During nightshift you are presented the following ECG of a 12 years old boy. What diagnosis can you spot at a glance?
Your report reads: sinus rhythm, 75 bpm, QRS 65°, PR 200ms, QTc 390ms (Bazett).
The diagnosis you made at a glance is first degree AV block, as the PR interval should not exceed 170ms at this heart rate.
Below you find another example of AVB I°. The ECG was taken in a 17 years old female complaining of dizziness:
As you see, the PR interval in this case is quite long, equaling 380ms. In adults the PR interval should not exceed 200ms.
The PR interval represents the time it takes for the depolarizing wavefront to travel through the AV node and bundle of His to the ventricular myocardium. Since AV nodal conduction is influenced by vagal and sympathetic tone, AV nodal conduction time differs with heart rate.
Especially in pediatric cardiology it is always helpful to have reference values available, as timing and intervals will differ at different ages and heart rates.
Most patients with AVB I remain asymptomatic and therapy is hardly ever needed.