Under the microscope

29th June 2018

This article is taken from our April issue of My Life magazine. You can read the whole magazine here, or to subscribe to receive a free copy via email or post please sign up here.

Cardiomyopathy specialist and consultant cardiologist to Liverpool FC, Professor John Somauroo, says assessing longitudinal strain is an exciting new technique in the diagnosis and treatment of many cardiac diseases.

Regular exercise is important to help reduce cardiovascular disease and hearts can change in shape and function after only a few hours of exercise per week. These changes are usually physiological and normal, (athletic heart). However, hearts can change in shape and function as a result of damage from many conditions, including myocardial infarction, or due to inherited cardiac conditions eg. dilated or hypertrophic cardiomyopathies.

Echocardiography is commonly used for assessing cardiac structure and function because of its ease of application, non-invasive nature, safety and ability to provide a vast amount of information. For many decades, measurement of ‘ejection fraction’ (percentage of blood volume leaving heart) has been used as the main determinant of left ventricular systolic function (contraction). Although modern

Echocardiography techniques have improved the accuracy of assessing ejection fraction, this may still not correctly assess left ventricular function, especially when subtle cardiac dysfunction is present.

Picking up subtle changes in cardiac function has been difficult in the past, but newer echocardiographic techniques now give us a microscopic view of the heart. The heart is made up of layers of cardiac fibres, which are orientated in different directions around the heart. Ejection fraction is predominantly a measure of radial function (inwards motion). However, a great proportion of cardiac function is determined by longitudinal function (vertical movement apex towards valves), similar to the action of an accordion. It is important to measure longitudinal function, as this may be one of the first markers of cardiac disease, before changes in ejection fraction. Speckle-tracking echocardiography, which looks at the way small areas of the heart (speckles) move in different directions, is an innovative method of assessing cardiac function or ‘myocardial strain’. It can precisely measure the heart’s longitudinal function and also radial and circumferential strain rather than just in one direction (which ejection fraction measures). Detailed assessment can be made of specific areas of the heart, or a global assessment can be made (global longitudinal strain = GLS). Initially, these measurements were time-consuming, but advances in technology mean this is now practical enough to apply in a busy NHS clinic.

Results are often comparable to cardiac MR scans, but much quicker and no contrast agent is required as with cardiac MR. GLS may detect subclinical left ventricular dysfunction in a wide range of cardiac disorders, including ischaemic heart disease and valve disease before impact on the ejection fraction, so that patients can be offered early valve surgery. Patients with hypertrophic cardiomyopathy often have normal ejection fractions, whereas the longitudinal function may be reduced due to areas of damage (fibrosis). This is especially useful in differentiating athletic heart from cardiomyopathies. Patients being treated with chemotherapy (e.g. Herceptin in breast cancer) may have their treatment stopped if the ejection fraction falls too low. However, GLS can correctly identify those that do not have a true reduction in cardiac function allowing them to continue with chemotherapy. Ejection fraction has been a useful tool in assessing cardiac function in the past, but the use of speckle-tracking to assess longitudinal strain is an exciting new technique and a game-changer in diagnosis and treatment of many cardiac diseases.

*Have a word with your cardiologist to see if assessing the longitudinal function of your heart is something that would be useful for you