Atrial Tachycardia vs SVT: Understanding the Relationship
Atrial tachycardia (AT) is not different from SVT—rather, AT is one specific type of SVT. 1
The Hierarchical Relationship
SVT is an umbrella term that encompasses multiple distinct arrhythmias, including atrial tachycardia, atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reciprocating tachycardia (AVRT), inappropriate sinus tachycardia, junctional tachycardia, and macroreentrant atrial tachycardia (atrial flutter). 1, 2
- SVT definition: Any tachycardia with heart rate >100 bpm at rest where the mechanism involves tissue from the His bundle or above 1
- AT is a subset within SVT, not a separate entity 1, 2
Types of Atrial Tachycardia Within the SVT Umbrella
Focal Atrial Tachycardia
- Arises from a localized atrial site with regular, organized atrial activity 1
- Characterized by discrete P waves with typically an isoelectric segment between 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
- A specific focal AT subtype due to microreentry in the sinus node complex 1
- Has abrupt onset and termination 1
- P-wave morphology is indistinguishable from normal sinus rhythm 1
Multifocal Atrial Tachycardia (MAT)
- Irregular SVT with ≥3 distinct P-wave morphologies at different rates 1
- The rhythm is always irregular 1
- Typically requires treatment of underlying conditions rather than ablation 2
Macroreentrant Atrial Tachycardia (Atrial Flutter)
- Includes cavotricuspid isthmus-dependent flutter (typical and reverse typical) 1
- Atypical flutter involves circuits around mitral valve annulus or atrial scar tissue 1
Clinical Implications: Why the Distinction Matters
Management strategies differ significantly based on the specific SVT mechanism, making precise diagnosis crucial. 2
Different Treatment Approaches
- AVNRT and AVRT respond well to vagal maneuvers and adenosine 2
- Focal AT requires different ablation approaches targeting the specific atrial focus 2
- MAT typically needs treatment of underlying conditions (COPD, electrolyte abnormalities) rather than ablation 2
Ablation Success Rates Vary by Type
- AVNRT and AVRT: >88% effectiveness 3
- Atrial tachycardia: >86% effectiveness 3
- Atrial flutter: >88% effectiveness 3
Diagnostic Approach to Identify the Specific SVT Type
ECG Analysis Algorithm
- Examine P wave morphology: AT shows discrete P waves that differ from sinus rhythm, while AVNRT often shows pseudo-r waves in V1 or no visible P waves 1, 2
- Assess regularity: Focal AT is regular (except at onset/termination), while MAT is always irregular 1, 2
- Check RP interval: RP longer than PR suggests atypical AVNRT, PJRT, or AT 1
- Response to adenosine: AT may show transient AV block revealing underlying atrial activity, while AVNRT/AVRT typically terminate abruptly 2, 4
Common Pitfall to Avoid
Do not assume all regular narrow-complex tachycardias are the same. The specific mechanism determines optimal treatment, and misidentification can lead to inappropriate therapy choices. 2 For example, using vagal maneuvers as definitive treatment for AT when catheter ablation targeting the focal source would be curative. 2