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.     

Direct visualization of epicardial structures and ablation utilizing a visually guided laser balloon catheter: preliminary findings

Epicardial Laser Balloon Ablation. Background: Intrapericardial mapping and ablation can be utilized to target epicardial arrhythmic circuits. Current epicardial ablation strategies are associated with risk of damage to adjacent structures, including the coronary vasculature and phrenic nerves. Objectives: The purpose of this study was to evaluate the feasibility of an investigational, visually guided laser balloon catheter for manipulation within the pericardial space, visualization of epicardial structures, and delivery of laser ablation lesions to the ventricular myocardium. Methods: Pericardial access was obtained in 4 anesthetized swine by subxyphoid puncture. The laser balloon catheter was introduced into the pericardial space via a deflectable sheath, and was manipulated to predefined regions in all animals. Visually guided laser ablation was performed on the ventricular myocardium, with post mortem examination of lesion size and depth. Results: The laser ablation catheter could be manipulated to all targeted regions in all animals. Associated structures, including epicardial coronary arteries and veins as well as an endocardial catheter in the left atrial appendage, were easily visualized. A total of 9 laser energy applications at varying power/time settings were performed. Ablation utilizing moderate (7–8.5 W) power produced relatively uniform lesions (diameter 5–12 mm, depth 6–9 mm), while high (14 W) power produced a visible “steam pop” with a large, hemorrhagic lesion (22 × 11 × 11 mm). Conclusions: The investigational laser balloon catheter can be manipulated within the epicardial space, allowing for direct visualization of surrounding structures during ablation. Titration of laser power can be utilized to create moderate‐sized ablation lesions while avoiding steam pops . (J Cardiovasc Electrophysiol, Vol. 22, pp. 808‐812, July 2011)     

Chemical ablation by subendocardial injection of ethanol via catheter--preliminary results in the pig heart.

This study was set up to discover how a subendocardial application of ethanol administered via a catheter would affect an animal model. A 7 F bipolar catheter with a lumen, through which a 2 mm needle was inserted, was placed in the left ventricle of 11 pigs. Altogether, 33 subendocardial injections into the left ventricular myocardium were performed under fluoroscopic control using a mixture of 0.5-1.5 ml ethanol and 0.5-1 ml iopamidol as contrast medium. The mixtures were injected into the apical, lateral and septal walls of the left ventricle. After 25 days, the hearts were removed and the lesions examined pathologically. The calculated volume of the lesions was about 60 mm3, the area in projection to the endocardium about 35 mm2, the depth relative to the endocardium about 1.5 mm and the maximum diameter about 8 mm. Perforation of the myocardial wall by pericardial injection occurred twice without further complications. Subendocardial application of concentrated ethanol by catheter caused a controlled local necrosis. This technique may become a new approach with which to treat ventricular tachycardia by chemical ablation.     

Laser ablation of normal and diseased human ventricle

The feasibility and safety of laser photoablation in patients with ventricular tachycardia (VT) and accessory pathways are currently being examined. We studied the qualitative and quantitative effects of argon laser radiation on normal and diseased human ventricle to determine the relationship between the size of tissue lesion and delivered energy. Twenty-nine human ventricle segments (normal ventricle = 10; diseased ventricle = 19) were excised from patients during mapping-guided subendocardial resection for VT (seven patients), mitral valve replacement (five patients), or immediately at autopsy (three patients). Lasing was performed with a 15 W argon laser coupled to a 300 micron optical fiber. Incremental laser discharges from 10 to 1000 J were delivered in air and saline with the optical fiber 5 mm from the endocardial surface. Gross and microscopic damage was quantified and correlated with laser discharges at low (10 to 100 J), intermediate (101 to 300 J), and high (greater than 300 J) energies. Histologic examination of laser-induced lesions in both normal and diseased human ventricle in either medium showed focal thermal injury with crater formation, vacuolization, and coagulation necrosis of endocardium and myocardium. In normal ventricle, mean lesion diameter and depth in air increased with increasing energies up to 300 J. Over 300 J, tissue perforation was frequently observed. In saline, the mean lesion depth was significantly reduced (p less than 0.02) at comparable energies. In diseased ventricle, mean lesion diameter and depth in air and saline also increased with increasing laser discharge energies up to 300 J. Higher energy laser discharges did not increase mean lesion dimensions or result in tissue perforation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Application of ultrasound energy for intracardiac ablation of arrhythmias

Ultrasound is a potential energy source for cardiac ablation.Small ultrasound applicators were tested for their ability tocreate lesions in cardiac tissue. Ultrasound applicators weredesigned, constructed and tested in canine cardiac tissue indegassed normal saline, and both in vitro and in vivo, lesionswere produced by using transducers with frequencies of about10 MHz. Lesion depth increased with longer duration of energydelivery from 15–60 s, and there was a linear relationshipbetween increasing power and depth of lesions. Seven in vivoexperiments in open-chest dogs were performed, and the ultrasoundtransducers were mounted on the tip of 7-French angiographiccatheters. On the epicardium the maximum lesion depth was 9mm. When the transducer was inserted into the left ventricle,lesions of 8.7 ± 2.9 mm (n=4) were produced. It is concludedthat an ultrasound transducer mounted on a cardiac cathetercan produce lesions that may be useful for ablation of cardiacarrhythmias.     

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.     

Localizing and quantifying ablation lesions in the left ventricle by myocardial contrast echocardiography

INTRODUCTION: The inability to determine the extent and intramural depth of ablation lesions can hamper the success of catheter ablation. The study tested the feasibility of differentiating radiofrequency ablation lesions from normal myocardium and quantifying their dimensions by myocardial contrast echocardiography (MCE). METHODS AND RESULTS: In 11 normal dogs, we created 14 focal and 4 linear lesions at different left ventricular sites. MCE was performed both before and after ablation by using an intracardiac echocardiography catheter (9 MHz) and infusing contrast microbubbles through the left coronary artery. We initially used two-dimensional MCE to image focal lesions and subsequently three-dimensional MCE to image linear lesions. An independent observer examined the lesion pathology. We found that intracardiac echocardiography alone could not delineate lesion dimensions. However, after ablation, MCE localized the lesions as well-defined, low-contrast areas within the normally opacified myocardium. Lesion dimensions by MCE immediately after ablation and 30 minutes later were similar. In 12 focal lesions, the average maximum depth (5.55 +/- 1.38 mm) and average maximum diameter (10.38 +/- 2.09 mm) by MCE were in excellent agreement with the pathologic depth (5.20 +/- 1.45 mm) and diameter (10.61 +/- 1.67 mm). Two focal lesions could not be detected by MCE and later were found to be superficial. Three-dimensional MCE correctly reconstructed the extent and shape of linear lesions compared to pathology (length: 18.7 +/- 5.7 vs 18.5 +/- 5.6 mm; maximum longitudinal cross-sectional area: 81.2 +/- 9.6 vs 76.0 +/- 10.3 mm2). CONCLUSION: MCE accurately localized and quantified radiofrequency ablation lesions in the normal left ventricle. This new application of MCE may advance ablation for managing ventricular arrhythmias that involve intramural or epicardial regions by providing instantaneous anatomic feedback on the effects of ablation during catheterization.     

Use of harmonic echocardiographic contrast imaging and intravenous bolus of Levovist for evaluation of the left ventricle

Harmonic imaging is a new imaging modality using nonlinear acoustic response, which is particularly sensitive for the particles of contrast agents. Our study was designed to compare the potential of harmonic echocardiographic imaging of the left ventricle using a contrast agent, Levovist to improve the detection of endocardium in patients with suboptimal image quality. 40 patients were studied using standard transthoracic apical views of the left ventricle patients using fundamental frequency and second harmonic frequency after and intravenous injection of 2.5 g Levovist. The quality of endocardial delineation in 16 standard segments was scored from 0 to 2. Endocardial visualization index was calculated as a mean of the scores to express overall diagnostic quality. Harmonic imaging with contrast significantly improved left ventricular endocardial border detection (endocardial visualization index at baseline 1.24 +/- 0.41, with contrast 1.63 +/- 0.38; p < 0.001). The improvement was qualitatively observed in all parts of the left ventricle: in apex (2.4 +/- 0.8), in the middle part (2.5 +/- 0.9) and slightly less in the basal part (2.1 +/- 1.1) as scored on a 0-3 scale. The number of invisible segments decreased from 124 (fundamental) to 50 in contrast harmonic mode. The persistence of the contrast enhancement, prolonged in harmonic as compared to fundamental imaging (284 +/- 136s vs 117 +/- 87s; p < 0.001) enabled convenient recording of all necessary views. Harmonic imaging after an intravenous injection of Levovist significantly improves the visualization of left ventricular endocardial border. Prolonged contrast effect after a single bolus enhances the pertinence of the method in clinical practice.     

In Vitro and In Vivo Evaluation of the Thermal Patterns and Lesions of Catheter Ablation with a Microwave Monopole Antenna

BACKGROUND: Radiofrequency (RF) catheter ablation is an effective treatment for supraventricular tachycardia. The effectiveness of the technique is at times limited by the small lesion size produced by RF energy delivery. Previous reports have indicated that microwave energy is capable of producing a larger volume of heated tissue than radiofrequency energy, raising the possibility that microwave energy may offer a potential alternative energy source to radiofrequency for the substrate ablation of certain arrhythmias such as ventricular tachycardia or atrial flutter. METHODS: The present study evaluated the thermal profiles of a monopole microwave antenna delivering energy at 2.45 GHz frequency in a phantom tissue-equivalent material with dielectric and thermal properties similar to myocardium. In addition, microwave catheter ablations were performed in vivo in the ventricles of goats prior to the examination of the lesions. RESULTS: The measured thermal profiles in the phantom revealed that the antenna is capable of producing heating to a temperature associated with myocardial necrosis to a controllable depth that can be more than 8 mm, while the endocardial temperature is maintained relatively low. The ablation volume is significantly reduced but is still effective when there is only a partial contact between the antenna and the tissue surface. In vivo studies on goat models confirmed that the monopole antenna can produce a deep transmural lesion in the left ventricle without causing coagulation or charring on the endocardial surface.     

Catheter ablation for successful management of left posterior fascicular tachycardia: an approach guided by recording of fascicular potentials.

OBJECTIVE: To assess whether catheter ablation of fascicular tachycardia can be facilitated by the recording of sharp deflections arising from the mid-septum---inferior apical septum of the left ventricle. PATIENTS AND METHODS: Seven consecutive patients (mean age 29 (range 16-43) years) with ventricular tachycardia originating from the left posterior fascicle underwent electrophysiology study and detailed mapping of endocardial activation. Selection of ablation sites in the last five patients was based on the recording, during left posterior fascicular tachycardia and sinus rhythm, of a discrete potential preceding the earliest ventricular electrogram, which was thought to represent conduction through the posterior fascicle. RESULTS: Patients were treated with low energy direct current or radiofrequency current ablation. The median fluoroscopy and procedure times were 23 (range 6-42) min and 110 (range 50-176) min, respectively. In a follow up period of 4 to 16 months, six patients were asymptomatic and one had minor symptoms. No patient had any change in intraventricular conduction. Similar potentials were also recorded from the left posterobasal septum in three of eight patients who underwent catheter ablation of left free wall accessory pathways. CONCLUSION: Fascicular potentials can be reproducibly recorded in left posterior fascicular tachycardia and may serve as a reliable marker for successful ablation procedures. The relation of these potentials with the substrate of the tachycardia, however, remains obscure.     

Thrombus apposition on catheter ablation injuries

64 ablation catheter-induced injuries were studied macroscopicallyand microscopically to determine the incidence of endocardialthrombus formation. Ablation was performed in 16 mongrel dogs,7 days before necropsy, 16 endocardial necroses were locatedin the right atrioventricular (AV) junction, 16 in the non-coronarycusp of the aortic valve or the subaortic valve area, 16 inthe right and 16 in the left ventricle. Cathodal discharge at the distal electrode was employed againstan external anodal plate for ventricular ablation. Necrosesin the right AV junction and in the aortic area where the resultof transseptal His bundle ablation. Energies ranged from 100–360J. Pathologic examination was performed 1 week after ablation.13 thrombi were observed attached to the endocardial necrosisarea, of sizes ranging from 1–25 mm diameter (mean 6.9mm). Six thrombi were found in the septal valve of the tricuspidvalve, two in the aortic valve, two in the subaortic region,and three related to ventricular necroses. We conclude that the incidence of thrombosis is 20% in ablationinjuries, the majority, 77%, having a diameter 10 mm. No correlationwas found between thrombus formation and delivered energy orcatheter polarity.     

Percutaneous angioscopic evaluation of luminal changes induced by excimer laser angioplasty.

Angioscopy has been shown to provide more detailed information on lesion morphology before and after interventional procedures than angiography. Therefore to evaluate the effects of laser angioplasty, angioscopy was performed in five patients with peripheral or coronary vascular disease who underwent excimer laser angioplasty. The excimer laser was operated at 308 nm, 135 nsec, 25 Hz, and 40 to 60 mjoules/mm2 and was coupled into multifiber wire-guided catheters of 1.4 to 2.0 mm diameter for coronary lesions and into catheters of 2.2 mm diameter for peripheral lesions. There were three coronary (one left anterior descending, one circumflex, one right coronary artery) and two peripheral (one common iliac artery, one superficial femoral artery) lesions. Angioscopy was successfully performed before and after laser ablation without any complications in all five lesions. The characteristics of angioscopic findings after excimer laser angioplasty consisted of flaps, fractures of plaques, and abundant tissue remnants. There was no apparent thermal injury. Recanalized channels were small and irregular. These results indicate that (1) angioscopy is effective and safe for evaluation of lesion morphology after laser angioplasty; (2) laser ablation does not result in thermal injury; and (3) irregular channels after recanalization and abundant tissue remnants may explain the suboptimal results after laser angioplasty.     

左心室室壁瘤所致心律失常的6例外科治疗

目的:对左心室室壁瘤合并心律失常的患者进行左心室室壁瘤切除,同时行射频消融心脏手术的结果资料进行临床分析,评价其手术疗效。方法:入选我院2008年1月至2011年5月间,接受左心室室壁瘤合并心律失常的患者进行心脏手术6例。心律失常均为药物无法控制的顽固性心律失常,心电图术前证实。结果:6例患者手术后均痊愈出院,治愈率100%。单纯行左心室室壁瘤切除的同时,2例施行左心室室壁瘤颈部内膜射频消融术,4例施行左心室室壁瘤颈部外膜射频消融术。体外循环时间(100.7±48.6)min,循环阻断时间(67.9±36.1)min。本组病例的术前与术后左心室射血分数分别为(35.3±10.2)%与(51.6±10.4)%,术前和术后相比,差异有统计学意义(P<0.05);术前和术后的左心室舒张末径大小分别为(60.5±4.5)mm与(51.2±5.5)mm,术前和术后相比差异有统计学意义(P<0.01);呼吸机辅助时间为(1.2±0.4)d,ICU时间为(1.5±0.8)d,住院时间为(23.3±10.2)d。心电图恢复窦性心律,无各种心律失常出现。随访5例,随访时间3～14个月,治疗效果良好,心电图显示为窦性心律,无心律失常复发,心脏超声示心功能正常,心功能均达Ⅰ～Ⅱ级,生活质量较术前明显提高。结论:左心室室壁瘤患者进行左心室室壁瘤切除,同时进行射频消融术,使患者摆脱心脏疾病症状,这种心脏手术是安全可行的。     

Electrophysiologic effects of selective right versus left atrial linear lesions in a canine model of chronic atrial fibrillation

INTRODUCTION: Long linear lesions have been shown to eliminate atrial fibrillation in animal models, but little is known about the electrophysiologic response in one atrium to lesions in the contralateral atrium. METHODS AND RESULTS: Twelve dogs with chronic atrial fibrillation were randomized to either right atrial ablation (n = 4), left atrial ablation first (n = 4), or a sham procedure (n = 4). Simultaneous biatrial endocardial mapping was performed before and after three linear lesions were applied at specific points in either atrium, using an expandable ablation catheter. Atrial fibrillation was reinducible after single atrial ablation in each dog and no longer inducible after biatrial ablation in five dogs. At baseline, the mean atrial fibrillation cycle length was longer on the trabeculated (117+/-15 msec) compared with the smooth right (101+/-16 msec) or left atrium (88+/-10 msec; P < 0.01). Single right and left atrial ablation caused a significant cycle length increase in the ablated atrium. Left atrial ablation increased the cycle length on both the trabeculated (121+/-18 msec vs 137+/-11 msec; P < 0.05) and smooth right atrium (108+/-12 msec vs 124+/-9 msec; P < 0.05). Right atrial ablation, however, had no significant effect on left atrial fibrillation cycle length (82+/-8 msec vs 86+/-7 msec). CONCLUSION: Left atrial linear lesions affect right atrial endocardial activation, whereas right atrial lesions do not affect left atrial activation in a canine model of atrial fibrillation. These findings suggest that the left atrium is the driver during chronic atrial fibrillation in this animal model and may explain the limited success of right atrial ablation alone in human atrial fibrillation.     

Epicardial ablation with cooled tip catheter close to the coronary arteries is effective and safe in the porcine heart if the ventricular potential is being monitored in the epicardium and endocardium.

BACKGROUND: Transthoracic epicardial ablation can be an alternative to conventional treatment for critical pathways of ventricular tachycardia located in the epicardium. However, the usefulness and safety of epicardial ablation close to the coronary arteries (CA) is not clear. The purpose of the present experimental animal study was to analyze the efficacy and safety of epicardial radiofrequency (RF) ablation close to the CA. METHODS AND RESULTS: Of the left ventricle-epicardium ablated sites, 35 lesions (20 with cooling and 15 without cooling) were close to the CA (left anterior descending artery < or = 15 mm) and 33 lesions (23 with cooling and 10 without cooling) were further from the CA. For sites close to the CA, epicardial ablation was effective in 77% (15/20) with cooling and in 40% (6/15) without cooling. There was a significant difference of effective ablation between with cooling and without cooling (p < 0.05). For cooling, epicardial lesion size could be predicted by the change of endocardial ventricular potential using a basket catheter. No damage to major epicardial arteries was detected when the catheter tip was positioned 5 mm away from the CA. CONCLUSIONS: Close to the CA, RF ablation with cooling is more effective than RF without cooling and is safe if the ablation sites are located 5 mm away from the major CA.     

Left ventricular endocardial activation during right ventricular pacing: effect of underlying heart disease

Endocardial catheter mapping of the left ventricle was performed in 40 patients during right ventricular pacing to determine the effect of underlying myocardial infarction on endocardial activation. Group I comprised 18 patients without infarction, Group II 12 patients with inferior infarction and Group III 10 patients with anteroseptal infarction. Thirty-nine of the 40 patients had only a single left ventricular breakthrough site located on the midseptum in 33 cases, apical septum in 4 cases and basal septum in 2 cases. The earliest left ventricular local activation time during right ventricular pacing was earlier in Group III (40 +/- 11 ms) than in Group I (55 +/- 17 ms) and Group II (60 +/- 15 ms) (p less than 0.01). Total endocardial activation time was significantly longer in Group III (118 +/- 30 ms) than in Group I (76 +/- 14 ms) and Group II (72 +/- 20 ms) (p less than 0.001). The latest left ventricular site of activation during right ventricular pacing was the inferoposterior base in 14 (77%) of the 18 Group I patients, and 10 (83%) of the 12 Group II patients. The latest site of activation in Group III patients was variable. It is concluded that: left ventricular endocardial activation patterns and conduction times are influenced by the site of previous infarction. Longer total endocardial activation in Group III suggests that specialized conducting tissue in the septal and anterior walls may play an important role in left ventricular activation during right ventricular pacing.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transcatheter ablation: comparison between laser photoablation and electrode shock ablation in the dog

To characterize and compare the effects of transcatheter laser and electrical energy on endocardium, 35 laser pulses were delivered to the endocardial surfaces of isolated canine hearts, and 33 endocardial lesions were produced by the transarterial delivery of either transcatheter laser irradiation or electrical shock in closed-chest anesthetized dogs. Laser-induced lesion dimensions in vitro and in vivo increased with increased total dose of energy; however, the lesions produced in vivo were different in morphology and were significantly larger than lesions produced by equivalent doses of energy delivered in vitro (p less than .05). Endocardial lesions produced in vivo by laser at 40 and 80 J (7.9 X 5.4 X 6.6 and 7.9 X 5.1 X 7.5 mm) were comparable in gross morphology and size to those produced by electrical shock at 100 and 200 J (8.5 X 6.6 X 6.6 and 10.0 X 8.5 X 8.2 mm, respectively; p = NS), but transcatheter electrode shock produced significantly more ventricular tachycardia (p less than .003), premature ventricular beats in the 7 min after energy discharge (p less than .05), and wall motion abnormality (p less than .005). Transcatheter laser photoablation can create controlled endocardial lesions with less energy and fewer deleterious effects than transcatheter electrode shock.     

Accuracy of precordial palpation for detecting increased left ventricular volume

Objective data on the reliability of precordial palpation in detecting left ventricular enlargement are scarce. Therefore, we evaluated 41 patients by physical examination and two-dimensional echocardiography to determine the relation between the location of the apex and left ventricular end-diastolic volume. An apical impulse lateral to the mid-clavicular line or greater than 10 cm from the mid-sternal line was sensitive but not specific as an indicator of left ventricular enlargement. In patients without left ventricular hypertrophy, an apical diameter greater than 3 cm in the left lateral decubitus was sensitive (92%) and specific (91%) for an enlarged left ventricle. The positive and negative predictive values were 86% and 95% respectively. Therefore, the location of the apical impulse in relation to the mid-clavicular line or the mid-sternal line is not a reliable indicator of increased left ventricular end-diastolic volume. However, an apical impulse greater than 3 cm may be an accurate indicator of left ventricular enlargement.     

Radiofrequency Ablation of Idiopathic Left Anterior Fascicular Tachycardia

Left Anterior Fascicular Tachycardia. Introduction: A 45-year-old man with idiopathic ventricular tachycardia (VT) having a right bundle branch block configuration with right-axis deviation underwent au electrophysiologic test.
Methods and Results: Mapping demonstrated a site on the auterobasal wall of the left ventricle where there was an excellent pace map and an endocardial activation time of -20 msec, hut radiofrequency catheter ablation at this site was unsuccessful. At a nearby site, a presumed Purkinje potential preceded the QRS complex by 30 msec during VT and sinus rhythm, and catheter ablation was effective despite a poor pace map and an endocardial ventricular activation time of zero.
Conclusion: Idiopathic VT with a right bundle branch configuration and right-axis deviation may originate in the area of the left anterior fascicle. A potential presumed to represent a Purkinje potential may he more helpful than endocardial ventricular activation mapping or pace mapping in guiding ablation of this type of VT.     

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