The main cause of the degeneration of the cardiovascular system is atherosclerosis and the diagnosis of pathology related to atherosclerosis is often based on anatomic measurements alone. Functional severity cannot be determined based these anatomic data and requires hemodynamic measurements. Hemodynamic measurements throughout the cardiovascular system are the main focus of this work. A general introduction discussing the aims and outline of this thesis is presented in chapter 1.The consequences of degeneration resulting from atherosclerosis on particular aspects of the cardiovascular system, hereby introducing the separate chapters of this work, are discussed shortly in chapter 2. Percutaneous coronary intervention is often performed to treat coronary artery disease. To reopen the coronary artery a variety of stents might be used. In chapter3, two types of stents, a bare metal stent and a drug-eluting stent, were compared with respect to anatomic and physiologic measurements. The stents were implanted in pairs within the same patient to exclude differences as a result of the biologic diversity between patients. No differences were obtained just before and just after the stent-implantation. At six-month follow-up, however, the drug-eluting stent showed superior results compared to its bare metal counterpart, not only with respect to anatomic but also with respect to physiologic characteristics. It was found that, in contrast to the bare metal stent, the sirolimus stent maintained a normal wall shear stress value within the stented segment. This global wall shear stress estimation is a better indicator for the local hemodynamics within the stent than the anatomy-derived parameters alone because it accounts for the average cross-sectional velocity as well. Pressure derived fractional flow reserve was significantly higher and the hyperemic trans-stent gradient significantly lower for the drug eluting stent. Theoretically, the latter finding improves the possibilities of interventional treatment of patients with multiple non-adjacent lesions within one artery. However, despite the superiority based on anatomic and hemodynamic results,the increased risk of (sub-) acute in-stent thrombosis asks for a deliberate choice forusing multiple drug-eluting stents. Irrespective of the consequences of the results, it can be concluded that the drug-eluting sirolimus stent is superior to its bare metal counterpart with respect to hemodynamic characteristics at follow-up. Physiologic measurements have been used in chapter 4 as well to determine the influence of the orientation of a bi-leaflet valve prosthesis on coronary perfusion. It was hypothesized that coronary blood flow was altered by the ejection velocity of the blood through the mechanical valve prosthesis. This influence was assumed to be dependent on the orientation of the valve prosthesis. Therefore, three groups of patients were included in the study and compared with respect to coronary perfusion pressure. Patients receiving a mechanical bi-leaflet prosthesis were randomized to either the orientation with the hinge mechanism parallel to a line drawn between the coronary ostia, or the orientation with the hinge mechanism perpendicular to aline drawn between the coronary ostia. Patients receiving bio-prosthesis comprised the control group. Six months after aortic valve replacement a catheterisation was performed and pressures were measured at several spots in the aorta and under several circumstances. From the results of this study it can be concluded that the influence of a bileaflet prosthesis on coronary perfusion pressure was negligible and not dependent on valve orientation. Moreover, coronary perfusion pressures did not differ significantly between mechanical and biological prostheses.Chapters 3 and 4 have focussed on coronary physiology of the epicardial arteries. To interrogate the coronary microvasculature, the ability to measure absolute coronary blood flow would be desirable. In chapters 5, 6, and 7 a technique based on continuous infusion thermodilution has been developed and validated. Theoretically, absolute coronary blood flow through a selective coronary artery could be calculated from the temperature of the blood, the saline, and the mixture downstream of the injection site, combined with a known infusion rate. Application of the technique to obtain reliable values for coronary blood flow requires the blood and the saline to be completely mixed downstream of the site of injection. In the mixing process the design of the infusion catheter plays an eminent role. An in-vitro model is described in chapter 5 to validate the technique for several infusion catheter designs, infusion rates, and sensor positions. Safety and applicability of the continuous infusion thermodilution technique was tested in animals (chapter 6). Five mongrel dogs were instrumented with aperivascular flow probe to obtain true reference flow. During the experiments aspecially designed infusion catheter, as described in chapter 5, was used. Bloodflow values determined with the continuous infusion thermodilution method were compared to the true reference flow measured by the perivascular flow probe. Next, the technique was applied in humans which is described in chapter 7.
|Qualification||Doctor of Philosophy|
|Award date||18 Dec 2008|
|Place of Publication||Eindhoven|
|Publication status||Published - 2008|