Complete heart block (third degree AV block) on ECG for new nurses and students
Lead II; 25mm/sec
Recognizing and understanding complete heart block (CHB) appearance on the ECG:
The key features to look for on ECG include:
A relatively regular atrial (P wave) activity that marches out at the inherent rate relative to where the atrial impulse is originating. In the example above this would be sinus, at 60-100 beats per minute (BPM).
Relatively regular ventricular (QRS) activity (marching out). In the example above this would be a ventricular rate between 20-40 BPM.
Expect two independent atrial and ventricular rates since there’s no communication between upper and lower chambers in this case.
Variable and constantly changing PR interval (again, not a true PR interval since communication has been lost between upper and lower)
There is one special consideration regarding the ventricular activity: the QRS may be narrow or wide. This trips up many students and nurses that are new to telemetry in the beginning. A narrow QRS suggests a junctional escape, meaning the ventiricles are being paced somewhere in the area of the AV junction. A wide QRS would suggest ventricular escape (if no escape rhythm is present you may be dealing with ventricular standstill).
Let the PR interval characteristics aid in identifying complete heart block rather than relying strictly upon using presence of a wide QRS as inclusion criteria.
In my mind, I imagine a separate atrial and ventricular rhythm superimposed onto the rhythm strip (shown above) since neither has any idea what the other is doing. This helps me conceptualize the appearance.
*All of the above from a very basic rhythms perspective. Exceptions do exist in the real world.
Hope this helps!
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