Cardiology/original researchDiagnosis of ST-Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block With the ST-Elevation to S-Wave Ratio in a Modified Sgarbossa Rule
Introduction
Timely and accurate identification of acute coronary occlusion in the setting of ischemic symptoms is critical to initiating urgent angiography and appropriate reperfusion therapy. Although the increase or decrease of cardiac biomarker levels is essential to the diagnosis of acute myocardial infarction, positive biomarker results alone do not differentiate ST-elevation myocardial infarction (STEMI) from non-STEMI. ST elevation on the ECG is the primary indication for emergency reperfusion therapy; however, identification of STEMI in the setting of left bundle branch block remains challenging.1
In the setting of left bundle branch block, ST-segment elevation or ST-segment depression commonly occurs in the absence of acute myocardial infarction and is predictable in that the ST-segment and T-wave abnormalities are normally “discordant” to (in the opposite direction of) the majority of the QRS (Figure 1). “Concordant” is the term used when the ST segment or T wave is in the same direction as the QRS and is not normally observed in baseline (normal) left bundle branch block.
Sgarbossa et al proposed requiring at least 3 points from the following criteria for the diagnosis of acute myocardial infarction in the presence of left bundle branch block: (1) concordant ST-segment elevation of 1 mm (0.1 mV) in at least 1 lead (5 points), (2) concordant ST-segment depression of at least 1 mm in leads V1 to V3 (3 points), or (3) excessively discordant ST-segment elevation, defined as greater than or equal to 5 mm of ST-segment elevation when the QRS result is negative (2 points)2 (Figure 2). There have been many evaluations of Sgarbossa's criteria, with variable methodologies and patient populations.3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 In a systematic review, although specificity for greater than or equal to 3 Sgarbossa points was high (98%), sensitivity was only 20%.17 For a score greater than or equal to 2 (ie, the unweighted rule), the sensitivities in the studies ranged from 20% to 79%, and specificities ranged from 61% to 100%.
Two main issues may contribute to the low sensitivity of Sgarbossa's rule. First, all validating studies cited above used a reference standard of creatine kinase (CK) (with or without MB fraction) for acute myocardial infarction, not coronary occlusion by angiography, meaning non-STEMI (emergency reperfusion therapy unnecessary) and STEMI (emergency reperfusion required) were included in the acute myocardial infarction group. Second, anterior STEMI is most often diagnosed by ST-segment elevation in leads V1 to V4; however, in left bundle branch block, these leads normally already have discordant ST-segment elevation. Therefore, some means of assessment of excessive anterior ST-segment elevation is necessary to diagnose most anterior STEMI. Specifically, Sgarbossa's rule uses an absolute 5-mm cutoff for discordant ST-segment elevation when an ST-segment elevation proportional to the preceding QRS or S wave may be more useful. We sought to evaluate the performance of the Sgarbossa rule in patients with left bundle branch block and angiographic evidence of coronary occlusion. We hypothesized that changing the third component of the Sgarbossa rule to a proportional rule would improve its sensitivity and specificity.
Section snippets
Study Design and Setting
Data for this study were collected at 3 Minnesota hospitals: Hennepin County Medical Center, a trauma center in Minneapolis; at the Minneapolis Heart Institute at Abbott Northwestern Hospital, which has a large regional STEMI system; and at Fairview Southdale Hospital, a community hospital in suburban Minneapolis that also takes transfers for primary percutaneous coronary intervention (PCI). Institutional review board approval was obtained at all institutions.
Selection of Participants
ECGs from 2 groups of patients were
Characteristics of Study Subjects
At the 3 institutions, we identified 45 patients with acute coronary occlusion, 33 of whom had an ECG available for analysis. Overall, of 33 included cases, 27 had complete occlusion and 6 had incomplete occlusion and maximum cardiac troponin I level of at least 10 ng/mL. The culprit artery was the left anterior descending artery in 20 patients, the right coronary artery in 9, and the circumflex in 4.
A total of 129 patients met criteria for the control group. Of the 323 Hennepin County Medical
Limitations
It is likely that other patients with both left bundle branch block and an acute coronary occlusion were treated at the 3 institutions during this period and were not identified by our methods. All controls did not have angiograms; thus, we cannot rule out acute coronary occlusion, but this seems unlikely with our strict criteria. Some patients were excluded for lack of complete data, and how this might bias the study is unknown. Furthermore, we used angiographic reports. Our definition relied
Discussion
To our knowledge, this is the first and only study to use angiographic endpoints to evaluate the accuracy of the ECG in the diagnosis of acute myocardial infarction in the presence of left bundle branch block. The American College of Cardiology and American Heart Association guidelines for the treatment of STEMI recommend reperfusion therapy for patients with chest pain and new, or presumably new, left bundle branch block.1, 23 The 2004 updated version suggests also using the Sgarbossa ECG
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2023, Journal of ElectrocardiologyCitation Excerpt :In our case, the discordant ST segment depression was considered a sign of occlusive MI, as we factored in the amplitude of the R wave according to Barcelona algorithm. Studies on electrocardiographic identification of MI in RV paced rhythm have placed emphasis on the identification of occlusive MI (OMI). [2] OMI is defined as an acute “culprit” coronary lesion with either 1) TIMI 0 to 1 flow or 2) TIMI 2 to 3 flow that was intervened on and had an associated high peak cardiac troponin level (troponin I > 10 ng/mL or troponin T 1.0 ng/mL).
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Supervising editor: Judd E. Hollander, MD.
Author contributions: SWS conceived and designed the study, oversaw the review of the data for inclusion and exclusions, and drafted the article. SWS, KWD, and DMD participated in data collection. KWD and TDH participated in study design. KWD participated in study conception, reviewed and secured the data, and made and supervised measurements. TDH created and maintains the database at Minneapolis Heart Institute. KWD, TDH, and LAP participated in article preparation. LAP, KWD, and SWS were responsible for data analysis, statistics, presentation of the data, and article review. SWS takes responsibility for the paper as a whole.
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 as per ICMJE conflict of interest guidelines (see www.icmje.org). The authors have stated that no such relationships exist.
Publication date: Available online August 31, 2012.