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What is tachycardia?
April 25, 2011 9:47PM
The term is derived from the Greek tachy (fast) and cardia (heart) and is usually defined as a heart rate faster then 100 beats per minute.
Its significance is usually mainly as a sign that something else may be wrong and is only rarely dangerous in and of itself. Times when it can be dangerous include when the ventricles are contracting so fast that they do not have time to fill and pump effectively, and when the resulting increased oxygen demand causes some parts of the heart to not get enough oxygen, resulting in injury to the muscle tissue.
The commonly accepted definition of tachycardia as being above 100 beats per minute was selected by cardiologists in order to make it easier and faster for them to label EKG's in the days before computers calculated the heart rate for them, rather than being based on any study of "normals". Based on modern studies the normal upper limit for resting heart rate is probably closer to 90.
"Relative tachycardia" is when the heart rate is too high considering some circumstance.