The BIG 5 – are you confused?
There are five SVTs that we often talk about in EP. SVT meaning supraventricular tachycardia, so simply a fast rate that is occuring above the ventricles. This includes atrial fibrillation (AF), atrial flutter (AFL), AV nodal reentrant tachycardia (AVNRT), atrioventricular rentrant tachycardia (AVRT), and atrial tachycardia (AT). You may argue others such as inappropriate sinus tachycardia, junctional tachycardia, etc. but for our purposes we focus on the main five.
Today, we will give a brief description of each arrhythmia to help you differentiate. For more detailed information and examples, please refer to the Understanding EP: A Comprehensive Guide book set.
How would you describe atrial fibrillation (AF)?
Answer:
Most common arrhythmia seen, especially over age 80
• Disorganized atrial activity
• Irregularly irregular ventricular response
• Spontaneous, Persistent or Long Lasting Persistent
• Associated with Hypertension & Mitral Regurgitation
• Multiple reentry circuits
• Often originating in pulmonary veins
• AF begets AF
How would you describe atrial flutter (AFL)?
Answer:
Macro reentrant
• Can typically be terminated by pacing
• Usually accompanied by AV block
• Most common in the right atrium with counterclockwise propagation
• May also be located around areas of scar as well, such as post AF ablations
How would you describe AV nodal reentrant tachycardia (AVNRT)?
Answer:
• Most common reentrant SVT: 60%
• AV Node: micro-reentrant
• Dual AV Nodal Physiology (slow and fast)
• In typical AVNRT, a premature impulse enters the circuit when the fast pathway (FP) is still refractory, but the slow has recovered. By the time this impulse reaches the distal connection, the FP has recovered, and the impulse conducts retrograde to the atrium while simultaneously going down the ventricle.
• Block in the atrium or in the ventricle does not affect the tachycardia
• AV nodal blocking agents are effective
• Treatment of choice: slow pathway ablation
How would you describe atrioventricular reentrant tachycardia (AVRT)?
Answer:
• Macro reentrant circuit involving the atrium, AV node, His/Purkinje system, ventricle, and accessory pathway. 
• Block in the A or V will terminate the tachycardia
• WPW is an ECG finding that shows evidence of an antegrade conducting accessory pathway. A patient may have an accessory pathway without WPW on the ECG.
• Reentrant circuit during tachycardia:
-
- Antidromic (Delta waves): Down the pathway/ up the node
- Orthodromic: down the AV node/ up the pathway
• Orthodromic is more common
• Treatment: Ablation of pathway
How would you describe atrial tachycardia (AT)?
Answer:
Focus (origin) may be in the right or left atrium 
• Often located at the crista terminalis or pulmonary veins
- May be paroxysmal or persistent
• Ablation: use of activation mapping to identify the earliest atrial deflection.
• Ventricular Overdrive Pacing Response: VAAV
• Usually terminates with a V, termination with an atrial event if AV block is at the same time (uncommon)
• AV block may occur, and the tachycardia will be unaffected.
For more detailed information and examples, please refer to the Understanding EP: A Comprehensive Guide book set.
