Investigation of the Role of Hemodynamics in Re-stenosis of CABG Patients
Condition: Coronary Artery Disease; Stable Angina; Unstable Angina
MeSH terms: Coronary Artery Disease; Angina Pectoris; Angina, Stable; Angina, Unstable
Study type: Observational

Summary: 
      CFD simulations in this study provide detailed hemodynamics information, which cannot be
      obtained from cardiac images alone. The investigators hypothesize that our proposed
      simulations will provide strong correlation between hemodynamic parameters, such as WSSG and
      SPA, and clinically identified graft stenosis. These correlations will allow the
      investigators to identify the future patients at high risk of graft stenosis and lead to
      future researches on optimizing and refining surgical plans, such as finding optimal proximal
      and distal anastomoses locations, optimal graft length and diameter, which could lead to
      improved longevity of the graft. Once CFD coupled shape optimizer is validated, it could be
      part of the surgical simulator to help in training the next generation physicians. It could
      provide new viewpoints for assessing whether some modified surgical techniques are better or
      not. It could also aid in designing and evaluating the vascular medical devices, including
      stent, artificial graft, and etc., which would lead to better surgical outcome.
    

Detailed description: 
      Since the introduction of saphenous vein grafting in the late 1960s, CABG, with or without
      arterial conduits, remains the gold standard for management of intractable angina due to
      coronary artery occlusive disease. According to the statistics of American Heart Association,
      571,000 of bypass procedures were performed on 355,000 patients in 1999. In Singapore, 831
      CABG surgeries were carried out in 2011. With the aging of society, the number of bypass
      operations is suspected to keep increasing over the years.

      However, the CABG was not without complications. The saphenous vein, which is the most
      commonly used vessel for grafting, provides only palliation of the ongoing process.
      Approximately 15% to 20% saphenous vein grafts occlude in the first year. An additional 2% to
      5% grafts occlude each year between 2 to 10 years postoperatively. At 10 to 14 years, 50% of
      the grafts are occluded. Similar data is reported in 2011 ACCF/AHA CABG guideline. Although
      thrombosis, intimal hyperplasia and atherosclerosis are found by pathological examinations,
      the exact mechanism of stenosis is still not fully understood. The investigators hypothesize
      that localized hemodynamic parameters is related to the sites of graft occlusion.

      Hemodynamic parameters are propounded to be involved in localization of arterial stenosis in
      literatures. High wall shear stress was found to lead abnormal endothelia cells by Fry on the
      study of thoracic aorta in dogs. Intimal thicken and atherosclerosis was found to be
      developed in the low WSS region when studying stenosis on postmortem human carotid
      bifurcations, synthetic grafts on dog's carotid arteries and human coronary arteries. Both
      high and low WSS segments was found to interplay with plaque development on human coronary
      arteries. Bovine aortic endothelial cells density was found to increase in the high wall
      shear stress gradient regions by Depaola and colleagues. Significantly increased WSSG was
      found at the throat of the cervical carotid stenosis by Schirmer and colleagues for 8
      patients. Stress phase angle was proposed to be a useful indicator in predicting sites prone
      to atherosclerosis by Torii et al. when investigating a patient's right coronary artery with
      stenosis. Low-density lipoprotein transportation was proposed to be a useful indicator in
      predicting sites prone to atherosclerosis on human left coronary artery by Olgac and
      colleagues.

      All of these hemodynamic parameters are related to the forces acting on the endocellar cells,
      especially the wall shear stress. Signaling pathways have been proposed, which mediate the
      mechano- chemical transduction in endothelial cells in response to disturbed WSS. Among the
      WSS-related parameters, WSSG and SPA may be the most important, as WSSG measures the impact
      of changes in surface forces, while SPA refers to the phase angle between WSS and WCS.
      Therefore direct study on the human with CABG is necessary to provide strong correlation
      between graft stenosis and hemodynamic parameters, which would be helpful in identifying the
      patients at high risk of re-stenosis and optimizing the surgery from a mechanical standpoint.
      The current project aims to fill in this gap.
    

Intervention name(s): Computed Tomography Angiography; Intra-operative graft flow rate measurement
Intervention type(s): Other; Other
Intervention description(s): The CTA is non-invasive and is used commonly for patients who have chest pain to assess the coronary artery disease, prior to the more invasive coronary angiogram.; This procedure involves the insertion of a Medistim Ultrasound Transit Time Flow Probe into the graft vessel to measure its flow rate. This technique is commonly used for evaluating graft opening during CABG surgery.
Observational model: Case-Control
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Potential patients scheduled for Coronary Bypass Surgery identified at NHCS cardiology
        inpatient and patients with stable/unstable angina from cardiology inpatient and outpatient
        clinic.