Safety and efficacy of a steerable temperature monitoring microwave catheter system for ventricular myocardial ablation.

INTRODUCTION: Radiofrequency current delivered during cardiac ablation is limited by a rise in impedance secondary to coagulum formation on the ablation electrode. Microwave antennas continue to deliver energy despite the presence of coagulum; thus, temperature control of the ablation electrode may be even more important for microwave than for radiofrequency ablations to avoid thromboembolic risks. The purpose of this study was to test the safety and efficacy of an ablation system utilizing a feedback control system to maintain a fixed target temperature for creating lesions with multiple applications of microwave energy. METHODS AND RESULTS: Microwave ablation was assessed using an 8.5-French catheter at 2 to 4 sites in 11 dogs. Microwave energy delivery was performed for 60 seconds three times at the same site. Power was regulated using a feedback control mechanism to maintain a target temperature of 75 degrees C. Ambulatory ECG monitoring was performed before and after ablation to assess arrhythmia occurrence. After follow-up, the dogs were euthanized, and lesion dimensions measured after fixation. The mean power applied to achieve the target temperature of 75 degrees C was 9.3+/-44 W. The mean depth of the lesions was 8.8+/-4.2 mm. The mean volume of the lesions was 304+/-240 mm3. Forty-four percent of the lesions were transmural. No endocardial thrombus was found. Ventricular tachycardia was observed acutely but resolved after 1 week. CONCLUSION: Temperature feedback control systems for microwave ablation using a temperature-controlled system is feasible for myocardial ablation and creates uniform and large lesions; however, such large lesions can be acutely proarrhythmic.

Unstable radii in muscular blood vessels.

A model of a muscular blood vessel in equilibrium that predicts stable and unstable control of radius is presented. The equilibrium wall tension is modeled as the sum of a passive exponential function of radius and an active parabolic function of radius. The magnitude of the active tension is varied to simulate the variable level of smooth muscle activation. This tension-radius relationship is then converted to an equilibrium pressure-radius relationship via Laplace's law. This model predicts the traditional ability to control the radius below a critical level of activation. However, when the active tension is raised above this critical level, the pressure-radius relationship (with pressure plotted on the ordinate and radius on the abscissa) becomes N shaped with a relative maximal pressure (Pmax) and a relative minimal pressure (Pmin). For this N-shaped curve, there are three equilibrium radii for any pressure between Pmin and Pmax. Analysis shows that the middle radius is unstable and thus cannot be maintained at equilibrium. Previously unexplained experimental data reveal evidence of this instability.

An investigation on the influence of steroidal contraceptives on milk lipid and fatty acids in Hungary and Thailand. WHO Special Programme of Research, Development and Research Training in Human Reproduction. Task Force on oral contraceptives.

A double-blind clinical trial to examine the effects of oral and long-acting injectable contraceptive steroids on milk lipid and its fatty acid content has been done in Szeged, Hungary, and Khon-Kaen, Thailand. In Szeged, a combined and a progestin-only pill did not significantly alter total milk lipid. In Khon-Kaen, treatment with the combined pill was followed by a significant increase in the proportion of milk lipid. In the group treated with the long-acting injectable contraceptive, depot-medroxyprogesterone acetate (DMPA), the milk lipid decreased significantly in the first six weeks in comparison with the control group and the individual pretreatment values. A similar but weaker effect was noticed with the progestin-only pill in Khon-Kaen. Few consistently significant differences were found in the shorter chain fatty acids (myristic, lauric and palmitic acids) during treatment. The percentage proportions were increased during the combined pill treatment in Szeged and Khon-Kaen, and reduced in DMPA and progestin-only treatment in Khon-Kaen milks. The possibility that these reflected a response to a milk volume decrease in the combined pill treatment and a reduction in milk lipid synthesis in association with DMPA and the progestin-only pill is discussed. In Khon-Kaen, linoleic acid (which is not synthesized in the body) was increased by comparison with the controls, as a percentage proportion of the fatty acids in the progestin-only and DMPA groups. Calculation of the amounts of linoleic acid per litre of milk revealed that there had been a significant decrease of linoleic, eicosadienoic, dihommo-gamma-linolenic, arachidonic, docosatetraenoic acids in the w6 family and alpha-linolenic acid in the w3 family in the first two post-treatment visits (3 and 4). This reduction in essential fatty acid output follows the reduction in milk volume. In Khon-Kaen, the combined pill group showed a significant decrease compared with the controls, in the proportions of dihommo-gamma-linolenic acid. The difference in response of the mothers in Khon-Kaen and Szeged is discussed in relation to their different nutritional backgrounds.