Asymptomatic First Degree AV Block on ECG Management

First of all remember I said “This ecg of “ asymptomatic “ individual ! 

However even then the following needed to be known!!!!! As far as managment is concerned !!

So indeed very prolong PR !!! Or in other words the “ the famous first degree AV block “ 

So technically The P to R interval is measured from the” beginning of the P complex to the beginning of the QRS complex “ 

The normal P to R interval in adults is 120 to 200 msecond. It is generally shorter in children and gets longer as one ages. 

“ And this interval ! is actually representative of the time required for the current to flow from the atrium through the AV node, then His bundle , then BB and then system of PF until the ventricular myocardium begins to depolarise!!!!!”

The biggest caveat or the biggest challenge ! 

Since normally almost all of the Drs & especially the Jnr Drs either don’t actually measure it & go on eye balling or if they do measure , they don’t know from where to start or where to end !!! As even a small box ( representing 40 msec) add or minus can significantly affect the outcome !!!!           

So Before establishing the length of the P to R interval , the most important step is to be able to correctly measure this on the 12 lead surface ecg !!!!! So here are few tips & tricks ! 

1. Firstly This interval should only be measured in the lead with the widest and longest P wave and the longest QRS duration . 

2. So This will avoid confusion by not using the leads in which the early part of the P wave or QRS complex may be isoelectric. 

3. luckily most modern surface ECG machines record several ECG leads simultaneously & also sequentially so the onset of the exact P wave and the exact QRS complex can be reconfirmed by measuring while being able to recfm with the other simultaneously recorded leads.

Now comes the million dollar question and along with answer to the what will one do !!! 

Or So How long or longer can be the P to R interval ? 

Well sometime this can be more of academic Intrest but remember sometimes this can be become very significant depending on the associated symptoms . 

So known to all EP Splts , and proven During EP studies, this surface ecg PR interval is actually comprising of two sub intervals or (intra cardiac intervals & not one) 

The A to H interval

The H to V interval 

A catheter appropriately placed on The His bundle inside heart , records both the A & His proper deflection & V simultaneously!

The A to H interval ! is representative of current flow through the AV node or till proximal to the His bundle!!

(the time between the potential recorded from the lower part of the RA till the His bundle spike) 

this interval is generally in the range of 50 to 130 ms out of usually normal 200 msec PR duration . However Sometimes this AH can be very long or out of the range and still no symptoms !!!!

The H to V time, which start from His deflection to the start of Intra cardiac ventricular deflection, normally taken as the first uptake of R wave and this usually in range of 35 to 55 ms out of normal 200 msec interval! 

However the longer this interval becomes is then more reflective of the conduction sys disease also better known as infra nodal disease & one of the indication of implanting an pace maker can be if this interval is more than 100 sec !!! Even if patient is asymptomatic !!!

Thanks