A 69-year-old man is admitted to the cardiac intensive care unit after an anterior ST-elevation myocardial infarction. Coronary angiography demonstrates a proximal left anterior descending artery occlusion, and he undergoes successful percutaneous coronary intervention. His initial hospital course is uncomplicated. Eight hours later, he develops sudden lightheadedness, nausea, and confusion. He denies recurrent chest pain. His medications include aspirin, ticagrelor, atorvastatin, and intravenous heparin. Metoprolol has not yet been started. Temperature is 36.6°C (97.9°F), blood pressure is 76/44 mm Hg, pulse is 28/min, respiratory rate is 20/min, and oxygen saturation is 95% on room air. On physical examination, he appears pale and diaphoretic. Jugular venous pressure is mildly elevated, and the extremities are cool with delayed capillary refill. The lungs are clear. ECG shows regular P waves at a rate of 88/min and regular wide QRS complexes at a rate of 28/min. There is no consistent relationship between the P waves and QRS complexes.
Which of the following is the most appropriate immediate management?
The correct answer is:
B) Begin transcutaneous cardiac pacing
This patient has third-degree atrioventricular block, also called complete heart block, complicated by hemodynamic instability. The atria and ventricles are depolarizing independently, producing AV dissociation. The slow, wide-complex ventricular escape rhythm suggests that the escape pacemaker originates below the AV node within the His-Purkinje system.
Immediate transcutaneous pacing is indicated because the patient has profound bradycardia accompanied by hypotension, altered mental status, diaphoresis, and evidence of poor peripheral perfusion. Pacing provides rapid stabilization while preparations are made for temporary transvenous pacing and subsequent evaluation for permanent pacemaker implantation.
The location of the infarction is clinically important. Complete heart block associated with an anterior myocardial infarction usually reflects extensive necrosis of the interventricular septum and damage to the infranodal conduction system. The resulting escape rhythm is often slow and wide, and the condition carries a worse prognosis than AV block associated with an inferior infarction. Inferior MI–associated block is more often transient, occurs at the AV node, and may respond to atropine.
A high-yield management principle is that unstable bradycardia requires immediate intervention. The clinician should not delay pacing while waiting to determine whether medications will restore conduction.
Answer choice A: Administer intravenous atropine and observe for a sustained response, is incorrect.
Atropine blocks parasympathetic input to the sinus and AV nodes and may improve bradycardia caused by nodal conduction disease. However, this patient has a wide-complex escape rhythm after an anterior MI, suggesting infranodal block. Atropine is often ineffective in this setting and should not delay pacing in a patient with shock and altered mental status.
Answer choice C: Implant a permanent pacemaker without temporary stabilization, is incorrect.
A permanent pacemaker will likely be required if the conduction abnormality persists, particularly because anterior MI–associated complete heart block commonly reflects irreversible His-Purkinje injury. However, permanent device placement cannot provide the immediate stabilization required for a patient with profound hypotension. Transcutaneous pacing should be initiated first, followed by temporary transvenous pacing when needed.
Answer choice D: Initiate an intravenous diltiazem infusion, is incorrect.
Diltiazem slows conduction through the AV node and is used for ventricular rate control in selected supraventricular tachyarrhythmias. In a patient with complete heart block and severe bradycardia, it could further suppress conduction and worsen hemodynamic instability.
Answer choice E: Perform synchronized electrical cardioversion, is incorrect.
Synchronized cardioversion is used for hemodynamically unstable tachyarrhythmias, such as atrial fibrillation with rapid ventricular response or supraventricular tachycardia. It does not correct failure of atrioventricular conduction and is inappropriate for profound bradycardia.
Key Learning Point
Complete heart block with hypotension, altered mental status, or other evidence of poor perfusion requires immediate transcutaneous pacing. A slow, wide-complex escape rhythm after anterior myocardial infarction suggests infranodal conduction-system injury and often requires subsequent permanent pacing.
