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Sinus Tachycardia (tachy - fast)
Sinus tachycardia occurs when the sinus rhythm is faster than 100 beats per minute. The
rhythm is similar to normal sinus rhythm with the exception that the RR interval is shorter,
less than 0.6 seconds. P waves are present and regular and each P-wave is followed by a QRS
complex in a ratio of 1:1. At very rapid rates, the P-waves might become superimposed on the
preceding T waves such that the P waves are obscured by T waves.
The EKG on the top shows normal sinus rhythm. The EKG at the bottom shows sinus tachycardia
Sinus tachycardia may be accompanied by a decrease in stroke volume because the ventricles do not
have enough time to fill (after atrial systole) before ventricular contraction.. The pulse pressure may
decrease due to a lower stroke volume and decreased time for diastolic run-off.
Sinus tachycardia results from increased automaticity of the SA node, for instance, due to increased
sympathetic stimulation of the heart, fever or cardiac toxicity.