What is the initial management for Supraventricular Tachycardia (SVT) versus Ventricular Tachycardia (VT)?

Initial Management: SVT vs VT

For hemodynamically unstable patients with either SVT or VT, proceed immediately to synchronized cardioversion at 50-100J without attempting vagal maneuvers or pharmacologic therapy—this is the definitive treatment for both rhythms when the patient is unstable. 1, 2, 3

Critical First Decision: Assess Hemodynamic Stability

Hemodynamic instability is defined by the presence of hypotension, altered mental status, signs of shock, chest pain, or acute heart failure. 2, 3

• If any of these signs are present, the patient is unstable and requires immediate cardioversion regardless of whether the rhythm is SVT or VT. 1, 2
• Synchronized cardioversion has essentially a 100% success rate in restoring sinus rhythm for both SVT and VT. 2, 3

Hemodynamically Unstable Patients (SVT or VT)

Immediate synchronized cardioversion is mandatory:

• Start with 50-100J for SVT; higher energy may be needed for VT. 2
• Do not waste time with vagal maneuvers or medications—every second counts. 1, 3
• Have defibrillation capability ready in case the rhythm degenerates to ventricular fibrillation. 1

Hemodynamically Stable Patients: The Critical Distinction

Step 1: Obtain 12-Lead ECG Immediately

Before administering any treatment, you must determine if the QRS is narrow (<120 ms) or wide (≥120 ms). 1, 2, 3

• Narrow-complex tachycardia (QRS <120 ms) = SVT (proceed with SVT algorithm below). 1
• Wide-complex tachycardia (QRS ≥120 ms) = Treat as VT until proven otherwise, even if you suspect SVT with aberrancy. 2, 3

Critical Pitfall to Avoid

Never give verapamil, diltiazem, or other AV nodal blocking agents to wide-complex tachycardia of uncertain etiology—this can cause hemodynamic collapse or ventricular fibrillation if the rhythm is actually VT or pre-excited atrial fibrillation. 1, 2, 3

Management Algorithm for Stable SVT (Narrow-Complex)

First-Line: Vagal Maneuvers

• Modified Valsalva maneuver (bearing down for 10-30 seconds to achieve 30-40 mmHg intrathoracic pressure, then lying supine with legs elevated) is 2.8-3.8 times more effective than standard Valsalva. 1, 2, 4
• Carotid sinus massage for 5-10 seconds (only after confirming absence of bruit by auscultation). 1
• Ice-cold wet towel to the face or facial immersion in 10°C water. 1
• Success rate: 27.7-43% for terminating SVT. 1, 2
• Do not apply pressure to the eyeball—this is dangerous and abandoned. 1, 3

Second-Line: Adenosine

If vagal maneuvers fail, adenosine 6 mg IV rapid bolus through a proximal/large vein, followed immediately by saline flush. 1, 2

• Success rate: 90-95% for AVNRT and orthodromic AVRT. 1, 2
• Adenosine will also unmask atrial flutter or atrial tachycardia by causing transient AV block without terminating the rhythm. 1
• Minor side effects (flushing, chest discomfort, dyspnea) occur in ~30% but last <1 minute. 1
• Have cardioversion ready, as adenosine may precipitate atrial fibrillation that could conduct rapidly down an accessory pathway. 1

Third-Line: IV Calcium Channel Blockers or Beta Blockers

Only proceed if you are certain the rhythm is NOT VT or pre-excited atrial fibrillation. 1, 3

• IV diltiazem or verapamil: 64-98% conversion success rate; administer as slow infusion over up to 20 minutes to minimize hypotension risk. 1, 3
• IV beta blockers (metoprolol, esmolol, propranolol): Reasonable alternative with excellent safety profile, though less effective than calcium channel blockers. 1
• Avoid calcium channel blockers in patients with suspected systolic heart failure. 1

Fourth-Line: Synchronized Cardioversion

When pharmacologic therapy fails or is contraindicated in stable patients, proceed to synchronized cardioversion. 1, 3

• Perform after adequate sedation/anesthesia. 3
• Initial energy: 50-100J. 2, 3
• Success rate approaches 100%. 2

Management Algorithm for Stable VT (or Wide-Complex of Uncertain Etiology)

Treat as VT Until Proven Otherwise

The safest approach when facing wide-complex tachycardia is to assume VT, as giving AV nodal blockers to VT can be catastrophic. 2, 3

Pharmacologic Options for Stable VT

• IV amiodarone is indicated for hemodynamically stable VT refractory to other therapy. 5
• IV procainamide is an alternative for stable VT. 1
• Do not use adenosine as primary therapy for VT, though it can help differentiate SVT with aberrancy (adenosine will unmask VT by causing transient AV block without terminating it). 3

When to Proceed to Cardioversion

If pharmacologic therapy fails or the patient begins to decompensate, proceed immediately to synchronized cardioversion. 3, 5

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

If the wide-complex tachycardia is irregular and you suspect pre-excited atrial fibrillation (WPW with AF):

• Unstable patients: Immediate synchronized cardioversion. 1, 2
• Stable patients: IV ibutilide or IV procainamide (these slow conduction over the accessory pathway). 1, 2
• Never give adenosine, verapamil, diltiazem, or beta blockers—these can accelerate ventricular rate and cause ventricular fibrillation. 1

Post-Conversion Management

• After successful cardioversion, patients often have atrial or ventricular premature complexes that may reinitiate tachycardia. 1, 2
• An antiarrhythmic drug may be required to prevent acute reinitiation. 1, 2
• Arrange cardiology follow-up for consideration of catheter ablation (94.3-98.5% single-procedure success rate for SVT). 2

Summary Algorithm

1. Unstable (SVT or VT) → Immediate synchronized cardioversion 1, 2, 3
2. Stable + Narrow-complex → Vagal maneuvers → Adenosine → IV calcium channel blocker/beta blocker → Cardioversion 1, 2
3. Stable + Wide-complex → Treat as VT (IV amiodarone or procainamide) → Cardioversion if fails 2, 3, 5
4. Stable + Irregular wide-complex → Suspect pre-excited AF → IV ibutilide or procainamide (never AV nodal blockers) 1, 2