What are the dangers of Supraventricular Tachycardia (SVT)?

Dangers of Supraventricular Tachycardia (SVT)

Supraventricular tachycardia is rarely life-threatening but can lead to serious complications including heart failure, pulmonary edema, myocardial ischemia, and in adults with congenital heart disease, it increases the risk of stroke and sudden cardiac death. 1

Overview of SVT Risks

SVT encompasses various tachyarrhythmias with atrial and/or ventricular rates exceeding 100 beats per minute at rest, originating from atrial or atrioventricular nodal tissues. While generally not immediately dangerous, SVT carries several potential risks:

Major Complications

• Heart failure development (occurs in up to 20% of infants and children with incessant tachycardia) 1
• Pulmonary edema (from sustained elevated heart rates) 1
• Myocardial ischemia (due to increased oxygen demand with rapid rates) 1
• Tachycardia-mediated cardiomyopathy (in approximately 1% of cases with persistent SVT) 2

Special Population Risks

• Adults with congenital heart disease: Significantly increased risk of heart failure, stroke, and sudden cardiac death 1
• Pediatric patients: May require mechanical cardiopulmonary support during initial therapy in severe cases 1
• Pregnant women: Fetal SVT with hydrops carries high mortality rate 1

Risk Factors for Complications

The likelihood of developing serious complications from SVT depends on several factors:

• Duration of tachycardia: Persistent SVT lasting weeks to months carries higher risk of cardiomyopathy 1
• Ventricular rate: Extremely rapid rates increase risk of hemodynamic compromise
• Underlying heart disease: Structural heart abnormalities significantly increase complication risk 1
• Age: Elderly patients (≥65 years) have five-fold greater risk of SVT than younger people 1
• Type of SVT: Some forms carry higher risks than others (e.g., pre-excitation syndromes)

Warning Signs of Dangerous SVT

Pay particular attention to these symptoms that may indicate a more serious situation:

• Syncope (occurs in approximately 15% of patients) 1
• Severe dyspnea or respiratory difficulties 3
• Persistent hypotension 3
• Chest pain suggesting myocardial ischemia 3
• Signs of heart failure (edema, shortness of breath at rest)

Management Considerations

When SVT presents with concerning features:

• Hemodynamically unstable patients: Require immediate synchronized cardioversion 4, 2
• Stable patients: Vagal maneuvers first (43% effective), followed by adenosine (91% effective) 2
• Long-term management: Catheter ablation is highly effective (94-98% success rate) and recommended as first-line therapy for recurrent, symptomatic SVT 2

Pitfalls and Caveats

1. Misdiagnosis risk: SVT is often misattributed to anxiety, especially when episodes terminate before medical evaluation 5

2. Adenosine cautions: Can cause serious adverse effects including:

   • Cardiac arrest
   • Sustained ventricular tachycardia
   • Myocardial infarction
   • AV block (occurs in approximately 6% of patients)
   • Hypotension
   • Bronchospasm 3

3. Pre-excitation syndromes: Patients with Wolff-Parkinson-White syndrome and AF require immediate evaluation due to risk of sudden death 1

4. Medication interactions: Methylxanthines (caffeine, theophylline) interfere with adenosine effectiveness 3

5. Pediatric considerations: Higher complication rates with ablation in children weighing <15kg 1

While SVT can cause significant discomfort and anxiety, with proper diagnosis and management, serious complications are relatively uncommon in patients without structural heart disease. However, persistent or recurrent episodes should always be evaluated by a heart rhythm specialist to prevent potential long-term complications.