18/01/2016
Cardiac MRI – Revolutionizing The Management Of Cardiovascular Disease
Cardiovascular disease is the leading cause of death around the world, and the Middle East is no exception – according to the World Health Organization (WHO), the Middle East has one of the highest rates of cardiovascular disease-related mortality in the world. The prevalence of smoking, the high rates of obesity and diabetes, and low rates of physical activity in the Arab world are all to blame.
Although primary prevention of cardiovascular disease, tackling risk factors is always an important goal, timely and accurate diagnosis of heart disease remains an important challenge that is integral to improving disease outcomes. In this regard, new imaging technologies, including cardiac magnetic resonance imaging (MRI), are changing the diagnosis landscape. By allowing non-invasive visualization of the structure and function of the heart as a whole, these new technologies facilitate diagnosis as well as detection of early disease, with the aim to begin treatment and prevent further damage.
Imaging modalities have significantly evolved over the years and now encompass, in addition to the traditional ultrasound and nuclear techniques, special X ray called computed tomography and cardiac MRI. Most of these techniques are available to any facility that takes care of patients with cardiovascular disease and along with appropriately trained staff, have the potential to revolutionize diagnosis and treatment. As such, we need to ensure that clinicians and patients take advantage of this potential and become more familiar with their uses. Will focus today on cardiac MRI.
What is cardiac MRI?
Cardiac MRI has emerged as a key non-invasive imaging approach that has proven to be useful both for diagnosis as well as prognosis for a wide range of cardiovascular diseases. Like other MRI applications, cardiac MRI uses radiofrequency waves, a powerful magnet (around 30,000–60,000 times the strength of the earth's magnetic field) and a computer to create a detailed two-dimensional or three-dimensional picture of the heart. This means that it can be used for real-time imaging of the heart, heart valves and the aorta, as well as the flow of blood through these tissues, and also offers an assessment of the properties of the heart muscle itself.
There are different cardiac MRI techniques that together can offer a more comprehensive assessment of the heart. For example, cardiac MRI can involve the use of a dye (to measure, for instance, the extent of heart damage) or can acquire images of the heart during different stages of the cardiac cycle over several heart beats.
From a clinical perspective, this offers us the ability to visualize and quantify where damage has taken place in patients who have suffered a heart attack, but also to identify areas of the heart that have reduced blood flow owing to blockages or narrowing of the arteries. Other cardiovascular diseases, including valvular heart disease, congenital heart disease, and their effects on the heart function and remodelling can also be imaged.
Beyond diagnosis, cardiac MRI can be used as a prognostic tool, offering useful insights on the effectiveness of a particular treatment, which could be invaluable in the context of clinical trials. Indeed, it is now arguably the gold standard for assessing new interventions for myocardial infarction3.
Benefits over other diagnostic tools
This ability to obtain a more complete picture of the heart, its structure, physiology and function is the key benefit of cardiac MRI over more traditional diagnostic tools such as an electrocardiogram (ECG) or nuclear imaging. Specifically, an ECG records the electrical impulses that are produced by the heart to make the heart muscle contract. Although this is still clinically useful in diagnosing rhythm abnormalities and whether an acute injury of the heart is occurring (acute heart attack or myocardial infarction), among others, such information is greatly limited when compared with the more complete picture offered by cardiac MRI.
Other imaging techniques, including cardiac computed tomography (CT) and ultrasound, also offer invaluable insights that help in the early diagnosis of disease. Indeed, these methodologies complement each other for diagnosis and treatment, and more than one technique will frequently be used to get a better picture of the condition. But in terms of safety, cardiac MRI offers the advantage over CT of not using radiation to generate the image of the heart.
It is, however, important to note here that, like with other MRI applications, cardiac MRI uses a magnetic field, which may be contraindicated in some patients, for example those with older pacemakers. This further emphasizes the importance of selecting an imaging approach based on the patient’s specific circumstances.
Uses of cardiac MRI
It is clear that cardiac MRI has the potential to inform the diagnosis and treatment of a range of cardiovascular conditions. Below is a list of current applications of cardiac MRI to help guide clinicians during the decision-making process. Of course the applications are not limited to the below, and new uses, including T1 mapping and coronary MRI, are also emerging.
Myocardial viability.
Being able to distinguish between viable and dead tissue is a key requirement when evaluating patients who have suffered a heart attack or show cardiac dysfunction. Cardiac MRI is a highly accurate method for assessing and quantifying the presence of scar tissue in the heart. In this context, cardiac MRI is also referred to as viability imaging as it is the only technique that can image and quantify a scar in the heart; it is now the standard approach to measure heart damage, be it secondary to an infarct or from other conditions such as heart inflammation or infection (myocarditis, cardiomyopathy, sarcoid disease). Other characteristics of the infarct, including oedema and haemorrhage in the myocardium, can also be assessed through cardiac MRI.
Ischaemia.
Cardiac MRI allows the visualization of blood flow to the heart (perfusion) and can therefore be an important diagnostic tool for blood flow restriction, or ischaemia particularly during stress testing. Simple visual evaluation of ischaemia is very common in clinical practice with nuclear techniques or echocardiography, but cardiac MRI also offers the ability to quantify the extent of ischaemia3 along with pre-existing scar and total heart function in the same setting.
Valvular disease.
Although echocardiography remains the first-line method of assessing the morphology of heart valves and any related abnormalities that could affect heart size and function, cardiac MRI has become an essential tool in evaluating valvular diseases. Cardiac MRI can be used to identify narrowing of the heart valves as well as leakage of blood back into the heart owing to improper closing of the heart valves (regurgitation) such as aortic regurgitation and mitral regurgitation. Importantly, it is the most accurate modality in quantitating the amount of regurgitation. It is also ideal in situations where the aortic valve is also associated with diseases of the aorta such as a congenitally malformed aortic valve.
Pericardial disease.
Unlike other fields in cardiology, pericardial disease (that is, disease affecting the sac tissue surrounding the heart), has received little interest, and diagnosis is complicated by the fact that pericardial disease can mimic other cardiac or lung diseases. In this regard, imaging approaches, and in particular cardiac MRI, offer invaluable insights on pericardial morphology and effects on cardiac function, and especially the ability to integrate these two aspects in one single examination. Cardiac MRI is increasingly becoming the gold standard non-invasive technique for assessing pericardial disease, including pericarditis (inflammation of the pericardium), pericardial effusion (an increased amount of pericardial fluid) and pericardial constriction (an abnormal thickening of the pericardium).
Congenital heart disease. Imaging is essential for the diagnosis of congenital heart disease, and cardiac MRI now has an integral role, facilitating early diagnosis and treatment. Although echocardiography is the first-line imaging approach used for paediatric patients, cardiac MRI is indicated for patients for whom echocardiography data have been insufficient to facilitate decision-making, particularly complex congenital heart disease.
Non-ischaemic cardiomyopathy.
Cardiac MRI offers invaluable insights on the cause, progression, treatment response and prognosis of non-ischaemic cardiomyopathies, such as sarcoidosis, hypertrophic cardiomyopathy, idiopathic dilated cardiomyopathy or that secondary to iron overload, and infiltrative disease like amyloidosis.
New imaging technologies have really expanded our ability to visualize the heart without having to use invasive procedures such as heart catheterization. Cardiac MRI in particular has shown great promise in the early and accurate diagnosis of a range of heart conditions and is rapidly becoming the gold standard. We now need to ensure that clinicians (and patients) are familiar with its uses to promote its wider clinical acceptance and, ultimately, improve clinical outcomes for patients.
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