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Notes: Conventional transvenous defibrillation is performed with an ICD using a dual current pathway. The defibrillation energy is delivered from the RV electrode to the superior vena cava (SVC) electrode and the metallic case (CAN) of the ICD. Biventricular defibrillation uses an additional electrode placed in the LV free wall with sequential shocks to create an additional current vector. Clinical studies of biventricular defibrillation have reported a 45% reduction in mean defibrillation threshold (DFT) energy. The aim of the study was to use computational methods to examine the biventricular defibrillation fields together with their corresponding DFTs in a variety of patient derived models and to compare them to simulations of conventional defibrillation. A library of thoracic models derived from nine patients was used to solve for electric field distributions. The defibrillation waveform consisted of a LV → SVC + CAN monophasic shock followed by a biphasic shock delivered via the RV → SVC + CAN electrodes. When the initial voltage of the two shocks is the same, the simulations show that the biventricular configuration reduces the mean DFT by 46% (3.5 ± 1.3 vs 5.5 ± 2.7 J, P = 0.005). When the leading edge of the biphasic shock is equal to the trailing edge of the monophasic shock, there is no statistically significant difference in the mean DFT (4.9 ± 1.9 vs 5.5 ± 2.7 J, P 〉 0.05) with the DFT decreasing in some patients and increasing in others. These results suggest that patient-specific computational models may be able to identify those patients who would most benefit from a biventricular configuration. (PACE 2004; 27:586–593)

Notes: Abstract: The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96±0.72 mm (range 0.0–3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.

Notes: Abstract: In this study a computer aided navigation technique for accurate positioning of oral implants was assessed. An optical tracking system with specially designed tools for monitoring the position of surgical instruments relative to the patient was used to register 5 partially or completely edentulous jaw models. Besides the accuracy of the tracking system, the precision of localizing a specific position on 3-dimensional preoperative imagery is governed by the registration algorithm which conveys the co-ordinate system of the preoperative computed tomography (CT) scan to the actual patient position. Two different point-to-point registration algorithms were compared for their suitability for this application. The accuracy was determined separately for the localization error of the position measurement hardware (fiducial localization error – FLE) and the error as reported by the registration algorithm (fiducial registration error – FRE). The overall error of the navigation procedure was determined as the localization error of additional landmarks (steel spheres, 0.5 mm diameter) after registration (target registration error – TRE). Images of the jaw models were obtained using a high resolution CT scan (1.5 mm slice thickness, 1 mm table feed, incremental scanning, 120 kV, 150 mAs, 512 · 512 matrix, FOV 120 mm). The accuracy of the position measurement probes was 0.69±0.15 mm (FLE). Using 3 implanted fiducial markers, FRE was 0.71±0.12 mm on average and 1.00±0.13 mm maximum. TRE was found to be 1.23±0.28 mm average and 1.87±0.47 mm maximum. Increasing the number of fiducial markers to a total of 5 did not significantly improve precision. Furthermore it was found that a registration algorithm based on solving an eigenvalue problem is the superior approach for point-to-point matching in terms of mathematical stability. The experimental results indicate that positioning accuracy of oral implants may benefit from computer aided intraoperative navigation. The accuracy achieved compares well to the resolution of the CT scan used. Further development of point-to-point/point-to-surface registration methods and tracking hardware has the potential to improve the precision of the method even further. Our system has potential to reduce the intraoperative risk of causing damage to critical anatomic structures, to minimize the efforts in prosthetic modelling, and to simplify the task of transferring preoperative planning data precisely to the operating room in general.

Notes: Abstract A 70-year-old woman presented with a large femoropopliteal aneurysm. A covered nitinol stent was implanted successfully and complete exclusion of the aneurysm was achieved. At follow-up 5 months later the stent was still patent and the patient was free of symptoms. However, moderate stenosis was seen at the proximal end of the stent.