The Dynamic Interaction of Coronary Circulation, Left Ventricle and Aortic Valve during Exercise

Abstract

Introduction
The left ventricle, aortic valve and coronary circulation are intimately related. In studying physiology and developing risk stratification models, these systems cannot be considered in isolation. The main aim of the thesis was to improve our understanding of the coupling mechanisms between left ventricle, aortic valve and coronary circulation during exercise in two patient populations: aortic stenosis and coronary microvascular disease.
Methods
To characterize the microcirculation and define the forces governing flow, patients with aortic stenosis, coronary microvascular disease and a control cohort underwent simultaneous intra-coronary pressure and Doppler flow assessment, at rest, during exercise and hyperemia.
In addition, patients with moderate to severe aortic stenosis, underwent exercise stress echocardiography and predictors of exercise capacity and the development of symptoms were examined.
Results
Despite a greater myocardial workload in AS patients compared to controls at rest and during exercise, coronary flow was similar. Hyperemic flow was less in AS compared to controls. At rest coronary flow was higher and microvascular resistance was lower in patients with micorvascular disease compared to controls.
With exercise and hyperemia, the relative contribution of accelerating waves increased in controls. The opposite pattern was seen in aortic stenosis and microvascular disease.
The cardiac output reserve, defined as the ratio of cardiac output on maximal exercise to the cardiac output at rest was the only independent predictor of exercise capacity in aortic stenosis and the best predictor of the development of symptoms on exercise.
Conclusions
Under conditions of stress, patients with aortic stenosis develop a mismatch between myocardial supply and demand. Both patients with aortic stenosis and microvascular disease have a pathophysiological reduction in coronary perfusion efficiency in response to exercise and hyperemia.
Cardiac output reserve is an objective measure that integrates the physiological contributions of valve, ventricle, systemic circulation and chronotropic competence and may proof a useful tool in the risk stratification in aortic stenosis.

Date of Award	2016
Original language	English
Awarding Institution	King's College London
Supervisor	Divaka Perera (Supervisor) & John Chambers (Supervisor)