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. The ventricular rate is 90 beats per minute, and the patient is hemodynamically stable. The nurse realizes that the patient's rhythm is:

A. Atrial flutter typically presents with regular atrial activity, often at a rate of 250–350 beats per minute, producing sawtooth “flutter” waves on the ECG. The ventricular response can be regular or irregular, but the defining feature is the visible flutter waves, which are not present in this patient. B. Rapid ventricular response occurs when the ventricular rate exceeds 100–150 beats per minute. In this patient, the ventricular rate is 90 bpm, which is within normal limits, making rapid response unlikely. Additionally, flutter waves are absent. C. Atrial tachycardia is a regular rhythm originating from an ectopic atrial focus, usually with distinct P waves preceding each QRS. This patient’s rhythm is extremely irregular and lacks discernible P waves, so atrial tachycardia is not consistent with the findings. D. Atrial fibrillation is characterized by completely irregular rhythm, absent P waves, and fibrillatory waves that are too fine to discern. The ventricular rate is variable and can be slow, normal, or rapid. This patient is hemodynamically stable, and the ventricular rate of 90 bpm is consistent with controlled atrial fibrillation.