Scenario: This ECG (lead V2) was obtained from a 90-year-old woman presenting to the emergency department with complaints of “dizziness.” The patient’s only history includes weekly dialysis for renal insufficiency; otherwise she had been healthy and living independently. The patient’s vital signs are normal: blood pressure 135/43 mm Hg, respirations 18/min, and O2 saturation 100% via pulse oximetry.

Third-degree atrioventricular (AV) block with junctional escape rhythm

Although the second, third, and sixth QRS complexes appear to have a P wave associated with them, careful evaluation of the entire strip indicates several problems: (1) the atrial rate is faster than the ventricular rate (atrial = 82/min, ventricular = 33/min), (2) there are more P waves than QRS complexes, and (3) none of the P waves are associated with any QRS complex.

Together these criteria indicate complete AV dissociation, meaning the atria and ventricles are functioning independently. The terms...

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