Stress Echocardiography in the Era of Fractional Flow Reserve

It is the aim of this review to demonstrate the relevance of stress echocardiography in the era of fractional flow reserve by establishing the current use of stress echocardiography and fractional flow reserve, underlining their physiological basis and through this demonstrating the clear differences in their application. The importance of the microcirculation is only now being understood, no more so than in the fact that abnormalities in the microcirculation, determined by abnormal coronary flow reserve, predict adverse mortality regardless of the normality of the epicardial coronary lesions. Stress echocardiography therefore gives a fuller picture of the overall cardiovascular risk to our patients in its ability to interrogate the epicardial vessels down to the microcirculation, with a number of techniques available to measure coronary flow reserve such as myocardial perfusion stress echocardiography and transthoracic Doppler stress echocardiography of epicardial coronary vessels. Fractional flow reserve can then add further information by determining whether a coronary artery lesion is responsible for myocardial ischaemia. In an era of fractional flow reserve affording the resolution of myocardial ischaemia down to the specific lesion, it can be tempting to think that other generally non-invasive techniques no longer have a role in the investigation and management of coronary artery disease. This, however, betrays a lack of understanding of the scope and complexity of coronary artery disease from epicardial vessels down to the microvasculature, the physiological basis of the tests available and therefore what, in fact, is actually being measured. For some, fractional flow reserve is held as a gold standard by which to compare other techniques such as stress echocardiography as correct or incorrect. However, these tests do not measure the same thing, and therefore, they cannot be directly compared. Stress echocardiography gives a fuller picture through its ability to account for the coronary flow reserve, considering the epicardial vessels down to the microvasculature. Fractional flow reserve is far more specific, looking at the effect of the lesion being interrogated. Furthermore, where fractional flow reserve is normal, we now know that knowledge of the coronary flow reserve is critical as it is this that allows us to predict the overall mortality risk of our patient. We therefore require a combination of the two techniques.