Scenario: This 12-lead ECG was obtained in a 79-year-old male patient presenting for an elective cardiac catheterization procedure. The cardiac catheterization was ordered because the patient has experienced increasing chest pain during the past 2 weeks. The patient has a history of coronary artery disease, anterior myocardial infarction (MI), and hypertension.

Interpretation: Normal sinus rhythm at 75 beats per minute with a premature junctional complex (PJC); ST T-wave morphology suggestive of recent anterior myocardial injury; and Q waves in V2 and V3, indicating an anterior infarct.

Looking at the rhythm strip, the R-R interval is regular until the sixth beat, at which time a premature beat occurs. There is a visible P wave prior to the QRS complex; however, the P wave is inverted (lead II), indicating that the impulse was generated outside of the sinus node and then conducted retrogradely (backward) into the atria. The inverted...

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