Supra in Supraventricular Tachycardia is Latin for above and references the origin of the electrical signal "above the ventricles." Tachycardia applies to any rhythm with a Heart Rate (HR) of 100 or more. As a category, Supraventricular Tachycardia technically includes such rhythms as Sinus Tachycardia and Junctional Tachycardia. Both of those examples are tachycardic rhythms with origins above (superior to) the ventricles (Sinus and Junctional origins, respectively.)
However, in clinical practice the term Supraventricular Tachycardia is reserved for EKG tracings which are too fast to differentiate which specific origin is present. While a high HR and narrow QRS Complex (origin above the ventricles) are easy to recognize, SVT is defined by not being able to identify the specific origin. This is because, at high rates, waves become so close together that they can obscure one another.
Supraventricular Tachycardia can also be called Narrow Complex Tachycardia.
The origin of an electrical signal is marked by the first feature of the repeating complex on an EKG. In order to recognize this, QRS complexes must be spaced far enough apart to expose details between them. As the HR increases waves become overlapping, sometimes making it impossible to determine specifics.
You will hear clinicians talk about "looking for the underlying rhythm of an SVT" which is: attempting to further classify a Supraventricular Tachycardia into a specific cardiac rhythm. Some treatments of SVT can cause a pause in the extremely fast rate allowing interpretation of the "underlying rhythm" and thereby guiding further treatment.
See your clinical textbook for further information as interventions are out of the scope of this page.
Once a clinician has identified that an EKG does not have enough information visible to determine which specific tachycardia is present, the tracing can be called the more general Supraventricular Tachycardia. Supraventricular Tachycardia means:
A tachycardic ECG tracing with narrow QRS complexes (non-ventricular origin) on which there is not enough information to make a more specific interpretation.
The factors that define a Supraventricular Tachycardia are:
- Rate: > 99 | R-R Intervals shorter than 0.60sec (15mm) [3 large boxes].
- QRS Complexes: Maximum 0.12sec (3mm) [3 small boxes].
More important than meeting these criteria though is the absence of a clearly defined electrical origin.
The Rates of Supraventricular Tachycardia
Some textbooks report SVT as being a Narrow Complex Tachycardia with a HR above 160. While this simplification is understandible, the interpretation of an EKG as SVT in a clinical setting is not based on its rate alone. A high rate and narrow QRS complex are required but an EKG would only be described as SVT if there was no clear origin of the electrical signal.
As a tachycardia, SVT must have a rate of at least 100. In practice, only excessive rates of tachycardia obscure the origin of a cardiac rhythm, generally over 160. At rates below this the origin of a rhythm is usually visible between complexes and the specific Supraventricular Tachycardia (e.g. Sinus Tachycardia, Atrial Fibrillation with RVR, etc.) can be named.
While a specific rate isn't the determining factor of SVT's it is the high rate (frequent QRS complexes) which obscures other waveforms from interpretation.
QRS Complexes in SVT
The QRS complex in Supraventricular Tachycardia's are normal, as defined in the prototypical NSR:
- QRS Complexes: Maximum 0.12sec (3mm) [3 small boxes]
Normal QRS Complexes (< 0.12sec (3mm) [3small boxes]) as defined in NSR are also called narrow.
QRS Complexes which are longer than 0.12sec (3mm [3small boxes]) are called wide.
The narrow QRS complex of Supraventricular Tachycardia is confirmation of the supraventricular origin of the electrical signal. Electrical origins in the ventricles create wide QRS Complexes, so Narrow Complex Tachycardias are always of supraventricular origin.
The Unclear supraventricular Origin of SVT's
The key hallmark of Supraventricular Tachycardia is the indistinct origin. Narrow (< 0.12sec [3mm]) QRS Complexes indicate the origin above the ventricles, but the area where P Waves, fibrillation waves, or baseline would be is obscured by the end of the previous complex (marked in green above.)
The above tracing could be a Sinus Tachycardia, an Atrial Fibrillation with a Rapid Ventricular Response, or a Junctional Tachycardia, there is simply not enough information present to differentiate. This is the case when an EKG would be called only Supraventricular Tachycardia, until a specific underlying rhythm could be identified.
Below are several more examples of Supraventricular Tachycardia presented as monitor captures as well as on EGK graphs.
Once you're comfortable with the category of Supraventricular Tachycardia take a look at at Atrial Fibrillation or Sinus Tachycardia, two rhythms which may present as SVT when they have excessive rates. Or head back to our EKG Rhythm Index to find information on another ECG. Otherwise, practice interpreting novel EKG's with our EKG Generator:
Basic EKG App
Our Basic EKG Generator is free with an email signup and covers Normal Sinus Rhythm along with common arrhythmia.
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Our Pro EKG Generator covers over 40 different rhythm categories, multiple display options, has Quiz and Simulation modes, and more! Try it out for just $5 for a month.