Late left ventricular summit premature ventricular contractions elimination with new TactiFlex irrigation technology

Abstract

BACKGROUND

Premature ventricular contractions (PVCs) originating from the left ventricular summit (LVS) could be challenging to ablate due to anatomical reasons.

AIM

To study the role of new irrigation technologies, like the TactiFlex catheter, could facilitate deeper radiofrequency (RF) penetration and thus increase success in the ablative treatment of this PVC subset.

METHODS

Three PVCs focus (left bundle branch block morphology, inferior axis on the frontal plane, early R/S transition in V1-V2) were accurately mapped with Ensite X omnipolar technology.

RESULTS

RF was delivered at mitroaortic continuity by TactiFlex catheter (4-9 lesions, max 35 W, 43 °C, 13 mL/minute, max 60 seconds, mean impedance drop 11.9 ± 1.7 ohms) with acute PVCs suppression but early recurrence in all cases. In one case, an anatomical approach in the posteroseptal right ventricular outflow tract was performed without acute success. After 6-10 hours, no PVCs/ventricular arrhythmias have been detected, and no arrhythmia recurrences in all 3 cases at a 180-day follow-up visit. These data were compared with a cohort of 10 patients with LVS PVCs with immediate disappearance treated with the same technology; the only difference, although not statistically significant, was in the greater drop in impedance (13.5 ± 2.1 ohms).

CONCLUSION

Late PVCs elimination could be due to the porous flexible distal tip design of the TactiFlex catheter that allows deeper RF penetration in the myocardium due to a greater adhesion of the saline irrigation system to tissue. It is reasonable to assume that this new technology makes lesions more transmural, determining a delayed lesion maturation, thus not limited to the duration of energy delivery.

Key Words: Anatomical approach; Left ventricular outflow tract; Left ventricular summit; Radiofrequency catheter ablation; Ventricular arrhythmia; TactiFlex catheter

Core Tip: Premature ventricular contractions from left ventricular summit could be challenging to ablate due to anatomical reasons. New irrigation technologies, like the TactiFlex catheter, could facilitate deeper radiofrequency penetration and thus increase success in the ablative treatment. Late premature ventricular contractions elimination could be due to the porous flexible distal tip design of the TactiFlex catheter that allows deeper radiofrequency penetration in the myocardium due to a greater adhesion of the saline irrigation system to tissue. It is reasonable to assume that this new technology makes lesions more transmu-ral, determining a delayed lesion maturation, thus not limited to the duration of energy delivery.

INTRODUCTION

Symptomatic premature ventricular contractions (PVCs) originating from the left ventricular outflow tract (LVOT), including the left ventricular summit (LVS), in an otherwise normal heart, can be treated by catheter ablation if antiarrhythmic medications are ineffective, not tolerated, or not the patient’s preference. The most common sites of idiopathic endocardial LVOT-PVCs are the aortic root, aortomitral continuity, and the mitral annulus, whereas the most common epicardial structure involved in ventricular arrhythmias (VAs) genesis is the LVS.

LVS is a triangular epicardial region of the left ventricular surface bounded by the bifurcation between the left anterior descending and the left circumflex coronary arteries, bisected by the great cardiac vein into superior and inferior regions. Given the proximity to major coronary vessels and the presence of a thick layer of epicardial fat, catheter ablation by the epicardial approach of the basal region of LVS is particularly challenging, given safety and efficacy reasons[1]. Radiofrequency (RF) ablation is avoided within 5 mm of a coronary artery, and therefore, coronary angiography needs to be performed before epicardial ablation to confirm a safe distance between the catheter tip and coronary vessels. Ablation over epicardial fat results in decreased lesion depth because of inadequate RF penetration of conductive heating[2]. These factors reduce the safety and efficacy of LVS VAs ablation. Therefore, both epicardial ablation through the coronary sinus (CS) and endocardial ablation from anatomically opposite sites (anatomic approach) may be a good option to overcome these limitations, despite the limits of high impedance inside cardiac veins and, sometimes, inaccessibility to the site of the earliest activation with the ablation catheter[3]. In case of persistence or recurrence of LVS-PVCs after a first ablation procedure, the patient should be followed up rather than treated by repeated ablation approaches that could only increase the risk of complications[4]. In 1992, Klein et al[5] reported a case in which idiopathic VAs could not be induced 6 weeks after an unsuccessful ablation. Subsequently, several studies showed the possibility of delayed disappearance of VAs after a single ablation procedure. The main mechanism of the RF delayed effect concerns lesion maturation. At first, the RF lesion is an area of central coagulative necrosis surrounded by inflammatory cells and diffused microhemorrhages. The inflammatory response and microcirculatory damage may lead to fibrosis of this peripheral zone, therefore resulting in lesion size increase. Besides, ultrastructural disorders have been reported up to 6 mm beyond the macroscopic RF lesion because of plasma membrane and microvasculature alterations[6].

TactiFlex™ Sensor Enabled™ catheter is made with a flexible porous tip electrode to facilitate saline irrigation during the ablation procedure. The flexible tip helps reduce procedural risk by directing and ensuring uniform flow orientation, potentially favoring a deeper lesion with an irrigated circuit. The flexible tip of the TactiFlex catheter, compared to the fixed tip, is able to atraumatically rest on the cardiac tissue and increase the surface area of the scaling catheter in contact with the tissue (Figure 1). The catheter has been studied in the treatment of atrial fibrillation with a high-power short-duration approach, demonstrating shortening of procedural times, greater stability, and greater impedance drop[7].

Figure 1 TactiFlex™ Sensor Enabled™ Catheter. In the left panel, the flexible porous tip electrode is shown, in the right panel difference in energy delivery between a conventional catheter (on the top) and a flexible porous tip (on the bottom) (Supplementary material).

MATERIALS AND METHODS

We present 3 consecutive cases of LVS PVCs ablations treated with TactiFlex catheter ablation. All 3 cases underwent ablation for drug-refractory and highly symptomatic PVCs presenting left bundle branch block morphology, inferior axis on the frontal plane, and early R/S transition in V1-V2. The pre-procedural mean PVC burden was 25000/24 hours with repetitive forms (couples, non-sustained ventricular tachycardia). High-density mapping with Ensite X omnipolar technology and a high-density mapping catheter (Advisor HD grid) was performed first in the right ventricular outflow tract (RVOT) (without, however, documenting a significant precocity on the bipolar signal) and, later, in LVOT. In the latter, accurate activation mapping of the aortic root, mitroaortic continuity, and endocardial surface facing LVS was performed.

To further investigate the potential predictive role of impedance drop in lesion efficacy, we created a comparison group of 10 patients with similar clinical and electrophysiological characteristics [PVCs from LVS, same electrocardiogram (ECG) morphology, high PVC burden, mapping and ablation strategy], but in which the ablation resulted in immediate and lasting suppression of PVCs, treated with a Tactiflex catheter. The V2S/V3R amplitude ratio of the PVC on the surface ECG described in detail by Yoshida was used for lateralization of the source of origin[8]. All cases were treated with normal saline irrigation solution (0.9% NaCl). The clinical and instrumental characteristics of the two groups are summarized in Table 1.

Table 1 Case study general data, mean ± SD.

	Case study (n = 3)	Control group (n = 10)
Age (years)	46.3	52.3
LVEF (%)	52.3	53.5
V2S/V3R ratio	1.61	1.68
Beta blockers	3/3	8/10
Flecainide	3/3	9/10
Amiodarone	0/3	1/10
Total RF delivery time (minutes)	5.0 ± 1	4.3 ± 1.8
Single lesion impedance drop (ohms)	11.9 ± 1.7	13.5 ± 2.1
PVCs recurrence (6 months follow-up)	0/3	1/10

LVEF: Left ventricular ejection fraction; RF: Radiofrequency; PVC: Premature ventricular contraction.

RESULTS

In all three cases (Figures 2 and 3), a set of ablation lesions (4-9 lesions, max 35 W, 43 °C, 13 mL/minutes, max 60 seconds) has been performed in mitroaortic continuity if these hallmarks were achieved: (1) The local ventricular activation time recorded at the ablation site on bipolar signal preceded the onset of the Q, R, and S peaks complex with a precocity between -25 milliseconds and -34 milliseconds; (2) QS morphology at the unipolar mapping; and (3) Optimal pacemapping. However, after acute suppression of the VAs, ablation was not successful due to early recurrence of VAs in all cases. Only in the third case (Figure 3), an anatomical approach has also been attempted, and 4 RF pulses were delivered at the posteroseptal region of RVOT, even if electrophysiological measures were significantly worse than the first ablation left ventricular site. The CS approach and so great cardiac vein mapping have not been performed. At the end of the procedure, the PVC burden was not different from the preprocedural one. Arrhythmia behavior was evaluated using continuous ECG telemonitoring, and all antiarrhythmic drugs were withdrawn. In all three cases, after a time interval of 6-10 hours following the procedure, the sudden disappearance of PVCs was detected by continuous telemetric monitoring in the department. A 24-hour Holter ECG revealed no arrhythmias recurrences in all 3 cases at a 180-day follow-up visit. In all three cases, the mean impedance drop per single lesion ranged between 10.2 ohms and 14.3 ohms, and PVC suppression occurred with a late onset (6-10 hours post-ablation). In contrast, the comparison group showed a mean impedance drop per single lesion of 13.5 ± 2.1 ohms, with immediate elimination of PVCs during the procedure and no recurrence at 6 months.

Figure 2 Electrocardiogram/electrogram signals. A: Left ventricular activation map and electrocardiogram/electrogram signals. Best signals recorded (-27 milliseconds) in mitroaortic continuity, 6 lesions (max 35 W, 60 seconds, medium impedance drop 14.3 ohms) were performed without disappearance of arrhythmias; B: Left ventricular activation map and electrocardiogram/electrogram signals. Best signals (-25 milliseconds) recorded in mitroaortic continuity, 4 lesions (max 35 W, 60 seconds, medium impedance drop 11.4 ohms) were performed without disappearance of arrhythmias (Supplementary material).

Figure 3 Left ventricular/right ventricular activation map and electrocardiogram/electrogram signals. Best signals recorded (-34 milliseconds) in mitroaortic continuity, 5 lesions (max 35 W, 60 seconds, medium impedance drop 10.2 ohms) were performed without disappearance of arrhythmias. An anatomical approach was performed with the other 4 lesions in the posteroseptal right ventricular outflow tract. The arrow indicates catheter direction during mapping (Supplementary material).

DISCUSSION

Several clinical and electrophysiological predictors of the success of LVS ablation have been described, among them: The absence of structural heart disease, gender, and the earliest activation > 26 milliseconds before Q, R, and S peaks onset on bipolar electrogram[9,10]. However, the mechanism of the late elimination of LVS arrhythmias after ablation has not been completely understood and can be ascribed to a delayed RF effect related to lesion maturation[6]. RF catheters with new systems of irrigation flow to the tip-tissue interface have been developed, aiming to complete lesion transmurality and thus elimination of deep substrates. The porous distal end of the TactiFlex catheter also has a combination of a flexible tip with a fiber optic-based contact force sensing, which allows for greater adhesion between the saline irrigation system and myocardial tissue. As demonstrated by Ptaszek et al[11], TactiFlex has 2x greater stability during intracardiac movement of the catheter and during the ablation itself, allowing better contact to be achieved more easily, performing more effective lesions in less time, also due to the greater adhesion to the tissue (Figure 1). In light of all this, it is reasonable to assume that this new technology makes more transmural lesions, in a process of lesion maturation with effects of RF energy not limited to the duration of energy delivery. We hypothesize that the TactiFlex catheter, even when it does not produce a significant impedance drop, can create a deeper tissue lesion due to reduced edema formation. This process likely begins with microcirculatory damage and inflammatory infiltration, eventually leading to fibrotic evolution. It is also conceivable that a more effective lesion could limit perilesional edema in the acute phase, thereby facilitating deeper RF penetration. Therefore, the TactiFlex catheter could be a new therapeutic opportunity for LVS ablation to avoid more aggressive approaches like epicardial or through CS branches. In our cases, we opted for a safer approach to minimize potential risks associated with RF ablation within the CS, such as cardiac tamponade, CS stenosis, and coronary artery injury[10]. Nevertheless, there is a need for comparative studies assessing the performance of this novel technology relative to traditional irrigation systems. To date, the literature on PVC treatment remains inconsistent, with conflicting findings, particularly regarding the role of the contact force sensor in enhancing procedural safety and effectiveness. This ongoing debate on the usefulness of the contact sensor, which may not significantly affect procedural efficacy, highlights the considerable heterogeneity of techniques and approaches in the treatment of this type of arrhythmia[12]. However, to the best of our knowledge, the present single-center data are the first reported data on efficacy and safety of the novel TactiFlex catheter on PVC ablation, therefore we aim to contribute to the current literature on PVC ablation by means of cutting-edge technology. The comparison with the control group of 10 patients, which shows an immediate disappearance, suggests that a higher impedance drop may be associated with more immediate transmural lesion formation, thus contributing to early arrhythmia suppression, and this data is not surprising at all and has already been demonstrated in literature[13]. However, it is new that, although there was no acute disappearance in the three cases reported, with a lower impedance drop, the result at a 6-month follow-up was not affected.

Limitations

This case-control study clearly presents the major limitation of a small sample size. Further controlled randomized trials are certainly needed to assess the efficacy of irrigated catheter ablation for PVCs and to determine whether differences exist according to the technology used. Moreover, demonstrating a consistent response to RF ablation in a larger series of patients with LVS PVCs could potentially lead to a change in clinical practice, reserving more invasive (i.e., epicardial) approaches only for cases of recurrence. Another limitation of the study - although it also paves the way for future comparative research - is the use of a single catheter type to evaluate differences between the two groups. Future studies should include various RF technologies, including devices from different manufacturers, to comprehensively evaluate their efficacy and safety.

CONCLUSION

LVS ablation is a challenging procedure with life-threatening risks. New catheter technologies, with new irrigation systems (with or without an anatomical approach in the RVOT region), could be a treatment option, avoiding more aggressive treatments like the epicardial/CS approach.