Cardiac Imaging is Central to the Diagnosis and Treatment of Cardiovascular Disease. Dr Christopher McAloon Assesses the Different Modalities Available, the Factors Affecting Efforts to Expand Access, and its Potential Role in the Future
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Cardiologists work in both secondary and tertiary care settings, and diagnostic cardiology services are also increasingly being provided in community centres. Imaging modalities—echocardiography, cardiac magnetic resonance imaging (MRI), cardiac computed tomography (CT), and nuclear cardiology—have a fundamental and evolving role in the diagnosis and management of cardiovascular disease (CVD), the early diagnosis of which is a clinical priority in the NHS Long-Term Plan.1 In addition, advances in technology offer great potential for how imaging can be used in the future.
The initial assessment of the structures and function of the heart is usually through echocardiography. Every acute hospital in the UK providing a cardiology service will have access to an echocardiography machine. In addition to its ready availability, the test is portable (an echocardiography machine can be wheeled to a patient’s bedside anywhere in the hospital and is therefore extremely useful for acute management), it provides good spatial and excellent temporal resolution, is cost effective, and does not expose patients to radiation.2 The standard test is transthoracic echocardiogram (TTE), which can be used in a multitude of cardiovascular conditions. Recent improvements in the technology of standard scans include the development of 3-dimensional imaging and strain techniques.3 Advanced echocardiography allows more details to be visualised and a dynamic assessment of the heart. Transoesophageal echocardiogram (TOE) captures detailed images of the heart from the oesophagus, which TTE is unable to do. Stress echocardiography is a dynamic (either through pharmacology or exercise) assessment of the heart.
Cardiac Magnetic Resonance Imaging
Although it is not as widely available, as portable, or as cost effective as echocardiography, the diagnostic and prognostic value of cardiac MRI has expanded exponentially in the past 20 years.
Cardiac MRI has been shown to be superior to other non-invasive techniques for the assessment of biventricular morphology and function.2 It has excellent reproducibility, and is also unique in its ability to identify specific tissue characteristics that may be diagnostic of the underlying disease process.4
Cardiac MRI can be used to investigate cardiomyopathies, ischaemic heart disease (stress perfusion and viability), heart failure, heart valve disease, and congenital heart disease.2 It has both diagnostic and prognostic abilities for a range of cardiovascular conditions, and is central to patient management.5–7
Cardiac Computed Tomography
Most hospitals will have access to cardiac CT. It is less expensive than cardiac MRI, but it is not portable, and patients are exposed to higher levels of radiation than with some other techniques—although this has reduced with the use of high slice scanners. It provides good spatial resolution, but has lower quality temporal resolution than that of echocardiography. It is principally used to assess coronary artery disease, but also has applications for heart valve disease, cardiac masses, and pericardial disease.2
The role of cardiac CT expanded after the publication of an update to NICE Clinical Guideline (CG) 95 on stable chest pain in 2016,8,9 driven by observations in the SCOT-HEART and PROMISE trials on outcomes with the use of cardiac CT.10,11 (Click here for the Guidelines summary on the NICE guideline on recent-onset chest pain of suspected cardiac origin: assessment and diagnosis in secondary care)
SCOT-HEART found that cardiac CT improved diagnosis, management, and outcomes for patients referred with suspected stable chest pain due to coronary heart disease.10 It heralded a major change in imaging guidelines for ischaemia, with NICE recommending cardiac CT as the first-line diagnostic test for patients with stable chest pain.8
The challenge has been in meeting the increased demand for cardiac CT. Forecasting predicted that implementing the guideline would mean an additional 200,000 patients would require cardiac CT across the UK, necessitating an increase in capacity of more than 700%.12
The modelling was based on geographical variation in the availability and delivery of cardiac CT: as a relatively new technique, the number of healthcare professionals trained and able to use and report it is limited, with modern equipment required for its delivery.12 Currently, there is very significant variation in how CG95 is being implemented, primarily relating to lack of access.13 Many centres have significant backlogs for cardiac CT, and these appear to be increasing.
Nuclear cardiology is the most frequently used imaging test,2 and consists of single-photon emission computed tomography (SPECT) and positron emission tomography (PET). SPECT is comparable to cardiac CT in terms of availability and cost. It provides poorer spatial and temporal resolution than other modalities, and a higher level of radiation exposure. SPECT is used to assess ventricular function, ischaemia, and viability.
Nuclear cardiology faces stiff competition from other imaging modalities, although tracer techniques have led to greater applicability. The tracer principle integrates the measurement of molecular pathways with physiological and functional measurements, allowing blood flow to the heart muscle to be visualised. Radionuclide imaging is now being used in cardiovascular medicine to assess myocardial infiltration, device infection, and cardiovascular inflammation. This has revolutionised the diagnosis, management, and prognostication of these conditions.14
Mix and Match
The properties and uses of the different cardiac imaging modalities are summarised in Table 1. In reality, a multimodal approach is often taken. For example, to evaluate complex valve disease, a cardiac MRI and an echocardiogram are often both performed, and the combined results used to build up a detailed clinical picture. Imaging cardiologists who can use, understand, and report on these modalities play an important role within multidisciplinary teams.
Table 1: Properties of Cardiac Imaging Modalities15–17
|Spatial Resolution||<1 mm||<1 mm||1–2 mm||5–10 mm|
|Temporal Resolution||20 msec||20–160 msec||30 msec||60–120 msec|
CT=computed tomography; CMRI=cardiac magnetic resonance imaging; SPECT=single-photon emission computed tomography; TOE= transoesophageal echocardiogram; CT-FFR= computed tomography fractional flow reserve
Improving Access to Diagnostic Services
The number of patients referred for diagnostic tests rose by 25% between 2014 and 2019, but capacity has not kept pace with this growth in demand; the UK has fewer CT and MRI scanners per head of population than most Organisation for Economic Cooperation and Development (OECD) countries.18 In addition, patient access to CT and cardiac MRI varies considerably between trusts, as does reporting time, leading to longer waiting times and delays in diagnosis.13 CMRI demand has increased by 573% from 2008 to 2019, with a 14.7% increase between 2017 and 2018.19 In addition, patients recovering from COVID-19 may face long-term respiratory and cardiac problems, which will place additional demands on diagnostic services, including CT, cardiac MRI, and echocardiography.20
Improving access to imaging is one of the 25 recommendations of the Getting it Right First Time (GIRFT) clinically led review of NHS cardiology services across England, published in 2021.13 The GIRFT recommendations align with those made by Professor Sir Mike Richards in an earlier wide-ranging review of diagnostic services, which called for an increase in capacity in imaging, most notably a 100% increase in CT capacity.20
GIRFT recommends a network model of delivery for cardiac services, with care organised around pathways rather than hospital sites.13 It proposes that all hospitals must be part of a network with access to four levels of service. Level 1 services for acute cardiology patients should consist of emergency echocardiogram provision and review, including virtual review, 24 hours a day, 7 days a week, and elective/urgent echocardiography 7 days a week.13
In terms of imaging, this means that all hospitals must be able to provide:13
- access to emergency echocardiography and review, including virtual review, 24 hours a day, 7 days a week, and elective/urgent echocardiography 7 days a week
- access, either on site or at network level, to cardiac CT, including CT-fractional flow reserve, with all of the images reported by appropriately trained cardiologists and/or radiologists
- dedicated sessions of cardiac MRI, including stress cardiac MRI, with all of the images reported by appropriately trained cardiologists and/or radiologists.
Community Diagnostic Centres
The Richards review of diagnostic services recommended the rapid set up of community diagnostic hubs—now called community diagnostic centres (CDCs)—with an important role for cardiac imaging, particularly echocardiography.20 It proposed that echocardiography could be performed in these centres by experienced echocardiographers rotating from acute hospitals. The Department of Health and Social Care announced that 40 CDCs would start providing services across England from October 2021.21
CDCs aim to provide quicker access to testing and earlier diagnosis of cardiac, cancer, respiratory, and other conditions by providing a one-stop shop where a patient referred by their GP has all of their diagnostic tests performed on the same day in the same place. The traditional model of GP referral to secondary care entails a likely wait of several months for one test. By reducing waiting times, CDCs aim to decrease the pressure on acute care and allow hospitals to focus on patients requiring urgent treatment.
However, CDCs place yet more demand on very limited resources. Although they may lower hospital admissions, they generally increase the number of scans being performed; these require sufficient healthcare professionals to perform them and assess the results, which is a continuing challenge.
But, as demand for echocardiography increases, cardiac physiologists, the healthcare professionals who perform these tests, are in short supply. A 2022 survey from the British Society of Echocardiography (BSE) highlights the shortfall in echocardiographers and the expanding demand of this service. A sobering statistic is that 10% of the whole-time equivalent physiologist workforce are locums.22 This can partly be explained by the fact that locum positions are more lucrative than a permanent NHS role. To address the deficit, an accelerated programme was developed in 2020 to enable cardiac physiologists to achieve BSE accreditation in 18 months, through a combination of academic and workplace training.23 This collaboration between the National School of Healthcare Science and the BSE saw its first trainees complete the Echocardiography Training Programme (ETP) in summer 2022. Applications for the programme have far exceeded availability—in my trust alone there were 30 applicants for one post—and it promises a potential solution to workforce problems in the future.
The review of diagnostic services by Professor Richards also recognised that workforce capacity had not kept up with demand, particularly in echocardiography, and called for an expansion in these roles.20 The GIRFT review recommended that upskilling the workforce and extending their roles is key to addressing workforce shortages, and would help to increase retention by creating opportunities for career progression.13 It identified that, although cardiac physiologists were conducting stress echocardiography and running valve surveillance clinics in many hospitals, in others they were not operating with this extended skill set.13
It could be argued that echocardiographers should be paid more for what they do, and the level of service they provide, given the shortages. The BSE recommends a minimum 45-minute time slot for a routine triaged outpatient echocardiography appointment, which is challenging to achieve, particularly given the technological advances in the modality.24
Artificial Intelligence in Imaging
The application of artificial intelligence (AI)25 in cardiac imaging provides opportunities for further advances. Thanks to its use, image generation in echocardiography has vastly improved; the ability to generate 3-dimensional images of the heart and valve disease, in particular, is very helpful. This allows a cardiac surgeon to visualise a patient’s heart or valve in advance of surgery, allowing clinicians to plan more effectively. AI can measure heart muscle contractility with greater precision and accuracy than the human eye, which is what we rely upon in stress echocardiography.
In cardiac MRI, AI can increase the speed at which reports are generated. Functional analysis requires contouring of the heart to produce volumetric assessments. AI modules within reporting software have become more intuitive, allowing contouring to be performed more quickly.
An AI research technique developed by researchers at Oxford University enables contrast-free cardiac MRIs, and produces clear images of heart muscle scarring. The technique, called virtual native enhancement, could reduce both the time that patients need to spend in an MRI scanner and the cost of scanning,26 as well as avoiding the need for contrast injections. However, these techniques remain in the research realm at the moment.
The AI in Health and Care Awards were launched by the Accelerated Access Collaborative in 2020 to accelerate promising AI technologies. The winners of the second round included CaRi-Heart, which uses AI to detect invisible signatures of inflammation in cardiac CT scans and, therefore, predict the risk of CVD. Its effectiveness is now being tested in healthcare settings to produce evidence for routes to implementation.27
The role of non-invasive cardiovascular imaging in diagnosis and management continues to expand. Multimodality imaging has revolutionised how we manage and treat patients, minimising the need for more invasive tests, and is a central tool for physicians in the provision of excellent patient care. These modalities can be applied to a broad spectrum of cardiology conditions, with strong evidence of benefit. As demand continues to grow, difficulties in access and variations in capacity in the UK remain an obstacle. The advent of more efficient scanning processes and the development of new technologies, including AI, are potential solutions to this challenge.
Dr Christopher McAloon
Consultant Cardiologist with a specialist interest in cardiovascular imaging, Worcestershire Acute Hospitals NHS Trust