心脏冷冻和射频消融的组织病理学研究

射频消融和冷凝消融在心律失常方面的应用已经有了突破性的进展，尤其是对某些快速性心律失常已成为根治性治疗手段。现综述旨在阐明射频和冷凝消融在组织病理学方面的研究进展，从而克服常规消融的一些缺陷。     

Production of Chronic First Degree Atrioventricular Block in Dogs, Using Closed-Chest Electrode Catheter with Radiofrequency Energy

Atrioventricuiar (AV) ablation to yield chronic first degree block was attempted in six mongrel dogs. Radio frequency energy (RFE) at 750 KHz, ranging from 3.4 to 4.5 W, was delivered from the distal pole of a USCI 6F quadripolar electrode catheter to a site near the AV node. RFE delivery times ranged from 5 to 60 sec and were repeated in each animal tintil the PR interval was prolonged by 25% or more, if possible. Immediately after ablation, during autouomic blockade, 5 of the 6 dogs had PR-interval prolongation of 25% or more, averaging 36%. The mean PR prolongation in 4 of these dogs was +41% at 1 week, +50% at 1 month ami +50% at 4 months after ablation in the absence of autonomic blocking agents and +54%, +42%, and +44%, respectively, for the same periods after autonomic blockade. The fifth dog had less than 20% increase in PR during subsequent measurements and the sixth dog experienced permanent third degree block after multiple KFE shocks. In the 4 dogs with chronic PR prolongation, the maximum damage was found in the approaches to and in the AV node, less in the His bundle, and least in the bundle branches. It is concluded that chronic modification of AV conduction can be produced in a majority of dogs with RFE with lesions located in the approaches to the AV node and at the AV node, with minimal or moderate involvement of surrounding tissues.     

Parahisian Radiofrequency Catheter Ablation in Dogs: Comparison of the above-valve and below-valve approaches

In patients with an accessory pathway close to the His bundle, radiofrequency catheter ablation (RFCA) requires additional care to avoid damage to the normal conduction system. To assess differences between approaches from above or below the tricuspid valve (TV), we performed RFCA in 20 dogs (from above, group A, n=10; from below, group B, n=10). RF energy with temperature control at 60° 60 seconds was administered at the site where a small His potential was recorded from the ablation catheter guided by fluoroscopy and transesophageal echocardiography (TEE) (in the latter six dogs). Before and after RFCA, electrophysiological testing was performed and histological findings were compared. An ablated lesion was created in 7 of 10 (2 of 2 guided by TEE) dogs in group A and 5 of 10 (3 of 4 TEE) dogs in group B. In group A, an ablated lesion involved the atrium and ventricle in the anterior site of His bundle, but the lesion was only in the ventricle in group B. An atrioventricular block (AVB) and severe damage to the penetrating bundle was observed in one dog of group A. A large hematoma on the TV was made in 2 dogs and the complete right bundle branch block (CRBBB) occurred in 3 dogs of group B. The approach from below the TV was safer than that from above the TV in parahisian RFCA, because it did not create an AVB, although it has a high incidence of CRBBB and associated technical difficulties.     

Radiofrequency Modification of the Atrioventricular Node in Patients with Chronic Atrial Fibrillation:

RF Modification of AVN in AF. Introduction : We compared, in a prospective and randomized fashion with a cross-over design, the anterior and posterior approaches to radiofrequency (RF) modification of the AV node in patients with chronic atrial fibrillation.
Methods and Results : Thirty-three patients were randomized to receive first an anterior (group I) or posterior (group II) approach for RF modification of AV nodal conduction. Patients who did not fill the endpoint ventricular rate (< 90 beats/min) were crossed over to the alternative approach. After the anterior approach in group I patients, mean ventricular rate was significantly lower than in group II patients after the posterior approach (79.6 ± 18.8 beats/min vs 110.8 ± 16.2 beats/min, P < 0.001). In group I, 14 (82%) of 17 patients fulfilled the endpoint, 1 (6%) had complete AV block, and 2 (12%) were crossed over to the posterior approach fulfilling the endpoint. In group II, 4 (25%) of 16 patients fulfilled the endpoint. No transient or permanent high-degree AV block was observed. Among the 12 patients who were crossed over to the anterior approach, 8 fulfilled the endpoint, whereas 4 had permanent high-degree AV block. RF ablation carried out only in the anterior region was safer than a stepwise approach (6% vs 33% incidence of AV block), even though the difference did not reach statistical significance (P = 0.09).
Conclusion : Posterior AV nodal modification is less effective but safer than anterior AV nodal modification. However, to reduce the incidence of AV block, the anterior approach is preferable to a stepwise approach from the posterior to the anterior zone.     

Steroids Prevent Late Extension of Radiofrequency Lesions in the Thigh Muscle of Infant Rats: Implications for Pediatric Ablation

Introduction: Marked late enlargement of radiofrequency (RF) lesions may occur in immature myocardium, suggesting that late proarrhythmic effects may occur in infants and small children undergoing RF ablation. Because late lesion extension may be involved in this phenomenon, we evaluated the impact of corticosteroids on the healing of RF lesions created in the thigh muscle of 29 infant Wistar rats (30 days; 55 g). Methods: Lesion dimensions and histological characteristics were assessed acutely (n = 11), and at 30 days in controls (n = 11, 183 g) and rats (n = 7, 173 g) receiving hydrocortisone after ablation and betametasone for 29 days. Acute (n = 16) and chronic (30 days; n = 5) lesions were also evaluated in adult Wistar rats (300 g). Results: Acutely, lesions in adults and infants were well demarcated from the surrounding tissue. In adults, chronic lesions did not increase in size and were well demarcated histologically. Controls and treated infant rats did not differ with respect to the gross appearance of chronic lesions. Late lesions doubled in size (20 mm in diameter) and were poorly demarcated from the surrounding tissue, exhibiting multiple collagen strands extending from the lesion into normal muscular tissue. In the treatment group, healing was markedly delayed and the extent of collagen proliferation was significantly less than controls. Conclusion: RF lesions created in the thigh muscle of infant rats reveal late enlargement and invasion of normal muscle by intense collagen proliferation. Steroids seem to limit late extension of RF lesions. These findings may have implications for RF ablation procedures in pediatric populations.     

心外膜射频消融治疗心房颤动的实验研究

为探索心房颤动（ＡＦ）心外膜消融简便方法，选用健康犬及二尖瓣关闭不全模型犬各５只，应用自制线形射频电极沿左、右心耳根部，左房顶部，右心耳根部至下腔静脉根部连线及横跨界沟的线路行心外膜线形消融，同时经冠状静脉窦导管电极消融冠状静脉窦远端。开胸前、关胸后及术后２～５周分别测定ＡＦ诱发率（快速心房起搏、持续静脉滴注乙酰胆碱的条件下）、校正窦房结恢复时间（ＣＳＮＲＴ）、窦率－异丙肾上腺素反应性及高位右房有效不应期（ＨＲＡ－ＥＲＰ）。结果：与术前相比，关胸后及术后２～５周均不能诱发ＡＦ，ＣＳＮＲＴ、ＨＲＡ－ＥＲＰ无变化（Ｐ均＞０．０５），窦率－异丙肾上腺素反应性不降低（Ｐ均＞０．０５）。术后２～５周超声心动图显示心房运动正常、无血栓形成。病理检查证实射频消融区透壁性损伤，而窦房结无损伤。结果表明在心外膜按一定路线射频消融治疗ＡＦ是可行的。     

Comparison of Standard and Irrigated Radiofrequency Ablation in the Canine Ventricle

Standard and Irrigated RF Ablation Lesions. Introduction : radiofrequency ablation is successful for treating some arrhythmias but not for CAD-VT, possibly due to insufficient lesion size. Irrigated electrodes were developed to apply higher power for longer duration to create larger lesions. Our objective was to characterize and compare irrigated and standard ablation in terms of lesion size, crater, and coagulum formation. Additionally, a method is proposed for creating large irrigated lesions without craters.
Methods and Results : Three ablation protocols were conducted in canine ventricles. Protocol I: standard ablation was performed in power mode at 10, 20, 30, and 50 W, and electrode-temperature mode at 70° and 90°C (120 sec). Protocol II: irrigated ablation was conducted with 30 and 50 W (30 and 120 sec). Protocol III: to create large lesions without craters, irrigated ablation was performed at 20 W (5 and 10 min). With a standard electrode, the largest lesions were created using 20 W (358 ± 194 mm³) and using 90°C (301 ± 130 mm²). Ablation duration decreased with power for the power mode standard ablations. The largest irrigated lesions were formed using 50 W (986 ± 357 mm²). Large lesions without craters were created with irrigation using 20 W for 10 minutes (602 ± 175 mm²). Coagulum was seen for most standard ablations but infrequently for irrigated ablations. Craters were observed with 30 and 50 W irrigated ablation but were not observed with 20 W irrigated ablation.
Conclusion : Irrigated ablation created larger lesions than standard; large lesions may be created without craters using moderate power and long duration.     

Temperature Monitoring in Radiofrequency Catheter Ablation of Atrial Flutter Using the Linear Ablation Technique

Temperature Monitoring of Ablation. Introduction: Information about temperature and impedance monitoring during radiofrequency catheter linear ablation of atrial flutter bas not been reported. We proposed that a radiofrequency catheter ablation system using a closed-loop temperature control model could decrease the incidence of coagulum formation and shorten the radiation exposure and procedure times compared with those found in a power control model.
Methods and Results: Forty patients (8 women and 32 men; mean age 64 ± 7 years) with atrial flutter were referred for radiofrequency ablation. The patients were randomized into two groups: group I patients underwent radiofrequency catheter linear ablation of atrial flutter using a power control of energy output model; and group II patients underwent the closed-loop temperature control model with a target electrode temperature of 70°C. As compared with group II, group I patients bad a higher incidence of coagulum formation (12% vs 2%, P < 0.05), temperature shutdown (11% vs 0%, P < 0.01), and impedance shutdown (16% vs 3%, P < 0.01), more radiofrequency applications (7 ± 3 vs 4 ± 2, P < 0.01), and longer procedure time (100 ± 25 vs 75 ± 23 minutes, P < 0.05) and radiation exposure time (31 ± 10 vs 20 ± 7 minutes, P < 0.05) required for successful ablation. Larger deviations of temperature (9.0°± 2.4°C vs 5.0°± 1.2°C, P < 0.0001) and impedance (9.2 ± 2.6 ω vs 5.3 ± 1.6 ω, P < 0.0001) were also found in group I patients compared with those in group II.
Conclusions : This study demonstrated that a closed-loop temperature control model could facilitate the effects of radiofrequency catheter ablation of the atrial flutter circuit by decreasing coagulum formation, temperature and impedance shutdown, and procedure and radiation exposure times.     

Radiofrequency Catheter Ablation of the Anterosuperior and Posteroinferior Atrial Approaches to the AV Node for Treatment of AV Nodal Reentrant Tachycardia

Catheter Ablation Techniques in AVNRT. Radiofrequency catheter ablation has been established as a first-line curative treatment modality in patients with symptomatic AV nodal reentrant tachycardia (AVNRT). The successful sites of stepwise catheter ablation approaches of the so-called fast and slow pathways strongly suggest that AVNRT involves the atrial approaches to the AV node. The typical fast pathway ablation sites are located anterosuperior toward the apex of the triangle of Koch, which also contains the compact AV node, whereas the usual slow pathway ablation sites are located posteroinferior toward the base of the triangle of Koch at a greater distance to the compact AV node and bundle of His. Accordingly, ablation studies with large patient cohorts have demonstrated that fast pathway ablation carries a higher risk of inadvertent complete AV block. Thus, the slow pathway is clearly the primary target site, and fast pathway ablation is rarely necessary. Different approaches for slow pathway ablation have been elaborated: anatomically oriented stepwise techniques, ablation guided by double potentials recorded within the area of the slow pathway insertion, and combined techniques. The modern concept of AVNRT suggests that this arrhythmia involves the highly complex three-dimensional nonuniform anisotropic AV junctional area. Accordingly, mapping and ablation studies demonstrated that the anterior approach is not identical with fast pathway ablation, and the posterior approach is not identical with slow pathway ablation. Therefore, it is essential for interventional electrophysiologists to familiarize themsdves with the anatomic and electrophysiologic details of this complex and variable specialized AV junctional region. In this review, the anatomic and pathophysiologic aspects of the AV junctional area as they relate to interventional therapy are summarized briefly, and the catheter techniques for ablation of the so-called fast and slow AV nodal pathways for the treatment of AVNRT are described.     

Catheter Ablation of Ventricular Endocardium Using Radiofrequency Energy: Determinants of Lesion Volume and Shape

Radiofrequency energy was delivered at varying powers and durations to excised portions of canine left ventricle that were mounted in a tank of saline at room temperature. A radiofrequenciy generator delivered alternating current in a sine wave pattern at a frequency of 500 kHz, at variable voltage. In each of five excised ventricles, 49 lesions were created, at delivered RMS voltages from 18 to 40 V and durations of ablation from 5 to 180 seconds. Lesion diameter and depth were measured grossly, and lesion volume and shape (ratio of radius/depth) were calculated. Lesion diameter, depth, and volume increased with increasing power and duration of energy delivery, and the relation of delivered energy (joules) to calculated lesion volume (mm³) was linear (r = 0.88, P < 0.001). Shallower lesions were produced by shorter duration of energy delivery at all power levels, and similar volume but deeper, more symmetric lesions by lower power and longer duration of energy delivery. Radiofrequency energy in vitro thus produces reproducible lesions whose volume is proportional to delivered energy, and whose shape can be altered by delivering similar total energies, but varying the power and duration of energy delivery     

Comparison of Radiofrequency and Cryoballoon Pulmonary Vein Ablation for the Early and Late Recurrence of Atrial Fibrillation

Objective Early recurrence (ER) after pulmonary vein isolation (PVI) for atrial fibrillation (AF) is expected to resolve within the recommended 3-month blanking period, irrespective of the ablation device used. To compare the occurrence and relationship of AF within the blanking period and subsequent late recurrence (LR) with radiofrequency (RF) and cryoballoon (CB) ablation. Methods A retrospective analysis of 294 patients (mean age=62±9, 70.0% male) undergoing PVI for drug-refractory paroxysmal AF was done. After categorizing the patients into the RF group (n=152) and the CB group (n=142), a group-wise comparison was done to investigate the impact of ER on LR throughout a 2-year follow-up. Results The groups were similar regarding the occurrence of ER (RF=22.4%, CB=24.6%, p=0.62), while LR was significantly higher in the RF group (p=0.003). ER was associated with LR in the RF group (p<0.01) but not in the CB group (p=0.08), while a significant independent association with an increased LR risk was observed [hazard ratio (HR) 6.12; 95% confidence interval (CI) 3.56-10.51, p<0.01]. RF ablation also significantly increased the risk of LR (HR=2.93; 95% CI=1.64-5.23, p<0.01). Conclusion A recurrence of atrial arrhythmia is more frequent with RF-PVI than with CB-PVI for patients with paroxysmal AF. ER and RF-ablation are strong predictors for LR after the 3-month blanking period.     

Comparison of Ventricular Radiofrequency Lesions in Sheep Using Standard Irrigated Tip Catheter versus Catheter Ablation Enabling Direct Visualization

Comparison of Ventricular Radiofrequency Lesions in Sheep. Introduction: In vivo assessment of RF ablation lesions is limited. Improved feedback could affect procedural outcome. A novel catheter, IRIS? Cardiac Ablation Catheter (IRIS), enabling direct tissue visualization during ablation, was compared to a 3.5 mm open‐irrigated tip ThermoCool? Catheter (THERM) for endocardial ventricular RF ablation in sheep. Methods: Sixteen anesthetized sheep (6 ± 1 years old, 60 ± 10 kg) underwent ventricular RF applications with either the THERM (Biosense Webster) or IRIS (Voyage Medical) ablation catheter. In the THERM group, RF was delivered (30 W, 60 seconds) when electrode contact was achieved as assessed by recording high‐amplitude electrogram, tactile feedback, and x‐ray. In the IRIS group, direct visualization was used to confirm tissue contact and to guide energy delivery (10–25 W for 60 seconds) depending on visual feedback during lesion formation. Results: A total of 160 RF applications were delivered (80 with THERM; 80 with IRIS). Average power delivery was significantly higher in the THERM group than in the IRIS group (30 ± 2 W [25–30 W] for 57 ± 14 seconds vs 21 ± 4 W [10–25 W] for 57 ± 27 seconds; P<0.001). At necropsy, 62/80 (78%) lesions created with THERM were identified versus 79/80 (99%) with IRIS (P<0.001). The lesion dimensions were not significantly different between THERM and IRIS. Conclusion: Despite best efforts using standard clinical assessments of catheter contact, 22% of RF applications in the ventricles using a standard open‐irrigated catheter could not be identified on necropsy. In vivo assessment of catheter contact by direct visualization of the tissue undergoing RF ablation with the IRIS? catheter was more reliable by allowing creation of 99% prescribed target lesions without significant complications. (J Cardiovasc Electrophysiol, Vol. 23, pp. 869‐873, August 2012)     

Pneumopericardium Following Radiofrequency Ablation for Atrial Fibrillation: Insights into the Natural History of Atrial Esophageal Fistula Formation

Pneumopericardium Following Atrial Fibrillation Ablation. We present a case of large pneumopericardium resulting from an esophageal pericardial fistula following ablation for atrial fibrillation (AF). The presentation, evaluation, and management of this specific patient, along with a review of present techniques to diagnose esophageal injury, provide a unique insight into the pathophysiology of left atrial‐esophageal fistula formation. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1046‐1049, September 2010)     

Location of the lower turnaround point in typical AV nodal reentrant tachycardia: a quantitative model

INTRODUCTION: Recent observations suggest that the circuit of AV nodal reentrant tachycardia (AVNRT) may extend down to the His bundle. The purpose of this study was to develop a quantitative model indicating the location of the lower turnaround point in AVNRT. METHODS AND RESULTS: Slow pathway modification was performed in 70 patients with typical AVNRT. During sinus rhythm, ventricular pacing was performed with the AVNRT cycle length. During AVNRT, the HinitAinit interval was measured from initial His to the initial atrial deflection recorded in the His-bundle lead. During ventricular pacing, the HendAinit interval was measured from end of the His to the beginning of the atrial deflection. It was hypothesized that x reflects conduction time from the lower turnaround point to Ainit, whereas y reflects conduction time from the lower turnaround point to Hinit. Anterograde conduction during AVNRT and retrograde conduction during ventricular pacing were assumed to be identical if there was 1:1 retrograde conduction at the AVNRT cycle length. The following formulas describe the relation of the measured parameters: x - y = HinitAinit; and x + y = HendAinit. Resolving both formulas yields the unknown x and y: y = (HendAinit - HinitAinit)/2, x = (HendAinit + HinitAinit)/2. These criteria were present in 52 of 70 patients. The mean cycle length of AVNRT was 355 +/- 42 msec, mean HinitAinit was 54 +/- 27 msec, and mean HendAinit was 60 +/- 29 msec. Accordingly, in 20 of 52 patients, the lower turnaround point was located within the His bundle (y = -15.4 +/- 16.1 msec), in 3 of 52 it was in the nodal-His junctional area (y = 0), and in 29 of 52 it was above the His bundle (y = +12.7 +/- 10.3 msec). The HinitAinit interval was significantly longer (66 +/- 32 msec vs 47 +/- 20 msec; P = 0.02) and the HendAinit interval was significantly shorter (45 +/- 30 msec vs 69 +/- 24 msec; P = 0.004) when the first group was compared with the others. CONCLUSION: In about 1 of 3 of patients with typical AVNRT, the lower turnaround point of the circuit is within the His bundle; in more than half of the patients it is above the His bundle. These data do not support the concept that all AVNRTs have an intranodal circuit, but are in accordance with the finding of longitudinal dissociation of the His bundle.     

Radiofrequency Catheter Ablation Versus Modification of the AV Node for Control of Rapid Ventricular Response in Atrial Fibrillation

AV Node Modification vs Ablation in AF. Atrial fibrillation is a common arrhythmia, which is frequently difficult to control. Symptoms and ventricular dysfunction may be caused by a rapid ventricular response to atrial fibrillation. Radiofrequency catheter ablation techniques for ventricular rate control have been developed, including AV node modification and AV node ablation with pacemaker implantation. For both AV node modification and ablation, radiofrequency energy is applied via a 4-mm tipped electrode catheter. For AV node ablation radiofreqnency energy is applied near the compact AV node or His bundle via the right atrium, or occasionally at the His bundle via the left ventricle. For AV node modification radiofrequency energy is applied in the low middle or posterior septal right atrium near the tricuspid valve annulus. Both techniques can effectively control ventricular response to atrial fibrillation and the associated symptoms, although AV node modification is effective in only about 70% of patients compared to AV node ablation, which is effective in nearly 100%. In patients responding to AV node modification, maximal and mean ventricular response to atrial fibrillation is reduced by 25% to 35% chronically. Inadvertent AV block may occur during attempted AV node modification. It seems appropriate to attempt AV node modification prior to AV node ablation in patients with refractory atrial fibrillation and rapid ventricular response, in order to avoid the need for permanent pacemaker implantation. Although unproven, studies suggest that the mechanism by which AV node modification achieves ventricular rate control may he slow-pathway ablation in the low posterior septal right atrium.     

Hybrid Therapy of Radiofrequency Catheter Ablation and Percutaneous Transvenous Mitral Commissurotomy in Patients With Atrial Fibrillation and Mitral Stenosis

AF Ablation and PTMC. Background: The rhythm control of atrial fibrillation (AF) associated with mitral stenosis (MS) is often difficult using antiarrhythmic drugs (AADs), even after a percutaneous transvenous mitral commissurotomy (PTMC). Few studies have examined the efficacy and safety of simultaneously performing radiofrequency catheter ablation (RFCA) and a PTMC in patients with MS and AF. Methods: Twenty consecutive patients with drug‐resistant AF and rheumatic MS underwent RFCA combined with a PTMC (n = 10; persistent AF‐8, long‐lasting [>1 year] persistent AF‐2; RFCA group) or transthoracic direct cardioversion (DC) following a PTMC (n = 10; persistent AF‐7, long‐lasting persistent AF‐3; DC group). In all patients, the mitral valve morphology was amenable to a PTMC, and more than 2 AADs had been ineffective in maintaining sinus rhythm (SR). In the RFCA group, a segmental pulmonary vein isolation (PVI) was performed in the initial 5 patients, and an extensive PVI was performed in the remaining 5. Results: During a mean follow‐up period of 4.0 ± 2.7 years, 8 patients (80%) in the RFCA group were maintained in SR, as compared to 1 (10%) in the DC group (hazard ratio, 0.16; 95% confidence interval, 0.03 to 0.75; P = 0.008 by the log‐rank test). The prevalence of the concomitant use of class I and/or class III AADs was comparable between the 2 groups (P = 0.70). No complications occurred during the procedure or follow‐up period in either group. Conclusions: The hybrid therapy using RFCA and a PTMC was safe and feasible, and significantly improved the AF free survival rate compared to DC following a PTMC. (J Cardiovasc Electrophysiol, Vol. 21, pp. 284–289, March 2010)     

超声引导下实施射频消融房室结安置VVI起搏器初步探讨

探索经胸心脏超声引导心内射频消融房室结的可行性和安全性。对11例持续/永久性心房颤动/心房扑动拟行房室结消融加VVI起搏,在经胸心脏彩超引导下,采取多切面观察、导管运动中观察,密切结合心内电生理定位,尝试左锁骨下静脉永久起搏导管和右股静脉消融导管的心内定位和靶点消融。以出现稳定的房室分离判为消融成功。结果:11例房室结消融及VVI起搏均顺利完成,手术时间70～180min,放电期间超声切面可见能量释放征,消融后靶点区心内膜回声明显增强。手术成功率100%,随访期内患者恢复良好。结论:经胸切面超声引导射频消融房室结安置VVI起搏安全、简便、可行、经济。