What is the initial treatment for a patient presenting with Supraventricular Tachycardia (SVT)?

Initial Treatment for Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers immediately in all hemodynamically stable patients, followed by IV adenosine if vagal maneuvers fail; proceed directly to synchronized cardioversion in any hemodynamically unstable patient. 1, 2, 3

Step 1: Assess Hemodynamic Stability First

Your immediate decision point is whether the patient is hemodynamically stable or unstable. 3

Hemodynamically unstable is defined by the presence of:

• Hypotension
• Altered mental status
• Signs of shock
• Chest pain suggesting acute ischemia
• Acute heart failure 3

If ANY of these signs are present, skip all other interventions and proceed immediately to synchronized cardioversion at 50-100J. 2, 3 Do not waste time with vagal maneuvers or medications—every second counts. 3

Step 2: For Hemodynamically Stable Patients - Vagal Maneuvers

The modified Valsalva maneuver is your first-line intervention (Class I, Level B evidence). 1, 2

Modified Valsalva Technique (Most Effective):

• Patient bears down against a closed glottis for 10-30 seconds while supine (generating 30-40 mm Hg intrathoracic pressure) 1, 2
• Immediately after the strain phase, lay the patient flat and elevate their legs 2
• This modified technique is 2.8-3.8 times more effective than standard Valsalva, with success rates of 27.7-43% 3, 4

Alternative Vagal Maneuvers (if modified Valsalva unavailable):

• Carotid sinus massage: Apply steady pressure over right or left carotid sinus for 5-10 seconds after confirming absence of bruit 1
• Ice-cold wet towel to face (diving reflex) 1

Critical pitfall: Never apply pressure to the eyeball—this is dangerous and abandoned. 1

Step 3: If Vagal Maneuvers Fail - Adenosine

Adenosine 6 mg rapid IV bolus is your next intervention (Class I, Level B evidence). 1, 2, 3

Adenosine Administration Protocol:

• Give as rapid IV push through a large peripheral vein 3
• Immediately follow with 20 mL saline flush 3
• If no response after 1-2 minutes, give 12 mg rapid IV bolus 3
• If still no response, may give one additional 12 mg dose 3
• Success rate: 90-95% for AVNRT and orthodromic AVRT 1, 2, 3

Critical Dosing Adjustments:

• Reduce to 3 mg for patients taking dipyridamole, carbamazepine, or with transplanted heart 2
• Larger doses may be needed with theophylline, caffeine, or theobromine 2

Absolute Contraindications to Adenosine:

• Asthma or bronchospastic lung disease (can cause severe bronchoconstriction) 2, 5
• Second- or third-degree AV block without pacemaker 5
• Sick sinus syndrome without pacemaker 5
• Known hypersensitivity to adenosine 5

Safety Requirements:

• Have electrical cardioversion equipment immediately available when administering adenosine 1, 2
• Adenosine may precipitate atrial fibrillation that can conduct rapidly and even cause ventricular fibrillation 1
• Appropriate resuscitative measures must be available 5

Step 4: If Adenosine Fails - Alternative Pharmacologic Therapy

For hemodynamically stable patients who fail adenosine:

IV diltiazem or verapamil (Class IIa, Level B evidence) 1

• Effective in 80-98% of cases 1

IV beta blockers are reasonable alternatives (Class IIa, Level C evidence) 1

Critical Safety Warning:

Never give verapamil, diltiazem, or beta blockers if:

• Wide-complex tachycardia (QRS ≥120 ms) of uncertain etiology 2, 3
• Known accessory pathway or pre-excitation on baseline ECG 1, 2
• Systolic heart failure 2

These agents can precipitate ventricular fibrillation or hemodynamic collapse in these scenarios. 1, 2

Step 5: If Pharmacologic Therapy Fails - Synchronized Cardioversion

Synchronized cardioversion is recommended when pharmacological therapy is ineffective or contraindicated (Class I, Level B evidence). 1, 2

• Perform after adequate sedation/anesthesia in stable patients 1, 2
• Start with 50-100J biphasic energy 3
• Increase stepwise if initial shock fails 3
• Success rate approaches 100% 1

Special Case: Pre-Excited Atrial Fibrillation (Irregular Wide-Complex)

If you suspect pre-excited AF (irregular wide-complex tachycardia in patient with known WPW):

Unstable: Immediate synchronized cardioversion 1, 3

Stable: IV ibutilide or procainamide 1, 3

NEVER give adenosine, verapamil, diltiazem, or beta blockers—these can accelerate ventricular rate and cause ventricular fibrillation. 3

Post-Conversion Management

• Patients often have atrial or ventricular premature complexes immediately after conversion that may reinitiate tachycardia 1
• An antiarrhythmic drug may be required to prevent acute reinitiation 1, 3
• Arrange cardiology follow-up for consideration of catheter ablation, which has 94.3-98.5% single-procedure success rate 3