Supraventricular Tachycardia (SVT) • LITFL • ECG Library Diagnosis

Definition

The 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

• It is often used synonymously with AV nodal re-entry tachycardia (AVNRT), a form of SVT
• In the absence of aberrant conduction (e.g. bundle branch block), the ECG will demonstrate a narrow complex tachycardia
• Paroxysmal SVT (pSVT) describes an SVT with abrupt onset and offset – characteristically seen with re-entrant tachycardias involving the AV node such as AVNRT or atrioventricular re-entry tachycardia (AVRT)

Supraventricular tachycardia (SVT): Rhythm strip demonstrating a regular, narrow-complex tachycardia

Classification

• SVTs can be classified based on:
  • Site of origin (atria or AV node) or;
  • Regularity (regular or irregular)
• Classification based on QRS width is unhelpful as this is also influenced by the presence of pre-existing bundle branch block, rate-related aberrant conduction, or presence of accessory pathways.

Classification of SVT by site of origin and regularity

Regular Atrioventricular

• AVRT
• AVNRT
• Automatic junctional tachycardia

AV Nodal Re-entry Tachycardia (AVNRT)

• This is the commonest cause of palpitations in patients with structurally normal hearts
• AVNRT is typically paroxysmal and may occur spontaneously or upon provocation with exertion, caffeine, alcohol, beta-agonists (salbutamol) or sympathomimetics (amphetamines)
• It is more common in women than men (~ 75% of cases occurring in women) and may occur in young and healthy patients as well as those suffering chronic heart disease
• Patients will typically complain of the sudden onset of rapid, regular palpitations. Other associated symptoms may include:
  • Presyncope or syncope due to a transient fall in blood pressure
  • Chest pain, especially in the context of underlying coronary artery disease
  • Dyspnoea
  • Anxiety
  • Rarely, polyuria due to elevated atrial pressures causing release of atrial natriuretic peptide
• The tachycardia typically ranges between 140-280 bpm and is regular in nature. It may self-resolve or continue indefinitely until medical treatment is sought
• The condition is generally well tolerated and is rarely life threatening in patients with pre-existing heart disease

Pathophysiology

In 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 node

There are two pathways within the AV node:

• The slow pathway (alpha): a slowly-conducting pathway with a short refractory period.
• The fast pathway (beta): a rapidly-conducting pathway with a long refractory period.

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

• During normal sinus rhythm, electrical impulses travel down both pathways simultaneously. The impulse transmitted down the fast pathway enters the distal end of the slow pathway and the two impulses cancel each other out
• However, if a premature atrial contraction (PAC) arrives while the fast pathway is still refractory, the electrical impulse will be directed solely down the slow pathway (1)
• By the time the premature impulse reaches the end of the slow pathway, the fast pathway is no longer refractory, and the impulse is permitted to recycle retrogradely up the fast pathway (2)
• This creates a circus movement whereby the impulse continually cycles around the two pathways, activating the Bundle of His anterogradely and the atria retrogradely (3)
• The short cycle length is responsible for the rapid heart rate
• This most common type of re-entrant circuit is termed Slow-Fast AVNRT
• Similar mechanisms exist for the other types of AVNRT

Electrocardiographic Features

ECG features of AVNRT

• Regular tachycardia ~140-280 bpm
• Narrow QRS complexes (< 120ms) unless there is co-existing bundle branch block, accessory pathway, or rate-related aberrant conduction
• P waves if visible exhibit retrograde conduction with P-wave inversion in leads II, III, aVF. They may be buried within, visible after, or very rarely visible before the QRS complex

Associated features include:

• Rate-related ST depression, which may be seen with or without underlying coronary artery disease
• QRS alternans – phasic variation in QRS amplitude associated with AVNRT and AVRT, distinguished from electrical alternans by a normal QRS amplitude

Subtypes of AVNRT

Different 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 (80-90%)
2. Fast-Slow AVNRT (10%)
3. Slow-Slow AVNRT (1-5%)

1. Slow-Fast AVNRT (common type)

• Accounts for 80-90% of AVNRT
• Associated with slow AV nodal pathway for anterograde conduction and fast AV nodal pathway for retrograde conduction
• The retrograde P wave is obscured in the corresponding QRS or occurs at the end of the QRS complex as pseudo R’ or S waves

ECG features:

• P waves are often hidden – being embedded in the QRS complexes
• Pseudo R’ wave may be seen in V1 or V2
• Pseudo S waves may be seen in leads II, III or aVF
• In most cases this results in a ‘typical’ SVT appearance with absent P waves and tachycardia

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)

• Accounts for 10% of AVNRT
• Associated with Fast AV nodal pathway for anterograde conduction and Slow AV nodal pathway for retrograde conduction
• Due to the relatively long ventriculo-atrial interval, the retrograde P wave is more likely to be visible after the corresponding QRS

ECG features:

• QRS-P-T complexes
• Retrograde P waves are visible between the QRS and T wave

3. Slow-Slow AVNRT (Atypical AVNRT)

• 1-5% AVNRT
• Associated with Slow AV nodal pathway for anterograde conduction and Slow left atrial fibres as the pathway for retrograde conduction.

ECG features:

• Tachycardia with a P-wave seen in mid-diastole, effectively appearing “before” the QRS complex.
• May be misinterpreted as sinus tachycardia

Summary of AVNRT subtypes

• No visible P waves? –> Slow-Fast
• P waves visible after the QRS complexes? –> Fast-Slow
• P waves visible before the QRS complexes? –> Slow-Slow

Management of AVNRT

• May respond to vagal maneuvers with reversion to sinus rhythm.
• The mainstay of treatment is adenosine
• Other agents which may be used include calcium-channel blockers, beta-blockers and amiodarone
• DC cardioversion is rarely required
• Catheter ablation may be considered in recurrent episodes not amenable to medical treatment.

Other types of SVT

Most other types of SVT are discussed elsewhere (follow links in classification table). Two less common types include:

Inappropriate Sinus Tachycardia

• Typically seen in young healthy female adults
• Sinus rate persistently elevated above 100 bpm in absence of physiological stressor
• Exaggerated rate response to minimal exercise
• ECG indistinguishable from sinus tachycardia

Sinus Node Reentrant Tachycardia (SNRT)

• Caused by reentry circuit close to or within the sinus node
• Abrupt onset and termination
• P wave morphology is normal
• Rate usually 100 – 150 bpm
• May terminate with vagal manoeuvres

ECG Examples

Example 1a

Slow-Fast (Typical) AVNRT:

• Narrow complex tachycardia at ~ 150 bpm
• No visible P waves
• There are pseudo R’ waves in V1-2

Pseudo R’ waves in V1-2

Example 1b

The same patient following resolution of the AVNRT:

• Sinus rhythm
• The pseudo R’ waves have now disappeared

Pseudo R’ waves in V1-2 have resolved

Example 2a

Slow-Fast AVNRT:

• Narrow complex tachycardia ~ 220 bpm
• No visible P waves
• Subtle notching of the terminal QRS in V1 (= pseudo R’ wave)
• Widespread ST depression — this is a common electrocardiographic finding in AVNRT and does not necessarily indicate myocardial ischaemia, provided the changes resolve once the patient is in sinus rhythm

Example 2b

The same patient following resolution of the AVNRT:

• Sinus rhythm
• Pseudo R’ waves have disappeared
• There is residual ST depression in the inferior and lateral leads (most evident in V4-6), indicating that the patient did indeed have rate-related myocardial ischaemia (± NSTEMI)

Example 3

Patient with Slow-Fast AVNRT undergoing treatment with adenosine:

• The top rhythm strip shows AVNRT with absent P waves and pseudo R’ waves clearly visible
• The middle strip shows adenosine acting on the AV node to suppress AV conduction — there are several broad complex beats which may be aberrantly-conducted supraventricular impulses or ventricular escape beats (this is extremely common during administration of adenosine for AVNRT)
• The bottom section shows reversion to sinus rhythm; the pseudo R’ waves have resolved.

Example 4a

Fast-Slow (Uncommon) AVNRT:

• Narrow complex tachycardia ~ 120 bpm.
• Retrograde P waves are visible after each QRS complex — most evident in V2-3.

Retrograde P waves

Example 4b

The same patient following resolution of the AVNRT:

• Now in sinus rhythm.
• The retrograde P waves have disappeared.

Retrograde P waves

Example 5a

Fast-Slow AVNRT:

• Narrow complex tachycardia ~ 135 bpm.
• Retrograde P waves following each QRS complex — upright in aVR and V1; inverted in II, III and aVL.

Upright retrograde P waves in aVRInverted retrograde P waves lead II

Example 5b

The same patient following resolution of the AVNRT:

• Sinus rhythm
• The retrograde P waves have disappeared

Retrograde P waves in aVR resolvedRetrograde P waves in lead II resolved

Example 6a

Fast-Slow AVNRT:

• Narrow complex tachycardia at ~ 125 bpm
• Retrograde P waves follow each QRS complex: upright in V1-3; inverted in II, III and aVF

Inverted retrograde P waves in lead IIUpright retrograde P waves in V2

Example 6b

The same patient following resolution of the AVNRT:

• Sinus rhythm.
• Retrograde P waves have disappeared.

Retrograde P waves in lead II have resolvedRetrograde P waves in V2 have resolved

Example 7

SVT with QRS alternans:

• Narrow complex tachycardia ~ 215 bpm
• Retrograde P waves are visible preceding each QRS complex (upright in V1, inverted in lead II)
• There is a beat-to-beat variation in the QRS amplitude without evidence of low voltage (= QRS alternans)
• The PR interval is ~ 120 ms, so this could be either a low atrial tachycardia or possibly an AVNRT with a long RP interval (i.e. either Fast-Slow or Slow-Slow varieties)

• Sinus tachycardia
• Atrial tachycardia
• Atrioventricular re-entry tachycardia (AVRT)
• Atrial flutter
• Atrial fibrillation
• Multifocal atrial tachycardia
• VT versus SVT with aberrancy

References

• Jazayeri MR, Massumi A, Mihalick MJ, Hall RJ. Sinus node reentry: case report and review of electrocardiographic and electrophysiologic features. Tex Heart Inst J. 1985 Sep;12(3):249-52
• Fox DJ, Tischenko A, Krahn AD, Skanes AC, Gula LJ, Yee RK, Klein GJ. Supraventricular tachycardia: diagnosis and management. Mayo Clin Proc. 2008 Dec;83(12):1400-11

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Hampton J. The ECG Made Practical 7e, 2019
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
• Smith SW. The ECG in Acute MI. 2002 [PDF]

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest

Cite this article as: Robert Buttner and Ed Burns, “Supraventricular Tachycardia (SVT),” In: LITFL – Life in the FastLane, Accessed on June 22, 2023, https://litfl. com/supraventricular-tachycardia-svt-ecg-library/.

Robert Buttner

MBBS (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 Burns

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

Paroxysmal Supraventricular Tachycardia (SVT, PSVT) – Heart and Blood Vessel Disorders

By

L. Brent Mitchell

, MD, Libin Cardiovascular Institute of Alberta, University of Calgary

Reviewed/Revised Jan 2023

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Topic Resources

Paroxysmal supraventricular tachycardia is a regular, fast (160 to 220 beats per minute) heart rate that begins and ends suddenly and originates in heart tissue other than that in the ventricles.

• Most people have uncomfortable awareness of heartbeats (palpitations), shortness of breath, and chest pain.

• Episodes can often be stopped by maneuvers that stimulate the vagus nerve, which slows the heart rate.

• Sometimes, people are given drugs to stop the episode.

(See also Overview of Abnormal Heart Rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are… read more .)

Paroxysmal supraventricular tachycardia is most common among young people and is more unpleasant than dangerous. It may occur during vigorous exercise.

Paroxysmal supraventricular tachycardia may be triggered by a premature heartbeat that repeatedly activates the heart at a fast rate. This repeated, rapid activation may be caused by several abnormalities that people are born with. There may be two electrical pathways in the atrioventricular node, which is the electrical junction box between the upper chambers (the atria) and lower chambers (the ventricles) of the heart. Sometimes there is an abnormal electrical pathway between the atria and the ventricles . Much less commonly, the atria may generate abnormal rapid or circling impulses .

VIDEO

The fast heart rate tends to begin and end suddenly and may last from a few minutes to many hours. It is almost always experienced as an uncomfortable awareness of the heartbeat, such as feeling like the heart is pounding or racing (palpitations Palpitations Palpitations are the awareness of heartbeats. The sensation may feel like pounding, fluttering, racing, or skipping beats. Other symptoms—for example, chest discomfort or shortness of breath—may… read more ). It is often associated with other symptoms, such as weakness, light-headedness, shortness of breath, and chest pain. Usually, the heart is otherwise normal.

The doctor confirms the diagnosis by doing electrocardiography Electrocardiography Electrocardiography (ECG) is a quick, simple, painless procedure in which the heart’s electrical impulses are amplified and recorded. This record, the electrocardiogram (also known as an ECG)… read more (ECG).

Episodes of paroxysmal supraventricular tachycardia often can be stopped by one of several maneuvers that stimulate the vagus nerve and thus decrease the heart rate. These maneuvers are usually conducted or supervised by a doctor, but people who repeatedly experience the arrhythmia often learn to do the maneuvers themselves. Maneuvers include

• Straining as if having a difficult bowel movement

• Rubbing the neck just below the angle of the jaw (which stimulates a sensitive area on the carotid artery called the carotid sinus)

• Plunging the face into a bowl of ice-cold water

These maneuvers are most effective when they are used shortly after the arrhythmia starts.

If these maneuvers are not effective, if the arrhythmia causes severe symptoms, or if the episode lasts more than 20 minutes, people are advised to seek medical intervention to stop the episode. Doctors can usually stop an episode promptly by giving an intravenous injection of a drug, usually adenosine, verapamil, or diltiazem. Rarely, drugs are ineffective, and cardioversion Cardioversion-Defibrillation There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,… read more (delivery of an electrical shock to the heart) may be necessary.

Prevention is more difficult than treatment. When episodes are frequent or bothersome, doctors usually recommend catheter ablation Destroying Abnormal Heart Tissue (Ablation) There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,. .. read more . For this procedure, radiowaves, laser pulses, high-voltage electrical current, or cold is delivered through a catheter inserted in the heart. This energy or cold temperature destroys the tissue in which paroxysmal supraventricular tachycardia originates.

If catheter ablation is not an option, almost any antiarrhythmic drug may be effective. Drugs commonly used include beta-blockers, digoxin, diltiazem, verapamil, propafenone, and flecainide (see table ).

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

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