No abstract

The design and fatigue strength of a nitinol iliac vein stent (NIVS) proposed in this study are assessed using the finite element analysis method. The influence of stent diameter and different release scales on its strength, lifespan and biomechanical properties of the vein wall is analyzed for self-developed NIVS of three different diameters (12, 14 and 16mm) and length of 26mm, which were implanted into the corresponding iliac vein with different release scales (80% and 90%). The results obtained strongly indicate that with an increase in the release scale, the equivalent elastic strain, safety factors of fatigue strength, and equivalent stress of the vessel wall exhibit a downward trend, while the most stressed cross-section coincides with the arc of stent-connecting rods. The efficiency and safety of the above stents were verified by in vivo tests (with observation periods of 30, 90 and 180 days after operation) on ten lab pigs, which underwent NIVS implantation into the iliac veins, with observation of hemodynamics, stent deployment, presence/absence of thrombosis, and monitoring of stent lumen loss and its rate. During the animal test verification, the stent release was satisfactory, while the radiography revealed no obvious stent displacement at different time points. In addition, the patency rate of the stent was 100%. Except for the control group, where a small amount of old thrombus was found, other stents exhibited no thrombus; at the same time, there was no significant difference in the lumen loss rate of the stent at each time point. Therefore, the proposed nitinol NIVS samples demonstrated a good performance, accurate positioning, and release, in addition to the reduced risk of lateral iliac vein thrombosis.

In this study we compared the effects of radiofrequency (RF) energy applied to the swine endocardium in a unipolar fashion and in a bipolar one with two different interelectrode distances (5 mm, 10 mm). RF energy (500 kHz) delivered to the swine endocardium was divided into eight categories: 100 J, 101-200 J, 201-300 J, 301-400 J, 401-500 J, 501-600 J, 601-1000 J, and > 1000 J. The results showed that when RF energy was applied in a bipolar fashion, the lesions involved the catheter/tissue interface and partly the interelectrode spacing, while in a unipolar fashion. They were found in the catheter/tissue interface only. At any energy level, there were no statistically significant differences in lesion depths among all the three fashions, and the lesion surface areas produced by the bipolar fashion (with 5 mm or 10 mm interelectrode spacing) were all greater than those by the unipolar fashion (P < 0.05). When the delivered energy was under 500 joules, a greater lesion surface area was found in 5 mm bipolar fashion than in 10mm bipolar fashion (P < 0.05), while energy exceeded 500 joules, the differences in the lesion surface areas were no longer significant between these two bipolar fashions.

No abstract