Ding Sheng He

The feasibility of using ultrasound for cardiac ablation

The feasibility of using ultrasound to induce cardiac tissue necrosis for the treatment of arrhythmias was investigated. A theoretical model was used to optimize the operating frequency for necrosis of highly perfused muscle tissue. From these simulations it appeared that frequencies from 10-15 MHz produce the deepest lesions at ultrasound intensities between 15 and 30 W/cm/sup 2/. Test catheters with a planar ultrasound transducer (diameter 2.3 mm=7 F) were also constructed and in vitro and in vivo tests with canine heart muscle were performed. Both of these tests showed that the ultrasound catheters could deliver adequate energy to necrose cardiac tissue. The in vivo lesion depths of 5-9 mm indicated that ultrasound has significant potential for cardiac ablation for the treatment of arrhythmias.<<ETX>>

Cylindrical ultrasonic transducers for cardiac catheter ablation

This study was designed to evaluate the feasibility of using cylindrical ultrasound transducers mounted on a catheter for the ablation of cardiac tissues. In addition, the effects of ultrasound frequency and power was evaluated both using computer simulations and in vitro experiments. Frequencies of 4.5, 6, and 10 MHz were selected based on the simulation studies and manufacturing feasibility. These transducers were mounted on the tip of 7-French catheters and applied in vitro to fresh ventricular canine endocardium, submerged in flowing degassed saline at 37/spl deg/C. When the power was regulated to maintain transducer interface temperature at 90-100/spl deg/C, the 10-, 6-, and 4.5-MHz transducers generated a lesion depth of 5.9/spl plusmn/0.2 mm, 4.6/spl plusmn/1.0 mm, and 5.3/spl plusmn/0.9 mm, respectively. The 10-MHz transducer was chosen for the in vivo tests since the maximum lesion depth was achieved with the lowest power. Two dogs were anesthetized and sonications were performed in both the left and right ventricles. The 10-MHz cylindrical transducers caused an average lesion depth of 6.4/spl plusmn/2.5 mm. In conclusion, the results show that cylindrical ultrasound transducers can be used for cardiac tissue ablation and that they may be able to produce deeper tissue necrosis than other methods currently in use.

Radiofrequency Ablation of the Ventricular Tachycardia with Arrhythmogenic Right Ventricular Cardiomyopathy Using Non-contact Mapping

Background: Intracardiac non‐contact mapping provides a rapid and accurate isopotential mapping that facilitates catheter ablation of the ventricular tachyarrhythmias in arrhythmogenic right ventricular cardiomyopathy (ARVC).

Preliminary results using ultrasound energy for ablation of the ventricular myocardium in dogs

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Correlation of ventricular arrhythmias with genotype in arrhythmogenic right ventricular cardiomyopathy.

Background—Although mutations of several genes are associated with arrhythmogenic right ventricular cardiomyopathy (ARVC), the exact correlation between genotype and ventricular arrhythmia features remains unclear. This study was aimed to examine the possible association of the 9 known genes of ARVC with clinical and electrophysiological characteristics. Methods and Results—Ninety subjects diagnosed with ARVC who underwent electrophysiological study were recruited for screening the 9 known ARVC-causing genes. A total of 53 mutations were identified in 57 (63%) subjects. Mutation carriers had more frequent clinical ventricular tachycardia (VT; 89% versus 55%; P<0.001) and negative T waves in V1 to V3 (61% versus 33%; P=0.016). Subjects with plakophilin-2 (PKP2) mutations also had more frequent VT than those without mutations in PKP2. Comparison between subjects with multiple and single mutations showed that syncope occurred more often in the former group (58% versus 24%; P=0.018). VT was significantly more often induced in mutation carriers compared with noncarriers (75% versus 39%; P=0.001), as well as in PKP2 mutation carriers compared with subjects without PKP2 mutations (80% versus 48%; P=0.002). Induced VT with a rate ≥200 bpm was more often documented in mutation carriers (88% versus 54%; P=0.013), as well as in PKP2 mutation carriers (91% versus 67%; P=0.041). Conclusions—Pathogenic gene mutations were found in nearly two thirds of subjects diagnosed with ARVC. Mutation carriers, especially PKP2, had a higher proportion of a history of VT and more inducible fast VT.

Comparison of Gold Versus Platinum Electrodes on Myocardial Lesion Size Using Radiofrequency Energy

During radiofrequency (RF) catheter ablation of arrhythmias, temperatures that approach 100°C cause a coagulum to form on the ablation electrode that results in an increase in electrical impedance and prevents further energy delivery. Since gold has nearly four times the thermal conductivity as platinum, the metal commonly used, it was postulated that gold tip electrodes could deliver more power and produce deeper lesions because of its greater heat dissipation from the electrodetissue interface to the circulating blood. To test this hypothesis, RF energy was applied to fresh bovine ventricular myocardium using 6 French catheters with 2‐mm long distal electrodes made from gold or platinum. Similar studies were also conducted using 7 French catheters with 4‐mm long distal electrodes. Maximum lesion depth was defined as that produced with the level of energy just below that causing an impedance rise. A maximum lesion depth of 6.2 ± 0.7 mm (mean ± SD) was obtained with the gold 2‐mm electrode and 4.7 ± 0.5 mm with the platinum electrode (P = 0.003). The 4‐mm gold electrode produced a maximum lesion depth of 7.2 ± 1.4 mm, while a catheter with a 4‐mm platinum electrode caused a maximum lesion depth of 5.8 ± 0,7 mm (P = 0.05). We conclude that deeper lesions should be able to be made when RF energy is delivered to a gold rather than platinum tip electrode.

Assessment of myocardial lesion size during in vitro radio frequency catheter ablation

We report our experience with a system that utilizes changes in several biophysical characteristics of cardiac tissue to determine lesion formation and to estimate lesion size both on and off-line in vitro during radio frequency (RF) energy delivery. We analyzed the reactive and resistive components of tissue impedance and tracked the change of phase angle during RF ablation. We correlated the amount of tissue damage with these and other biophysical parameters and compared them with off-line analysis. We found that there are irreversible changes in the reactive and resistive components of impedance that occurred during tissue ablation. The irreversible changes of these components are greater in magnitude, and correlate better with the size of lesions than that of impedance alone that is currently used. Numerically, the best single on-line and off-line correlation for combined perpendicular and parallel electrode orientation was with phase angle. On-line and off-line capacitance and susceptance correlations were essentially similar suggesting that they may be useful as lesion size predictors, given these parameters persistent change without temperature sensitivity. This study indicates that it is technically feasible to assess lesion formation using biophysical parameters.

Accelerometer‐Derived Time Intervals during Various Pacing Modes in Patients with Biventricular Pacemakers: Comparison with Normals

Introduction: Changes due to biventricular pacing have been documented by shortening of QRS duration and echocardiography. Compared to normal ventricular activation, the presence of left bundle branch block (LBBB) results in a significant change in cardiac cycle time intervals. Some of these have been used to quantify the underlying cardiac dyssynchrony, assess the effects of biventricular pacing, and guide programming of ventricular pacing devices. This study evaluates a simple noninvasive method using accelerometers attached to the skin to measure cardiac time intervals in biventricularly paced patients.

Organized Left Atrial Tachyarrhythmia During Stepwise Linear Ablation for Atrial Fibrillation

Introduction: This study attempted to delineate the mechanism of organized left atrial tachyarrhythmia (AT) during stepwise linear ablation for atrial fibrillation (AF) using noncontact mapping.

Blocking the Pulmonary Vein to Left Atrium Conduction in Addition to the Entrance Block Enhances Clinical Efficacy in Atrial Fibrillation Ablation

Background: The unidirectional pulmonary vein (PV) to left atrium (LA) conduction after achieving PV entrance block has not been evaluated.