LBBB doesn’t have to block an MI diagnosis

What we are taking about:

Sgarbossa EM, et al. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators. N Engl J Med. 1996 Feb 22;334(8):481-7.


Main Points:

In the presence of a left bundle branch block, suspect acute infarction when:

  1. ST-segment elevation ≥1 mm and concordant with QRS complex
  2. ST-segment depression ≥1 mm in lead V1, V2, or V3
  3. ST-segment elevation ≥5 mm and discordant with QRS complex

Background:

The presence of left bundle branch block on the electrocardiogram may conceal the changes of acute myocardial infarction, which can delay both its recognition and treatment. This study aimed to identify electrocardiographic criteria for the diagnosis of acute infarction in the presence of left bundle-branch block.


Methods:

This was a retrospective cohort study looking at electrocardiograms of North American patients enrolled in the GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial who presented with chest pain, had left bundle-branch block on baseline EKG, and acute myocardial infarction confirmed by enzyme studies (total of 131 patients). These EKGs were blindly compared with the electrocardiograms of control patients from the Duke Databank for Cardiovascular Disease who had chronic coronary artery disease and left bundle-branch block. The patients in the control group did not have acute chest pain at the time of the electrocardiographic recording.

Multivariate Analysis was used to determine independent predictors of acute myocardial infarction. These criteria were used to develop a scoring system to identify patients with acute myocardial infarction.


Results:

ST-segment deviation was the only electrocardiographic finding that was useful in the diagnosis of acute myocardial infarction in the presence of left bundle-branch block. For leads with a predominantly negative QRS complex, ST-segment elevation (discordance) of at least 5 mm identified patients with evolving infarction. Any degree of ST-segment elevation in a lead with a positive QRS complex (concordance) was a highly specific sign of acute myocardial infarction. ST-segment depression in lead V1, V2, or V3 was also an independent marker of acute myocardial infarction as the QRS complex is predominantly negative in those leads (concordance).


Some Details:

EKG criteria were utilized to create a scoring system based on their weight as determined by a logistic model. An accurate diagnosis, a specificity of 90 percent, requires a minimal total score of 3 (see table below).

EKG Criterion Odds Ratio Score
ST-segment elevation ≥1 mm and concordant with QRS complex 25.2 (11.6–54.7) 5
ST-segment depression ≥1 mm in lead V1, V2, or V3 6.0 (1.9–19.3) 3
ST-segment elevation ≥5 mm and discordant with QRS complex 4.3 (1.8–10.6) 2

Therefore, patients presenting with ST-segment elevation of at least 5 mm in leads with a QRS complex in the opposite direction (score = 2) should undergo further testing.

The criteria derived from the model and their index scores were tested in the validation sample, which included 22 patients with enzymatic evidence of acute infarction and 23 with only unstable angina (the control group). Sensitivity of criteria were 90% and 96% for the derivation and validation samples respectively and specificities were 78% and 36% respectively.


Level of Evidence:

ACEP Clinical Policy Committee Level IIB (2006)


Relevant articles:

Cai Q, et al. The left bundle-branch block puzzle in the 2013 ST-elevation myocardial infarction guideline: From falsely declaring emergency to denying reperfusion in a high-risk population. Are the Sgarbossa Criteria ready for prime time? Am Heart J 2013;166:409-13.

Fesmire F, et al. Clinical Policy: Indications for Reperfusion Therapy in Emergency Department Patients with Suspected Acute Myocardial Infarction. Ann Emerg Med. 2006;48:358-383.

The GUSTO Investigators. An international randomized trial comparing four thrombolytic strategies for acute myocardial infarction. N Engl J Med 1993;329:673-82.

 

Submitted by Adam Janicki, MD PGY4

One thought on “LBBB doesn’t have to block an MI diagnosis

  1. Always great discussion and debate, but some emerging data may slightly adjust this Re: new LBBB.
    (Some of this below, I heard from Amal Mattu, MD talk last year.)

    LBBB should be considered a STEMI equivalent only if…
    –Patient is hemodynamically unstable or has acute heart failure, OR
    –Patient has concordant ST segment changes (Sgarbossa rules A or B)

    ―Sgarbossa rules A and B
    A.STE > 1 mm in same direction as QRS
    B.STD > 1 mm in same direction as QRS in leads V1, V2, or V3

    Left Bundle Branch Block and Acute MI
    (Neeland, et al. JACC 2012)
    •proposed that new/presumed LBBB should not be considered a STEMI equivalent…

    2013 ACC/AHA STEMI Guidelines
    (O’Gara, et al. Circulation 2013)
    •New/presumed LBBB is no longer an indication for emergent CLA/lytics

    Left Bundle Branch Block and Acute MI
    (Cai, Mehta, Sgarbossa et al. AHJ 2013)
    •LBBB should be considered a STEMI equivalent only if…
    –Patient is hemodynamically unstable or has acute heart failure, OR
    –Patient has concordant ST segment changes (Sgarbossa rules A or B)
    –Patient has ST:S ratio 25% of the size of the R or S and discordant

    Ratio may be much better and the discordant rule may not be as important.

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