Introduction

1. Ratio of Discordant ST Segment Elevation or Depression to QRS Amplitude is an Accurate Diagnostic Criterion of Acute Coronary Occlusion in the Presence of Left Bundle Branch Block Kenneth W. Dodd, BS/NREMT-B1,3; Timothy D. Henry, MD2,3; Linda Aramburo, MD1; David Dvorak4, MD; Stephen W. Smith, MD1,3 1Department of Emergency Medicine, Hennepin County Medical Center; 2Minneapolis Heart Institute ; 3University of Minnesota School of Medicine; 4 Fairview Southdale Hospital • Introduction • Left bundle branch block (LBBB) is notorious for obscuring the ECG diagnosis of acute myocardial infarction (AMI) and, therefore, the decision to undergo reperfusion therapy. • Current diagnosis guidelines recommend the Sgarbossacriteria: • Discordant ST segment elevation (STE) of ≥ 5 mm • Concordant STE of ≥ 1 mm • Concordant ST depression (STD) ≥ 1 mm in any of V1 to V3 • However, there are limitations to the Sgarbossa criteria: • CK (± MB) reference standard was used, not angiography • In normal conduction (normal QRS, no LBBB) • Sensitivity of STE for AMI by CK-MB is only 45% • (Sensitivity of STE for AMI by troponin is 20-25%) • Sensitivity of STE for occlusion is 90% (Schmitt et al. Chest 120:1540, 2001) • Proportionality of ST-T to QRS was not considered Results • Discussion • Study Group patients had significantly higher mean STE and ST/QRS ratios as compared to control group patients (Table 1). • ST/QRS < -0.25 yielded true negatives (Fig. 1) and true positives (Fig. 2) on ECGs also correctly diagnosed by Sgarbossa criteria. • However, proportionality must be accounted for when diagnosing AMI in LBBB: • All 9 false positives by the Sgarbossa criteria had deep S waves and subsequently > 5 mm STE. All such cases were true negatives by the ST/QRS < -0.25 criteria (Fig. 3). • Five (5) of 9 false negatives by the Sgarbossa criteria had shallow S waves and subsequently < 5 mm STE. Such cases were true positives by ST/QRS < -0.25 criteria (Fig. 4). • The only false negative by ST/QRS < -0.25 was negative by Sgarbossa as well. • ST/QRS < -0.25 was significantly more sensitive and accurate for the diagnosis of acute coronary occlusion of any artery than the Sgarbossa criteria (Table 2). • ST/QRS < -0.25 or Sgarbossa 2 or 3 was significantly more sensitive and accurate than the Sgarbossa criteria (Table 2). • Original hypothesis was significantly more sensitive than the Sgarbossa criteria (Table 2). • ST/QRS < -0.25 in 2 or more leads was significantly more specific and accurate than the Sgarbossa criteria (Table 2). • If confirmed with a validation study, this ST/QRS ratio < -0.25 may provide an important tool to determine the need for immediate reperfusion and also to prevent the potential risks associated with immediate reperfusion therapy in the absence of occlusion. • Study Group (n = 34) • Mean age = 73 • Troponin I measured in 28 patients: • 28 patients (100%) > 0.3 ng/ml • Control Group (n=130) • Mean age = 67 • Troponin I measured in 116 patients: • 39 (34%) with troponin I ≥ 0.1 ng/ml • 22(19%) > 0.3 ng/ml • 77 (66%) < 0.1 ng/ml (negative) Fig 2. True (+) by both: ≥ 5mm STE and ST/QRS ratio = 6/-16 = -0.38 Fig1. True (-) by both: < 5 mm STE, no concordance and ST/QRS ratio = 2/-12 = -0.17 Fig 4. False (-) by Sgarbossa: 4mm STE in V3 True (+) by ST/QRS ratio: -0.33 in V3 and V4 Baseline STE was 2 mm STE, ST/QRS = 2/-12 = -0.17 Fig 3. False (+) by Sgarbossa: 6 mm STE in V2; True (-) by ST/QRS ratio: 6/-63 = -0.10 in V2 Table 1. ST Segment Deviation • Hypothesis • Combination of ratio of excessively discordant STE as measured by amplitude ratios (ST/QRS) < -0.25 in any one lead or any concordant STE, or STD in V1-V3, is superior to the Sgarbossa crit. • We also attempted to derive a still better rule by solely examining • ST/QRS < -0.25 in any one lead. Table 2. Comparison of Diagnostic Criteria Methods Records of consecutive patients (pts) with LBBB and chest pain and/or dyspnea who presented to the ED at one of three hospitals, and were taken to the catheterization lab for suspected STEMI, were reviewed by reviewers blinded to the ECGs. Study group pts had a cardiac catheterization report supporting acute coronary occlusion (TIMI-0 or -1 flow) at the time of the ECG. Controls had no evidence of occlusion. Non-STE MI pts were included as controls if acute occlusion could be excluded. Exclusions from both groups were: hyperkalemia, respiratory distress, and unreadable ECG. ECGs recorded at the time of symptoms were blindly compared. Measurements included ST segment at the J-point and QRS amplitude relative to the TP segment in all 12 leads. The highest discordant ST/QRS ratio of all leads was selected for each ECG. Statistics were by Fisher’s exact test and Student’s t-test. Conclusions When acute coronary occlusion occurs with LBBB, a discordant ST/QRS ratio < -0.25 is significantly more sensitive and accurate for the diagnosis of acute coronary occlusion than the Sgarbossa criteria, and may guide reperfusion decisions. Further research should be done to determine if thrombolysis, in the absence of any concordant STE, is contraindicated when the ST/QRS ratio is low.