ECG Quiz, Focusing Mainly on Rhythm

Here is the transcript of the video: Now we will have an ECG, focusing mainly on the rhythm analysis. That is what we are going to see. Clinical history is currently not available, let us see, what we can make out from the ECG.

If you have a look at this ECG, sometimes, in this region, you may pass off it as just a low normal heart rate with nothing else. But careful analysis in this region will easily tell you that, this is one P wave with a fairly normal PR interval. But you have another P wave here, which is not conducted. So, for two P waves, you have one QRS. You might be tempted to think that this is 2:1 AV block. Then there are T wave inversions. What could be the reason for that T wave inversions? Have a look at this rhythm strip. You can very well see that it is not as simple as you thought. It is not a 2 to 1 AV block. There is a lot of variation in the PR interval. This is a near normal PR interval, you have a blocked P wave superimposed on the T wave here as in this case, and another P wave here, very long PR interval, a slight prolongation of PR interval, long PR interval, a medium prolongation, very long PR interval, a slight prolongation of PR interval, very long PR interval. So there is total variation in the PR interval and the heart rate is around 60 per minute. But the rate of P wave is higher. It is nearly, a little lower than 100 per minute. So, overall it will qualify for a complete atrioventricular block, complete heart block. T inversion being a narrow T inversion, could be a juvenile T inversion and with a better heart rate and a narrow QRS, supra Hisian complete heart block. If this is in a child, or a young adult, you will think that this is juvenile T inversion and the heart block is congenital complete heart block, in which heart rate is usually better as it is supra Hisian and narrow QRS as junction will be controlling. AV junction, lower part of the AV junction will be controlling the ventricles.

That brings us to four simple criteria which are needed for the diagnosis of complete heart block on the ECG. Regular PP interval. You have seen in the ECG that the PP interval is regular. Regular RR interval, that also we have seen. ECG had regular RR interval and PP interval shorter than RR interval, meaning that atrial rate is higher. You have seen that atrial rate is nearly 100 per minute while ventricular rate was only 60 per minute and totally varying PR interval. That we have seen in the rhythm strip. Totally varying PR interval would mean atrioventricular dissociation. There is no relationship between the atrial activity and ventricular activity. Both are occurring at their own rates without any definite relation, unlike the initial thought that it is a 2:1 atrioventricular conduction. And, from these four criteria, if you change or skip any one criteria, then the condition may be different. For example, instead of PP interval shorter than RR interval, if you have PP interval longer than RR interval, and all the other criteria are satisfied, it will not be complete heart block. Instead usually you will have ventricular tachycardia with AV dissociation. When the PR interval is varying, you have AV dissociation. But when the ventricular rate is more than atrial rate, usually it is a ventricular tachycardia with AV dissociation, with ventricular rate more than atrial rate. Then there is also another condition in which there could be AV dissociation with atrial rate (error) or this narrow QRS rate more than the atrial rate. That is junctional ectopic tachycardia where you can have AV dissociation. Junctional ectopic tachycardia with AV dissociation is another possibility.