The nurse is reading the cardiac monitor and notes that the patient's heart rhythm is extremely irregular and there are no discernible P waves with a ventricular rate of 90 beats per minute. Which of the following is the patient's rhythm?

Rationale: A. Atrial fibrillation with PACs (premature atrial contractions) is incorrect because PACs are isolated early atrial beats that may cause occasional irregularities but do not produce a sustained, extremely irregular rhythm. In this case, the irregularity is continuous, indicating a persistent arrhythmia rather than occasional PACs. B. Atrial fibrillation is correct because this rhythm is characterized by absence of discernible P waves, irregularly irregular ventricular response, and variable R-R intervals. The ventricular rate of 90 beats per minute is within a controlled range (<100 bpm), which is typical in some patients with atrial fibrillation. The hallmark features of atrial fibrillation include chaotic atrial activity, leading to an irregularly irregular rhythm on the monitor. C. Atrial flutter is incorrect because atrial flutter typically presents with sawtooth-shaped flutter waves (F waves) instead of absent P waves. The ventricular response may be regular or irregular depending on conduction ratios, but the absence of P waves and extremely irregular rhythm points away from flutter. D. Atrial flutter with rapid ventricular response is incorrect because while this can present with a fast ventricular rate, the rhythm is often more regular, and flutter waves (sawtooth pattern) are still visible. The description in this scenario—extremely irregular rhythm with no P waves—does not match atrial flutter.