Page 80 - Small Animal Internal Medicine, 6th Edition

52 PART I Cardiovascular System Disorders

OTHER TECHNIQUES vasculature is better accomplished using nonselective
angiocardiography.
VetBooks.ir MEASUREMENT cardiac catheters into specific areas of the heart or great
CENTRAL VENOUS PRESSURE
Selective angiocardiography is performed by advancing
CVP is the fluid pressure within the RA and, by extension,
and blood sample acquisition for oxygen content assessment
the intrathoracic cranial vena cava. It is influenced by intra- vessels. Intracardiac and vascular pressure measurements,
vascular volume, venous compliance, and cardiac function. (oximetry), generally are done before making radiopaque
CVP measurement helps in differentiating high right heart- contrast injections. Selective angiocardiography allows iden-
filling pressure (as from right heart failure or pericardial tification of abnormalities in anatomy and the path of blood
disease) from other causes of pleural or peritoneal effusion. flow. Doppler echocardiography often can provide compa-
However, it is important to note that pleural effusion itself rable diagnostic information noninvasively. However, selec-
can increase intrapleural pressure and raise CVP even in the tive angiography is a necessary component of many cardiac
absence of cardiac disease. Therefore CVP should be mea- interventional procedures.
sured after thoracocentesis in patients with moderate- to
large-volume pleural effusion. CVP sometimes is used to CARDIAC CATHETERIZATION
monitor critical patients receiving large intravenous fluid Cardiac catheterization allows measurement of pressure,
infusions. However, CVP is not an accurate reflection of left cardiac output, and blood oxygen concentrations from spe-
heart-filling pressure and thus is not a reliable way to monitor cific intracardiac locations. Specialized catheters are selec-
for cardiogenic pulmonary edema. The CVP in normal dogs tively placed into different areas of the heart and vasculature
and cats usually ranges from 0 to 8 (up to 10) cm H 2 O. Fluc- via the jugular vein, carotid artery, or femoral vessels. Con-
tuations in CVP that parallel those of intrapleural pressure genital and acquired cardiac or vascular abnormalities can
occur during respiration. be identified with these procedures in combination with
CVP is measured via a large-bore jugular catheter that selective angiocardiography. The advantages of Doppler
extends into or close to the RA. The catheter is placed asep- echocardiography often outweigh those of cardiac catheter-
tically and connected by extension tubing and a three-way ization, especially in view of the good correlation between
stopcock to a fluid administration set and container of crys- certain Doppler- and catheterization-derived measurements.
talloid fluid. Free flow of fluid through this catheter system However, cardiac catheterization is necessary for balloon
into the patient should be verified (stopcock side-port valvuloplasty, ductal occlusion, and other interventional
turned off). A water manometer is attached to the stopcock procedures.
and positioned vertically with the stopcock (representing Pulmonary capillary wedge pressure (PCWP) monitor-
0 cm H 2 O) placed at the same horizontal level as the patient’s ing is done rarely to measure left heart-filling pressure in
RA. Usually the patient is placed in lateral or sternal recum- dogs with heart failure. A Swan-Ganz (end-hole, balloon-
bency for CVP measurement. The stopcock is turned off tipped) monitoring catheter is passed into the main pulmo-
to the animal, allowing the manometer to fill with fluid; nary artery. When the balloon is inflated, the catheter tip
then the stopcock is turned off to the fluid reservoir so that becomes wedged in a smaller pulmonary artery, occluding
the fluid column in the manometer equilibrates with the flow in that vessel. The pressure measured at the catheter tip
patient’s CVP. Repeated measurements are more consistent reflects pulmonary capillary pressure, which is essentially
when taken with the animal and manometer in the same equivalent to LA pressure. This invasive technique allows dif-
position and during the expiratory phase of respiration. ferentiation of cardiogenic from noncardiogenic pulmonary
Small fluctuations in the manometer’s fluid meniscus occur edema and provides a means of monitoring cardiac output
with the heartbeat, and slightly larger movement is associ- as well as the effectiveness of heart failure therapy. However,
ated with respiration. Marked change in the height of the its use requires meticulous, aseptic catheter placement and
fluid column associated with the heartbeat suggests either continuous patient monitoring.
severe tricuspid insufficiency or that the catheter tip is within
the RV. Endomyocardial Biopsy
Small samples of endocardium and adjacent myocardium
ANGIOCARDIOGRAPHY can be obtained using a special bioptome passed into the RV
Nonselective angiocardiography can be used to define several via a jugular vein. Routine histopathology and other tech-
acquired and congenital diseases, including cardiomyopathy niques to evaluate myocardial metabolic abnormalities can
and heartworm disease in cats, severe pulmonic or (sub) be performed on the samples. Endomyocardial biopsy some-
aortic stenosis, patent ductus arteriosus, and tetralogy of times is used for myocardial disease research but is rarely
Fallot. Intracardiac septal defects and valvular regurgitation used in clinical veterinary practice.
cannot reliably be identified. The quality of such studies is
higher with a rapid injection of radiopaque contrast agent Suggested Readings
via a large-bore catheter and with smaller patient size. In Cardiac Biochemical Markers
most cases, echocardiography more safely provides similar Borgeat K, Connolly DJ, Luis Fuentes V. Cardiac biomarkers in cats.
or more information. However, evaluation of the pulmonary J Vet Cardiol. 2015;17:S74–S86.