Download Echocardiography studies

II. Echocardiography studies
Mice were anesthetized with Halothane (0.75 – 1.25%, 1 l/min). Images
were obtained with the transducer placed on the animal’s shaved chest (lateral
recumbance). To optimize the image, a transmission gel was used between the
transducer and the animal chest (General Imaging Gel, ATL. Reedsville, USA).
Animals were scanned from below through a hole in the surgical bed, at 2-cm
depth with the focus optimized at 1-cm. All measurements were based on the
average of three consecutive cardiac cycles. Two-dimensional (2-D) images of the
heart were first obtained in the parasternal long-axis view, followed by short-axis
and apical 4-chamber views. Left ventricular end-systolic (LVESD) and enddiastolic dimensions (LVEDD), interventricular septal thickness (IVST), and
posterior wall thickness (PWT), both in diastole and systole, were measured at the
level of the papillary muscles on the short-axis view using 2-D guided M-mode
imaging. The angle of interrogation of the M-mode beam was carefully aligned at
the anteroposterior axis to be perpendicular to the LV walls, and LVEDD, IVST,
and PWT were measured by the leading edge method. LVESD was measured at
the time of maximum anterior motion of the posterior wall. LV fractional shortening
(FS) was calculated from the M-mode recordings using the following equation: FS
(%) = [(LVEDD-LVESD)/LVEDD] x 100.
Two-dimensionally guided pulsed Doppler recordings of LV transmitral flow
were obtained from the apical four-chamber view. To obtain the transmitral flow,
the sample volume was placed just below the mitral valve leaflets. The sample
volume was then placed between the mitral valve and LV outflow tract so the aortic
valve closure line and the onset of mitral flow could be clearly identified. Isovolumic
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relaxation time (IVRT) was taken as the time from aortic valve closure to the onset
of mitral flow. To minimize influence of heart rate, IVRT was divided by square root
of RR interval (IVRTcor). Velocity of circumferential shortening (VCF) was
measured using the formula: (LVEDD-LVESD)/(LVEDDxET), where ET is the
ejection time. LV outflow velocity pattern was recorded from the apical long-axis
view, with the sample volume positioned just below to the aortic valve.
Myocardial Performance Index (MPI) is the ratio of total time spent in
isovolumic activity (isovolumic contraction time and isovolumic relaxation time) to
the ejection time (ET). These Doppler time intervals were measured from the mitral
inflow and LV outflow time intervals. Interval “a”, from the cessation to onset of
mitral inflow, is equal to the sum of the isovolumic contraction time, ET and
isovolumic relaxation time. Ejection time “b” is derived from the duration of the LV
outflow Doppler velocity profile. The MPI was calculated using the formula: (a-b)/b.
Both M-mode and Doppler tracing were recorded at a sweep speed of 200 mm/s,
and images were stored on videotape for off-line analysis. To measure
simultaneous heart rate, single channel electrocardiography was performed for at
least three consecutive RR intervals with the electrodes placed on the upper and
lower limbs of the animal.
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