Extrastimulus Testing

What type of conduction occurs here with extrastimulus pacing of the atrium via CS 5, 6?

• AVN ERP

• AERP

• VERP

• AP ERP

Answer explanation

The patient has an ablation catheter which shows atrial and ventricular deflections, a CS catheter showing atrial and ventricular deflection, and an RVa catheter showing ventricular deflection.

This physician is usuing the CS catheter for the atrial pacing instead of pacing an additional line for the HRA. This accomplishes the same thing; however, pacing is from the low RA at the CS ostium. However, when looking for right sided accessory pathways a HRA catheter can be helpful. Atrial extrastimulus testing is when the physician paces the heart using a drive train of eight paced beats at a fixed cycle length followed by a PAC. The eight drive beats are to establish a reasonable steady state. In AERP, there would be a pacing spike with no atrial deflection to follow. In VERP, pacing would be occurring in the ventricle and the S2 would show a pacing spike with no ventricular waveform to follow. AP ERP (accessory pathway ERP) would show either the loss of the delta wave or a conduction shift (VA separation on the ablation channel or on the CS if left sided), but there is no pathway in this example.

On this 56 year old patient with documented SVT, what type of conduction occurs post AEST?

• VERP

• AERP

• Jump w/Echo

• AVN ERP

Answer explanation

AV node effective refractory period. This is similar to the previous example. Again, the physician is pacing the atrium via the CS catheter. Typically if a HRA (High right atrial) catheter is used, it would be used to pace the atrium; however' the physician was not getting reliable capture when pacing, so instead of adjusting the catheter they used the CS instead. Capture is occurring in the atrium, as seen by the pacing spike with an A wave following ; however' there is no H or V wave to follow. Here, the PAC (S2) was so early that it could not conduct through the AV node (AVN ERP).

During VEST (Ventricular extrastimulus testing) on this patient with a documented wide-complext-tachycardia, what type of conduction occurs after S2? (Ablation catheter being used for HRA)

• Infrahisian Block

• VA Jump

• VERP

• AP ERP

Answer explanation

VERP - Ventricular Effective Refractory Period, or the point at which the impulse came in so early that the ventricular myocardium was unable to depolarize (refractory). There is no H seen because pacing is in the ventricle, so the His is typically hidden within the ventricular signal. After S1, there appears to be a retrograde A on C19,20 & ABL (HRA) catheter. After S2 there is no conduction indicating block.

There is no ventricular capture during the eight beat drive train (s1) as apparent by the V signal & the wide QRS. However, the S2 does not capture the ventricular myocardium whereas the previous run (600/230) did... It came in too early

Looking at the ventricular action potential diagram. After our 8 beat drive train if we put a PVC in at #1, Capture occurs (not shown). At #2 pacing a little earlier, Capture occurs (not shown). At #3 a little earlier, (as in the example above) it can no longer capture the ventricular myocardium. This is different than testing thresholds in that you are providing enough voltage to capture. The impulse is in the ERP, and just too early to capture.

In AP ERP, VA jump, and Infrahisian block from VEST, there would be capture of the ventricular myocardium. VERP is the only answer in which the ventricular myocardium is not captured.

During initial testing on this 56 year old SVT patient, this EGM shows:

• AVN ERP

• VERP

• AERP

• Retrograde AVN ERP

Answer explanation

These 2 EGMs were recorded during AES testing with a drive train of 400ms. With a closer S2, what change in conduction happens between #4 and #5? (Small H wave is marked at #5).

• AVRT starts at 159 bpm

• AVNRT starts at 159 bmp

• Jump from slow to fast AVN pathway

• Jump from fast to slow AVN pathway

Answer explanation

In the same patient above, AEST induces:

• AVRT starting at 159 bpm

• AVNRT starting at 159 bpm

• AVRT starting at 182 bpm

• AVNRT starting at 182 bpm

Answer explanation

AVNRT starting at 182. There is a jump in the S2-H interval which starts the narrow complex tachycardia. The A waves are simultaneous with the QRS complexes, typical of AVNRT. Use calipers to measure the tachycardia cycle length at 330 msec, which is 182 bpm. (60,000/330=182). Small H waves are seen on HISd.

The ladder diagram shows how AES induced the jump from the fast to the slow pathway and induction of AVNRT. The first antegrade conduction down the slow pathway passes the AV node and causes a narrow QRS. At the same time, the conduction passes the fast pathway and conducts into the atrium retrograde causing "echo" beats.