Sinus Tachycardia
Sinus Tachycardia is a Sinus Rhythm with a rate greater than 99bpm and is otherwise identical to NSR. This fast rate results in short RR Intervals on the EKG tracing and more frequent complexes per length.
As a type of Sinus Rhythm, Sinus Tachycardia will have the prototypical P-QRS-T pattern of Normal Sinus Rhythm. The tachy in Sinus Tachycardia means fast. A Sinus Rhythm is fast when its heart rate is greater than 99 beats per minute (bpm): the fastest rate of NSR.
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 heart rate:
- RR Intervals less than 0.60sec (15mm) [3 large boxes] in duration.
In the below example (fig. 1) R Waves are marked with black triangles and several RR Intervals are labeled. The distance between two R Waves is the RR Interval. The maximum RR Interval that a Sinus Tachycardia can have is 15mm (0.60sec) [3 large boxes]. A longer RR Interval would result in a HR of 99bpm or lower.
Sinus Tachycardia is in the category of Narrow Complex Tachycardia.
Very Fast Rates of Sinus Tachycardia
When the P-QRS-T pattern of Sinus Rhythm is present and the rate is over 99bpm, a rhythm is Sinus Tachycardia, regardless of how fast it becomes. However, as the rate of Sinus Tachycardia increases, complexes become closer and closer together. At a certain point, P Waves may start to be slurred or buried in preceding T Waves, which can make identifying them more difficult. In the below example (fig. 2) of Sinus Tachycardia P Waves are marked with green triangles. Note that P Waves begin before T Waves have returned to baseline. The P Waves are buried in the final portion of the preceding T Waves.
Slurred and buried are terms used to describe when two waves of the tracing overlap. If two waves occur at the same time, the EKG displays the average of the two during the overlap. This is usually described as the smaller wave (often the P Wave) being slurred or burried in the larger wave (often the T Wave or QRS Complex).
As long as P Waves can be identified, even if they are buried or slurred into the preceding T Waves, the rhythm can be interpreted as Sinus Tachycardia.
Extremely Fast Rates of Sinus Tachycardia
At some point, it becomes impossible to see the details of P and T Waves. The specific rate at which this happens varies 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.
Supraventricular Tachycardia (SVT) is a category of all tachycardic rhythms that originate above the ventricles. This means that Sinus Tachycardia is an SVT all of the time. In practice, the term SVT is only used if the specific type of SVT cannot be identified due to the extreme rate. So, if upright, uniform P Waves can be identified before every QRS Complex, Sinus Tachycardia is the correct interpretation.
The above EKG (fig. 3) cannot be called a Sinus Tachycardia because the P-QRS-T pattern of Sinus Rhythms is not visible. The segment between QRS Complexes has been marked by green triangles; 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 is not room for P and T waves to be seen between them.
Physiologically, this example (fig. 3) may be Sinus Tachycardia, but that cannot be determined from this tracing, so the more general category (SVT) is used in interpretation.
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 ECG 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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