Third-Degree AV Block

Complete, or third-degree, AV block means that no atrial impulse reaches the ventricles. The sinoatrial node may continue to generate P waves, but the ventricles must rely on a separate escape rhythm to contract. That separation can sharply reduce cardiac output because atrial contraction no longer supports ventricular filling and the escape rhythm is slow and potentially unreliable. The ventricular rate may appear regular while tissue perfusion is failing. A clinician therefore looks first at blood pressure, mental status, symptoms, and the escape QRS—not at the heart rate alone. Once complete block is confirmed, pacing is the central safety strategy. Atropine may be trialled in selected patients, but it commonly fails when conduction is completely interrupted and must never delay electrical pacing for a patient with compromised perfusion.