Sinus tachycardia is caused by a physiologic, pharmacologic or endocrine stimulus. It can be identified by a number of characteristic findings on the electrocardiogram (ECG).
(1) atrial rate
(2) P waves
(3) ventricular rate and rhythm
Atrial rate: 100-200 beats per minute (rarely up to 220)
P waves have a normal morphology and precede every QRS complex. At high atrial rates it may be masked by the preceding T wave.
Ventricular rate: 100-200 beats per minute (each atrial wave is followed by a ventricular contraction) unless an atrioventricular conduction defect is present
Ventricular rhythm is regular.
Indications that apparent sinus tachycardia is due to another cause (Wagner):
(1) prolonged PR interval
(2) abnormal frontal plane P wave axis
(3) P wave inversion
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