Unusual echocardiographic evidence of hypercoagulation in usual left atrial appendage as the first and only sign of COVID-19.

Coronavirus disease 2019 (COVID-19) is a condition caused by a novel virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The disease's course ranges from entirely asymptomatic to severely ill patients. Hypercoagulation is often a complication of this disease, worsening the prognosis, which is extremely important in patients at higher risk of thromboembolic events, such as atrial fibrillation (AF), where thrombus formation in the left atrial appendage (LAA) is frequent. LAA could be of various sizes, volumes, and shapes, distinguish several morphologies, from which the WindSock LAA is the most frequent. In contrast, thromboembolic complications occur most frequently in patients with AF and the Cactus LAA. We present a clinical case of a 70-year-old woman with an initial negative real-time polymerase chain reaction (RT-PCR) test for SARS-CoV-2, suspicion of device-related infection after dual pacemaker implantation, AF, and LAA without thrombus in the initial transoesophageal echocardiography (TEE). Despite apixaban treatment, spontaneous restoration of sinus rhythm, and WindSock LAA morphology, the sludge in LAA was diagnosed in control TEE. The patient did not present any typical clinical COVID-19 symptoms but re-checked the RT-PCR test for SARS-CoV-2 infection was positive. The described case presents echocardiographic evidence of hypercoagulation as the first and only feature of SARS-CoV-2 condition besides the usual morphological presentation of the WindSock LAA.

Formation and properties of a synthetic bone composite: hydroxyapatite-collagen.

Composites composed of microcrystalline calcium-deficient hydroxyapatite (HAp) and collagen were formed at 38 degrees C via an acid-base reaction between calcium phosphate precursors in the presence of a collagen matrix. Formation of composites having HAp:collagen weight ratios of 4.5:1, 11:1, and 22:1, along with that of pure mineral were investigated. Isothermal calorimetry and X-ray diffraction indicated complete reaction within 5 h resulting in hardened monoliths. The rate of HAp formation increased with an increase in the proportion of collagen present. Electron microscopy indicated that the acceleratory effect of collagen was associated with the provision of nucleation sites for HAp crystallization. Analysis of the solution chemistry also showed that collagen affected the calcium and phosphate concentrations and the pH. While collagen was shown to effect the kinetics of HAp formation, the rate limiting step, as shown by X-ray diffraction and solution chemistry, was the dissolution of the acidic calcium phosphate precursor, CaHPO4. Preliminary mechanical data indicated that the Young's modulus, yield strength, and work to fracture were at the lower end of the range of those values reported for bone. The porosities observed in these composites suggest that they might be osteoinductive while their compositions should allow their eventual resorption. Thus, microstructure, kinetics, and mechanical data suggest that these composites might be suitable as bone substitutes which form in vivo.

Examples of evolution of microstructure in ceramics and composites.

In this article we describe a number of studies involving the direct observation of microstructural evolution. In general these investigations were carried out to establish the mechanistic paths involved. The materials studied range from fibers being evaluated for use in high-temperature ceramic composites to energetic materials used as propellants. In particular we discuss the room temperature imaging of materials difficult to image by conventional means and the use of the chamber atmosphere to influence microstructural evolution. Imaging of hydroxyapatite formed by chemical means is briefly described as an example of a difficult microstructure. Microstructural evolution during calcium aluminate cement hydration relies on the chamber atmosphere to control moisture loss from the hydrating specimens. In some instances microstructural evolution with heating occurred independently of the chamber atmosphere. Grain growth in PZT films formed by sol-gel processes depends strongly on temperature but does not appear to depend on the chamber atmosphere. This is also the case for the combustion of nitroamine propellants in that their combustion does not depend on access to an external source of oxygen. In other studies, the chamber atmosphere played an indirect role in determining microstructure. However, the mechanistic path driving microstructural evolution in copper-based inks used as conductive paths on electronic substrates is atmosphere dependent. These inks are formulated from copper powder, glass, and an organic binder, and the interaction of the binder with an oxidizing atmosphere allows it to be burned out before significant interaction occurs between the copper powder and the glass. Finally, the microstructural variations during the oxidation of structural composites at high temperature were used to allow assessments of their likely failure mechanisms.