As a type of Sinus Rhythm, Sinus Tachycardia will have the prototypical P-QRS-T pattern of Normal Sinus Rhythm and Sinus Bradycardia. The tachy in Sinus Tachycardia means fast. A Sinus Rhythm is fast when its HR is greater than 99 (the highest rate of NSR.)
Sinus Bradycardia is shortened to "sinus tach" by many healthcare providers.
Once a tracing is identified as a Sinus Rhythm with a Heart Rate (HR) of more than 99bpm it can be called Sinus Tachycardia. Sinus Tachycardia means:
An EKG rhythm starting at the SA Node with a rate above 99 which follows the expected electrical path through the heart.
Defining Characteristic of Sinus Tachycardia in Lead II
The only differentiating factor of Sinus Tachycardia from other Sinus Rhythms is the rate:
- Rate: > 99 | R-R Intervals shorter than 0.60sec (15mm) [3 large boxes].
In the below example you can see the maximum R-R Interval (marked in dark green) that a Sinus Tachycardia can have, 15mm (0.60sec) [3 large boxes]. A longer R-R Interval would result in a HR of 99bpm or fewer (making it NSR or Sinus Bradycardia.)
Sinus Tachycardia is in the category of Narrow Complex Tachycardias.
Extremely Fast Rates of Sinus Tachycardia
When the P-QRS-T pattern of all Sinus Rhythm's is present a rhythm is Sinus Tachycardia regardless of how fast it becomes. As the rate of Sinus Tachycardia increases, complexes become closer and closer together. At some point, it becomes impossible to see the details of P and T waves. The specific rate at which this happens varries from case to case.
Once a rhythm reaches a rate where the waves between QRS complexes can't be clearly interpreted it is referred to as Supraventricular Tachycardia.
The above EKG cannot be called a Sinus Tachycardia because the P-QRS-T pattern of Sinus Rhythms is not visible. The S-Q Segment has been highlighted in grey, note how P and T waves are not discernible. In a clinical setting it would be called Supraventricular Tachycardia because the complexes are so frequent that there isn't room for P and T waves to be seen between them.
Below are several more examples of Sinus Tachycardia presented as monitor captures as well as on EKG graphs.
After becoming familiar with identifying Sinus Tachycardia EKG tracings you can read about other Narrow Complex Tachycardias in Supraventricular Tachycardia or review Normal Sinus Rhythm. Head back to our EKG Rhythm Index to find information on another ECG. Otherwise, practice interpreting novel EKGs with our EKG Generator:
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