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Radiofrequency current is a promising alternative to high voltage direct current defibrillator discharges for catheter ablation of arrhythmias. However, lesions produced with radiofrequency current are relatively small and use of high power is limited by the impedance rise that occurs with desiccation of tissue and coagulum formation. The effect of electrode size on radiofrequency ablation was assessed by comparing results of radiofrequency application using a standard 6 French electrode catheter (distal electrode 2 mm in length) to those using catheters modified with longer distal electrodes (3, 4, 6, 8, and 10 mm in length). Radiofrequency ablation was performed at 47 left ventricular endocardial sites in 20 anesthetized dogs. A constant power of 13.3 +/- 1.3 watts at 550 kHz was applied between the distal catheter electrode and a skin electrode until a total of 500 joules had been delivered or a rise in impedance occurred. Increasing electrode length from 2 to 4 mm more than doubled lesion volume from a mean of 143 to 326 mm3 (P = 0.025). Increasing electrode length beyond 4 mm produced progressively smaller lesions (157 mm3, 155 mm3, and 67 mm3 for 6-, 8-, and 10-mm electrode lengths, respectively). Impedance rise was significantly less likely with larger electrodes and took longer to occur. Increasing the size of electrodes used for radiofrequency ablation allows application of higher power without an impedance rise. Optimizing electrode size (3 or 4 mm in this study) results in larger lesions and may improve the effectiveness of radiofrequency ablation of arrhythmias.  相似文献   
517.
The possibility that propranolol may exert its beneficial actions in thyrotoxicosis by an effect on thyroid hormone concentrations has been investigated by measuring these and oxygen consumption in a group of thyrotoxic patients before and after treatment with propranolol. Following treatment a significant fall in plasma T3 concentration and oxygen consumption occurred and a direct correlation was found between these two variables. Propranolol may, therefore, exert some of its beneficial effects in thyrotoxicosis by an action on T3 metabolism.  相似文献   
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The records of 91 nasopharyngeal carcinoma patients who were treated with external radiotherapy for recurrent neck node disease were reviewed. All patients had received prior radiotherapy for cervical nodal disease or prophylactic neck irradiation. The node size (product of the greatest perpendicular diameters) at the time of treatment for nodal relapse ranged from 1cm2 to 35cm2 (median 2.25cm2). The radiation dose ranged from 823 RETs to 1949 RETs (median 1520 RETs). The recurrent node size and radiation dose were found significant prognostic factors for local control. The local tumour control for nodes 4cm3 or smaller was 51% at five years, for nodes greater than 4cm3 was 16% at 18 months (p=0.0'l). The overall 5 year survival was 19.7%. Radiation dose greater than 1600 RETs was significantly associated with better survival for patients with recurrent nodes measured 4cm or smaller, but higher radiation dose did not improve the survival of patients with recurrent nodes greater than 4cm2. Because of the dilemma of suboptimal control resulting from inadequate radiation dose when compared with surgical treatment, and possible radiation complication from higher dose, surgery should be the treatment of choice for neck node recurrence after primary radiotherapy for nasopharyngeal carcinoma.  相似文献   
519.
Cystinosis is a rare autosomal recessive inherited disorder of amino acid metabolism. Little is known of the affects of general anaesthesia on the disease (Tobias 1993) and complications relating to anaesthesia have not been previously reported. Infantile cystinosis presents as progressive renal failure and the Fanconi syndrome and metabolic bone disease often develop. We describe the case of a child who presented with signs of apparent malignant hyperthermia (MH) under general anaesthesia and was treated with dantrolene. During a repeat ‘trigger-free’ general anaesthetic he developed a fever which responded to paracetamol. The metabolic effects of cystinosis and its similarity to MH will be discussed.  相似文献   
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