John Hare

The Effects of Electrode‐Tissue Contact on Radiofrequency Lesion Generation

During the generation of radiofrequency (RF) lesions in the ventricular myocardium, the maintenance of adequate electrode‐tissue contact is critically important. In this study, lesion dimensions and temperature and impedance changes were evaluated while controlling electrode‐tissue contact levels (−5, 0, +1, and +3 mm) and power levels (10, 20, and 30 W). This data was used to assess the ability of impedance and temperature monitoring to provide useful information about the quality of electrode‐tissue contact. The results show that as the electrode‐tissue contact increases, so does the amount of temperature rise. Witb the electrode floating in blood (‐5 contact), the average maximum temperature increase with 20 and 30 W was only 7 ± 1 and 11 ± 2°C, respectively. At 20 and 30 W the temperature plateaued sbortly after the initiation of power application. With good electrode‐tissue contact (+1 mm or +3 mm), the temperature increase within the first 10 seconds was significantly greater than the temperature increase from baseline with poor contact (0 mm or −5 mm) and reached a maximum of 60 ± 1°C after 60 seconds of power application. As the electrode‐tissue contact increased, so did the rate and level of impedance decrease. However, the rate of impedance decrease was slower compared to the rate of temperature rise. With the electrode floating in blood, the maximum impedance decreases with 20 and 30 W were 6 ± 6 Ω and 9 ± 5 Ω, respectively. The impedances plateaued after a few seconds of power application. With the electrode in good contact, the maximum impedance decreases with 20 and 30 W were 25 ±2Ω and 20 ± 6 Ω, respectively. In these cases the rate of the impedance decrease plateaued after 40 seconds of power application.The increase in lesion diameter and depth correlate well with decreasing impedance and increasing temperature. However, lesion depth appears to correlate better with impedance than temperature. We conclude that, since the electrode‐tissue contact is not known prior to the application of power to the endocardium, in the absence of a temperature control system, the power should initially be set at a low level. The power sbould be increased slowly over 20–30 seconds, and then maintained at its final level for at least 90 seconds to allow for maximal lesion depth maturation. The power level should be lowered if the impedance drop exceeds 15 Ω.

Physics and engineering of transcatheter cardiac tissue ablation

Ablation of arrhythmogenic cardiac tissues has emerged as one of the most important advances in cardiac electrophysiology. With the introduction of transcatheter ablation, the treatment of ventricular tachycardia, Wolff-Parkinson-White syndrome and other cardiac arrhythmias has progressed from an expensive and painful surgical therapy accompanied by a long recovery period to the less expensive, less traumatic transcatheter approach. The feasibility of cardiac ablation, along with the increasing number of physicians using the technique, requires understanding of the anatomic and electrophysiologic bases of transcatheter ablation as well as the different technologies, their limitations and complications. This report provides an overview of the physical, scientific and technical aspects of cardiac ablation performed with the methods currently available and a summary of the limitations of each method and expected future technologic developments in this growing field. Emphasis is placed on radiofrequency and direct current energies, the primary methods now used. Methods such as cryoablation and laser, and microwave and chemical ablation are discussed with less detail because the method of delivering energy for these ablative procedures has not been fully developed.

Distribution of atrial electrogram types during atrial fibrillation: Effect of rapid atrial pacing and intercaval junction ablation

OBJECTIVESnThis study examined the anatomic distribution types and possible determinant of atrial electrogram types during atrial fibrillation.nnnBACKGROUNDnDifferent types of atrial electrograms during atrial fibrillation have been observed and classified, but their anatomic distribution patterns, determinants and potential usefulness in guiding future catheter ablation are unknown.nnnMETHODSnTwo animal models of atrial fibrillation were used: the sterile pericarditis model (n = 10) and the rapid atrial pacing model (400 beats/min for 6 weeks, n = 6). The atrial electrogram of atrial fibrillation and the atrial effective refractory period were obtained from multiple sites of the right and left atrium. In addition, decremental rapid atrial stimulation was applied to the site of shortest and longest atrial effective refractory periods until atrial fibrillation induction in a subgroup of nine dogs. Ablation of the intercaval junction was performed using the radiofrequency catheter technique in dogs with atrial fibrillation duration > 1 min.nnnRESULTSnIn both models, organized atrial electrograms (type I) were predominantly observed at the left atrial sites and the right atrial appendage, whereas disorganized atrial electrograms (type III) were mainly observed at the right posterolateral atrium. The distribution of the atrial electrogram types closely followed that of the atrial effective refractory period, with the shortest atrial effective refractory period corresponding to organized atrial electrograms (type I) and the longest atrial effective refractory period corresponding to disorganized atrial electrograms (type III). The correlation of atrial electrogram type with the atrial effective refractory period was further demonstrated by the effect of rapid atrial stimulation. When rapid atrial stimulation was applied to the site with the shortest atrial effective refractory period, disorganized atrial electrograms were observed at sites with the longest atrial effective refractory period, whereas 1:1 atrial capture was still present at the stimulation site. Ablation of the intercaval junction made atrial fibrillation noninducible or tended to shorten the atrial fibrillation duration (from 26.4 +/- 24.2 to 8.8 +/- 22.6 min in the pericarditis group, p = 0.02, and from 33.7 +/- 29.2 to 12.1 +/- 23.8 min in the rapid pacing group, p = 0.09) but did not change the atrial electrogram types during atrial fibrillation.nnnCONCLUSIONSnVarious types of atrial electrograms are present at different locations during atrial fibrillation. The atrial electrogram characteristics of atrial fibrillation at a specific location are related to the atrial effective refractory period, with short effective refractory periods associated with organized atrial electrograms and long effective refractory periods associated with disorganized electrograms.

Repeated use of ablation catheters: A prospective study

OBJECTIVESnThe objective of this study was to provide insight into the time course of electrical, physical and mechanical changes in ablation catheters after each use that may affect the safety and efficacy of the ablation procedure.nnnBACKGROUNDnAn increasing number of institutions are reusing deflectable ablation catheters. At present, there are no data concerning the safety of reusing ablation catheters.nnnMETHODSnOver a period of 1 year, 69 Webster/Mansfield deflectable catheters used in 336 ablation procedures were prospectively studied. An additional 18 new catheters were tested after multiple sterilizations only. The catheters were evaluated for electrical and physical integrity and mechanical capabilities. These include deflection at room temperature and 37 degrees C, shaft compression and buckling during deflection, tip craters, torquing ability, glue separation and tip attachment using a stereoscope at x30 magnification and electrical resistance for each electrode. After each use, the catheters were gas-sterilized with ethylene oxide.nnnRESULTSnThe most common reasons for catheter rejection were tip electrode glue separation after 4.3 +/- 4.3 uses and loss of deflection after 5.0 +/- 3.3 uses. Electrical discontinuity between the catheter handle and electrodes was observed after 10.0 +/- 3.7 uses. There was no significant decrease in catheter torquing ability with repeated use. In this study the total estimated savings was

Cardioversion, Defibrillation, and Overdrive Pacing of Ventricular Arrhythmias: The Effect of Moricizine in Dogs with Sustained Monomorphic Ventricular Tachycardia

128,133, which includes the cost of catheter reprocessing. The reuse of Webster/Mansfield ablation catheters has not resulted in any major catheter failure or any major adverse clinical complications.nnnCONCLUSIONSnOn the basis of these observations, we believe that the Webster/Mansfield catheter can be reused an average of five times. It is strongly recommended that after each use catheters be carefully examined under appropriate magnification (x30) and that special attention be given to the ablation tip electrode. The catheters should also be tested for deflection and electrical integrity.

The Anatomical Determinants for the Design of Intracardiac Mapping and Ablation Catheters

The purpose of this investigation is to define whether the antiarrhythmic drug moricizine has beneficial or adverse effects on currently used antitachycardia and antifibrillatory devices. These studies were performed in a dog model of sustained monomorphic ventricular tachycardia (VT). In 11 dogs, the left anterior descending artery and all surrounding epicardial collateral feeder vessels were ligated. Defibrillator patches were implanted and the dogs were allowed to recover. After a 7‐day recovery period, effective refractory period (ERP), end diastolic threshold (EDT), VT induction, and VT and ventricular fibrillation (VF) termination data were collected before and after moricizine infusion (2 mg/kg). In this experimental model, moricizine caused the folIowing electrophysiological changes: a prolongation of the ERP from 173 ± 14 to 182 ± 15 fP < 0.02) with no significant effect on the EDT for pacing; a prolongation of the VT cycle length from 175 ± 18 to 201 ± 23 msec (P < 0.003); an increased cycle length required for overdrive pacing from 136 ± 20 to 157 ± 22 msec (P < 0.01); no effect on the energy required to cardiovert VT; an increase in the defibrillation threshold from 7.5 ±4 to 9.4 ± 4 joules (P < 0.006) and; in 5 of the 8 dogs with VT, theVT could be initiated with somewhat less aggressive stimulation. Significant beneficial electrophysiological effects were noted on theVT cycle length, including a proportionately prolonged overdrive pacing cycle length for VT termination. These changes were contrasted by the significant increase in the VF conversion energy required and the ease with which the VT could be induced postmoricizine. These findings suggest a possible proarrhythmic effect of moricizine.

LD-PACE II: a new cardiomyostimulator for cardiac bioassist.

An important factor in the efficient and successful completion of the ablation procedure is the design characteristics of the mapping/ablation catheters. These procedures are often hampered by the inability to maneuver the catheter to the desired location, in part because the catheters only have a single plane deflection capability and are not designed for the specific cardiac anatomical structures that contain the arrhythmogenic substrate. Single and Biplane Deflectable Catheters: Using measurements taken from six normal human cadaver hearts, ablation catheter design characteristics are presented for posterior, posterior septal, lateral, and posterior lateral pathways for retrograde and transseptal approaches. Three catheter designs based on anatomical characteristics were also evaluated. Pigtail Catheter: This catheter adapts to the atrial side of the mitral ring and improves positioning and stability for mapping and ablation of left‐sided accessory pathways. Loop Catheter: This catheter is positioned at the perivalvular tricuspid ring and provides simultaneous mapping and aNation capabilities without the need to move the catheter or the need for additional catheters. Rotating Tip Catheter: The tip of this catheter is made up of three elongated teeth, which were curved 120° apart into the rotating tip electrode. This electrode was designed to negotiate the surfaces of the atrial and intraventricular chambers. It is capable of discrete movements and has a large electrode‐tissue contact area for the ablation of atrial and ventricular arrhythmias. Catheter designs presented in this article are based on the ability of the catheter to adapt to the anatomical location of the arrhythmogenic tissue as well as the maneuverability of the catheters mapping and ablation elec‐trodes. An anatomical approach to the design of ablation catheter technology is likely to reduce the x‐ray radiation exposure for patient and operator, and may further increase the success rate of the procedure.

Iontophoretic transmyocardial drug delivery. A novel approach to antiarrhythmic drug therapy.

The LD-PACE II was designed for use in cardiomyoplasty, aortomyoplasty, and skeletal muscle ventricles. All parameters specified as programmable can be changed in a noninvasive manner (using a programming interface wand connected to a computer using the Windows 95/98 environment). Two new functions may be very useful clinically, based on experimental research. 1. Work-rest regimen. The LD-PACE II is able to deliver alternating periods of muscle contractions and rest. Work and rest periods may be programmed independently between 1 and 120 minutes in increments of 1 minute. The work-rest regimen may be useful clinically if muscle contractions are needed for cardiac assist postoperatively. 2. Night/day regimen. This feature allows for a change in the ratio of muscle contractions according to a patient’s activity level. During the day the cardiosynchronization ratio may be set from 1:1 to 1:4, and during the night it may be set for 1:8 to 1:16. This allows the muscle to have a long rest period, prevents overuse, and prolongs battery life. These two new features make this cardiomyostimulator very attractive for cardiomyoplasty in particular. The addition of the work-rest and night-day regimens allow the muscle to rest for periods during the day to prevent overuse, subsequent damage, and potential atrophy.