13 Jun Atrio-ventricular nodal (AVN) blocks for exercise professionals part 1
Atrio-ventricular nodal (AVN) blocks for exercise professionals: part 1: categories of AVN blocks and indications and contraindications for exercise; case study 1
This is the first of my small series on atrioventricular nodal blocks (AVN blocks) specifically for exercise professionals and in part one of this two part series I will categorise AVN blocks and give a summary of the indications and contraindications for exercise for different categories of AVN blocks. I will finish with a case study.
There are three main categories of AVN blocks: 1st degree, 2nd degree and 3rd degree. There are two subcategories in 2nd degree AVN blocks.
1st degree ANV block is defined as a prolongation of the interval between the beginning of atrial contraction as represented by the P wave on ECG and the beginning of ventricular contraction as represented by the QRS wave on ECG. This interval is known as PR interval and if it is greater than 0.20 seconds, then this indicates 1st degree AVN block. One word of caution though: this must be for all or at least most of the time, not just for one or a few beats. The latter indicate ectopics or some other arrhythmia but not 1st degree ANV block.
Second-degree AV node or block can be broken down into two types: type 1 of 2nd degree AVN block is also known as Mobitz Type 1. For this, there is a gradual lengthening of PR interval, eventually leading to a dropped ventricular beat, that a P wave that is not followed by a QRS for that beat, and then the whole cycle repeats. Mobitz type 2 is either a normal or prolonged PR interval, with some dropped QRS ventricular beats.
Third° AVN block is also known as complete AVN block. This is where there is a total dissociation of atrial contractions and ventricular contractions; on ECG there is no visible connections between P waves and QRS waves. Clients who have this condition need to have a permanent pacemaker fitted to prevent ventricular arrhythmias. I have gone into this in the video on this post and some of my other YouTube videos.
In my case study, I have given you an example of an elderly female who was in 1st degree AVN block at rest, but the level of block increased with increasing exercise intensities, and was the reason for stopping the exercise test.