Percutaneous intrapericardial echocardiography during catheter ablation: a feasibility study

BACKGROUND: Percutaneous pericardial access, epicardial mapping, and ablation have been used successfully for catheter ablation procedures. OBJECTIVES: The purpose of this study was to evaluate the safety and feasibility of closed-chest direct epicardial ultrasound imaging for aiding cardiac catheter ablation procedures. METHODS: An intracardiac ultrasound catheter was used for closed-chest epicardial imaging of the heart in 10 patients undergoing percutaneous epicardial access for catheter ablation. All patients underwent concomitant intracardiac echocardiography and preprocedural transesophageal echocardiography. Using a double-wire technique, two sheaths were placed in the pericardium, and a phased-array ultrasound catheter was manipulated within the pericardial sinuses for imaging. RESULTS: Multiple images from varying angles were obtained for catheter navigation. Notably, image stability was excellent, and structures such as the left atrial appendage were seen in great detail. No complications resulting from use of the ultrasound catheter in the pericardium occurred, and no restriction of movement due to the presence of the additional catheter in the pericardial space was observed. Wall motion was correlated to voltage maps in five patients and showed that areas of scars correlated with wall-motion abnormalities. Normal wall-motion score correlated to sensed signals of 4.2 +/- 0.3 mV (normal myocardium >1.5 mV), and scores >1 correlated to areas with signals <0.5 mV in that territory). CONCLUSION: Intrapericardial imaging using an ultrasound catheter is feasible and safe and has the potential to provide additional valuable information for complex ablation procedures.     

Epicardial radiofrequency ablation of ventricular myocardium: Factors affecting lesion formation and damage to adjacent structures

We evaluated the factors affecting epicardial radiofrequency (RF) lesion formation in normal ventricular myocardium. In 16 dogs, a minithoracotomy was made and a sheath was placed in the pericardial space. Standard ablation lesions (4-mm tip catheter; 70 ( composite function) C/60 seconds) were created in each ventricle under fluoroscopy guidance (n = 7) or hand-held with direct visualization of the catheter to assure optimal electrode-tissue contact (n = 6). In the latter, thermally-shielded (TS) electrodes (50% tip surface along its 4 mm length) were used in 3/6 dogs. Catheter tip (4 mm) irrigation (13 mL/minutes; 40 ( composite function) C/60 seconds) was employed with conventional techniques in 3 additional dogs. RESULTS: With optimal electrode-tissue contact (11 lesions), power (3.4 +/- 2.3 W vs. 16 +/- 13 W; p < 0.001) and pacing thresholds (0.2 +/- 0.0 mA vs. 3.6 +/- 5.7 mA; p = 0.004) were lower than standard RF (25 lesions). However, lesion dimensions were similar and transmural lesions did not occur (depth 2.8 +/- 1.1 mm vs. 3.0 +/- 1.5 mm). Catheter irrigation allowed high power outputs (43 +/- 6.1 W; p < 0.001) generating transmural lesions, 5/9 (55%), depth 6.4 +/- 2.1 mm. At constant power (2 W), catheter-tip temperature (52 +/- 5.2( composite function) C vs. 57 +/- 6.6( composite function) C; p = NS) and lesion (10 in each group) dimensions were similar for conventional and TS electrodes, but damage to parietal pericardium and lungs occurred with conventional electrodes only (70% vs. 0% p = 0.02). CONCLUSION: Standard epicardial RF ablation does not produce deep lesions and exhibits a significant energy loss probably due to poor electrode-tissue contact. Catheter irrigation allows delivery of high power outputs to the epicardium consistently creating deeper lesions than standard ablation. TS electrodes may reduce damage to neighboring structures during epicardial RF ablation.     

Tissue-specific variability in human epicardial impedance

Epicardial Impedance Mapping . Introduction: Epicardial ablation can be employed to treat ventricular tachycardia. Voltage attenuation in regions of fat can mimic epicardial scar, limiting its specificity. Ablation over fat may not be as effective. Prior animal data have shown that infarcted myocardium has lower impedance than normal, and human bioimpedance studies suggest peripheral fat displays higher impedance. Therefore, we tested the hypothesis that human epicardial fat has higher impedance than myocardium when measured with standard ablation tools. Methods: Patients undergoing elective surgery for coronary artery or valve disease were enrolled. A reference patch was placed on the patients’ back between the scapulae and connected to a standard RF generator (Stockert, GmBH, Germany). Impedance was measured by passing a 1 μA, 50 kHz current from the catheter tip to the patch. After sternotomy but before initiation of cardiopulmonary bypass, an ablation catheter (Celsius, Biosense Webster, Diamond Bar, CA, USA) was placed onto the epicardial surface in ventricular regions visually identified as fat or myocardium. At each site, impedance was recorded from the generator. Results: A total of 37 (7 patients) points were sampled. Impedance was significantly higher in regions of fat versus normal muscle (697 Ω vs. 301 Ω; P = 0.01). Moreover, normal sites from the LV had higher impedance than from the RV (381 Ω vs. 271 Ω; P = 0.01). Conclusions: Human epicardial fat has higher tissue impedance than normal muscle. Using epicardial impedance and voltage mapping in conjunction may improve differentiation of arrhythmia substrate from epicardial fat and improve the efficacy of epicardial ablation. (J Cardiovasc Electrophysiol, Vol. 22, pp. 436‐439)     

A Novel Catheter Design for Laser Photocoagulation of the Myocardium to Ablate Ventricular Tachycardia

Nd:YAG laser energy has been proposed as an alternative to radiofrequency energy for ablation of ventricular tachycardia (VT) associated with coronary artery disease (CAD) in an effort to increase lesion size and success rates. However, issues of catheter design to maintain flexibility and ensure adequate tissue contact have hindered development of laser catheters.We developed and tested a prototype 8 Fr. steerable catheter with a flexible and extendible tip (designed to ensure tissue contact and efficient ventricular mapping), which projects the laser beam through a side port containing a lens-tipped optical fiber that rests against the endocardial surface. The catheter has a channel for simultaneous saline irrigation to displace the interceding blood and discharge a laser beam between two electrodes for bipolar mapping and a thermocouple for temperature monitoring. The catheter was tested on bench top using the epicardial surface of freshly slaughtered bovine hearts and in vivo using six anaesthetized closed-chest sheep. In vitro experiments demonstrated that lesion size increased linearly with applied power up to 40 watts. When compared to radio frequency, laser energy penetrated more deeply into the myocardium. In the in vivo studies, using increasing powers of up to 40 watts for application times of 60 to 120 seconds created circular or elliptical lesions with surface dimensions up to 12 mm × 12 mm and depth of 9 mm (full LV wall thickness with a mean lesion diameter of 9.9 ± 5.2 mm and depth 5.8 ± 3.2 mm). Most lesions, 16 total in both right and left ventricular walls were transmural or near transmural in thickness. Lesions demonstrated coagulation necrosis with smooth well-demarcated borders. No animal suffered cardiac perforation, hypotension, hemopericardium, damage to cardiac valves, or cavitation effect from any of the ablations. Runs of VT were seen during energy application at the highest laser outputs in two animals.In conclusion, this catheter design provides effective endocardial delivery of laser energy and is capable of creating transmural or nearly transmural lesions in vivo and in vitro, thereby potentially increasing the efficiency of VT ablation in CAD patients.     

Endocardial and Epicardial Ablation Guided by Nonsurgical Transthoracic Epicardial Mapping to Treat Recurrent Ventricular Tachycardia

Nonsurgical Epicardial Ablation. Introduction : An epicardial site of origin of ventricular tachycardia (VT) may explain unsuccessful endocardial radiofrequency (RF) catheter ablation. A new technique to map the epicardial surface of the heart through pericardial puncture was presented recently and opened the possibility of using epicardial mapping to guide endocardial ablation or epicardial catheter ablation. We report the efficacy and safety of these two approaches to treat 10 consecutive patients with VT and Chagas' disease.
Methods and Results : Epicardial mapping was carried out with a regular steerable catheter introduced into the pericardial space. An epicardial circuit was found in 14 of 18 mapable VTs induced in 10 patients. Epicardial mapping was used to guide endocardial ablation in 4 patients and epicardial ablation in 6. The epicardial earliest activation site occurred 107 ± 60 msec earlier than the onset of the QRS complex. At the epicardial site used to guide endocardial ablation, earliest activation occurred 75 ± 55 msec before the QRS complex. Epicardial mid-diastolic potentials and/or continuous electrical activity were seen in 7 patients. After 4.8 ± 2.9 seconds of epicardial RF applications, VT was rendered noninducible. Hemopericardium requiring drainage occurred in 1 patient; 3 others developed pericardial friction without hemopericardium. Patients remain asymptomatic 5 to 9 months after the procedure. Interruption during endocardial pulses occurred after 20.2 ± 14 seconds (P = 0.004), hut VT was always reinducible and the patients experienced a poor outcome.
Conclusion : Epicardial mapping does not enhance the effectiveness of endocardial pulses of RF. Epicardial applications of RF energy can safely and effectively treat patients with VT and Chagas' disease.     

Repeat percutaneous epicardial mapping and ablation of ventricular tachycardia: safety and outcome

Safety and Efficacy of Repeat Epicardial Access. Introduction: Epicardial mapping and ablation of ventricular tachycardia (VT) has been increasingly performed. Occasionally additional ablation is necessary, requiring repeat percutaneous access to the pericardial space. Methods and Results: We studied 30 consecutive patients who required a repeat epicardial procedure. We specifically examined the success and safety of repeat percutaneous pericardial access as well as the ability to map and ablate epicardial VT targets. Percutaneous pericardial access at a median of 110 days after the last procedure was successful in all 30 patients. Significant adhesions interfering with catheter mapping were encountered in 7 patients (23%); 6 had received intrapericardial triamcinolone acetate (IPTA) with prior procedures. Using blunt dissection with a deflected ablation catheter and a steerable sheath, adhesions were divided allowing for complete catheter mapping in 5 patients with areas of dense adherence compartmentalizing the pericardium in 1 patient and precluding ablation over previously targeted ablation site in the second. Targeted VT noninducibility was achieved in 27 (90%) patients including 7 patients with adhesions. No direct complications related to pericardial access or adhesions disruption occurred. One periprocedural death occurred from refractory cardiogenic shock in patient with LV ejection fraction of 10%. Another patient developed asymptomatic positive Haemophilus influenzae pericardial fluid cultures identified at second procedure, which was successfully treated. Conclusions: Repeat access can be obtained after prior epicardial ablation. Adhesions from prior procedures may limit mapping, but can usually be disrupted mechanically and allow for ablation of recurrent VT. IPTA may not completely prevent adhesions. (J Cardiovasc Electrophysiol, Vol. 23, pp. 744‐749, July 2012)     

Correlative Anatomy for the Electrophysiologist,Part I: The Pericardial Space,Oblique Sinus,Transverse Sinus

The Pericardial Space, Oblique Sinus, Transverse Sinus . There is an increasing need for invasive electrophysiologists to appreciate the exact anatomy of the epicardial space and the coronary veins. The location of the epicardial fat, the complementary relationship with the main cardiac veins, and the location of sensitive structures (arteries, phrenic nerve, esophagus) have become required knowledge for electrophysiologists, and accessing the epicardial space with this thorough knowledge of the pericardial sinuses and recesses is essential to allow radiographic correlation during catheter manipulation. In this review, we briefly describe the anatomy of the pericardial space and then discuss the specific correlation for the invasive electrophysiologist, highlighting epicardial access, catheter navigation, and avoidance of collateral injury with specific attention to the important recesses of the pericardial space, their regional anatomy, and radiographic correlation when navigating catheters to these locations. We also discuss the anatomy of the main cardiac veins in the context of catheter mapping and ablation of the epicardial substrate through the venous system and without subxiphoid pericardial access. In Part I of this two‐part series, we discuss the regional anatomy of the pericardial space, oblique sinus, and transverse sinus. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1421‐1426, December 2010)     

In vivo evaluation of virtual electrode mapping and ablation utilizing a direct endocardial visualization ablation catheter

Visualization Catheter with Virtual Electrode Ablation. Background: Radiofrequency (RF) ablation utilizing direct endocardial visualization (DEV) requires a “virtual electrode” to deliver RF energy while preserving visualization. This study aimed to: (1) examine the virtual electrode RF ablation efficacy; (2) determine the optimal power and duration settings; and (3) evaluate the utility of virtual electrode unipolar electrograms. Methods and Results: The DEV catheter lesions were compared to lesions formed using a 3.5 mm open irrigated tip catheter within the right atria of 12 sheep. Generator power settings for DEV were titrated from 12W, 14W and 16W for 20, 30 and 40 seconds duration with 25 mL/min saline irrigation. Standard irrigated tip catheter settings of 30W, 50°C for 30 seconds and 30 mL/min were used. The DEV lesions were significantly greater in surface area and both major and minor axes compared to irrigated tip lesions (surface area 19.43 ± 9.09 vs 10.88 ± 4.72 mm, P<0.01) with no difference in transmurality (93/94 vs 46/47) or depth (1.86 ± 0.75 vs 1.85 ± 0.57 mm). Absolute electrogram amplitude reduction was greater for DEV lesions (1.89 ± 1.31 vs 1.49 ± 0.78 mV, P = 0.04), but no difference in percentage reduction. Pre‐ablation pacing thresholds were not different between DEV (0.79 ± 0.36 mA) and irrigated tip (0.73 ± 0.25 mA) lesions. There were no complications noted during ablation with either catheter. Conclusions: Virtual electrode ablation consistently created wider lesions at lower power compared to irrigated tip ablation. Virtual electrode electrograms showed a comparable pacing and sensing efficacy in detecting local myocardial electrophysiological changes. (J Cardiovasc Electrophysiol, Vol. 23, pp. 88‐95, January 2012)     

Correlative Anatomy for the Electrophysiologist,Part II: Cardiac Ganglia,Phrenic Nerve,Coronary Venous System

Cardiac Ganglia, Phrenic Nerve, Coronary Venous System . There is an increasing need for invasive electrophysiologists to appreciate the exact anatomy of the epicardial space and the coronary veins. The location of the epicardial fat, the complementary relationship with the main cardiac veins, and the location of sensitive structures (arteries, phrenic nerve, esophagus) have become required knowledge for electrophysiologists, and accessing the epicardial space with this thorough knowledge of the pericardial sinuses and recesses is essential to allow radiographic correlation during catheter manipulation. In this review, we briefly describe the anatomy of the pericardial space and then discuss the specific correlation for the invasive electrophysiologist, highlighting epicardial access, catheter navigation, and avoidance of collateral injury, with specific attention to the important recesses of the pericardial space, their regional anatomy, and radiographic correlation when navigating catheters to these locations. We also discuss the anatomy of the main cardiac veins in the context of catheter mapping and ablation of the epicardial substrate through the venous system and without subxiphoid pericardial access. In part II of this series we discuss the detailed regional anatomy of the cardiac ganglia, phrenic nerve, and coronary venous system. (J Cardiovasc Electrophysiol, Vol. 22, pp. 104‐110, January 2011)     

Mitral isthmus ablation with and without temporary spot occlusion of the coronary sinus: a randomized clinical comparison of acute outcomes

Role of CS Occlusion for Mitral Isthmus Ablation . Objective: To evaluate the safety and outcomes of mitral isthmus (MI) linear ablation with temporary spot occlusion of the coronary sinus (CS). Background: CS blood flow cools local tissue precluding transmurality and bidirectional block across MI lesion. Methods: In a randomized, controlled trial (CS‐occlusion = 20, Control = 22), MI ablation was performed during continuous CS pacing to monitor the moment of block. CS was occluded at the ablation site using 1 cm spherical balloon, Swan–Ganz catheter with angiographic confirmation. Ablation was started at posterior mitral annulus and continued up to left inferior pulmonary vein (LIPV) ostium using an irrigated‐tip catheter. If block was achieved, balloon was deflated and linear block confirmed. If not, additional ablation was performed epicardially (power ≤25 W). Ablation was abandoned after ～30 minutes, if block was not achieved. Results: CS occlusion (mean duration ?27 ± 9 minutes) was achieved in all cases. Complete MI block was achieved in 13/20 (65%) and 15/22 (68%) patients in the CS‐occlusion and control arms, respectively, P = 0.76. Block was achieved with significantly small number (0.5 ± 0.8 vs 1.9 ± 1.1, P = 0.0008) and duration (1.2 ± 1.7 vs 4.2 ± 3.5 minutes, P = 0.009) of epicardial radiofrequency (RF) applications and significantly lower amount of epicardial energy (1.3 ± 2.4 vs 6.3 ± 5.7 kJ, P = 0.006) in the CS‐occlusion versus control arm, respectively. There was no difference in total RF (22 ± 9 vs 23 ± 11 minutes, P = 0.76), procedural (36 ± 16 vs 39 ± 20 minutes, P = 0.57), and fluoroscopic (13 ± 7 vs 15 ± 10 minutes, P = 0.46) durations for MI ablation between the 2 arms. Clinically uneventful CS dissection occurred in 1 patient Conclusions: Temporary spot occlusion of CS is safe and significantly reduces the requirement of epicardial ablation to achieve MI block. It does not improve overall procedural success rate and procedural duration. Tissue cooling by CS blood flow is just one of the several challenges in MI ablation. (J Cardiovasc Electrophysiol, Vol. 23, pp. 489‐496, May 2012)     

Initial Experience with a Novel Focused Ultrasound Ablation System for Ring Ablation Outside the Pulmonary Vein

Introduction: Atrial fibrillation has been shown to initiate from triggers within pulmonary veins. Several studies have documented that electrical isolation of those triggers can lead to maintenance of sinus rhythm. The complication of pulmonary vein stenosis has limited the utility of delivering ablation energy within the pulmonary vein. We utilize a focused ultrasound catheter ablation system for delivery of transmural ablation lines proximal to the pulmonary vein ostium. Methods: Nine dogs (weight 30–39 kg) were anesthetized and ventilated. Through a transseptal approach, pulmonary veins were engaged with the focused balloon ultrasound catheter. Ultrasound power was delivered at 40 acoustic watts outside the pulmonary vein ostium, focused 2 mm off the balloon surface, with a depth of approximately 6 mm, for 30–120 seconds. Following ablation, lesions were histopathologically analyzed. Results: Of nine animals studied, fourteen pulmonary veins were ablated. We found successful delivery of near circumferential and transmural ablation lines in 6/14 pulmonary veins. In each of the six circumferential ablations, successful alignment of the ultrasound transducer along the longitudinal axis of the parabolic balloon occurred. The final four ablations were conducted with an enhanced catheter design that assured axial alignment. Of these ablations, all four were circumferential. The remaining 8 pulmonary veins had incomplete delivery of lesions. In each of these veins the ultrasound transducer was misaligned with the balloon axis when therapy was delivered. Conclusion: Focused ultrasound ablation is a new means of performing pulmonary vein isolation. This method provides delivery of lesions outside the vein, limiting the risk of pulmonary vein stenosis for the treatment of atrial fibrillation.     

Substrate Characterization and Catheter Ablation for Monomorphic Ventricular Tachycardia in Patients With Apical Hypertrophic Cardiomyopathy

VT Ablation in Apical Hypertrophic Cardiomyopathy . Introduction: Monomorphic ventricular tachycardia (VT) is uncommon in apical hypertrophic cardiomyopathy (HCM). The purpose of this study was to define the substrate and role of catheter ablation for VT in apical HCM. Methods: Four patients with apical HCM and frequent, drug refractory VT (mean age of 46 ± 10 years, left ventricular [LV] ejection fraction; 54 ± 14%) underwent catheter ablation with the use of electroanatomic mapping. Endocardial mapping was performed in 4 patients and 3 patients underwent epicardial mapping. Results: In 3 patients, VT was related to areas of scar in the apical LV where maximal apical wall thickness ranged from 14.5 to 17.8 mm, and 2 patients had apical aneurysms. Endocardial and epicardial substrate mapping revealed low voltage (<1.5 mV) scar in both endocardial and epicardial LV in 2 and only in the epicardium in 1 patient. Inducible VT was abolished with a combination of endocardial and epicardial ablation in 2 patients, but was ineffective in the third patient who had intramural reentry that required transcoronary ethanol ablation of an obtuse marginal vessel for abolition. The fourth patient had focal nonsustained repetitive VT from right ventricular outflow tract (RVOT), consistent with idiopathic RVOT‐VT, that was successfully ablated. During follow‐ups of 3‐9 months, all patients remained free from VT. Conclusion: Monomorphic VT in apical HCM can be due to endocardial, epicardial or intramural reentry in areas of apical scar. Epicardial ablation or transcoronary alcohol ablation is required in some cases. (J Cardiovasc Electrophysiol, Vol. 22, pp. 41‐48, January 2011)     

Comparison of epicardial cryoablation and irrigated radiofrequency ablation in a Swine infarct model

Epicardial Cryoablation in Swine. Introduction: Cryoablation is an alternative to radiofrequency (RF) energy used in some ablation procedures. Its role and effectiveness compared to irrigated RF in epicardial tissue and epicardial substrates is not yet fully established. Methods and Results: Using a swine chronic infarct model, we compared RF lesions produced by an open‐irrigated 3.5 mm tip catheter with those produced by an 8 mm tip cryocatheter in epicardial infarct border zone, epicardial normal tissue, and normal endocardium. In the infarct border zone, cryolesions were larger than RF lesions in maximum diameter (9.3 ± 2.9 mm vs 6.2 ± 2 mm, P < 0.001) and volume (171.7 ± 173.1 mm³ vs 77 ± 53.5 mm³, P = 0.021). In normal epicardial tissue, cryolesions were larger in maximum diameter (11.2 ± 4.3 mm vs 7.7 ± 3.1 mm, P = 0.012), depth (5.8 ± 1.6 mm vs 4.7 ± 1.4 mm, P = 0.034), and volume (274.7 ± 242.2 mm³ vs 112 ± 102.9 mm³, P = 0.002). In normal endocardium, no significant differences were found. Conclusions: Epicardial cryoablation with an 8 mm tip cryocatheter led to larger lesion volume in infarcted myocardium compared to a 3.5 mm irrigated RF catheter. This is likely related to a combination of cryoadherence, more efficient energy delivery with horizontal orientation, and lack of warming by circulating blood. Cryoablation merits further investigation as a modality for treating ventricular tachycardia of epicardial origin in humans. (J Cardiovasc Electrophysiol, Vol. 23, pp. 1016‐1023, September 2012)     

Ablation efficacy and electrical morphology of a novel 18-hole open-irrigated catheter

Ablation Efficacy and Electrical Morphology. Introduction: The 6‐hole open‐irrigated catheter (SHOI) is increasingly used in radiofrequency (RF) ablation of arrhythmias. However, deep transmural lesions are not always achieved, and volume overload caused by irrigated ablation is another problem that should be concerned. The purpose of this study was to analyze and compare the ablation effect and electrical morphology between a novel 18‐hole open‐irrigated catheter (EHOI) and SHOI. Methods and Results: The heart was exposed through a median sternotomy in 12 anesthetized dogs, and the chest cavity was filled with heparinized saline. Bipolar contact pericardial electrograms of both catheters were recorded. Lesions were created under all permutations of the following conditions: RF energy 30 and 40 W for 60 seconds, contact force at 10, 30, and 50 g, electrode orientation horizontal to the tissue, irrigation rate 10 mL/min for EHOI and 17 mL/min for SHOI. The EHOI created deeper lesions than SHOI (5.77 ± 1.37 mm vs 4.98 ± 1.22 mm at power of 30 W, P < 0.05; 7.16 ± 1.15 mm vs 6.02 ± 1.04 mm at power of 40 W, P < 0.01), and there was a trend of larger lesion volume for EHOI (312 ± 141 mm³ vs 259 ± 108 mm³ at power of 30 W, 536 ± 200 mm³ vs 451 ± 180 mm³ at power of 40 W, P > 0.05). No significant difference in electrogram morphology between 2 catheters was detected. Conclusions: The mapping electrograms of EHOI and SHOI were not significantly different. Compared with SHOI, EHOI more effectively produced deeper lesions at a lower rate of irrigation perfusion. (J Cardiovasc Electrophysiol, Vol. 22, pp. 691‐697, June 2011)     

An In Vitro Assessment of Acoustic Radiation Force Impulse Imaging for Visualizing Cardiac Radiofrequency Ablation Lesions

Ablation Lesion Quantification with ARFI Imaging . Introduction: Lesion placement and transmurality are critical factors in the success of cardiac transcatheter radiofrequency ablation (RFA) treatments for supraventricular arrhythmias. This study investigated the capabilities of catheter transducer based acoustic radiation force impulse (ARFI) ultrasound imaging for quantifying ablation lesion dimensions. Methods and Results: RFA lesions were created in vitro in porcine ventricular myocardium and imaged with an intracardiac ultrasound catheter transducer capable of acquiring spatially registered B‐mode and ARFI images. The myocardium was sliced along the imaging plane and photographed. The maximum ARFI‐induced displacement images of the lesion were normalized and spatially registered with the photograph by matching the surfaces of the tissue in the B‐mode and photographic images. The lesion dimensions determined by a manual segmentation of the photographed lesion based on the visible discoloration of the tissue were compared to automatic segmentations of the ARFI image using 2 different calculated thresholds. ARFI imaging accurately localized and sized the lesions within the myocardium. Differences in the maximum lateral and axial dimensions were statistically below 2 mm and 1 mm, respectively, for the 2 thresholding methods, with mean percent overlap of 68.7 ± 5.21% and 66.3 ± 8.4% for the 2 thresholds used. Conclusion: ARFI imaging is capable of visualizing myocardial RFA lesion dimensions to within 2 mm in vitro. Visualizing lesions during transcatheter cardiac ablation procedures could improve the success of the treatment by imaging lesion line discontinuity and potentially reducing the required number of ablation lesions and procedure time. (J Cardiovasc Electrophysiol, Vol. 21, pp. 557‐563, May 2010)     

Is There a Potential Benefit to Increased Irrigation Channels During Radiofrequency Ablation? Results From a Two‐Center Prospective Randomized Study

Potential Benefit to Increased Irrigation Channels During Radiofrequency Ablation. Introduction: Open irrigation during radiofrequency (RF) application allows a higher power delivery in the setting of temperature‐controlled ablation, without causing blood clots. This study sought to evaluate the clinical value of the additional 6 supplementary channels at the proximal catheter tip compared to a standard irrigated RF catheter with 6 conventional channels present at the distal tip only. Methods and Results: Ninety‐five consecutive patients were prospectively randomized to cavotricuspid isthmus ablation using an 3.5 mm tip ablation catheter with 6 distal irrigation channels (6C; 48 patients) or an 4 mm tip ablation catheter with 12 irrigation channels (12C; 47 patients) disposed at the distal (6 channels) and proximal (6 additional channels) catheter tip. There was no significant difference between the 12C and the 6C irrigated‐tip catheter concerning the total procedural duration, the RF duration, the fluoroscopic duration, and the amount of irrigation. Conversely, there were significantly more patients who experienced at least one steam pop while using the 12C as compared to the 6C irrigated‐tip catheter (0% vs 13%, respectively, P = 0.018). Conclusion: The addition of proximal irrigation holes at the catheter tip do not facilitate lesion formation during RF ablation, but significantly increases the risk of steam pop. This is probably the consequence of an increase distortion of the temperature feedback . (J Cardiovasc Electrophysiol, Vol. 22, pp. 516‐520 May 2011)     

Cooled needle catheter ablation creates deeper and wider lesions than irrigated tip catheter ablation

OBJECTIVES: To design and test a catheter that could create deeper ablation lesions. BACKGROUND: Endocardial radiofrequency (RF) ablation is unable to reliably create transmural ventricular lesions. We designed an intramural needle ablation catheter with an internally cooled 1.1-mm diameter straight needle that could be advanced up to 14 mm into the myocardium. The prototype catheter was compared with an irrigated tip ablation catheter. METHODS: Ablation lesions were created under general anesthesia in 14 male sheep (weight 44 +/- 7.3 kg) with fluoroscopic guidance. Each of the catheters was used to create two ablation lesions at randomly allocated positions within the left ventricle. The irrigation rate, target temperature, and maximum power were: 20 mL/min, 85 degrees C, 50 W for the intramural needle catheter and 20 mL/min, 50 degrees C, 50 W for the irrigated tip catheter, respectively. All ablations were performed for 2 minutes. After the last ablation, blue tetrazolium (12.5 mg/kg) was infused intravenously. The heart was removed via a left thoracotomy after monitoring the sheep for one hour. RESULTS: There was no evidence of cardiac tamponade in any sheep. The intramural needle catheter lesions were significantly wider (10.9 +/- 2.8 mm vs 10.1 +/- 2.4 mm, P = 0.01), deeper (9.6 +/- 2.0 mm vs 7.0 +/- 1.3 mm, P = 0.01), and more likely to be transmural (38% vs 0%, P = 0.03). CONCLUSIONS: Cooled intramural needle ablation creates lesions that are significantly deeper and wider than endocardial RF ablation using an irrigated tip catheter in sheep hearts. This technology may be useful in treating ventricular tachycardia resistant to conventional ablation techniques.     

The Effect of Radiofrequency Catheter Ablation on Myocardial Creatine Kinase Activity

RF Ablation and Creatine Kinase. Introduction: The primary mechanism of myocardial injury during radiofrequency (RF) catheter ablation in the heart is presumed to be thermal. Creatine Kinase has been measured in serum to assess the volume of myocardial injury after ablation. However, its thermal inactivation by RF ablation could lead to underestimation of the true volume of injury. Methods and Results: Serial RF lesions were created in 10 canine left ventricles in vivo, and serial serum Creatine Kinase activities were measured and compared to lesion volume. To assess the stability of myocardial Creatine Kinase during RF catheter ablation, 29 RF ablations were made on the epicardial surface of porcine left ventricle in vivo and a 2-mm core biopsy was rapidly removed. The cores were rapidly frozen, sectioned longitudinally in 1-mm slices, and homogenized in 0.3 M Tris buffer solution containing EDTA and dithiothreitol for subsequent analysis of Creatine Kinase activity. An additional 19 tissue cores from RF lesions were stained and used to determine mean lesion depth. Normal tissue biopsies were exposed to 60 seconds of hyperthermia (37° to 85°C, n = 190), or high-density RF current at 50X (0 to 100 mA/mm², n = 50), and tissue Creatine Kinase activity was measured. There was no evidence of Creatine Kinase washout within the first 2 hours, and peak values were measured 5 to 7 hours postablation. Tissue Creatine Kinase activity in the first mm depth of RF lesions averaged 10% of control values and increased over the first 5 mm of lesion depth. The mean Creatine Kinase activity within the hemisphere of ablated myocardium was calculated to be 31% of control. Creatine Kinase activity declined significantly at temperatures above 65°C, but no difference in tissue Creatine Kinase activity was observed among differing levels of RF current exposure in the absence of significant heating. Conclusions: Creatine Kinase activity in myocardial tissue is significantly diminished within the RF lesion. Creatine Kinase activity is not stable at temperatures above 65°C, which are routinely achieved within the central zone of RF ablation, and is unaffected by RF current in the absence of hyperthermia. Measurements of serum Creatine Kinase activity after RF catheter ablation may significantly underestimate the volume of myocardial injury.     

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)     

Epicardial mapping and radiofrequency catheter ablation of ischemic ventricular tachycardia using a three-dimensional nonfluoroscopic mapping system

Endocardial radiofrequency catheter ablation of ischemic left ventricular tachycardia has been of variable success due to multiple factors. Two such factors include the location of the reentrant circuit in the deep myocardium or on the epicardial surface and the inherent limitations of fluoroscopy as a guide for target localization. We report a patient in whom successful epicardial mapping and radiofrequency catheter ablation of an ischemic left ventricular tachycardia was performed using pericardial access and the CARTO electroanatomic mapping system.