Dual chamber open-window mapping with a novel multispline mapping catheter for a left posterolateral atrioventricular accessory pathway

The conventional mapping approach for atrioventricular accessory pathways (APs) involves point-by-point mapping to identify the connection sites of the AP to the atria or ventricle, or the site where the AP potential is recorded. However, this approach requires an accurate interpretation of local electrograms. Some earlier reports have shown the efficacy of open-window mapping (OWM) for localizing the AP.^, The accuracy of the OWM may be enhanced by a novel multispline mapping catheter (Octaray, Biosense–Webster, Inc., Diamond Bar, CA).

A 60-year-old man with atrioventricular reentrant tachycardia (AVRT) was referred to our institution for catheter ablation. During the procedure, the atrioventricular AP was detected on the posterolateral wall of the mitral annulus, and radiofrequency application at the atrial connection site successfully eliminated the AP. However, a narrow QRS tachycardia recurred 3 weeks after the procedure. Therefore, we performed the repeat ablation procedure. Prior to the procedure, a patient's written informed consent was obtained.

The baseline surface electrocardiogram did not show delta waves (Figure 1A). AH and HV intervals were 100 and 47 ms during sinus rhythm, respectively. The recurrence of left posterolateral AP was suggested by eccentric atrial activation without decremental conduction properties during right ventricular pacing. A narrow QRS tachycardia with a tachycardia cycle length of 380 ms was induced by atrial extra-stimulation (Figures 1B and C). The standard electrophysiological study made the diagnosis of orthodromic AVRT due to the left posterolateral AP. Although the sequence of atrial potentials during the AVRT was the same as that observed in the initial procedure, the VA interval was prolonged from 94 ms to 114 ms. Therefore, we considered that the left posterolateral AP was identical to that ablated in the initial procedure, but the previous ablation had caused the conduction delay in the AP. An epicardial AP was unlikely because the blunt component preceded the sharp component in coronary sinus electrograms. High-density mapping was performed with the CARTO 3 mapping system (Biosense–Webster, Inc.). We performed OWM in this case. Using the Octaray mapping catheter, sequential contact mapping of the left atrium and basal left ventricle was performed during the AVRT. The maximum peak of the local electrogram in the coronary sinus served as the reference point for the window of interest, which was set to cover both atrial and ventricular activation (from −158 to 124 ms).

The local activation time was annotated to a unipolar signal with the highest −dV/dt value. The early-meets-late (EML) algorithm was applied to the map to visualize the conduction block (depicted by a white line) at the mitral annulus. We used a lower threshold of 15% during mapping and thereafter adjusted it to 22% for better visualization of the EML gap, which served as a visual estimation of the AP conduction. After the automatic annotation, we did not re-annotate the local activation time. The AP potential was recorded on the EML gap, which was seen on the posterolateral wall of the mitral annulus (Figure 2 and Supplementary Video S1). Notably, the AP potential was automatically annotated in the EML gap. Radiofrequency energy was delivered to the site where the AP potential was recorded, eliminating the retrograde conduction through the AP in 6 s. The additional radiofrequency application was performed to close the entire width of the EML gap. AP conduction did not recur during the procedure. The patient has remained symptom-free with no evidence of the recurrence of AVRT throughout 3 months of follow-up.

The OWM is based on the automatic annotation process in which the signals with the highest −dV/dt are automatically annotated at each obtained point, irrespective of the cardiac chamber. This mapping approach differs from conventional mapping, where signals can be annotated to the incorrect cardiac chamber. The OWM can visualize the AP connection as a breakout of the activation to the chamber of interest. Additionally, the OWM is easier to interpret thanks to the combination of the EML algorithm, which displays the local conduction block by a white line. The AP conduction is visualized as an EML gap.

The Octaray is a novel multispline mapping catheter with 48 closely spaced small microelectrodes. This catheter has several advantages that enhance the efficacy of the OWM. First, due to its ability to create denser mapping points, this catheter may improve OWM’s accuracy. Second, the catheter’s small electrode (0.9 mm²) may improve OWM’s accuracy as it can reduce the recording of far-field potentials.^, Third, this catheter has a reference electrode in the middle of the splines (TRUEref technology, Biosense–Webster, Inc.). This reference electrode might increase the OWM’s quality by reducing the impact of the far-field potentials on unipolar signals.

It should be noted that the VA interval during the AVRT was prolonged due to the previous ablation in this case. Prolongation of the VA interval may have given rise to a separation of ventricular and atrial potentials and contributed to the clear visualization of the AP conduction by the OWM. The efficacy of OWM using the Octaray mapping catheter should be confirmed in the de novo cases.

To the best of our knowledge, this is the first case report of OWM performed with the Octaray mapping catheter. This catheter may improve the accuracy of OWM for identifying the AP location.