What are the classifications of tachyarrhythmias and the guideline‑based acute management steps?

Classification and Guideline-Based Management of Tachyarrhythmias

Primary Classification System

Tachyarrhythmias are classified based on QRS complex width, regularity, and anatomic origin, which directly determines acute management strategy. 1

Narrow QRS-Complex Tachycardias (QRS <120 ms)

Listed in order of frequency: 1

• Sinus tachycardia - Heart rate >100 bpm appropriate to physiologic, pathological, or pharmacologic stress 1
• Atrial fibrillation - Irregular rhythm without discrete P waves 1
• Atrial flutter - Regular atrial rate typically 250-350 bpm with variable AV conduction 1
• AV nodal reentrant tachycardia (AVNRT) - Most common paroxysmal SVT; P waves typically hidden within QRS 1, 2
• Accessory pathway-mediated tachycardia (AVRT) - P wave visible in ST segment, separated from QRS by >70 ms 1, 2
• Atrial tachycardia - P wave morphology differs from sinus rhythm, long RP interval (RP > PR) 1, 2
• Multifocal atrial tachycardia (MAT) - Irregular rhythm with ≥3 distinct P wave morphologies 1
• Junctional tachycardia - Rare in adults; rate 120-220 bpm with possible AV dissociation 1

Wide QRS-Complex Tachycardias (QRS ≥120 ms)

Most wide-complex tachycardias are ventricular in origin, and when uncertain, treat as ventricular tachycardia. 1, 2

• Ventricular tachycardia (VT) - Monomorphic or polymorphic 1, 2
• SVT with aberrant conduction - Pre-existing bundle branch block 2
• Pre-excited tachycardias - Anterograde conduction over accessory pathway (WPW syndrome) 3, 2
• Ventricular paced rhythms 1

Acute Management Algorithm for Hemodynamically Unstable Patients

Immediate synchronized DC cardioversion is the treatment of choice for ANY hemodynamically unstable tachycardia, regardless of mechanism. 1, 3, 2

• Start with 100-200 joules synchronized 3
• This applies to both narrow and wide QRS-complex tachycardias 1, 2

Acute Management for Hemodynamically Stable Regular Narrow QRS Tachycardia

First-Line Interventions

Vagal maneuvers are the initial recommended intervention. 1, 2

• Valsalva maneuver or carotid sinus massage 1, 2
• If ineffective or not feasible, proceed immediately to adenosine 1

Adenosine Administration

Adenosine is the preferred pharmacologic agent for acute termination of regular narrow QRS SVT. 1, 2

• First dose: 6 mg rapid IV push, followed by normal saline flush 1
• Second dose: 12 mg if first dose ineffective 1
• Critical contraindications: Severe asthma, pre-excited atrial fibrillation (can precipitate ventricular fibrillation) 3, 4, 2
• Use with extreme caution in cardiac transplant patients (paradoxical effects possible) 1

Alternative Pharmacologic Options

If vagal maneuvers and adenosine fail: 1

• IV diltiazem or verapamil - Effective for hemodynamically stable SVT 1
• IV beta blockers - Reasonable alternative 1

Synchronized Cardioversion

If pharmacologic therapy is ineffective or contraindicated in stable patients, proceed to synchronized cardioversion. 1

Acute Management for Wide QRS-Complex Tachycardia

Critical Decision Point

When the diagnosis is uncertain, treat as ventricular tachycardia. 2

Diagnostic Clues Favoring VT

• AV dissociation - Ventricular rate faster than atrial rate (pathognomonic but only visible in 30% of cases) 2
• Fusion beats - Pathognomonic for VT 2
• QRS width >140 ms with RBBB pattern or >160 ms with LBBB pattern 4, 2
• RS interval >100 ms in any precordial lead 4
• QR complexes (abnormal Q waves) - Suggest myocardial scar, present in ~40% of post-MI VT 4

Pharmacologic Management for Stable Wide QRS Tachycardia

Procainamide IV: 1

• 20-50 mg/min until arrhythmia suppressed, hypotension develops, QRS widens >50%, or maximum dose 17 mg/kg reached
• Maintenance: 1-4 mg/min
• Avoid if prolonged QT or CHF

Amiodarone IV: 1

• First dose: 150 mg over 10 minutes
• Maintenance: 1 mg/min for first 6 hours

Critical Pitfall to Avoid

Never administer verapamil or diltiazem for wide-complex tachycardia of uncertain etiology—can cause severe hypotension or accelerated ventricular rate in VT or pre-excited AF. 2

Specific Tachycardia Management

Sinus Tachycardia

The mainstay is identifying and treating the underlying cause. 1

Pathological causes include: 1

• Pyrexia, hypovolemia, anemia, infections
• Drugs: caffeine, alcohol, nicotine, salbutamol, aminophylline, atropine, catecholamines, amphetamines, cocaine
• Anthracycline chemotherapy (doxorubicin, daunorubicin)

Beta blockade is effective for: 1

• Symptomatic physiological sinus tachycardia from emotional stress
• Post-myocardial infarction (prognostic benefit)
• Congestive heart failure (symptomatic and prognostic benefit)
• Symptomatic thyrotoxicosis (with carbimazole or propylthiouracyl)

Inappropriate Sinus Tachycardia (IST)

IST is defined as persistent resting heart rate elevation unrelated to or out of proportion with stress level. 1

Evaluation for and treatment of reversible causes is mandatory. 1

Ivabradine is reasonable for ongoing management of symptomatic IST. 1

• Beta blockers may be considered but are often ineffective or poorly tolerated due to hypotension 1
• Combination of beta blockers and ivabradine may be considered 1
• Prognosis is generally benign; treatment is for symptom reduction and may not be necessary 1

Atrial Flutter

Acute rhythm control options: 1

• Synchronized cardioversion (Class I)
• Oral dofetilide or IV ibutilide
• IV beta blockers
• Rapid atrial pacing

Acute rate control: 1

• IV diltiazem, verapamil, or amiodarone

Ongoing management: 1

• Rate control: Beta blockers, IV diltiazem, or verapamil (Class I)
• Rhythm control: Amiodarone, propafenone, flecainide or dofetilide (in absence of structural heart disease), or sotalol
• Antiarrhythmics should be combined with AV nodal-blocking agents to reduce risk of 1:1 conduction

Junctional Tachycardia

Mechanism is enhanced automaticity from ectopic focus in AV junction. 1

• Uncommon in adults; typically seen postoperatively in infants after congenital heart surgery 1
• May show AV dissociation, which excludes AVRT and makes AVNRT highly unlikely 1
• Catheter ablation may be reasonable when medical therapy is ineffective or contraindicated 1

Common Pitfalls and Caveats

Adenosine in pre-excited atrial fibrillation can precipitate ventricular fibrillation. 3, 4, 2

QRS width criteria are not helpful for differentiating VT from SVT with AV conduction over an accessory pathway. 3

In cardiac transplant patients, avoid relying on atropine or adenosine due to lack of vagal innervation. 1

Always obtain a 12-lead ECG during sinus rhythm after the episode to look for pre-excitation (short PR, delta wave, wide QRS) to confirm WPW syndrome. 3

Patients with symptomatic pre-excitation and documented tachycardia are candidates for catheter ablation, which has >95% success rate and is curative. 3