Microwave Ablation Of Atrial Fibrillation Research Articles

Application of hyperbolic heat transfer model in atrial fibrillation microwave ablation

The effect of relaxation time in hyperbolic heat transfer model on the temperature field of microwave ablation of atrial fibrillation was investigated. And the results were compared with those calculated by Pennes model. A three-dimensional model of microwave ablation of atrial fibrillation was constructed. The relaxation time ( τ) was 0, 1, 5, 8, 10, 15 and 20 s, respectively. And the temperature field of myocardial tissue was obtained. The results showed that the highest temperature of the hyperbolic model was 21.8 ℃ lower than that of the Pennes model at the beginning of ablation. With the increase of ablation time, the highest temperature tended to be the same. The lesion dimensions appeared at 3, 4, 6, 7, 8, 9, and 10 s, respectively after ablation. Therefore, the influence of hyperbolic model on temperature will decrease with the increase of the ablation time. At the beginning of ablation, the relaxation time will hinder the speed of myocardial thermal diffusion. The larger the relaxation time is, the slower the speed of thermal diffusion is. This study provides a reference for the application of hyperbolic model in microwave ablation of atrial fibrillation.

Study on the effect of different blood flow velocities of pulmonary vein on endocardial microwave ablation of atrial fibrillation.

To cure atrial fibrillation, the maximum ablation depth (⩾ 50∘C) should exceed the myocardial thickness to achieve the effect of transmural ablation. The blood flow of pulmonary vein in the endocardium can cause the change in the myocardial temperature distribution. Therefore, the study investigated the effect of different pulmonary vein blood flow velocities on the endocardial microwave ablation. The finite element model of the endocardial microwave ablation of pulmonary vein was simulated by electromagnetic thermal flow coupling. The ablation power was 30 W and the ablation time was within 30 s. The blood flow in the coupling of fluid mechanics equation and heat transfer equation results in the heat damage. Furthermore, the cause of the different lesion dimensions is the blood flow velocity. The flow velocities were set as 0, 0.02, 0.05, 0.07, 0.12, 0.16, 0.20, 0.25 and 0.30 m/s. When the flow velocities were 0, 0.02, 0.05, 0.07, 0.12, 0.16, 0.20, 0.25 and 0.30 m/s, the maximum ablation depth were 6.00, 5.56, 5.16, 5.12, 5.04, 5.01, 4.98, 4.96 and 4.94 mm, respectively; the maximum ablation width were 12.53, 9.63, 9.23, 9.16, 9.07, 9.05, 8.94, 8.91 and 8.90 mm, respectively; the maximum ablation length were 12.00, 11.61, 8.98, 8.59, 8.37, 8.23, 8.16, 8.06 and 8.04 mm respectively. To achieve transmural ablation, the time was 3, 3, 3, 3, 3, 4, 4, 4, 4 s, respectively when the myocardial thickness was 2 mm; the time was 7, 8, 8, 8, 9, 9, 9, 9, 9 s, respectively when 3 mm; the time was 15, 16, 18, 19, 19, 20, 20, 20, 20 s, respectively when 4 mm. When the velocity increases from 0 m/s to 0.3 m/s, the microwave lesion depth decreases by 1.06 mm. To achieve transmural ablation, when the myocardial thickness is 2 mm, 3 and 4 s should be taken when the velocity is 0-0.12 and 0.12-0.30 m/s, respectively; when the myocardial thickness is 3 mm, 7, 8 and 9 s should be taken when 0, 0-0.07 and 0.07-0.30m/s respectively; when the myocardial thickness is 4 mm, 15, 16, 18, 19, 20 s should be taken when 0, 0-0.02, 0.02-0.05, 0.05-0.12, 0.12 m/s-0.30 m/s.

How effective is microwave ablation for atrial fibrillation during concomitant cardiac surgery?

A best evidence topic in cardiothoracic surgery was written according to a structured protocol. The question addressed was whether performing microwave ablative procedures during concomitant cardiac surgical procedures is effective for the treatment of atrial fibrillation (AF). In total, 200 papers were found using the reported search, of which 12 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Major exclusion criteria included studies exclusively using bipolar ablation, ambiguous or unspecified ablation technique, other energy modalities and studies with highly variable or undisclosed follow-up time. One study reported that 66% of patients were in sinus rhythm (SR) with follow-ups ranging from 1 to 14 months and suggested that the risk of AF recurrence was significantly increased with a larger left atrial diameter (OR = 1.21, P = 0.02) and an increased duration of preoperative AF (OR = 2.14, P = 0.03). A separate study found no significant difference in the success rate on the basis of the concomitant procedure (coronary artery bypass grafting or mitral valve surgery, P > 0.5). In the only randomized trial identified, microwave ablation delivered significantly inferior SR restoration rates to radiofrequency (RF) ablation at all time points from discharge to 24 months. There is a large degree of heterogeneity in the studies, with patients' characteristics, for example type of AF, and patient management postoperatively, for example administration of anti-arrhythmias, being inconsistent. Of the 12 studies, nine assessed SR at a mean of 6-12 months and found postoperative success rates between 62 and 87%. One study looked at the medium range follow-up of 24 months with SR restoration at 71%. Two studies looked at the long-term follow-up (5 and 5.37 years) with SR restoration at 39 and 61%, respectively. We conclude that microwave ablation, as an intervention for the treatment of AF during concomitant surgery, is not currently recommended on the limited available evidence. This is because the success rates in the longer term are less clear and the only randomized study to date has found inferior outcomes compared with RF-based ablation.

Is there an evidence of pulmonary vein stenosis following epicardial microwave ablation of atrial fibrillation?

Surgical ablation techniques using microwave energy are an alternative to catheter based ablation therapy in the treatment of atrial fibrillation (AF). However, little is known about potential procedure-related complications. We investigate, whether there is evidence of pulmonary vein stenosis (PVST) in patients with atrial fibrillation undergoing epicardial microwave ablation. 14 patients (ten males and four females) with AF and structural heart disease underwent cardiac surgery for the underlying disease and concomitant ablation of AF using microwave energy. In these patients with a mean age of 71 +/- 8 years microwave energy was applied epicardially on the beating heart. Ablation was implemented using a flexible microwave tool with a 40 mm long tip to create isolation of the pulmonary veins. Each application was performed with 65 watt for 90 s. Follow-up was performed twice at a mean of 207 +/- 73 days and 395 +/- 102 days. Patients were evaluated by 12-lead-ECG and echocardiography. Multidetector helical computer tomographic (MDCT) imaging was done in seven patients to show morphology of the pulmonary veins. On second follow-up 11 patients were seen. ECG showed sinus rhythm in six patients (55 %) and atrial fibrillation in five patients (45%). MDCT showed a moderate pulmonary vein stenosis (50-70%) in one patient. The patient did not suffer from palpitations, dyspnea, angina or syncope. Epicardial microwave ablation is an accepted treatment of atrial fibrillation. The procedure can be done off-pump on the beating heart. Nevertheless, pulmonary vein stenosis is a possible complication of this procedure, which should be kept in mind and evaluated during the follow-up.

Concomitant Intraoperative Radiofrequency and Microwave Ablation of Atrial Fibrillation and Repair of Atrial Septal Defect

A B S T R A C T Atrial fibrillation (AF) is the most frequent form of atrial arrhythmias in adults with congenital heart disease. Some serious complications are related with the presence of AF after surgery. Because of the complexity and the risk of bleeding, the Maze III procedure has been largely replaced by alternative energy sources. A patient with multiple atrial septal defects (ASD) and AF underwent surgical closure with autologous pericardial patch and radiofrequency and microwave ablation of AF.

Thoracoscopic microwave ablation of atrial fibrillation

The aim of the study was to assess the safety and efficacy of thoracoscopic microwave ablation in treating atrial fibrillation (AF). AF predisposes to embolic complications and may cause heart failure. The treatment of AF is still challenging in spite of the promising results of endocardial radiofrequency approach. The present study is a follow-up study of 22 patients (mean age 45 years, range 21-59) with disabling paroxysmal (n=10) or persistent (n=12) AF who underwent a thoracoscopic microwave isolation of pulmonary veins. The patients had a lone AF. All the patients had suffered from severely disabling AF for >1 year (range 1-16 years) without any response to antiarrhythmic medication. The patients have been followed-up on an average of 11 months (range 3-22 months). During the follow-up, 13 (60%) patients have become asymptomatic without any documentation of AF since at least two months, six (27%) patients with anti-arrhythmic medication have clinically improved. Because of major intrathoracic bleeding and because of liver damage the thoracoscopy wound had to be expanded to open thoracotomy in two patients. Thoracoscopic AF microwave ablation seems to be a promising alternative to endocardial ablation in the treatment of highly symptomatic paroxysmal and persistent AF.

Microwave Ablation for Atrial Fibrillation: Dose-Response Curves in the Cardioplegia-Arrested and Beating Heart

Microwave ablation has been used to replace the traditional incisions used in the surgical treatment of atrial fibrillation. However, dose-response curves have not been established in surgically relevant models. The purpose of this study was to develop dose-response curves for the Flex 10 (Guidant, Inc) microwave device in both the acute cardioplegia-arrested heart and on the beating heart. Twelve domestic pigs (40 to 45 kg) were subjected to microwave ablation in either the arrested (n = 6) or beating heart (n = 6). The cardioplegia-arrested heart was maintained at 10 degrees to 15 degrees C while six atrial endocardial and seven right ventricular epicardial lesions were created in each animal. On the beating heart, six right atrial and seven ventricular epicardial lesions were created. Ablations were performed for 15, 30, 45, 60, 90, 120, and 150 seconds (65 W, 2.45 GHz). The tissue was stained with 2,3,5-triphenyl-tetrazolium chloride, and sectioned at 5-mm intervals. Lesion depth and width were determined from digital micrographs. Mean atrial wall thickness was 2.8 mm (range, 1 to 8 mm). In the arrested heart, 94% of atrial lesions were transmural at 45 seconds and 100% were transmural at 90 seconds. In the beating heart, only 20% of atrial lesions were transmural despite prolonged ablation times (90 seconds). Ventricular lesion width and depth increased with duration of application, and were similar on the arrested and beating hearts. Microwave ablation produces linear dose-response curves. Transmural lesions can be reliably produced on the arrested heart, but not consistently on the beating heart.

Combining Robotic Mitral Valve Repair and Microwave Atrial Fibrillation Ablation: Techniques and Initial Results

Left atrial microwave ablation for atrial fibrillation has become popular for isolating autonomous atrial foci. Previously, mitral valve repairs (MVP) with atrial fibrillation ablation have been performed through sternotomy. We present a technique that combines robotic MVP with left atrial fibrillation ablation. Through a 4-cm right minithoracotomy and using cardiopulmonary bypass, the transverse and oblique sinuses are accessed. A Flex-10 microwave catheter is passed around the pulmonary veins, and after weaning from cardiopulmonary bypass, peripulmonary vein microwave ablations are performed. After cardioplegic arrest, the da Vinci system is used to manipulate the catheter to create endocardial lesions around the left atrial appendage. Another endocardial lesion is made connecting the pulmonary venous line with the mitral annulus near P3. The left atrial appendage is closed, and the MVP performed robotically. Data are expressed as mean +/- standard deviation. Sixteen patients underwent this combined procedure, with 80% returning to a normal sinus rhythm at 6 weeks and 73% remaining in normal sinus rhythm at 6 months. Only 1 patient was in atrial fibrillation at 6 months. The ablation procedure added 42 +/- 16.1 minutes to a robotic MVP. The average length of hospital stay was 6.3 +/- 2.2 days, 1.3 days longer than the mean of the prior 50 consecutive robotic MVP patients without a concomitant ablation. Robotic microwave ablation during robotic MVP is a safe, effective way to resolve atrial fibrillation. These methods offer a promising prelude to the combined totally endoscopic treatment of atrial arrhythmias and mitral insufficiency.

The Completely Endoscopic Treatment of Atrial Fibrillation: Report on the First 14 Patients with Early Results

We report the early results of a new completely endoscopic technique for the treatment of atrial fibrillation (AF). Fourteen patients underwent surgery solely for the treatment of AF. The thoracoscopic technique delivered microwave energy to the epicardial surface of the beating heart. Access was obtained through 3 right-sided and 3 left-sided thoracic ports. The AFx/Guidant Flex-10 catheter was employed to produce a box lesion around the pulmonary veins along with additional right- and left-sided lesions. The left atrial appendage was amputated. Ten patients had paroxysmal fibrillation, 1 had persistent fibrillation, and 3 were in permanent AF. Mean age of the group was 60 years, and their mean duration of AF was 74 months. Half had undergone unsuccessful attempts at chemical and/or electrical cardioversion. There were no deaths. Two patients required conversion to open procedure to control bleeding from the left atrial appendage. Average procedure time was 221 minutes, with the last 2 procedures taking less than 2 hours. Median length of hospital stay was 6 days, with 7 patients staying less than 3 days. Seventy-one percent of patients were in sinus rhythm at discharge, 100% at 6 months follow-up, and 67% at 12 months. Totally endoscopic microwave ablation of atrial fibrillation appears to be safe and truly minimally invasive. It is associated with a short length of stay, short procedure time, and acceptable rhythm results. This procedure has the potential to greatly expand the indications for surgery in patients suffering from AF and deserves longer-term investigation.

Microwave ablation of atrial fibrillation in conjunction with treatment of early postoperative massive left atrial thrombosis

Left atrial thrombosis is a rare complication of both atrial fibrillation and mitral valve surgery. A patient with a massive atrial thrombosis associated with symptoms of severe heart failure is presented. Restoration of rhythmical ventricular contraction and, ultimately, atrial contractility is of great benefit for providing relief from symptoms and for preventing thrombus recurrence. We present an approach to surgically treat atrial fibrillation using a new microwave energy source in a patient with left atrial thrombosis who requires a mitral valve prosthesis replacement.

Microwave ablation of atrial fibrillation during mitral valve operations

Although the Cox-Maze III procedure cures atrial fibrillation in the majority of patients, it has not had widespread application. Development of new operations that use alternate energy sources and different lesion sets have caused resurgence in the surgical treatment of atrial fibrillation. Microwave creates lines of conduction block by thermal damage and subsequent scar formation. We describe a rapid and simple technique for microwave ablation of atrial fibrillation in patients having mitral valve operations.

Beating-heart surgical treatment of atrial fibrillation with microwave ablation

Background In this feasibility study, early results are presented of our first series of patients with microwave ablation for atrial fibrillation (AF) on the beating heart. Methods From June 2001 until December 2001, a total of 24 patients underwent beating-heart epicardial ablation for AF. With a microwave antenna, the left and right pulmonary veins were isolated and connected to each other followed by amputation of the left atrial appendage. Subsequently, patients underwent either off-pump coronary artery bypass graft or valve surgery on pump. The mean age of the patients was 67.4 ± 6 years. Three patients experienced paroxysmal atrial fibrillation and all others chronic AF. Mean left atrial diameter was 5.4 ± 0.6 cm, and mean ablation time was 13 min. Results All procedures but one were completed successfully on the beating heart. All patients were in sinus rhythm after the procedure. A total of 15 patients experienced periods with postoperative AF during hospital stay; 9 of these patients were discharged with AF. All patients received either sotalol or amiodarone. At latest follow-up (3 to 9 months), 20 of 23 patients were in sinus rhythm. Conclusions With microwave ablation, electrical isolation of the pulmonary veins can be achieved epicardially without cardiopulmonary bypass support.