Scenario: This ECG (V1 and lead II) was obtained from a 68-year-old woman following cardiac surgery for mitral valve repair. The patient has a history of hypertension as well as mitral valve disease, which had been followed for 10 years. At the time of the electrocardiogram the patient was recovering in the intensive care unit, intubated, sedated, and hemodynamically stable.

Interpretation: Sinus rhythm at 88/min, accelerated junctional escape rhythm at 68/min, P waves suggestive of left atrial enlargement, and ST elevation in lead II suggestive of early repolarization pattern.

Following the second beat the R-to-R interval lengthens slightly from .76 seconds to .92 seconds and a small portion of the P wave is buried in the QRS complex. In situations in which sinus node automaticity is decreased, a lower pacemaker site compensates by generating a beat. Because the width of the QRS complex in this example is normal, this...

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