It never came up to me when I was reading 12L ECG before that we are just presented with a 10 seconds event of a lifelong cardiac activity. Then with those 10 seconds, you are expected to make a great diagnosis. My perspective of looking at cardiac activity changed when I got this task of watching them for 12 hours. That is 43,200 beats being watched for 12 hours (each) and if you are watching about 40 then it is about 1,728,000 beats. This is if they are beating at 60 per minute. Most of them are regular but some of them will “drive you nuts”.
After several years of being here, I have developed my way of looking at things. Take for example this 10 second strip.
We have here an irregular narrow complex rhythm. Is this atrial fibrillation? Complete heart block or there is AV dissociation?
Move backwards and appreciate the “scenery”.
If you move backwards, you will see some “group-beating).
From my previous post, these are telltale signs of a Wenckebach phenomenon.
Look for the P’s - Use all the available leads to look for the P wave
Classically ECG class would say to analyze a strip is to ask: IS THERE A P? I still follow it but I LOOK FOR THE P IN ALL AVAILABLE LEADS. The wonderful lead II is not at all wonderful and trusted. Other leads will reveal the elusive nib.
In this particular case, it is hard to find the rest of the P waves if viewed from lead II. So, I look at them in full disclosure (all 7 channels).
My best candidate is to look at V1.
But where are the rest of the P waves?
Going back to V1, One way of looking for the P waves is to look at normal-looking QRS. When I say normal looking QRs, I mean a QRS that is not deformed by anything (artifacts or extra nibs). The best candidate I can find here is QRS complex #3.
QRS complex #3 (blue box) is the best normal-looking QRS. The other complexes are distorted (with green dots). This distortion is due to the presence of a P wave at the terminal (end) portion of the QRS.
Where are the rest of the P waves?
Bring out your calipers or if you have an electronic caliper then use it to march and look for the P waves.
By the magic of the caliper, hidden P waves are marked (blue dots). Some of them are not so obvious and some are fully hidden from view. At a rate of less than 3 big boxes or about 14 small squares then the atrial rate is about 107 per minute (SINUS TACHYCARDIA). So, we solved the first part of the mystery.
Which sinus impulse is making the QRS (capturing the ventricles)? Ladder diagram
To answer this question, the ladder diagram is needed. Simply put, it is a line diagram representing the transit of an impulse from 3 levels (tiers) – A or atrial tier, AV or AVJ or AV node or AV junction and the V or ventricular tier.
We have here groups of 4 P’s with 3 QRS (conducted) or 4:3 AV conduction and 3 P’s with 2 QRS (conducted) or 3:2 AV conduction and a long PRI at the beginning of the groupings.
So, the strip is sinus tachycardia with long PRI (aka first degree AV block) with 4:3 and 3:2 AV conduction. There is lengthening of the PRI. Thus is a Wenckebach.
For this case what we did are the ff:
1. Move backwards and look at the rhythm (group-beating).
2. Use full disclosure (7 channel/leads) in looking for the P’s.
3. Use a normal-looking QRS as reference to look for the hidden P waves in the QRS.
4. Use a caliper to look for those P waves that are hidden from view.
5. Made a ladder diagram.