DefinitionThe term supraventricular tachycardia (SVT) refers to any tachydysrhythmia arising from above the level of the Bundle of His, and encompasses regular atrial, irregular atrial, and regular atrioventricular tachycardias Show
Classification
Classification of SVT by site of origin and regularity Regular Atrioventricular
AV Nodal Re-entry Tachycardia (AVNRT)
PathophysiologyIn comparison to AVRT, which involves an anatomical re-entry circuit (Bundle of Kent), in AVNRT there is a functional re-entry circuit within the AV node.
Alrternate re-entry loops: Functional circuit in AVNRT (left), anatomical circuit in AVRT (right) Functional pathways within the AV nodeThere are two pathways within the AV node:
1) A premature atrial contraction (PAC) arrives while the fast pathway is still refractory, and is directed down the slow pathway 2) The ERP in the fast pathway ends, and the PAC impulse travels retrogradely up the fast pathway 3) The impulse continually cycles around the two pathways Initiation of re-entry
Electrocardiographic FeaturesECG features of AVNRT
Associated features include:
Subtypes of AVNRTDifferent subtypes vary in terms of the dominant pathway, and the R-P interval, which is the time between anterograde ventricular activation (R wave) and retrograde atrial activation (P wave).
1. Slow-Fast AVNRT (common type)
ECG features:
Bottom strip: Paroxysmal SVT. The P wave is seen as a pseudo-R wave (circled) in lead V1 during tachycardia. This very short ventriculo-atrial time is frequently seen in typical Slow-Fast AVNRT 2. Fast-Slow AVNRT (Uncommon AVNRT)
ECG features:
3. Slow-Slow AVNRT (Atypical AVNRT)
ECG features:
Summary of AVNRT subtypes
Management of AVNRT
Other types of SVTMost other types of SVT are discussed elsewhere (follow links in classification table). Two less common types include: Inappropriate Sinus Tachycardia
ECG ExamplesExample 1aSlow-Fast (Typical) AVNRT:
The same patient following resolution of the AVNRT:
Slow-Fast AVNRT:
The same patient following resolution of the AVNRT:
Patient with Slow-Fast AVNRT undergoing treatment with adenosine:
Fast-Slow (Uncommon) AVNRT:
The same patient following resolution of the AVNRT:
Fast-Slow AVNRT:
The same patient following resolution of the AVNRT:
Fast-Slow AVNRT:
The same patient following resolution of the AVNRT:
SVT with QRS alternans:
References
Advanced ReadingOnline
Textbooks
LITFL Further Reading
ECG LIBRARYElectrocardiogram
Robert ButtnerMBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner Ed BurnsEmergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library | Is sinus tachycardia considered SVT?Supraventricular tachycardia is a type of tachycardia (heart rate >100 beats per minute) that originates in an area of the heart other than the ventricular area. Supraventricular tachycardias are classified as to origin. The classes include sinus tachycardia, which arises from the sinoatrial node (Fig.
Is tachycardia the same as SVT?SVT is also called paroxysmal supraventricular tachycardia. The typical heart beats about 60 to 100 times a minute. A heart rate of more than 100 beats a minute is called a tachycardia (tak-ih-KAHR-dee-uh).
What are the 3 types of SVT?Types of Supraventricular Tachycardia (SVT). Atrioventricular Node Re-Entrant Tachycardia (AVNRT). Atrioventricular Reciprocating Tachycardia (AVRT). Atrial Tachycardia.. What heart rate is considered SVT?If you have supraventricular tachycardia (SVT) you'll usually feel your heart racing in your chest or throat and a very fast pulse (140-180 beats per minute). You may also feel: chest pain. dizziness.
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