Lesion Size in Relation to Ablation Site During Radiofrequency Ablation

This study was designed to investigate the effect of the convective cooling of the tip of the ablation electrode during temperature controlled radiofrequency ablation. In vivo two different application sites in the left ventricle of anaesthetised pigs were ablated and in vitro ablation was performed during two different flow-velocities in a tissue bath, while electrode contact pressure and position were unchanged. Target temperature was 80 °C. Obtained tip temperature, power consumption and lesion dimensions were measured. In vivo lesion volume, depth and width were found significantly larger for septal applications than apical applications (p<0.01) and more power was used (p<0.001). Obtained tip temperature was significantly lower in the septal applications (p<0.001). In vitro increased convective cooling by induction of flow yielded larger lesion volume, depth and width (p<0.01), and had higher power consumptions (p<0.01). Obtained tip temperature did not differ significantly. For the given chosen target temperature power consumption was positively related to lesion volume (r= 0.66 in vivo and 0.65 in vitro), whereas obtained tip temperature was not (r = - 0.49 in vivo and - 0.61 in vitro). We conclude that during temperature controlled radiofrequency ablation lesion size differs for septal and apical left ventricular applications. Differences in convective cooling might play an important role in this respect. This is supported by our in vitro experiments, where increased convective cooling by induction of a flow around the electrode tip increases lesion dimensions and power consumptions. Furthermore we conclude that for the given target temperature the power consumption is positively correlated with lesion volume (p<0.001), whereas the obtained tip temperature is not.     

Ablation strategies for atrial fibrillation

Atrial fibrillation remains the most common arrhythmia in the USA and is associated with an increased risk for stroke, congestive heart failure and overall mortality. There has been a tremendous advance in the field of catheter ablation of atrial fibrillation that has resulted in better outcomes for patients. The approach for ablation of atrial fibrillation can be different depending on patients’ presentation of paroxysmal or persistent atrial fibrillation. Pulmonary vein isolation remains the cornerstone of any ablation strategy for atrial fibrillation; however, further ablation, end points of the procedure, clinical end points for successful ablation and appropriate follow-up remain controversial. We aim to discuss these different approaches and the major controversies in catheter ablation of atrial fibrillation.     

超声引导下微波消融与无水乙醇硬化联合治疗甲状腺囊实性结节的临床研究

目的探讨超声引导下微波消融与无水乙醇硬化联合治疗甲状腺囊实性结节的有效性和安全性。方法选取51例甲状腺囊实性结节患者。测量术中(囊液抽尽后)及术后1、3、6、12个月结节体积大小,观察术前及术后1、3、6、12个月甲状腺功能指标,观察术中、术后并发症情况。结果本研究51例患者共51个甲状腺囊实性结节均一次性完全消融。治疗后3、6、12个月结节体积逐渐减小,差异有统计学意义(P<0.05);体积缩小率逐渐增加,差异有统计学意义(P<0.05)。术后1、3、6、12个月甲状腺功能均正常。无1例患者复发。无严重并发症发生。结论微波消融与无水乙醇硬化二者联合治疗甲状腺囊实性结节,手术时间较短,并发症较少,是一种安全有效的治疗方法。     

Atrial Flutter Mapping and Ablation II. Radiofrequency Ablation of Atrial Flutter Circuits

The definition of the anatomical substrate of reentry in at rial flutter has allowed the recognition of narrow, critical areas of the circuit, where radiofrequencv ablation can interrupt reentry. In common flutter the isthmus between the inferior vena cava and the tricuspid valve appears the best target, but ablation between the coronary sinus and tricuspid valve can also be effective in some cases. In atypical flutter using the same circuit as common flutter in a “clockwise” direction, ablation of the same isthmus is effective. Flutter interruption is the main objective, but it does not mean complete isthmus ablation. If flutter remains inducible, new applications are delivered in the isthmus, until it is made noninducible. Complications are rare. Despite attaining noninducibility, flutter may recur, and new procedures may he needed to prevent recurrence. Atrial fibrillation can occur in up to 30% of the cases during follow-up, but it is generally well controlled with antiarrhythmic drugs, that were ineffective to treat flutter before ablation. In reentry circuits based on surgical atrial scars, ablation of an isthmus between the scar and the inferior vena cava can also be effective. Left atrial circuits are not known well enough to guide successful ablation.     

乙醇消融与射频消融治疗甲状腺囊实性结节疗效的评价分析

目的 研究乙醇消融和射频消融治疗甲状腺囊实性结节方面的疗效,并比较两种方法的治疗效果。方法 回顾性分析我院2014年2月至2015年6月在我院接受乙醇消融或射频消融的患有单个甲状腺囊实性结节的患者的住院资料,依据患者接受治疗方法的不同,将患者分为乙醇组(n=46)和射频组(n=49)。分析比较两组患者接受治疗后3个月、6个月、9个月及12个月甲状腺结节体积减少的情况;观察两种治疗方法在甲状腺结节不同囊实性比例情况下的治疗效果,同时分析不同体积情况下两种治疗方法的治疗效果。并对两组患者出现不良反应情况进行分析比较。结果 两组患者甲状腺结节均减小,但射频组患者结节体积缩小率（90.78±7.47）%明显高于乙醇组（69.71±4.95）%,差异具有统计学意义(P<0.05);随着甲状腺结节体积的增大,囊实性比例的缩小,两组患者甲状腺结节体积缩小率均减小。而当结节体积大于30ml时,结节囊实性比例不足50%,乙醇组体积缩小率不足50%,治疗无效。不论结节体积及囊实性比例的大小,射频组患者结节体积缩小率均显著高于乙醇组,结果具有统计学意义（P<0.05）;两组患者出现不良反应情况未见明显差异,结果无统计学意义(P>0.05)。结论 甲状腺囊实性结节小于30ml、囊实性比大于50%,乙醇消融经济且疗效确切,可做为首选;而结节体积较大,囊实性占位不足50%应用射频消融术治疗。     

Catheter Ablation of Idiopathic Left Ventricular Tachycardia

ZARDINI, M., etal .: Catheter Ablation of Idiopathic Left Ventricular Tachycardia . Idiopathic left ventricular tachycardia (ILVT) characterized by right bundle branch block, left axis morphology, response to verapamil and inducibility from the atrium in patients without structural heart disease may represent a distinct clinical entity. We report our experience with catheter ablation of this uncommon arrhythmia using radiofrequency energy (RF) and/or direct current (DC) shocks. Six men and 2 women, aged 16–50 years (mean ± SD, 32 ± 13), had recurrent VT for 16 ± 16 years with a mean frequency of 4 ± 3 episodes/ year. Three patients had syncope during VT. None had identifiable structural heart disease. Catheter ablation was guided by earliest endocardial activation, presence of a high frequency presystolic potential and/or pacemapping of the left ventricle. The left ventricle was accessed via a retrograde aortic approach in 6 patients, a transeptal approach in 1 patient, and a combined approach in the remaining patient. All patients had inducible right bundle branch block morphology, left axis VT with a mean cycle length (CL) of 361 ± 61 ms. A presystolic potential preceding ventricular activation and the His potential during VT was identified in 4 patients. All ablation sites were identified in a relatively uniform location, in the inferoapical left ventricle. Noninducibility of VT was obtained with RF in 3 patients and with DC in 5 patients. In 1 patient, DC delivery after unsuccessful RF prevented further inducibility. Similarly, RF was successful in 1 patient in whom an initial DC attempt was ineffective. Mean total procedure time was 282 ± 51 minutes and mean total fluoroscopy time was 40 ± 15 minutes. There were no complications. One patient treated with DC shock had recurrence of VT during treadmill test the day after ablation and refused repeat ablation. During a mean follow-up of 17 ± 13 months, no VT recurrences or other cardiovascular events occurred. In conclusion, catheter ablation in the inferoapical left ventricle is an effective treatment for this type of ILVT. RF energy can be safely complemented by low energy DC shocks when the former is ineffective.     

Temperature Controlled RF Ablation in Canine Ventricle and Coronary Sinus using 7 Fr or 5 Fr Ablation Electrodes

The safety and lesion volume of temperature controlled radiofrequency ablation (TCRFA) in the right ventricle (RV), left ventricle (LV), and coronary sinus (CS) comparing long 5 Fr to standard tip electrodes have not been previously reported In 1O canines, TCRFA was delivered at a 70°C set point for 30 seconds. Lateral and septal RV lesions were made with either a 5 Fr/5 mm or 7 Fr/4 mm tip. Lateral and septal LV lesions were made with either a 5 Fr/7 mm or 7 Fr/4 mm tip. Proximal and distal CS lesions were made with either a 7 Fr/4 mm, 5 Fr/5 mm or 5 Fr/7 mm tip. Gross and histologic examination of the lesions was completed. Lesion size, tip temperature and power required are related to electrode surface area (SA) when ablating in the RV, LV or CS. 5 Fr/7 mm tips (SA = 36 mm²) tended to create larger lesions than 7 Fr/4 mm tips (SA = 29 mm²) in the LV. 7 Fr4 mm tips tended to create larger lesions than 5 Fr/5 mm tips (SA - 26 mm²) in the RV. 7 Fr/4 mm LV lesions exceeded 7 Fr/4 mm RV lesions due to thicker LV walls. In the CS, 5 Fr/7 mm tips tended to create the largest lesions. In the RV, LV and CS, tips with larger SA tended to have lower temperatures and require higher power. No high temperature or high impedance shutdowns were observed. In conclusion, varying 5 Fr tip length can safely produce larger or smaller lesions compared to those created with 7 Fr/4 mm tips.     

Catheter Ablation for Recurrent Tachyarrhythmias. Clinical Experience with Two Different Techniques of Ablation in 21 Patients

Between 1984 and 1988, 21 patients underwent catheter ablation for drug refractory arrhythmias. Nine patients presented atrial flutter, atrial fibrillation or atrial tachycardia, nine had supraventricular tachycardia (one AV nodal reentrant tachycardia, one reciprocating tachycardia due to concealed accessory pathway and seven XMPW syndrome). Three had ventricular tachycardia. Fourteen patients were treated with direct current shock ablation (DC) and seven patients with radiofrequency ablation (RF). Eight patients underwent ablation of the His bundle. In six patients permanent AV block could be induced and in two first-degree AV block. All became asymptomatic (two with additional antiarrhythmic drug therapy). In four patients with WPW syndrome DC ablation of the accessory pathway was attempted. In one patient a permanent block in the accessory pathway and in another an intermittent block were obtained. In the two remaining patients with accessory pathways the ablation failed to interrupt the retrograde conduction in one the retrograde conduction was modified: however, in the other no change could be demonstrated. Two patients underwent ventricular foci ablation, with one partial success (arrhythmia controlled with associated drug therapy) and one failure. Three patients had RF His bundle ablation (two for atrial flutter and one for atrial fibrillation). One complete atrioventricular block, one first degree AV block and one first degree AV block associated with right bundle branch block were induced. Recurrence of tachyarrhythmias was prevented only in the patient with complete atrioventricular block. RF ablation of accessory pathway was performed in three patients. It resulted in anterograde block in the accessory pathway in the first patient; a slight modification of the retrograde refractory period in the second and no change was noted in the last one. The first of these three patients could then be controlled with drug therapy. The other two patients underwent surgical dissection of the pathway. One patient underwent an unsuccessful attempt of ventricular focus ablation with RF energy. Complications were more common with DC than with RF ablation but serious ventricular arrhythmias were also observed during RF ablation. Thus, DC ablation was completely successful in eight of 14 patients (57%), partially successful with the addition of drug therapy in three patients (21%) and failed in 22%. HF ablation was successful in only one patient (14.5%) and partially successful in another one (14.5%). This relatively low success rate is due in part to the design of the device and the electrodes used in this study. With technical improvements of RF ablation it seems reasonable to expect that this method will play a significant role in the management of drug refractory arrhythmias, since RF ablation, when compared to DC ablation, has the major advantage not to require general anesthesia during the procedure.     

阵发性心房颤动的环肺静脉电隔离单环消融及双环消融术的比较

目的 比较环肺静脉电隔离单环消融和双环消融治疗阵发性心房颤动(简称房颤)的疗效.方法 将40例抗心律失常药治疗无效或出现严重不良反应的阵发性房颤患者,按随机数字表法分为单环消融组和双环消融组,每组20例.单环消融组距肺静脉口0.5 cm作肺静脉单环电隔离线;双环消融组距肺静脉口0.5 cm和1 cm处,分别作肺静脉单环电隔离线.对2组患者手术时间、X线曝光时间,术后6、12个月治愈情况及肺静脉狭窄并发症的发生进行比较.结果 术前2组年龄,房颤发病时间、发作频率,左房内径等比较差异均无统计学意义(均P＞0.05).2组手术时间、术中X线曝光时间比较差异均无统计学意义(均P＞0.05).术后6个月,双环消融组的一次手术治愈率为90％,高于单环消融组的80％(P＜0.05);术后12个月,双环消融组二次手术治愈率为95％,明显高于单环消融组的二次手术治愈率的90％ (P＜0.05).术后6个月2组均未发生肺静脉狭窄.结论 环肺静脉电隔离双环消融治疗阵发性房颤较单环消融效果好.     

Thoracoscopic Radiofrequency Ablation of the Myocardium

Radiofrequency (RF) catheter ablation has been used for the treatment of ventricular tachycardia (VT), however, in some patients VT might result from subepicardiai macroreentry that could be successfully terminated by epicardial approach. This study examined the feasibility of thoracoscopic RF ablation of myocardium from epicardium using a custom made electrode. In five mongrel dogs, the thoracoscope was introduced through the 7th intercostal space. A 500-kHz continuous wave RF energy was connected to a custom made multiple electrode probe. Under thoracoscopic guidance, the heart was exposed and the RF probe was introduced. RF ablation was performed on the nonvascular ventricular wall of the beating heart. The left ventricular free wall and right ventricular outflow tract were satisfactorily visualized and ablated. The total dose of RF energy ranged from 50 to 500 J. and the estimated volume of ablated lesions ranged from 41.0–799 mm³. There were significant correlations between the RF discharge output and the irradiated lesion volume (P < 0.01), and the depth of the lesions (P < 0.01). Grossly, after RF ablation the ventricular myocardium demonstrated a circular, well-demarcated area of thermal injury. Volume and depth of the lesion depended upon the total dose of delivered RF energy. Thoracoscopic RF ablation appears to be a minimally invasive and useful method for creating irradiated myocardial lesions from epicardial surface. This method could he technically feasible for the treatment of Vts for which endocardial RF ablation is ineffective.     

Direct Current Shock Ablation: Quantitative Assessment of Proarrhythmic Effects

Catheter ablation using direct current (DC) shock has proved invaluable in the management of a variety of tachycardias. However, sporadic reports of fatal arrhythmias following ablation have raised the question of the proarrhythmic potential of DC shock ablation. The present study was undertaken in 45 patients to assess prospectively any proarrhythmia related to DC shock ablation, using matched pre- and postablation Holter monitors and programmed electrical stimulation (PES). Nineteen of these patients had Holter monitors for three successive postablation days to observe trends. There was unmatched data in 11 additional patients. All 56 patients provided prospective follow-up for clinical events. There was no immediate sustained VT/VF at the time of the ablation. Four patients had sustained VT in the first 72 hours after ablation; three episodes were similar to the preablation clinical arrhythmias; one patient had torsades de pointes interrupting bradycardia. Twelve patients met Holter, PES, or clinical criteria for proarrhythmia; none were treated on the basis of these findings. On Holter monitoring, there were significant increases in VPCs/hour and couplets/hour in patients undergoing atrial or atrioventricular junctional ablations; and an increase in couplets after accessory pathway ablations. Increases in these categories were not significant for VT patients; nor were increases in episodes of VT/hour or atrial arrhythmias significant in any group. Patients were followed for 44 +/- 33 months, with an actuarial survival of 95% at 1 year, 88% at 3 years, and 85% at 4 years. There were six deaths during follow-up. Two patients had sudden death: one at 2 months had early evidence of proarrhythmia; the other at 32 months may have represented later myocardia deterioration. One patient died of heart failure at 77 months; and there were three noncardiac deaths. DC shock ablation in humans is much less proarrhythmic than in dogs. The low incidence of clinical proarrhythmic events during prolonged follow-up after discharge resulted in low sensitivity, specificity, and positive predictive values for Holter and PES, although the negative predictive values of these tests were greater than 90%. Only one of 12 patients who met criteria for proarrhythmia in the days immediately following ablation had subsequent clinical events consistent with proarrhythmia. These results may be useful as standards for comparison with results of radiofrequency or other ablation modalities.     

Physiology of the Escape Rhythm After Radiofrequency Atrioventricular Junctional Ablation

The physiology of the escape rhythm (ER) and its response to pharmacological modulation under varying autonomic conditions were studied in 48 patients undergoing radiofrequency ablation of the atrioventricular junction (AVJ) for refractory atrial fibrillation. The QRS morphology and cycle length (CL) of the baseline ER were measured 15 minutes postablation. The CL of the ER was measured in response to doses of isoproterenol, atropine, adenosine, lidocaine, and verapamil. The ER QRS was narrow (QRS < 120 ms) in 20 patients and wide (QRS > 120 ms) in 28 patients. Of the 28 patients with wide QRS ER, 11 patients had a new bundle branch block (8 patients new right bundle branch block [RBBB] and 2 patients new left bundle branch block [LBBB]). The ERCL was similar in both narrow and wide ERs (1,593 ± 376 ms and 1,516 ± 296 ms, P = 0.44). In 23 patients receiving isoproterenol infusion, the ER CL decreased with increasing doses from 1 mcg/min to 2 mcg/min (1,378 ± 200 to 1,240 ± 229 ms, P < 0.001), but did not decrease further at 3 mcg/min [1,201 ±192 ms, P = 0.48 vs 2 mg/min). Seven patients received 0.02 mg/kg of atropine, and ER decreased significantly (1,572 ± 408 ms to 1,319 ± 333 ms, P = 0.028). In 30 patients who received intravenous boluses of adenosine (6–18 mg), the ER did not change significantly. In 28 patients who received 150 mg of lidocaine, the ER increased from 1,462 ± 286 ms to 1,715 ± 467 ms (P < 0.001), and one patient developed transient asystole. Nineteen patients received 7.5 mg of verapamil, and the ER did not change (1,488 ± 313 ms to 1,513 ± 666 ms, P = 0.80). There was no significant difference in response to isoproterenol, adenosine, lidocaine, or verapamil between the patients with wide and narrow QRS ERs. We conclude that patients may have stable ERs immediately following AVJ ablation even when a wide complex ER results. The ER is responsive to sympathetic stimulation and vagal blockade. The ER is prolonged after lidocaine but not after verapamil, suggesting response to sodium but not to calcium channel blockade. These data are consistent with an ER originating in the distal compact AV node or proximal His bundle.     

Electrophysiological Studies on Cardiac Catheter Ablation

Clinical and animal investigations have pointed out that high energy electrical shocks are associated with the development of cardiac arrhythmias and with variable success in permanent ablation. The effects of electrode configuration and location on the size of the recorded electrogram was investigated to help explain variable catheter ablation results. We analyzed the cellular effects of catheter ablation shocks and found depression of resting potential, action potential amplitude, dV/dt and action potential duration. The most severe effects were noted with high current densities in tissues located between the cathode and anode. Damage was worse nearest the cathode. Similar cellular studies were completed using argon laser photoablation. Again, there was a decrease in resting potential, action potential amplitude and dV/dt. Laser energy led to a more focal region of myocardium void of action potentials and the border zone of injury was smaller. We also investigated the effects of lower energy shocks)1 to 10 joule) on cardiac tissues. Using microelectrodes, we observed that the membrane potential can "hang up" at the depolarized levels for varying periods of time and that conduction is altered during this membrane "hang-up" period. The duration and membrane hang-up level correlated with shock intensity and shock duration. Sequential shocks resulted in additive membrane "hang-up". We believe that membrane hang-up may be associated with brief arrhythmias observed following catheter ablation since conduction, refractoriness and excitability are all altered.     

Closed Chest Radiofrequency Ablation of the Sinoatrial Node in Dogs

Transcatheter ablation of the sinoatrial node with radiofrequency energy (0.6 MHZ, 2.5-5 watts) was performed in 10 dogs under fluoroscopic monitoring and autonomic blockade. Sinus function was previously studied in terms of cycle length, recovery time and atrial activation pattern by catheter mapping. Several discharges (8-22) were applied for variable periods of time (maximum 1 minute). Sinus tachycardia and/or sinus arrest during ablation confirmed correct catheter position. Sinus rhythm was abolished in eight dogs. The ectopic rhythm was atrial in six and AV nodal in two dogs. Ectopic atrial cycle length and recovery time were longer than the baseline sinus values: 724 +/- 321 versus 509 +/- 147, P less than 0.05; 1103 +/- 775 versus 618 +/- 151, P less than 0.05 (values in msec). The study was repeated 10-14 days later in six dogs; three maintained the same atrial rhythm, one persisted in sinus rhythm, and one dog changed from atrial to sinus rhythm, whereas another changed from sinus to atrial rhythm. Gross findings revealed transmural lesions in all dogs, without perforation. Histology in chronic dogs showed sinus cell necrosis and its replacement by granulation tissue. In conclusion: sinus function may be abolished by closed chest radiofrequency ablation.