Which sinus rhythm indicates a heart rate of less than 60 bpm?

The correct choice indicates sinus bradycardia, which is characterized by a heart rate of less than 60 beats per minute (bpm). This rhythm occurs when the heart's natural pacemaker, the sinoatrial node, generates impulses slower than normal. While normal sinus rhythm (often referred to as NSR) typically maintains a rate of 60 to 100 bpm, bradycardia specifically refers to any heart rate that falls below this threshold. Understanding this distinction is crucial for monitoring cardiac health, as bradycardia can be a sign of various underlying conditions or a response to physiological factors, such as rest or medication effects. Recognizing sinus bradycardia allows healthcare professionals to assess and manage patient care appropriately based on the patient's overall clinical context.