What is the next best step for a patient with shortness of breath (SOB) or anterior chest pain, electrocardiogram (ECG) showing tachycardia with new left bundle branch block (LBBB), previously normal ECG, and pending cardiac enzymes, who is already on morphine, nitroglycerin, and beta blockers (BB)?

Immediate Coronary Angiography

In a patient presenting with chest pain/SOB, new LBBB on ECG (previously normal), and high clinical suspicion for acute coronary syndrome, proceed directly to coronary angiography without waiting for cardiac enzyme results. 1

Rationale for Immediate Invasive Strategy

New LBBB as a STEMI Equivalent

• New or presumed new LBBB in the setting of acute chest pain should be treated as a STEMI equivalent, warranting immediate reperfusion therapy 1
• The 2003 ESC guidelines explicitly state: "One should not wait for the results [of cardiac markers] to initiate reperfusion treatment!" 1
• The 2020 ESC guidelines clarify that while more than 50% of patients with chest pain and LBBB ultimately have diagnoses other than MI, the combination of symptoms plus new LBBB (compared to previous normal ECG) significantly elevates the pre-test probability 1

Why Not Wait for Cardiac Enzymes (Option A is Wrong)

• Cardiac troponins may not be elevated in the first hours after symptom onset, even with high-sensitivity assays 1
• Waiting for biomarkers delays definitive diagnosis and treatment, directly increasing mortality and morbidity 1
• The patient already has ongoing symptoms despite maximal medical therapy (morphine, nitroglycerin, beta-blockers), indicating refractory ischemia 1

Why Not Perfusion Scanning (Option B is Wrong)

• Myocardial perfusion scintigraphy is useful for ruling out MI when the diagnosis is uncertain, but requires a previously normal baseline scan for comparison 1
• In this acute presentation with new LBBB and refractory symptoms, perfusion scanning would only delay definitive diagnosis and treatment 1
• LBBB itself causes reversible perfusion defects in the absence of obstructive coronary disease, making interpretation problematic 2

Clinical Context Supporting Angiography

High-Risk Features Present

• Refractory ischemic symptoms despite optimal medical therapy (morphine, nitroglycerin, beta-blockers already administered) 1
• New conduction abnormality (LBBB) with documented previous normal ECG 1
• Tachycardia in the setting of acute chest pain suggests hemodynamic stress or ongoing ischemia 1

Diagnostic Challenges with LBBB

• LBBB makes ECG diagnosis of acute MI extremely difficult, as it obscures ST-segment changes 1
• Standard ECG criteria for ischemia are unreliable in the presence of LBBB 1, 3
• Even specialized signs like Chapman's sign (notching in upslope of R wave) require awareness and may be missed 3

Management Algorithm

For patients with acute chest pain/SOB + new LBBB (previously normal ECG):

1. Immediate coronary angiography is the definitive diagnostic and therapeutic approach 1
2. Continue medical therapy during preparation (aspirin, heparin, antiplatelet agents) 1, 4
3. Primary PCI should be performed within 120 minutes if STEMI/acute occlusion is confirmed 4
4. If angiography shows no culprit lesion, alternative diagnoses can be pursued (Takotsubo, myocarditis, pulmonary embolism) 1

Common Pitfalls to Avoid

• Do not delay for serial troponins in the setting of new LBBB with ongoing symptoms—this increases door-to-balloon time and worsens outcomes 1
• Do not assume LBBB is benign even if initial troponins are negative—troponin rise may be delayed 1, 3
• Do not rely on ECG criteria alone (Sgarbossa criteria, etc.) as they have limited sensitivity in acute settings 1, 3
• Recognize that intermittent LBBB can occur with ischemia, making the new LBBB particularly concerning 3, 5