What are the types and management strategies of supraventricular tachycardia (SVT)?

Types of Supraventricular Tachycardia

Supraventricular tachycardia encompasses several distinct arrhythmias that require atrial and/or atrioventricular nodal tissue for initiation and maintenance, including AVNRT, AVRT, atrial tachycardia, atrial flutter, inappropriate sinus tachycardia, junctional tachycardia, and multifocal atrial tachycardia. 1

Primary SVT Categories

Reentrant Tachycardias (Most Common)

Atrioventricular Nodal Reentrant Tachycardia (AVNRT):

• The most common form of paroxysmal SVT, caused by microreentry within the AV node using dual pathways (fast and slow conduction pathways) 1, 2
• Characterized by regular narrow-QRS tachycardia with pseudo-r waves in V1 and accentuated S waves in leads II, III, and aVF 1
• P waves are typically buried within or immediately after the QRS complex (RP interval <70 ms) 1

Atrioventricular Reentrant Tachycardia (AVRT):

• Involves reentry circuit using an accessory pathway (bypass tract) connecting atria and ventricles 2, 3
• Orthodromic AVRT (most common): Antegrade conduction down AV node, retrograde up accessory pathway, producing narrow-QRS tachycardia with visible P waves separated from QRS by >70 ms 1, 4
• Antidromic AVRT: Antegrade conduction down accessory pathway, retrograde up AV node, producing wide-QRS tachycardia with LBBB morphology 1
• Associated with Wolff-Parkinson-White syndrome when pre-excitation is present 3, 4

Atrial Tachycardias

Focal Atrial Tachycardia:

• Arises from a localized atrial site with regular, organized atrial activity and discrete P waves with isoelectric segments between them 1
• May show irregularity at onset ("warm-up") and termination ("warm-down") 1
• Includes sinus node reentry tachycardia as a specific subtype with P-wave morphology indistinguishable from sinus rhythm 1

Multifocal Atrial Tachycardia (MAT):

• Irregular SVT characterized by ≥3 distinct P-wave morphologies at different rates 1
• Always irregular rhythm, commonly associated with pulmonary disease 1

Macroreentrant Atrial Tachycardia (Atrial Flutter):

• Typical atrial flutter: Cavotricuspid isthmus-dependent macroreentry circuit 1
• Produces characteristic "sawtooth" flutter waves, typically at atrial rates of 250-350 bpm 1

Other SVT Types

Inappropriate Sinus Tachycardia:

• Sinus heart rate >100 bpm at rest with mean 24-hour heart rate >90 bpm, not due to appropriate physiological responses or secondary causes (hyperthyroidism, anemia) 1
• Mechanism remains incompletely defined 1

Junctional Tachycardia:

• Arises from the AV junction, less common than other SVT types 1
• Limited data exist on optimal management strategies 1

Critical Diagnostic Distinction: Wide-QRS Tachycardia

When QRS is wide (>120 ms), three mechanisms must be differentiated 1:

1. SVT with bundle branch block (pre-existing or rate-related aberrancy) 1
2. SVT with AV conduction over accessory pathway (antidromic AVRT, pre-excited AF) 1
3. Ventricular tachycardia 1

Critical pitfall: If SVT cannot be definitively proven, treat as ventricular tachycardia, as verapamil or diltiazem given for presumed SVT may precipitate hemodynamic collapse in VT patients 1, 5

Epidemiology

• Prevalence: 2.29 per 1,000 persons in general population 1
• Incidence: 36 per 100,000 person-years, with approximately 89,000 new cases annually in the US 1
• Women have twice the risk of men for developing paroxysmal SVT 1
• Individuals ≥65 years have >5-fold increased risk compared to younger persons 1