Page 64 - Feline Cardiology

Chapter 7: Echocardiography 59

ET Diagnostic Testing
PEP

Figure 7.6. Pulsed-wave Doppler echocardiogram obtained at the aorta with correctly positioned calipers for measuring the preejection
period (PEP) and the ejection time (ET). Note that the laminar blood flow appears as a single systolic envelope.

Systolic time intervals assess LV systolic performance amounts of valve regurgitation (a subjective assessment
but are also affected by heart rate, preload, and afterload. that varies depending on ultrasound software and set-
The preejection period (PEP) represents the time tings, but generally is too small to produce an audible
between initial ventricular electrical activity (the onset murmur on physical exam) are common in normal cats,
of the QRS) and the onset of LV ejection (opening of particularly of the pulmonic and tricuspid valves (Adin
the aortic valve); the LV ejection time (LVET) is mea- and Diley-Poston 2005). The color-flow sample volume
sured from aortic valve opening to closure. Total elec- should also be placed over the interventricular and
tromechanical systole is represented by the interval from interatrial septae to evaluate for turbulent flow through
QRS initiation to aortic valve closure (PEP + LVET). septal defects that are not visible two-dimensionally.
The PEP/LVET index compensates for cardiac loading Color-flow Doppler investigation of the left ventricular
conditions and is superior to either index alone. These outflow tract in the right parasternal long axis view is
measurements can be obtained using M-mode or particularly important in cats to identify systolic ante-
Doppler tracings (Figure 7.6), but they are infrequently rior motion of the mitral valve (SAM). If SAM is present,
used in feline cardiology, because they have not convinc- aliasing, turbulent flow typically will be noted in the left
ingly been shown to provide clinically important infor- ventricular outflow tract in conjunction with eccentric
mation. See Table 7.2 for normal echocardiographic mitral regurgitation (i.e., mitral regurgitation directed
feline systolic performance parameters. to the left atrial free wall rather than left atrial roof)
After the short axis views are obtained, the probe during systole. See Chapter 11 for further discussion of
should be rotated 90° at the right parasternal position hypertrophic obstructive cardiomyopathy. Pulmonary
to obtain the long axis images. The two standard images artery flow is recorded from the right parasternal short-
include the left ventricular outflow tract view (Figure axis view (or less commonly from the left cranial para-
7.7A) and the 4-chamber view (Figure 7.7B). The trans- sternal position). Normal outflow will have a single
ducer is shifted between these two planes by slight systolic envelope away from the transducer in a pulsed-
cranial to caudal angulation. Before turning the cat to wave Doppler tracing (with a velocity less than 1 m/s).
the other side for evaluation from the left cardiac For left-sided imaging the cat is turned so that the left
windows, Doppler imaging from the right should be parasternum (ventralmost aspect of the left side of the
performed. Color-flow Doppler should be performed at thorax) is located over the cutout in the table. The left
every valve to screen for abnormal transvalvular flow. apical views (the 4- and 5-chamber views) are used so
Screening for valvular insufficiency can be performed that the transducer beam will be parallel to blood flow
using color-flow Doppler at the right parasternal for accurate Doppler assessment of flow across the
window; however, it is important to recognize that trace aortic, mitral, and tricuspid valves. The location for this