Discussion
This is the first and largest study to report the safety and efficacy of the mapping of atrial arrhythmias using the planar ‘grid’ design. The novel organization of electrodes allows for multidirectional determination of signal conduction that has not been previously available from other HD mapping catheters through the simultaneous recording of electrograms in multiple bipolar orientations.1 The use of fixed 3mm equidistant electrodes in a two-dimensional square organization allows bi-directional and omnipolar interpretations of signal conduction both along and across the splines. This unique feature contrasts from other non-spiral multi-spline mapping catheters that adopt flexible spline arrangements. Notably, the continuous fluctuations of electrode distances between splines in these catheters may compromise the integrity of voltage maps collected due to minute discrepancies in wavefront interpretations. In addition, the grid design does not allow for deformation and crowding of electrodes that results in some mathematical benefit to putative rotor mapping during atrial fibrillation, allowing an increase in atrial area covered for possible rotor identification.2 However, to the best of our knowledge, the new design catheter has been largely absent in large case series and real-world efficacy and risk associated with the Grid design are not reported.
After initial use in more complex cases, our operators quickly became familiar with the handling and performance of the new design and its use became first-line in the majority of patients. Given that the planar design does not conform to the circular fit of most catheters used for mapping pulmonary veins, one might question the role in pulmonary vein mapping and isolation. We found the use of the catheter did not compromise acute procedural success and during long-term follow-up we observed low recurrence rates. Complications reported in our case series are low and in keeping with contemporary data on complications and risks. The pericardial tamponade occurred after the catheter ablation and remote from mapping. Both incidents of cerebral ischemic insult occurred in long standing (2.9 and 3.3 years) persistent atrial fibrillation patients with cardiomyopathy and severe left atrial (LA) enlargement (46.4 and 48.1 ml/m2). Previous studies have demonstrated an independent association of mortality with increased LA volume index after 5-year follow-up, with a 2.4 relative risk of stroke for every 10-mm increase in LA size.3,4 We did not attribute these complications to the novel catheter design particularly, as one patient omitted oral anticoagulation for several days post discharge.
A possibility of recurrence due to inadequate mapping in significant LA enlargement rather than ablation failure was not observed in our patient cohort, as there were no significant differences in LA volume and size observed in the reported recurrent arrhythmia cases. Acute procedural success was reported in all patients, supporting the use of the HD Grid as a mapping tool. Our rate of arrhythmia recurrence (21.3%) is similar to rates previously described by multiple circular mapping catheter studies (21% and 26%).5,6
The low rates of complications reported in the current study (2.0%) demonstrate comparable levels of mapping safety to established circumferential pulmonary vein ablations using traditional circular mapping catheters (3.5%) with similar reports of complications causes including stroke and cardiac tamponade.7 Cardiac tamponade arising due to the use of contact force-sensing catheters remains low in our study (0.67%) and is consistent with the low incidence of tamponade in non-contact force catheters (0.44%).8
The highest recurrence rate reported from atrial tachycardia was somewhat surprising given the potential advantages of the mapping technology and catheter. However, these patients were a mixed bag of incisional atrial tachycardia and focal sources. Recurrence in 6 of the 7 cases were classified with the same type of arrhythmia, suggesting a failure of ablation strategy rather than diagnosis and mapping. The group collectively had shorter procedure and ablation times, with one case reported to have observed only 10 seconds of RF lesions to achieve termination of tachycardia, therefore no further lesions were delivered. Recurrence was mapped to the same location and longer ablation was delivered to achieve durable success.