Electrocardiographic Diagnosis of Acute Myocardial Infarction During Ventricular Pacing
A 51-year-old man presented to the emergency room with a 30-minute history of sudden, severe, crushing retrosternal chest discomfort with radiation to both shoulders. Cardiac risk factors included a history of tobacco abuse and a family history of premature coronary atherosclerosis. A single-chamber pacemaker programmed to the VVI mode had been implanted 12 years earlier for a bradycardia-tachycardia syndrome, and the patient was considered pacemaker dependent. Physical examination was unremarkable. A previous baseline ECG (Figure 1⇓) was compared with the ECG on admission (Figure 2⇓) that showed significant ST-T–segment changes in the interim. The patient underwent emergency coronary angiography that revealed an occluded proximal left circumflex coronary artery with minimal other disease (Figure 3⇓). Primary percutaneous coronary angioplasty was performed, and the remainder of the hospital course was uneventful.
The ECG is the most important source for the early diagnosis of an acute myocardial infarction. This information will influence the decision to restore coronary blood flow with thrombolytic agents or direct angioplasty. Pacing-induced repolarization changes may mask acute myocardial injury. Various ECG criteria have been proposed in the past as indicators for myocardial infarction during ventricular pacing.1 The QRS complex during transvenous right ventricular apical pacing resembles that of spontaneously occurring left bundle-branch block, and the ST-T–segment changes are usually discordant from the QRS complex. From the GUSTO-1 trial experience of 131 patients with acute myocardial infarction in the presence of left bundle-branch block,2 three ECG criteria were found to have independent value in the diagnosis of acute myocardial infarction: ST-segment elevation of ≥1 mm in the presence of a positive QRS complex; ST-segment depression of ≥1 mm in lead V1, V2, or V3; and ST-segment elevation of ≥5 mm in the presence of a negative QRS complex. Although the first two criteria were present in our patient, the sensitivity and specificity of these criteria in the diagnosis of acute myocardial infarction during ventricular pacing are unknown. However, despite the presence of ventricular pacing, the ECG findings with concordant ST-T–segment changes were highly suggestive of myocardial injury.
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
Circulation encourages readers to submit cardiovascular images to Dr Hugh A. McAllister, Jr, St Luke’s Episcopal Hospital and Texas Heart Institute, 6720 Bertner Ave, MC1–267, Houston, TX 77030.
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