A new model for the pressure relaxation of the left ventricle is proposed. The model presumes that the myocardium relaxes asynchronously, but that when regions begin to relax, after a delay, the local wall stress decays as a mono-exponential process. This formulation results in an apparently bi-exponential process (two time constants) which has been previously reported. It is shown that the ratio of the two time constants (T2/T1) can be interpreted as the fraction of the myocardium which relaxes synchronously. Data are presented illustrating the Model during transient coronary occlusion in patients undergoing percutaneous transluminal coronary angioplasty.
The introduction of the coronary stent in 1986 was one of the most far-reaching changes in the practice of interventional cardiology since its inception in 1977. Despite all the benefits of the using a metallic drug eluting stent (DES), their limitations have generated interest towards biodegradable technology. These biodegradable stents, which are made of polymers or metal alloys with or without a drug coating, have the potential to scaffold the artery to allow natural healing to take place, and then biodegrade. The development of this technology has been slow, however several biodegradable stents have entered into clinical trials, with many more at the preclinical stage of development. Concurrently conventional metallic DES have tried to address their limitations; in particular they have sought to repair their damaged reputation following concerns over stent thrombosis. Accordingly, stents with a more biocompatible polymer and DES which are polymer-free have been developed, and are currently being evaluated in clinical trials. This article will review the status of biodegradable stents, and these newer DES, during this exciting period in interventional cardiology as technology strives to develop the ideal coronary stent.
A 54-year-old female presented with inferoposterior ST-segment elevation myocardial infarction. Coronary angiogram revealed total occlusion of the proximal left circumflex artery. Following a thrombus aspiration, without administration of glycoprotein IIb/IIIa inhibitor, direct stenting with a drug-eluting metallic stent was performed. After stent implantation, angiogram showed thrombolysis in myocardial infarction (TIMI) grade III flow, without any evidence of intraluminal defect …
Abstract The odd-even behaviour observed for liquid crystal dimers has been predicted to be a sensitive function of the geometry of the link joining the mesogenic groups to the flexible spacer. Here we report the synthesis of two cyanobiphenyl dimers with methylene links, together with a determination of their transitional properties. In particular we have probed their orientational order via the major and biaxial orientational order parameters of a solute molecule, anthracene-d 10, using NMR spectroscopy. For comparison we have also determined the corresponding quantities for the cyanobiphenyl dimers with ether links. The enhanced odd-even effect observed for the methylene linked dimers relative to those with ether links is in good accord with theory.