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Cardiac CT: The Future of Diagnostic Cardiology?

As a medical student eyeing the field of radiology, the science of imaging of was all too seductive.  Ultimately, a love for cardiac physiology won me over, but an interest in imaging lingered.  As it turns out, cardiologists are part-time radiologists with expertise in a number of cardiac imaging modalities.

CT has become the latest frontier in cardiac imaging with a number of useful applications.

By now, coronary calcium scoring is a well-established tool for risk stratification in subclinical coronary artery disease.  Cross-sectional imaging is also useful for evaluating pericardial thickening in restrictive cardiomyopathy.  Beyond these traditional applications, newer techniques are poised to change the way we use CT to evaluate heart disease.

 

Coronary CT Angiography

Using fast, EKG-gated scanners, coronary CT angiography (CCTA) is a noninvasive means to detect coronary anomalies and obstructive plaque.  CCTA is a sensitive tool for excluding coronary disease, with a nearly perfect negative predictive value in the ACCURACY trial1.  However, specificity is poor and the presence of stents or calcium degrades image quality.

The specificity of CCTA is improved with FFR-CT (HeartFlow), a noninvasive method that mimics invasive fractional flow reserve measurements.  Computational fluid dynamics are applied to a 3D model of coronary anatomy in order to simulate the hemodynamic effects of stenotic lesions.  The PLATFORM trial2 showed how these technologies can safely reduce unnecessary catheterizations with no detriment to outcomes.

 

CT Myocardial Perfusion Imaging

CT myocardial perfusion imaging is also possible.  Indeed, a key advantage of CT is the ability to combine anatomic and physiologic evaluation in a single study.  However, exposure to radiation and iodinated contrast is an important consideration when comparing this to SPECT imaging.

 

As our diagnostic tools multiply, cardiac testing will become less invasive yet choosing the right study will become more complicated.  Cardiology is a fortunate field that controls much of its own imaging, but with the emergence of cardiac CT, we will need to collaborate with our radiology colleagues to push our fields forward in tandem.

 

References:

1Budoff MJ, Dowe D, Jollis JG, et al. Diagnostic performance of 64-multidetector row coronary computed tomographic angiography for evaluation of coronary artery stenosis in individuals without known coronary artery disease: results from the prospective multicenter ACCURACY (Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography) trial. J Am Coll Cardiol 2008;52:1724-32.

2Douglas PS, Pontone G, Hlatky MA, et al. Clinical outcomes of fractional flow reserve by computed tomographic angiography-guided diagnostic strategies vs. usual care in patients with suspected coronary artery disease: the prospective longitudinal trial of FFR(CT): outcome and resource impacts study. Eur Heart J. 2015;36:3359–3367. doi: 10.1093/eurheartj/ehv444.

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Relevance Of Imaging In The Setting Of Advanced Age Related Complexities

The population older than 65 years of age is expected to peak at 20 percent of the population in 2030. By that year, more than 19.5 million U.S. adults will be older than 80 years of age. Due to this large increase in the geriatric population, major efforts are needed to ensure adequate and appropriate health care for the elderly. The prevalence of systolic and diastolic heart failure, atrial fibrillation, aortic stenosis, and electrical conduction defects increases with age, resulting in a significant burden of cardiovascular disease (CVD). Aging itself creates distinctive dimensions to CVD management as both absolute risk reduction, and the potential for harm from treatment, increase with advancing age.

Cardiovascular imaging (CVI) is used for screening (detecting asymptomatic cardiac disease), diagnosing the cause of symptoms, defining the extent of cardiac disorder in a patient with known disease (including risk stratification), monitoring the progression (or regression) of disease, and guiding therapeutic management, including decisions about aggressive therapy. There is a paucity of evidence to guide the rational use of many CVI modalities in patients of advanced age. There are senescent effects in cardiac morphology and physiology as well as broader organ systems changes in elderly patients. Older patients used to be clinically heterogeneous with different age related arterial compliance and left ventricular (LV) diastolic dysfunction. Although, the Appropriate Use Criteria (AUC) do not integrate age as a factor in determining the appropriateness of an imaging test, in part due to a lack of data. Nonetheless, there are a number of other important factors associated with aging which impact the use of cardiac imaging in the senior population. Older patients, regardless of underlying disease severity or comorbidities, undergo fewer invasive cardiovascular evaluations than younger patients.

A key aspect of advanced age, is that the concept of high risk burden must be considered in the context of age-related management efficacy. In contrast to younger populations, the high risk, high prevalence and high burden of disease in the elderly population leads to a situation in which CVI is likely to detect disease for which the implications of therapy are uncertain. Thus, if structural or functional abnormalities are detected in an asymptomatic patient, management decisions may still remain ambiguous. Detection of non-obstructive atherosclerotic coronary artery disease (CAD) in an elderly diabetic with peripheral vascular disease will, for example, not likely lead to any intensification of medical therapy beyond that which is already indicated. In contrast, in other scenarios imaging has substantial clinical impact, including rationale for selecting patients mostly likely to benefit from interventions that may prolong and improve quality of life.

The elderly group had a lower prevalence of CAD risk factors but high degrees of ischemic events and cardiac mortality. Given the high pretest probability of CAD in relation to advanced age, the prognostic utility of a stress study may be particularly useful. CVI adds additional prognostic power and is necessary as part of pharmacological stress, for the majority of the elderly who cannot complete a treadmill exercise protocol. With the growing focus on transcatheter aortic valve replacement (TAVR) the particular value of imaging for common valvular decisions in older adults has advanced as a clinical priority. Transthoracic echocardiography (TTE) is the central imaging modality to detect and characterize the degree of aortic stenosis. In addition to TTE, contrast-enhanced computer tomography imaging in necessary to ensure that vasculature will be able to tolerate the large bore catheters that are required for the procedure. Newer percutaneous mitral valve repair techniques are also options for some elderly patients who are poor surgical candidates and TEE is necessary to demonstrate leaflet anatomy amenable to novel percutaneous interventions.

Approximately 1%–2% of the adult population in developed countries has heart failure (HF), with the prevalence rising to ≥10% among persons 70 years of age or older. HF is underdiagnosed in elderly patients who often lack specific symptoms and usually present with comorbidities that can confound diagnostic assessments based primarily on symptoms. Therefore, TTE plays an important complementary role in establishing a diagnosis for patients with HF symptoms. In addition to guiding management, cardiac imaging plays a central role in prognostication in HF. Currently, LV ejection fraction (LVEF) is the primary imaging criteria to determine which patients are candidates for implantation with a biventricular pacemaker for cardiac resynchronization therapy. While such devices have demonstrated to improve survival and quality of life, they also entail procedural risk, particularly for older candidates.

CVI is essential in the treatment of CVD in the elderly, but more data are needed on the optimal use of imaging in this population. Better delineation of clinical indications for imaging relevant for older adults in the context of broader age related complexity is a key need. While decisions should be individualized for each patient, investigations into imaging in subpopulations of the elderly may provide clinicians (and, perhaps, future AUC task forces) necessary data to consider patient-level factors such as comorbidities, frailty, functional limitations and cognitive decline in determining the appropriateness of imaging modalities for certain indications.

Fawaz Alenezi Headshot
Dr. Fawaz Abdulaziz M Alenezi is a Clinical Imaging Fellow at the Duke University Health Systems. He conducts medical research on the derivation and validation of novel echocardiographic approaches to myocardial deformation and a new echocardiographic technique which assists patients with heart ventricular function.

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Cardiology Beyond Single Imaging Modality

Cardiovascular (CV) imaging plays a crucial role in declining mortality and optimal disease management. Knowledge of various imaging modality is vital for understanding and management of patients of various CV diseases. Since the first A-mode echocardiogram, there have been great revolutional changes. However, the imaging principal is exactly the same. Echocardiogram and nuclear modality were the only clinically available imaging for management in patients with different CV diseases. The introduction of cardiac magnetic resonance (CMR), computer tomography (CT), three-dimensional (3D) printing, and strain echocardiography makes things quite different. Multi-modality imaging (MMI) plays a role in all CV diseases that includes ventricular function, coronary artery disease, valvular disease, congenital heart disease, intervention guidance, and vascular diseases.

In less than fifteen years, as a non-invasive imaging option, CMR has grown from a being a mere curiosity to becoming a widely used clinical tool for evaluating CV disease. CMR is now routinely used to study myocardial structure, cardiac function, macro vascular blood flow, myocardial perfusion, and myocardial viability. CMR provides a number of key tools to the clinician to evaluate cardiovascular pathologies. Among available imaging modalities to assess global and regional ventricular function, cine CMR based measurements are considered the ‘gold standard.’ While more involved than echocardiogram, CMR based phase contrast methods are robust in the evaluation of regurgitant volume and valvular function.

CT scan have been able to segment the heart better than Echocardiogram. Computers can combine these pictures to create a 3D model of the whole heart. This imaging test can help doctors detect or evaluate coronary heart disease, calcium buildup in the coronary arteries, problems with the aorta, problems with heart function and valves, and pericardial disease. This test may be also used to monitor the results of coronary artery bypass grafting or to follow up on abnormal findings from earlier chest x-rays. Different CT scanners are used for different purposes. A multidetector CT is a very fast type of CT scanner that can produce high-quality pictures of the beating heart and can detect calcium or blockages in the coronary arteries. An electron beam CT scanner can also show calcium in coronary arteries.

3D printing is a fabrication technique used to transform digital objects into physical models. Also known as additive manufacturing, the technique builds structures of arbitrary geometry by depositing material in successive layers based on a specific digital design. Several different methods exist to accomplish this type of fabrication and many have recently been used to create specific cardiac structural pathologies. While the use of 3D printing technology in cardiovascular medicine is still a relatively new development, advancement within this discipline is occurring at such a rapid rate that a contemporary review is warranted.

With rapid advances in imaging technology, current fellows in training and future consultants will frequently be required to use MMI in patient care. CV imaging is fundamentally about the information in the image, not how it is acquired. MMI has been the area of discussions for more than a decade, and the 2015 Core Cardiology Training Symposium guidelines published in May 2015 have further reinforced its importance. Nearly everyone agrees that MMI training is imperative, and most fellows in cardiology programs who are interested in careers in noninvasive imaging have expressed strong interest in acquiring such expertise and eagerly ask about its formal inception. However, despite all of the interest and goodwill, the practical implementation of MMI training has been slow.

Cardiac MMI is a highly dynamic field of continuing research driven by the constant technological advances and innovation of noninvasive imaging and the increasing clinical interest. Its impact extends beyond its clinical utility onto the organization of diagnostic healthcare structures. Furthermore, there is a belief that too much imaging is being done at significant cost and without strong evidence that this amount of imaging is needed or indeed improves outcomes. As part of U.S. healthcare reform efforts, physicians will be required to document that they are following appropriate use criteria (AUC) for outpatient medical imaging orders by using clinical decision support software documentation. The software must be certified by the Centers for Medicare and Medicaid Services in order to receive full reimbursement for diagnostic imaging services for Medicare and Medicaid patients. This will affect advanced outpatient imaging for CT, MRI and nuclear imaging. These new AUC are intended to provide guidance for clinicians when choosing among available testing modalities for various cardiac diseases.

In the assessment of CV disease, multiple imaging modalities may contribute toward determining the diagnosis, prognosis, and approach to treatment. However, each imaging modality may provide relevant information regarding more than one of these clinical needs. Therefore, to explore fully the potential impact of imaging, the strategy should be individualised according to the specific clinical needs and AUC.

Fawaz Alenezi Headshot
Dr. Fawaz Abdulaziz M Alenezi is a Clinical Imaging Fellow at the Duke University Health Systems. He conducts medical research on the derivation and validation of novel echocardiographic approaches to myocardial deformation and a new echocardiographic technique which assists patients with heart ventricular function.