Established and Emerging Applications of Magnetic Resonance Late Enhancement Imaging in Cardiology
Frank Grothues Director, Echocardiography Service, University Hospital Magdeburg
Hypertrophic Cardiomyopathy
Patients with hypertrophic cardiomyopathy (HCM) are at risk of
arrhythmic SCD. However, due to diverse phenotypic expression, the
definition of high-risk subgroups is challenging. Concordantly, studies
by Choudhury et al.58 and Moon et al.59 demonstrated areas of LE in
81% and 79%, respectively. Based on conventional clinical parameters
Moon et al. could further show that the extent of LE was greater in
patients with risk factors for SCD and in patients with progressive
disease. In this excellent study he also tried to correlate different LE
patterns to future cardiovascular risk. These findings are encouraging
and it is conceivable that LE, in the future, could add important
information for risk stratification in HCM.
Myocarditis
Owing to the lack of currently available adequate diagnostic techniques,
the diagnosis of myocarditis has, in the past, mainly been made on the
basis of clinical examination, electrocardiogram and inflammatory
laboratory markers. The considered gold standard of endomyocardial
biopsy carries a certain peri-procedural risk with additional limited
diagnostic sensitivity and specificity and is therefore clinically not widely
used. A first report by Friedrich et al.60 in 1998 using the spin echo
technique already indicated the diagnostic potential of contrastenhanced
CMR. With the development of the LE technique, CMR
imaging of myocarditis has become a promising field. Mahrholdt et al.61
could demonstrate LE in 88% of 32 patients with clinically diagnosed
myocarditis and guided endomyocardial biopsy in 21 of these patients,
and revealed histological evidence of myocarditis in 91%. In
concordance with findings at autopsy,62,63 LE was predominantly seen in
the epicardial layer of the lateral free wall (see Figure 3). Moreover, a
recent report of 128 patients with suspected myocarditis from the same
author group could demonstrate differences in the clinical course and
the LE pattern between patients with myocarditis caused by parvovirus
B19 and human herpesvirus 6.64
Sarcoidosis
Sarcoidosis is a systemic inflammatory disease of unknown aetiology in
which heart involvement presents as a major cause of death.65 While
accurate assessment of cardiac involvement has so far proved difficult, its
treatment can improve prognosis.66 In a recent study in 70 patients with
biopsy-proven sarcoidosis, Patel et al.67 detected cardiac involvement by
LE more frequently (24%) than had been detected by use of the Japanese
Ministry of Health Criteria (14%). The LE pattern was inconsistent with
that of typical myocardial infarction in 88% (mostly mid-myocardial
and/or epicardial enhancement) and, according to the results of
Smedema et al.,68 LE is frequently localised in the basal and lateral
segments. Since a majority of patients with cardiac sarcoidosis die of
arrhythmic SCD,65 like HCM, LE possibly could have a future role in risk
stratification for implantation of an ICD.
Cardiac Amyloidosis
Cardiac amyloidosis occurs in up to 50% of patients with light chain (AL)
amyloidosis and is associated with a median survival of usually less than
one year.69 Identification of cardiac involvement is critical, since therapy
might improve cardiac function and prognosis.70,71 In a series of 30
patients with proven cardiac amyloidosis Maceira et al.72 detected global
subendocardial LE in 69% coupled with abnormal myocardial and bloodpool
gadolinium kinetics. The findings of LE distribution correlated to the
transmural histological distribution of amyloid protein and the cardiac
amyloid load in an autopsy study of one patient. The authors hence
concluded that LE imaging “may prove to have value in diagnosis and
treatment follow-up”.
Anderson-Fabry Disease
Anderson-Fabry disease (AFD), an X-linked disorder of sphingolipid
metabolism, is characterised by the deposition of glycosphingolipid (GB3)
within myocytes73,74 and can present a possible cause of left ventricular
hypertrophy, especially in middle-aged men.75 Enzyme replacement therapy has recently become available and can lead to regression of
hypertrophy and improvement of regional myocardial function in a
subset of patients. Thus, identification of patients with AFD is desirable.
In a study of 26 patients with confirmed AFD, LE was present in 13
patients, occurred in the basal inferolateral wall and was not subendocardial.
76 The question arises of how an intracellular storage disease
can cause focal LE, and could be answered in a subsequent autopsy study
in one of these patients. Moon et al.77 demonstrated that LE is caused by
focal myocardial collagen scarring, which also might be the arrhythmic
substrate for SCD occurring in some patients.73,78
Chagas Disease
Chagas disease is caused by infection with Trypanosoma cruzi and
predominantly occurs in Latin America, with an estimated 200,000
new cases annually.79 In approximately one-third of infected
individuals Chagas disease shows cardiac involvement with
development of myocardial fibrosis leading to progressive heart failure
and cardiac arrhythmias including SCD. LE imaging in a study by
Rochitte et al.80 showed areas of hyperenhancement in 69% of 51
patients with various stages of Chagas disease. The degree of LE
increased progressively from the mildest to the most severe disease
stages, thus there is a chance that LE can guide future development of
new therapeutic interventions designed to halt myocardial fibrosis
early in the subclinical phases of the disease process.
Arrhythmogenic Right Ventricular Cardiomyopathy
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterised
by fibro-fatty infiltration of the right ventricle81,82 leading to regional or
global right ventricular (RV) dysfunction, ventricular tachyarrhythmias and
SCD. Although CMR was recognised early on as a valuable tool in
identifying patients having ARVC,83 diagnostic difficulties remain,
especially in the early stages of the disease.84 LE may in future contribute
to diagnostic accuracy. Tandri et al.85 studied 30 patients with suspected
ARVC, of whom 12 met the Task Force criteria for ARVC.86 Eight of these
12 patients (67%) showed LE compared with none of the 18 remaining
patients classified as not having ARVC. Furthermore, LE results showed
an excellent correlation with histopathology and predicted inducible
ventricular tachycardia on programmed electrical stimulation. However,
further studies are needed to assign LE a possible role in the evaluation
of patients with suspected ARVC.
Summary
While initially used for the diagnosis and sizing of myocardial infarction,
LE imaging has the potential of contributing to other aspects of
ischaemic heart disease, namely SCD risk stratification and detection of
intra-cardiac thrombi. Additionally, it has already proven its usefulness in
the evaluation of non-ischaemic forms of myocardial disease such as
viral myocarditis, HCM and sarcoidosis. Possible future applications
comprise imaging of eosinophilic myocarditis,87,88 Churg-Strauss
Syndrome,89,90 rejection of heart transplants,91 cardiac involvement in
muscular dystrophies92,93 and assessment of cardiotoxicity in
chemotherapy.94,95 The relative simplicity and robustness of the LE
imaging technique and its novel diagnostic potential will result in a
further expansion of CMR in cardiac imaging.
