Virtually a full review of AV blocks from a single patient…in 14 minutes!
When interpreting rhythms, always do these three things:
1. Find out what the atrium is doing
2. Find out what the ventricle is doing
3. Figure out the relationship between the atrium and ventricle (PR-interval)
The answer usually lies in the PR-interval!
1st Degree AV Block = “delay” > 200ms at AV node or His bundle.
When the P:QRS>1, consider 2nd and 3rd degree AV Blocks
2nd Degree AV Block = Not every atrial impulse goes through to the ventrcles. (ie P:QRS >1)
Mobitz Type I (Wenckebach) -Each atrial impulse has longer and longer delay until it fails to conduct to the ventricle. Progressive PR-interval lengthening before a dropped beat.
Mobitz Type II - typically due to block below AV node in His bundle. Some but not all impulses are transmitted to the ventricles WITHOUT progressive PR lengthening.
3nd Degree AV Block = P waves march out normally at 60-100 bpm with no relation to the ventricular rate which is typically slower than sinus or the atrial rate.
RBBB vs PVC’s
Wide QRS complexes, with large R waves in V1 can be caused by both RBBB and PVC’s. An RSR’ pattern or the “rabbit ear appearance” is typically seen in V1 with RBBB. PVC’s from a left ventricular source will also have dominant R waves in V1. One way to differentiate between RBBB and a PVC is to pay attention to the morphology of the QRS complex.
RBBB - typically has a small R wave (left rabbit ear) and a tall R’ (right rabbit ear).
PVC’s - will have a larger R wave (left rabbit ear) and a smaller R’ (right rabbit ear) or a “hitched” downslope to the wave.
R wave > 15mm in setting of RBBB + Rightward Axis = Right ventricular hypertropy (RVH)
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