The nurse is reviewing telemetry for an adult client. Which finding indicates sinus bradycardia?

Sinus bradycardia is a cardiac dysrhythmia originating from the sinoatrial node where the intrinsic pacing rate falls below standard parameters. The electrical conduction pathway remains normal, featuring a regular rhythm with consistent P waves preceding each ventricular depolarization. This lower rate can compromise cardiac output if stroke volume fails to rise to meet systemic metabolic demands. A. No P waves: The absence of distinct P waves indicates a lack of organized atrial depolarization, which is a defining hallmark of atrial fibrillation or junctional rhythms. Sinus rhythms require a functioning sinoatrial node that produces identifiable atrial waveforms before every ventricular beat. This finding rules out a sinus-driven rhythm. B. HR >100 bpm: A resting cardiac frequency exceeding 100 beats per minute constitutes sinus tachycardia, reflecting increased sympathetic nervous system drive or catecholamine exposure. Bradycardia specifically designates a slow, depressed heart rate rather than an accelerated pacing frequency. This value is the exact opposite of bradycardia. C. HR <60 bpm: An adult heart rate dropping below 60 beats per minute fulfills the strict electrocardiographic definition of bradycardia. When paired with standard sinus morphology like upright P waves, it confirms the sinoatrial node is pacing at a decelerated rate. This serves as the primary diagnostic threshold. D. Irregular rhythm: Sinus bradycardia typically maintains a regular, rhythmic cadence because the sinoatrial node discharges at a steady, un-disrupted interval. An irregular, variable rhythm points toward arrhythmias like atrial fibrillation, sinus arrhythmia, or frequent premature contractions. It is inconsistent with standard sinus bradycardia.