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Electrocardiographic diagnosis of myocardial infarction in patients with left bundle branch block
S F Li1, P L Walden, O Marcilla
1Department of Emergency Medicine, Albert Einstein College of Medicine, Jacobi Medical Center, Montefiore Medical Center, and the Department of Emergency Medicine, New York-Presbyterian Hospital, New York, NY, USA.
Insights
Sgarbossa criteria cannot exclude myocardial infarction (MI) in left bundle branch block (LBBB) patients due to low sensitivity. However, concordant ST-segment elevation is a strong indicator of MI in these patients.
Area of Science:
- Cardiology
- Electrocardiography
- Diagnostic Accuracy
Background:
- Left bundle branch block (LBBB) complicates the electrocardiogram (ECG) diagnosis of myocardial infarction (MI).
- Previous criteria by Sgarbossa et al. aimed to improve MI detection in LBBB patients.
Purpose of the Study:
- To validate the Sgarbossa ECG criteria for detecting MI in patients with LBBB and suspected ischemia.
- To assess the diagnostic performance of individual Sgarbossa criteria.
Main Methods:
- Retrospective cohort study of patients with suspected ischemia and LBBB.
- MI defined by elevated creatine kinase MB levels.
- ECGs interpreted by blinded physicians using Sgarbossa criteria.
Main Results:
- Low sensitivities (0-16%) and high specificities (93-100%) for Sgarbossa criteria.
- Concordant ST-segment elevation (≥1 mm) showed a high positive likelihood ratio (16) for MI.
- New LBBB was associated with a 5.1-fold increased risk of MI.
Conclusions:
- Sgarbossa criteria are unreliable for excluding MI in LBBB patients due to low sensitivity.
- Concordant ST-segment elevation is a valuable indicator for identifying MI in LBBB.
- New LBBB in the setting of suspected ischemia significantly increases the likelihood of MI.
Study Objective:
To validate ECG criteria previously proposed by Sgarbossa et al for the detection of myocardial infarction (MI) in patients with left bundle branch block (LBBB) and suspected ischemia.
Methods:
A retrospective cohort study was performed at an urban teaching hospital. All patients admitted with suspected ischemia and LBBB were eligible. MI was defined as an elevated creatine kinase (CK) isoenzyme MB (>14 IU/L) that was at least 5% of total CK level. ECGs were interpreted by 2 physicians blinded to patient outcome. Interpreters were asked to rate ECGs for the presence of each of the 3 criteria proposed by Sgarbossa et al: (1) ST-segment elevation greater than or equal to 1 mm concordant with the QRS complex; (2) ST-segment elevation greater than or equal to 5 mm discordant with the QRS complex; and (3) ST-segment depression in leads V(1) through V(3). Interobserver agreement was assessed.
Results:
Of 190 eligible patients, 25 (13%) had MI. Sensitivities of the 3 criteria varied from 0 to 16%, with specificities of 93% to 100%. Only the first criterion demonstrated a clinically useful likelihood ratio (positive likelihood ratio=16 [95% confidence interval 4 to >100]). Patients with new LBBB were more likely to have MI (relative risk=5. 1 [95% confidence interval 2.6 to 10]). Interobserver agreement among ECG interpreters ranged from 93% to 98%.
Conclusion:
The criteria of Sgarbossa et al cannot be used to exclude MI in patients with LBBB because of low sensitivities and poor negative likelihood ratios. ST-segment elevation concordant with the QRS complex had a high positive likelihood ratio for identification of MI. Patients with new LBBB and suspected ischemia are 5 times more likely to have MI than patients with LBBB of chronic or unknown duration.