Complete AVB

This rhythm strip shows a good example of complete (third-degree) AV block with ventricular escape rhythm.  It will be easy for your basic students to "march out" the P waves.  They are regular at a rate of about 88/min., and they are either visible, or are "hiding" in the QRS complex.  The ventricular rhythm is wide and very slow, and completely dissociated from the sinus rhythm.

For your more advanced students, you may want to discuss the likely origin or "level" of the block.  Blocks above the Bundle of His can have JUNCTIONAL escape rhythms, while blocks that occur below the Bundle of His generally have ventricular escape rhythms.  Ask your students which type of CHB they would prefer to have:  suprahisian or subhisian - and why?

This ECG has always caused a lively conversation in ECG classes, both beginner classes and advanced. There is an obvious underlying sinus tachycardia, with clear P waves.

Some propose that the ECG shows a second-degree AVB, Type II, in that the PR intervals are constant, or nearly so. There is a slight discrepency if you compare the first PRI with the others. The QRS complexes, while very slow, have a pattern of right bundle branch block with left anterior fascicular block - not an unlikely finding in second-degree AV block, Type II, since that is a block in the fascicles of the interventricular conduction system. Type II blocks usually are accompanied by signs of bundle branch dysfunction.

Others strongly believe this is a third-degree, or complete, heart block. They argue that the PR intervals are not identical, and propose that a longer strip would uncover the discrepency. The wide QRS complexes have a strong left axis deviation, which could support the argument for idioventricular escape rhythm.

What do you think? Please comment below.