What Is Heart Block?

Cardiac conduction block means that impulse conduction can slow down or block in any part of the heart's conduction system. If it occurs between the sinoatrial node and the atrium, it is called sinoatrial block. Between the atrium and ventricle, the atrioventricular block is called. Located in the atrium, called intraatrial block. Located in the ventricle, it is called indoor block.

Basic Information

English name

heart block

Visiting department

Cardiology

Common causes

Acute myocardial infarction, coronary artery spasm, viral myocarditis, endocarditis, cardiomyopathy, acute rheumatic fever, etc.

Common symptoms

Fatigue, fatigue, dizziness, syncope, angina pectoris, heart failure, etc.

According to the severity of conduction block, it can usually be divided into three degrees. The conduction time of the first conduction block is extended, and all impulses can still be conducted. Second-degree conduction block is divided into two types: Mobitz type I and type II. Type I block manifests as a progressive increase in conduction time until an impulse fails to conduct; type II blocks present as intermittent blocks. The third degree is also called complete conduction block, at which time all impulses cannot be conducted.

Causes of cardiac block

Atrioventricular block

Ventricular atrioventricular block (Mohs type I) can occur in normal people or athletes, which is related to increased vagal tone, which often occurs at night. Other pathologies leading to atrioventricular block include: acute myocardial infarction, coronary spasm, viral myocarditis, endocarditis, cardiomyopathy, acute rheumatic fever, calcified aortic valve stenosis, cardiac tumors (especially pericardial mesothelioma) ), Congenital cardiovascular disease, essential hypertension, cardiac surgery, electrolyte disorders, drug poisoning, Lyme disease (spiron infection, can cause myocarditis), Chagas disease (protozoan infection, can cause myocarditis), myxedema and so on. LeV disease (calcification and sclerosis of the heart fiber scaffold) and Leneg'e disease (primary sclerotic degenerative disease of the conduction system itself) are probably the most common causes of isolated chronic cardiac block in adults.

2. Indoor conduction block

Right bundle branch block is more common and often occurs in rheumatic heart disease, hypertension heart disease, coronary heart disease, cardiomyopathy and congenital cardiovascular disease. It can also be seen after large-scale pulmonary infarction and acute myocardial infarction. In addition, normal people can also have right bundle branch block.

Left bundle branch block often occurs in congestive heart failure, acute myocardial infarction, acute infection, quinidine and procainamide poisoning, hypertension heart disease, rheumatic heart disease, coronary heart disease, and syphilitic heart disease. Left anterior branch block is more common, and left posterior branch block is less common.

Cardiac block classification

Divided into: atrioventricular block, indoor block.

Atrioventricular block

Atrioventricular block, also known as atrioventricular block, refers to the delayed or inability of the atrial impulse to conduct to the ventricle after the atrioventricular junction zone is out of the physiological refractory period. Atrioventricular block can occur in different parts of the atrioventricular node, the His bundle, and the bundle branch.

2. Indoor conduction block

Indoor conduction block, also called indoor block, refers to the conduction block below the bifurcation of the His bundle. The indoor conduction system consists of three parts: the right bundle branch, the left anterior branch, and the left posterior branch. The lesions of the indoor conduction system can spread to one branch, two branches, or three branches.

Clinical manifestations of cardiac block

Atrioventricular block

Patients with first-degree atrioventricular block are usually asymptomatic. Second-degree atrioventricular block may cause arrhythmia, may have palpitations, and may be asymptomatic. Symptoms of third-degree atrioventricular block depend on the rate of ventricular rate and accompanying lesions. Symptoms include fatigue, fatigue, dizziness, syncope, angina pectoris, and heart failure. If combined with ventricular arrhythmias, patients may feel palpitations and discomfort. When the first or second degree AV block suddenly progresses to complete AV block, cerebral ischemia due to slow ventricular rate, the patient may experience temporary loss of consciousness, or even convulsions, known as Adams-Strokes syndrome, severe Can cause sudden death.

2. Indoor conduction block

Single and double branch blocks are usually asymptomatic. The clinical manifestations of complete triblock are the same as those of complete atrioventricular block.

Cardiac block test

Atrioventricular block

(1) At the time of auscultation, the first heart sound was weakened due to prolonged PR intermission. The intensity of the first heart sound of the second-degree type I atrioventricular block gradually weakened and there was a heart attack. Second-degree atrioventricular block also has intermittent arrhythmia, but the first heart sound intensity is constant. The first heart sound intensity of third-degree atrioventricular block often changes. The second heart sound may be normal or abnormally divided. Occasionally I heard a loud, hyperactive first heart sound. When atrial and ventricular contractions occur at the same time, a huge a wave (cannon wave) appears in the jugular vein.

(2) ECG performance

1) Once atrial block, every atrial impulse can be transmitted to the ventricle, but the PR interval exceeds 0.20 seconds. Slow conduction in any part of the atrioventricular conduction beam can lead to prolonged PR interval. For example, the QRS complex is normal in shape and time limit, almost all of the atrioventricular conduction delays are in the atrioventricular node, and very few are in the His bundle. (Or) Heath bundle-Pulkenyer system. Heath beam recordings can assist in identifying the location. If conduction delay occurs in the atrioventricular node, the AH interval is prolonged; in the His bundle-Pulkenyer system, the HV interval is prolonged. Conduction delay may also occur in two places at the same time. Occasionally, the delay of intra-conduction conduction can also lead to prolonged PR interval.

2) Second-degree atrioventricular block is usually divided into type I and type II. Type I is also known as Venturi block. Second-degree atrioventricular block This is the most common type of second-degree atrioventricular block. It is manifested as: a. The PR interval is prolonged until a P wave is blocked and it cannot pass down the ventricle. b. Adjacent RR intervals are progressively shortened until a P wave cannot pass down the ventricle. c. The RR interval including the blocked P wave is less than twice the normal sinus PP interval. The most common atrioventricular conduction ratios are 3: 2 and 5: 4. In most cases, the block is located in the atrioventricular node, the QRS complex is normal, and very few can be located in the lower part of the His bundle. Second-degree atrioventricular block rarely develops into third-degree atrioventricular block. Second-degree atrioventricular block Atrial impulse block suddenly, but the PR interval is constant. Most of the down-beat pulsatile PR intervals are normal. When the QRS complex is widened and the morphology is abnormal, the block is located in the His bundle-Pukenier system. If the QRS complex is normal, the block may be located in the AV node. 2: 1 atrioventricular block may be type I or type II. Normal QRS complexes may be type I; if 3: 2 block is recorded at the same time, the second cardiac cycle: PR interval prolongation can be diagnosed as type I block. When the QRS complex shows a bundle branch block pattern, an electrophysiological examination is needed to determine the block site.

3) Third degree (complete) atrioventricular block

At this time, no atrial impulse can be transmitted to the ventricle. Its characteristics are: atrial and ventricular activity are independent and independent of each other; atrial rate is faster than ventricular rate, atrial impulses come from the sinoatrial node or ectopic atrial rhythm (atrial tachycardia, flutter or fibrillation); The pacing point is usually slightly below the block. If it is located in the His bundle and its neighbors, the ventricular rate is about 40-60 beats / min, the QRS complex is normal, and the rhythm is stable. If it is located at the distal end of the indoor conduction system, the ventricular rate can be as low as 40 beats / min or less. QRS The wave group widens and the ventricular rhythm is often unstable. If the electrocardiographic examination can record the Heath beam wave, it will help determine the block site. If the block occurs in the atrioventricular node, there is no Hip bundle wave after the atrial wave, but there is a Hip bundle wave in each ventricular wavefront. If the block is located at the far end of the His bundle, each atrial wave has a His bundle after the atrial wave and no ventricular wave before the His bundle.

2. Indoor conduction block

It is divided into complete and incomplete bundle branch block according to whether the QRS time limit is extended for 0.12 seconds. According to the block site, it is divided into left bundle branch block and right bundle branch block. Bundle branch block can be permanent or intermittent. The ECG performance: right bundle branch block. When the right bundle branch is blocked, the excitability is transmitted through the left bundle branch. The initial vector of ventricular excitation is normal, and the second half of the QRS complex is changed. When the left anterior branch is blocked, the excitement is transmitted down the left posterior branch. It shows that the QRS complex has a longer time limit, but has no typical changes in left and right bundle branch block.

Heart block treatment

Atrioventricular block

Should be treated for different causes. Ventricular rates of first-degree atrioventricular block and second-degree type I atrioventricular block are not too slow, and no special treatment is required. Second-degree type II and third-degree atrioventricular block, such as significantly slow ventricular rate, accompanied by obvious symptoms or hemodynamic disorders, and even authors of Adams-Strokes syndrome should be given pacing therapy.

Atropine (0.5-2.0mg, intravenous injection) can increase the heart rate of atrioventricular block, and is suitable for patients with atrioventricular node block. Isoproterenol is suitable for atrioventricular block in any part, but it should be used with caution in acute myocardial infarction, as it may cause severe ventricular arrhythmias. The above drugs are used for more than several days, often with poor results and prone to serious adverse reactions, and are only suitable for emergency situations without cardiac pacing conditions. Therefore, for those with obvious symptoms and slow ventricular rate, temporary or permanent cardiac pacing should be given early.

2. Indoor conduction block

The main treatment is the treatment of the cause, and avoid using drugs that may worsen the conduction block. When the block seriously affects the atrioventricular conduction function, the deterioration of cardiac function or corresponding clinical symptoms can be treated with artificial pacemakers.