Supraventricular Tachycardia

• Supraventricular tachycardia is caused by the electrical signal re-entering the atria from the ventricles
• Paroxysmal SVT describes a situation where SVT reoccurs and remits in the same patient over time
• There are four main differentials of a narrow complex tachycardia: Sinus tachycardia, Supraventricular tachycardia, Atrial fibrillation, Atrial flutter
• Supraventricular tachycardia (SVT) refers to when abnormal electrical signals from above (supra-) the ventricles cause a fast heart rate (tachycardia)
• In SVT, the QRS complex will fit within 3 small squares on a standard ECG
• Pathophysiology of heart electrical signals

  Start in the sinoatrial node, located at the junction between the superior vena cava and the right atrium. Signal travels through the right and left atrium, then through the atrioventricular (AV) node to the ventricles, causing them to contract
• Supraventricular tachycardia causes a self-perpetuating electrical loop without an endpoint, resulting in narrow complex tachycardia
• On an ECG, SVT looks like a QRS complex followed immediately by a T wave, QRS complex, T wave and so on
• Narrow complex tachycardia is a fast heart rate with a QRS complex duration of less than 0.12 seconds
• Sinus tachycardia will take the normal P wave, QRS complex, and T wave pattern
• SVT can cause a broad complex tachycardia if the patient also has a bundle branch block
• Supraventricular tachycardia

  • QRS complex followed immediately by a T wave
  • P waves often buried in T waves
  • Distinguished by regular rhythm and absence of saw-tooth pattern
• Atrial flutter


  • Atrial rate usually around 300 beats per minute
  • Saw-tooth pattern on ECG
  • Two atrial contractions for every one ventricular contraction
  • Ventricular rate of 150 beats per minute
• SVT vs. sinus tachycardia

  • SVT has abrupt onset and very regular pattern without variability
  • Sinus tachycardia has more gradual onset and variability in rate
• Atrial fibrillation


  • Absent P waves
  • Narrow QRS complex tachycardia
  • Irregularly irregular ventricular rhythm
• SVT causes a narrow complex tachycardia
• Types of SVT

  • Atrioventricular nodal re-entrant tachycardia
  • Atrioventricular re-entrant tachycardia
  • Atrial tachycardia
• Wolff-Parkinson-White syndrome is caused by an extra electrical pathway connecting the atria and ventricles
• ECG changes in Wolff-Parkinson-White syndrome

  • Short PR interval
  • Wide QRS complex
  • Delta wave (slurred upstroke in the QRS complex)
• Sinus tachycardia

  • Normal P wave, QRS complex, and T wave pattern
  • Not an arrhythmia, usually a response to an underlying cause like sepsis or pain
• Definitive treatment for Wolff-Parkinson-White syndrome is radiofrequency ablation of the accessory pathway
• In someone with a combination of atrial fibrillation or atrial flutter and WPW, there is a risk of a polymorphic wide complex tachycardia, which is a life-threatening medical emergency
• Anti-arrhythmic medications increase the risk

  By reducing conduction through the AV node and promoting conduction through the accessory pathway
• Heart rate can get above 200, or even 300, beats per minute, and ventricular fibrillation and cardiac arrest can follow
• Acute Management

  Summarises the Resuscitation Council UK guidelines (2021) to help with exam preparation
• Management of supraventricular tachycardia in patients without life-threatening features

  Involves a stepwise approach, trying each step to see whether it works before moving on
• Vagal Manoeuvres

  Stimulate the vagus nerve, increasing the activity in the parasympathetic nervous system
• Step 2

  Adenosine
• Adenosine

  Slows cardiac conduction, primarily through the AV node, interrupts the AV node or accessory pathway during SVT and “resets” it to sinus rhythm
• Step 4

  Synchronised DC cardioversion
• Intravenous amiodarone is added if initial DC shocks are unsuccessful
• Carotid sinus massage

  Involves stimulating the baroreceptors in the carotid sinus by massaging that area on one side of the neck (not both sides at the same time)
• Adenosine is avoided in patients with asthma, COPD, heart failure, heart block, severe hypotension, potential atrial arrhythmia with underlying pre-excitation
• The patient should be warned about the scary feeling of dying or impending doom when it is injected. This feeling quickly passes
• Most anti-arrhythmic medications

  • Beta blockers
  • Calcium channel blockers
  • Digoxin
  • Adenosine
• With fibrillation or atrial flutter and WPW

  Chaotic atrial electrical activity can pass through the accessory pathway into the ventricles, causing polymorphic wide complex tachycardia, which is a life-threatening medical emergency
• The patient should have continuous ECG monitoring during management
• Anti-arrhythmic medications are contra-indicated in patients with WPW that develop atrial fibrillation or flutter
• Step 3

  Verapamil or a beta blocker
• Patients with life-threatening features

  Are treated with synchronised DC cardioversion under sedation or general anaesthesia