00:00 Definition
00:15 Normal sinus node physiology
01:37 First degree sinoatrial block
02:48 Second degree sinoatrial block type I. Wenckebach conduction.
04:43 ECG criteria of second degree sinoatrial block type I explanation
05:46 Real ECG example of second degree sinoatrial block type I
06:47 Second degree sinoatrial block type II explanation
08:00 ECG criteria of Second degree sinoatrial block type II
08:51 Heal ECG example of Second degree sinoatrial block type II
09:53 Second degree sinoatrial block type II 2:1 vs severe sinus bradycardia
10:45 Third degree sinoatrial block explanation
11:31 Third degree sinoatrial block explanation vs sinus arrest

New video about pathophysiology of sinoatrial exit block.

Sinoatrial exit block occurs as a result of disorder with the delivery of impulses from the sinus node to atria tissue.
The first degree of sinoatrial block is characterized by a prolongation of the sinoatrial conduction time through the T cells without dropping of PQRST.
When the impulse from sinus node reaches the atria tissue on ECG we see it as P wave, but depolarization of sinus node it self can’t be detected by routine ECG examination due to very low amplitude of Sinus node depolarization.
As a result first degree sinoatrial block also can’t be detected by routine ECG.

The second-degree exit block is represented by droping of PQRST also is further classified into type one and type II just like AV block classification.
Second degree of sinoatrial block type one is characterized by wenckebach conduction.

Unlike second degree block type one in type two there are no progressive lengthening of sinoatrial conduction time.
In the Type two SA block we have rapid drop of P-QRS-T complexes without any problem with sinoatrial conduction before the drop and after the drop.

Also we can characterize severity of exit block type two by comparing number of expected sinus impulses and conducted sinus impulses that is indicated as Pwave)

Important to say that Permanent second degree sinoatrial exit block type two with conduction 2 to one can imitate severe sinus bradycardia.

In case of severe sinus bradycardia Pq interval is near to the upper limit but in case of permanent sinoatrial block with conduction two to one Pq interval is relatively shorter.

Third degree SA exit block is characterized by absence of conduction between sinus node and atria tissue.
During the sinus pause latent pacemakers are activated and start to pace the heart.

As a result in case of third degree SA block the sinus pause isn’t equal to multiple distance of previous P-P interval.

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