In atrioventricular (AV) block the electrical signal from the atria is delayed or stopped on its way to the ventricles. First-degree and Mobitz I blocks are often benign, while Mobitz II and third-degree (complete) block can cause dangerously slow rates and usually need a pacemaker.
Key symptoms
- Fatigue and less exercise tolerance
- Lightheadedness or fainting
- Shortness of breath
- Confusion in older adults
- No symptoms in first-degree block
What you find on exam
- Slow pulse, regular or with dropped beats
- Blood pressure and signs of poor perfusion
- Cannon a waves in the neck veins in complete block
- First heart sound of varying loudness in complete block
Tests
- 12-lead ECG to grade the block: first degree, Mobitz I, Mobitz II or third degree
- Electrolytes, especially potassium; thyroid tests; troponin
- Drug review: beta blockers, calcium channel blockers, digoxin
- Lyme serology in endemic areas
- Holter monitor if episodes come and go
Treatment basics
- Unstable slow rate: atropine, then transcutaneous pacing or an epinephrine or dopamine infusion
- Stop or reduce drugs that slow conduction
- Permanent pacemaker for Mobitz II and third-degree block
- Treat reversible causes: ischemia, high potassium, Lyme disease
- Observe first-degree and Mobitz I block without symptoms
Red flags
- Fainting or near fainting
- Low blood pressure, chest pain or confusion with a slow rate
- New Mobitz II or complete block on the ECG
Practice it in Making Synapses
Making Synapses cases
Related guides
Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.