Third-Degree (Complete) Heart Block — ECG Academy Lesson

Learn to identify third-degree AV block by its completely dissociated P waves and QRS complexes, understand why the atria and ventricles beat independently, and recognize the critical emergency response required when escape rhythms are slow or ventricular in origin.

Learning Objectives

• Define third-degree AV block as complete failure of AV conduction with independent atrial and ventricular rhythms
• Explain why P waves and QRS complexes have no relationship to each other (variable PR intervals)
• Distinguish junctional escape (40-60 bpm, narrow QRS) from ventricular escape (20-40 bpm, wide QRS)
• Identify that wide QRS escape rhythms represent a more critical emergency than narrow QRS escape rhythms
• List common causes including MI, medication toxicity, congenital heart block, and post-surgical injury
• Describe the immediate monitor tech response for third-degree heart block
• Recognize why third-degree block is the most dangerous of the AV blocks