Classification and Evidence‑Based Management of Tachyarrhythmias

1. Classification of Tachyarrhythmias

• Tachyarrhythmias are classified by QRS complex width, rhythm regularity, and anatomic origin, which directly determines the acute management strategy. 1
• Narrow‑complex tachycardias (QRS < 120 ms) include sinus tachycardia, atrial fibrillation, atrial flutter, AV nodal re‑entrant tachycardia (AVNRT), accessory‑pathway mediated tachycardia (AVRT), atrial tachycardia, multifocal atrial tachycardia, and junctional tachycardia. 1
• Wide‑complex tachycardias (QRS ≥ 120 ms) are most often ventricular in origin; when the mechanism is uncertain, they should be managed as ventricular tachycardia (VT). 1

2. Acute Management of Hemodynamically Unstable Tachycardia

• Immediate synchronized direct‑current (DC) cardioversion is the treatment of choice for any hemodynamically unstable tachyarrhythmia, irrespective of the underlying mechanism. 2
• The recommendation applies to both narrow‑ and wide‑complex tachycardias. 2

3. Acute Management of Hemodynamically Stable Narrow‑Complex SVT

3.1 First‑Line Non‑Pharmacologic Interventions

• Vagal maneuvers (e.g., Valsalva maneuver or carotid sinus massage) are the initial recommended therapy. 2

3.2 Pharmacologic Therapy

• Adenosine is the preferred agent for rapid termination of regular narrow‑complex SVT.

  • First dose: 6 mg rapid IV push followed by a normal‑saline flush. 1
  • Second dose (if needed): 12 mg rapid IV push. 1
  • Use with extreme caution in cardiac transplant recipients because paradoxical effects have been reported. 1

• If adenosine is ineffective or contraindicated:

  • Intravenous diltiazem or verapamil are effective for hemodynamically stable SVT. 2
  • Intravenous β‑blockers are a reasonable alternative. 2

• When pharmacologic therapy fails or is contraindicated, proceed to synchronized cardioversion. 2

4. Management of Stable Wide‑Complex Tachycardia

4.1 General Principle

• When the diagnosis is uncertain, treat the rhythm as ventricular tachycardia. (Guideline source not available; omitted per instruction to avoid Praxis‑only citations.)

4.2 Anti‑arrhythmic Drug Therapy

• Procainamide (IV) – Infuse at 20–50 mg/min until the arrhythmia is suppressed, hypotension develops, QRS widens >50 %, or a maximum dose of 17 mg/kg is reached. 1
• Amiodarone (IV) – Initial dose of 150 mg administered over 10 minutes. 1

5. Specific Tachycardia Entities

5.1 Sinus Tachycardia

• Defined as a heart rate > 100 bpm that is appropriate to physiologic, pathologic, or pharmacologic stress. 3
• Management focuses on identifying and treating underlying causes (e.g., fever, hypovolemia, anemia, infection, stimulants, anthracycline chemotherapy). 3
• β‑blockade is effective for symptomatic physiological sinus tachycardia related to emotional stress. 3

5.2 Inappropriate Sinus Tachycardia (IST)

• IST is persistent resting heart‑rate elevation disproportionate to stress. 4
• Evaluation for reversible causes is mandatory. 4
• Ivabradine is a reasonable therapeutic option; β‑blockers may be added but are often limited by hypotension. Combination therapy can be considered. 4
• The condition is generally benign; treatment aims at symptom relief. 4

5.3 Atrial Flutter

• Acute rhythm control: synchronized cardioversion (Class I recommendation). 5
• Pharmacologic options include oral dofetilide or IV ibutilide. 5
• Long‑term rhythm control (in patients without structural heart disease) can be achieved with amiodarone, propafenone, flecainide, or dofetilide; anti‑arrhythmics should be combined with AV‑node‑blocking agents to prevent 1:1 conduction. 5

5.4 Junctional Tachycardia

• Caused by enhanced automaticity of an ectopic focus in the AV junction. 5
• Rare in adults; most commonly observed post‑operatively in infants after congenital heart surgery. 5
• May exhibit AV dissociation, which helps exclude AVRT and makes AVNRT unlikely. 5
• Catheter ablation is a reasonable option when medical therapy is ineffective or contraindicated. 5

6. Special Populations

• In cardiac transplant recipients, atropine and adenosine should be avoided because vagal innervation is absent, limiting their efficacy and safety. 1

Tachycardia Management Guidelines (American Heart Association)

Definitions and Clinical Thresholds

• Tachycardia is defined as a heart rate > 100 bpm; however, a rate ≥ 150 bpm is generally considered clinically significant because symptoms are more likely attributable to the arrhythmia itself unless ventricular function is impaired. 6
• Heart‑rate thresholds:
  
  • > 100 bpm – technical definition of tachycardia.
  • < 150 bpm – symptoms of instability are unlikely to be caused primarily by the tachycardia unless there is impaired ventricular function.
  • ≥ 150 bpm – rate becomes clinically significant and usually warrants intervention. All derived from the same evidence base. 6

QRS Duration–Based Classification

• Narrow‑complex tachycardia (QRS < 120 ms) is always supraventricular in origin and includes sinus tachycardia, atrial fibrillation, atrial flutter, AV nodal re‑entrant tachycardia (AVNRT), AV re‑entrant tachycardia (AVRT), atrial tachycardia, multifocal atrial tachycardia, and junctional tachycardia. 6
• Wide‑complex tachycardia (QRS ≥ 120 ms) is most often ventricular tachycardia (VT); when the mechanism is uncertain, it should be managed as VT. The differential diagnosis also encompasses VT/VF, supraventricular tachycardia with aberrancy, pre‑excited tachycardias (e.g., Wolff‑Parkinson‑White), and ventricular paced rhythms. 6

Hemodynamic Assessment

• Signs of hemodynamic instability—such as hypotension or altered mental status—mandate immediate synchronized direct‑current (DC) cardioversion, irrespective of QRS width or presumed mechanism. 6

Acute Management of Stable Narrow‑Complex SVT

• Adenosine is the first pharmacologic agent when vagal maneuvers fail:
  
  • Initial dose = 6 mg rapid IV push followed by a normal‑saline flush.
  • If ineffective, a second dose = 12 mg may be administered. 6

Acute Management of Stable Wide‑Complex Tachycardia (Presumed VT)

• Procainamide IV infusion: 20–50 mg/min until the arrhythmia terminates, hypotension develops, QRS widens > 50 %, or a maximum of 17 mg/kg is reached; then maintain at 1–4 mg/min. Contraindicated in prolonged QT interval or congestive heart failure. 6
• Amiodarone IV: 150 mg administered over 10 minutes, repeat if VT recurs; maintenance infusion of 1 mg/min for the first 6 hours. 6

Management of Irregular Narrow‑Complex Tachycardia

• Irregular narrow‑complex tachycardias are most commonly atrial fibrillation or multifocal atrial tachycardia; atrial flutter with variable conduction is also possible. Treatment focuses on ventricular rate control and assessment for anticoagulation. 6