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Left bundle branch block is a condition in which the impulse cannot be transmitted to the left atrioventricular bundle, so the impulse will go to the right atrioventricular bundle to depolarize the right ventricle first, then conduction to the left to depolarize the left ventricle.
1. Recognizing signs of left bundle branch block
bundle branch block is a noun to refer to the electrocardiogram image when there are disturbances of impulse conduction in one branch of the bundle of His, also known as intraventricular conduction disturbances.
Observed on the electrocardiogram, we will see left bundle branch block with the following signs:
Wide QRS duration: >= 0.12 seconds QRS has the form: rS in V1, V2 R monophasic may be notched in V5, V6 . ST segment depression and negative T in V5, V6, Dl, aVL
2. Mechanism of formation of left bundle branch block
Hình ảnh block nhánh trái
Because the impulse goes around the right atrioventricular bundle and then conduction to the left atrioventricular bundle (due to left bundle branch block) leads to wide QRS on the electrocardiogram.
Depolarization procedure in left bundle branch block:
Impulse conduction down to the atrioventricular bundle but blocked (due to block) will cause the impulse to generate a right depolarization vector (towards V1, V2 produces small R waves) ) After the right ventricular depolarization is complete, the impulses pass to the left, forming a second vector that is more directed to the left (lateral wall and basal) depolarizes to the left (towards V5, V6 forming a positive R wave) , an increase in voltage occurs. Repolarization process in left bundle branch block:
Right side repolarizes anteriorly, left side repolarizes posteriorly. The left repolarization potential is higher than the right. The vector repolarizes from left to right. ST-T depression in the left leads. ST-T elevation in the right leads.
3. Causes of left bundle branch block
Left (or right) bundle branch block can be caused by that branch being severed, degenerated or damaged, the impulse from the atria descending will have to go into the other side and conduct depolarization of that side first before switching to ventricular depolarization is posteriorly blocked.
Possible causes of left bundle branch block include:
Aortic stenosis . Ischemic heart disease. End-stage heart failure (left ventricular enlargement causing 2 ventricular out-of-sync) Hypertension . Dilated cardiomyopathy.
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Myocardial infarction (LAD branch occlusion) anterior MI. Primary degenerative disease of the conduction system (Lenegre disease). Hyperkalemia. Digoxin toxicity.
4. Criteria for diagnosis of left bundle branch block
Criteria for left bundle branch block include the procedure that the doctor will examine and determine whether the patient has symptoms of acute myocardial infarction, left heart failure or myocardial ischemia.
Assess the possibility of acute myocardial infarction based on:
Recent chest pain Sgarbossa criteria to determine new or long-standing left bundle branch block. Heart enzyme test. Assess the possibility of left heart failure based on:
Fatigue, shortness of breath (if any). Clinical examination revealed signs of an enlarged heart. Signs of arrhythmia. Results of a straight chest X-ray, echocardiography to look for abnormalities in the heart. Assess the possibility of myocardial ischemia based on:
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