Overview
Supraventricular tachycardia (SVT) describes arrhythmias that originate at or above the atrioventricular node (AVN) characterised by a narrow complex (QRS duration <120 ms or <3 small squares) tachycardia (heart rate >100 bpm).
Paroxysmal supraventricular tachycardia (PSVT) describes intermittent SVT without provoking factors and usually presents with a pulse rate of 140-250 bpm.
Causes
SVT is caused by:
- Re-entrant tachycardias – due to accessory pathways resulting in re-entry:
- Atrioventricular nodal re-entry tachycardia (AVNRT)
- Atrioventricular re-entrant tachycardia (AVRT):
- A notable type of AVRT is Wolff-Parkinson-White syndrome
- Macro-re-entrant atrial tachycardia (e.g. atrial flutter)
- Automatic tachycardias:
- Focal atrial tachycardia
- Focal junctional tachycardia
Epidemiology
- Women are twice more likely to have SVT than men
- The risk of SVT is much higher >65 years old
- SVT also often occurs in young people in the absence of heart disease
Presentation
Features include:
- Palpitations
- Chest pain
- Shortness of breath
- Anxiety
- Haemodynamic instability (tachycardia and hypotension)
- Acute heart failure
Investigations
- ECG:
- Shows a narrow complex, regular tachycardia
- P waves may be absent
- Delta waves suggest the presence of Wolff-Parkinson-White syndrome
- Holter monitoring:
- If an ECG misses an episode of SVT
Management
Initial steps
- Assess all patients with an ABCDE approach:
- Give oxygen if oxygen saturations are <94%
- Obtain IV access
- Monitor ECG, blood pressure, and oxygen saturations, and record a 12-lead ECG
- Identify and treat reversible causes (e.g. electrolyte abnormalities, hypovolaemia)
- Assess for the presence of life-threatening features such as:
- Shock
- Syncope
- Myocardial ischaemia
- Heart failure
Evidence of life-threatening features present
- Give a synchronised DC shock and repeat up to 3 attempts
- If the patient is conscious, give sedation or anaesthesia
- If unsuccessful: give amiodarone 300 mg over 10-20 minutes and repeat synchronised DC shock
No evidence of life-threatening features present
- Vagal manoeuvres:
- Valsalva manoeuvre – blow into an empty plastic syringe
- Carotid sinus massage – preferably in younger patients due to the risk of stroke from emboli
- IV adenosine as a rapid bolus if not asthmatic:
- Give 6 mg first, then 12 mg if unsuccessful, then 18 mg if unsuccessful
- Use continuous ECG monitoring
- Adenosine is contraindicated in asthma, use verapamil instead
- If ineffective: synchronised DC shock up to three attempts
- Give sedation or anaesthesia if conscious
Long-term management
Long-term management depends on the underlying cause. This may involve radiofrequency catheter ablation or drug management (such as beta-blockers or calcium channel blockers).
