Validation of MRI measurements in myocardial biopsies

This research protocol aims to validate two novel magnetic resonance imaging
(MRI) techniques to visualize cardiac muscle properties against histology
obtained in myocardial biopsy material. MRI is the gold standard imaging
modality for patients with dysfunction of the cardiac muscle, called
cardiomyopathy. In many patients, the exact cause of cardiomyopathy cannot be
diagnosed because current imaging modalities have important limitations. One of
these limitations is the fact that mild and diffuse myocardial fibrosis cannot
be visualized, even though this is an important hallmark of cardiomyopathy. A
second limitation is the fact that myocardial metabolism and myocardial
triglyceride (TG, i.e. fat) depositions cannot be quantified noninvasively.
Potential solutions for these limitations are a novel MRI technique called T1
mapping to quantify diffuse myocardial fibrosis, and a 1H-MR spectroscopy
protocol (1H-MRS) to visualize myocardial metabolism and quantify myocardial TG
content, respectively. However, these novel MRI protocol have not been
validated properly against histology.
Patients who have a clinical indication for open heart surgery and are
on the waiting list for the operation will be asked to participate in this
research protocol. We will enroll (a) patients with severe aortic valve
stenosis who are on the waiting list for surgical aortic valve replacement, and
(b) patients with hypertrophic cardiomyopathy (HCM) with left ventricular
outflow tract obstruction who are on the waiting list for surgical septal
myectomy according to Morrow. Patients from both categories will be asked to
undergo an MRI scan while on the waiting list. The research MRI acquisition
procedures will be similar to routine MRI procedures and all safety precautions
will be in place. The MRI protocol will consist of ECG triggered sequences for
T1 mapping (MOLLI sequence) and for 1H-MRS measurements of tissue creatine (Cr)
and TG content (PRESS and STEAM sequences, respectively). The research protocol
requires one contrast bolus administration. In addition, patients with severe
aortic valve stenosis undergoing aortic valve replacement will be asked
permission for myocardial biopsies to be taken during surgery. The risk of this
procedure is negligible. In patients with HCM undergoing Morrow septal
myectomy, surgical excision of part of the basal septal myocardium is the
indication for surgery. In this patient category, we will request patients*
permission for the use of the excised myocardium. Myocardial biopsy samples
will be used for quantification of histologically documented diffuse myocardial
fibrosis, which will be correlated with extracellular matrix volume fraction as
calculated based on pre- and post-contrast T1 times of the myocardium measured
during the pre-surgery MRI. Myocardial biopsy material will also be used to
quantify myocardial Cr and TG concentrations with biochemical assays. Results
will be used to verify measurements obtained during the pre-surgery MRI.
In addition to MRI parameters, microRNAs (miRNAs) hold great promise as
a new class of circulating biomarkers in peripheral blood. This unique study
protocol which will acquire myocardial tissue biopsies will also be used as a
platform to validate the miRNA-signatures in peripheral blood against
miRNA-signatures in myocardial biopsy tissue. Together with the miRNA-signature
in peripheral blood obtained 6 months post-surgery, this will provide us with
new insights into the function of identified miRNAs and improve their
prognostic and in the future possibly even therapeutic value.
We expect to observe statistically significant correlations between
noninvasive MRI-measured extracellular matrix volume and histologically proven
diffuse myocardial fibrosis, between noninvasively 1H-MRS quantified tissue TG
content and biochemically determined TG concentrations, and between 1H-MRS of
tissue Cr content and biochemically determined Cr concentrations.

The main objective of this study is to biochemically and histologically
validate two novel MRI techniques to characterize myocardial properties that
are expected to be useful for the diagnosis of various forms of cardiomyopathy.
A second objective is to validate miRNA signatures in peripheral blood samples
against myocardial miRNA content.

We will perform an MRI protocol on patients who have a clinical indication for
open heart surgery and are on the waiting list for either surgical aortic valve
replacement or surgical septal myectomy. We will employ a novel MRI sequence
called T1 mapping to quantify the extent of diffuse myocardial fibrosis, and a
1H-MRS protocol to visualize myocardial creatine and triglyceride content. A
total of 5 blood samples will be drawn at the time of the MRI. If patients have
given signed informed consent, a myocardial biopsy will be taken during aortic
valve replacement surgery. Patients undergoing surgical septal myectomy will be
asked permission for the use of the routinely excised myocardium. At the
routine outpatient visit 6 months post-surgery, an additional blood sample will
be obtained. Myocardial parameters obtained using noninvasive pre-surgery MRI
will be validated against biochemical assays and histology in the myocardial
biopsies. Furthermore, miRNA profiling will be performed on both peripheral
blood and myocardial tissue of these patients.

Patients on the waiting list for open heart surgery will be asked to undergo an
MRI scan before the operation. Surgery will not be delayed for the research MRI
protocol. The MRI is a noninvasive procedure, except for the insertion of an
intravenous canula for contrast administration. The MRI protocol takes 60 min.
The research MRI acquisition procedures will be similar to routine MRI
procedures and all safety precautions will be in place. Patients with
established contra-indications for MRI will not be recruited. When patients
wish to stop the scanning procedure and get out of the scanner they can press a
*panic button*, which is standard procedure for every MRI. Patients are also
able to talk to the researchers in the control room at any time during the
experiment. Potential hazards from high-energy radiofrequency or gradient
pulses are not any higher than in the manufacturer*s sequences. MRI does not
require ionizing radiation, and gadolinium contrast is well tolerated with only
very rare cases of gadolinium allergy ever reported in the literature. The
intravenous canula will be used to draw blood for research purposes (5 tubes =
15.8 ml in total).

Patients undergoing surgical aortic valve replacement will be asked permission
for myocardial biopsies to be taken during surgery. During surgery, myocardial
biopsy specimens will be taken from the basal LV septum using a Tru-cut type
biopsy needle. A total of 4 biopsies will be obtained. The size of each biopsy
sample is <0.1 g, which is less than a thousandth of the total myocardial
volume. Obtainment of LV septal biopsies in patients with aortic valve stenosis
(and consequent left ventricular hypertrophy) is regarded safe, due to the
concentric left ventricular hypertrophy that is present in these patients, due
to extensive experience of operators, clear visibility of the interventricular
septum after thoracotomy, and because the MRI will be used to guide the
operator to the most optimal biopsy site. In addition, the size of the biopsies
is small (3 x 3 x 3 mm). As a result, the risk for conduction abnormalities as
a result of the biopsies is negligibly small. Patients undergoing surgical
septal myectomy will be asked permission for the use of the myocardium that is
excised routinely during this procedure. The risks of this type of surgery are
inherent to the operation that is clinically indicated. At the routine
outpatient clinic visit 6 months post-surgery, we will draw an additional blood
sample (2 tubes of 2.7 ml = 5.4 ml).