Abstract | November 9, 2021

Acute ST Elevation Myocardial Infarction with Left Bundle Branch Block: Beyond Sgarbossa and Smith Modified Sgarbossa Criteria

Presenting Author: Ibrahim Mohsin, MD, Internal Medicine Resident PGY2, Department of Medicine, Norton Community Hospital, Norton, VA, Norton, VA

Coauthors: Christos Deamont, DO, Internal Medicine, PGY3, Ballad Health Norton, VA; Arisha Carreon, DO, Internal Medicine, PGY3, Ballad Health Norton, VA; Richard Rhodes DO, Internal Medicine, PGY3, Ballad Health Norton, VA

Learning Objectives

  1. Diagnose and identify patients with STEMI using Sgarbossa and/or Smith Modified Sgarbossa Criteria;
  2. Demonstrate competence in reading EKGs;
  3. Identify; left bundle branch block, paced rhythm and left ventricular hypertrophy on EKG.

Introduction: Incidence of left bundle branch block (LBBB) and acute coronary syndrome (ACS) events are on the rise as the global aging population increases. LBBB frequently has a baseline ST segment elevation (STE) which makes ST segment elevation myocardial infarction (STEMI) challenging to interpret on an electrocardiogram (ECG). Sgarbossa criteria and Smith modified sgarbossa criteria are used to assist in ECG interpretation for diagnosis of STEMI in patients with a baseline LBBB rhythm. Here, we present a case of a 57-year-old male patient whose ECG showed a ST segment elevation that did not meet the Sgarbossa or Smith modified Sgarbossa criteria. However, the patient had elevated troponins and underwent coronary angiogram which revealed total occlusion of the distal left anterior descending artery (LAD). 

Case Presentation: A 57-year-old male with a past medical history of coronary artery disease, ischemic congestive heart failure, hypertension, and hyperlipidemia presented to our emergency department (ED) with complaints of shortness of breath. Six years prior, the patient had an ACS event requiring percutaneous transluminal coronary angioplasty (PTCA) with stenting to mid-LAD and mid-left circumflex (LCX) artery. The patient developed ischemic cardiomyopathy with an ejection fraction of 15%, and follow-up echocardiogram in 2017 revealed normal ejection fraction of 55-60% and grade 1 diastolic dysfunction. The patient had poor follow-up and self-discontinued all medications except for Furosemide. 

The patient presented with complaints of worsening shortness of breath and pleuritic left sided chest pain for two hours. The patient acknowledged progressive dyspnea, paroxysmal nocturnal dyspnea and orthopnea over one month. Initial vital signs in the ED showed elevated blood pressure 190/90 mm Hg, heart rate in 120s, and oxygen saturation of 89% on room air. The physical examination showed elevated jugular venous pressure of 10 cm and bilateral rales at the lung bases. Pertinent laboratory findings included a troponin I of 0.14 (normal <0.03) and B type natriuretic peptide of 1,180. Chest x-ray revealed cardiomegaly and small bilateral pleural effusions with some superimposed pulmonary edema. ECG revealed a rate of 120 beats per minute, a QRS duration of 155 milli seconds, 1–2-millimeter ST segment elevation in V2-V6. Transthoracic echocardiogram revealed an ejection fraction of 15%, severely hypokinetic anterior and lateral walls, and moderate to severely increased left ventricular cavity size. Diagnosis of Non-ST-Elevation Myocardial Infarction (NSTEMI) was made because the STE did not meet Sgarbossa or Smith modified sgarbossa criteria. The patient was given aspirin, clopidogrel, and statin; intravenous heparin was started as per the NSTEMI ACS protocol. Troponin I increased to 9.34 after two hours. The patient was urgently taken for coronary angiogram which revealed patent mid-LAD stent, 100% occlusion of distal LAD, patent mid-LCX stent. Further management was done with balloon angioplasty and stenting of distal LAD with 2.5 x 28 mm size Xience Skypint drug eluding stent (DES). 

Final Diagnosis: Left bundle branch block frequently manifests with baseline ST segment and T-wave deviations due to abnormal depolarization followed by abnormal repolarization and do not necessarily indicate acute ischemia. It is considered an uncomplicated LBBB if secondary repolarization occurs in a direction opposite of the main QRS vector. If discordance is less than 5 mm, then it is also acceptable. Timely diagnosis of STEMI is important to decrease mortality and is assisted by Sgarbossa et al and Smith modified sgarbossa et al criteria. The first two rules of Sgarbossa are the same regarding concordant STE and ST depression of less than 1 mm in precordial leads V1-V3. The third Sgarbossa rule defines 5 mm disconcordant STE in precordial leads. Smith Modified Sgarbossa criteria replaces the third Sgarbossa rule with a ratio of STE to S wave of more than 0.25 in order to increase sensitivity (1), (2). A positive finding in either criteria is diagnostic of STEMI. Although both the criteria are highly specific (90-96%), the sensitivity is around 36% and 91% for Sgarbossa criteria and Smith Modified sgarbossa criteria respectively (3). This wide range of specificity can potentially cause a missed diagnosis of STEMI, as in our case. The serial elevation of troponin I level and regional wall motion abnormalities on echocardiogram prompted urgent coronary angiography in our patient. In order to increase sensitivity for diagnosis of STEMI, we recommend adding new criteria to the existing Sgarbossa and Modified Smith Criteria. These are evidence of significant troponin elevation, rise in STE on serial ECG, regional wall motion abnormality, and new onset of heart failure.