heart block types:

In this article i am going to discuss in detail about heart block types.If you visit this site you will get clear, simple and best answer on heart block types.Heart block types includes SA nodal block, AV nodal block , Bundle branch block .

What is heart block ?

Slowing down or blockage of cardiac impulse (generated from the SA node-the peacemaker of the heart ) along the cardiac conductive pathway is known as heart blocks.

Conduction blockage may occur as:

SA nodal block ,AV nodal block , Bundle branch block .

1. SA nodal block -Sinoatrial block:

SA nodal block is also known as SA block,this condition is charecterized by the blockage of impulse conduction from the Sinoatrial node to atria.

SA nodal block occurs in the elderly people and in paitents recovering from coronary artery occlusion.

Sinoatrial block may manifest as sick sinus syndrome.

SA nodal block occurs suddenly and initially the heart stops.

The atrioventricular node becomes the pacemaker(the part of the heart from which rhythmic impulses for heart beat are produced is known as pacemaker of the heart) of the heart after an interval of approximately two cardiac cycles.

As the atrioventricular node becomes the pacemaker of the heart,the heart starts functioning again(the heart starts beating with  decreased rate of 40 to 60/min). This is known as AV nodal rhythm.

AV nodal rhythm is also known as junctional rhythm. This rhythm is characterized by an inverted P wave and normal QRS complex.

The rate of the junctional rhythm is slower than the sinus rhythm.

2.AV (atrioventricular) nodal block :

In atrioventricular block impulses from the atria are not transmitted to the ventricles because of defective conductive system.

Atrioventricular block is of two categories incomplete heart block(which includes first degree and second degree heart block) and complete heart block (third degree heart block).

Heart block

a.First degree AV nodal block:

First degree AV nodal(or heart ) block is characterized by slowing of conduction at the level of AV node .

In the first degree AV nodal block though all the atrial impulses reach the ventricles but the PR interval is abnormally long(more than 0.21sec) but seldom increases more than 0.30sec.

In the trained athletes and also in the young adults,the first degree heart block is a common case.

First degree heart block is also caused by rheumatic fever and some drugs.

b.Second degree AV nodal block:

In the second degree AV nodal block some of the atrial impulses are not conducted to ventricles. second degree heart block is also known as partial heart block.

Second degree heart block is usually associated with organic heart diseases. Consequently, there may be one ventricular contraction after every 2,3 or 4 atrial contractions producing the so called 2:1,3:1,4:1 block . Others forms of second degree heart blocks are:

¡.Wenckebach phenomenon (Mobitz type 1 block ):

Wenckebach phenomenon or syndrome is a type of heart block which is characterized by a progressive lengthening of the PR interval in successive beats and finally a failure of one impulse to be transmitted.

¡¡. Periodic block (Mobitz type II ):

Mobitz type II heart block is characterized by an occasional failure of conduction that results in an atrial to ventricular rate ,for example 6:5 or 8:7. In the periodic heart block the PR interval is constant.

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c.Third degree AV nodal block :

In the third degree (complete) AV nodal block ,no impulse from atria can pass to the ventricles.

In third degree AV nodal block ventricles start beating at their own rhythm (about 40 beats/min),which is known as idioventricular rhythm.

The atria however continues to beat at the normal sinus rhythm of about 72 beats/min .

Because of these reason in the ECG it is seen that, between the P waves and QRS complexes ,a complete dissociation is present. This condition is known as atrioventricular dissociation.

The third degree heart block is serious condition because it decreases the pumping activity of the heart.

The third degree heart block occurs due to organic heart diseases,septal myocardial infarction,and damage to bundle of His during surgical repair of congenital interventricular septal defects.

3.Bundle branch block:

Bundle branch block refers to the heart block in which there is a blockage in one or more branches of the bundle of His.

In the bundle branch block , down the bundle on the intact side excitation passes normally and then sweeps back through the muscle to activate the ventricle on the blocked side.

In the bundle branch block ECG shows normal ventricular rate ,but the QRS complexes are prolonged (beyond 0.12s)  and deformed.

➡️Right bundle branch block:

Right bundle branch block may occur in otherwise healthy individuals or secondary to chronic pulmonary disease.

➡️Left bundle branch block:

 Left bundle branch block may occur in organic heart diseases.

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