What medication should be administered for severe tachycardia?

Medication for Severe Tachycardia

For severe tachycardia, immediate synchronized cardioversion is the definitive treatment when the patient is hemodynamically unstable (hypotension, altered mental status, chest pain, shock, or acute heart failure), restoring sinus rhythm in nearly 100% of cases without attempting pharmacologic therapy first. 1

Immediate Assessment: Stability Determines Everything

The first critical decision is whether the patient is unstable—defined by hypotension (systolic BP <90 mmHg), altered mental status, signs of shock, chest pain suggesting ischemia, or acute heart failure. 1

• Unstable patients require immediate synchronized cardioversion (starting at 50–100 J) without delay for vagal maneuvers or medications. 1
• Stable patients can proceed with pharmacologic therapy after obtaining a 12-lead ECG during tachycardia to differentiate narrow-complex (supraventricular) from wide-complex (ventricular) tachycardia. 1

Narrow-Complex Tachycardia (QRS <0.12 seconds) – Stable Patients

First-Line: Vagal Maneuvers

• Modified Valsalva maneuver (patient supine, bearing down 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 no carotid bruit) is an alternative. 1
• Never apply pressure to the eyeball—this technique is dangerous and abandoned. 1

Second-Line: Adenosine (First-Line Pharmacologic Agent)

Adenosine is the drug of choice for acute SVT termination, achieving conversion in 90–95% of AVNRT and 78–96% of AVRT cases. 1, 2

Dosing protocol: 1, 2

• 6 mg rapid IV push (over 1–2 seconds) through a proximal vein, followed immediately by 20 mL saline flush
• If no conversion in 1–2 minutes, give 12 mg rapid IV push with flush
• May repeat 12 mg once more (maximum cumulative dose 30 mg)

Dose adjustments: 1, 2

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when given via central line
• Increase dose in patients with high caffeine, theophylline, or theobromine levels

Absolute contraindications: 1, 2

• Active asthma or bronchospasm (risk of severe bronchospasm)
• Second- or third-degree AV block or sick sinus syndrome without pacemaker
• Pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome)

Critical safety point: A defibrillator must be immediately available because adenosine can precipitate rapid atrial fibrillation, especially in WPW syndrome. 1, 2

Third-Line: Calcium-Channel Blockers or Beta-Blockers

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

Diltiazem dosing: 1

• 15–20 mg (≈0.25 mg/kg) IV over 2 minutes
• A slower infusion over 20 minutes reduces hypotension risk

Verapamil alternative: 1

• 2.5–5 mg IV over 2 minutes, with clinical effect in 3–5 minutes

Beta-blocker options: 1, 3

• Metoprolol: 2.5–5 mg IV every 2–5 minutes (maximum 15 mg over 10–15 minutes)
• Esmolol: 500 mcg/kg bolus over 1 minute, followed by 50 mcg/kg/min infusion (can titrate up to 200 mcg/kg/min)

Absolute contraindications for calcium-channel blockers: 1

• Inability to exclude ventricular tachycardia
• Pre-excited atrial fibrillation (WPW syndrome)—can precipitate ventricular fibrillation
• Suspected systolic heart failure
• Hemodynamic instability

Never combine IV calcium-channel blockers with IV beta-blockers due to synergistic hypotension and bradycardia. 1

Fourth-Line: Synchronized Cardioversion

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

Wide-Complex Tachycardia (QRS ≥0.12 seconds)

Assume all wide-complex tachycardia represents ventricular tachycardia until proven otherwise; misdiagnosis and treatment as SVT can be fatal. 1

Unstable Wide-Complex Tachycardia

• Immediate synchronized cardioversion without attempting pharmacologic therapy. 1

Stable Monomorphic VT

For stable monomorphic VT without severe heart failure or acute MI, procainamide is the first-line agent. 1

For patients with left-ventricular dysfunction, severe heart failure, or acute MI, amiodarone is preferred due to its safer profile in structural heart disease: 1

• Amiodarone 150 mg IV over 10 minutes
• May repeat up to cumulative 2.2 g IV within 24 hours
• Maintenance infusion: 1 mg/min for 6 hours, then 0.5 mg/min

Sotalol alternative: 1

• 1.5 mg/kg IV over 5 minutes
• Avoid in patients with prolonged QT interval

Polymorphic VT (Torsades de Pointes)

IV magnesium is the primary treatment for torsades de pointes (polymorphic VT with prolonged QT). 1

Additional measures: 1

• Immediately discontinue all QT-prolonging medications
• Correct electrolyte abnormalities (potassium, magnesium, calcium)
• If bradycardia or pauses accompany torsades, consider overdrive pacing or IV isoproterenol

Critical Contraindication

Calcium-channel blockers (verapamil, diltiazem) are absolutely contraindicated for wide-complex tachycardia of unknown origin because they can precipitate hemodynamic collapse if the rhythm is VT. 1

Special Clinical Scenarios

Pregnancy

• Vagal maneuvers remain first-line. 1
• Adenosine is safe and effective during pregnancy. 1, 2
• If unstable, proceed to synchronized cardioversion. 1

Tachycardia on Nicardipine Drip

Beta-blockade is specifically recommended for patients receiving vasodilators when reflex tachycardia develops. 4

• Esmolol preferred: 0.5–1 mg/kg IV bolus followed by 50–300 mcg/kg/min infusion 4
• Metoprolol alternative: 2.5–5 mg IV bolus over 2 minutes, may repeat every 5 minutes to maximum 15 mg 4
• Labetalol (combined alpha/beta blockade): 0.25–0.5 mg/kg IV bolus or 2–4 mg/min continuous infusion 4

Critical Pitfalls to Avoid

• Do not delay cardioversion in unstable patients to attempt vagal maneuvers or drug therapy. 1
• Do not administer calcium-channel blockers when VT or pre-excited AF is possible—this may precipitate ventricular fibrillation and death. 1
• Do not use adenosine in patients with asthma due to severe bronchospasm risk. 1, 2
• Do not apply pressure to the eyeball as a vagal maneuver. 1
• Always obtain a 12-lead ECG during tachycardia to differentiate SVT from VT and identify pre-excitation. 1
• Do not combine IV calcium-channel blockers with IV beta-blockers. 1

Post-Conversion Management

• Continuous cardiac monitoring is essential immediately after conversion because premature complexes frequently trigger recurrent episodes within seconds to minutes. 1, 2
• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker (e.g., oral diltiazem or beta-blocker) to prevent re-initiation. 1, 2
• Refer to cardiology for consideration of catheter ablation (94–98% single-procedure success) for recurrent symptomatic SVT. 1