1. 52 yr old lady Recurrent narrow QRS tachy Normal echo

2. Analyse- Minimal preexcitation basally, maximal preexcitation with basal atrial train, block in AP with S2. The maximal preexcitation suggests a left posterior AP; there is a wide notched negative delta in II and a predominant S in V5/V6.

3. Intracardiacs…The HV is low normal basally. The CS56 channel is being paced. The Stim-V time is very short (50 ms) 25 ms

4. Route of VA conduction? Non-decremental, A earliest in CS56. The A in CS910 is diminutive, suggesting this is outside the CS os. Possibly AP conduction.

5. Tachy induced- likely ORT, terminating retrogradely

6. Another tachy episode. HIS catheter deep in RV. Termination in AV node. Diagnosis? Likely ORT with LBBB.

7. Sustained tachy could not be induced. Isoprenaline was not tried. At this stage, a ‘test’ was performed.

8. The ‘test’: Angiogram via an AL1 catheter inserted into the CS-RAO 30

9. LAO 40- The diverticulum has a narrow neck, communicates directly with proximal CS

10. RF site signal-A>v, early local V, continuous electrical activity.

11. RF site signal- early A in RFD (same in in CS78) during RV pacing

12. RF site-LAO 40

13. RF site- RAO 30

14. RF energy- successful

15. Intracardiacs during energy- A nd V separate with loss of preexcitation immediately after energy starts

16. After ablation-interpret. RV pacing from HISD channel. VA Wenckebach with ‘reverse’ AV nodal echo. Hence the next pacing stimulus finds the RV refractory 120 ms 135 ms

17. Adenosine- CS pacing; no preexcitation, transient AV block

18. Final diagnosis? WPW syndrome. Epicardial left posteroseptal AP, CS diverticulum. ORT. Successful RF ablation.