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The diagnostic procedures for CAD will be discussed in more depth in the following section on Coronary Heart Disease. Reviewed here is the use of noninvasive testing for noncoronary heart disease.
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Echocardiography & Doppler Ultrasound Imaging
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Two-dimensional echocardiography provides information regarding all four chamber sizes, regional and global systolic function, and chamber wall thickness (VIDEO 10–2). Excellent images of valve motion, intracardiac masses, abnormal or absent cardiac structures, and pericardial fluid can all be distinguished. Pulsed wave Doppler provides a semiquantitative or qualitative estimation of the severity of transvalvular gradients, RV systolic pressure (based on a tricuspid regurgitation jet velocity), PA pressure, valvular regurgitation severity, and the presence of intracardiac shunts. The Doppler mitral inflow pattern can help confirm diastolic dysfunction and can help verify a restrictive cardiomyopathic picture or constrictive pericarditis. Color flow Doppler provides a visual pattern of blood flow velocities superimposed over the anatomic two-dimensional echocardiographic image. This allows for the demonstration of turbulence from stenotic or regurgitant valves, and for the visualization of intracardiac defects. Since some regurgitant flow occurs normally, especially when the AV valves close, the presence of minor amounts of regurgitant color flow should not be construed as pathology. Tissue Doppler methods help define the extent of either annular or ventricular wall motion independent of intracardiac flow velocity, and the relationship between the two may prove useful for defining diastolic pressure elevation, identifying abnormalities in ventricular contraction or diastolic relaxation, or optimizing pacemaker therapy. The E wave of the mitral inflow Doppler pattern reflects the rate of blood flow from the LA to LV. The E′ of the tissue Doppler reflects how rapid the LV relaxes. The E/E′ ratio increases if the LA pressure pushing blood into the LV is relatively greater than the rate of relaxation. An E/E′ ratio greater than 15–18, therefore, suggests an elevated LA pressure.
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Echocardiography with contrast agents that fill both heart chambers improves the visualization of wall motion. Other contrast agents have been developed that produce echocardiographic contrast within the myocardium, providing gross myocardial perfusion data. Such perfusion methods have yet to be standardized and have not found wide acceptance.
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The use of Doppler tissue imaging can also provide visual descriptions of wall stress and strain. Measures of longitudinal stress and strain can be displayed visually overlying the image. The value of stress/strain imaging is improving as the techniques have become more standardized; it may be particularly useful in patients where early diastolic dysfunction is present and in defining abnormal myocardium when attempting to separate the athlete’s heart (and associated LV hypertrophy) from a diseased heart (such as hypertrophic cardiomyopathy). Abnormalities have been observed prior to a fall in the LV ejection fraction (LVEF) in patients undergoing chemotherapy. The timing of right and left ventricular contraction can also be measured (cardiac synchronization) and the results have been used to better define the need for biventricular pacing, though recent data suggest its value may be limited.
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Transesophageal echocardiography (TEE) with Doppler ultrasound is used to obtain echocardiographic data when surface sound transmission is poor; to derive information about posterior structures (especially the atria or atrial appendage and AV valves), prosthetic heart valves, and intracardiac masses not well seen on chest wall echocardiography (eg, vegetations in endocarditis or thrombi on pacemaker leads). It is standard practice to use TEE to monitor patients during valvular or other structural heart surgery. It can confirm the location of the pulmonary veins and define septal defects or the presence of a patent foramen ovale (PFO). It is superior to surface echocardiography in diagnosing LA appendage thrombi and regurgitant lesions associated with prosthetic valves. It is also quite sensitive in detecting aortic dissection and severe atherosclerosis of the ascending aorta, which may be the source for transient ischemic attacks (TIAs) or embolic strokes (VIDEO 10–3).
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Three-dimensional echocardiography allows for visualization of cardiac structures in multiple dimensions, though there remains few diagnoses where transthoracic three-dimensional imaging adds significant value. Three-dimensional echocardiography technology, though, has been a particularly useful adjunct to TEE during invasive cardiac procedures and cardiac surgery, where it helps define the relationships among the various heart structures in real time. In addition, three-dimensional echocardiographic imaging appears to provide improved volumetric data compared to two-dimensional echocardiographic imaging.
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Stress echocardiography can be used in valvular as well as ischemic heart disease. Echocardiograms may be performed during or immediately following exercise. Valvular gradient changes after exercise or during dobutamine infusion can be evaluated. Transient segmental wall motion abnormalities during or immediately following exercise or pharmacologic stress suggest ischemia (VIDEO 10–4). Improvement in wall motion during low-dose dobutamine infusions is an indicator of myocardial viability. Changes in the estimated pulmonary pressure and valvular gradients can occasionally help decide whether symptoms are related to valvular disease.
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Abraham
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Doherty
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Wolk
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et al. ACCF/AHA/ASE/ASNC/HFSA/HRS/SCAI/SCCT/SCMR/STS 2013 multimodality appropriate use criteria for the detection and risk assessment of stable ischemic heart disease: a report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2014 Feb 4;63(4):380–406.
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Cardiac MRI & Multislice CT
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Cardiac MRI continues to evolve rapidly and its use is expanding. Currently available systems provide high-quality and high-resolution images of cardiac and adjacent vascular structures. Cardiac MRI also provides excellent images that can quantify cardiac function and structure. It is particularly useful for defining myocardial scarring, including the presence of infiltrative myocardial diseases such as sarcoidosis or amyloidosis. Flow measurements, valve orifice sizes, and shunt sizes can all be determined. With the use of gadolinium contrast agents, cardiac MRI can be used to assess myocardial perfusion during adenosine pharmacologic stress and to assess myocardial viability. Contrast-enhanced images can provide accurate measurement of MI size and location. Delayed enhancement following gadolinium administration helps quantify myocardia scar. Cardiac MRI can also provide accurate three-dimensional reconstruction of the great vessels and abdominal aorta. The study can also be used to screen for renal artery stenosis in patients with hypertension. However, patients with pacemakers or defibrillators are not generally believed to be candidates for cardiac MRI, although some groups are willing to perform cardiac MRI in this situation, and there are newer pacemakers that are “MRI compatible.” Intracardiac pacemakers or defibrillators may result in artifacts obscuring the myocardium, though. Nephrogenic systemic fibrosis, a syndrome that leads to skin and organ fibrosis believed to be due to the gadolinium contrast agent, may develop in patients with severe kidney dysfunction. Therefore, acute or chronic kidney disease is considered a relative contraindication to cardiac MRI with gadolinium, although newer contrast agents using tiny superparamagnetic iron particles do not appear to cause nephrogenic systemic fibrosis and can usually provide diagnostic images when hyperenhancement is not needed.
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Cardiac multislice CT, at lower resolution, has primarily been used to screen patients for CAD. The extent of calcium within the coronary vessels has been found to correlate with the extent of atherosclerotic CAD. Higher resolution imaging modes and faster acquisition times enable noninvasive coronary angiography to be obtained. The negative predictive value of a negative coronary study is high (around 95%), suggesting that it is an excellent test to confirm normal coronaries. Calcium in the arterial wall may limit its ability to define the severity of coronary disease, but the inherent resolution of cardiac multislice CT allows it to better visualize coronaries than cardiac MRI. Multislice CT, with its impressive three-dimensional reconstruction algorithms, also provides outstanding images in valvular, myocardial, and congenital heart disease. However, there remains some concern regarding the radiation dose with multislice CT, which is not an issue with MRI where there is no ionizing radiation involved. Issues regarding the radiation dosage have been addressed by gating scans with the ECG and acquiring data only in early diastole, for instance. This has led to a reduced concern regarding the dose of radiation and, in general, the radiation dose for CT is similar to that for a diagnostic heart catheterization. In patients in the emergency department with symptoms suggestive of acute coronary syndromes, incorporating imaging of the coronary tree (to exclude CAD), pulmonary arteries (to exclude pulmonary emboli), and the aorta (to exclude aortic dissection) is increasingly performed. The cost-effectiveness of this triple rule out method is being debated. With the publication of the importance of fractional flow reserve in assessing coronary lesions invasively (the FAME trials), the potential ability to obtain fractional flow reserve data noninvasively using coronary CT angiography has led to the growing promise that the coronary CT angiography will provide information regarding the functional significance of individual lesions. This would be a major step forward in the noninvasive assessment of CAD.
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Kaul
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Pursnani
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et al. Cardiac computed tomography and cardiac MRI: complementary or competing? EuroIntervention. 2016 May 17;12(Suppl X):75–80.
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Robson
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SCOT-HEART Investigators
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Tanigaki
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et al. QFR versus FFR derived from computed tomography for functional assessment of coronary artery stenosis. JACC Cardiovasc Interv. 2019 Oct 28;12(20):2050–9.
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Wolk
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