Atrial conduction block

Introduction Intraventricular conduction block refers to impulsive interstitial bundles or room bundle block in the atria. Can be divided into incomplete atrial block and complete atrial block and sinus block: Incomplete atrial block is due to the ectopic activation of the impulse in the atria, which invades the sinus node during the depolarization process, so that the activation cannot be transmitted or delayed. Complete atrial conduction block refers to the atrium being stimulated by two pacemakers in the room without mutual inhibition. The sinus agitates part of the atrium and can be transmitted to the ventricle. The remaining atrial part is covered by an ectopic atrial pacemaker. Excited, but not transmitted to the ventricles.

Cause

1. Common causes of incomplete atrial block

(1) The cause of incomplete atrial block: the fibrosis of the atrial muscle. Fatty. Degeneration of amyloidosis. Hypertrophy and/or dilatation of the left atrium and/or right atrium. Acute or chronic inflammation of the atrial muscle. The atrial muscles are urgent. Chronic ischemia or atrial infarction can lead to atrial block. Incomplete atrial block is mostly seen in organic heart disease. For example, rheumatic heart disease mitral stenosis. High blood pressure. Heart failure. Coronary heart disease. Myocardial infarction. Myocarditis. Some congenital heart disease (such as atrial septal defect, etc.). cardiac disease. Chronic pericarditis. Hyperkalemia. Increased vagal tone. Digitalis and quinidine effects can lead to incomplete atrial block. Incomplete atrial blockade is not just a block of conduction between the bundle of cells or the internode. In fact, it is often left atrial hypertrophy. Left atrial volume and persistent or temporary pressure increase in the left atrium. Or signs of increased left ventricular end-diastolic pressure.

(2) Causes of intermittent incomplete atrial block: Intermittent intraventricular block can be seen in all age groups. It is 7 to 97 years old. There are many cases of organic heart disease reported in China. Such as coronary heart disease. cardiac disease. Hypertensive heart disease. Rheumatic heart disease. Chronic obstructive pulmonary disease. Constrictive pericarditis. Sick sinus syndrome and so on. Intraventricular conduction disorders in the elderly may be associated with degeneration of cardiac conduction tissue. About 36% of those with intermittent intraventricular blockage reported abroad have structural heart disease. Some cases are observed for several months. After several years, it changes from intermittent to fixed (persistent) intraventricular block. The occurrence of intermittent intraventricular blockade suggests atrial lesions.

2. The common cause of complete atrial block (atrial dislocation. Atrial separation) is common in the late stage of rheumatic heart disease. Critically ill patients with coronary heart disease. Digitalis poisoning. Uremic disease. Quinidine poisoning, etc., part of the ECG performance before dying.

3. Common causes of sinus-ventricular conduction are more common in hyperkalemia.

4. The etiology of diffuse complete atrial block is more common in hyperkalemia.

an examination

Related inspection

ECG heart sound map check

Electrocardiogram

1. Electrocardiogram with incomplete atrial block

(1) ECG characteristics of incomplete incomplete atrial block:

1 determined as sinus rhythm.

2 There is a dynamic change in P wave morphology and/or polarity.

At the same time of the 3P wave change, the PR interval is generally unchanged. Due to the delayed conduction in the atrial, some patients may have a prolonged PR interval.

4 ECG typing:

A. Immobility incomplete left atrial block: also known as Bachmann beam block, due to room beam breakage, degeneration or fibrosis, ECG performance: P wave time widening >0.11s, its amplitude is not high; P wave can appear as notch, frustration, double peak, biphasic, if it is double peak, the peak distance of double peak is 0.04s, showing a fixed mitral valve P wave, which is related to left atrial hypertrophy and atrial overload. The P wave morphology is difficult to identify, and this diagnosis can only be made after echocardiography is used to exclude left atrial overload or left atrial hypertrophy.

B. Immobility incomplete right atrial block: delayed conduction in the right atrium, depolarization time extension, top-down depolarization vector increases, and overlap with the subsequent left atrial depolarization vector to make left and right atrial depolarization Synchronization in the same direction, ECG performance: P wave amplitude increases, II, III, aVF lead on the P wave high tip, at this time and the lung type P wave (right atrial depolarization increased) morphology is difficult to identify, should do echocardiography, Combined with clinical exclusion, the cause of pulmonary P wave and the expansion of right atrium can be diagnosed.

Incomplete atrial conduction block is divided into the following four types by recording the P-ring amplification and synchronizing the electrocardiogram.

Type 1A: P wave is dome-shaped, corresponding P ring is large and deformed; Type 2B: most common, showing double-peak P wave, P ring is bidirectional, the two parts of the ring are nearly equal in size, horizontal or left The shape is often "8" shape; 3C type: less common, P wave is high and sharp, P ring has different sizes of notch; 4D type: seen in elderly patients, P wave low level, P vector ring small and dense .

The most reliable diagnostic method for incomplete atrial block is atrial endometrial mapping. Incomplete atrial block is caused by inhomogeneous conduction and refractory period, which can cause atrial reentry tachycardia. Atrial flutter, atrial fibrillation and other atrial arrhythmias.

(2) ECG characteristics of intermittent incomplete atrial block: it can be divided into intermittent left atrial block or room block and intermittent right atrial block, both of which are incomplete Intraventricular conduction block, the incidence is significantly lower than the fixed (persistent) incomplete intraventricular block.

The electrocardiogram is a sudden change in the morphology of the sinus P wave when the sinus rhythm is uniform, and the shape of "pulmonary P wave" or "mitral valve P wave" appears.

The diagnosis of intermittent intraventricular block is only reliable based on the same sinus P wave change in the same lead, because there are many factors affecting and causing P wave morphology and frequency anomaly, but there are also different P-wave forms. The dynamic changes are reported for diagnosis.

2. ECG characteristics of complete atrial conduction block

(1) There are two kinds of P waves in the same lead: usually one is the dominant rhythm of sinus rhythm (sinus rhythm can be too slow, too fast, irregular and normal), can be transmitted, followed by QRS wave; the other is Atrial ectopic P? wave, its frequency can be fast or slow, regularity is poor, can not be transmitted, sinus P wave is completely unrelated to ectopic P? wave, but can overlap rather than fusion wave, occasionally dominate the heart rhythm for atrial or handover Regional rhythm.

(2) A part of the atrial wave is fluttering, and the other part is vibrating.

(3) The right atrial wave is sinus, and the left atrial wave is fluttering or vibrating.

3. Electrocardiographic features of diffuse complete atrial block

There is no sinus P wave, no ectopic atrial rhythm (no atrial P' wave, atrial flutter or atrial fibrillation wave), diffuse complete atrial block on the electrocardiogram and persistent sinus arrest, Third-degree sinus block, sinus-ventricular conduction, etc. cannot be identified.

4. Characteristics of sinus-ventricular conduction ECG

P wave disappears, QRS wave width is deformed, indoor block, ventricular or junctional escape rhythm, T wave high tip is called hyperkalemia T wave change, if blood potassium continuously increases, the QRS wave is wider and deformed, T The wave then becomes blunt, and continues to increase, eventually forming a very slow waveform similar to ventricular flutter or ventricular fibrillation.

Differential diagnosis

Clinically, it is necessary to identify physiological or pathological second degree atrioventricular block, and it must be combined with clinical examinations, etiology and clinical manifestations.

1, physiological atrioventricular block: Most people with normal atrioventricular conduction function, rapid atrial pacing can induce Venturi-type atrioventricular block. Atrial pacing graded pacing and paroxysmal atrial, atrial flutter, borderline tachycardia, because the atrial cycle is significantly shorter than the effective refractory period of the atrioventricular node, resulting in some supraventricular sexual excitement can not be transmitted to the ventricle And atrioventricular block. This is an interference phenomenon of physiological atrioventricular block.

2, pathological atrioventricular block:

(1) The influence of vagal tone and the effect of drugs can cause atrioventricular block. The movement or use of atropine can eliminate the influence of vagal tone, significantly improve the function of atrioventricular node, and the atrioventricular block disappears. Clinically, many drugs such as digitalis drugs, calcium antagonists, and central and peripheral sympathetic blockers can cause atrioventricular block.

(2) Atrioventricular block in acute myocardial infarction is more common than acute anterior myocardial infarction, and the mechanism of atrioventricular block is related to the increased ischemic and significant vagal tone. Inferior myocardial infarction with atrioventricular block often presents intermittent features, and the QRS morphology is normal and can disappear after a few days. Acute anterior wall myocardial infarction is associated with type II atrioventricular block, and the mechanism of its blockade is related to the extensive infarction range leading to conduction bundle branching. Dynamic electrocardiogram showed that type II atrioventricular block in anterior myocardial infarction was often accompanied by intermittent or persistent bundle branch block (left and right bundle branch or branch block pattern). This type of block is prone to develop complete atrioventricular block.

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