Tachycardia

Definition

Tachycardia refers to an abnormally rapid heart rate, and in clinical practice this is often taken to be a resting heart rate in excess of 100 beats per minute. Tachycardia may be seen with fever and sympatho-excitation. It also results from specific disorders affecting the generation and transmission of impulses in the electrical conduction system of the heart. With extreme tachycardia cardiac output declines because the high rate of ventricular contraction does not permit adequate flow of blood into the ventricles. Hence, rates in the range of 250–300 beats per minute are unsustainable and carry a high risk of ventricular fibrillation followed by cardiac arrest.