Which condition is most likely to require emergent transvenous (temporary internal) pacing in the Emergency Department (ED)?

Anterior Myocardial Infarction with Complete Heart Block Requires Emergent Transvenous Pacing

Anterior myocardial infarction complicated by complete heart block is the condition most likely to require emergent transvenous pacing in the ED, as it reflects His-Purkinje necrosis that will not respond to atropine and is typically accompanied by cardiogenic shock requiring urgent heart rate support. 1

Key Pathophysiologic Distinctions

Anterior MI with Heart Block

• Complete heart block in anterior MI reflects tissue necrosis in the His-Purkinje system, not reversible dysfunction 1
• Heart rate support is required urgently because complete heart block is usually accompanied by cardiogenic shock 1
• His-Purkinje necrosis will not respond to atropine, making ventricular pacing the minimum requirement 1
• Mortality ranges from 40-100% in anterior wall infarction with complete AV block, compared to only 5-20% in inferior infarctions 1

Inferior MI with Heart Block

• Heart block in inferior MI often results from reversible AV nodal dysfunction due to tissue edema or adenosine release, not necrosis 1
• A satisfactory heart rate can often be achieved without artificial pacing by using atropine (0.3-1.2 mg titrated against heart rate response) 1
• Pacing should be reserved only for patients who fail to respond to atropine AND show signs of cardiogenic shock (low heart rate and blood pressure, poor urine output, poor peripheral perfusion) 1
• Recent evidence suggests primary PCI without temporary pacing is acceptable in complete AVB-complicated acute inferior STEMI to avoid delays in reperfusion 2

Asystolic Cardiac Arrest

• Transvenous pacing is NOT indicated for asystolic cardiac arrest 1
• Transthoracic (external) pacemakers may have some role in bradyarrhythmias and asystolic arrest, but the role of transvenous pacing must be reevaluated in such circumstances 1
• The procedure would cause unacceptable delays in definitive resuscitation measures

Sick Sinus Syndrome

• This is typically a chronic condition requiring elective permanent pacemaker placement, not emergent transvenous pacing 3
• Temporary pacing may be used as preparation for noncardiac surgery or as a bridge to permanent pacing, but this is not an emergent ED indication 3

Clinical Algorithm for Decision-Making

When evaluating MI patients for emergent transvenous pacing:

1. Identify infarct location (anterior vs. inferior) 1
2. Assess for complete heart block or high-degree AV block 1
3. For anterior MI with heart block: Proceed directly to transvenous pacing preparation, as atropine will be ineffective 1
4. For inferior MI with heart block: Trial atropine first; only proceed to pacing if patient fails atropine AND demonstrates cardiogenic shock 1

Important Caveats

• Central venous cannulation carries risks, particularly soon after thrombolysis, which must be weighed against benefits 1
• The femoral venous route is preferred for temporary transvenous pacing as it allows easy compression if bleeding occurs 1
• Unstable patients are more likely to develop serious arrhythmias related to electrode passage and positioning 1
• In inferior MI, prioritize primary PCI over temporary pacing to avoid delays in reperfusion 2