Combining cardiopulmonary exercise testing and exercise echocardiography

: Understanding the relationship between cardiac contractile function and exercise tolerance

Abstract

Most diseases of cardiac function are defined by a description of the heart at rest. However, at rest, symptoms are often less evident and are often exacerbated when patients are exerting themselves. Resting examination shows a high degree of overlap between normality and disease. Cardiopulmonary exercise testing (CPET) provides an overall assessment of a patient’s well-being and can be combined with echocardiography. This thesis uses the highly quantifiable and validated measures from CPET to describe how anatomical and physiological augmentation measured during exercise echocardiography relates to exercise tolerance. In order to do this a distinct population of 69 patients with atrial fibrillation (AF) were examined in study one. The absence of any relationship between resting echocardiographic parameters and exercise parameters justified the subsequent range of studies to assess different disease states under stress conditions to try and establish a relationship between heart function and exercise tolerance. Study two, examined 80 patients with systolic heart failure and demonstrated that of all the measured parameters, systolic longitudinal velocity (S’) measured on exercise was a powerful predictor for survival and cardiac hospitalisation. Study three was established to determine if this powerful relationship to prognosis translated into a greater response to cardiac resynchronisation therapy (CRT) in 38 patients with systolic heart failure clinically selected for CRT. However peak exercise S’ was unable to predict a positive response to patients receiving CRT. Study four examined the relationship between exercise S’ and other echocardiographic parameter to VO_2peak and clinical outcomes in 32 patients with severe aortic stenosis. Exercise tolerance was an important predictor of adverse events rather than valve severity and heavily dependent on the ability of the left ventricle to augment its longitudinal velocity during exercise. All of these studies highlight the powerful relationship between systolic myocardial velocity VO_2peak, and prognosis. However focus has always been on peak values. The normal augmentation of heart function described using S’ throughout exercise and its relation to increasing VO₂ was still poorly described. Study five investigated this augmentation curve in 57 healthy first time marathon runners. The shape of the myocardial augmentation curve and its relation to ̇is described as a linear function with good relationships between VO₂ and S’. The slope between S’ and ̇VO₂ showed a strong positive relationship with peak suggesting that submaximal slope values are able to predict VO_2peak values which is valuable in patients who are not able to exercise to maximal exertion. This is new way to describe heart function and critically appraised in more detail than ever before. Integrating CPET with exercise echocardiography provides unique and robust data that can provide new and valuable insights into disease processes. It provides greater insights into contracting of diseased myocardium and exercise tolerance. This thesis demonstrates that contractile reserve and VO₂ are strongly related and examining them both simultaneously provides mechanistic and diagnostic insights.

Date of Award	Nov 2018
Original language	English
Awarding Institution	University of Brighton
Supervisor	Gary Brickley (Supervisor)