DIAGNOSTIC PACING MANEUVERS DURING PAROXYSMAL SUPRAVENTRICULAR TACHYCARDIA

Case presented by:

AMAN CHUGH, MD AND FRED MORADY, MD

A 25-year-old woman with recurrent palpitations and documented supraventricular tachycardia (SVT) presents to the electrophysiology (EP) laboratory. The electrocardiogram (ECG) shows no evidence of preexcitation. In the baseline state, there is no evidence of ventriculoatrial (VA) conduction or dual atrioventricular (AV) nodal pathways. There is no inducible tachycardia. During isoproterenol infusion (up to 10 mcg/min), there is an evidence of dual AV nodal physiology and a single AV nodal echo beat.

Question No. 1A: Which of the following is the most appropriate next step?

A.Since there is no inducible tachycardia, terminate the procedure and prescribe low-dose propafenone and metoprolol.

B.Perform the induction protocol with atropine to increase the likelihood of sustained tachycardia.

C.Perform slow pathway ablation.

D.Perform fast pathway modification.

E.Target the earliest atrial activation during ventricular pacing and isoproterenol infusion since the clinical tachycardia is likely mediated by a decrementally conducting concealed accessory pathway.

Question No. 1B: While performing radiofrequency ablation (RFA) of the slow pathway, you note junctional ectopy (cycle length 400 ms) with prolongation of the VA interval. What is the most appropriate next step?

A.Continue RF energy delivery as long as there is 1:1 VA conduction.

B.Increase the power to increase the likelihood of more rapid junctional ectopy.

C.Discontinue RF energy delivery and target a more superior site along the tricuspid annulus.

D.Discontinue RF energy delivery and target a more caudal site near the ostium of the coronary sinus.

E.Continue RF energy delivery since you have discussed the possibility of AV block and pacemaker implantation with the patient prior the procedure.

Question No. 2: 23-year-old woman is referred for an electrophysiologic study for a history of palpitations. The ECG reveals preexcitation compatible with an anteroseptal accessory pathway (QRS duration 90 ms). The baseline His-ventricular interval is 20 ms and remains unchanged during programmed atrial stimulation. With a single atrial extrastimulus, a tachycardia is induced with a cycle length of 320 ms. The HV interval remains unchanged during tachycardia. Diagnostic maneuvers during tachycardia are consistent with the diagnosis of typical atrioventricular nodal reentrant tachycardia (AVNRT). What is the next appropriate step?

A.First, ablate the accessory pathway, followed by the slow pathway, so that you can reliably document VA conduction during RFA of the slow pathway for AVNRT.

B.First, ablate the slow pathway, followed by the accessory pathway.

C.First, eliminate the accessory pathway using cryoablation, and then the slow pathway using conventional RF energy.

D.In order to minimize the risk of AV block, target the accessory pathway via the coronary cusp with conventional RF energy, and then target the slow pathway.

E.Target the slow pathway.

Question No. 3A: A narrow complex tachycardia is induced in the electrophysiologic laboratory in a patient with a history of recurrent palpitations. The cycle length is 350 ms and the septal VA time is 140 ms. A His-synchronous premature ventricular complex (PVC) introduced during tachycardia advances the subsequent atrial electrogram (EGM) and the tachycardia continues at the same rate and with the same atrial activation pattern. Which of the following is true regarding this observation?

A.It is diagnostic of orthodromic reciprocating tachycardia (ORT) using a concealed AV accessory pathway.

B.It is diagnostic of the presence of an accessory pathway.

C.It is diagnostic of atypical (fast-slow) AVNRT with a bystander concealed accessory pathway.

D.It is diagnostic of ORT utilizing a concealed nodofascicular accessory pathway.

Question No. 3B: Following ablation of a manifest midseptal accessory pathway, you perform high-output pacing from a catheter placed at the bundle of His. You note that the paced QRS complex suddenly widens as the pacing output is decreased. The stimulus-atrial (SA) interval with a narrow paced QRS complex is 100 ms compared to 130 ms with a wide paced QRS complex. Which of the following is true regarding these findings?

A.There is evidence of retrograde conduction over the accessory pathway requiring further ablation.

B.These findings are consistent with retrograde conduction over the AV node.

C.These findings are consistent with retrograde activation over the AV node and a partially ablated accessory pathway.

D.These findings are inconclusive; need more data.

Discussion

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