Supraventricular Tachycardia
Supraventricular tachycardia (SVT) is a group of arrhythmias causing sudden episodes of rapid heart rate — typically 150–250 bpm — that start and stop abruptly. Catheter ablation is curative in the majority of cases with success rates exceeding 95% for the most common forms.
Shortness of breath and chest discomfort can be warning signs of abnormal heart rhythm
Supraventricular tachycardia encompasses a group of arrhythmias originating above the bundle of His, causing paroxysmal episodes of rapid heart rate — typically between 150 and 250 beats per minute — that characteristically start and stop abruptly. SVT is among the most common arrhythmias referred for specialist evaluation and is highly amenable to curative catheter ablation. Accurate subtype identification through electrophysiological assessment is essential to guide treatment strategy and risk stratification.
Types of SVT
- Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common SVT — accounting for approximately 60% of cases — caused by a re-entrant circuit utilising dual pathways within or near the AV node. It predominantly affects women and produces sudden-onset regular palpitations, often with neck pulsations from simultaneous atrial and ventricular contraction. Catheter ablation of the slow pathway is curative in over 95% of cases.
- Atrioventricular reciprocating tachycardia (AVRT) involves a re-entrant circuit using an accessory pathway — an anomalous electrical connection between the atria and ventricles — in addition to the AV node. When the accessory pathway is capable of rapid anterograde conduction and is visible on the resting ECG as a delta wave and short PR interval, it constitutes Wolff-Parkinson-White (WPW) syndrome. WPW carries a small but important risk of sudden cardiac death in patients who develop atrial fibrillation, as rapid pre-excited conduction across the accessory pathway can degenerate into ventricular fibrillation. Risk stratification and accessory pathway ablation are recommended for symptomatic WPW. Catheter ablation of the accessory pathway is curative in the majority of AVRT cases.
- Atrial tachycardia (AT) originates from a focal ectopic site within the atrial myocardium, independent of the AV node. It is less common than AVNRT and AVRT, may be incessant, and — when persistent — can cause tachycardia-mediated cardiomyopathy with reduced ejection fraction. Ablation success rates are lower than for AVNRT and AVRT and depend on accurate mapping of the tachycardia focus.
Symptoms
SVT characteristically presents with sudden-onset palpitations — a rapid, regular, and forceful heartbeat — that terminate abruptly, often with a vagal manoeuvre or spontaneously. Associated symptoms include breathlessness, chest tightness, dizziness, and presyncope. Neck pulsations during tachycardia — caused by atrial contraction against a closed tricuspid valve — are a clinically distinctive feature of AVNRT. Syncope is uncommon in isolated SVT without structural heart disease but raises concern for WPW with rapid pre-excited atrial fibrillation or an alternative diagnosis.
Diagnosis
A 12-lead ECG during tachycardia is the most informative investigation — identifying a narrow complex regular tachycardia, P wave morphology and position relative to the QRS, and any evidence of pre-excitation. The resting ECG in sinus rhythm identifies a delta wave in WPW. For patients with infrequent episodes, ambulatory Holter monitoring or a prolonged event recorder captures the rhythm during spontaneous attacks. Electrophysiology study (EPS) maps the precise tachycardia mechanism, identifies the circuit or focus, and is performed in the same setting as catheter ablation when intervention is planned.
Acute Termination
Many SVT episodes terminate spontaneously or with vagal manoeuvres. The modified Valsalva manoeuvre — performed supine with leg elevation immediately following the strain phase — achieves significantly higher termination rates than the standard Valsalva and is the recommended first-line technique. Carotid sinus massage is an alternative in appropriate patients. When vagal manoeuvres fail, intravenous adenosine terminates the majority of AV node-dependent SVTs within seconds and is the drug of choice in the acute setting. Electrical cardioversion is reserved for haemodynamically unstable SVT.
Long-Term Treatment
Catheter ablation is the definitive treatment for symptomatic SVT and is recommended as first-line therapy for patients wishing to avoid long-term medication. Ablation uses radiofrequency energy or cryotherapy to eliminate the re-entrant circuit or accessory pathway under electrophysiological guidance. Success rates exceed 95% for AVNRT and are high for most AVRT cases. It is performed as a day procedure under conscious sedation with rapid recovery. For patients with WPW and high-risk accessory pathway characteristics, ablation is recommended regardless of symptoms to prevent sudden cardiac death. Long-term antiarrhythmic medication — beta-blockers, calcium channel blockers, or flecainide — is an alternative for patients who prefer to defer or are unsuitable for ablation, providing rate or rhythm control without addressing the underlying substrate.
Experiencing sudden episodes of rapid heartbeat or diagnosed with SVT in Singapore? Dr. Peter Chang consults at Paragon Medical Centre, Orchard Road. Book a specialist assessment today.