What are the causes of Supraventricular Tachycardia (SVT)?

Causes of Supraventricular Tachycardia (SVT)

Supraventricular tachycardia is primarily caused by reentry phenomena or abnormal automaticity in atrial or atrioventricular nodal tissue, with the three most common mechanisms being atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), and atrial tachycardia (AT). 1

Primary Mechanisms of SVT

Reentry Mechanisms (Most Common)

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT): 50-60% of SVT cases 1

  • Involves dual pathways within the AV node (alpha and beta) with different conduction times and refractory periods
  • Both pathways confined to AV nodal and perinodal atrial tissue

• Atrioventricular Reentrant Tachycardia (AVRT): 20-30% of SVT cases 1

  • Depends on an accessory pathway that bypasses the AV node
  • Includes Wolff-Parkinson-White syndrome
  • Accessory pathway provides an alternative route between atria and ventricles

• Atrial Tachycardia (AT): 10-20% of SVT cases 1

  • Focal atrial tachycardia arises from a localized atrial site with enhanced automaticity (5-10%)
  • Atrial flutter characterized by macroreentrant circuit in the atria (10-20%)

Abnormal Automaticity

• Enhanced automaticity in atrial tissue
• Triggered activity from early or delayed afterdepolarizations

Underlying Conditions and Risk Factors

Structural Heart Disease

• Valvular heart disease, especially mitral valve prolapse 1
• Hypertrophic cardiomyopathy 1
• Congenital heart disease 1

Physiological Triggers

• Physical exertion 1
• Emotional stress 1
• Stimulant use:
  • Caffeine consumption 1
  • Alcohol intake 1
  • Nicotine use 1

Other Medical Conditions

• Hyperthyroidism 2
• Fever and infection 2
• Dehydration 2
• Anemia 2
• Electrolyte abnormalities 1

Demographic Factors

• More common in females (67.5% of cases) 3
• Most common in ages 45-64 years (approximately 50% of patients) 3
• Prevalence of 10-20% in the general population 1

Clinical Presentation

• Palpitations (86% of cases) 3
• Chest discomfort (47%) 3
• Dyspnea (38%) 3
• Other symptoms may include lightheadedness, fatigue, and altered consciousness 4

Complications

• Tachycardia-mediated cardiomyopathy (rare, approximately 1% of cases) 3
• Heart failure if left untreated 1
• Syncope 1
• Increased risk of stroke in adults with congenital heart disease 1

Diagnostic Considerations

• Diagnosis confirmed by 12-lead ECG during tachycardia 1
• Holter monitoring or event recorders for intermittent symptoms 1
• Electrophysiological studies for definitive diagnosis 1

Important Pitfalls to Avoid

1. Failing to distinguish SVT from ventricular tachycardia (obtain 12-lead ECG)
2. Overlooking underlying structural heart disease that may be contributing to SVT
3. Missing electrolyte abnormalities that can trigger or exacerbate SVT
4. Neglecting to refer patients for specialist evaluation, especially when symptoms are recurrent

Understanding the specific mechanism of SVT is crucial for appropriate management, with catheter ablation offering the highest success rates (94.3-98.5%) for long-term treatment 3.