We performed percutaneous transluminal coronary angioplasty as an emergency procedure in 60 patients with unstable angina pectoris that was refractory to treatment with maximally tolerated doses of beta-blockers, calcium antagonists, and intravenous nitroglycerin. The initial success rate for angioplasty was 93 per cent (56 patients). There were no deaths related to the procedure, although total occlusion occurred in four patients. Despite emergency bypass grafting, all four sustained a myocardial infarction. All the patients were followed for at least six months. Late cardiac death occurred in one patient, whereas eight had recurrent angina pectoris. There was no progression to myocardial infarction. The re-Stenosis rate was 28 per cent (13 of 46) in the patients with initially successful coronary angioplasty who had repeat angiography. Improved cardiac functional status after sustained successful coronary angioplasty was demonstrated by an almost normal capacity on bicycle exercise testing and the absence of ischemia during thallium isotope studies in 80 per cent. We conclude that emergency percutaneous transluminal coronary angioplasty may be useful for the treatment of selected patients with unstable angina pectoris who are unresponsive to intensive pharmacologic treatment. (N Engl J Med 1985; 313:342–6.)
Abstract In contrast to conventional structural steel and stainless steel, wire and arc additively manufactured (WAAM) material can exhibit a strongly anisotropic response. To investigate the degree of anisotropy in WAAM sheet material, data obtained from tensile tests on machined and as‐built stainless steel coupons are utilised. The WAAM material was tested in three different loading directions relative to the deposition direction and the response was captured using digital image correlation; a summary of the key results is presented. In the elastic range, the observed mechanical response is characterised using an orthotropic plane stress material model, which requires the definition of two Young's moduli, the Poisson's ratio and the shear modulus. Good agreement between the test results and the theoretical predictions based on the orthotropic material model is demonstrated. In the inelastic range, to describe the anisotropic yielding of the material, the well‐known Hill's criterion utilising the 0.2% proof stresses is employed. Overall, the elastic and inelastic properties of the studied material are shown to vary significantly with the direction of loading.
The coronary bioresorbable scaffolds (BRSs) are composed of either an aliphatic polymer or bioresorbable metal alloy. This chapter explores how to facilitate the understanding of mechanical features of the materials used for bioresorbable scaffolds. The leading bioresorbable scaffolds are primarily comprised of poly (L-lactide) (PLLA) or magnesium alloy (WE43-type). The mechanical properties of magnesium alloys are improved by inclusion of other chemical elements in the alloy formulation. A problem with some magnesium (Mg) alloys is their high corrosion rate at physiological conditions, which can make their biodegradability faster than the treatment time. PLLA exhibits a gradual reduction in molecular weight over time without an appreciable mass loss for most of the time. PLLA hydrolyzes more slowly under neutral pH and more quickly under acidic and alkaline conditions. The investment in resources to develop bioresorbable scaffolds suitable for use in complex lesions offers the benefit of unconstrained, treated arteries.
