What is the initial management of Supraventricular Tachycardia (SVT) according to the newest Advanced Cardiovascular Life Support (ACLS) algorithm?

ACLS Algorithm for SVT Management

For hemodynamically stable SVT, begin with the modified Valsalva maneuver (supine position with leg elevation after strain), followed by adenosine 6 mg IV rapid push if unsuccessful, then proceed to synchronized cardioversion if pharmacologic therapy fails; for hemodynamically unstable patients, proceed immediately to synchronized cardioversion. 1, 2, 3

Initial Assessment and Stabilization

Determine hemodynamic stability immediately - look for hypotension, altered mental status, signs of shock, chest pain, or acute heart failure symptoms, as these mandate immediate synchronized cardioversion. 1, 2

• Obtain a 12-lead ECG during tachycardia to identify QRS duration and rhythm characteristics, which is essential to exclude ventricular tachycardia or pre-excited atrial fibrillation before proceeding with treatment. 2
• Critical pitfall: Never give AV nodal blocking agents (adenosine, diltiazem, verapamil, beta-blockers) if pre-excited AF is present, as this may accelerate ventricular rate and precipitate ventricular fibrillation. 2

Hemodynamically Stable SVT Algorithm

Step 1: Modified Valsalva Maneuver (First-Line)

• Position the patient supine before beginning the maneuver. 3
• Have the patient bear down against a closed glottis for 10-30 seconds, generating intrathoracic pressure of at least 30-40 mmHg. 2, 3
• The modified Valsalva maneuver is 2.8-3.8 times more effective than the standard Valsalva maneuver, with success rates around 28-44% for initial conversion. 3, 4
• Alternative vagal maneuvers include carotid sinus massage (only after confirming absence of carotid bruits), though this is less effective than Valsalva techniques. 3

Step 2: Adenosine (Second-Line)

• Administer adenosine 6 mg as a rapid IV bolus through a proximal/large vein, followed immediately by a saline flush. 1, 3
• If unsuccessful after 1-2 minutes, give 12 mg IV rapid push (can repeat once). 1
• Recent evidence suggests starting with 12 mg may be more effective (54.2% vs 40.6% conversion rate) compared to 6 mg initial dosing. 5
• Adenosine achieves 78-96% success rates for AVNRT and AVRT, with 90-95% effectiveness in orthodromic AVRT and AVNRT specifically. 1, 2, 3
• Maintain continuous ECG recording during administration to distinguish drug failure from successful termination with immediate reinitiation. 1
• Expected side effects: chest discomfort, shortness of breath, flushing (serious adverse effects are rare due to very short half-life). 1
• Diagnostic utility: Adenosine may unmask atrial flutter or atrial tachycardia but rarely terminates these rhythms. 1

Step 3: IV Calcium Channel Blockers or Beta-Blockers (Third-Line)

• Use IV diltiazem or verapamil if adenosine fails, with success rates of 64-98% in hemodynamically stable patients. 2, 3
• Critical contraindication: Do not give verapamil or diltiazem if you cannot definitively exclude ventricular tachycardia or pre-excited AF, as this may cause hemodynamic collapse or ventricular fibrillation. 2

Step 4: Synchronized Cardioversion

• Perform synchronized cardioversion when pharmacological therapy is ineffective or contraindicated in stable patients. 1
• Use 50-100J initial energy for SVT. 3
• Ensure adequate sedation or anesthesia before cardioversion in stable patients. 1

Hemodynamically Unstable SVT Algorithm

Proceed immediately to synchronized cardioversion when vagal maneuvers or adenosine are ineffective or not feasible. 1

• Synchronized cardioversion successfully restores sinus rhythm in essentially all hemodynamically unstable patients. 1
• For pre-excited AF specifically: Synchronized cardioversion is mandatory; do not attempt AV nodal blockade. 2
• If the patient is stable enough and the tachycardia is regular with narrow QRS, adenosine may be considered first even in the presence of concerning symptoms. 1

Special Considerations for Irregular SVT

• Irregular rhythm suggests atrial fibrillation, multifocal atrial tachycardia, or premature depolarizations rather than AVNRT or AVRT. 2
• For hemodynamically stable pre-excited AF, use ibutilide or IV procainamide (not AV nodal blockers). 2
• Multifocal atrial tachycardia is most common in patients with underlying pulmonary disease. 2

Post-Conversion Management

• Monitor for atrial or ventricular premature complexes immediately after conversion. 3
• An antiarrhythmic drug may be required to prevent acute reinitiation of the arrhythmia. 3
• Have cardioversion equipment ready throughout the treatment process. 3