Causes of Supraventricular Tachycardia
Supraventricular tachycardia is primarily caused by three electrophysiological mechanisms: re-entry (most common), abnormal automaticity, and triggered activity, with the specific etiology depending on the SVT subtype and presence of underlying cardiac or systemic conditions. 1
Primary Electrophysiological Mechanisms
Re-entry (Most Common Mechanism)
Re-entry is the dominant mechanism underlying most SVTs, involving repetitive electrical impulse conduction around a fixed obstacle in a defined circuit. 2 This mechanism requires:
- Unidirectional conduction block in one limb of the circuit, which occurs when heart rate acceleration or a premature impulse encounters the refractory period of the pathway 2
- Slow conduction through at least one pathway to allow recovery of the other pathway for continued circuit propagation 2
- Re-entry is the mechanism for AVNRT, AVRT, and atrial flutter 2, 1
Abnormal Automaticity
Tissues with enhanced automaticity exhibit increased diastolic phase 4 depolarization, causing faster firing rates than normal pacemaker cells. 2, 1 These ectopic foci can be located in:
- The atria 2
- The AV junction 2
- Vessels communicating directly with the atria (vena cava or pulmonary veins) 2
When the ectopic focus firing rate exceeds the sinus node, it overdrives the sinus node and becomes the dominant pacemaker, producing either incessant (>50% of the day) or episodic tachycardia. 2
Triggered Activity
This mechanism involves disturbances in cardiac repolarization where afterdepolarizations reach threshold and trigger early action potentials during the repolarization phase. 2, 1
Specific SVT Types and Their Causes
Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
- Caused by a re-entry circuit within the AV node involving dual pathways (fast and slow conducting pathways) 1
- Most common form of paroxysmal SVT 3
- Both pathways are confined to AV nodal and perinodal atrial tissue 3
Atrioventricular Reciprocating Tachycardia (AVRT)
- Involves an anatomically distinct accessory pathway (bypass tract) between atria and ventricles that bypasses the AV node 1, 3
- Associated with Wolff-Parkinson-White syndrome 4
- The accessory pathway may have branched structure and can support micro-reentry 5
Atrial Tachycardia
- Can arise from enhanced automaticity, triggered activity, or micro-reentry within atrial tissue 1
- Characterized by long RP interval with P wave morphology different from sinus rhythm 1
Atrial Flutter
- Macro-reentrant circuit typically around the tricuspid annulus through the cavotricuspid isthmus 2
- Incidence increases markedly with age (from 5 per 100,000 in those >50 years to 587 per 100,000 over age 80) 2
Predisposing Factors and Associated Conditions
Structural Heart Disease
- Heart failure, hypertension, and valvular disease are major predisposing factors 1
- In one study, only 1.7% of atrial flutter cases had no structural cardiac disease (lone atrial flutter) 2
- Chronic comorbid conditions including chronic lung disease 2, 1
Congenital Heart Disease
- Ebstein anomaly, Tetralogy of Fallot, transposition of great arteries, and atrial septal defects 1
- These patients carry significantly higher risks of complications including heart failure, stroke, and sudden cardiac death 1
Acute Precipitating Events
Metabolic and Systemic Disorders
Medications and Substances
- Stimulants, certain antiarrhythmics, and caffeine 1
Critical Clinical Considerations
Pre-excitation Syndromes
Wolff-Parkinson-White syndrome requires prompt evaluation due to risk of sudden cardiac death if atrial fibrillation develops, as inappropriate treatment may result in potentially lethal rapid ventricular response. 1, 7
Tachycardia-Mediated Cardiomyopathy
Prolonged SVT (persistent for weeks to months) can lead to tachycardia-induced cardiomyopathy, particularly when ventricular rates remain elevated. 1