What is the immediate management of a patient with paroxysmal supraventricular tachycardia, including both hemodynamically stable and unstable presentations?

Immediate Management of Paroxysmal Supraventricular Tachycardia

For hemodynamically unstable patients with paroxysmal SVT, proceed directly to synchronized cardioversion (50–100 J) without attempting vagal maneuvers or pharmacologic therapy; for hemodynamically stable patients, begin with vagal maneuvers followed by adenosine 6 mg rapid IV push if vagal maneuvers fail. 1, 2

Step 1: Assess Hemodynamic Stability Immediately

Unstable patients exhibit any of the following:

• Hypotension (systolic BP <90 mmHg) 1, 2, 3
• Altered mental status or syncope 2, 3
• Signs of shock (cold extremities, poor perfusion, diaphoresis) 2, 3
• Chest pain with ST-segment changes indicating myocardial ischemia 2
• Acute heart failure or pulmonary edema 2, 3

Stable patients have none of the above and can tolerate sequential interventions. 1

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Management of Hemodynamically Unstable SVT

Immediate Synchronized Cardioversion (First-Line)

• Perform synchronized cardioversion at 50–100 J immediately after providing procedural sedation if the patient is conscious; this restores sinus rhythm in nearly 100% of unstable SVT cases. 1, 2, 3
• Do not delay cardioversion to attempt vagal maneuvers or adenosine administration, as this increases mortality risk. 3

Exception: Consider Adenosine First (Only If Specific Criteria Met)

• If the tachycardia is regular with narrow QRS complex and cardioversion equipment is being prepared, one dose of adenosine 6 mg rapid IV push through a proximal vein followed by 20 mL saline flush may be attempted, with 90–95% success for AVNRT and orthodromic AVRT. 1, 2
• Have a defibrillator immediately available because adenosine may precipitate atrial fibrillation with rapid ventricular conduction, potentially causing ventricular fibrillation. 1, 2

Absolute Contraindications in Unstable Patients

• Never administer calcium-channel blockers (diltiazem, verapamil) or beta-blockers (metoprolol, esmolol) in unstable SVT, as they precipitate cardiovascular collapse. 1, 2, 3
• Never use digoxin in acute unstable SVT; it has no established role and is too slow-acting. 3

Special Case: Pre-Excited Atrial Fibrillation (Wolff-Parkinson-White)

• If the ECG shows irregular wide-complex tachycardia consistent with pre-excited AF, proceed immediately to synchronized cardioversion. 2
• Avoid adenosine, calcium-channel blockers, beta-blockers, and digoxin entirely, as they enhance accessory-pathway conduction and can trigger ventricular fibrillation. 1, 2

Post-Cardioversion Management

• Continuous cardiac monitoring is essential because premature atrial or ventricular complexes frequently re-initiate SVT within seconds to minutes. 1, 2, 3
• Have longer-acting AV-nodal blockers ready (diltiazem or metoprolol) to prevent acute recurrence if premature complexes appear. 2, 3

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Management of Hemodynamically Stable SVT

Step 1: Vagal Maneuvers (First-Line)

• Modified Valsalva maneuver (patient supine, bearing down for 10–30 seconds to generate 30–40 mmHg intrathoracic pressure) terminates SVT in approximately 43% of attempts. 1
• Carotid sinus massage (5–10 seconds steady pressure after confirming absence of carotid bruit) is an effective alternative. 1
• Ice-water facial immersion (cold wet towel on face) activates the diving reflex. 1
• Never apply pressure to the eyeball—this technique is dangerous and abandoned. 1
• Overall success rate of all vagal techniques is approximately 27–28%. 1

Step 2: Adenosine (First-Line Pharmacologic Agent)

Dosing Protocol:

• 6 mg rapid IV push (over 1–2 seconds) through a large proximal vein (antecubital preferred), followed immediately by 20 mL saline flush. 1
• If no conversion within 1–2 minutes, give 12 mg rapid IV push with saline flush. 1
• If still no response, give a second 12 mg dose (maximum cumulative dose 30 mg). 1

Efficacy:

• Adenosine terminates 90–95% of AVNRT and 78–96% of AVRT episodes. 1, 4, 5

Dose Adjustments:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when administered via central venous access. 1
• Increase dose in patients with high caffeine, theophylline, or theobromine levels. 1

Absolute Contraindications:

• Active asthma or bronchospasm (risk of severe bronchospasm). 1
• Second- or third-degree AV block or sick-sinus syndrome without a pacemaker. 1

Common Side Effects (transient, <60 seconds):

• Flushing, dyspnea, chest discomfort. 1, 5

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

Calcium-Channel Blockers (Preferred Alternative):

• Diltiazem 15–20 mg IV over 2 minutes achieves 64–98% conversion and is the preferred alternative. 1
• Verapamil 2.5–5 mg IV over 2 minutes is an acceptable alternative, with clinical effect in 3–5 minutes. 1, 6

Beta-Blockers:

• Metoprolol 2.5–5 mg IV every 2–5 minutes (maximum 15 mg over 10–15 minutes). 1
• Esmolol is useful for short-term control, particularly when hypertension coexists. 1

Critical Safety Warnings for Calcium-Channel Blockers:

• Do NOT administer if:
  • Ventricular tachycardia cannot be excluded 1
  • Pre-excited atrial fibrillation (WPW) is present 1
  • Suspected systolic heart failure 1
  • Any hemodynamic instability 1

Step 4: Synchronized Cardioversion (Rescue for Stable Patients)

• When all pharmacologic options fail or are contraindicated, elective synchronized cardioversion with appropriate sedation yields 80–98% success. 1

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Post-Conversion Management (Both Stable and Unstable)

• Continuous cardiac monitoring immediately after conversion is essential, as premature complexes trigger recurrent SVT within seconds to minutes. 1
• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker (diltiazem or beta-blocker) to prevent re-initiation. 1
• If adenosine unmasks atrial flutter or atrial tachycardia, manage with a longer-acting AV-nodal blocker for rate control rather than attempting rhythm conversion. 1

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Special Populations

Pregnancy:

• Vagal maneuvers remain first-line. 1
• Adenosine is safe and effective during pregnancy. 1
• If hemodynamically unstable, synchronized cardioversion is indicated. 1

Adult Congenital Heart Disease:

• Adenosine is appropriate for SVT termination. 1
• IV diltiazem or esmolol may be used cautiously, monitoring for hypotension. 1
• Avoid flecainide in significant ventricular dysfunction. 1

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Critical Pitfalls to Avoid

• Do not delay cardioversion in unstable patients to attempt vagal maneuvers or drug therapy. 1, 3
• Do not administer calcium-channel blockers or beta-blockers when hypotension is present or ventricular tachycardia cannot be excluded, as this may precipitate cardiovascular collapse or ventricular fibrillation. 1, 2, 3
• Do not use adenosine in asthma due to severe bronchospasm risk. 1
• Do not apply pressure to the eyeball during vagal maneuvers—this is hazardous. 1
• Always obtain a 12-lead ECG during tachycardia to differentiate SVT from VT and identify pre-excitation. 1