Non-invasive and contemporaneous cardiac imaging in heart failure

Heart failure remains a major public health problem with just under 1 million people in the UK known to be living with it (Conrad et al, 2018). The past 20 years have been marked by important medical advances in diagnostic and treatment options; however, a diagnosis of heart failure carries worse survival outcomes than most common cancers, such as breast, lung, prostate and bladder (Mamas et al, 2017). Heart failure is not a single pathological process, but a chronic and complex clinical syndrome secondary to structural or functional changes of the heart. According to its classical definition (Braunwald, 1988), heart failure is described as the heart's inability to pump blood across the body at the rate needed to match its physiological needs. Any cardiac disease damaging the functional or structural components of the heart has the potential to cause heart failure and identifying the cause is essential to guide decision-making on evidence-based treatment options. The most common contributors to heart failure include coronary artery disease, diabetes, hypertension and obesity. Less common are cardiomyopathies (defined as a disease of the heart muscle affecting size, shape or thickness), infections, toxins and valvular diseases (Groenewegen et al, 2020).

Heart failure patients report high symptomatic burden and functional limitations on daily activities due to symptoms of breathlessness, fatigue and peripheral or central oedema, contributing to reported low health-related quality of life. In addition, non-cardiac comorbidities such as diabetes mellitus, renal disease and chronic obstructive pulmonary disease are frequently associated with heart failure, being predictors for mortality and further increasing hospital admission rates (Gimeno-Miguel et al, 2019). There exists a strong evidence base, supported by the results of randomised controlled trials (Strömberg et al, 2003; Oyanguren et al, 2021), showing that the role of heart failure specialist nurses improves patients' outcomes. They are also independent practitioners ideally placed to co-ordinate these patients' care plans by evaluating, assessing, and making informed and evidence-based decisions. The 2021 British Society for Heart Failure Nurse Forum competency framework for heart failure specialist nurses acknowledges the importance of understanding and interpreting the role of cardiac imaging investigations throughout each patient's disease trajectory (Barton et al, 2021). It is important that specialist nurses have not only good history taking and physical examination skills, but also knowledge regarding the currently accepted non-invasive cardiac imaging modalities used in heart failure, enabling them to meet their clinical competencies and deliver efficient high-quality patient care. This article will review the current non-invasive cardiac imaging modalities used in the diagnosis and management of heart failure patients.

Current recommendations to determine causes of heart failure

Heart failure is a complex multifactorial syndrome with various possible underlying causes. Most patients will initially present to primary care with signs and symptoms of heart failure, such as breathlessness, fatigue and peripheral swelling without being given a correct diagnosis, due to many potential differential diagnoses presenting with similar symptoms (such as breathlessness). Currently there is an average delay of almost 10 months from the onset of symptoms to diagnostic testing (Hayhoe et al, 2019).

Non-invasive cardiac imaging modalities play an important role in clinical practice by supporting early objective diagnosis and subsequent appropriate treatment. Advanced information on structure and function of the heart is now possible through techniques such as cardiac magnetic resonance (CMR) imaging, computed tomography (CT) and echocardiography (transoesophageal or transthoracic) (Groenewegen et al, 2020). Decisions regarding which cardiac imaging modality is to be used depend on the patient's own characteristics, clinical presentation, and the differential aetiology behind suspected heart failure (Table 1).

Transthoracic echocardiogram

Echocardiography remains the most used cardiac imaging investigation because it is reproducible (the same measurement can be done even when the condition changes) and repeatable (the same measurement can be re-measured under identical conditions), allowing easy accessibility and lower costs when compared with other imaging methods (Armstrong, 2018; Bunting et al, 2019). Transthoracic echocardiography uses ultrasound technology to image the heart via a probe that sends sound waves through the patient's chest wall. To standardise practice and obtain clear pictures of the different structures of the heart, including valves, chambers and vessels, four ‘echo windows’ have been created, corresponding to the location where the technician places the probe (Houghton, 2009) (Figure 1).

Pictures are collected throughout the cardiac cycle, and this is done via three modalities: 2D moving images, motion mode (M-mode) and Doppler measurements (Robinson et al, 2020). The images in 2D are displayed in a shape of a cone with the narrow top corresponding to the probe's location on the chest wall. Still images offer information on dimensions of chamber sizes, whereas moving images of the cardiac cycle allow assessment of left ventricular systolic and diastolic function as well as right ventricular and left atrial function (Houghton, 2009).

LV function assessment – an essential measurement in heart failure

Left ventricular systolic function is measured and described as ejection fraction. Left-ventricular ejection fraction (LVEF) measures the left ventricular function during systole and calculates the fraction of blood ejected from the left ventricle in systole (stroke volume) in relation to the volume of blood at the end of diastole, expressed in percentage (Bonita, 2002). Measuring LVEF has an important role in clinical practice, due to prognostic value and treatment option. Patients with reduced or mildly reduced systolic phenotypes are offered disease-modifying therapies, supported by well-accepted randomised controlled trials, improving mortality, morbidity, and quality of life. On the other hand, for patients diagnosed with heart failure with preserved ejection fraction (HFpEF), often referred to as diastolic heart failure, there are currently no effective pharmacological treatments, despite multiple randomised controlled trials (Pitt et al, 2014; Solomon et al, 2019). Figure 2 illustrates the changes in ejection fraction in both systolic and diastolic dysfunction as a consequence of the morphological changes in the cavity, mass, and geometry of the heart, often referred to as cardiac remodelling.

Left ventricular function is mostly quantified using the Simpson biplane method, where tracings of the left ventricle cavity are used to calculate ejection fraction (Figure 3). The choice between methods depends on the type of modality used (2D, M-mode or 3D), but the biplane method is the current 2D method for assessment of LVEF recommended by the American Society of Echocardiography and the European Association of Cardiovascular Imaging, requiring fewer geometrical assumptions of the left ventricle when compared with other methods (Lang et al, 2015). Adding to practice challenges and ambiguities, reporting can differ between imaging centres, as it can be carried out in a quantitative (ejection fraction value) or qualitative manner but both descriptors should relate, as in Table 2.

Valvular disease and transoesophageal echocardiography

Significant valvular heart disease has been found in 14% of patients undertaking an echocardiogram because of suspicion of heart failure, with 37.5% displaying only mild valvular disease (Marciniak et al, 2017). Moderate and severe mitral regurgitation is known to be the one of most common valvular diseases in western populations (Podlesnikar et al, 2018) and in an observational study of 79 043 patients with suspected heart failure, 12.5% of the patients were found to have mitral regurgitation. The second most common valve pathology was aortic stenosis, affecting 10% of the studied cases (Marciniak et al, 2017). This has significant implications for practice as at least a third of severe aortic stenosis cases are not referred for surgery despite severe symptoms of heart failure and evidence of left ventricular compromise (Everett et al, 2018).

Historically, valvular heart disease has been at the heart of non-invasive imaging technological advances, with imaging techniques seeking to provide information on the pathophysiology, progression, and repercussion of valvular heart disease. Echocardiography remains the key modality to confirm valvular heart disease, through colour-flow mapping it allows assessment on its severity and prognosis. Despite technical advances, body habitus can result in suboptimal image quality on both obese or underweight patients. Furthermore, 2D images often lose the image quality resolution needed to evaluate smaller structures such as valves, thus transoesophageal echocardiography (TOE) methods are often recommended as providing far superior quality results. These are also considered when there is suspicion of thrombosis, prosthetic valve dysfunction or endocarditis. These methods involve placing an ultrasound probe into the patient's oesophagus, providing more detailed images of smaller structures such as valves (Vahanian et al, 2022).

When in the presence of mitral regurgitation, the ejection fraction might falsely appear normal (often described as overestimated) since a considerable amount of blood ejected from the left ventricle is passing back through the left atrium and not into the aorta (Armstrong, 2018).

Another challenge in patients presenting with concomitant valvular disease and heart failure symptoms is to determine whether the left ventricular impairment is being caused by the valvular or ventricular pathology. In those exhibiting heart symptoms with confirmed aortic stenosis, the left ventricular dysfunction tends to be a consequence of this valve disease. On the other hand, patients with heart failure symptoms with confirmed functional mitral regurgitation, left ventricular impairment and cardiac remodelling are the primary culprits, subsequently responsible for mitral valve malcoaptation (Podlesnikar et al, 2018). This distinction and diagnosis are relevant to clinical practice as it allows clinicians to guide treatment options, targeting the primary and likely cause of symptoms. When a diagnosis is made of severe mitral regurgitation with high symptomatic burden for patients, the type of valve intervention varies depending on the degree of left ventricular functional impairment, evidence of myocardial viability in imaging diagnostic methods and revascularisation feasibility. Valvular surgery in severe mitral regurgitation is indicated when valvular heart disease is the primary cause of patients' symptoms and left ventricular systolic dysfunction. Guidelines suggest valve repair should be preferred over replacement. On the other hand, if revascularisation is indicated and feasible for patients with concomitant coronary artery disease, a decision to treat ischaemic mitral regurgitation needs to be made before valvular surgery as this intervention might reduce the severity of mitral regurgitation (Vahanian et al, 2022).

Cardiac magnetic resonance (CMR)

The diagnosis of heart failure is usually obtained via echocardiography, but this complex syndrome can have several different causes leading to structural and functional heart damage, often difficult to identify through echocardiogram or clinical presentation only. Cardiac magnetic resonance (CMR), also referred to as cardiac MRI, has gained recognition in the past decade and is now recommended with high-graded evidence in recent heart failure European guidelines (McDonagh et al, 2021). Although more costly, it presents several advantages in comparison with other imaging modalities, by exhibiting higher accuracy, reproducibility, larger field of view and lack of need to expose patients to radiation (Cosyns et al, 2015).

Ischaemic cardiomyopathy and CMR

CMR has become the gold standard in the field of non-invasive assessment by providing valuable parameters that allow specification of heart failure's underlying aetiology when other imaging modalities fail to do so. By adding invaluable information to the diagnosis, it guides specialists on both treatment decisions and prognosis estimates, identifying potentially reversible causes, such as coronary artery disease (Webb et al, 2018). It allows evaluation of the ventricular size, volume, and functions, further determining myocardial perfusion, viability and any mechanical dyssynchrony. Precise determination of myocardial viability is important in the management of any patient with cardiac dysfunction and identification of an infarcted muscle possibly indicates an ischaemic cardiomyopathy. When a viable muscle is recognised through CMR, this indicates a potential for recovery through myocardial revascularisation or angioplasty, dramatically changing the clinical management plan and survival outcomes (Perin et al, 2002; Souto et al, 2017).

Late gadolinium enhancement (LGE) imaging, often described in CMR reports, refers to regions of scar, necrosis or inflammation exposed in a pictorial way from normal tissue due to prolonged retention of gadolinium-based contrast agents (Table 3). It is a fundamental technique to make a distinction between an ischaemic or a non-ischaemic cardiomyopathy, based on where scar distribution is seen (Kramer, 2015). For example, a transmural myocardial infarction often involves the full thickness of the heart's myocardium (believed to be associated with presence of Q waves in ECGs), and can be made visible through LGE distribution. This provides valuable clinical information as it is often associated with poor likelihood of functional recovery even after revascularisation (Child and Das, 2012; Pontone et al, 2016). Although ischaemic heart disease is one of the most common causes of cardiac dysfunction, other causes of heart failure (regardless of ejection fraction) can be found through CMR, such as dilated cardiomyopathies.

Dilated cardiomyopathy and non-ischaemic cardiomyopathies

Dilated non-ischaemic cardiomyopathy is characterised by left or biventricular dilatation with impaired contractility, not associated with abnormal loading conditions or significant coronary artery disease (Pinto et al, 2016). The use of CMR with LGE allows its diagnosis via the presence of mid-wall scar or fibrosis. For patients, it has been identified as a predictor of significant mortality and cardiovascular hospitalisation, due to progressive heart failure and sudden cardiac death (Japp et al, 2016).

For the difficult cohort of patients labelled as HFpEF, CMR has the potential to reveal clinically relevant undiagnosed cardiac pathology after echocardiography. In an observational study of 150 patients, Kanagala et al (2018) found a portion of their otherwise categorised HFpEF participants had unknown coronary artery disease or microvascular dysfunction. This is likely secondary to these patients not being routinely referred for CMR and coronary artery disease investigation unless exhibiting symptoms of angina that were not responding to medical therapy.

Computed tomography coronary angiography

The management of chest pain remains challenging, accounting for 5-10% of accident and emergency visits in England and 25% of hospital admissions (Bidmead et al, 2015). Protocols on acute coronary syndromes are in place; however, most of the chest pain complaints are unrelated to acute coronary syndromes (Body, 2008). One of the most frequent causes of heart failure is coronary artery disease and often nurses will encounter patients with a history of chest pain. It is important to establish whether the chest pain is of cardiac origin, and guidelines suggest the first step is to employ good history taking and physical examination, focusing on assessment on the typicality of chest pain (National Institute for Health and Care Excellence (NICE), 2016). When clinical assessment suggests typical or atypical angina, further diagnostic investigations should be requested, with computed tomography coronary angiography (CTCA) being the primary choice if the patient is also presenting with ECG changes (ST-T changes or Q waves).

Cardiac computed tomography (CCT) is mainly an anatomical technique rather than a functional technique, using ECG recordings to synchronise cardiac data acquisition within specific phases of the cardiac cycle. Both images are mostly captured during diastole where the heart relaxes and is less dynamic. The presence and quantification of coronary artery calcification can predict the risk of future cardiovascular events, and the degree of calcification can be quantified through a multidetector computer tomography (CT) using a calcium scoring method called the Agatston score. Performed without contrast, the Agatston score is used to quantify the burden of coronary calcified plaque. Since this method does not capture obstructed coronary lesions that are not calcified, it is not recommended in cases of stable angina and should only be used for assessing risk of cardiac events (Mordi et al, 2017).

Besides the calcium scoring, CTCA is another CCT modality available, which due to significant technological improvements is now capable of offering detailed anatomical assessment of coronary artery disease, with high sensitivity and low false-negative diagnostic rates (Moss et al, 2017). Diagnostically, it is comparable to invasive coronary angiography, and due to its low cost and high sensitivity, it is the currently recommended non-invasive test in all patients presenting with typical or atypical anginal symptoms (NICE, 2016). Another advantage is that radiation exposure is also lower than invasive coronary angiography and nuclear stress perfusion testing.

Conclusion

Heart failure is a complex chronic syndrome with high symptomatic burden and an unpredictable trajectory, requiring not only early diagnosis but also timely access to disease-modifying therapies to achieve better health-related outcomes. Although good history taking and physical examination are essential in clinical practice to guide diagnosis and treatment choices, imaging modalities provide conclusive diagnosis on heart failure aetiology adding prognostic value, and therefore, guiding transparent conversations with patients.

Different imaging modalities have distinct strengths and limitations (see Table 4), and their use should be decided based on a patient's clinical presentation and characteristics.

It is important that specialist nurses understand the role that each cardiac imaging investigation can add to a patient's disease trajectory. This enables them to contribute to each patient's education in understanding of their own disease processes, and in devising individually tailored management plans.

KEY POINTS

• Heart failure is a syndrome with signs and symptoms that include but are not limited to breathlessness, fatigue and peripheral oedema – it can be the consequence of any cardiac disease causing damage to the structure or function of the heart
• Although good clinical assessment is fundamental to allow early diagnosis, referral to relevant cardiac imaging modalities is fundamental to confirm diagnosis, identify underlying cardiac problems, and guide treatment
• Transthoracic echocardiogram remains the most commonly used modality to assess the structures of the heart and study its function through the cardiac cycle, including left ventricular function
• Heart failure can be associated with coronary artery disease, disease of the valves and pathology of layers of the heart's walls (myocardium, pericardium or endocardium) – depending on the suspected cause, different cardiac imaging modalities will be suitable
• CT coronary angiography and cardiac MRI are more recent developments than echocardiography, but both provide valuable information otherwise not possible through other modalities

CPD reflective questions

• What is the value and importance of assessing left ventricular ejection fraction and how can it inform heart failure classification and diagnosis?
• If a patient presents with signs and symptoms suggestive of heart failure which imaging modality is considered first line and most commonly used? When will patients need to be referred for cardiac magnetic resonance?
• When is CT coronary angiography recommended and how does it compare (diagnostically) with invasive coronary angiography?