Paroxysmal Supraventricular Tachycardia (PSVT)

Definition

• Fuster and Hurst's The Heart, 15th Edition

Mechanisms / Types

• AVNRT: Reentry within the AV node using a slow and fast pathway. The most common mechanism.
• AVRT (orthodromic): Antegrade conduction via the AV node; retrograde via an accessory pathway - produces narrow QRS.
• AVRT (antidromic): Antegrade via accessory pathway - produces wide QRS (preexcited tachycardia).
• Harrison's 22E; Fuster and Hurst's The Heart

Epidemiology

• Incidence ~35 cases per 100,000 person-years; prevalence ~2.25 per 1,000
• More frequent in females (2:1 ratio for AVNRT)
• Peak onset in late teenage and young adult years (emergency medicine) or beyond the 4th decade for AVNRT specifically
• Majority of patients have no active cardiovascular disease
• Fuster and Hurst's The Heart; Tintinalli's Emergency Medicine

ECG Features

• Absence of normal sinus P waves (no normal P wave with normal PR interval)
• Narrow QRS complex (<100 ms) - unless aberrant conduction
• Rate: typically 170-180 bpm; range 130-300 bpm
• P waves buried within the QRS in ~70% of cases
• Retrograde P waves (inverted, immediately adjacent to QRS) in ~30%
• Regular rhythm

Clinical Presentation

• Palpitations (most common), lightheadedness, dyspnea
• Abrupt onset and termination - patients can often identify the exact moment it starts and stops
• Usually hemodynamically stable, but can cause presyncope/syncope
• Associated with WPW syndrome in some cases (up to 50% of WPW patients develop paroxysmal tachyarrhythmias)

Acute Management

Step 1: Assess hemodynamic stability

• Unstable (hypotension, unconsciousness, respiratory distress): Synchronized DC cardioversion immediately
  • For PSVT/atrial flutter: initial energy 50-100 J

Step 2: Stable patient - Vagal Maneuvers

• Carotid sinus massage - only if no carotid bruits or prior stroke history
• Valsalva maneuver - effective and patient can be taught self-administration
• Apply early in the dysrhythmia for best results

Step 3: IV Adenosine (first-line drug)

• Terminates the vast majority of PSVT by transiently blocking AV nodal conduction
• Side effects: transient chest pain, dyspnea, anxiety (very short half-life ~10 sec)
• Contraindicated in prior cardiac transplant (hypersensitivity due to denervation)
• Use caution in WPW - adenosine can precipitate AF in up to 15% of patients, which may cause hemodynamic instability in WPW
• Use caution in asthma/bronchospasm

Step 4: If adenosine fails - AV nodal blocking agents

• IV beta-blockers or non-DHP calcium channel blockers (verapamil, diltiazem)
• Effective but may cause hypotension; longer duration of action
• Can also be given orally on an as-needed basis ("pill in pocket") combined with Valsalva

Wide-Complex PSVT

• Differential: ventricular tachycardia (VT), PSVT with bundle branch block aberrancy, preexcited tachycardia
• Default: treat as VT until proven otherwise
• If regular, patient stable, trial of IV adenosine is reasonable
• Very irregular wide-complex tachycardia = likely preexcited AF/flutter → manage with cardioversion, IV procainamide, or ibutilide
• Harrison's 22E

Long-Term / Chronic Management

• Most patients with recurrent PSVT are candidates for catheter ablation
• Success rates very high (>95% for AVNRT)
• Antiarrhythmic drug therapy for patients unwilling or unsuitable for ablation
• Harrison's 22E; Fuster and Hurst's The Heart

Summary Table