Treatment of Macro-Reentry Atrial Tachycardia with Very High-Power, Short-Duration, Temperature-Controlled Ablation of Anterior Line Using an Open-Irrigated Ablation Catheter with Microelectrodes

Background

Catheter ablation has proven to be a very successful procedure for patients with atrial fibrillation (AF), with excellent outcomes on long-term follow-up. Recently, a radiofrequency (RF)-based, power-controlled ablation mode called high-power, short-duration (HP-SD) has been introduced that delivers a maximum of 50 W for treatment with pulmonary vein isolation (PVI) and deployment of linear lesions [1,2] With HP-SD, the length of the procedure and RF time are shorter and rates of isolation on the first past are increased, compared with standard RF ablation [1].

A novel ablation catheter (QDOT Micro, Biosense Webster, Diamond Bar, United States) has been introduced that permits temperature-controlled ablation with contact force (CF) sensing. This catheter has 6 thermocouples and 3 microelectrodes at its distal tip for accurate and immediate temperature surveillance [3,4]. The QDOT Micro catheter allows for conventional temperature-controlled ablation (QMODE, maximum of 50 W) and very HP-SD (vHPSD) ablation (QMODE+, 90 W/4 s) [5]. In QMODE, temperature-controlled ablation is achieved by adjusting the power and rate of flow of irrigation. In QMODE+ mode only, power can be adjusted to alter temperature [5].

With QMODE+ ablation, the aim is to create wider and shallower lesions by simultaneously reducing the conductive and increasing the resistive heating areas. Previous reports about AF treatment with PVI have shown significantly reduced total RF time and procedure duration and excellent safety outcomes [5,6]. As yet, however, no reports exist documenting creation of lesions other than PVI. vHPSD ablation could be an efficient ablation technique for deploying linear lesions in addition to PVI. The microelectrodes also could offer unique findings from mapping and ablation of macroreentrant atrial tachycardia (AT). Here, we present the treatment of peri-mitral AT in a patient with ablation of an anterior line performed solely using the vHPSD QMODE+ mode of the QDOT Micro catheter.

Case Report

A 74-year-old man (CHA2DS2-VASc score: 2) presented to the emergency care unit because he had been experiencing dyspnea, palpitations, and persistent tachycardia (European Heart Rhythm Association class IIb) for a few days. He had a >5-year history of recurrent, persistent AF and typical atrial flutter despite receiving antiarrhythmic drug therapy with flecainide (2×100 mg) and oral anticoagulation with rivaroxaban (2×20

mg). A 12-lead electrocardiogram (ECG) showed a heart rate of 105/min with small P waves, suggesting AT (Figure 1). Treatment options (cardioversion, drug therapy, and catheter ablation) were discussed with the patient and he gave informed consent for an ablation procedure, which was scheduled for the next day. Transesophageal echocardiography (TEE) performed before the ablation showed no left anterior (LA) thrombus.

At the beginning of the ablation procedure, the patient had clinical AT (cycle length, [CL] 300 ms) (Figure 2A). Intraprocedural management has been described in detail in reports from our group’s previous studies [6–8]. The ablation was performed with the patient under deep sedation. Four ultrasound-guided fem-oral vein punctures were performed, 3 on the right and 1 on the left side. A decapolar diagnostic catheter was introduced and positioned inside the coronary sinus (CS). Entrainment maneuvers suggested that the patient had a left AT. A double transseptal puncture (TSP) was performed under fluoroscopic guidance using the modified Brockenbrough technique with an 8.5F transseptal sheath and puncture needle (SL1 sheath and BRK-1 TSP needle, St. Jude Medical, St. Paul, Minnesota, United States). Heparin boluses were administered to target an activated clotting time of >300 s. An S-shaped temperature probe (CIRCA S-CATH, Circa Scientific, Englewood, New Jersey, United States) was advanced into the patient’s esophagus to monitor the temperature there (Teso). The Teso cut-off value was set at 38.5°C. Three-dimensional electroanatomic LA reconstruction (CARTO 3 V7; Biosense Webster) was performed via fast anatomical mapping with a multi-electrode spiral mapping catheter (15-mm fixed size, 20 electrodes, Lasso Nav; Biosense Webster). For the bipolar LA voltage map, the voltage interval was set from 0.1 mV to 0.5 mV. A total of 6590 mapping points were acquired using a local activation time (LAT) map with a window of interest of −145 ms/+145 ms and the complete CS electrodes (center of energy) as a reference. The Coherent module (Biosense Webster) was utilized for LAT calculation and a peri-mitral marcoreentrant tachycardia with a potential critical isthmus at the anterior wall was seen on the dynamic visualization setup (Figure 2B).

Therefore, and given that the scar area on the LA anterior wall was massive, the most effective strategy for this patient was ablation of an anterior line. Catheter applications were done solely with the vHPSD mode (90 W, 4 s; QMODE+ mode). The target temperature was 60°C. For anterior lesions, we aimed to achieve an inter-lesion distance of 3 mm to 4 mm, and for posterior lesions, an inter-lesion distance of 5 to 6 mm was chosen. The CF target range was 10 g to 20 g.

The ablation on the anterior wall was started at the critical isthmus area. Within the zone of slow or no conduction, fragmented potentials were detected on the microelectrodes (Figure 2C), whereas no signals were detected on the standard electrodes of the ablation catheter. During the third vHPSD application, the CL was prolonged from 300 ms to 400 ms (Figure 2D) after an application time of <1 s. The total RF time at the end of this application was 12 s. The anterior line was continued up to the anterior mitral annulus. Then the critical isthmus area was targeted again, with the aim of completing the anterior line. Sharp potentials were detected on the microelectrodes and fragmented potentials were detected on the distal electrode of the ablation catheter (Figure 3A–3D). The 10th application was started and the AT was terminated after an application time of 1200 ms. At the end of this application, the total RF time was 40 s. Afterward, the anterior line was completed with a total of 29 vHPSD applications and a RF time of 116 s, connecting the anterior mitral annulus to the antero-superior aspect of the right superior PV [6]. Blockage of the anterior line was verified with pacing maneuvers from the spiral mapping catheter positioned inside the left atrial appendage (LAA) and with the CS catheter and the appearance of local double potentials on the ablation catheter along the line. In addition, pacing from the spiral mapping catheter placed in the LAA was performed and early and late signals on either side of the line were checked.

PV angiography then was performed to identify the PV ostia and the ipsilateral PVs were tagged. During PVI, the spiral mapping catheter was placed inside the PVs [6]. Only the QMODE+ mode was used. Sixty-four vHPSD RF applications (RF time 256 s) were performed for septal PVs and 62 vHPSD RF applications (RF time 248 s) were performed for lateral PVs. On both sides, first-pass isolation was observed. Temperature increases to 42.1°C and 41.5°C were observed during ablation at the posterior part of the left inferior PV.

Because the patient was known to have a typical atrial flutter, a cavotricuspid isthmus (CTI) block was ablated under pacing with the proximal CS electrode. Only QMODE+ was used to deliver 29 applications of vHPSD (RF time 116 s) and achieve a first-line isthmus block. The CTI block was verified with differential pacing maneuvers.

No steam pops occurred during the procedure and no charring was visible on the ablation catheter tip at the end of the procedure. The total procedure time (skin-to-skin) was 107 min. A total of 144 vHPSD RF applications were performed, with a total RF time of 576 s. To test the likelihood of AT recurring, programmed stimulation with up to 3 extra beats and burst pacing from the spiral catheter in the LAA and the CS catheter was performed. It was not possible to induce AT with the maneuvers.

Both a figure-of-eight suture and a pressure bandage were placed on the area that was ablated. The pressure bandage was removed after 4 h and the figure-of-eight suture was removed the next day. The patient was given rivaroxaban 10 mg 6 h after the procedure and the dosage was increased to 20 mg/d the next day. He was prescribed flecainide (2×100 mg) and metoprolol for 3 months and proton-pump inhibitor therapy for 6 weeks. At follow-up 2 weeks later, he had not experienced a recurrence of either AF or AT.

Discussion

We report the case of a patient who underwent AT ablation with a QDOT Micro ablation catheter using solely vHPSD mode. Our main finding was that vHPSD LA ablation was feasible and a first-pass linear lesion block was achieved with an RF ablation time of <2 min.

In a previous study, HP-SD artificial intelligence-guided ablation at a maximum of 50 W was evaluated [2]. The technique seemed to be safe and effective, but no real-time temperature surveillance was possible with conventional CF sensing catheters. The tip of the novel QDOT Micro catheter incorporates 6 thermocouples, enabling real-time monitoring of catheter-to-tissue temperature and, therefore, a temperature-controlled ablation [5,6]. In the QMODE+ vHPSD ablation mode, lesions are created that are similar in volume but shallower and wider than result from conventional ablation with standard catheters. Therefore, using vHPSD could reduce collateral tissue damage. In the present study, no steam pops or peri-procedural complications occurred. However, the Teso probe detected relatively high temperatures during ablation of the posterior wall. Whether the shallower and wider lesions created with vHPSD are suitable for ablation in the relatively thick anterior mitral isthmus area and epicardial structures such as Bachmann bundle has not been studied.

Here we describe the feasibility and efficacy of ablation with vHPSD in a case report. Our findings, while positive, are only preliminary because larger studies are needed to prove the value of the technique. The limited depth of vHPSD could be a limitation of this approach compared to conventional ablation. Furthermore, our findings are limited to a single patient who had anterior fibrosis and limited areas of healthy myocardial tissue. The microelectrodes of the QDOT Micro catheter provided sharp and fragmented potentials at the area of interest even though the standard electrodes showed no visible signals [4]. The combination of microelectrodes and vHPSD ablation seems to be an ideal option for AT ablation. Long-term clinical outcomes and durability of linear lesion blocks created using vHPSD strategies are unknown and further investigation of the technique is needed in larger studies and trials.

Conclusions

Here, we have presented the case of a patient who underwent AT ablation with the QDOT microcatheter. Our findings underscore the benefit of using microelectrodes during AT ablation. Furthermore, we have provided proof-of-concept of vHPSD for ablation of LA linear lesions.