left anterior fascicular block
Introduction
Introduction to left anterior branch conduction block The left anterior branch block (LAH) is also called the left anterior block. The left anterior branch is a relatively slender branch of the left bundle branch, which is superficial at the position of the interventricular septum and is prone to ischemic injury. The left anterior branch is a relatively slender branch of the left bundle branch. It is superficial at the location of the ventricular septum and is prone to ischemic injury, most commonly in coronary heart disease, accounting for about 75%. basic knowledge The proportion of illness: 0.003% Susceptible people: no specific population Mode of infection: non-infectious Complications: syncope A-S syndrome
Cause
Left anterior branch block
Ischemic injury (50%):
Left anterior branch conduction block The left anterior branch is a relatively slender branch of the left bundle branch. It is superficial in the ventricular septum and is prone to ischemic injury. It is most common in coronary heart disease, accounting for about 75%. In a group of 353 patients, there are In the autopsy materials with significant left-axis deviation, 85% of the patients were found to have coronary heart disease. Some people think that in the middle-aged and elderly people over 50 years old, if there is a left anterior branch block, the possibility of coronary heart disease should be considered, and should be traced. Within 2 years, there is an indication for the diagnosis of coronary heart disease.
It is also the most common single-branched block in acute myocardial infarction, mostly occurring in the anterior or anterior wall myocardial infarction. The incidence of infarction in the anterior wall is 24.2%, and the inferior wall infarction is 16.5%. In addition to injury, it may be a functional block around the infarction or a delay in the conduction of the ventricular wall at the distal end of the junction between the Purkinje fiber and the myocardium, or a longitudinal separation of the His bundle, causing an abnormal pattern of wall activation and non-anatomical lesions. The left front branch is blocked.
In addition, part of the left anterior branch is the blood supply to the atrioventricular node from the right coronary artery or the left coronary artery circumflex artery, so the left anterior branch block is not necessarily a sign of occlusion of the anterior descending coronary artery or extensive infarction.
Organic heart disease (30%):
Also seen in hypertension, cardiomyopathy, myocarditis, aortic valve disease (aortic stenosis, etc.), congenital heart disease, rheumatic heart disease, myocardial amyloidosis, cardiac surgery, scleroderma, hyperthyroidism , carbon monoxide poisoning, hyperkalemia or hypokalemia, high dose of lidocaine, etc., it is reported that the left anterior branch block in the population over 35 years old increases with age, 66% to 78% of patients with left anterior branch Organic heart disease; 86% of men with left anterior branch block under 35 years of age have no heart disease.
Pathogenesis:
The left anterior branch is a relatively slender branch of the left bundle branch. It is superficial at the location of the ventricular septum and is prone to ischemic injury. In acute infarction, functional blockage around the infarct or distal to the junction of Purkinje fiber and myocardium Delayed conduction in the ventricular wall, or longitudinal separation of the His bundle, causing an abnormal pattern of wall activation, resulting in a left anterior branch block of non-anatomical lesions. In addition, some of the left anterior branch is receiving either the right coronary artery or the left coronary artery. The blood supply to the atrioventricular node of the circumflex branch, so the left anterior branch block is not necessarily a sign of a blockage of the anterior descending coronary artery or a wide range of infarct lesions.
Prevention
Left anterior branch block prevention
1. Active treatment of the cause, such as treatment of coronary artery disease, hypertension, pulmonary heart disease, myocarditis, etc., can prevent the occurrence and development of indoor block.
2. Appropriate work and rest, diet, holidays, and appropriate physical exercise. In addition to promoting blood circulation, lowering the production of cholesterol, and enhancing the formation of muscle, bone and joint stiffness, exercise can increase appetite, promote gastrointestinal motility, prevent constipation, improve sleep, and have the habit of continuous exercise: it is best to do It will help if you have aerobic exercise. Aerobic exercise can lower blood pressure like weight loss, such as walking, jogging, Tai Chi, cycling and swimming.
Complication
Left anterior branch block complication Complications syncope A-S syndrome
Simple left anterior branch block often has no serious complications. For example, syncope, convulsions, and A-S syndrome can occur when combined with double or triple block.
Symptom
Left anterior branch block symptoms Common symptoms Chest pain with chest tightness, palpitations block palpitations
The left anterior branch block male and female incidence ratio is about 4:1, male is more common, the age of onset is 15 to 88 years old, the average age of onset of male is 61.41 years old, and the female is 59.83 years old. There is no obvious clinical manifestation of left anterior branch block itself. Symptoms and signs, if any, are mostly the symptoms and signs of the primary disease.
Examine
Left front branch block
ECG features:
1. The QRS axis is skewed from -45° to -90°.
2. The IavL lead is qR type, but the q wave does not exceed 0.02s, the R wave is higher, RaVL>RI, aVR usually I lead without S wave II, III, aVF lead is rS type, S wave is deep, SIII>SII.
3. The QRS time is normal or slightly extended, mostly in the range of 0.10 to 0.11 s.
4. The chamber wall activation time (R peak time) of the aVL lead is 45 ms.
5. There was no significant change in the QRS complex of the chest lead.
Basically meet the above criteria, but the left axis of the electric axis is only -30 ° ~ -44 °, the diagnosis is probably left anterior branch block or incomplete left anterior branch block.
Diagnosis
Diagnosis of left anterior branch conduction block
1. Identification of myocardial infarction with anterior wall and anterior wall
Because the left anterior branch is blocked, the q-wave can appear in the right chest lead (V1, V2 lead) or even in the middle of the chest lead (V3, V4 lead), so it is easy to be confused with the anterior wall and anterior wall myocardial infarction. The difference between the two is: 1 the next intercostal mapping of the electrocardiogram V1, V2 lead such as q wave disappears, it is prompted by the left anterior branch block; 2 if ST-T dynamic changes suggest acute myocardial infarction; 3 original stale When the left anterior branch block occurs in the anterior myocardial infarction, the original QS pattern of the right chest V1V2 lead can be converted into the rS pattern. The left anterior branch block of this system masks the myocardial infarction of the anterior wall.
2. Identification of inferior myocardial infarction
When the left anterior branch blocks the II, III, and aVF leads, the r wave is small, and it is easy to be mistaken for QS type, which is misdiagnosed as inferior myocardial infarction. The difference between the two is: 1 When the ECG three-lead simultaneous recording, if RII appears before RIII, RaVL appears to be left anterior branch block before RaVR; if it is opposite, it suggests lower wall myocardial infarction; 2 ECG vector The frontal QRS ring is transposed in the opposite direction, suggesting that the left anterior branch is blocked; if it is in the clockwise direction, it is suggestive of inferior myocardial infarction.
3. Identification of myocardial infarction with lateral wall
When the left anterior branch is blocked, the I and aVL leads can exhibit q waves but the q wave is <40ms; while in the high wall myocardial infarction, the q waves of I and aVL leads 40ms4. Pseudogenicity in patients with emphysema and pulmonary heart disease Distortion of the left axis of the electric axis to identify emphysema, pulmonary heart disease can call the left axis, with low voltage SII> SIIIII, III, aVF lead P wave high tip, I lead no S wave, these characteristics can rule out left anterior branch block . The mechanism of emphysema and pulmonary heart disease leading to left-axis deviation of the electric axis is: 1 extreme electric axis is caused by right deviation; 2 pulmonary emphysema has weakened electrical conductivity of the lung tissue, and right lung tissue is more obvious than left lung tissue. The right thoracic conduction is weaker than to the left thorax, and the electric field around the heart is deformed, causing the QRS axis to be left-biased.
