Author + information
- Takumi Yamada, MD∗ ()
- ↵∗Reprint requests and correspondence:
Dr. Takumi Yamada, Division of Cardiovascular Disease, University of Alabama at Birmingham, FOT 930A, 510 20th Street South, 1530 3rd Avenue South, Birmingham, Alabama 35294-0019.
Recent studies have reported that idiopathic focal ventricular arrhythmias (VAs) can originate from the papillary muscles (PAMs) in the left ventricle (LV) and it is consistent that catheter ablation of these VAs is challenging as compared with the other VAs in the LV (1–4). The exact reasons for this challenge remain unclear, but several possible reasons have been discussed in consideration of the unique anatomy of the PAMs as well as the unique electrophysiological characteristics of the PAM VAs.
First, in PAM VAs, standard electrophysiological parameters for successful ablation may not be as reliable as in the other idiopathic VAs. PAM VAs often exhibit variable QRS morphologies spontaneously and/or after the initial ablation (4). A discrete radiofrequency lesion at the site with an excellent pace map often fails to eliminate the PAM VAs, and instead there is a change in the QRS morphology of the VAs after a radiofrequency application. These findings may be explained by a single VA origin with preferential conduction to multiple breakout sites resulting from the complex structure of the PAMs. This mechanism is likely to operate with anisotropic conduction from the anatomic background that the LV PAMs are composed of a complex of myocardial strands with some separations between them on the basal and apical sides (4). Therefore, pace mapping often fails to identify a successful ablation site. In identifying the origin of idiopathic PAM VAs, activation mapping is the most reliable method. The peripheral Purkinje network extends to the surface of the PAMs. However, Purkinje potentials are not always recorded at the successful ablation sites of the PAM VAs, likely because most of PAM VAs arise from the myocardium itself and not from the Purkinje fibers (2,4). A low-amplitude ventricular prepotential representing the activation of the VA origin deep from the surface of the PAMs, is also recorded at the successful ablation sites of the PAM VAs. Therefore, during activation mapping, the earliest ventricular activation should be sought, and the particular ventricular potentials should not be a main concern.
Second, the location of the VA origin deep relative to the endocardial surface of the PAMs may render catheter ablation of the PAM VAs challenging (4). Anatomically, the PAMs of the heart are the thickest myocardial structure and conical projections into the ventricular myocardium covered by endocardium. Because of a deep origin of the PAM VAs, suppression of PAM VAs by a mechanical compression is rare and instead, touching of a mapping catheter on the PAMs easily induces PVCs, which preclude activation mapping. The creation of a deep ablation lesion may be necessary for the long-term success of the catheter ablation of PAM VAs because of the distance between the PAM VA origin and endocardial surface. Therefore, the use of high radiofrequency power settings delivered from an irrigated or nonirrigated 8-mm tip ablation catheter is strongly recommended in the catheter ablation of PAM VAs.
Third, the difficulty in maintaining stable contact of the catheter tip at the PAMs with the vigorous motion associated with normal PAM contraction may render it challenging to create a sufficient ablation lesion. Understanding the location of the PAMs and monitoring the relationship between the ablation catheter and the PAMs are important to improve the contact and stability of the ablation catheter on the PAMs. An LV gram is helpful for understanding the fluoroscopic location of the PAMs (1,3,4), but an intensive monitoring with transthoracic and intracardiac echocardiography and/or a 3-dimensional mapping system with an image integration should be used as a guide for mapping (1–4). A contact force sensing catheter should be helpful for achieving a good contact of the ablation catheter on the PAMs, although it does not warrant a stable location of the ablation catheter. A retrograde transaortic approach is usually used for mapping and catheter ablation of LV PAM VAs. A transseptal approach may be used to improve the contact and stability of the ablation catheter on the posteromedial PAM, whereas that is not an option for mapping at the LV anterolateral PAM.
In this issue of JACC: Clinical Electrophysiology, Rivera et al. (5) investigated the efficacy and safety of a cryocatheter in the catheter ablation of LV PAM VAs. They used an 8-mm tip cryocatheter through a transseptal approach in 10 patients with 10 VAs originating from the posteromedial PAM and 1 VA from the anterolateral PAM. An excellent pace map was obtained in all cases. Purkinje potentials were recorded at the successful ablation sites of the PAM VAs in 6 patients. Eight patients had no recurrence of the PAM VAs. One patient had an early recurrence of symptomatic ventricular tachycardia and required a second catheter ablation with radiofrequency energy. Another patient had a recurrence, but significant suppression of the PAM VAs. No complications were reported.
This report may be the first case series in which the efficacy and safety of a cryocatheter in the catheter ablation of the LV PAM VAs were investigated, and has brought up several concerns about the catheter ablation of the VAs originating from this specific structure. A cryocatheter with a large tip was used in this study. However, a large tip catheter is not suitable for detailed mapping because it is likely to record far-field electrograms and also capture a larger myocardium for a pace mapping. The biggest concern is whether the cryocatheter can maintain good contact on the PAMs and create sufficient lesion to eliminate the origins of the LV PAM VAs that are likely to be located deep below the endocardium. Once the cryocatheter is frozen directly on the surface of the PAMs without any space between them, it can rarely be dislodged. However, if ice is formed between the cryocatheter and tissue, the cryocatheter may be easily dislodged and otherwise the efficacy of the cryoablation is significantly diminished. Because the PAMs are moving vigorously, it may be difficult to freeze the cryocatheter to the tissue without any ice between them. It has been reported that, in contrast with radiofrequency ablation, the cryoablation lesion size would be smaller with a high blood flow around the catheter, and larger with a low blood flow due to the warming effects of the local convective flow (6). Anatomically, the basal end of the PAMs is attached to the mitral leaflets by multiple tendons, and there should be a high blood flow around the LV PAMs. Therefore, it remains questionable whether cryocatheter ablation can achieve a better outcome in the catheter ablation of the LV PAM VAs than radiofrequency catheter ablation. Acute mitral valve dysfunction due to injury to the PAM caused by a large lesion and steam pop is another major concern while delivering radiofrequency energy at the PAMs. Because this potential complication has never been reported, it would not be appropriate to discuss its risk as compared with cryocatheter ablation at this point.
The paper by Rivera et al. (5) showed the safety and feasibility of cryocatheter ablation for LV PAM VAs. However, the number of the study patients was too small, and the efficacy and safety were not compared between radiofrequency catheter ablation and cryocatheter ablation. Further study will be required to demonstrate that cryocatheter ablation can be an alternative to radiofrequency catheter ablation in the treatment of LV PAM VAs.
↵∗ Editorials published in JACC: Clinical Electrophysiology reflect the views of the authors and do not necessarily represent the views of JACC: Clinical Electrophysiology or the American College of Cardiology.
Dr. Yamada has reported that he has no relationships relevant to the contents of this paper to disclose.
- American College of Cardiology Foundation
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