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
Supraventricular tachycardia (SVT): Rhythm strip demonstrating a regular, narrow-complex tachycardia 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:
Mechanism of re-entry in “slow-fast” AVNRT: 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:
Top strip: Normal sinus rhythm. Absence of pseudo-R waves 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:
Pseudo R’ waves in V1-2 Example 1b The same patient following resolution of the AVNRT:
Pseudo R’ waves in V1-2 have resolvedExample 2a Slow-Fast AVNRT:
The same patient following resolution of the AVNRT:
Patient with Slow-Fast AVNRT undergoing treatment with adenosine:
Fast-Slow (Uncommon) AVNRT:
Retrograde P wavesExample 4b The same patient following resolution of the AVNRT:
Retrograde P waves Example 5a Fast-Slow AVNRT:
Upright retrograde P waves in aVR Inverted retrograde P waves lead IIExample 5b The same patient following resolution of the AVNRT:
Retrograde P waves in aVR resolved Retrograde P waves in lead II resolvedExample 6a Fast-Slow AVNRT:
Inverted retrograde P waves in lead II Upright retrograde P waves in V2Example 6b
The same patient following resolution of the AVNRT:
Retrograde P waves in lead II have resolved Retrograde P waves in V2 have resolvedExample 7 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 | What is the difference between tachycardia and sinus tachycardia?When you have tachycardia, your heart rate is faster than 100 beats per minute. With sinus tachycardia, electrical signals from your heart's sinoatrial (SA) node are telling your heart to beat faster than normal.
Is SVT and tachycardia the same thing?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 defines a supraventricular tachycardia?Supraventricular tachycardia (SVT) is a condition where your heart suddenly beats much faster than normal. It's not usually serious, but some people may need treatment.
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