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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).

In sinus tachycardia, the sinus node accelerates and initiates an impulse at a rate of 100 times per minute or more (see Fig. 17-19B). The upper limits of sinus tachycardia extend to 160 to 180 beats/min. All other ECG characteristics, except for heart rate, are the same as in normal sinus rhythm.
Sinus tachycardia is usually caused by factors relating to an increase in sympathetic tone. Stress, exercise, and stimulants such as caffeine and nicotine can produce this dysrhythmia. Sinus tachycardia is also associated with such clinical problems as fever, anemia, hyperthyroidism, hypoxemia, heart failure, and shock. Drugs, such as atropine, which blocks vagal tone, and the catecholamines (eg, epinephrine, dopamine) also can produce this rhythm.
The cause of the sinus tachycardia and the underlying state of the myocardium determine the prognosis. Sinus tachycardia alone is not a lethal dysrhythmia but often signals an underlying problem that should be pursued. In addition, the rapid rate of sinus tachycardia increases oxygen demands on the myocardium and decreases the filling time of the ventricles. In people who already have depleted cardiac reserve, ischemia, or heart failure, the persistence of a fast rate may worsen the underlying condition.
Treatment of sinus tachycardia is usually directed at eliminating the underlying cause. Specific measures may include sedation, oxygen administration, digitalis, and diuretics if heart failure is present, or β-blockers if the tachycardia is caused by thyrotoxicosis.