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An 86-year-old woman arrived in the emergency department complaining of 1 hour of chest pain. She had a history of myocardial infarction (MI), atrial fibrillation, placement of a dual-chamber pacemaker, stroke, gout, and hypertension.
On arrival, her blood pressure was 88/68 mm Hg, heart rate was 75 beats/min and irregular, respirations were 22/min, and blood oxygen saturation was 97% with 2 L/min supplemental oxygen. She looked uncomfortable and had no appreciable jugular venous distention, no abnormal heart sounds, clear lung fields, trace lower extremity edema, and weak radial pulses. The blood lactate level was 4.0 mg/dL (reference value, <2.3 mg/dL) (to convert to millimoles per liter, multiply by 0.111). A chest radiograph was normal except for pacemaker leads in the expected positions and an enlarged cardiac silhouette. An electrocardiogram (ECG) was obtained (Figure 1).
Arrowheads represent automated computerized interpretation of pacing stimuli.
Large arrowheads identify premature ventricular contractions; small arrowheads identify paced beats.
Prior electrocardiogram demonstrates atrial fibrillation with ventricular pacing without substantial ST deviation. Note the small, ventricular pacer spikes visible in leads V4 through V6.
Vertical lines identify the end of the QRS complex and start of the ST segment. Horizontal dashed lines identify the TP baseline for ST deviation measurement. Lead V1 demonstrates 1 mm concordant ST-segment elevation (STE), diagnostic for acute ST-segment elevation myocardial infarction (MI). Lead V2 demonstrates 4 mm discordant STE with an S-wave amplitude of 3 mm, yielding an ST:S-wave ratio of 4:3 that is diagnostic of acute MI (≥0.25). Lead V3 demonstrates 5 mm discordant STE with an S-wave amplitude of 15 mm, yielding an ST:S-wave ratio of 0.33 that is diagnostic of acute MI.
Comparison of the inferior leads from electrocardiograms obtained 6 weeks before presentation (A) and on arrival at the emergency department (B), revealing new ST-segment elevation (STE). In (B), lead II demonstrates new STE of 2 mm and S-wave amplitude of 14.5 mm, yielding an ST:S wave ratio that is less than 0.25 and therefore not diagnostic of acute myocardial infarction (MI). Lead III demonstrates STE of 4.5 mm and S-wave amplitude of 17.5 mm, yielding an ST:S wave ratio of 0.25, which is diagnostic of acute MI. Lead aVF reveals STE of 4.5 mm and S-wave amplitude of 17.5 mm, yielding an ST:S wave ratio of 0.25, which is diagnostic of acute MI.
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