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5. An overhand knot is tied with two pieces of suture to arrest
blood flow for 20-90 min before release of the knot (reperfu-
sion); a permanent knot is tied in case of permanent ischemia.
Body temperature of the mouse/rat must be strictly con-
trolled and maintained at 37°C to obtain reproducible infarcts
with ischemia-reperfusion. In case of permanent ischemia,
temperature is not so critical since the procedure is much
shorter: chest is closed under negative pressure right after
coronary ligation.
6. Proper placement of the ligature is confirmed by the appear-
ance of ventricular ectopy and blanching of the myocardium.
The chest is the closed under negative pressure and mice are
weaned from mechanical ventilation. Postsurgical analgesia is
achieved by buprenorphine (0.1 mg/kg s.c. q12h for 1 day).
3.2 In vivo imaging
for serial assessment
of progression of
cardiac remodeling,
function and MI size
The two most widely used noninvasive imaging techniques in stud-
ies in small rodents are
echocardiography and magnetic resonance
imaging
.
Echocardiography
, which can easily be performed on awake or
lightly sedated mice, has become the procedure of choice for most
studies of the mouse heart for its flexibility. While echocardiogra-
phy in small rodents, first in the rat then in the mouse, has been
performed with apparatuses used for clinical activity, choosing
mostly vascular probes of 7-15 MHz, in the last decade, new
instruments designed for small animal exams have been made com-
mercially available. The high-frequency probes (30 MHz) allow a
higher spatial resolution (30 mm) and, consequently, a more accu-
rate assessment of heart dimensions and function. However, the
major difficulties of this technique are the geometric assumptions,
image positioning errors, and use of subjective visual methods thus
making necessary a skilled sonographer. Other limitations are LV
wall motion assessment because of postsurgical adhesions and chest
deformations, and a not well visualization of the right ventricle.
Magnetic resonance imaging
(
MRI
) represents the gold standard
for measurement of cardiac morphology and function either in
humans or in small rodents. It is noninvasive, accurate, free from
geometric assumptions compared to echocardiography. The con-
tiguous stack of short-axis images of the heart covers the entire
length of the LV and allows for an accurate estimation of both left
and right ventricular mass, volumes, and ejection fraction. Even
though MRI is a more reliable method than echocardiography for
the characterization of the pathophysiological consequences of
experimental MI and of treatments response in rodents, MRI
exams usually last more than 1 h, require deep anesthesia, and is
much more expensive. For these reasons it is not routinely used in
large series of animals.
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