In sinus tachycardia, the sinus node accelerates and initiates an impulse at a rate of 100 times per minute or more (see Fig.In people who already have depleted cardiac reserve, ischemia, or heart failure, the persistence of a fast rate may worsen the underlying condition.In addition, the rapid rate of sinus tachycardia increases oxygen demands on the myocardium and decreases the filling time of the ventricles.Specific measures may include sedation, oxygen administration, digitalis, and diuretics if heart failure is present, or ?-blockers if the tachycardia is caused by thyrotoxicosis.Sinus tachycardia is also associated with such clinical problems as fever, anemia, hyperthyroidism, hypoxemia, heart failure, and shock. 17-19B).