What is the initial management for a patient with supraventricular tachycardia (SVT) and sustained tachycardia?

Initial Management of Supraventricular Tachycardia

For a 26-year-old woman with sustained SVT, immediately attempt vagal maneuvers as first-line treatment, followed by intravenous adenosine 6 mg rapid bolus if vagal maneuvers fail, with synchronized cardioversion reserved only if she becomes hemodynamically unstable. 1, 2

Immediate Assessment

Determine hemodynamic stability first - assess for hypotension, altered mental status, chest pain, acute heart failure, or signs of shock. 1

• If hemodynamically unstable: proceed directly to synchronized cardioversion 1
• If hemodynamically stable: proceed with stepwise approach below 1, 2

First-Line Treatment: Vagal Maneuvers

Perform vagal maneuvers immediately - these have a 27.7% success rate when alternating techniques and should be attempted with the patient in the supine position. 1, 2

Specific Techniques (in order of preference):

• Modified Valsalva maneuver: Patient bears down against a closed glottis for 10-30 seconds, generating at least 30-40 mm Hg of intrathoracic pressure 1, 2
• Carotid sinus massage: Apply steady pressure over the right or left carotid sinus for 5-10 seconds after confirming absence of bruit by auscultation 1, 2
• Diving reflex: Apply an ice-cold, wet towel to the face 1, 2
• Critical warning: Never apply pressure to the eyeballs - this is potentially dangerous and has been abandoned 1, 2

Second-Line Treatment: Adenosine

If vagal maneuvers fail, immediately administer adenosine 6 mg IV as a rapid bolus - this terminates SVT in 90-95% of patients. 1, 2

Key Points About Adenosine:

• Functions as both therapeutic and diagnostic agent, unmasking atrial activity in other arrhythmias like atrial flutter 1, 2
• Side effects are minor and brief (<1 minute), occurring in approximately 30% of patients 1, 2
• Critical precaution: Have electrical cardioversion equipment immediately available, as adenosine can precipitate atrial fibrillation that may conduct rapidly and potentially cause ventricular fibrillation 1, 2

Third-Line Treatment: Alternative Pharmacologic Agents

If adenosine fails or is contraindicated, consider intravenous diltiazem or verapamil - these have 80-98% success rates in hemodynamically stable patients. 1

• Intravenous beta blockers are also reasonable alternatives 1
• Do not use these agents if there is any evidence of ventricular pre-excitation on the resting ECG without immediate cardioversion capability 1

Management of Hemodynamically Unstable Patients

Perform immediate synchronized cardioversion if the patient develops hypotension, altered consciousness, chest pain, or acute heart failure at any point. 1

• Synchronized cardioversion is highly effective in terminating SVT 1
• This should be done after adequate sedation/anesthesia in stable patients, but immediately in unstable patients 1
• Patients may have atrial or ventricular premature complexes immediately after cardioversion that can reinitiate tachycardia 1

Common Pitfalls to Avoid

• Never delay cardioversion in unstable patients to attempt pharmacologic therapy 1
• Never use adenosine without cardioversion equipment available due to risk of precipitating rapidly-conducted atrial fibrillation 1, 2
• Never perform carotid massage without first auscultating for bruits 1, 2
• Never use calcium channel blockers or beta blockers in patients with pre-excitation (Wolff-Parkinson-White pattern) without cardioversion capability, as they can enhance accessory pathway conduction during atrial fibrillation 1

Documentation Requirements

Obtain a 12-lead ECG during tachycardia before treatment if the patient is stable, to differentiate tachycardia mechanisms and diagnose the specific type of SVT. 1

• This allows for proper diagnosis and guides long-term management decisions 1
• Record rhythm strips during vagal maneuvers and medication administration 1