Which statements correctly define tachycardia and bradycardia thresholds?

• A. Tachycardia: heart rate greater than 100 beats per minute; Bradycardia: heart rate less than 60 beats per minute.
• B. Tachycardia: HR greater than 90; Bradycardia: HR less than 50.
• C. Tachycardia: HR greater than 110; Bradycardia: HR less than 70.
• D. Tachycardia: HR greater than 100; Bradycardia: HR less than 50.

Answer: (A)

Tachycardia and bradycardia thresholds are about where the heart rate moves outside the normal resting range. In adults, a normal resting heart rate is roughly 60–100 beats per minute. Tachycardia is defined as a heart rate greater than 100 bpm, and bradycardia as a heart rate less than 60 bpm. This pairing correctly separates typical normal variation from clinically significant fast or slow heart rates. Other thresholds (like 90 for tachycardia or 50 for bradycardia, or 110 with 70) don’t align with standard definitions, since 70 bpm is not bradycardic and would misclassify many normal or mildly elevated rates.