Conduction block

Introduction A heart block is called when a part of the heart is unable to conduct normally. The mechanism of cardiac blockade is the pathological extension of the absolute refractory period or relative refractory period of the myocardium, or both. The refractory period of pathological prolongation is affected by many factors, mainly in the heart itself. If there is a clear cause, the cause should be actively treated. Such as digitalis overdose, acute myocardial infarction, viral myocarditis infection, and poisoning. The cause of acute atrioventricular block is often acute inferior myocardial infarction, acute myocarditis, or other extracardiac factors such as drugs affecting electrolyte imbalance.

Cause

A certain part of the heart is not able to conduct normally. The mechanism of cardiac blockade is the pathological extension of the absolute refractory period or relative refractory period of the myocardium, or both. The refractory period of pathological prolongation is affected by many factors, mainly in the heart itself. The refractory period of the myocardium changes with changes in the cardiac cycle. When the cardiac cycle is shortened, the refractory period is shortened accordingly, and the cardiac cycle is prolonged. In the extracardiac factors, it mainly refers to the two major factors of nerve and body fluid. When the sympathetic nerve is excited, the refractory period should be shortened.

an examination

Related inspection

Electrocardiogram cardiac vascular ultrasound

Cardiac block can be divided into three degrees according to the degree of block: one-time block, second block, and third block. The first and second degree conduction block is called incomplete conduction block. At one point, only the conduction time is prolonged, but the activation can pass through the block, and the individual agonism is blocked, so that the activation cannot pass through the block at the second degree, and more than two consecutive stimuli are blocked, called high conduction. Blocking, if only a few excitations pass through the block, is called almost complete block. If all the excitement can not be transmitted, it is called third-degree block, also known as complete block.

Differential diagnosis

Cardiac block needs to be identified as follows:

(1) right bundle branch block, the excitability of the atrioventricular bundle can not be transmitted to the right bundle branch, only from the left bundle branch, still first stimulate the middle third of the ventricular septum, in the left ventricle When the wall depolarization is completed, the excitement is transmitted to the right ventricle through the interventricular septum.

(2) left bundle branch block, refers to the conduction from the atrioventricular bundle can not be transmitted to the left bundle branch, only along the right bundle branch, and then slowly through the ventricular septum to stimulate the left ventricular septum and left ventricle, so that the interval The excitement is opposite to the normal direction.

(3) Left anterior branch conduction block means that the left anterior branch cannot be transmitted to the left anterior branch when it is excited into the left bundle branch, and only descends along the left posterior branch. Then, on the one hand, the right ventricle, on the other hand, the left ventricle lower wall and the apex are excited at the same time.

(4) Left posterior branch conduction block refers to the conduction delay of the posterior branch of the left bundle branch. The agitation first goes from the left anterior branch to depolarize the anterior wall of the left ventricle, and then passes through the Pujinye fiber anastomosis branch to the lower left. The posterior branch area depolarizes the inferior wall of the left ventricle.

(5) Interstitial conduction block, also known as forward conduction delay. When the ventricle is excited, the left front branch is excited by the depolarization direction, pointing to the left front upper side and the left rear branch opposite. The initial vector of the chamber interval activation is determined by the depolarization vector of the interval to the right front and bottom. After blocking the spacer, the initial vector points to the left front. Later impulses are transmitted through the anastomosis or myocardium to the distribution of the septum, and the middle of the interventricular septum and the anterior wall of the left ventricle are depolarized.

(6) Bilateral bundle branch block refers to the indoor conduction block caused by the conduction of the left and right bundle branches.

(7) Three-segment conduction block means that the right bundle branch, the left front and the left posterior branch all have conduction disorders.

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