Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Imaging of Cardiomyopathy and Myocarditis
▪
Introduction
Cardiomyopathies and myocarditis are disorders frequently encountered in clinical practice, and imaging plays a major role in the diagnosis, management, and follow-up of these diseases. This chapter will describe imaging of the cardiomyopathies that have characteristic imaging features and that are most commonly imaged in clinical practice.
▪
Imaging: What, Why, and How
Definition of a Cardiomyopathy
Cardiomyopathies are diseases of the heart muscle that may eventually lead to cardiac dysfunction or arrhythmias. They encompass a heterogeneous group of several myocardial disorders that manifest with various structural and functional phenotypes. Despite the common clinical use of the terms ischemic and hypertensive cardiomyopathies, cardiomyopathy does not include impaired cardiac function caused by cardiovascular disorders, such as atherosclerotic coronary artery disease (CAD), cardiac valve disease, systemic hypertension, or congenital heart disease, as defined by the 2006 American Heart Association (AHA) and 2008 European Society of Cardiology statements. The AHA classification divides the cardiomyopathies into primary and secondary cardiomyopathies, based on the predominant organ of involvement. Primary cardiomyopathies are confined to heart muscle and may be genetic, acquired, or mixed genetic and acquired ( Table 31.1 ). Secondary cardiomyopathies represent pathologic involvement of the myocardium in the context of a generalized systemic disorder ( Table 31.2 ).
TABLE 31.1
American Heart Association Classification of Primary Cardiomyopathies
| TYPE | EXAMPLES |
|---|---|
| Genetic | HCM, ARVC/D, LVNC |
| Acquired | Myocarditis, stress, and PPCM |
| Mixed | DCM, restrictive cardiomyopathy |
ARVC/D, Arrhythmogenic right ventricular cardiomyopathy or dysplasia; DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; LVNC, left ventricular noncompaction; PPCM, peripartum cardiomyopathy.
TABLE 31.2
American Heart Association Classification of Secondary Cardiomyopathies
| TYPE | EXAMPLES |
|---|---|
| Infiltrative | Amyloidosis; Gaucher, Hurler, and Hunter disease |
| Storage | Hemochromatosis, glycogen storage, Anderson-Fabry and Niemann-Pick diseases |
| Toxicity | Drugs, heavy metals, chemical agents |
| Endomyocardial | Tropical endomyocardial fibrosis, hypereosinophilic syndrome |
| Granulomatous | Sarcoidosis |
| Endocrine | Diabetes mellitus, hyperthyroidism, hypothyroidism, hyperparathyroidism, pheochromocytoma, acromegaly |
| Cardiofacial | Noonan syndrome, lentiginosis |
| Neuromuscular, neurologic | Friedreich ataxia, Duchenne-Becker muscular dystrophy, Emery-Dreifuss muscular dystrophy, myotonic dystrophy, neurofibromatosis, tuberous sclerosis |
| Nutritional deficiencies | Thiamine, vitamin C (scurvy), carnitine |
| Autoimmune, collagen | Systemic lupus erythematosus, dermatomyositis, rheumatoid arthritis, scleroderma, polyarteritis nodosa |
| Consequence of cancer therapy | Anthracyclines, cyclophosphamides, radiation |
Reasons for Imaging Cardiomyopathy
An important role of imaging patients with cardiomyopathy is to differentiate the ischemic from nonischemic pattern of disease because heart failure is usually caused by myocardial ischemia and infarction. Ischemic disease is important to diagnose with coronary angiography, coronary CT angiography (CTA), or cardiac magnetic resonance imaging (CMR) because left ventricular (LV) function can improve following coronary revascularization in the presence of substantial viable myocardium. On CMR, abnormal late gadolinium enhancement (LGE) involving the subendocardium with a variable degree of transmurality and distributed in the vascular myocardial territory of a coronary artery is compatible with ischemic disease. CMR is a validated tool to differentiate viable from scarred myocardium with decreased potential of recuperation (nonviable) based on abnormal LGE involving less (viable) or more (nonviable) than 50% of the wall thickness.
Imaging is essential to assess the phenotypic expression of nonischemic cardiomyopathy and degree of cardiac dysfunction. CMR can identify infarcted or scarred myocardium by the presence of abnormal LGE, which has prognostic value and may influence clinical management—for example, deciding on the implantation of an automatic implantable cardioverter-defibrillator. Finally, the lack of ionizing radiation makes echocardiography and CMR important tools for screening relatives of patients with hypertrophic cardiomyopathy (HCM) or arrhythmogenic right ventricular cardiomyopathy or dysplasia (ARVC/D) and for the serial assessment of treatment response and complications of various cardiomyopathies.
Procedural Considerations
Problem Solving With Echocardiography
Transthoracic echocardiography is usually the first-line imaging modality to identify various cardiomyopathy phenotypes, assess for wall motion abnormalities, and measure chamber volume, ventricular ejection fraction, and wall thickness. Doppler echocardiography is helpful to evaluate cardiac valves and diastolic dysfunction. However, echocardiography is limited by substantial interstudy and interobserver variability. It may be inconclusive because of suboptimal acoustic window (e.g., obese patients) or because some areas (e.g., cardiac apex and the right ventricular [RV] free wall) are poorly visualized by transthoracic echocardiography. Transesophageal echocardiography improves visualization, but it is an invasive procedure requiring intubation of the esophagus, with a small risk of esophageal perforation, bleeding, and aspiration.
Problem Solving With Coronary CT Angiography
In newly diagnosed cardiomyopathy, it is important to ensure that the cardiac dysfunction is not caused by CAD-related ischemia or infarction. Although catheter angiography is the gold standard test, coronary CTA is a validated noninvasive alternative in patients with a low pretest probability of CAD (e.g., young patients with no risk factors for CAD). Functional data can be acquired to assess for wall motion abnormalities and measure the chamber volume, ventricular ejection fraction, and myocardial wall thickness. Delayed imaging after injection of iodinated contrast may also be performed to detect myocardial fibrosis, a technique similar to the LGE sequence in CMR. Although the contrast resolution, accuracy, and reproducibility of CMR to assess cardiac function and myocardial fibrosis are superior, coronary CTA is a helpful alternative in patients with contraindications to CMR (e.g., pacemaker). Incidental CT findings in the lung or mediastinum may suggest the cause of a cardiomyopathy. For example, abnormal LGE in the myocardium in the presence of mediastinal and hilar lymphadenopathy with lung nodules is suspicious for sarcoidosis. Signs of congestive heart failure may be seen on CT, including interlobular septal thickening, ground-glass opacity, pleural effusion, and borderline enlarged bilateral hilar lymph nodes.
Problem Solving With Cardiac Magnetic Resonance Imaging
CMR has become the most valuable modality to image cardiomyopathies and will be the focus of this chapter. It is complementary to other imaging modalities to assess for cardiac and pericardial morphology and cardiac and valve function, as well as myocardial perfusion. It also provides uniquely distinct data on the characterization of myocardial tissue. The imaging technique and protocols need to be tailored to the suspected pathology; therefore proper clinical information should be obtained prior to scanning time, and acquisition of the CMR images should be closely monitored.
Assessing Myocardial Morphology
Black blood imaging, using a fast spin-echo sequence with blood suppression performed through a double-inversion recovery pulse technique, is used to acquire static images with high in-plane spatial resolution of the morphology of the heart, pericardium, and great vessels. This sequence produces images in which the myocardium has intermediate signal intensity (SI) contrasting with the adjacent dark blood and bright epicardial fat.
Bright blood imaging, using a balanced steady-state free precession (SSFP) sequence acquired in multiple planes (vertical and horizontal long axis, three chamber, and short axis), provides cine images of high temporal resolution in which the blood pool is bright relative to the adjacent intermediate SI of the myocardium.
Assessing Myocardial Function
Bright blood imaging, using an ECG-segmented balanced SSFP sequence, yields dynamic functional imaging of the heart and can be acquired in any plane. The presence of regional wall motion abnormality can be depicted on SSFP sequence, with or without myocardial tagging technique. A stack of 20 to 30 consecutive, breath-hold, short-axis SSFP images, each acquired during a different cardiac cycle, from the base to the apex, can be interrogated with dedicated viewing software. It is the most accurate and reproducible method for the quantitative assessment of biventricular end-diastolic volumes, end-systolic volumes, ejection fractions, and myocardial mass. Quantitative assessment of the LV volume, ejection fraction, and mass of comparable accuracy can be achieved using a series of long-axis views radially acquired around the anatomic axis of the left ventricle. When CMR is performed to evaluate for ARVC/D, additional SSFP sequences are usually acquired in the right ventricular outflow tract (RVOT), as well as in the long-axis view of the right ventricle and axial plane for a better depiction of the motion of the RVOT and RV free walls.
Characterizing Myocardial Tissue
Myocardial Edema.
T2-weighted imaging, using a dual-echo, double-inversion recovery, fast spin-echo sequence in the short-axis plane, is used to detect fluid accumulation in the myocardium caused by focal myocardial edema and/or necrosis. It is depicted by abnormally high T2-weighted SI compared to the adjacent intermediate SI of the normal myocardium. However, diffuse myocardial edema with a homogeneous increase in the T2-weighted SI is more difficult to detect than focal edema. To improve detection of diffuse myocardial edema, the T2 ratio can be calculated to normalize the SI of the myocardium to that of the skeletal muscle. Myocardial T2 mapping, generated by acquiring multiple T2-weighted images repeated with different T2 preparation times, provides both visual and quantitative analyses of the myocardial edema and is a promising tool to diagnose diffuse myocarditis.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here
