Systematic Assessment of Competitive Flow in Coronary Artery Bypass Grafts by Wave Intensity Analysis

Lead Research Organisation: Imperial College London
Department Name: National Heart and Lung Institute

Abstract

Narrowing of the arteries that supply blood to the heart can lead to heart attacks and death. One way of treating this is to use artery and vein grafts from other parts of the body to bypass the narrowing. However, the blood flow from these grafts competes with flow through the natural coronary artery. This is called competitive flow and it is thought to contribute to grafts becoming blocked.

During this fellowship I will study patients who have had bypass surgery to determine the pressure changes responsible for competitive flow. This has never been performed in humans; however our unit has now developed the technology to make this possible. It will improve our understanding of why some grafts last longer than others and help surgeons decide more objectively, where to place grafts. In addition further studies based on these result may allow the development of a novel test guiding doctors when to treat a narrowed graft on order to prevent subsequent blockage.

Technical Summary

Coronary artery disease is the leading cause of morbidity and mortality in the developed world. Coronary artery bypass grafting is one of the main therapeutic options. However, approximately 50% of Saphenous Vein Grafts (SVG) and 10% of Internal Mammary Artery (IMA) grafts are occluded at 10 years. One factor thought to contribute to this is competitive flow. Competitive flow is a result of the interaction between native vessel and graft flow. In the coronary circulation this is influenced by both proximal (aortic) and distal (intramyocardial microvascular) pressures affecting both native and graft vessels. These pressure changes have never been measured in humans in relation to coronary grafts.

A new technique (Wave Intensity Analysis), which takes advantage of commercially available wires with pressure and Doppler flow sensors, has been used to assess changes in pressure arising proximally and distally in coronary arteries. During this fellowship I will apply Wave Intensity Analysis (using such wires) to patients undergoing coronary angiography with previous bypass surgery. I propose to assess the changes in proximal and distal pressures in grafted coronary arteries and grafts to determine the pressure gradients responsible for competitive flow. I will determine how flow at the native-graft junction varies according to (i) the timing of the pressure changes in graft versus native vessel, (ii) the mass of viable myocardium supplied and (iii) the severity of native vessel stenosis.

This study offers a unique opportunity to define competitive flow and its effect on graft haemodynamics and how this varies with graft length, severity of native vessel stenosis and myocardial viability. The findings of these studies will lead to a better understanding of the factors responsible for graft failure and may subsequently lead to improvements in surgical practice (influencing type of graft and location of its insertion) with a consequent reduction in occlusion. Furthermore, current investigations to determine the haemodynamic significance of a coronary stenosis, such as Fractional Flow Reserve are not employed in bypass grafts due to the confounding effect of competitive flow. Hence defining its effect on coronary graft haemodynamics may allow the development of a novel means of assessing the haemodynamic significance of bypass graft stenoses, providing guidance to the interventional cardiologist regarding the treatment of graft disease; a common long term complication of bypass surgery.

Publications

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Broyd CJ (2016) Estimation of coronary wave intensity analysis using noninvasive techniques and its application to exercise physiology. in American journal of physiology. Heart and circulatory physiology

 
Title instantaneous wave-free ratio 
Description A novel pressure only vasodilator free index of coronary artery stenosis severity that can be applied to a wider group of patients than existing measures. 
Type Of Material Physiological assessment or outcome measure 
Provided To Others? No  
Impact Manuscript: Development and validation of a new adenosine-independent index of stenosis severity from coronary wave intensity analysis Results of the ADVISE (ADenosine Vasodilator Independent Stenosis Evaluation) study, Journal of the American College of Cardiology, in press. Instantaneous wave-free ratio will permit the study of coronary haemodynamics in conditions previously excluded due to the need for pharmacological vasodilatation. 
 
Description Development and validation of instantaneous wave-free ratio 
Organisation San Carlos University Hospital
Department Cardiovascular Institute
Country Spain 
Sector Academic/University 
PI Contribution Application of wave intensity analysis to patients recruited to collaborating centre
Collaborator Contribution 1. Increased rate of patient recruitment 2. Permitted study in a different subgroup of patients 3. Contribution to data analysis and interpretation
Impact Manuscript: Development and validation of a new adenosine-independent index of stenosis severity from coronary wave intensity analysis Results of the ADVISE (ADenosine Vasodilator Independent Stenosis Evaluation) study. The Journal of the American College of Cardiology
Start Year 2010
 
Description Pressure and flow assessment of coronary haemodynamics 
Organisation Academic Medical Center
Country Netherlands 
Sector Academic/University 
PI Contribution Pooling of data. Joint analysis and manuscript writing. Joint recruitment
Collaborator Contribution Pooling of data. Joint analysis and manuscript writing. Joint recruitment
Impact In progress
Start Year 2012