Final answer:
The correct documentation for the cardiac rhythm described, which includes a heart rate of 58 bpm and a consistent PR interval of 0.24 seconds, is sinus bradyarrhythmia.
Step-by-step explanation:
The nurse should document the cardiac rhythm as C. sinus bradyarrhythmia. This diagnosis is made based on the following observations: the heart rate is 58 bpm (below the normal range of 60-100 bpm for an adult), P waves are normal in size and shape, the QRS complex is normally shaped and measures 0.08 seconds, indicating that the ventricles are being depolarized normally, and the PR interval is consistent but measures 0.24 seconds, which is slightly longer than the normal range of 0.12-0.20 seconds, yet it still indicates that the conduction from the atria to the ventricles is happening, albeit slightly slower. Therefore, despite the lower heart rate and elongated PR interval, the overall pattern is consistent with a slower than normal but otherwise normal cardiac rhythm originating from the sinoatrial node, known as sinus bradyarrhythmia.