Established and Emerging Applications of Magnetic Resonance Late Enhancement Imaging in Cardiology
Frank Grothues Director, Echocardiography Service, University Hospital Magdeburg
Sudden cardiac death (SCD) represents a major cause of mortality after
myocardial infarct38 with the presence of infarct tissue forming the
substrate for malignant re-entry arrhythmias.39,40 Histopathological
studies have shown that especially the infarct border zone can exhibit
marked spatial heterogeneity with areas of necrosis interspersed with
bundles of viable myocytes.41–43 Tissue heterogeneity in the peri-infarct
zone can originate areas of slow electrical conduction leading to lifethreatening
re-entrant tachycardias.44,45 Hence, recent work also aimed to
look closer at the heterogeneity of the infarct periphery in LE images.46–48
While Bello et al.49 had already demonstrated a significant correlation
between infarct surface area/total infarct size and the inducibility of
tachycardias, a study by Yan et al.48 reported an association between the
extent of the peri-infarct zone by LE and all-cause mortality in patients
with ischaemic heart disease. Schmidt et al.46 studied a high-risk group of
47 patients who underwent implantation of an implantable cardioverter
defibrillator (ICD) for primary prevention of sudden cardiac death.
Quantification of tissue heterogeneity at the infarct periphery was
strongly associated with inducibility for monomorphic ventricular
tachycardia and remained the single significant factor in a stepwise
logistic regression. Although these preliminary results hold the potential
for risk stratification in post-infarct patients, further studies are required
to explore the reproducibility and the prognostic capability in a large
post-infarct population.
Detection of Intra-cardiac Thrombi
LV thrombi present a frequent complication after myocardial infarct with
a substantial risk of systemic embolisation occurring in approximately
13% of patients.50 Transthoracic echocardiography (TTE) is generally used
as the main diagnostic technique.51 However, due to insufficient image
quality and problems assessing the LV apex (near-field probe) thrombi
can be difficult to image and therefore can be missed. On the other hand,
false-positive findings are not infrequent on TTE.52 On LE images the LV
cavity shows a homogeneous, strong enhancement after gadolinium
administration, with abnormal intraventricular structures having a dark
appearance (see Figure 2).53 LE imaging allows for the visualisation of
small thrombi (<1cm3), which are missed on cine CMR and TTE, especially
when trapped within trabeculations. Mollet et al.54 could demonstrate
this instance in a study of 57 patients with acute myocardial infarction,
chronic myocardial infarction, or ischaemic cardiomyopathy. LE CMR
detected mural thrombi (size ranging from 0.5–8.6cm3) in 12 of 57
patients whereas only six and five of them were visible on cine CMR and
TTE, respectively. With LE considered as the gold standard, TTE falsely
suggested an apical thrombus in three patients. Although differentiation
of mural thrombus and zones of MVO at times can be challenging, LE
imaging yields a better identification of LV thrombi than presently used
clinical imaging modalities.
Late Enhancement in Non-ischaemic Myocardial Disease
LE techniques have, over time, also gained increasing interest for the
evaluation of non-ischaemic forms of myocardial disease. The following
section will cover the latest advances.
Discrimination of Ischaemic and Dilated Cardiomyopathy
Initial observations by Wu et al.55 had shown that in contrast to
ischaemic cardiomyopathies, none of the control patients with nonischaemic
cardiomyopathy nor any of the enrolled healthy volunteers
demonstrated LE areas. The ability of differentiating ischaemic from
non-ischaemic cardiomyopathies has subsequently been tested in a
prospective manner in several trials.56–57 McCrohon et al. found areas of
LE in 41% of patients, which were located in the mid-wall in the
majority of cases (28%). In 13% LE resembled the pattern of prior myocardial infarct with subendocardial enhancement. In contrast, all
patients with angiographically proven significant coronary artery disease
showed LE with the subendocardium involved. Another study could
demonstrate LE areas in 81% of patients with coronary artery disease
and in only 9% with angiographically classified non-ischaemic
cardiomyopathy. Although not diagnostic as a sole investigational tool,
the absence or the pattern of LE can, in selected cases, point to a nonischaemic
cardiomyopathy.
