Annals of Emergency Medicine
Volume 53, Issue 5 , Pages 691-692, May 2009

Electrocardiographic Research on Left Bundle Branch Block Must Use Angiographic Outcomes and Proportionality If It Is to Guide Reperfusion Therapy

Hennepin County Medical Center, University of Minnesota School of Medicine, Minneapolis, MN

Article Outline

 

To the Editor:

There are 2 important issues to clarify in the article by Tabas et al on the Sgarbossa criteria to help guide reperfusion therapy for acute myocardial infarction in the presence of left bundle branch block.1 First, none of the studies included in this meta-analysis address reperfusion therapy or its indications in the setting of left bundle branch block. All studies address the biomarker (CK or CK-MB) diagnosis of acute myocardial infarction in the presence of left bundle branch block; thus, they all had a combined outcome measure of both STEMI and non-STEMI. The original study by Sgarbossa et al was derived from all 133 left bundle branch block patients in the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries trial (GUSTO-1) who had CK-MB positive, not from patients with proven coronary occlusion.2 Reperfusion therapy is, of course, only indicated for STEMI; it is for patients not just with any myocardial infarction, but with evidence of acute coronary occlusion, for which we use ST elevation as an imperfect surrogate.

ST elevation on the ECG is very insensitive not only for acute myocardial infarction (as diagnosed by biomarkers) in the presence of left bundle branch block, but also in normal conduction (no bundle branch block); ST elevation is approximately 45% sensitive for myocardial infarction as diagnosed by CK-MB.3, 4, 5, 6 However, ST elevation in normal conduction is very sensitive for epicardial coronary occlusion, at approximately 85%.7 Furthermore, change in ST elevation with balloon occlusion is equally sensitive between those with and without left bundle branch block.8 Thus, it is not clear that left bundle branch block hides coronary occlusion substantially more than in normal conduction, and few definite conclusions can be made from biomarker studies about the accuracy of the Sgarbossa criteria for guiding reperfusion therapy.

Second, we see from this study that concordant ST segments are indeed very specific for acute myocardial infarction, but that excessive discordance of ≥5 mm is not. Excessive discordance, much more than concordance, is affected by proportionality: a large preceding QRS (in this case, a deep S-wave) is expected to produce a large amount of discordant ST elevation,9, 10 resulting in false positives. Conversely, a very small preceding QRS may result in a proportionately small amount of ST elevation, even in the presence of myocardial infarction, resulting in false negatives. One study, published as an abstract only, showed high sensitivity and specificity for excessively discordant ST elevation in V1-V4, as defined by the ratio of ST elevation to S-wave depth of ≥ 0.25.11 This was far more accurate than the Sgarbossa absolute cutoff of 5 mm. This method is explained in more detail in a recent case report.12

Before we can make definite ECG indications for reperfusion therapy in the setting of left bundle branch block, more angiographic research on the accuracy of the ECG for diagnosis of acute coronary occlusion, not the biomarker diagnosis myocardial infarction (which includes non-STEMI), is necessary. Such studies also need to take proportionality into account.

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References 

  1. Tabas JA, Rodriguez RM, Seligman HK, et al. Electrocardiographic criteria for detecting acute myocardial infarction in patients with left bundle branch block: a meta-analysis. Ann Emerg Med. 2008;52:329–336
  2. GUSTO Investigators. An international randomized trial comparing four thrombolytic strategies for acute myocardial infarction. N Engl J Med. 1993;329:673–682
  3. Fesmire FM, Percy RF, Bardoner JB, et al. Usefulness of automated serial 12-lead ECG monitoring during the initial emergency department evaluation of patients with chest pain. Ann Emerg Med. 1998;31:3–11
  4. Fesmire FM, Percy RF, Wears RL, et al. Initial ECG in Q wave and non-Q wave myocardial infarction. Ann Emerg Med. 1989;18:741–746
  5. Rouan GW, Lee TH, Cook EF, et al. Clinical characteristics and outcome of acute myocardial infarction in patients with initially normal or nonspecific electrocardiograms (a report from the Multicenter Chest Pain Study). Am J Cardiol. 1989;64:1087–1092
  6. Rude RE, Poole WK, Muller J, et al. Electrocardiographic and clinical criteria for recognition of acute myocardial infarction based on analysis of 3,697 patients. Am J Cardiol. 1983;52:936–942
  7. Schmitt C, Lehmann G, Schmieder S, et al. Diagnosis of acute myocardial infarction in angiographically documented occluded infarct vessel: limitations of ST-segment elevation in standard and extended ECG leads. Chest. 2001;120:1540–1546
  8. Stark KS, Krucoff MW, Schryver B, et al. Quantification of ST-segment changes during coronary angioplasty in patients with left bundle branch block. Am J Cardiol. 1991;67:1219–1222
  9. Madias JE, Sinha A, Ashtiani R, et al. A critique of the new ST-segment criteria for the diagnosis of acute myocardial infarction in patients with left bundle branch block. Clin Cardiol. 2001;24:652–655
  10. Madias JE, Sinha A, Agarwal H, et al. ST-Segment elevation in Leads V1-V3 in Patients with Left Bundle Branch Block (LBBB). Journal of Electrocardiology. 2001;34:87–88
  11. Smith SW, Bertog SC, Lathrop LM, et al. ST/S Ratio Distinguishes Left Bundle Branch Block from Left Bundle Branch Block with Simultaneous Anterior Myocardial Infarction [abstract]. Acad Emerg Med. 2006;13:S160–S161
  12. Smith SW, Heegaard W, Bachour FA, et al. Acute myocardial infarction with left bundle-branch block: disproportional anterior ST elevation due to right ventricular myocardial infarction in the presence of left bundle-branch block. Am J Emerg Med. 2008;26:342–347

 Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article that might create any potential conflict of interest. The author has stated that no such relationships exist. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement.

PII: S0196-0644(08)02015-5

doi:10.1016/j.annemergmed.2008.10.034

Refers to article:

  • Electrocardiographic Criteria for Detecting Acute Myocardial Infarction in Patients With Left Bundle Branch Block: A Meta-analysis , 17 March 2008

    Jeffrey A. Tabas, Robert M. Rodriguez, Hilary K. Seligman, Nora F. Goldschlager
    Annals of Emergency Medicine October 2008 (Vol. 52, Issue 4, Pages 329-336.e1)

Annals of Emergency Medicine
Volume 53, Issue 5 , Pages 691-692, May 2009

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