Warning : Use the following information at your own risk. While accuracy is one my goals, there is always the possibility that some of the information could be wrong. There could be typos. I could also be severely mistaken in some of my knowledge. This site is meant to help clarify certain concepts of ECG and at no point should any life-or-death decision be made based upon the information contained within. Remember, this is just some page on the internet. (If you do find errors, please notify me by feedback.)
The term supraventricular tachycardia (SVT) has at least two different meanings that are commonly in use.
- MORE GENERAL : Any tachycardia that originates in or depends on parts above the ventricles. In other words, any tachycardia that is not from the ventricles. This is mostly used in the context of describing an unknown tachycardia. All tachycardia will fall under the categories of ventricular or supraventricular. Under this definition, sinus tachycardia is a type of supraventricular tachycardia.
- MORE SPECIFIC : This group of rhythms is often called "paroxysmal SVT", or PSVT. A group containing certain tachycardia rhythms (of supraventricular origin) which all have a similar appearance. Some in the rhythms in this group are AV nodal reentrant tachycardia, unifocal atrial tachycardia, and sinus reentry tachycardia. The different rhythms of this group are usually classified under the term SVT because they cannot be easily distinguished from one another.
The term American is similar in that it has two meanings : in its most general sense, it refers to people and things of North America and South America. In the more specific sense of the word, it is used to refer to people and things of the U.S.
Paroxysmal supraventricular tachycardia (PSVT)
We will focus on the second definition of SVT (top of page) right now. This definition includes a number of rhythms- knowledge of each of the individual rhythms is not usually required for someone learning basic ECG interpretation. Instead, be familiar with this group. These rhythms tend to be between the rates of 150-250 and are paroxysmal.
The word paroxysmal means sudden; when used with arrythmias, it denotes one that begins and ends suddenly. This means that someone can go from a normal sinus rhythm to a PSVT with a rate of 180 in only second.
|
|
|
Figure 8-1 : A supraventricular tachycardia (SVT) |
AV nodal reentrant tachycardia (AVNRT)
This is the most common type of PSVT. As the name suggests, this rhythm is due to a reentrant impulse at the site of the AV node.
Because the mechanism depends on the AV node, we can reason that if we were to temporarily disable the AV node, this rhythm might "break," that is, convert to a sinus rhythm. Vagal maneuvers (e.g. carotid sinus massage, breathing against a closed glottis) will often slow conduction down at the AV node to the point that this rhythm breaks. Adenosine is a drug that temporarily blocks conduction in the AV node, also causing this rhythm to break. If it is your job to offer treatment, then check with your local protocols on how to proceed.
AV reentrant tachycardia (with accessory pathway)
Like AVNRT, this type also depends on reentry. However, it involves an accessory pathway. An accessory pathway (in this case) is an abnormal connection between the atria and ventricles. Patients who are prone to this type of PSVT tend to have two pathways : the AV node and this accessory pathway.
Circus movement tachycardia, while sometimes applied to any tachycardia involving a loop, is often used to specifically refer to this rhythm.
Atrial tachycardia
Atrial tachycardia is usually considered a type of PSVT; it can be subdivided even further based on its mechanism. It can be caused by a intra-atrial reentrant circuit or by automaticity (i.e. ectopic pacemaker).
The important thing to note is that these tachycardias are not dependent on the AV node for their survival.
©2004 Mauvila.com