Idiopathic PVCs from the PM may present in patients without structural heart disease and may play a role in triggers of NSVT, sustained recurrent VT, or even ventricular fibrillation [8–9]. Mapping and catheter ablation of clinical PM PVCs are challenging because of the complexity of PM anatomy and their constant motion during the cardiac cycle [10]. In this study, we performed detailed activation mapping using a duodecapolar mapping catheter in order to achieve faster and more precise delineation of the site of origin of arrhythmia in a relatively small PM PVCs cohort. The most important finding of the present study is that the use of a duodecapolar catheter is feasible and highly efficient for finding the sites of earliest prepotential bipolar activity and good/perfect pace maps, leading to successful elimination of PM PVCs.
As is known, high-density mapping with multipolar catheters is a technique with proven value for activation mapping and electroanatomic substrate delineation in macroreentrant atrial tachycardia, atrial fibrillation as well as ventricular tachycardia [4, 11–13]. In the current study, to our knowledge, we are the first to describe a technique using a duodecapolar catheter for endocardial electroanatomic mapping and as a guide for ablation of PM PVCs. Significantly earlier activation potentials were identified during mapping with the duodecapolar mapping catheter in this study. With 2-mm interelectrode spacing, good or perfect pace maps can be generated within a given small area after high-density activation mapping with a multipolar catheter. The present results have demonstrated that patients with duodecapolar catheter mapping had short procedure and fluoroscopy times, and had short ablation duration as well as few ablation applications. Furthermore, the rate of complete PM PVCs elimination tended to be high when using multipolar catheters.
Notably, ablation of PM PVCs has a variable success rate because of challenges in mapping and catheter stability. Acute procedural success for ablation of PM PVCs is generally fair (60%-100%) and recurrence of similar morphology arrhythmias that require a repeat ablation procedure is common (approximately 5–58%) [10, 14–16]. The outcome of catheter ablation in our series was reasonably good. In our study, a higher efficiency and higher success rate when using the duodecapolar catheter may be attributed to the following aspects. Firstly, localization of PM PVCs foci relies mainly on accurate activation mapping of clinical PVCs, usually complemented with pace mapping, which is important for successful ablation of such arrhythmias. Using a 20-pole mapping catheter with 2-mm interelectrode spacing can yield a greater electrophysiologic understanding of the earliest ventricular activation areas during PVCs and therefore a more efficient targeting of arrhythmia sources and exit sites is achievable. Potential ablation targets can be identified expeditiously and an ablation catheter can be directed to these sites. A more favorable outcome using the duodecapolar catheter seems to be mediated by a more comprehensive treatment of PVC substrate. Secondly, making adequate catheter contact of catheter tip with the contracting muscle during systole is also essential for successful ablation. It was helpful to confirm adequate contact between the ablation catheter and the endocardial surface with fluoroscopy, mapping system geometry, and the quality of local electrograms. The high mapping density created by the duodecapolar catheter and subsequent earliest activation potentials with sharp initial signals are specific for avoiding poor contact. We also found that for a given targeted area, the near-field electrogram quality on the duodecapolar catheter was often superior to the ablation catheter. This may be due to the smaller size of sensing electrode and tighter bipole spacing of the duodecapolar catheter compared to larger electrode sizes of conventional point-by-point mapping catheter. Moreover, it is not clear whether a transseptal or retrograde aortic approache is superior for ablation of PM PVCs. Published research investigating patients requiring ablation of PM PVCs tended to use the retrograde aortic approach and may offer greater catheter stability especially in the PPM while ablation for APM PVCs are better approached with a transseptal access [14, 17–18]. In our series, PPM PVCs accounted for 66.7% of cases and adequate catheter contact by the retrograde aortic approach may be an underlying reason for the high acute ablation success rate. Finally, in patients with structurally normal hearts, the mechanism of PM PVCs tended to be focal, due to either triggered activity or enhanced automaticity [19]. The phenomenon of spontaneous PVCs with single QRS morphologies as well as lack of change in QRS morphology after ablation were seen in this cohort of patients with structurally normal heart, which is inconsistent with the literature that has reported almost half of patients with PM PVCs may exhibit spontaneous multiple QRS morphologies during an electrophysiology study [14]. Only single PVCs QRS morphologies observed in this study may lend credence to the hypothesis that PVC origin was from a single intrapapillary focus with conduction to a solitary breakout site [15], and made it possible that less extensive ablation at sites of PVCs origin with excellent pace maps was successful in this study.
Apart from a duodecapolar catheter, high-density mapping catheters frequently used include the Inquiry Afocus 20-pole deflectable spiral catheter (St. Jude Medical) and Pentaray (Biosense Webster, Diamond Bar, CA, USA). Koutbi et al. [19] used a 20-pole deflectable spiral catheter for ablation of PVCs originating from the left ventricular PM in four patients with structural heart disease, and they found that this mapping technique was more straightforward and feasible and complete PVCs abolition was achieved for all patients. However, technically, although its rounded shape is minimally arrhythmogenic, which makes it easier to map PVCs by avoiding mechanical ectopic beats, there is the risk of the spiral being caught on the submitral apparatus and traumatizing this region of the left ventricle. Therefore, counterclockwise rotation or traction must be avoided and each time the catheter was caught in the chordae tendineae, a clockwise rotation easily extricated the spiral. Furthermore, the Pentaray shape is more arrhythmogenic and does complicate interpretation of the activation map and can be detrimental for PVC mapping, but has been shown to be accurate and expeditious in the mapping of complex reentrant atrial arrhythmias and atrial fibrillation [4]. As mentioned above, it may be advantageous to use a duodecapolar mapping catheter in the ventricle for rapid mapping and to guide ablation. On the one hand, due to the steerable and straight shape, it has less probability of arrhythmogenicity and damaging the submitral apparatus such as chordae tendineae. On the other hand, by using a 20-pole catheter with 2-mm interelectrode spacing for mapping, it can create a high sampling mapping density and multiple targets of earliest activation potentials can be identified rapidly and simultaneously. Matching pace maps can be generated within a given area with reference to the activation mapping target, and an ablation catheter can be directed to these sites previously tagged on electroanatomic mapping systems, which may significantly decrease mapping time. Finally, the increased mapping density created and high quality of the earliest activation potentials as well as near-field electrogram with sharp early signals identified by duodecapolar catheter, due to simultaneous recordings of local potential from different pairs of electrode with a relative short interelectrode distance, are specific for confirming adequate catheter contact and further ablation.
Limitations
Firstly, the design of the study is retrospective and single-center in a relatively small sample size cohort with no structural heart disease, which was therefore subject to a myriad of biases, particularly selection bias and statistical power limitations. Hence, results from the current data need to be confirmed by further large-scale studies, which would be helpful to validate the reproducibility of the duodecapolar catheter mapping technique. Secondly, although the acute clinical success rate and the PVC burden during follow-up in our series were satisfactory, long-term outcomes are needed to demonstrate feasibility and efficacy. Moreover, the technique was only employed using single ventricular access via retrograde transaortic approach in this study, and studies on double ventricular access obtained via double transseptal or double retrograde approach may be an area of future investigation optimizing the capability to manipulate the ablation catheter to the targeted multipolar electrode. Furthermore, intracardiac echocardiography (ICE), which may create a detailed ICE-based anatomic reconstruction of the LV, allows assurance of adequate catheter-tissue contact and optimal alignment of the catheter tip with the PM axis, although the post procedure echocardiographic appearance in our cases confirms that the lesions have indeed been generated on the PM. Finally, an ablation catheter with contact force (CF) capabilities was not utilized in this study, which not only provides CF information but also shows vector orientation of the catheter tip.