How to diagnose myocardial infarction (MI) in a patient with left bundle branch block (LBBB)?

From the Guidelines

Diagnosing myocardial infarction (MI) in patients with left bundle branch block (LBBB) is best achieved by using the Sgarbossa criteria, which includes ST-segment elevation ≥1 mm concordant with the QRS complex, ST-segment depression ≥1 mm in leads V1, V2, or V3, and ST-segment elevation ≥5 mm discordant with the QRS complex, as evidenced by 1. The Sgarbossa criteria are a set of ECG findings that can help identify MI in patients with LBBB. These criteria include:

• ST-segment elevation ≥1 mm that is concordant with (in the same direction as) the QRS complex
• ST-segment depression ≥1 mm in leads V1, V2, or V3
• ST-segment elevation ≥5 mm that is discordant with (in the opposite direction of) the QRS complex A score of ≥3 points suggests acute MI with high specificity, as reported by 1.

Beyond ECG, cardiac biomarkers like troponin are essential for diagnosis, with serial measurements recommended to detect rising or falling patterns characteristic of acute MI, as supported by general medical knowledge. Echocardiography can also help by identifying wall motion abnormalities. When diagnostic uncertainty persists, coronary angiography may be necessary, especially in patients with ongoing chest pain or hemodynamic instability, as suggested by 1.

The challenge in diagnosing MI with LBBB stems from the secondary repolarization changes of LBBB that affect ST segments and T waves, making standard ST-elevation criteria unreliable, as noted in 1 and 1. However, the use of the Sgarbossa criteria and other diagnostic tools can help improve the accuracy of MI diagnosis in patients with LBBB. Some key points to consider when diagnosing MI in patients with LBBB include:

• The importance of using the Sgarbossa criteria to identify MI
• The need for serial cardiac biomarker measurements to detect rising or falling patterns characteristic of acute MI
• The potential usefulness of echocardiography in identifying wall motion abnormalities
• The consideration of coronary angiography when diagnostic uncertainty persists, especially in patients with ongoing chest pain or hemodynamic instability.

From the Research

Diagnosis of Myocardial Infarction in Left Bundle Branch Block

Diagnosing myocardial infarction (MI) in patients with left bundle branch block (LBBB) can be challenging due to the altered electrocardiogram (ECG) patterns. The following points highlight the key considerations:

• The presence of LBBB can mask or mimic the ECG signs of MI, making diagnosis more difficult 2, 3.
• Current guidelines recommend that patients with new or presumed new LBBB undergo early reperfusion therapy, but data suggest that only a minority of patients with LBBB are ultimately diagnosed with acute MI 2.
• ECG criteria, such as ST-segment elevation or depression, can be used to diagnose MI in patients with LBBB, but these criteria have low sensitivity and high specificity 3, 4.
• High-sensitivity cardiac troponin (hs-cTn) testing can be useful in diagnosing MI in patients with LBBB, with high diagnostic accuracy and efficacy when combined with ECG criteria 3.
• A diagnostic algorithm combining ECG criteria with hs-cTnT/I concentrations and their absolute changes at 1 hour or 2 hours can accurately diagnose MI in patients with LBBB 3.

Clinical Considerations

The following clinical considerations are important when diagnosing MI in patients with LBBB:

• Patients with LBBB are often older and have a greater burden of risk factors and comorbidities, which can affect treatment and outcome 5.
• LBBB patients may be less likely to receive evidence-based treatments, such as aspirin, P2Y12 inhibitors, β-blockers, and statins, or undergo percutaneous coronary interventions 5.
• Mortality rates for LBBB patients are higher than for those with ST-elevation MI, but have decreased over the past 20 years 5.
• Further studies are needed to identify patients with LBBB who may benefit from an early invasive treatment strategy 5.

Diagnostic Approaches

The following diagnostic approaches can be used to diagnose MI in patients with LBBB:

• ECG criteria, such as ST-segment elevation or depression, can be used to diagnose MI in patients with LBBB 3, 4.
• High-sensitivity cardiac troponin (hs-cTn) testing can be useful in diagnosing MI in patients with LBBB, with high diagnostic accuracy and efficacy when combined with ECG criteria 3.
• A diagnostic algorithm combining ECG criteria with hs-cTnT/I concentrations and their absolute changes at 1 hour or 2 hours can accurately diagnose MI in patients with LBBB 3.
• Serial or previous ECGs can be useful in increasing the sensitivity of ECG criteria for diagnosing MI in patients with LBBB 4.