What is the recommended acute management (vagal maneuvers, adenosine dosing and contraindications), maintenance pharmacotherapy (dose and side‑effects of beta‑blockers, non‑dihydropyridine calcium‑channel blockers, flecainide, propafenone, amiodarone), criteria for catheter ablation, and outpatient discharge plan for a hemodynamically stable patient presenting with a regular narrow‑complex tachycardia consistent with paroxysmal supraventricular tachycardia (PSVT)?

Approach to PSVT Management

Immediate Hemodynamic Assessment

Assess hemodynamic stability within the first 60 seconds: hypotension (systolic BP <90 mmHg), altered mental status, shock, ischemic chest pain, or acute heart failure mandates immediate synchronized cardioversion at 50–100 J without attempting vagal maneuvers or medications. 1, 2

• Synchronized cardioversion restores sinus rhythm in nearly 100% of hemodynamically unstable PSVT cases. 1, 2
• Do not delay cardioversion to attempt adenosine or vagal techniques in unstable patients—this increases risk of cardiovascular collapse. 1, 2

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Acute Management of Hemodynamically Stable PSVT

Step 1: Vagal Maneuvers (First-Line)

• Modified Valsalva maneuver is the preferred initial intervention: patient supine, bearing down for 10–30 seconds to generate ≥30–40 mmHg intrathoracic pressure. 1, 2, 3
• Modified Valsalva terminates PSVT in approximately 43% of attempts—2.8–3.8× more effective than standard Valsalva. 1, 2
• Carotid sinus massage: apply steady pressure over the carotid sinus for 5–10 seconds after confirming absence of a bruit; avoid in elderly patients or those with known carotid disease. 1, 2
• Ice-water facial immersion: place an ice-cold wet towel on the face to activate the diving reflex. 1, 3
• Overall success rate across all vagal techniques is approximately 27–28%. 1, 2, 3
• Critical safety warning: Never apply pressure to the eyeball—this technique is dangerous and abandoned. 1, 2

Step 2: Adenosine (First-Line Pharmacologic Agent)

Adenosine is the drug of choice after failed vagal maneuvers, terminating 90–95% of AVNRT and 78–96% of AVRT episodes. 1, 2, 3, 4

Dosing Protocol

• Initial dose: 6 mg rapid IV push (over 1–2 seconds) through a large proximal vein (antecubital preferred), followed immediately by a 20 mL saline flush. 1, 2
• Second dose: If no conversion within 1–2 minutes, give 12 mg rapid IV push with saline flush. 1, 2
• Third dose: If still no response, administer a final 12 mg rapid IV bolus. 1, 2
• Maximum cumulative dose: 30 mg (6 mg + 12 mg + 12 mg). 1
• Average time to termination after an effective dose is approximately 30 seconds. 1

Dose Adjustments

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients (denervated hearts), or when administered via central venous access. 1, 2
• Increase dose in patients with significant blood levels of theophylline, caffeine, or theobromine (competitive adenosine receptor antagonists). 5, 1, 2

Absolute Contraindications

• Active asthma or bronchospasm (risk of severe bronchospasm). 1, 2, 3
• Second- or third-degree AV block or sick sinus syndrome without a pacemaker. 1, 2
• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White syndrome)—risk of rapid ventricular response and ventricular fibrillation. 1, 2

Common Side Effects (Transient, <60 seconds)

• Flushing, dyspnea, and chest discomfort occur in approximately 30% of patients but resolve within 60 seconds. 1, 2, 3, 4
• Transient AV block and premature ventricular contractions may occur. 1

Safety Requirement

• A defibrillator must be immediately available when administering adenosine because it can precipitate rapid atrial fibrillation, especially in patients with Wolff-Parkinson-White syndrome. 1, 2

Diagnostic Value

• Adenosine serves a dual therapeutic-diagnostic role: failure to convert but transient AV block that unmasks atrial flutter or atrial tachycardia directs therapy toward rate control with a longer-acting AV-nodal blocker. 1, 2, 3

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

When adenosine fails or is contraindicated (e.g., asthma), intravenous diltiazem is the preferred alternative, achieving conversion in 64–98% of cases. 1, 2, 3

Diltiazem

• Dose: 15–20 mg (≈0.25 mg/kg) IV over 2 minutes; a slower infusion over up to 20 minutes reduces hypotension risk. 1, 2
• Diltiazem is superior to esmolol in head-to-head trials. 1

Verapamil

• Dose: 2.5–5 mg IV over 2 minutes; clinical effect typically within 3–5 minutes. 1, 2, 3
• Conversion rate comparable to diltiazem (64–98%). 1, 2

Beta-Blockers

• Metoprolol: 2.5–5 mg IV every 2–5 minutes; maximum cumulative dose 15 mg over 10–15 minutes. 1, 2
• Esmolol: useful for short-term rate control, particularly when concurrent hypertension is present. 1, 2
• Use cautiously in severe COPD. 1, 2

Absolute Contraindications for Calcium-Channel Blockers

• Ventricular tachycardia cannot be excluded (may precipitate hemodynamic collapse). 1, 2, 3
• Pre-excited atrial fibrillation (WPW)—AV-nodal blockade can enhance accessory-pathway conduction and trigger ventricular fibrillation. 1, 2, 3
• Suspected systolic heart failure or severe left-ventricular dysfunction (negative inotropic effects). 1, 2
• Any hemodynamic instability (hypotension, shock). 1, 2

Critical Drug Interaction

• Never combine IV calcium-channel blockers with IV beta-blockers because of synergistic hypotension and bradycardia. 1, 2

Step 4: Synchronized Cardioversion (Rescue for Stable Patients)

• Elective synchronized cardioversion (starting at 50–100 J) with appropriate sedation is indicated when pharmacologic therapy fails or is contraindicated. 1, 2
• Success rates are 80–98% in hemodynamically stable patients and near-100% termination of AVRT/AVNRT. 1, 2

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Post-Conversion Management

Immediate Monitoring

• Continuous cardiac monitoring is essential immediately after conversion because premature atrial or ventricular complexes frequently trigger recurrent PSVT within seconds to minutes. 1, 2
• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker (e.g., oral diltiazem or a beta-blocker) to prevent re-initiation. 1, 2

Diagnostic Work-Up

• Obtain a 12-lead ECG in sinus rhythm to assess for pre-excitation (delta waves). 1, 2
• Check serum electrolytes (potassium, magnesium, calcium) and correct abnormalities. 1

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Long-Term Management & Outpatient Discharge Planning

First-Line: Catheter Ablation

Catheter ablation should be offered as first-line definitive therapy for all patients with symptomatic recurrent PSVT, with single-procedure success rates of 94.3–98.5% and low complication rates. 1, 2

Indications for Electrophysiology Referral

• Recurrent symptomatic PSVT (≥2 episodes per year). 1
• Patient preference for definitive cure. 1
• Occupational requirements (e.g., pilots, bus drivers). 1
• Failure of pharmacologic prophylaxis. 1

Alternative: Long-Term Pharmacologic Prophylaxis (When Ablation Declined)

First-Line Oral Agents

• Oral beta-blockers, diltiazem, or verapamil are recommended for ongoing prevention of recurrent AVNRT. 1, 2, 3
• Verapamil dosing: up to 480 mg/day (or diltiazem equivalent), titrated to effect. 1

Second-Line Oral Agents

• Flecainide or propafenone: 86–93% effective at 12 months but absolutely contraindicated in patients with structural heart disease, ischemic heart disease, or left-ventricular dysfunction. 1, 2
• These agents should only be used in patients without any structural cardiac abnormalities. 1, 2

Third-Line Oral Agents

• Sotalol or dofetilide: considered when first-line agents fail. 2

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Patient Education for Outpatient Discharge

Self-Management Techniques

• Teach patients how to perform vagal maneuvers (modified Valsalva, carotid sinus massage, ice-water facial immersion) for self-termination of future PSVT episodes. 1, 2
• Consider "pill-in-the-pocket" therapy as a personalized self-directed intervention developed in partnership with the patient. 1, 2

Discharge Criteria

• Patient has been in stable sinus rhythm for several hours without recurrence. 1
• Patient demonstrates understanding of vagal maneuvers. 1, 2
• Outpatient cardiology follow-up is arranged for consideration of catheter ablation or long-term pharmacologic therapy. 1, 2

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Special Populations

Pregnancy

• Vagal maneuvers remain the first-line therapy. 1, 2
• Adenosine is safe and effective during pregnancy and is the first-line pharmacologic agent. 1, 2
• If the patient becomes hemodynamically unstable, synchronized cardioversion is safe at any gestational stage; place pads away from the uterus and perform fetal monitoring if feasible. 1, 2

Adult Congenital Heart Disease

• Adenosine is appropriate for PSVT termination. 1, 2
• IV diltiazem or esmolol may be used cautiously with close monitoring for hypotension. 1, 2
• Flecainide should be avoided in the presence of significant ventricular dysfunction. 1, 2

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Critical Pitfalls to Avoid

• Do not delay cardioversion in unstable patients to attempt vagal maneuvers or drug therapy. 1, 2
• Do not administer calcium-channel blockers when ventricular tachycardia or pre-excited atrial fibrillation is possible—this may precipitate ventricular fibrillation and death. 1, 2, 3
• Do not use adenosine in patients with asthma due to the risk of severe bronchospasm. 1, 2, 3
• Do not combine IV calcium-channel blockers with IV beta-blockers because of synergistic hypotension and bradycardia. 1, 2
• Do not prescribe flecainide or propafenone to any patient with structural heart disease, ischemic heart disease, or left-ventricular dysfunction. 1, 2
• Do not apply pressure to the eyeball as a vagal maneuver—this technique is dangerous and abandoned. 1, 2
• Always obtain a 12-lead ECG during tachycardia to differentiate PSVT from ventricular tachycardia and to identify pre-excitation. 1, 2