What causes recurrent supraventricular tachycardia (SVT)?

Causes of Recurrent Supraventricular Tachycardia (SVT)

Recurrent supraventricular tachycardia is most commonly caused by reentry mechanisms (particularly AVNRT and AVRT), followed by abnormal automaticity and triggered activity in the atria or AV nodal tissue. 1

Primary Electrophysiologic Mechanisms

1. Reentry (Most Common Mechanism)

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT): 50-60% of SVT cases 2

  • Involves dual pathways within the AV node
  • Requires unidirectional block and slow conduction
  • More common in females and those with onset age >30 years 1

• Atrioventricular Reentrant Tachycardia (AVRT): 20-30% of SVT cases 2

  • Requires an accessory pathway
  • Can be orthodromic (narrow QRS) or antidromic (wide QRS)
  • More common in younger patients 1
  • May present as Wolff-Parkinson-White syndrome or concealed bypass tract 3

• Atrial Tachycardia (AT): 10-20% of SVT cases 2

  • Focal or macroreentrant mechanisms

2. Enhanced Automaticity

• Cells with enhanced diastolic phase 4 depolarization
• Increased firing rate exceeding that of the sinus node
• Can be incessant (>50% of the day) or episodic 1

3. Triggered Activity

• Associated with disturbances of repolarization
• Caused by afterdepolarizations that reach threshold and trigger early action potentials 1

Predisposing Factors and Conditions

1. Structural Heart Conditions

• Valvular heart disease (especially mitral valve prolapse) - RR 2.0 (95% CI 1.5-2.5) 2
• Hypertrophic cardiomyopathy 2
• Congenital heart disease 2

2. Metabolic and Systemic Factors

• Hyperthyroidism - increases automaticity and adrenergic sensitivity 2
• Fever and infection - increases metabolic demand and automaticity 2
• Dehydration - affects electrolyte balance 2
• Anemia - increases cardiac workload 2
• Electrolyte abnormalities - particularly hypokalemia 2

3. Autonomic Influences

• Altered autonomic tone - can trigger episodes 2
• Stress and anxiety - increases sympathetic tone 1
• Exercise - can precipitate episodes in susceptible individuals 1

4. Demographic Factors

• Age: AVNRT is more common in middle-aged or older individuals, while AVRT is more prevalent in adolescents 1
• Sex: AVNRT is more common in females 1

Clinical Patterns and Presentation

• Paroxysmal pattern: Characterized by abrupt onset and termination 1
• Incessant pattern: Tachycardia present >50% of the day 1
• Symptoms: Palpitations (86%), chest discomfort (47%), dyspnea (38%), lightheadedness, fatigue, presyncope, or syncope (15%) 1, 4

Complications of Recurrent SVT

• Tachycardia-mediated cardiomyopathy: Occurs in approximately 1% of cases with persistent SVT 2, 4
• Syncope: Observed in approximately 15% of patients, usually just after initiation of rapid SVT or with a prolonged pause after abrupt termination 1

Important Considerations

• The frequency and duration of episodes, along with the patient's age of onset, can provide clues to the underlying mechanism 1
• Termination by vagal maneuvers suggests a reentrant mechanism involving AV nodal tissue (AVNRT or AVRT) 1
• The incidence of manifest pre-excitation (WPW pattern) in the general population is 0.1% to 0.3%, but not all patients with pre-excitation develop SVT 1

Understanding the specific mechanism of recurrent SVT is crucial for appropriate management, as treatment approaches may differ based on the underlying cause.