Mobitz Type II may not seem that bad when it doesnвЂ™t conduct one QRS complex through every few minutes, but what if it decides not to conduct through three QRS complexes in a row? Or 5? Or 10? Remember that with no QRS complex, you have no blood pressure! The loss of predictability makes Mobitz Type II a worse type of heart block than Wenckebach/Mobitz Type I. Many people have a first degree heart block without even knowing it and it generally does not cause any problemsвЂ¦

Every P wave should be conducted through the AV node to result in a narrow QRS complex meaning that if there is no follow through with a QRS complex at anyВ point, you have a blockage through the AV node and therefore an issue with your AV nodeДЇirst degree heart block is simple it is merely a prolonged PR interval of more than 0.2 seconds or one big ECG box! Every P wave conducts through the AV node and results in a QRS complex, there is just a bit of a longer delay betweenВ the two than normal.

Therefore, a normal PR interval should always be less or equal to than 1 big ECG box!

As people donвЂ™t remember numbers as well as they remember patterns, I always remind people that 1 little ECG box is 0.04 seconds which means that the 5 little boxes that make up 1 big ECG box is 0.2 seconds.

The PR interval is normally 0.12 вЂ“ 0.2 seconds meaning that if the PR interval is longer than this, you have a delay through the AV node and therefore an issue with your AV node.

There are two important things to remember regarding this:

If there is an issue with your AV node, you have some type of heart block. It could range from merely causing some delayed traffic through the boom gate (first degree), to someВ trafficВ getting through and some traffic getting blocked (second degree), or no traffic getting through at all (third degree). The severity of this road block determines the degree of the heart block. The same applies for the AV node not allowing the electrical impulse to pass through normally. When working normally, it will allow each car to pass through from point A to point VвЂ¦pun intended! However, an issue with the boom gate will result in a road block. Think of the AV node like a boom gate in the middle of a road that controls traffic. This is observed by the QRS complex on an ECG. The electrical impulse then travels down the bundle of His, left and right bundle branches and to the Purkinje fibres where it causes ventricular contraction. This is observed by the PR interval on an ECG. The electrical conduction travels to the AV node where it is slowed down momentarily to allow time for the blood from the contracted atria to enter the ventricles, prior to ventricular contraction. In a normal functioning conduction system, the SA node firing off causes atrial contraction and results in the P wave on an ECG.

This entire system works on the principle of hierarchy meaning that there is a clear nurse unit manager (SA node) that runs the show for the majority of the time, an associate nurse unit manager (AV node) that will take over running the show when the nurse unit manager goes on annual leave, and the clinical staff (Purkinje fibres) that do not want to run the show but will try their best if they absolutely have to! In AV heart blocks, the NUM is present and the clinical staff are willing to work вЂ“ however, the ANUM who is important for communicating information from management to the clinical floor is missing in action. The cardiac conduction system in its simplest form consists of the sinoatrial (SA) node, atrioventricular (AV) node, Bundle of His, left and right bundle branches and Purkinje fibres.

Heart blocks