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Research progress of high-power short-term radiofrequency ablation for atrial fibrillation
Research progress of high-power short-term radiofrequency ablation for atrial fibrillation. Traditional standard power radiofrequency ablation for atrial fibrillation has the disadvantages of long operation time and high conduction recovery rate.
High-power short-term radiofrequency ablation increases the impedance thermal damage and reduces the conduction thermal damage. Compared with the conventional power, the damage is wider and slightly shallower. It significantly reduces the operation time and increases the continuity of the damage without increasing the correlation The incidence of complications.
At present, a number of animal experiments and clinical studies have preliminarily verified the effectiveness and safety of its application in atrial fibrillation ring pulmonary vein isolation. The research progress is now reviewed.
Atrial fibrillation is the most common arrhythmia in clinical practice. After global age adjustment, its prevalence is 0.60% in men and 0.37% in women. It can lead to serious complications such as stroke, heart failure, and embolism, with high The fatality rate and disability rate [1, 2].
In addition to conventional drug treatments based on anticoagulation, ventricular rate or rhythm control, percutaneous catheter radiofrequency ablation with the main goal of achieving long-term continuous pulmonary vein electrical isolation has also been widely used in the treatment of atrial fibrillation .
Recent studies have shown that high power short duration radiofrequency ablation (HPSD-RFA) can significantly improve the continuity of injury while shortening the operation time, increase the single-lap isolation rate without increasing complications Incidence rate. This article reviews the research progress of atrial fibrillation HPSD-RFA.
1. Current status of radiofrequency ablation for atrial fibrillation
Pulmonary vein isolation (PVI) is the cornerstone of radiofrequency ablation for the treatment of atrial fibrillation. At present, relatively low power is usually used for ablation for a long time: 20~40 W power, 10~20 g contact force, continuous discharge After 20-40 s, the recovery rate of the left atrium-pulmonary vein electrical conduction after the operation is still maintained at a high level (22% and 15% in the acute phase and 3 months after the operation) [3, 4, 5].
The recurrence of atrial fibrillation after ablation is closely related to the recovery of electrical conduction between the left atrium and the pulmonary vein, and the transmural (sufficient depth of injury) and continuity of the injury caused by ablation are the decisive factors for conduction recovery [4,6]. How to improve the transmural and continuity of ablation injury to obtain long-term sustained PVI has become the key to reducing the recurrence of atrial fibrillation after surgery.
In addition, traditional low-power ablation takes a long time during PVI surgery. Longer time of cardiac intervention increases the risk of complications such as cerebral infarction and pericardial tamponade during the perioperative period. The large amount of intraoperative radiation also increases the patient’s risk. And the risk of long-term malignant tumors and genetic abnormalities of the surgeon [3,7].
At the same time, the amount of liquid perfused by the cold saline perfusion catheter during ablation will also increase with the ablation time and operation time, which may induce acute heart failure in patients with impaired left ventricular function and elderly patients .
The traditional concept believes that the HPSD-RFA safety window is narrow, and in order to obtain a larger ablation focus, the first choice is to increase the ablation time instead of increasing the output power to avoid the occurrence of excessive power-related complications .
With the emergence of new quantitative ablation technologies such as pressure monitoring catheter , improved temperature monitoring catheter , ablation index (AI) , VisitagTM, etc., the depth of injury is more controllable, which can effectively avoid Tissue overheating makes it possible for radiofrequency ablation with higher power than standard .
2. HPSD-RFA principle
The local tissue thermal effect of radiofrequency ablation is mainly composed of two phases: resistive heating and conductive heating, which together mediate the formation of ablation damage. Resistive heating mainly occurs in the elliptical tissue area <1 mm in contact with the tip of the ablation electrode. The deeper tissue heating is mainly passively conducted by the heat of the resistive heating zone, that is, conductive heating.
The heating method is passive heating, which is temperature and time dependent. When the local temperature is greater than 50 ℃, protein denaturation and dehydration effects will mediate cell death and local tissue coagulation necrosis, forming irreversible damage, and the damage is reversible when the temperature is lower than this threshold.
Since conductive heating is passive heating, it weakens with the increase of heat conduction distance and time, so reversible damage mostly occurs in the conductive heating area . The traditional standard power ablation discharge time is long, and the heating phase is mainly conducted heat. Although it is beneficial to obtain deeper ablation damage, the thermal latency effect can damage the deep adjacent tissues of the myocardium, which is related to serious complications such as atrial esophageal fistula and phrenic nerve injury. .
In contrast, HPSD-RFA is based on resistive heating, which can irreversibly damage the full-thickness pulmonary vein vestibular myocardium in a short period of time with the largest proportion of the damage. The damage diameter is wide, which helps to improve the transmural and continuity of ablation damage [ 4] At the same time, the conduction heating phase is significantly shortened, which can avoid the damage of passive conduction heating and thermal latent effects to adjacent tissues, and reduce the occurrence of complications such as atrial esophageal fistula and phrenic nerve injury .
On the other hand, HPSD-RFA can also significantly shorten the single-point ablation time to avoid catheter instability and reduce tissue edema, and correspondingly reduce the ablation gap . The main factors that affect the stability of the catheter are breathing movement, heart beat and uncontrollable catheter swing.
In the actual ablation process, the longer the ablation time, the more difficult it is to maintain the catheter’s stable adherence. In HPSD-RFA, the single-point discharge time can be as short as a few seconds, which makes it easier to achieve stable adherence ablation [4,10]. In addition, HPSD-RFA significantly shortens the operation time while also greatly reducing the radiation exposure of patients and surgeons .
3. HPSD-RFA damage characteristics
Bourier et al.  used different power and time combinations (50 W/13 s, 60 W/10 s, 70 W/7 s, 80 W/6 s, 30 W/30 s) in the in vitro experiment. For ablation on the model, each group uses 500 as the target AI value. The results show that compared with 30 W/30 s, the volume of the lesion obtained in each HPSD-RFA group has no significant difference, but in terms of geometry, the diameter of the lesion (width) The larger the depth, the smaller the depth, and the higher the power, the more obvious this feature is . Similar characteristics have been reflected in many studies. Borne et al.  found in animal ablation experiments: 50 W/5 s compared with 20 W/30 s group has no significant difference in the volume and width of ablation injury, but the injury The depth is reduced (2 mm vs. 2.9 mm).
Leshem et al.  performed linear ablation in the right atrium of pigs at (90 W/4 s, upper temperature limit ≤65 ℃) and 25 W/20 s, respectively. The results showed that the ablation depth of the two groups was similar [( 3.58±0.3) mm than (3.53±0.6) mm], but the width increases [(6.02±0.2) mm to (4.43±1.0) mm] . In addition, the maximum ablation diameter of the 90 W/4 s group occurred on the endocardial surface, while the 25 W/20 s group appeared on the subendocardial plane. The reason may be that the 25 W/20 s ablation had a higher perfusion rate to power ratio.
The cooling on the contact surface of the catheter tissue is more effective, that is, the endocardial retention effect of perfusion cooling, which may be a potential factor for conduction recovery . In PVI, a complete ablation injury line not only needs to reach a sufficient depth of injury, but also needs to have enough width to reduce the ablation gap .
Therefore, according to the geometric characteristics of the HPSD-RFA ablation injury, the increase in its width and the largest diameter appearing on the endocardial surface is conducive to the uniformity and continuity of the injury and reduce the conduction recovery.
However, the damage depth of transient impedance heat is limited, so it is suitable for thin-walled myocardial tissues, such as the atrial wall, especially the vestibular area of the pulmonary vein, and is not suitable for thick tissue areas such as the mitral valve isthmus, ventricular muscle and other parts .
4. the effectiveness and safety of HPSD-RFA
1) HPSD-RFA related animal experiment results:
In the past, a number of in vitro models and animal experiments have proved the safety and effectiveness of cardiac HPSD-RFA. In 2017, Bhaskaran et al.  applied different power and time combinations (40 W/30 s, 50 W/5 s, 60 W/5 s, 70 W/5 s and 80 W/5 s) in the myocardial in vitro model and experiment. Ablation is performed in the right atrium of the sheep. The results show that under the same contact force (10 g) and perfusion rate (30 ml/min), 50~60 W/5 s ablation can form transmural ablation lesions like traditional 40 W/30 s ablation, and vapor bubbles occur.
The rate was lower, only occurring in the 40 W/30 s and 80 W/5 s ablation groups. This study proved the feasibility of HPSD-RFA for the first time. Leshem et al.  used an improved temperature monitoring catheter QDOTMicro catheter in pig experiments with extremely high power (90 W/4 s, upper limit temperature 65 ℃) and standard power (25 W/20 s) in 8 pigs.
Parallel line ablation and PVI were performed on the posterolateral and posterior septal parts of the right atrium in live pigs. Then, the transmural and continuity of the ablation injuries between the two groups were compared through histopathological analysis. The results showed that the HPSD-RFA group ablation lines consisted of continuous transmural injury (100%), while the standard power group ablation line injury gap and non-transmural injury rates were higher, respectively 25% and 29% [5 ].
No eschar or perforation of the heart occurred in the two groups, and only one steam bubble occurred when the contact force was greater than 40 g. In addition, damage to the phrenic nerve and lung parenchyma caused by the lateral wall line after ablation was less common in the HPSD-RFA group (0/4 vs. 2/4, 1/4 vs. 2/4, respectively). This study shows that HPSD-RFA can significantly improve the continuity of ablation injury and may reduce the risk of complications.
In addition, Barkagan et al.  further verified the long-term continuity of the injury line formed by HPSD-RFA in an animal experiment of pig right atrium ablation (decided whether the pulmonary vein isolation can be maintained for a long time). In this study, STSF catheter, 30 W/30 s and QDOTMicro catheter, 90 W/4 s were used to perform linear ablation of the right atrium of pigs.
The continuity of the ablation line was checked by voltage mapping and pacing at 30 days postoperatively. Perform histopathological treatment on the ablation lesions. The results show that the two experimental groups have obtained continuous ablation lines at the completion of the operation, but in the long-term (30 days after surgery) continuity, HPSD-RFA has an advantage over the standard power (continuous posterior wall line is 3/3 to 1 /3).
This suggests that the PVI formed by HPSD-RFA is more durable than traditional low-power ablation, and the long-term electrical conduction recovery rate is lower, which is expected to reduce the recurrence of atrial fibrillation after ablation. In addition, in this study, the discharge time required for ablation was reduced by more than 80% compared with the standard power (4 s per ablation point vs. 30 s), and there were no complications such as vapor bubbles, eschar, phrenic nerve injury, and lung parenchymal injury.
2) HPSD-RFA related clinical research:
Reddy et al.  In a multi-center prospective clinical study QDOT-FAST trial, 52 patients with paroxysmal atrial fibrillation were treated with HPSD-RFA using QDOTMicro modified temperature monitoring catheter PVI surgery. Intraoperative ablation parameters: 90 W/4 s, upper limit temperature ≤65 ℃, perfusion rate 8 ml/min, contact pressure 5-30 g. And adopts a temperature control mode (when the temperature reaches the upper limit temperature of 65 ℃, the closed-loop system automatically reduces the output power) to avoid tissue overheating.
The primary endpoint of the trial is the short-term effectiveness and safety of ablation. The results showed that all patients achieved PVI. The operation time and X-ray fluoroscopy time were (105.2±24.7) min and (6.6±8.2) min, respectively. Forty-nine patients (94.2%) were able to maintain sinus rhythm during the 3-month follow-up period.
Only 2 complications occurred in the trial: pseudoaneurysm and asymptomatic thromboembolism, and no serious complications such as death, stroke, atrial esophageal fistula, and pulmonary vein stenosis occurred. Kottmaier et al.  included a total of 197 patients with paroxysmal atrial fibrillation undergoing PVI surgery. Among them, the HPSD-RFA group (n=97) used 70 W to ablate the anterior wall of the left atrium for 7 s, and ablate the posterior wall for 5 s. For the power group (n=100), 30-40 W was used for ablation for 20-40 s. During the 1-year follow-up period, 83.1% and 65.1% of patients without atrial fibrillation in the HPSD-RFA group and the standard group accounted for 83.1% and 65.1%, respectively.
There were no complications such as pericardial tamponade, thromboembolism, or atrial esophageal fistula in both groups. In addition, the ablation time in the HPSD-RFA group was shortened [(12.4±3.4) min compared to (35.6±12.1) min]. Yavin et al.  also found in a comparative study on the long-term maintainability of atrial fibrillation HPSD-RFA ablation injury: the HPSD-RFA group (45~50 W/8~15 s, n=112) was better than the conventional power group ( 20~40 W/20~30 s, n=112) has a lower acute pulmonary vein conduction recovery rate (6.2% vs. 12.5%), and was followed up for 1.2 (0.2, 2.9) years and 1.9 (0.3, 3.7) years, respectively Later, it was found that HPSD-RFA can also reduce the long-term recovery rate of pulmonary vein conduction (16.6% vs. 52.5%).
Different from the above results, in another study, Ücer et al.  performed HPSD-RFA (50 W/6~10 s) on 25 patients with atrial fibrillation. The postoperative adenosine provocation test showed that the recovery rate of acute pulmonary vein conduction was as high as 18%. , Lower than expected effective rate, the possible reason for the difference is the different ablation parameters used in the study.
A meta-analysis that included 10 studies with 2467 patients showed that HPSD-RFA has a higher pulmonary vein isolation rate (RR=1.20, 95%CI 1.10~1.31) and a lower rate than conventional power in atrial fibrillation. The recurrence rate of atrial arrhythmia (RR=0.73, 95%CI 0.58~0.91) . At the same time, the operation time is shortened, and the main complications are not statistically different from the conventional power.
Castrejón-Castrejón et al.  In the POWER-FAST trial study, HPSD-RFA was performed on 48 patients, 18 of which were ablated at 50 W, with target injury index (lesion size index, LSI) ≥ 5 or AI ≥ 350, 30 One patient was ablated at 60 W for 5-7 s, and 47 patients in the control group were ablated at a standard power of 30 W/30 s. All patients were performed within 72 hours after surgery
Esophageal endoscopy. Results 100% and 98% of patients in the HPSD-RFA group and the control group achieved PVI, and the incidence of conduction recovery verified by pacing during the operation was 5% and 8%, respectively. The incidence of endoscopic esophageal injury in the 30 W, 50 W, and 60 W groups were 28%, 22%, and 0, respectively. It is suggested that HPSD-RFA has a lower risk of esophageal injury.
However, in another study, Barbhaiya et al.  used intraoperative esophageal temperature monitoring and found that 50 W/6 s ablation of the posterior wall of the left atrium can cause an increase in the esophageal lumen temperature in an area with a radius of about 2 cm. ~5.8 ℃, and reached the peak temperature 25 s after the ablation stopped.
The continuous HPSD-RFA damage in PVI surgery is relatively close in space and time, which will lead to heat accumulation and increase the risk of esophageal thermal injury.
In summary, there have been a number of clinical studies that have preliminarily verified the safety and effectiveness of HPSD-RFA for atrial fibrillation, but there are still controversies, and all of the above studies have small sample sizes, short follow-up time, use of catheters and different parameters, etc. Disadvantages, there is an urgent need for large-sample multicenter randomized controlled trials to further verify its clinical application value.
HPSD-RFA significantly shortens the ablation time and increases the continuity of the ablation focus, while having good safety and effectiveness. However, the clinical application of this technology requires further support from large-sample multi-center randomized controlled clinical studies. At present, the optimal power and time combination of HPSD-RFA needs to be further explored to minimize the risk of tissue overheating while obtaining effective ablation lesions.
In addition, the characteristics of HPSD-RFA damage width and shallowness determine that it is suitable for atrial thin-wall ablation treatment. Whether it can be used for ventricular ablation remains to be proved by further studies. As an emerging technology, HPSD-RFA is expected to bring greater benefits to the majority of patients with atrial fibrillation in the near future.
(source:internet, reference only)