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8. LV anterior and posterior diameters and wall thicknesses are
measured at the mid-papillary level. End-diastolic and sys-
tolic endocardial areas of each slice are traced manually. LV
volumes are calculated by the modified formula for Simpson's
rule.
9. As for echocardiography, it is recommended that two investi-
gators blind to the experimental conditions read MRI record-
ings even though the better definition of the images reduce the
inter and intra-reader variability.
Prior to euthanasia LV pressure or pressure-volume loop analyses
can be performed. Anesthesia can be provided by different routes
and with different agents. The authors routinely use (a) isoflurane
(2% in oxygen), rats are intubated and mechanically ventilated, or
(b) pentobarbital 40-60 mg/kg i.p.
Two approaches are possible:
1. The less invasive approach is by pushing a Millar pressure cath-
eter (indicatively SPC-320 for the rat, SPR-671 for the mouse)
or a Millar pressure-conductance catheter through the right
carotid artery to the left ventricle.
2. The open chest approach requires a bilateral thoracotomy in
fourth and fifth intercostal. After opening the pericardium, a
catheter (Millar Instruments Inc., Houston, TX) is inserted
into the LV from the apex.
3.3
Hemodynamics
Naturally, pressure catheters measures are limited to a LV
pressures and their derivatives. Pressure-conductance catheter
allow for a full array of pressure-volume loop analyses: LV end-
diastolic pressure (EDP), end-diastolic (EDV) and end-
systolic(ESV) volumes, stroke volume (SV), +d
P
/d
t
, −d
P
/d
t
,
isovolumic relaxation time (tau), and arterial elastance (Ea) are
determined in 10-20 digitally averaged cardiac cycles while the
ventilator is stopped. LV end-systolic elastance (Ees), preload
recruitable stroke work (PRSW) and end-diastolic stiffness (Eed)
are measured using a graded preload reduction technique. Arterio-
ventricular (AV) coupling is calculated as Ea/Ees. The test is con-
cluded by advancing the catheter into thoracic aorta to measure
arterial blood pressure.
3.4 Gross Pathology
and Histological
Assessment
The hearts and lungs are removed and weighed (wet weight).
Hearts are processed and the histological analyses are performed at
different time depending on experiment design. Three approaches
are used by the authors:
1. Hearts are cut into two pieces through the short axis. The
basal half is fast frozen and stored for different assays, and the
apical half is used for histological analysis.
2. Hearts are slightly frozen to reach a consistency which favors
thin and precise cutting, are cut with a chopper into 1 mm-thick
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