Page 46 - Small Animal Internal Medicine, 6th Edition

18 PART I Cardiovascular System Disorders

have pulmonary undercirculation. Overinflation of the lungs slices to produce detailed cross-sectional images from recon-
or overexposure of radiographs also minimizes the appear- structed three-dimensional (3-D) orientations. MRI uses
VetBooks.ir ance of pulmonary vessels. radio waves and a magnetic field, rather than ionizing radia-
Pulmonary arteries that are larger than their accompa-
tion, to create detailed tissue images. These techniques can
nying veins indicate pulmonary arterial hypertension. The
tures, varying tissue types, and the blood pool. Identification
pulmonary arteries become dilated, tortuous, and blunted, allow greater differentiation among cardiovascular struc-
and visualization of the terminal portions is lost. Heartworm of pathologic morphology, such as from cardiac congenital
disease often causes this pulmonary vascular pattern, in addi- malformations or mass lesions, is a major application. These
tion to patchy to diffuse interstitial pulmonary infiltrates. modalities also are more sensitive than plain radiographs
Prominent pulmonary veins are a sign of pulmonary for detecting pulmonary nodules. Because cardiac move-
venous congestion, usually from left-sided CHF. On lateral ment during the imaging sequence reduces image quality,
view, the cranial lobar veins are larger and denser than their physiologic (electrocardiographic) gating is used for optimal
accompanying arteries and may sag ventrally. Dilated, tortu- cardiac imaging. Evaluation of cardiac volumes, myocardial
ous pulmonary veins may be seen entering the dorsocaudal function, perfusion, or valve function also may be performed.
aspect of the enlarged LA in dogs and cats with chronic Different cardiac MRI imaging sequences are used depend-
pulmonary venous hypertension. However pulmonary ing on the application or type of information desired. For
venous dilation is not always visualized in patients with left- example, “black blood” MRI scans allow better assessment
sided heart failure. In cats with acute cardiogenic pulmonary of anatomical details and abnormalities, whereas “bright
edema, enlargement of both pulmonary veins and arteries is blood” sequences are used to evaluate cardiac function.
common.
Nuclear Cardiology
PATTERNS OF PULMONARY EDEMA Radionuclide, or nuclear, methods of evaluating cardiopul-
Pulmonary interstitial fluid accumulation increases pulmo- monary function are available at some veterinary referral
nary opacity. Pulmonary vessels appear ill-defined, and centers. These techniques can provide noninvasive assess-
bronchial walls look thick as interstitial fluid accumulates ment of cardiac output, ejection fraction, and other mea-
around vessels and bronchi. As pulmonary edema worsens, sures of cardiac performance, as well as myocardial blood
areas of fluffy or mottled fluid opacity progressively become flow and metabolism.
more confluent. Alveolar edema causes greater opacity in the
lung fields and obscures vessels and outer bronchial walls.
The air-filled bronchi appear as lucent, branching lines sur- ECHOCARDIOGRAPHY
rounded by fluid density (air bronchograms). Interstitial and
alveolar patterns of pulmonary infiltration can be caused by Echocardiography (cardiac ultrasonography) is an impor-
many pulmonary diseases, as well as by cardiogenic edema. tant noninvasive tool for imaging the heart and surrounding
The distribution of these pulmonary infiltrates is important, structures. Anatomic relationships and cardiac function can
especially in dogs. Cardiogenic pulmonary edema in dogs be assessed by evaluating cardiac chamber size, wall thick-
classically is located in dorsal and perihilar areas and is often ness, wall motion, valve configuration and motion, and
bilaterally symmetric. Nevertheless, some dogs develop an proximal great vessels and other parameters. Pericardial
asymmetric or concurrent ventral distribution of cardio- and pleural fluid are easily detected, and mass lesions within
genic edema. The distribution of cardiogenic edema in cats and adjacent to the heart can be identified. This section
is usually uneven and patchy, although some cats have a provides an overview of the basic echocardiographic exami-
diffuse, uniform pattern. The infiltrates can be distributed nation, and an introduction to Doppler echocardiography
throughout the lung fields or concentrated in ventral, middle, and other modalities. Readers looking for more detail are
or caudal zones. Both the radiographic technique and the referred to the excellent, in-depth Echocardiography chapter
phase of respiration influence the apparent severity of inter- by Bonagura and Luis-Fuentes (see Suggested Readings list).
stitial infiltrates. Other abnormalities on thoracic radio- Like other diagnostic modalities, echocardiography is
graphs are discussed in Chapter 20. best used within the context of a thorough history, cardio-
vascular examination, and other appropriate tests. Technical
OTHER IMAGING TECHNIQUES expertise is essential to adequately perform and interpret a
Cardiac Computed Tomography and complete echocardiographic examination. The importance
Magnetic Resonance Imaging of the echocardiographer’s skill and understanding of normal
Cardiac computed tomography (CT) and magnetic reso- and abnormal cardiovascular anatomy and physiology
nance imaging (MRI) are now more widely available in vet- cannot be overemphasized. Yet often, some important infor-
erinary practice and provide greater anatomic detail than mation is attainable with even rudimentary echocardio-
plain radiographs. Their requirements for greater technical graphic or “thoracic focused assessment with sonography for
expertise, study duration, and expense, as well as the need trauma” (TFAST) training and experience. For example, a
for heavy sedation or general anesthesia, may be limitations large pericardial effusion, marked LA enlargement, and
in some cases. CT combines multiple radiographic image severe LV dilation with poor versus vigorous ventricular wall