Tissue temperature-controlled radiofrequency ablation

During radiofrequency energy delivery, the catheter tip temperature can be significantly lower than the tissue temperature. The authors performed tissue temperature-controlled radiofrequency ablation in vitro and evaluated the effects of cooling, electrode to tissue contact, and target tissue temperature on lesion size. Pieces of porcine ventricle were immersed in a bath of isotonic saline solution at 37 degrees C. Radiofrequency energy was controlled by the tissue temperature as measured with a thermocouple needle placed 2 mm beneath the ablation electrode. Radiofrequency power was delivered for 30 seconds and limited to 50 W. A total of 81 radiofrequency ablations was performed with different electrode to tissue contact forces (0.04 N, 0.36 N, and 0.67 N) and target tissue temperatures (50 degrees C, 60 degrees C, and 70 degrees C) using an irrigated (27 ablations, 20 mL/min irrigation flow rate) or a nonirrigated ablation catheter. Twenty-seven nonirrigated applications were performed with fluid flow maintained by the pump of the thermostat and another 27 applications without flow. Every combination was applied three times and the average values were used for evaluation. For tissue target temperatures of 50 degrees C, 60 degrees C, and 70 degrees C, the lesion volume for nonirrigated ablations was on average 21 +/- 8 mm3, 45 +/- 23 mm3, and 109 +/- 45 mm3, respectively, and for irrigated ablations 12 +/- 7 mm3, 37 +/- 20 mm3, and 92 +/- 30 mm3, respectively. In both application groups the lesion size did not correlate with the electrode to tissue contact force. In the nonirrigated ablation group there was no difference in lesion size between the group with fluid flow and those without. Lesion size during tissue temperature-controlled radiofrequency delivery increases with increasing target tissue temperature and becomes independent of flow and electrode to tissue contact.     

Irrigated tip catheter ablation in right posteroseptal accessory pathways resistant to conventional ablation

Although RF ablation is an effective treatment of arrhythmias due to atrioventricular accessory pathways, there are cases refractory to conventional catheter ablation. Irrigated tip catheter ablation causes larger and especially deeper lesions than conventional ablation. This article discusses using irrigated tip catheter ablation in cases of right posteroseptal accessory pathways resistant to conventional ablation. Four consecutive patients with no structural heart disease and symptomatic arrhythmias related to right posteroseptal accessory pathways underwent irrigated tip catheter ablation. Conventional RF ablation had been unsuccessful in at least two procedures at more than one center (in three patients at the authors' center). The irrigated tip catheter (Chilli, Cardiac Pathways Corporation) uses a cooling system that is a closed circuit with a saline solution circulating at 0.6 mL/s. Temperature, power, and impedance were monitored during the RF applications. The procedure was successful in all four cases with no complications. In three of them, only one or two applications were necessary. Patients showed no recurrent arrhythmia during several months of follow-up. The results of the present study suggest that RF ablation using an irrigated tip catheter can be useful (and seems to be safe) for the treatment of some right posteroseptal accessory pathways resistant to conventional ablation.     

Catheter tip orientation affects radiofrequency ablation lesion size in the canine left ventricle

While some factors influencing size of RF lesions in ventricular tissue have been characterized, the effects of catheter electrode-endocardial surface orientation on lesion generation have not been investigated. Therefore, the effects of parallel versus perpendicular catheter electrode-endocardial surface orientation on dimensions of RF lesion produced with 4-, 6-, 8-, 10-, and 12-mm distal electrode lengths were studied in 20 closed-chested dogs. Orientation was established by biplane fluoroscopy and confirmed by intracardiac echocardiography for the majority of energy deliveries (71%). RF voltage was titrated to maintain constant catheter electrode temperature of 75 degrees C for 60 seconds. In the perpendicular orientation, lesion size did not change significantly with increasing electrode lengths. There was a statistically significant interaction between electrode orientation and maximum lesion length (analysis of variance [ANOVA] P = 0.04], lesion width (ANOVA P = 0.01), lesion area (ANOVA P = 0.02), and estimated lesion volume (ANOVA P < 0.005) over all electrode lengths. With parallel tip-tissue orientation, lesion size was a function of increasing electrode length. For 4-, 6-, 8-, 10-, and 12-mm electrodes, maximum lesion surface areas were 95 +/- 38, 97 +/- 38, 119 +/- 29, 147 +/- 52, and 147 +/- 67 mm2, respectively. For electrode lengths 8, 10, and 12 mm, estimated lesion volumes were significantly greater with parallel orientation (P < 0.05 for all). Thus, ventricular lesion size is dependent on catheter electrode length, but only when the catheter is oriented parallel to the endocardial surface. This information may be helpful in increasing lesion dimensions for RF ablation of ventricular tachycardias.     

Prospective randomized comparison of cooled radiofrequency versus standard radiofrequency energy for ablation of typical atrial flutter

In patients with atrial flutter, conventional RF ablation may not result in complete isthmus block. This prospective, randomized study tested the hypothesis that the cooled RF ablation is safe and facilitates the achievement of isthmus block with fewer RF applications than with standard ablation for typical atrial flutter. Isthmus ablation was performed in 59 patients (40 men, 64 +/- 14 years) with type I atrial flutter using standard RF (n = 31) or cooled RF (n = 28) catheters with crossover after 12 unsuccessful RF applications. The endpoint was bidirectional isthmus block or a total of 24 unsuccessful RF applications. After the first 12 RF applications, 17 (55%) of 31 standard RF and 22 (79%) of 28 cooled RF patients had bidirectional isthmus block (P < 0.05). After the remaining patients crossed over to the alternate RF ablation system and underwent up to 12 more RF applications, bidirectional isthmus block had been demonstrated in 27 (87%) of 31 standard RF and 25 (89%) of 28 cooled RF patients (P = NS). Isthmus block was not achieved within 24 RF applications in four standard and three cooled RF patients. Mean measured tip temperatures for cooled RF were lower than for standard RF (38.5 degrees C +/- 6.98 degrees C vs 57.2 degrees C +/- 7.42 degrees C, P < 0.0001). Peak temperatures were also lower for cooled RF compared to standard RF (45.7 degrees C +/- 22.7 degrees C vs 63.4 degrees C +/- 9.87 degrees C, P < 0.0001). Importantly, mean power delivered was significantly higher for cooled than for standard RF (42.3 +/- 9.48 vs 34.0 +/- 14.0 W, P < 0.0001). There were no serious complications for either ablation system. During a 12.8 +/- 3.76-month follow-up, there were two atrial flutter recurrences in the cooled RF group and four in the standard RF group (P = NS). In patients with type I atrial flutter, ablation with the cooled RF catheter is as safe as, and facilitates creation of bidirectional isthmus block more rapidly than, standard RF ablation.     

心房颤动导管消融的地位和进展

心房颤动(房颤)是临床常见的心律失常之一,最大风险是血栓栓塞,常见是脑卒中。随着人口的老龄化,房颤人数持续增加,治疗问题也逐渐成为人们关注重点。房颤导管消融是其重要治疗方法之一,可明显改善房颤患者预后。且随着技术发展,消融方法也日趋成熟,故导管消融术治疗房颤地位正在逐步提升。但消融方法尚无固定术式,发生机制尚未完全明确,尤其对于持续房颤。因此房颤消融术仍存在一些问题有待进一步探索。     

The results of radiofrequency catheter ablation of supraventricular tachycardia in children

BACKGROUNDS: Radiofrequency (RF) catheter ablation represents a major advance in the management of children with cardiac arrhythmias and has rapidly become the standard of care for the first-ling therapy of supraventricular tachycardias (SVTs). The purpose of this study was to investigate the results of the RF catheter ablation of SVTs in pediatric patients. METHODS: From December 1989 to August 2005, a total of 228 pediatric patients (age: 9 +/- 7 years, range: 5-18 years; male:female = 117:111) with clinically documented SVT underwent an electrophysiologic study and RF catheter ablation at our institution. RESULTS: The arrhythmias included atrioventricular reentrant tachycardia (AVRT; n = 140, 61%), atrioventricular nodal reentrant tachycardia (AVNRT; n = 66, 29%), atrial tachycardia (AT; n = 11, 5%), and atrial flutter (AFL; n = 11, 5%). The success rate of the RF catheter ablation was 92% for AVRT, 97% for AVNRT, 82% for AT, and 91% for AFL, respectively. Procedure-related complications were infrequent (8.7%; major complications: high grade AV block (2/231, 0.9%); minor complications: first degree AV block (6/231, 2.6%), reversible brachial plexus injury (2/231, 0.9%), and local hematomas or bruises (10/231, 4.3%)). The recurrence rate was 4.7% (10/212) during a follow-up period of 86 +/- 38 months (0.5-185 months). CONCLUSIONS: The RF catheter ablation was a safe and effective method to manage children with paroxysmal and incessant tachycardia. The substrates of the arrhythmias differed between the pediatric and adult patients. However, the success rate of the ablation, complications, and recurrence during childhood were similar to those of adults.     

The effect of ablation electrode length and catheter tip to endocardial orientation on radiofrequency lesion size in the canine right atrium

Although the determinants of radiofrequency lesion size have been characterized in vitro and in ventricular tissue in situ, the effects of catheter tip length and endocardial surface orientation on lesion generation in atrial tissue have not been studied. Therefore, the dimensions of radiofrequency lesions produced with 4-, 6-, 8-, 10-, and 12-mm distal electrode lengths were characterized in 26 closed-chested dogs. The impact of parallel versus perpendicular catheter tip/endocardial surface orientation, established by biplane fluoroscopy and/or intracardiac echocardiography, on lesion dimensions was also assessed. Radiofrequency voltage was titrated to maintain a steady catheter tip temperature of 75 degrees C for 60 seconds. With a perpendicular catheter tip/tissue orientation, the lesion area increased from 29 +/- 7 mm2 with a 4-mm tip to 42 +/- 12 mm2 with the 10-mm tip, but decreased to 29 +/- 8 mm2 with ablation via a 12-mm tip. With a parallel distal tip/endocardial surface orientation, lesion areas were significantly greater: 54 +/- 22 mm2 with a 4-mm tip, 96 +/- 28 mm2 with a 10-mm tip and 68 +/- 24 mm2 with a 12-mm tip (all P < 0.001 vs perpendicular orientation). Lesion lengths and apparent volumes were larger with parallel, compared to perpendicular tip/tissue orientations, although lesion depth was independent of catheter tip length with both catheter tip/tissue orientations. Electrode edge effects were not observed with any tip length. Direct visualization using intracardiac ultrasound guidance was subjectively helpful in insuring an appropriate catheter tip/tissue interface needed to maximize lesion size. Although atrial lesion size is critically dependent on catheter tip length, it is more influenced by the catheter orientation to the endocardial surface. This information may also be helpful in designing electrode arrays for the creation of continuous linear lesions for the elimination of complex atrial tachyarrhythmias.     

Electrophysiologic characteristics and radiofrequency catheter ablation in children with Wolff-Parkinson-White syndrome

BACKGROUND: The majority of cardiac arrhythmias in children are supraventricular tachycardia, which is mainly related to an accessory pathway (AP)-mediated reentry mechanism. The investigation for Wolff-Parkinson-White (WPW) syndrome in adults is numerous, but there is only limited information for children. This study was designed to evaluate the specific electrophysiologic characteristics and the outcome of radiofrequency (RF) catheter ablation in children with WPW syndrome. METHODS: From December 1989 to August 2005, a total of 142 children and 1,219 adults with atrioventricular reentrant tachycardia (AVRT) who underwent ablation at our institution were included. We compared the clinical and electrophysiologic characteristics between children and adults with WPW syndrome. RESULTS: The incidence of intermittent WPW syndrome was higher in children (7% vs 3%, P=0.025). There was a higher occurrence of rapid atrial pacing needed to induce tachycardia in children (67% vs 53%, P=0.02). However, atrial fibrillation (AF) occurred more commonly in adult patients (28% vs 16%, P=0.003). The pediatric patients had a higher incidence of multiple pathways (5% vs 1%, P<0.001).Both the onset and duration of symptoms were significantly shorter in the pediatric patients. The antegrade 1:1 AP conduction pacing cycle length (CL) and antegrade AP effective refractory period (ERP) in children were much shorter than those in adults with manifest WPW syndrome. Furthermore, the retrograde 1:1 AP conduction pacing CL and retrograde AP ERP in children were also shorter than those in adults. The antegrade 1:1 atrioventricular (AV) node conduction pacing CL, AV nodal ERP, and the CL of the tachycardia were all shorter in the pediatric patients. CONCLUSION: This study demonstrated the difference in the electrophysiologic characteristics of APs and the AV node between pediatric and adult patients. RF catheter ablation was a safe and effective method to manage children with WPW syndrome.     

Atrial fibrillation ablation: "perpetual motion" of open irrigated tip catheters at 50 W is safe and improves outcomes

Background: Point‐by‐point use of open irrigated tip catheters (OITCs) at 50 W increases atrial fibrillation (AF) ablation cure rates but also increases complications. We determined if constantly moving the OITC (perpetual motion) when using 50 W increases ablation cure rates without increasing complications. Methods: We evaluated procedural data, complications, and individual procedure cure rates (IPCRs) for AF ablation using closed tip catheters (CTC) versus OITC at 40, 45, and 50 W in 1,122 ablations. We used “perpetual motion” to move the OITC at 50 W every 3–10 seconds. Results: The OITC showed higher IPCR than CTC at 45 W (P = 0.012) and 50 W (P < 0.0005). For the OITC, IPCR increased from 44.6% to 60.7% as power increased from 40 to 50 W (P = 0.008). The OITC appeared superior to the CTC for all types of AF. For paroxysmal AF, increasing OITC power from 40 to 50 W provided no increase in IPCR (70.6% vs 71.2%, P = 0.827). For persistent AF, increasing power from 40 to 50 W increased IPCR from 34.5% to 59.5% (P = 0.001). Complications were similar for the CTC and the OITC at any power. The OITC at 50 W had shorter procedure, left atrial, and fluoroscopy times (P < 0.0005). Conclusions: Increasing OITC power from 40 to 50 W increases IPCR with no increase in complications as long as the 50 W setting is done using “perpetual motion.” The OITC 50 W power setting results in shorter procedure and fluoroscopy times and should be considered for AF ablations. (PACE 2011; 34:531–539)     

Successful radiofrequency catheter ablation of ventricular tachycardia originating from underneath the mechanical prosthetic aortic valve

A 67-year-old man who developed sustained ventricular tachycardia (VT) 4 years after a prosthetic aortic valve replacement, underwent electrophysiologic testing and catheter ablation. The mechanism of the VT was suggested to be triggered activity because the VT could be induced by programmed ventricular stimulation, and burst ventricular pacing demonstrated overdrive suppression without a transient entrainment. Successful catheter ablation using a transseptal approach was achieved underneath the mechanical prosthetic aortic valve on the blind side for that approach. This case demonstrated that catheter mapping and ablation of the entire LV using a transseptal approach might be possible.     

射频消融治疗特发性室性心动过速的临床观察

目的观察射频消融(RFCA)治疗9例特发性室性心动过速(IVT)方法和结果。方法分别行激动顺序标测法和起搏标测法,对左室特发性室速(ILVT)7例,右室特发性室速2例,行射频消融治疗。结果6例ILVT射频消融治疗成功,均起源于左室间隔面,有效消融靶点处P电位较体表心电图QRS起始点提前(34.6±8.9)m s(25~58 m s),2例IRVT射频消融成功,有效消融靶点处与心动过速时的12导联心电图QRS波形完全相同。无一例出现并发症。结论射频消融是治疗特发性室性心动过速的有效方法。     

Quality of life and cost for patients with premature ventricular contractions by radiofrequency catheter ablation

OBJECTIVE: To evaluate the quality of life (QoL), health-care resource utilization, and cost for the patients with premature ventricular contractions (PVCs) by radiofrequency catheter ablation (RFCA). METHODS: RFCA was performed in 58 patients with symptomatic PVCs that were refractory/easy to medication. A 24-hour ambulatory electrocardiographic monitoring, QoL, health-care resources utilization, and cost were assessed at a screening visit and 3 and 12 months after RFCA. RESULTS: RFCA was successfully performed in 56 patients (96.6%). This resulted in a significant improvement in the QoL at 3 and 12 months after the procedure. There were no major complications related to the procedure. Nine patients (15.5%) had residual arrhythmia. Seven of them underwent repeated ablation with successful results. It also improved the QoL and reduced health-care resource utilization and cost. CONCLUSIONS: RFCA is a safe and effective treatment for PVCs, and it is a viable alternative to drugs in the presence of disabling symptoms.     

Pulmonary artery: A pivotal site for catheter ablation in idiopathic RVOT ventricular arrhythmias

In patients without associated myocardial diseases, characterized by left bundle branch block and inferior axis morphologies, repetitive idiopathic right ventricular tachycardias and ventricular premature contractions typically arise from right ventricular outflow tract (RVOT). Accumulated evidences have shown that radiofrequency catheter ablation is a useful treatment for patients with RVOT ventricular arrhythmias (VAs). Interestingly, several medical centers have shown that pulmonary artery (PA) is a potential novel site for catheter ablation in RVOT‐like VAs, particularly in patients where termination of RVOT VAs at the usual site fails. In this review, we comprehensively demonstrated that RVOT VAs were successfully terminated at the site of PA, analyzed the characteristics of surface electrocardiogram and endocardial potentials, and explored the underlying mechanisms for these cases.     

The surface electrocardiographic changes after radiofrequency catheter ablation in patients with idiopathic left ventricular tachycardia

Surface electrocardiographic changes after radiofrequency (RF) catheter ablation (RFCA) were observed in patients with idiopathic left ventricular tachycardia (ILVT), and the possible mechanisms were analysed. In 41 cases with ILVT who underwent the RFCA, the surface electrocardiograms (ECGs) before and after RFCA were recorded and the serum cardiac troponin I (cTnI) were measured before, immediately after, 4 h after and 24 h after RFCA. Seven patients developed different models and degrees of fascicular block after successful RFCA. The configurations of fascicular block had no dynamic alteration during the follow-up periods. No significant difference in the duration of the RF energy delivered, the numbers of RF lesion and the serum levels of cTnI between the patients with or without the electrocardiographic alteration was observed. Thus, the RFCA can cause the fascicular block in some of the patients with ILVT. The different distribution models of the left bundle branch, but not the damage degree to the endocardium induced by RF current, is the primary factor to the changes of ECG.     

Idiopathic mitral annular PVCs with multiple breakouts and preferential conduction unmasked by radiofrequency catheter ablation

A 39-year-old man with idiopathic monomorphic premature ventricular contractions (PVCs), exhibiting a right bundle branch block and inferior axis QRS morphology, underwent electrophysiological testing. After a radiofrequency (RF) application to the anterior mitral annulus (MA) eliminated the spontaneous PVC morphology, a second PVC morphology occurred. Pacing from the first ablation site exhibited an excellent match to the second PVCs with a long stimulus to QRS interval. An RF application delivered near the first lesion eliminated all PVCs. The MA PVCs in this case exhibited a single origin with multiple breakouts and preferential conduction that were unmasked by RF ablation.     

Incidence, time course, and characteristics of microbubble formation during radiofrequency ablation of pulmonary veins with an 8-mm ablation catheter

BACKGROUND: Microbubble formation during pulmonary vein (PV) radiofrequency (RF) ablation of atrial fibrillation (AF) occurs relatively frequently. Prior studies have shown that microbubble formation may be associated with an increased risk of complications. However, the incidence, time course, and temperature characteristics of microbubble formation during AF ablation with an 8-mm catheter have not been prospectively described in humans. METHODS: We studied 46 (30 men, age 56+/-10 years) patients with AF who underwent RF ablation of PVs between January 2005 and December 2005 using an 8F, 8-mm Biosensetrade mark ablation catheter (Biosense-Webster, Diamond Bar, CA, USA). All patients underwent continuous intracardiac echocardiography (ICE). Microbubble patterns were classified as either type 1 (intermittent, scattered microbubble formation) or type 2 (explosive shower of dense microbubbles). Formation of any microbubbles was detected by ICE and the time, PV location, and electrode temperature were recorded. RESULT: A total of 1,479 (32+/-13, range 12-73) RF lesions were delivered to 167 veins. Twenty (2%) lesions were classified as type 2. Since the number of lesions resulting in type 2 bubbles was very small, only type 1 lesions were included in the final analysis. Thirty-nine (85%) patients had at least one lesion associated with bubble formation during ablation (mean: 7+/-7 lesions, range 1-28 lesions). Twenty-three percent (327) of the RF lesions resulted in bubble formation. RF generator power setting during lesions resulting in bubble formation was lower than lesions which did not result in bubble formation (47.9+/-7.4 W vs 49.7+/-7.1 W, P<0.001). Logistic regression analysis revealed a significant negative correlation (P<0.001) between RF generator power settings and a positive correlation between the generator temperature settings and formation of bubbles (both P<0.02). However, the maximum temperature attained was not different between lesions resulting in bubble formation (n=327) and those which did not result in bubble formation (n=1,139). Fifty-three (16%) of the lesions associated with bubble formation occurred within 2-10 seconds after RF was begun. Bubble formation was significantly more frequent in left superior PVs compared to the other PVs (left superior PV 27.3% left inferior PV 18.6%, right superior PV 20.5%, and right inferior PV 18.8%, P=0.005, left superior PV vs other PVs, P<0.001) even after adjustment for the other factors including generator power settings and the temperature setting. CONCLUSION: Bubble formation is common during RF ablation of PV with 8-mm tip catheter and can occur as early as 2 seconds after starting RF. RF generator power is negatively correlated with bubble formation while generator temperature settings are positively correlated with formation of bubbles. Microbubble formation is also more frequent with ablation of the left superior PV probably due to better catheter contact in that area.