Marsha A. Gallagher

Temperature-guided radiofrequency catheter ablation with very large distal electrodes.

BackgroundPrevious studies have shown that the size of lesions produced by radiofrequency catheter ablation correlates with the temperature and surface area of the electrode-tissue interface. The purpose of the present study was to compare the effects of ablation using very large distal electrodes (8F, 8 and 12 mm long) with those made by a conventional radiofequency ablation catheter (distal electrode 8F, 4 mm long). Methods and ResultsEach catheter had a thermistor in the tip of the distal electrode. Radiofrequency energy (500 kHz) was supplied by a generator that continuously monitored temperature and produced up to 100 W. In 10 dogs, each of the three ablation catheters were introduced percutaneously and positioned under fluoroscopic guidance at disparate left ventricular endocardial sites. Radiofrequency power output was titrated to achieve a temperature of 80°C for 60 seconds at each ablation site. The power required to produce a steady-state temperature of 80°C was directly proportional to electrode size (15

Epicardial administration of ibutilide from polyurethane matrices : effects on defibrillation threshold and electrophysiologic parameters

7, 46

Delta opioid receptors and low temperature myocardial protection

15, and 62

Effect of accessory pathway location on the efficiency of heating during radiofrequency catheter ablation

32 W using the 4-mm-, 8-mm-, and 12-mm-long electrodes, respectively). Lesions produced by the 8-mm electrode were nearly twice as deep (11+2.4 versus 6

Effect of coronary reocclusion after initial reperfusion on ventricular function and infarct size

+1.2 mm, P<.001) and four times as large (905

Intravascular ultrasound imaging of vascular responsiveness in isolated perfused canine arteries

410 versus 210

Adjustable model of chronic left ventricular dysfunction.

+100 mm3, P<.001) as those made with a conventional 4-mm electrode. Lesions produced by the 12-mm electrode were intermediate in size (depth, 8

Sotalol Controlled-Release Systems for Arrhythmias: In Vitro Characterization, in Vivo Drug Disposition, and Electrophysiologic Effects

1.2 mm; volume, 465

RSR13, a Synthetic Allosteric Modifier of Hemoglobin, Improves Myocardial Recovery Following Hypothermic Cardiopulmonary Bypass

225 mm3) and sometimes were associated with charring and crater formation. Ablation with the larger electrodes caused a drop in arterial pressure and more ventricular ectopy than ablation using a 4-mm distal electrode. ConclusionsThermistor-equipped elongated ablation electrodes coupled to high-power outputs can reproducibly produce lesions approximately 1 cm in diameter. This system may prove useful for ablation of ventricular tachycardias in patients with coronary artery disease.

Epicardial iontophoretic delivery of antiarrhythmic agents

Polymer-drug composites known as controlled-release systems have been used effectively to prevent and treat ventricular arrhythmias in experimental studies. We wished to determine if such systems could be useful in reducing ventricular defibrillation energy requirements in an acute canine model without producing undesirable electrophysiologic effects. Ibutilide-polyurethane monolithic controlled-release matrices were formulated with ibutilide fumarate and a polyether polyurethane. In vitro drug-release characteristics of the drug matrices were determined. Two formulations were investigated: (a) 20% ibutilide by weight in polyether polyurethane, and (b) 4% ibutilide/16% dimethyl tartrate in polyurethane. Based on in vitro release studies, 20% ibutilide matrices (25 mg) would provide a 25-kg dog with a dose of 25 micrograms/kg ibutilide in a 2-h acute experimental period, and 4% ibutilide matrices were estimated to provide 3.5 micrograms/kg. We used each of these types of matrices in acute open-chest dog studies to assess electrophysiologic effects and the influence of epicardial controlled-release ibutilide, as compared with intravenous (i.v.) administration, on defibrillation energy thresholds (DFTs), using epicardial defibrillation electrodes. In monophasic defibrillation waveform studies, 20% matrices significantly decreased DFT as compared with a predrug control period [2.54 +/- 0.59 (mean +/- SEM) vs. 7.23 +/- 1.73 J, respectively, p = 0.038]. Administration of the same dose i.v. did not cause significant reduction in energy requirement. With a biphasic defibrillation waveform, 4% ibutilide matrices significantly decreased DFT as compared with control (2.53 +/- 0.34 vs. 3.42 +/- 0.46 J, respectively, p = 0.003). Administration of an equivalent i.v. dose did not cause a significant reduction in biphasic energy requirement. Both types of controlled-release systems significantly prolonged refractoriness and conduction times of ventricular extrastimuli as compared with vehicle. No proarrhythmia events were observed. Epicardial polymeric controlled-release ibutilide significantly prolonged ventricular refractoriness and conduction and thus may enhance antiarrhythmia activity. In addition, controlled-release ibutilide formulations significantly decreased DFT requirements. Thus, ibutilide-polymeric controlled-release matrix systems may be useful in conjunction with implantable defibrillators in preventing ventricular arrhythmias and reducing defibrillation energy requirements.