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Chapter 40: ST-Segment Elevation Myocardial Infarction

All of the following electrocardiographic findings can potentially support the diagnosis of a myocardial infarction in the presence of a known old left bundle branch block except:

A. Precordial R-wave regression

B. ST-segment elevation ≥ 1 mm concordant with the QRS complex

C. ST-segment elevation ≥ 5 mm discordant with the QRS

D. ST-segment depression ≥ 1 mm in leads V1, V2, or V3

E. T-wave inversions in the anterior precordial leads

The answer is E. (Hurst’s The Heart, 14th Edition, Chap. 40) New-onset (or not known to be old) LBBB in the setting of chest pain is typically considered and treated as an STEMI. Conversely, the diagnosis of STEMI in the setting of old LBBB can be difficult. Findings suggesting STEMI include (1) a pathologic Q wave in leads I, aVL, V5, or V6 (two leads); (2) precordial R-wave regression (option A is incorrect); (3) late notching of the S wave in V1 to V4; and (4) deviation of the ST segment in the same direction as that of the major QRS deflection.

An analysis of ECG data from the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) I study identified three criteria for diagnosing myocardial infarction in the presence of the LBBB: (1) ST-segment elevation ≥ 1 mm concordant with the QRS complex; (2) ST-segment depression ≥ 1 mm in leads V1, V2, or V3; and (3) ST-segment elevation ≥ 5 mm discordant with the QRS (options B through D are incorrect).1 Such findings are often referred to as the Sgarbossa criteria.

A 55-year-old man with a history of coronary artery disease is brought to the emergency room with chest pain by his wife. His ECG demonstrates ST-segment elevation. Which of the following is true about his initial management?

A. If he presents to a non–PCI-capable hospital, lytic therapy should be administered promptly, in the absence of contraindications, and the patient should emergently be transferred to a PCI-capable hospital for “facilitated PCI”

B. If the patient presents to a PCI-capable hospital, the desired first medical contact (FMC)-to-device time is < 120 minutes

C. If the patient presents to a non–PCI-capable hospital, and the anticipated FMC-to-device time, including transfer to a PCI-capable hospital, is < 120 minutes, then the patient should be transferred for primary PCI without receiving fibrinolysis

D. When PCI is unavailable, a fibrinolytic should be administered within 90 minutes

E. Patients treated successfully with fibrinolysis do not ...

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