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Sinus Tachycardia (ST) is sinus rhythm at a rate equal to or greater than 100 bpm i.e.
Rate: Fast (100 bpm)
Rhythm: Regular
P Waves: Normal (upright and uniform)
PR Interval: Normal (0.12–0.20 sec)
QRS: Normal (0.06–0.10 sec)

**Causes:**

 1. Increased physiologic demand for oxygen: Stress, exercise, pain, fever, anemia, hypoxia, and shock
 2. Hyperthyroidism, heart failure, myocardial infarction, pulmonary embolism, medications (eg. atropine, epinephrine, isoproterenol), and excessive caffeine
 3. Physiologic ST commonly observed in neonates

**Treatment:**

Sinus tachycardia may be accompanied by rate-related symptoms, especially in patients with underlying heart disease. Shortened diastolic filling time can result in reduced forward stroke volume and may lead to heart failure. Tachycardia also increases myocardial oxygen demand, which may be detrimental in patients with coronary artery disease.

 1. Therapy should be guided by evaluating accompanying symptomatology (e.g., dizziness, weakness, anginal pain, hypotension). The tachycardia may subside spontaneously if the underlying cause is treated successfully, thereby negating the need for drug therapy.
 2. Consider the use of beta blockers and calcium channel blockers to slow the rate, if necessary, but be aware of the potential side effects of the drug therapy. Specifically, noncardioselective beta blockers (e.g., propranolol) may exacerbate asthma or other pulmonary condition; calcium channel blockers (e.g., iv verapamil) may produce significant hypotension and may also depress inotropic action of the heart leading to heart failure.

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