ECG Analysis - NCLEX-PN

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Question

You are taking care of an elderly patient who is hospitalized for sudden onset of severe, diffuse abdominal pain out of proportion to the patient's abdominal physical exam that is also accompanied by rectal bleeding and palpitations. You obtain an ECG and notice a tachycardic, irregularly irregular rhythm without any distinct P waves. Which of the following is the most likely cardiac rhythm seen on this patient's ECG?

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Answer

The most likely cardiac rhythm on this patient's ECG is a trial fibrillation.

Atrial fibrillation is a tachyarrhythmia that is characterized on ECG by absence of distinct P waves, oscillating "f" waves that cause an irregular baseline rhythm, and abnormal, inconsistent R-R intervals that produce an irregularly irregular rhythm.

When a patient is in atrial fibrillation, the patient may be asymptomatic, but at other times, the patient may complain of a rapid heartbeat, or a feeling of uneasiness. The clues in this case that the patient is in atrial fibrillation are that the ECG shows the characteristic irregularly irregular rhythm, with an absence of any distinct P waves.

Clinically, the other clues are that the patient is complaining of palpitations while simultaneously experiencing sudden onset of severe, diffuse abdominal pain that is out of proportion to the abdominal physical exam, and is accompanied by rectal bleeding. This is very consistent with mesenteric ischemia (a condition in which a patient, typically in atrial fibrillation, projects a blood clot to one of the mesenteric vessels, causing ischemia to the bowel served by the affected vessel). While, this was not asked in the question explicitly, and the question could be answered without this knowledge, this helps confirm the diagnosis if you are aware of it.

The other answers are incorrect for the following reasons:

  1. Atrial flutter typically presents with a "sawtooth" waveform and has more regularity in wavelength.

  2. Sick sinus syndrome is also known as tachy-brady syndrome, indicating that the patient has frequent fluctuations between tachycardia and bradycardia. In this instance, we have ECG findings that are very consistent with atrial fibrillation and show no evidence of bradycardia.

  3. First-degree heart block and complete heart block are each typically characterized by bradycardia rather than tachycardia, and do not appear like atrial fibrillation on ECG.

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