These results suggest that hyperenhancement
appears to reflect irreversible ischemic injury.
This led to the study hypothesis that a ceMRI image
with little hyperenhancement in a patient with severe
coronary artery disease and ventricular dysfunction
predicts significant viable myocardium that could
improve in contractility on revascularization.
In 50 patients scheduled to undergo
revascularization with resting wall motion abnormalities
found on routine clinical workup, cine MRI for wall
motion and ceMRI for regional viability assessment
was performed. Cine MRI was repeated post-revascularization
to document changes, if any, in wall motion. The
age range of the study patients was 40-85 years;
21 patients had a history of prior MI, 34 underwent
bypass surgery and 16 angioplasty. Follow-up cine
MRI was done in 41 of the 50 patients at about 3
months following revascularization.
Image analysis
For the cine MR images, each of
12 segments per each short axis slice was analyzed
for regional wall thickening, from 0 which was normal
to 5 which was dyskinetic. This was analyzed by
the consensus of two observers blinded to the patient
identity and to the ceMRI results. The ceMR images
were analyzed using the same segmental model, but
in each case assessment of the extent of transmural
hyperenhancement was performed. The analysis was
blinded for patient identity and changes in regional
wall motion.
Interestingly, 40 of the 50 patients
demonstrated some hyperenhancement, although only
21 of the patients had a history of MI. In total,
2083 segments were analyzed, 38% of which had a
wall motion abnormality at baseline. Of this 38%,
43% had mild to moderate hyperkinesis, 38% severe
hyperkinesis, and 20% akinesis or dyskinesis. After
revascularization, 59% of segments with mild to
moderate or severe hyperkinesis improved after revascularization,
whereas about 30% of segments that were akinetic
or dyskinetic improved.
Images from two patients were reviewed.
In the first patient, the cine MR end diastolic
still frame taken before revascularization showed
impaired wall thickening, particularly in the anteroseptal
region. However, the ceMRI performed before revascularization
did not show any hyperenhancement in that territory.
Therefore, based on the preliminary data from the
animal studies, it would be predicted that contractility
would improve after revascularization. Comparing
the still frames taken after revascularization showed
significant improvement in wall thickening. In the
second patient, the baseline wall motion abnormality
was in the anterolateral wall. However, the ceMR
image showed a significant hyperenhancement of this
territory before revascularization, predicting that
this area should not improve in contractility after
revascularization. Comparing the post-revascularization
images showed significant impairment of wall thickening
remains, and appeared to be to the same degree as
pre-revascularization. Notably, the contours and
location of the anatomical details were nearly the
same before and after revascularization. An advantage
of MR is true 3-D imaging that removes the registration
issues found in non-MR imaging techniques.
Prediction of wall motion improvement
For all dysfunctional segments,
the likelihood of wall motion improvement was inversely
related to the transmural extent of hyperenhancement.
In segments with no hyperenhancement, there was
about an 80% chance of wall function improvement
after revascularization, whereas segments with 76-100%
transmural extent of hyperenhancement, there was
a 2% chance of improvement.
A subgroup analysis restricted to
segments with severe hyperkinesis or akinesis at
baseline showed the same inverse relation between
the likelihood of wall motion improvement and the
transmural extent of hyperenhancement.
A patient-by-patient analysis calculating
the amount of the ventricle that was dysfunctional
and non-hyperenhanced compared to the change in
mean wall motion score after revascularization was
performed. The analysis showed that patients with
significant portions of dysfunctional ventricle
and with less than 25% hyperenhancement were more
likely to have wall motion improvement after revascularization
(r=0.75; p< 0.001). A very good relation between
this same group of patients and improvement in ejection
fraction (r=0.70; p<0.005) was also found.