Makindo Medical Notes

Related Subjects: |Wolff-Parkinson White syndrome (WPW) AVRT |Lown Ganong Levine Syndrome AVRT |Supraventricular Tachycardia (SVT) |Atrioventricular Nodal Reentrant Tachycardia AVNRT |Atrial Flutter |Atrial Fibrillation |Sinus Tachycardia |Sinus Arrhythmia |Multifocal Atrial Tachycardia |Resuscitation - Adult Tachycardia Algorithm |Resuscitation - Advanced Life Support

Supraventricular Tachycardia (SVT) encompasses a group of rapid heart rhythms originating above the ventricles, typically from the atria or the atrioventricular (AV) node. While SVT is usually benign, it can cause significant symptoms and, in certain cases, may lead to serious complications. Proper diagnosis and management are essential to alleviate symptoms and prevent adverse outcomes.

About

• Technically, SVT refers to any tachycardia arising from above the Bundle of His.
• Primarily includes reentrant tachycardias such as AV Reciprocating Tachycardia (AVRT) and AV Nodal Reentrant Tachycardia (AVNRT).
• Generally benign but can cause debilitating symptoms like palpitations, dizziness, and syncope.
• Often curable through catheter ablation, especially in cases associated with Wolff-Parkinson-White (WPW) syndrome.

Aetiology of Reentrant SVT

• Requires the presence of two distinct pathways (A and B) around a central point or the AV node:
• Slow Pathway: Longer refractory period.
• Fast Pathway: Shorter refractory period.
• Atrial ectopic beats travel down the slow pathway and return via the fast pathway, creating a reentrant circuit similar to a Catherine wheel firework.
• Classification of SVT based on reentrant pathways:
• Slow-Fast AVNRT: Most common (>90%). Refractory period of the fast pathway (RP') is less than that of the slow pathway (P'R).
• Fast-Slow AVRT: Accounts for 10-15%. RP' is greater than P'R.
• Slow-Slow AVRT: Rare (<5%). Both pathways have similar refractory periods.

Diagram Shows Pathways of AVRT and AVNRT

Definition Includes

• Sinus Tachycardia: Elevated heart rate originating from the sinus node.
• Atrial Tachycardia: Rapid heart rate originating from an ectopic focus within the atrium.
• Multifocal Atrial Tachycardia: Rapid atrial rate originating from multiple ectopic foci in the atria.
• Atrial Fibrillation: Irregular and often rapid heart rate originating from chaotic electrical activity in the atria.
• Atrial Flutter: Rapid, regular heart rate originating from a single ectopic focus in the atria.
• However, the term SVT is generally reserved for:
• AV Nodal Reentrant Tachycardia (AVNRT)
• AV Reentrant Tachycardia (AVRT) associated with WPW syndrome

Clinical Features

• Occurs in all age groups, though more common in younger individuals.
• More prevalent in females with a male-to-female ratio of approximately 1:2.
• Symptoms may include:
• Presyncope or syncope
• Dyspnea (breathlessness)
• Dizziness or lightheadedness
• Chest pain or discomfort
• Palpitations
• SVT can be mistaken for panic attacks, leading to delayed diagnosis.
• Triggers may include stress, caffeine, alcohol, smoking, and recreational drugs.

Investigations

• Laboratory Tests:
  • Full Blood Count (FBC)
  • Urea & Electrolytes (U&E)
  • Thyroid Function Tests (TFTs)
  • Liver Function Tests (LFTs)
  • Chest X-Ray (CXR)
• Electrocardiogram (ECG):
  • Most crucial diagnostic tool. Perform a 12-lead ECG during an SVT episode.
  • Typically shows narrow complex tachycardia (120-240 bpm) with P waves preceding each QRS complex.
  • May show bundle branch block patterns or mimic ventricular tachycardia (VT) in certain cases.
• Holter Monitoring: For transient or infrequent SVT episodes.
• Implantable Cardiac Recorder: If episodes are not captured by standard monitoring.
• Exclusion of Other Conditions:
  • Consider pheochromocytoma if hypertension is present, though it's rare.
  • Echocardiogram to rule out structural heart disease.
• Additional ECG Findings:
  • Narrow complex tachycardia (120-240 bpm), possibly with bundle branch block mimicking VT.

Clinical Pearls

• Sudden onset and termination of tachycardia strongly suggest paroxysmal supraventricular tachycardia (PSVT).
• “Shirt flapping” or “neck pounding” sensations may indicate AVNRT.
• Presence of hypotension, syncope, or presyncope indicates poor tolerance of SVT and necessitates immediate treatment and specialist referral.
• Underlying structural heart disease suggests atrial tachycardia over other SVT types.
• Evidence of preexcitation on ECG (e.g., delta waves in WPW) warrants referral to an arrhythmia specialist for potential catheter ablation.

Examples