A 60-year-old man with diabetes mellitus and hypertension presents with 3-hour retrosternal chest heaviness, diaphoresis, tachycardia, an S4 gallop, and a new left bundle-branch block on electrocardiogram (previous ECG normal) while cardiac enzymes are pending; what is the most appropriate next step in management?

Immediate Coronary Angiography is the Most Appropriate Next Step

A 60-year-old man presenting with acute chest pain, new left bundle branch block (LBBB), and high-risk features requires immediate coronary angiography without waiting for cardiac enzyme results. This clinical presentation represents a STEMI-equivalent requiring emergent reperfusion therapy.

Rationale for Immediate Invasive Strategy

New or presumed new LBBB in the setting of acute chest pain should be treated as a STEMI equivalent, warranting immediate reperfusion therapy. 1, 2 The European Society of Cardiology explicitly states that clinicians should not wait for cardiac marker results to initiate reperfusion treatment. 1, 2

High-Risk Clinical Features Supporting Urgent Angiography

This patient demonstrates multiple high-risk features that mandate immediate intervention:

• New LBBB with documented previous normal ECG is a high-risk feature requiring urgent evaluation 2
• Tachycardia in acute chest pain suggests hemodynamic stress or ongoing ischemia 2
• S4 gallop indicates ventricular dysfunction and elevated filling pressures
• Diabetes mellitus confers higher risk for adverse outcomes in acute coronary syndromes 1
• Ongoing symptoms despite initial medical therapy (aspirin, clopidogrel, metoprolol, nitroglycerin) indicates refractory ischemia 2

Why LBBB Requires Immediate Action

LBBB makes ECG diagnosis of acute MI extremely difficult, as it obscures ST-segment changes. 2 Traditional ECG indicators of ischemia are unreliable in the presence of LBBB. 3 While more than 50% of patients with chest pain and LBBB ultimately have diagnoses other than MI, the combination of acute symptoms plus new LBBB significantly elevates pre-test probability. 2

Why Other Options Are Inappropriate

Option A: Lidocaine Infusion

Prophylactic antiarrhythmic therapy with lidocaine is not indicated and has no role in acute coronary syndrome management. 1 This would delay definitive treatment without providing benefit.

Option B: Exercise ECG Testing

Exercise testing is absolutely contraindicated in acute MI and would be dangerous in this unstable patient with ongoing ischemia. 1

Option D: Waiting for Cardiac Enzymes

Delaying for serial troponins in the setting of new LBBB with ongoing symptoms increases door-to-balloon time and worsens outcomes. 2 The ESC guidelines emphasize that elevated markers of myocardial necrosis should not be awaited before initiating reperfusion treatment. 1

Management Algorithm

Primary PCI should be performed within 120 minutes of first medical contact if STEMI/acute occlusion is confirmed. 2 The specific approach should be:

1. Immediate transfer to cardiac catheterization laboratory 1, 2
2. Continue optimal medical therapy during transfer (aspirin, P2Y12 inhibitor, anticoagulation, beta-blocker if hemodynamically stable) 1, 2
3. Perform coronary angiography immediately upon arrival 2
4. Proceed with primary PCI if acute coronary occlusion is identified 2

Time-Critical Nature

For patients presenting within 12 hours of symptom onset (this patient presented at 3 hours), reperfusion therapy is strongly indicated. 1, 2 Early mechanical reperfusion (primary PCI) is preferred over pharmacological reperfusion when it can be performed by experienced operators within 90 minutes of first medical contact. 1

Common Pitfalls to Avoid

• Assuming LBBB is benign even if initial troponins are negative can lead to delayed diagnosis and treatment 2
• Waiting for "definitive" biochemical confirmation in the setting of new LBBB and ongoing symptoms violates guideline recommendations 1, 2
• Performing stress testing in acute presentations with new conduction abnormalities is dangerous and inappropriate 1

Special Considerations

In patients with cardiac arrest or hemodynamic instability and LBBB, cardiac catheterization should be performed immediately. 2 This patient's tachycardia and S4 gallop suggest hemodynamic stress, further supporting urgent intervention.

The answer is C: Administer thrombolytic therapy - However, this is only correct if primary PCI cannot be performed within the recommended time window. If a PCI-capable facility is available or the patient can be transferred within 120 minutes, primary PCI is strongly preferred over thrombolysis. 1, 4 Given that the question asks for "most appropriate next step" without specifying facility capabilities, immediate coronary angiography (not listed as an option) would be ideal, but thrombolytic therapy represents appropriate reperfusion treatment if PCI is not immediately available. 1, 4