septum length, LVOT eccentricity, annular oversizing, and deeper implant length were independent predictors of NP‐LBBB when the Evolut valve was used [48]. Additionally, a recent study used a cardiac CT‐based model to predict patient prosthesis mismatch (PPM) in patients undergoing TAVR using the Sapien 3 or Evolut R/Pro valves based on the aortic root anatomy. Severe PPM is a predictor of mortality and using cardiac CT to choose the appropriate valve could potentially reduce the incidence of PPM and in turn, play a significant role in improving overall survival of patients post‐TAVR [49]. Although routine post‐TAVR CT is not currently recommended, it should be considered if there is suspicion for endocarditis, valve thrombosis, or structural degeneration [50] (Figure 10.2a–c).
Pulmonary vein ablation
CTA is important for left atrial evaluation prior to pulmonary vein ablation for atrial fibrillation. It provides important information regarding the anatomy of the left atrium, the pulmonary veins, and helps confirm the absence of thrombus in the left atrial appendage. Current guidelines emphasize the importance of using either CT or MRI to evaluate the left atrium and integrating these images to expedite the procedure [51] (Figure 10.3a–d).
Cardiovascular magnetic resonance
Cardiac magnetic resonance (CMR) has emerged as a useful non‐invasive tool for the assessment of cardiovascular morphology and function in the absence of ionizing radiation. It has imaging sequences that can be manipulated to generate varying degrees of soft‐tissue contrast for cardiac tissue characterization. Additionally, the excellent spatial (1–2 mm in‐plane resolution), temporal (50ms or better), and contrast resolutions allow for routine assessment of cardiac function and blood flow [52, 53]. The main limitations of CMR are the inability to image very large or claustrophobic patients, long scan time, contraindications such as certain implanted devices/clips and the risk of nephrogenic systemic fibrosis from gadolinium contrast in patients with impaired renal function. However, the ability of CMR to provide comprehensive evaluations of cardiovascular morphology, function, and pathology makes it an attractive tool for the assessment and planning of patients undergoing cardiac interventional procedures.
Applications of CMR
Heart failure
CMR is useful for the initial evaluation of cardiac structure and function for known or suspected heart failure (HF), patients who are undergoing or are scheduled to begin chemotherapy, patients with familial or genetic dilated cardiomyopathies, suspected pulmonary hypertension, and to determine candidacy for implantation of permanent pacemakers and/or defibrillators [54].
It offers a more accurate assessment of function and morphology than most other imaging modalities. Cine sequences are used to visualize and quantify global atrial and ventricular systolic function relative to reference datasets. The pattern of scarring on late gadolinium enhancement (LGE) allows for accurate discrimination of ischemic from non‐ischemic cardiomyopathies [55]. Ischemic scar is subendocardial or transmural. Non‐ischemic cardiomyopathies either do not have detectable scars or have a non‐subendocardial distribution. In hypertrophic cardiomyopathy (HCM), LGE is patchy and intramyocardial, typically in the hypertrophied regions and in the interventricular septum close to the right ventricular (RV) insertion areas [56, 57] (Figure 10.4a–f). In dilated cardiomyopathy, a mid‐myocardial stripe of septal fibrosis is typical and is of strong prognostic value [58]. T2‐weighted CMR may be useful to detect myocardial inflammation due to acute myocarditis [59, 60]. Quantification of T2* relaxation times have proven useful for estimating intramyocardial iron content [61]. Non‐compaction cardiomyopathy is characterized by a thin compacted myocardium in the mid and apical segments of the LV. An end‐diastolic ratio of the non‐compacted to compacted LV myocardium of ≥2.3 is considered diagnostic [62]. ARVC is characterized by global or regional dilatation of the RV (and in some cases the LV) [63]. Cardiac amyloidosis has the classic appearance of a low signal “dark” blood pool and a very high signal intensity in the myocardium that is difficult to “null” on LGE images [64].
Figure 10.1 (a) Severe stenosis in the proximal RCA on CTA with high‐risk CT features such as positive remodeling and atherosclerotic plaque with low attenuation, (b) Stent in the proximal LAD without in‐stent restenosis. The lumen is well‐visualized, (c) Patent LIMA graft to the distal LAD, (d) Patent LIMA graft to LAD with a stent in the proximal LAD. Lumen of the LAD stent is difficult to visualize due to partial voluming artifact.
Figure 10.2 (a) Post‐TAVR, a bioprosthetic valve is seen in aortic position, (b) TAVR leaflets appear thickened, (c) Right coronary leaflet has restricted motion.
Coronary artery evaluation
CMR is evolving as an important diagnostic modality for evaluation of coronary anomalies and coronary artery aneurysms [65, 66]. Segments of anomalous coronaries that course between the aorta and pulmonary artery can cause myocardial ischemia and sudden cardiac death, especially among young adults [67, 68]. Coronary aneurysms, commonly seen in Kawasaki’s disease, are associated with morbidity and mortality [69]. Both are accurately characterized on CMR [70, 71].
CMR is not commonly used to evaluate coronary stenosis. A focal stenosis appears as signal attenuation. Several studies have evaluated the accuracy of CMR in assessing coronary artery stenosis. A recent article [72] summarized the results of these papers and discussed recent technological innovations, such as advanced motion correction and reconstruction techniques, that have improved MR coronary angiography. Two of the larger studies, with more than 100 patients each, demonstrated high sensitivity and NPV of MR coronary angiography compared to ICA [73, 74]. Coronary bypass grafts are relatively easier to image because of their minimal motion and larger lumens. The assessment of grafts has shown good correlation with quantitative X‐ray angiography for both occlusion and stenosis [75]. Currently, MR coronary angiography is being performed at large academic centers only.
Ischemic heart disease (IHD)
The combination of CMR stress perfusion, function, and LGE allows the use of CMR as a primary form of testing for: (i) diagnosing IHD, (ii) determining which patients are candidates for revascularization; and (iii) defining the distribution of CAD prior to revascularization [53].
Figure 10.3 (a) Early and (b) delayed contrast‐enhanced images of the left atrial appendage for evaluation prior to pulmonary vein ablation. There appears to be a filling defect in the early images concerning for thrombus but delayed images confirm that there is no LAA thrombus. Images (c) and (d) delineate the anatomy of the
