1. Sinus bradycardia usually does not require specific treatment unless the heart rate is below 50 and there is evidence of hypoperfusion.
2. Therapy should begin with atropine as previously described. Most patients will respond to one or two doses.
3. Isoproterenol can be used if atropine is ineffective.
4. External cardiac pacing can be used in the patient refractory to atropine or isoproterenol.
5. Internal pacing is required in the patient with symptomatic recurrent or persistent sinus bradycardia.
SINUS TACHYCARDIA Sinus tachycardia originates from acceleration of the sinus node discharge rate. The ECG characteristics of sinus tachycardia are (1) normal sinus P waves and PR intervals and (2) an atrial rate usually between 100 and 160 ( Fig 24-6).
Clinical Significance Sinus tachycardia represents an acceleration of the sinus node discharge rate, usually in response to three categories of stimuli: (1) physiologic (infants and children, exertion, anxiety, emotions), (2) pharmacologic (atropine, epinephrine and other sympathomimetics, alcohol, nicotine, caffeine), or (3) pathologic (fever, hypoxia, anemia, hypovolemia, pulmonary embolism). In many of these conditions, the increased heart rate is due to an effort to increase cardiac output to match increased circulatory needs.
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