Dobutamine stress CMR relies on wall motion evaluation with increasing doses of dobutamine and vasodilator perfusion stress CMR relies on the perfusion of gadolinium at stress compared to rest for evaluation of ischemia. A recent study [76] evaluated 2349 patients who underwent stress CMR perfusion imaging after presenting with chest pain over a period of 5.4 years and found that patients without ischemia and LGE had a low incidence of cardiac events, need for revascularization and subsequent ischemia testing. This adds to the growing body of evidence that in intermediate‐risk patients with IHD, a normal perfusion stress CMR perfusion can serve as an excellent initial screening test.
LV systolic function measured on CMR can be used to determine a patient’s eligibility for cardiac resynchronization therapy or for a defibrillator. CMR also plays an important role in evaluating myocardial viability which is defined as transmural scar of 50% or less as characterized by LGE. It has the unique advantage of directly visualizing scar and normal myocardium in the same image and is more sensitive for subendocardial scar than SPECT imaging [77]. Myocardial viability testing is currently recommended as a part of revascularization planning in patients with heart failure [78].
Pericardial disease
CMR can provide important information regarding various pericardial diseases [53]. Black blood T1‐ weighted SE CMR is used for morphologic assessment, including measurement of pericardial thickness, and black blood T2‐weighted SE CMR highlights fluid‐rich structures such as pericardial effusion or myocardial edema with concomitant myocarditis. LGE in the pericardium is strongly suggestive of pericarditis. Cine imaging allows visualization of pericardial effusions, paradoxical motion of the interventricular septum in constrictive pericarditis (CP) and RV or RA collapse.[79] Ventricular interdependence, which is the sine qua non of diagnosis of CP, can be evaluated on real‐time cine CMR. Tagged cine can be used to delineate adhesion of the pericardial layers [53, 79].
Congenital heart disease
CMR can be used to assess cardiac structure, function, and blood flow through the heart, great vessels, cardiac shunts, and extracardiac conduits in individuals with congenital heart disease (CHD) [new Congenital consensus statement]. The lack of ionizing radiation makes CMR particularly attractive in the pediatric age group as serial follow‐up studies are usually required [80] (Figure 10.5a–c).
Phase contrast velocity mapping (PCVM) is useful in quantifying pulmonic regurgitation in patients with Tetralogy of Fallot (TOF) and in quantifying the pulmonary to systemic flow ratio (Qp/Qs) (shunt fraction) in patients with atrial and ventricular septal defects [81–83]. Accurate quantification of ventricular size and function helps in determining the appropriate time for intervention. RVOT obstruction is a common complication in TOF repair. By providing accurate information on the anatomy and size of the RVOT and pulmonary arteries, CMR plays an important role in planning for percutaneous pulmonary valve implantation [84–86].
Figure 10.4 (a) and (c) diffuse LGE in the ventricles and atria. Classic finding for cardiac amyloid, (b) and (d) Intramyocardial LGE seen in myocarditis, (e) Patchy LGE seen in the hypeertrophied interventricular septum in a patient with HOCM, (f) LVOT obstruction secondary to systolic anterior motion (SAM) of the anterior mitral valve leaflet in a patient with HOCM.
CE‐MRA is particularly helpful for the assessment of abnormalities of the great vessels such as transposition, aortic arch anomalies, vascular rings, and aortic coarctation. CMR is superior to other imaging modalities including echocardiography for combined anatomic and physiologic assessment of coarctation. It can help distinguish true from pseudocaoarctation and assess for complications of repair such as restenosis or pseudoaneurysm formation [53].
Valvular heart disease
CMR is extremely useful in the evaluation of valvular heart disease – particularly in the assessment of severity of valvular regurgitation, stenosis and serial changes in LV volumes or mass that occur with valvular dysfunction. CMR has been shown to more accurately quantify mitral and aortic regurgitation which helps determine the appropriate intervention time. Cine SSFP is preferred for functional imaging and standard GRE sequences are preferred for jet visualization and qualitative assessment of the valve [87]. CMR planimetry of the aortic and mitral valves correlates with echocardiographic planimetry. PCVM can be used to measure aortic and pulmonary regurgitant volumes [88], and to calculate mitral or tricuspid regurgitant volumes from the measured LV and RV stroke volumes. PCVM can also be used to obtain the peak/mean velocities of the jet and the flow through a stenotic valve [89].
Figure 10.5 (a) Sinus venosus ASD with the right upper pulmonary vein draining into the SVC, (b) Bicuspid aortic valve, (c) A distal left main aneurysm.
Vascular disease
Aortic disease
CMR imaging techniques permit the comprehensive assessment of aortic diseases including aortic aneurysms, valve abnormalities, pseudoaneurysms, aortitis, and aortic dissection [53]. They are used to assess disease progression and complications post‐repair [90, 91]. CMR has become the preferred non‐invasive tool for selection for percutaneous intervention in patients with aortic coarctation. It is increasingly being used due to its ability to generate both 3D anatomic and hemodynamic information without radiation exposure [84,92–94].
Peripheral, carotid, and renal artery disease
CMR is increasingly being used in the evaluation of stenosis in the peripheral, carotid, and renal arteries. It has better contrast resolution compared to CT and ultrasound in the evaluation of peripheral arterial disease. CE MRA has greater than 95% sensitivity and specificity to detect stenosis with the benefit of avoiding blooming artifact secondary to atherosclerotic calcification as is seen on CTA. It is particularly useful in patients with advanced calcified atherosclerotic disease in the infrageniculate vessels [95]. By utilizing time‐of‐flight MRA, gadolinium can be avoided in patients with diminished renal function. CE MRA techniques now rival CTA and conventional angiography for the assessment of carotid stenosis and aneurysms [96–98]. CE MRA has been shown to be an excellent alternative to CTA without ionizing radiation in patients undergoing evaluation for fibromuscular dysplasia in the renal arteries [99].
CMR for interventional cardiac procedures
Transcatheter aortic valve replacement (TAVR)
CMR has evolved to play a pivotal role in TAVR planning [100]. Direct comparison of CMR and CTA measurements of the aortic root and aortic annulus has shown close agreement [101–103]. CMR is extremely useful in patients with renal insufficiency that are unable to undergo contrast‐enhanced CT. A gated non‐enhanced MRA serves as an alternative for accurate measurements of the aortic root, proximal aorta, LV function and evaluation of the aorto‐iliofemoral system [74,75]. [104, 105] PCVM can be used to quantify the severity of concomitant mitral or aortic regurgitation. The major limitation of CMR is inadequate visualization of aortic calcification [100].
CMR
