What are the treatment options for Supraventricular Tachycardia (SVT)?

SVT Treatment

Acute Management Algorithm

For hemodynamically stable SVT, begin with vagal maneuvers immediately, followed by adenosine if unsuccessful, then consider IV beta-blockers or calcium channel blockers as third-line agents. 1, 2

First-Line: Vagal Maneuvers

• Perform the modified Valsalva maneuver in the supine position: patient bears down against a closed glottis for 10-30 seconds (equivalent to 30-40 mmHg intrathoracic pressure), then immediately lies flat with legs raised 1, 2
• Alternative techniques include carotid sinus massage (after confirming absence of bruit, apply steady pressure for 5-10 seconds) or applying an ice-cold wet towel to the face 1
• Success rate is approximately 27.7% when switching between Valsalva and carotid massage techniques 1
• The modified Valsalva with leg elevation is superior to standard Valsalva based on recent evidence 3

Second-Line: Adenosine

Adenosine is the preferred pharmacologic agent with 90-95% effectiveness for terminating PSVT 1, 2

• Initial dose: 6 mg rapid IV bolus through a large (antecubital) vein, followed immediately by 20 mL saline flush 1, 4
• If no conversion within 1-2 minutes, give 12 mg rapid IV bolus using the same technique 1
• A third dose of 12 mg may be administered if needed 4
• Critical safety consideration: Have a defibrillator immediately available, as adenosine can precipitate atrial fibrillation with rapid ventricular rates in patients with WPW syndrome 1, 4

Important drug interactions and dosing modifications 1, 4:

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given via central venous access
• Higher doses may be required in patients taking theophylline, caffeine, or theobromine
• Contraindicated in patients with asthma due to risk of severe bronchoconstriction 1, 4

Common transient side effects include flushing, dyspnea, and chest discomfort 1, 4

Third-Line: IV Beta-Blockers or Calcium Channel Blockers

• IV diltiazem or verapamil are reasonable alternatives for hemodynamically stable patients who don't respond to adenosine 1, 2
• These agents are particularly effective for AVNRT but have slower onset than adenosine 1
• Critical warning: Do not use in patients with suspected VT, pre-excited atrial fibrillation, or systolic heart failure, as these patients may develop ventricular fibrillation or hemodynamic collapse 1
• IV beta-blockers are less effective than calcium channel blockers for acute termination 1

Synchronized Cardioversion

For hemodynamically unstable patients, perform immediate synchronized cardioversion 1

• Recommended initial biphasic energy: 50-100 J for SVT (120-200 J for atrial fibrillation) 1
• Increase dose stepwise if initial shock fails 1
• Also indicated for hemodynamically stable patients when pharmacologic therapy fails or is contraindicated 1

Special Populations

Pregnancy

• Vagal maneuvers remain first-line and are completely safe 1, 2, 5
• Adenosine is safe at all stages of pregnancy due to its extremely short half-life preventing fetal circulation exposure 1, 2
• Synchronized cardioversion can be performed safely at any trimester if necessary 2
• Avoid atenolol and verapamil due to teratogenic effects 5

Pre-excitation Syndromes (WPW)

• Avoid all AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers, digoxin) in pre-excited atrial fibrillation 2
• Use IV procainamide or ibutilide for hemodynamically stable pre-excited AF 2
• Proceed directly to cardioversion if hemodynamically unstable 1

Long-Term Management

Beta-blockers are the first-line option for chronic prevention of recurrent SVT 2

• Calcium channel blockers serve as an alternative to beta-blockers 2
• Catheter ablation is curative and should be offered to patients with: frequent symptomatic episodes, medication intolerance or ineffectiveness, or patient preference for non-pharmacological approach 2, 6
• All patients treated for SVT should be referred to a heart rhythm specialist 6

Critical Pitfalls to Avoid

• Never use AV nodal blockers before confirming the rhythm is not VT or pre-excited AF - this can cause cardiovascular collapse 1
• Do not give adenosine to asthmatic patients due to severe bronchoconstriction risk 1, 4
• Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia) will not respond to cardioversion and require rate control with AV nodal blocking agents 1
• Always obtain a 12-lead ECG before treatment to differentiate tachycardia mechanisms 2