What are the primary types of supraventricular tachycardia (SVT)?

Types of Supraventricular Tachycardia

Supraventricular tachycardia encompasses several distinct arrhythmias originating from tissue at or above the His bundle, with the three most common types being atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), and atrial tachycardia (AT). 1

Primary SVT Categories

1. Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

• The most common form of paroxysmal SVT, particularly in middle-aged and older adults 1
• Caused by reentry within the AV node using dual pathways (fast and slow conduction pathways) 1, 2
• Mean age of symptom onset is 32±18 years 1
• More common in females, especially with age of onset >30 years 1
• Patients frequently describe "neck pounding" or "shirt flapping" sensations due to atrial contraction against a closed tricuspid valve 1

2. Atrioventricular Reentrant Tachycardia (AVRT)

• Requires an accessory pathway connecting atrium and ventricle for the reentrant circuit 1
• Mean age of symptom onset is 23±14 years, younger than AVNRT 1
• More prevalent in adolescents and decreases in frequency with age 1

Two subtypes exist:

• Orthodromic AVRT: Anterograde conduction through the AV node, retrograde through the accessory pathway; produces narrow QRS complex 1
• Antidromic AVRT: Anterograde conduction through the accessory pathway, retrograde through the AV node; produces wide QRS complex (maximally pre-excited) 1

Special variant:

• Permanent Junctional Reciprocating Tachycardia (PJRT): A rare, nearly incessant form of orthodromic AVRT involving a slowly conducting, concealed, usually posteroseptal accessory pathway 1

3. Atrial Tachycardia (AT)

Focal AT:

• Arises from a localized atrial site with regular, organized atrial activity and discrete P waves 1
• May show irregularity at onset ("warm-up") and termination ("warm-down") 1
• Atrial mapping reveals a focal point of origin 1

Sinus Node Reentry Tachycardia:

• Specific type of focal AT due to microreentry in the sinus node complex 1
• Characterized by abrupt onset and termination with P-wave morphology indistinguishable from sinus rhythm 1

Multifocal Atrial Tachycardia (MAT):

• Irregular SVT with ≥3 distinct P-wave morphologies at different rates 1
• Always irregular rhythm 1
• Most commonly encountered in patients with pulmonary disease 1

4. Atrial Flutter

Cavotricuspid Isthmus-Dependent (Typical) Atrial Flutter:

• Macroreentrant circuit around the tricuspid annulus through the cavotricuspid isthmus 1
• Produces predominantly negative "sawtooth" flutter waves in leads II, III, and aVF 1
• Atrial rate typically 300 bpm (cycle length 200 ms), but can be slower with antiarrhythmic drugs or scarring 1

Reverse Typical Atrial Flutter:

• Propagates in reverse direction (clockwise) 1
• Flutter waves typically positive in inferior leads and negative in V1 1

Atypical (Non-Cavotricuspid Isthmus-Dependent) Atrial Flutter:

• Macroreentrant circuits not involving the cavotricuspid isthmus 1
• May involve reentry around mitral valve annulus or atrial scar tissue 1

Additional SVT-Related Conditions

Wolff-Parkinson-White (WPW) Syndrome

• Documented SVT or symptoms consistent with SVT in a patient with ventricular pre-excitation during sinus rhythm 1
• Manifest pre-excitation incidence in general population: 0.1% to 0.3% 1
• Not all patients with pre-excitation develop symptomatic SVT 1

Inappropriate Sinus Tachycardia

• Sinus heart rate >100 bpm at rest with mean 24-hour heart rate >90 bpm 1
• Not due to appropriate physiological responses or primary causes like hyperthyroidism or anemia 1

Critical Distinguishing Features

Paroxysmal SVT (PSVT) characteristics:

• Regular, rapid tachycardia with abrupt onset and termination 1
• Most commonly results from AVRT or AVNRT 1
• Termination by vagal maneuvers suggests reentrant tachycardia involving AV nodal tissue 1

Irregular SVT patterns suggest:

• Premature depolarizations, atrial fibrillation, or multifocal atrial tachycardia 1

Clinical Pitfalls

Wide QRS complex tachycardia requires differentiation from ventricular tachycardia:

• SVT with bundle-branch block (pre-existing or rate-related) 1
• SVT with AV conduction over an accessory pathway (antidromic AVRT) 1
• If diagnosis uncertain, treat as ventricular tachycardia to avoid hemodynamic collapse from inappropriate calcium channel blocker or beta blocker administration 1