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Arrhythmia Recognition Webcast Series
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Practice ECG 13
This ECG has some significant pathology. To begin with, we see that there are a lot of P waves and few QRS complexes. Are the Ps and QRSs related? No, they are not. So, the basic rhythm is either a third-degree heart block or AV dissociation. Do you remember the definitions? If not, go back to Chapter 10 to review them. In essence, if you see more Ps than QRSs and they are not related, you're looking at a third-degree heart block, which is what this patient is exhibiting.
Notice the low voltage in all of the limb leads. The patient has significantly low voltage that could represent a pericardial effusion or some infiltrative process such as amyloid deposition.
Did you pick up on the width of the QRS complex? It is 0.12 seconds wide, making this a third-degree heart block with either an idioventricular escape rhythm or a junctional escape rhythm with an underlying BBB. Which kind of block would it be? Go down and take another look if you didn't pick it up. There are slurred S waves in leads I and V6, as well as an RSR' complex in V1, so this would be an RBBB. In addition, we see a right axis with a small Q in II, III, and aVF, consistent with an LPFB. So how can you differentiate between the two possibilities? You need an old ECG to see if the patient had a chronic underlying bifascicular block. If the block was present on the old ECG, the answer is a junctional escape rhythm. If the block was not present, you have to decide between an acute bifascicular block and an idioventricular rhythm. In either case, treatment is the same: atropine and/or transcutaneous or transvenous pacing.
Note that if your answer is either an acute or chronic bifascicular block, the T waves in V2 to V6 are all concordant; the last part of the QRS complex indicates ischemia in this patient.
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