Scenario: This lead II ECG rhythm strip was obtained in a 52-year-old male patient being treated in the neurological intensive care unit for subarachnoid hemorrhage. The patient was unconscious and therefore could not be asked whether he was experiencing symptoms. His vital signs were stable: His blood pressure was 125/70, heart rate was 80 beats per minute (bpm), and he was receiving mechanical ventilation at 20 breaths/minute.

Interpretation: Accelerated junctional rhythm for the first 4 beats, with transition to sinus rhythm at 70 bpm.

There are 2 important characteristics that help diagnose the rhythm presented in this example. In the first 4 beats of the rhythm strip, (1) there are retrograde P waves and (2) the PR interval is shortened (.10 sec). The presence of a retrograde P wave in lead II indicates that the pacemaker impulse was generated below the SA node, in this case the AV node, and...

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