PVC’s during SVT – Worth paying attention to

Answer: Termination of SVT with a His-synchronous PVC that did not conduct to the atrium. Strongly predictive of AVRT and is not consistent with AVJRT & excludes Focal AT.

• The PV occurs approximately 41ms prior to the expected QRS onset, indicating that this is likely a truly His-synchronous pacing – this HV interval was 44ms when NOT pre-excited. This means that the bundle of His is committed during the ectopic ventricular beat.
  • Much of the following conjecture is based on the principle that the His bundle is committed. Of course, we only have a very tiny tiny His signal in this example, and ideally your His signal would be more obvious. But we can still appreciate the point being illustrated and learn something useful :) 

• If the His bundle is committed, then the PVC CANNOT pass through the bundle of His to the AV node & atria, but must remain confined to the ventricles (in the absence of an accessory pathway).

And yet the PVC terminated tachycardia…without perturbing the atrium, and very likely without perturbing the AV node or His Bundle…..what does this tell us?

• It is impossible for the PVC to have terminated focal AT, because the PVC never conducted to the atrium to disturb tachycardia.

• It is unlikely for the PVC to have terminated AVJRT, because the PVC likely never reached the AV node to disturb the AVJRT circuit (although there’s some evidence that some subsets of AVJRT may involve part of the His bundle..so we cant be 100% sure of this statement).

Diagrammatic explanation

My two cents:

• SVT termination can tell you a lot about the diagnosis and is very useful when pacing manoeuvres fail.

• His-Synchronous PVC (native or paced) which terminates tachycardia without conducting to the atrium is highly highly highly suspicious of AVRT.

• Always consider AVRT when you see a single PVC terminate tachycardia. AVRT is the only SVT which involves the ventricle as a critical limb of the circuit.

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

P.s Check out EP in Practice program 5 (AF) and program 1 (intro to AF). These programs have had >100 quiz questions added after most lectures, to test your knowledge and prep you for examination. I hope you enjoy them, I’m rolling out more in program 2 (SVT) as we speak.
Have a great weekend :) 

Using ventricular ectopy to differentiate SVT is taught in more depth in the SVT program of EP in Practice.