Page 60 - Feline Cardiology

Chapter 7: Echocardiography 55 Diagnostic Testing

Figure 7.3. A young cat restrained in lateral recumbency for an echocardiogram with the transducer located on the right parasternum.

• Butorphanol and midazolam (0.3 mg/kg of each, ideally suited to identification of structural lesions, but
IM or IV) quantitative assessment of cardiac dimensions and func-
• Deep sedation tion is also important. Most sonographers begin the
• Dexmedetomidine 0.01 mg/kg IM or IV alone, or examination at the right parasternal window (most
with either diazepam (0.2 mg/kg IV) or midazolam often the right 4th or 5th intercostal space). By conven-
(0.05–0.3 mg/kg IV or IM) if hypertrophic cardio- tion, the marker on the probe is directed toward the
myopathy has been confirmed previously and the patient’s elbow to obtain the short axis views and toward
patient is not hypertensive (for deep sedation), or the shoulder to produce the long axis views. Both short
• Low-dose ketamine (1–2 mg/kg IV or PO) with or and long axis views are required to thoroughly image a
without diazepam (0.02 mg/kg IV) or acepromazine 3D structure like the heart using a 2D modality like
(0.11–0.22 mg/kg IM or SQ) for severely fractious echocardiography. A simple analogy is to think of the
cats heart as a carrot and the ultrasound beam as a knife. The
knife both slices the carrot longitudinally (long axis) for
It is very important to obtain a simultaneous electrocar- a global overview of the carrot and, with a 90° rotation
diogram (ECG) during the echocardiographic examina- of the direction of the blade, chops the carrot from tip
tion to allow accurate timing of measurements. Without to top (series of short axis views) to provide a compre-
a simultaneous ECG, timing of cardiac measurements hensive evaluation of the structure.
can easily be incorrect and erroneous diagnoses are pos- Once the heart is visualized, the depth setting is opti-
sible. The teeth on metal alligator clips can be sanded mized and the time gain compensation controls, reject,
away to make the clips more comfortable for the patient. and compression settings are adjusted to ensure struc-
Alternatively, atraumatic clips may be used or human tures of interest are ideally visualized. Panning along the
ECG electrode patches can be applied with the gelled entire heart in this plane is important for a complete
surface directly against the patient’s metacarpal or meta- assessment. Specifically, the short axis view is evaluated
tarsal pad and a soft wrap to secure the electrode for the at the ventricular level (Figure 7.4A) and at the heart base
duration of the examination. where the aorta and left atrium are visualized (Figure
7.4B). In addition, M-mode studies at three standard
short axis planes should be obtained: the ventricular,
PERFORMING THE ECHOCARDIOGRAM
atrioventricular (AV) valve, and aortic valve levels (Figure
Accurate interpretation of echocardiographic findings 7.5). The left ventricular measurements are obtained
requires a complete and thorough examination. The best from the M-mode obtained at the level of the chordae
way to ensure one always obtains a complete study is to tendinae and include the interventricular septum and left
adopt a consistent technique. Echocardiography is ventricular free wall and the left ventricular end-diastolic