QDOT MICRO™ Catheter

To overcome those issues a novel ablation catheter was recently introduced. The QDOT MICROTM Catheter (Biosense Webster, Inc. Diamond Bar, CA, USA) is an open-irrigated CF sensing single-tip catheter (Figure 1) . The QDOT MICROTM Catheter incorporates three microelectrodes and six miniature thermocouples (1mm in diameter (3 proximal and 3 distal), at its tip for precise temperature monitoring. The thermocouples are embedded at distinct locations within the outer metal shell of the catheter, just 75 μm underneath the tip surface. The reason for this superficial location design was to obtain more accurate local temperature measurements from the catheter tip which is in direct contact with the tissue, in comparison to the conventional tip temperature measurements that is altered by the cooler parts of the tip that are not in touch with the tissue. It has been developed allowing for real-time catheter-to-tissue interface temperature measurements. Therefore, a real temperature-controlled catheter ablation with automatic adjustment of power and irrigation output based on real‐time temperature measurement is achieved which allows for save and effective RF-lesion formation.
The QDOT MICROTM Catheter offers two different ablation modes.
In QMODE (conventional temperature-controlled ablation mode with a maximum of 50W) the system adjusts 1) the irrigation flow rate and 2) power based on the measured temperature to stabilize the catheter tip temperature within the allowed temperature range avoiding over-heating and steam-pop. Lesions formation is guided by AI in the QMODE and is individualizable concerning power and ablation duration.
In QMODE+ (very high-power short-duration mode, vHPSD, 90W/4 seconds) only power is adapted to adjust the target temperature. The target temperature of the temperature-controlled ablation is usually 60°C based on the hottest surface thermocouple. The irrigation flow rate delays the energy application for a minimum of 2 seconds before and 4 seconds after each RF application. It is always possible to stop the lesion formation, however in QMODE+ it is only possible to ablate with 90W for a maximum of 4 seconds. The default irrigation setting is set at 2ml/min and 8 ml/min with a recommended CF working range 5 to 30g.
The vHPSD strategy aims to create shallower but wider lesions in a very short time by reducing conductive heating and increasing resistive heating at the same time. Additionally, collateral tissue damage might be reduced.
The three microelectrodes at the catheter tip of the QDOT MICROTM Catheter offer sharp potentials and a higher resolution during mapping. Previous analyses provided evidence for reduced RF ablation time and procedure duration while showing a good safety profile in comparison to conventional power-controlled ablation. Although the QDOT MICROTM Catheter was mainly designed for PVI its versatility to treat other types of arrythmias was recently evaluated and will be presented in this article.
Pulmonary vein isolation utilizing the QDOT MICROTM Catheter
With the ability to perform temperature-controlled ablation in combination with vHPSD the QDOT MICROTM Catheter is an ideal tool for thin-walled LA procedures especially for PVI (Figure 2 ). The vHPSD strategy aims to create shallower but wider lesions in a very short time by reducing conductive heating and increasing resistive heating at the same time. Additionally, collateral tissue damage might be reduced. Utilizing conventional power-controlled moderate-power long-duration RF applications the “close – protocol” with an inter-lesion distance (ILD) of 6mm has been introduced and verified for PVI. Lesion formation of vHPSD applications creates wider but shallower lesions. To achieve continuous lesions, we recently adapted the close-protocol to an individualized and tighter “very close-protocol”. Utilizing the “very close-protocol” an ILD of 3-4mm at anterior aspect and ILD of 5-6mm at the posterior aspect of the LA using vHPSD only is performed and safety, efficacy and follow-up in comparison to conventional CF sensing AI guided RF ablation has been shown in the FAST and FURIOUS AF and FAST and FURIOUS PVI studies.
FAST and FURIOUS PVI study was a prospective non-randomized trial which compared 50 AF patients (vHPSD group) treated by PVI with the QDOT MICROTM Catheter in QMODE+ only vs 50 previous patients (control group) with conventional point by point RF 40W AI guided ablation by the THERMOCOOL SMARTTOUCH SOURROUND FLOW ablation catheter (Biosense Webster). For patients of the vHPSD group the QMODE+ was exclusively used for all procedures. No switch to QMODE was necessary to achieve PVI. No differences were observed between the groups concerning catheter maneuverability and catheter stability. Here a significantly reduced mean RF time of 352±81s (vHPSD) vs 1657±570 seconds (control, p<0.0001) was observed. Furthermore, the mean procedure duration was 59±13 (vHPSD) and 101±38 (control, p<0.0001) and the first pass isolation rate was 74% (vHPSD) and 76% (control, p=0.817). Severe adverse events were reported in 2% (vHPSD) and 6% (control, p=0.307) and the 12-month recurrence free survival was 78% (vHPSD) and 64% (control, p=0.142). In conclusion PVI solely utilizing vHPSD via a very close-protocol was shown to provide safe and effective PVI with a high rate of first-pass isolations. No steam pops and no catheter tip charring were detected. An esophageal temperature probe was utilized in all vHPSD patients. A temperature of >38.5°C was detected in 18 (36%) patients solely at the posterior part of the left PVs. The mean maximum oesophageal temperature was measured at 42±2 °C. No clinical apparent esophageal lesions and no atrio-oesophageal fistulas were found.
The QDOT-FAST trial was a first-in-human, prospective, multicenter, single-arm, clinical study of the QDOT MICROTMCatheter conducted in four European countries (Austria, Belgium, Czech Republic, and Italy). It evaluated the safety and short-term performance of the QDOT MICROTM Catheter in QMODE+ for PVI in 52 PAF patients. The total procedure and fluoroscopy times were 105.2±24.7 min and 6.6±8.2 min, respectively. The total RF ablation time was 8.1 minutes. The longer procedure time compared to the FAST and FURIOUS PVI study might be explained by the fact that in only 78.8% of cases (41 of 52), PVI was achieved using the QMODE+ only.No severe adverse events occurred in this study.
The Q-FFICIENCY trial was a prospective, multicenter (n=22), nonrandomized study that aimed to evaluate the safety and effectiveness of the QDOT MICROTM Catheter in treating drug-refractory, symptomatic PAF patients (n=166) utilizing vHPSD only. The median procedural duration was 132 minutes and the median RF time was 8.0 minutes while the primary adverse event rate was 3.6%. The 12-month clinical success rate was 76.7%. Although the findings concerning safety and effectiveness were similar to the FAST and FURIOUS PVI study the procedure time was almost doubled which could be the consequence of its multicenter character with some centers unexperienced in QDOT MICROTM Catheter procedures.
The POWER PLUS trial was a multicenter, randomized controlled trial, the authors compared procedural efficiency, efficacy, and safety of PVI using 90-W/4-second ablation to 35/50-W ablation. The procedural time was shorter in the 90-W group vs the 35/50-W group (median 70 (60, 80) minutes vs. median 75 (65, 88.3) minutes;P  = 0.009). No major complications were observed in both groups with esophageal injury occurring in 1 patient per group.
A nonsignificant trend towards lower rates of first-pass isolation was seen in the 90-W group (83.9% vs 90%; P  = 0.0852). However, no differences in 6-month outcomes were observed. The authors suggest to test a hybrid approach combining QMODE+ for anterior and QMODE for posteriore aspects of the LA in futures studies.
Although rare atrio-oesophageal fistula after catheter ablation of AF is a devastating and potentially lethal complication. The fact that vHPSD applications create shallower and wider lesions might be a factor for preventing atrio-oesophageal fistulas. A recent study of ninety consecutive patients treated by vHPSD based PVI underwent post-ablation oesophageal endoscopy. None of the 90 patients demonstrated oesophageal ulceration (0%) which might support the above motioned positive effect of the lesion formation in prevention of oesophageal lesions. Furthermore, no steam pop, cardiac tamponade, stroke, or fistula was reported in this study. Although the rate of clinical apparent stroke and TIA is reported to be low initial cerebral MRI data after QMODE+ based PVI showed silent cerebral lesions in 6/23 (26%) patients. Since coagulation on the catheter tip was detected at the end of the procedure suggesting this observation to being related to those events. Therefore, the RF generator software has been recently modified aiming to reduce the rate catheter tip coagulation.
Recently, data on durability was assessed by cardiac MRI in 60 patients treated by vHPSD. Here complete PV encirclement was observed in 76.7% for RPVs, in 76.7% for LPVs, and in 66.7% for both PV pairs. These findings are promising and are in line with findings assessed in the FAST and FURIOUS PVI study. Here PVI durability assessed during redo-procedures was 75% (vHPSD) vs. 33% (control, P < 0.001). The FAST and FURIOUS REDO study is ongoing and will present data of PVI durability after initial vHPSD very close protocol based PVI.
The available data of the QDOT MICROTM Catheter for PVI is promising. While demonstrating a good safety profile, the total ablation time, and procedural duration, were impressively low utilizing vHPSD. The retrospective peQasus study (clinical trials.gov: ID: NCT05710822, Very high-power short-duration ablation utilizing the QDOT MICROTM Catheter for pulmonary vein isolation - A multicenter study) will evaluate safety and efficacy of the QDOT MICROTM Catheter for PVI in multiple centers in Europe in a large group of >500 patients.