How do we evaluate and treat Supraventricular Tachycardia (SVT)?

Evaluation and Treatment of Supraventricular Tachycardia

Immediate Assessment

Begin by determining hemodynamic stability—if the patient shows hypotension, altered mental status, shock, chest pain, or acute heart failure, proceed directly to synchronized cardioversion. 1, 2

Critical First Steps

• Obtain a 12-lead ECG immediately to confirm regular narrow-complex SVT and exclude ventricular tachycardia or pre-excited atrial fibrillation, as AV nodal blockers can cause ventricular fibrillation or hemodynamic collapse in these conditions 2
• Attach continuous ECG monitoring and establish IV access 1
• Assess for specific features: heart rate (typically 150-250 bpm), QRS width (<0.09 seconds for narrow-complex), P wave location, and rhythm regularity 1, 3

Acute Management Algorithm

For Hemodynamically UNSTABLE Patients

Perform immediate synchronized cardioversion—this successfully restores sinus rhythm in 100% of cases when pharmacologic therapy fails. 1, 2

• Do not delay for vagal maneuvers or adenosine if the patient is unstable 1
• Cardioversion is indicated for persistent SVT causing hypotension, altered mental status, signs of shock, chest pain, or acute heart failure 1

For Hemodynamically STABLE Patients

Follow this stepwise approach:

Step 1: Vagal Maneuvers (First-Line)

• Attempt vagal maneuvers immediately unless they will unduly delay definitive treatment 1, 2
• Valsalva maneuver achieves conversion in approximately 27.7-31% of cases and is more successful than carotid massage 2
• In infants and young children, apply ice to the face without occluding the airway 1
• In older children and adults, use Valsalva maneuver (blowing through narrow straw) or carotid sinus massage 1

Step 2: Adenosine (Drug of Choice)

If vagal maneuvers fail, adenosine is the preferred agent with 78-96% success rates for AVNRT and AVRT. 1, 2

• Administer as rapid IV bolus via proximal vein followed immediately by saline flush 1
• Initial dose: 6 mg rapid bolus; if unsuccessful, give 12 mg 1
• Continuous ECG recording during administration helps distinguish failure to terminate versus successful termination with immediate reinitiation 1
• Side effects (chest discomfort, shortness of breath, flushing) are common but transient due to very short half-life 1
• Caution: Use adenosine carefully when diagnosis is unclear—it may produce ventricular fibrillation in patients with coronary disease and rapid ventricular rates in pre-excited tachycardias 1

Step 3: Alternative Pharmacologic Agents

If adenosine fails or is contraindicated:

• IV diltiazem or verapamil: 80-98% conversion rate for AVNRT, but absolutely contraindicated if any possibility of ventricular tachycardia, pre-excited atrial fibrillation, or systolic heart failure 2
• IV beta-blockers: Reasonable alternative with excellent safety profile, though less effective than calcium channel blockers 2
• Procainamide: 15 mg/kg over 30-60 minutes for refractory cases 1
• Amiodarone: 5 mg/kg over 20-60 minutes; do not routinely combine with procainamide 1

Diagnostic Evaluation

ECG Analysis During Tachycardia

• P wave location: Hidden within QRS suggests AVNRT; P wave following QRS with RP >70 ms suggests AVRT 3
• QRS width: Narrow (<0.09 seconds) confirms supraventricular origin; wide complex requires differentiation from ventricular tachycardia 1
• Rhythm regularity: Regular rhythm supports AVNRT or AVRT; irregular suggests atrial fibrillation or flutter 1

Distinguishing SVT from Ventricular Tachycardia

When QRS is wide (>0.12 seconds), treat as ventricular tachycardia if diagnosis is uncertain—this is the safer approach. 1, 4

Key features favoring VT:

• AV dissociation (pathognomonic for VT) 4
• QRS width >0.14 seconds (RBBB pattern) or >0.16 seconds (LBBB pattern) 1
• RS interval >100 ms in any precordial lead 1, 4
• Fusion beats or QR complexes 1, 4
• History of prior myocardial infarction 1, 4

Extended Monitoring

• Holter monitor or event recorder may be needed to capture paroxysmal episodes if initial ECG is non-diagnostic 5, 6
• Transesophageal atrial stimulation can assess mechanism when diagnosis remains uncertain 7

Post-Conversion Management

• Be prepared for immediate SVT reinitiation from atrial or ventricular premature complexes—may require antiarrhythmic drugs to prevent recurrence 2
• Educate patients on performing vagal maneuvers for future episodes 2
• All patients should be referred to cardiology for heart rhythm specialist evaluation 6

Long-Term Management

Catheter ablation is first-line for recurrent, symptomatic paroxysmal SVT with 94.3-98.5% single-procedure success rates. 2, 5

• Ablation is particularly recommended for Wolff-Parkinson-White syndrome 5
• Beta-blockers and/or calcium channel blockers may be used for long-term suppressive therapy if ablation is declined or not feasible 5, 6
• Conservative management is appropriate only if symptoms are rare and patient is low risk 6

Critical Pitfalls to Avoid

• Never administer AV nodal blockers (adenosine, calcium channel blockers, beta-blockers) if pre-excited atrial fibrillation or ventricular tachycardia is possible 1, 2
• Do not rely solely on QRS width when patients have pre-existing bundle branch blocks or take antiarrhythmic medications 1, 4
• Do not delay cardioversion in unstable patients to attempt vagal maneuvers or medications 1
• Adenosine may unmask atrial flutter or atrial tachycardia but rarely terminates these rhythms 1