What is chronotropic reserve?

The capacity to increase the heart rate with exercise or other metabolic demands is known as chronotropic reserve. If the heart is unable to increase it as per demand, it is known as chronotropic incompetence. This occurs in sick sinus syndrome as well as during treatment with medicines which suppress the sinus node like beta blockers. Chronotropic reserve can also be reduced if the resting heart rate is already increased due to overactivity of the sympathetic nervous system as in heart failure or hyperthyroidism (increased activity of the thyroid gland, producing excessive amounts of the hormone thyroxine).

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