First-degree atrioventricular (AV) block is defined as an abnormally prolonged PR-interval >200ms. Although traditionally considered to be a benign clinical entity, not all first degree AV blocks are treated the same.
Markedly prolonged PR-intervals (PR >300ms) can cause symptoms and hemodynamic compromise due to inadequate timing of atrial and ventricular contractions. Consider the following ECG from a 32 YOF with intermittent episodes of syncope and dizziness…
There is marked first degree AV block (PR=434 ms). When the PR-interval gets too long, AV dyssynchrony compromises ventricular filling and decreases cardiac output, similar to the so-called pacemaker syndrome.
Current ACC/AHA guidelines state that permanent pacemaker implantation is reasonable for marked first degree AV block with hemodynamic compromise or symptoms similar to those of pacemaker syndrome. (Class IIa, Level of Evidence B). The guidelines caution that pacemakers are not indicated in asymptomatic patients with isolated first degree AV block.
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Special thanks to Dr. Brandon Cole for submitting the ECG
References / Further Reading (Attached)
First-Degree AV Block-An Entirely Benign Finding or a Potentially Curable Cause of Cardiac Disease? Annals of Noninvasive Electrocardiology.2013;18(3):215–224. doi:10.1111/anec.12062.
ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 2008;117(21):e350–e408. doi:10.1161/CIRCUALTIONAHA.108.189742.
