Bradycardia and AV Blocks: Field Management and Pacing Decisions

The only bradycardia that needs treatment is a symptomatic one. The block type tells you whether atropine has any chance of working.

The four blocks

• First-degree: PR over 0.20 s, every P conducts — benign, monitor
• Second-degree Type I (Wenckebach): PR lengthens until a beat drops — usually stable
• Second-degree Type II (Mobitz II): constant PR, sudden dropped beats — unstable, pacer pads on
• Third-degree: complete AV dissociation, P waves and QRS marching independently — pace

Symptomatic means

Hypotension, altered mental status, chest pain, dyspnea, or signs of poor perfusion. A resting rate of 48 in a marathon runner is not an emergency.

Treatment sequence

1. Oxygen if hypoxic, monitor, IV access, 12-lead
2. Atropine 1 mg IV every 3–5 minutes to a max of 3 mg
3. Transcutaneous pacing if atropine fails or the block is high-degree
4. Epinephrine 2–10 mcg/min or dopamine 5–20 mcg/kg/min infusion as an alternative

Where atropine fails

Atropine blocks vagal tone at the AV node. In Mobitz II and complete heart block the lesion is below the node, so atropine often does nothing and can worsen ischemia. Go to pacing early.

Pacing pearls

Set the rate around 60–80, increase current until you see electrical capture, then confirm mechanical capture with a femoral pulse. Sedate for the discomfort once perfusion improves.