What heart rate qualifies as sinus tachycardia?

Sinus tachycardia is defined as a rapid heart rate originating from the sinoatrial node, which is the natural pacemaker of the heart. Specifically, sinus tachycardia is diagnosed when the heart rate exceeds 100 beats per minute (BPM) in adults. This increase in heart rate can occur in response to various physiological triggers, such as exercise, stress, fever, or dehydration, which stimulate the body's sympathetic nervous system.

As the heart rate surpasses 100 BPM, the cardiac output can increase to meet the elevated metabolic demands of the body. It's important to distinguish sinus tachycardia from other forms of tachycardia that may arise from pathological conditions. The characteristic features of sinus tachycardia include a regular rhythm and P waves precede each QRS complex on an ECG, indicating that the heart is still being driven by the sinus node.

While heart rates below 60 BPM signify bradycardia and rates between 60-100 BPM fall within the normal sinus rhythm range, anything above 100 BPM qualifies as sinus tachycardia, making this option the correct answer.