in a hemiblock, altering cardiac electrical activity.
Purpose of the Study:
- To define the diagnostic criteria for left anterior hemiblock (LAH) and left posterior hemiblock (LPH).
- To discuss the clinical associations and prevalence of hemiblocks.
Main Methods:
- Analysis of electrocardiographic (ECG) findings, including axis deviation and QRS intervals.
- Review of clinical data to identify associated cardiovascular conditions.
Main Results:
- LAH criteria include marked left axis deviation, specific QRS morphology in leads I and III, and minimal QRS prolongation.
- LPH criteria include marked right axis deviation, different QRS morphology in leads I and III, and minimal QRS prolongation.
- Hemiblocks are uncommon in healthy individuals and frequently coexist with other conduction abnormalities like right bundle-branch block.
Conclusions:
- Hemiblocks are significant indicators of underlying heart disease, particularly coronary or hypertensive disease.
- Accurate ECG interpretation is vital for diagnosing hemiblocks and assessing cardiac health.
Abstract:
The left bundle branch separates into the left anterior and the left posterior divisions. The impulse travels to the left ventricle via both divisions when they are intact. When one division is blocked, the diagnosis is hemiblock. Diagnostic criteria for left anterior hemiblock are marked left axis deviation, small Q wave in lead I and small R wave in lead III, little or no prolongation of the QRS interval, and no evidence of other causes of left axis deviation. Criteria for left posterior hemiblock are marked right axis deviation, small R wave in lead I and small Q wave in lead III, little or no prolongation of the QRS interval, and no evidence of other causes of right axis deviation. A pure form of hemiblock is not uncommon, especially during acute anterior myocardial infarction, but right bundle-branch block often coexists with hemiblock. Like left bundle-branch block, hemiblocks rarely occur in healthy persons. They are commonly associated with coronary or hypertensive disease or both and are less commonly associated with cardiomyopathies and calcified aortic disease.
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