Effect of Electrode Length on Atrial Defibrillation Thresholds

Electrode Length for Atrial Defibrillation. Introduction: Catheter-based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation. Methods and Results: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could he successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 ± 102 V, 5.9 ± 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 ± 18 ω. For the electrode combination using the 11-cm electrode in the right atrium, the defibrillation threshold was 296 ± 107 V, 5.8 ± 3.9 J with an impedance of 61 ± 17 ω and was 294 ± 91 V, 5.6 ± 3.6 J with an impedance of 55 ± 11 ω for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P < 0.05). Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.     

Composite Electrode Tips Containing Externally Placed Drug Releasing Collars

We have developed a composite electode tip based on a new concept whereby the electrode is combined with a polymeric collar containing dexamethasone sodium phosphate (DSP). The collar is positioned immediately adjacent to the electrode. Initial evaluation of this concept employed the Telectronics Laserpor electrode and a collar containing approximately 1.8 mg of DSP (LPD). Conventional Telectronics Laserpor (LP) electrodes were used as controls. Further evaluation was performed using a DSP (< 0.5mg) eluting collar and a new 4 mm² mushroom shaped electrode with a high microsurface Pt/Ir coating (MD). Data for conventional Telectronics Laserdish (LD) electrodes were used for comparison. Unipolar ventricular leads were implanted transvenously in the right ventricular apex of sheep. Voltage thresholds, pacing (5V, 0.5ms) and sensing (50/100 mVRMS, 50 Hz) impedances were measured during the subchronic phase (< 6 weeks) and in the case of LD and MD for 6 months. The steroid eluting electrodes were elective in eliminating (2 weeks vs. Impl., N.S.) the 2 week threshold peaking seen with the control leads (2 weeks vs. Impl., P < 0.005). The small area MD electrode thresholds remained stable and low for up to 6 months (0.38 ± 0.09 (10) c.f. 0.46 ± 0.11(6); 14 and 180 days, respectively, N.S.). The composite electrode tips with steroid releasing collars thus show great potential for a substantial reduction in stimulation energy.     

Chloroform Inhibition of 1,2-Dimethylhydrazine-Induced Gastrointestinal Tract Tumors in the Fisher 344 Rat

The effect of chloroform (CHCl₃), administered at 0, 900, and1800 mg/liter in the drinking water, on the carcinogenic potencyof 1,2-dimethylhydrazine (DMH) was investigated. Groups of 40male Fisher 344 rats were given one of the three drinking watersolutions for 39 weeks following the subcutaneous injectionof 200 mg/kg DMH, a known gastrointestinal (GI) tract carcinogenin this animal strain. When tumors from the GI tract were pooledthere was a highly significant (p < 0.001) decrease in totalnumber of tumors per group with increasing concentration ofdrinking water CHG3. In the control group (0 mg/liter CHCl₃),14/39 (36%) of the animals developed tumors of the GI tract,including the duodenum, jejunum, stomach, cecum, and colon.In contrast, the incidence of tumors in the two groups of ratsgiven CHCl₃ in the drinking water was significantly lower (p< 0.001; 900 mg/liter CHCl₃, 12.8%; 1800 mg/liter CHCl₃,12.5%). A similar relationship was obtained when colon tumorswere analyzed independently (p = 0.01). The incidence of totalcolon tumors obtained in the control group of this study (10/39,26%) agrees well with the previous study by B. S. Reddy, K.Watanabe, and J. H. Weisburger (1977, Cancer Res. 37, 4156–4159)conducted in the same rat strain (7/30, 23%). These resultsdemonstrate that CHCl₃ in the drinking water inhibits carcinogenesisin the rat GI tract.     

Pulmonary Artery Catheter-Associated Thrombosis

Transesophageal echocardiography has become increasingly important in the assessment of critically ill patients. We report a 39-year-old patient who was incidentally noted to have a large right intraatrial thrombus associated with an indwelling pulmonary artery catheter identified by transesophageal echocardiography. This led to eventual catheter removal by open venotomy. Careful examination of intravascular devices during transesophageal echocardiography may lead to early diagnosis of catheter-associated thrombosis and thus alter management appropriately.