What is the appropriate management of a hemodynamically stable patient presenting with a regular narrow‑complex supraventricular tachycardia?

Management of Hemodynamically Stable Supraventricular Tachycardia

For a hemodynamically stable patient with regular narrow-complex SVT, begin with vagal maneuvers (modified Valsalva maneuver preferred), followed by adenosine 6 mg IV push if vagal maneuvers fail, then escalate to IV calcium channel blockers or beta-blockers if adenosine is unsuccessful or contraindicated. 1, 2

Step 1: Vagal Maneuvers (First-Line)

Vagal maneuvers must be attempted before any pharmacologic therapy. 2

• Modified Valsalva maneuver is the most effective vagal technique, achieving conversion in approximately 43% of cases and is 2.8-3.8 times more effective than the standard Valsalva maneuver 2, 3
• Position the patient supine before beginning the maneuver 2
• Instruct the patient to bear down against a closed glottis for 10-30 seconds, generating intrathoracic pressure of at least 30-40 mmHg 2
• Carotid sinus massage is an alternative but less effective option: apply steady pressure over the carotid sinus for 5-10 seconds after confirming absence of carotid bruits by auscultation 1, 2
• Overall success rate across all vagal techniques is approximately 27.7% 1, 4

Critical safety warning: Never apply pressure to the eyeball—this technique has been abandoned due to potential danger 1

Step 2: Adenosine (First-Line Pharmacologic Agent)

If vagal maneuvers fail, adenosine is the preferred drug with 90-95% success rates in AVNRT and 78-96% success in AVRT. 1, 2, 3

Adenosine Administration Protocol:

• Initial dose: 6 mg rapid IV push through a large proximal vein, followed immediately by a 20 mL saline flush 2, 5
• If no conversion within 1-2 minutes, administer 12 mg IV push with saline flush 2, 5
• A third dose of 12 mg may be given if rhythm persists 2
• Have a defibrillator immediately available when administering adenosine 5

Dose Modifications:

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 5
• Increase dose in patients with significant blood levels of theophylline, caffeine, or theobromine 5

Adenosine Contraindications:

• Absolute contraindication: Asthma or bronchospastic lung disease (risk of severe bronchospasm) 2, 5
• Second- or third-degree AV block, sick sinus syndrome 5

Common Side Effects:

• Flushing, dyspnea, and chest discomfort are most common but transient, lasting less than 60 seconds 5, 6

Step 3: Alternative Pharmacologic Agents (When Adenosine Fails or Is Contraindicated)

Calcium Channel Blockers (Preferred Alternatives):

• IV diltiazem 15-20 mg (≈0.25 mg/kg) over 2 minutes achieves 64-98% conversion rates and is the preferred alternative for patients with asthma or COPD 1, 2
• IV verapamil 2.5-5 mg over 2 minutes is an acceptable alternative with 80-98% success rates 1, 2

Critical safety warnings for calcium channel blockers—do NOT administer if: 1, 2

• Ventricular tachycardia cannot be excluded
• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White syndrome) is present—risk of ventricular fibrillation
• Suspected systolic heart failure exists
• Patient is hemodynamically unstable

Beta-Blockers:

• IV metoprolol or esmolol are reasonable alternatives with excellent safety profiles, though slightly less effective than calcium channel blockers 1, 2
• Use with caution in severe COPD 2
• Esmolol is particularly useful when concurrent hypertension is present 2

Step 4: Synchronized Cardioversion (Rescue Therapy)

If pharmacologic therapy is ineffective or contraindicated in a hemodynamically stable patient, perform synchronized cardioversion. 1, 2

• Synchronized cardioversion achieves near-100% termination of SVT (AVRT and AVNRT) 1, 2
• Initial energy: 50-100 J for SVT 2

Critical Decision Point: Hemodynamic Instability

If at any point the patient develops hypotension, altered mental status, shock, chest pain, or acute heart failure, proceed immediately to synchronized cardioversion without attempting further pharmacologic therapy. 1, 2

Diagnostic Considerations During Acute Management

• Obtain a 12-lead ECG during tachycardia whenever possible to confirm the mechanism and exclude ventricular tachycardia or pre-excited atrial fibrillation 2
• Adenosine serves dual therapeutic and diagnostic purposes—it can unmask underlying atrial flutter or atrial tachycardia if SVT does not terminate 1, 2
• Continuous ECG recording during adenosine administration helps distinguish between drug failure and successful termination with immediate reinitiation 2

Post-Conversion Management

• Monitor continuously for recurrence—atrial or ventricular premature complexes commonly occur immediately after conversion and may trigger recurrent episodes 2, 5
• If immediate recurrence occurs, consider a longer-acting AV nodal blocking agent such as diltiazem or a beta-blocker 2, 5
• An antiarrhythmic drug may be required to prevent acute reinitiation in patients with frequent premature complexes post-conversion 2

Special Population: Pregnancy

• Vagal maneuvers remain first-line 2
• Adenosine is safe and effective during pregnancy and is the recommended first-line pharmacologic therapy 2, 5
• Synchronized cardioversion is safe at all stages of pregnancy if pharmacologic therapy fails 2

Common Pitfalls to Avoid

• Never use calcium channel blockers or beta-blockers before confirming the rhythm is not ventricular tachycardia or pre-excited atrial fibrillation 1, 2
• Do not skip vagal maneuvers—they are simple, safe, and effective in approximately one-quarter of cases 1, 2
• Do not start with 12 mg adenosine—70% of patients convert with 6 mg or less, and side effects are dose-dependent 5
• Do not perform carotid massage without first auscultating for carotid bruits 2