Three-dimensional computer model of the entire human heart for simulation of reentry and tachycardia: Gap phenomenon and Wolff-Parkinson-White syndrome

Summary A computer model of the entire human heart has been developed for simulation of the excitation and repolarization process. Spatial distribution of refractory periods and conduction velocities in the different cardiac tissues, the anisotropy of conduction in the ventricles, and the cycle length dependence of refractory periods and conduction velocities are taken into account. The algorithm calculating the activation process is based on a modified version of Huygen's principle for constructing wavefronts. This study presents simulations concerning the gap phenomenon of the conduction system and the initiation of tachycardias in a heart with Wolff-Parkinson-White syndrome. Results are compared for different basic cycle lengths and for normal and prolonged refractory periods in the His-Purkinje system. The gap phenomenon was found to be present only when using the prolonged refractory periods in the His-Purkinje-system at a cycle length of 700 ms. Induction of tachycardia by a single extrastimulus in the high right atrium in a heart with a bidirectionally conducting accessory pathway is possible by properly timed extrastimuli. The coupling interval of the stimulus for initiating a reentrant tachycardia depends on the cycle length, the conduction velocities and the set of refractory periods used. The same parameters determine whether or not a gap phenomenon in atrioventricular conduction occurs. The model may be useful for investigating similar questions concerning the reentry phenomena of tachycardia.     

Teriparatide treatment in an adult patient with hypophosphatasia exposed to bisphosphonate and revealed by bilateral atypical fractures

Atypical femoral fractures are defined as atraumatic fractures located in the subtrochanteric region or femoral shaft. They have been mainly reported in patients taking bisphosphonates. We report the case of a 67-year-old female with osteoporosis treated by alendronate during ten years. Radiographies showed atypical femoral fractures. Serum levels of total and bone-specific alkaline phosphatase were low. In order to accelerate bone healing, teriparatide was introduced. After one year of teriparatide treatment, pain and functional difficulty have decreased, and alkaline phosphatase levels were normalized. In view of this history of recurrent fractures, of atypical femoral fractures, of early spontaneous loss of teeth, and of low serum total and bone-specific alkaline phosphatase levels, the diagnosis of hypophosphatasia has been considered and confirmed by genetic research. Other conditions than exposure to anti-resorptive therapies may promote atypical femoral fractures, such as in conditions associated with abnormal bone structures, as hypophosphatasia, a rare inherited bone metabolism disorder. A few case reports have reported adult hypophosphatasia treated by teriparatide with a good efficacy on bone pain and consolidation but with mixed results on biological markers. Teriparatide may be therefore a treatment option in adult hypophosphatasia. ALP levels should be carefully checked among osteoporotic patients and specially before introducing a bone resorption inhibitor. Low alkaline phosphatase levels have to be taken into account and an evocative history of hypophosphatasia has to be sought because this condition may expose patients to develop atypical femoral fractures during bisphosphonate treatment.     

Increased MIB-1 Labeling Index Is Associated with Abducens Nerve Morbidity in Primary Sporadic Petroclival Meningioma Surgery: Beyond Location and Approach

Abducens nerve palsy is a severe dysfunction after petroclival meningioma (PC MNG) surgery. The objective of this investigation was to analyze abducens nerve outcomes in patients who underwent the retrosigmoid approach in relation to the MIB-1 index. Thirty-two patients with primary sporadic PC MNG were retrospectively analyzed. Mean follow-up was 28.0 months. Analysis of the MIB-1 index was performed to evaluate the abducens nerve outcome. An optimal MIB-1 index cut-off value (<4/≥4) in the association with postoperative CN VI palsy was determined by ROC analysis (AUC: 0.74, 95% CI: 0.57–0.92). A new-onset CN VI palsy was present in 7 cases (21.88%) and was significantly associated with an increased MIB-1 index (≥4%, p = 0.025) and a peritumoral edema in the brachium pontis (p = 0.047) which might be caused by the increased growth rate. Tumor volume, cavernous sinus infiltration, auditory canal invasion, and Simpson grading were not associated with new CN VI deficits. Six (85.7%) of the 7 patients with both an increased MIB-1 index (≥4%) and new abducens nerve palsy still had a CN VI deficit at the 12-month follow-up. A peritumoral edema caused by a highly proliferative PC MNG with an elevated MIB-1 index (≥4%) is associated with postoperative abducens nerve deficits.     

Postbiliary drainage rates of cholangitis are impacted by procedural technique for patients with supra-ampullary cholangiocarcinoma: A SEER-Medicare analysis

Tumor biology and careful patient selection weigh heavily in determining the appropriate role of surgical resection in stage IV melanoma. Historically, surgical resection for highly selected patients with metastatic melanoma was the only treatment modality associated with improved long-term survival and the ability to provide palliation. With the new age of effective systemic therapies, the treatment of metastatic melanoma has become more intricate and future work is needed to better define the role for surgery within the current treatment paradigm.     

Prokeratosis Mibelli gigantea Fallbericht und Literaturübersicht

Zusammenfassung Die Porokeratosis Mibelli ist eine seltene, heredit?re epidermale Verhornungsst?rung mit verschiedenen Sonderformen und bis heute unklarer Pathogenese. Sie ist klinisch durch erythemat?se Plaques mit typisch hyperkeratotischem Randwall und histologisch durch die kornoide Lamelle gekennzeichnet. Berichtet wird über eine Porokeratosis gigantea, eine morphologische Variante der klassischen Porokeratosis Mibelli. Die Pathogenese der Porokeratosis wird unter besonderer Berücksichtigung der klonalen Hypothese und der Potenz zur malignen Transformation diskutiert. Eingegangen am 18. Juni 1997 Angenommen am 6. Februar 1998     

Imaging of the active B1 field in vivo

The authors describe a method for accurate In vivo muttislice imaging of the active component of the B₁ field which is based on a previously proposed method, which uses the signal intensity ratio of two images measured with different excitation angles, and a repetition time TR≥ 5 T₁ The new method essentially reduces repetition and scan time by means of an additional compensating pulse. The suppression of T₁ effects by this pulse are verified with simulations and measurements. Further investigations concerned the influence of slice selective excitation and magnetization transfer in multislice imaging to the B₁ field determination. The stability and accuracy of the presented method is shown by several phantom and in vivo measurements. With the described method the active B₁ field can be determined in vivo in 23 cross-sections in less than 6 min.     

The onset of fretting at the head‐stem connection in hip arthroplasty is affected by head material and trunnion design under simulated corrosion conditions

Mechanically assisted crevice corrosion (MACC) is a mechanism for trunnion damage in total hip arthroplasties (THAs). Retrieval studies have shown reduced MACC‐related damage for ceramic heads compared with cobalt–chromium (CoCr) heads. We propose that ceramic heads demonstrate fretting at higher cyclic compressive loads than CoCr heads on titanium alloy trunnions in a simulated corrosion model. A closed electrochemical chamber was used to measure fretting current onset loads for two modern titanium alloy trunnions (Zimmer 12/14 and Stryker V‐40) in which trunnion failure has been reported. Ceramic and CoCr alloy 36 + 0 mm heads were impacted on each trunnion and cyclically loaded at 3 Hz with increasing magnitude from 100 to 3,400 N for 540 cycles. Onset load was the cyclic compressive load at which the slope of the average fretting current increased significantly. A CoCr head with V40 trunnion demonstrated the lowest onset load (1,400 N), while the V40 trunnion with a ceramic head showed the highest onset load (2,200 N). Significant differences occurred in average fretting current between head materials for V40 trunnions (p < 0.001) at loads over 2,000 N. CoCr‐12/14 and ceramic‐12/14 couples demonstrated similar onset loads (2,000 N). All head–trunnion combinations showed cyclical fretting response to loading at 100 N. Head material composition was observed to increase fretting at the taper junction but the effect was taper geometry dependent. Using ceramic heads may reduce the phenomena of trunnion fretting and corrosion but the effect of both trunnion geometry and metallurgy warrants further investigation. Statement of clinical significance: Trunnion corrosion may occur with titanium alloy stems regardless of the head material used. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1630–1636, 2018.