Page 334 - Feline Cardiology

Chapter 22: Pericardial Effusion and Other Disorders 345

initiated in a physiologic attempt to maintain cardiac
output. Thus, sinus tachycardia, sodium and water
retention, and venoconstriction help compensate for
decreased cardiac output. However, increased systemic
venous pressure leads to fluid transudation from sys-
temic capillaries. Ascites accumulates once central
venous pressure increases to ≥15 mmHg (normal
≤6 mmHg). Signs of right heart failure predominate
because the right ventricle is thinner-walled and more
influenced by high intrapericardial pressures. Pleural
fluid accumulates secondary to venous hypertension
(similar to ascites), and reduced absorption of subpleu-
ral pulmonary lymphatic vessels. However, pulmonary
Figure 22.2. Right parasternal short-axis echocardiogram at the edema develops only when severe tamponade raises pul-
ventricular level. Note the presence of the liver within the pericar- monary venous pressure over 25 mmHg.
dium. RV = right ventricle; LV = left ventricle.
Clinical signs are determined by the rate of fluid accu-
mulation and the ability of the pericardium to stretch.
Typical historical signs include lethargy and weakness.
to the PPDH), with a postoperative mortality rate of Common physical exam findings include muffled heart
14%. Cats that had historical signs attributable to the sounds, a weaker than normal apex beat, generalized
PPDH often continued to have intermittent clinical systemic venous congestion (i.e., jugular venous disten-
signs. At follow-up, approximately 75% of owners sion, hepatomegaly), and possibly right-sided CHF signs,
believed their cats were clinically normal whether their such as tachypnea, dyspnea, pleural effusion ± ascites.
cat was treated surgically or conservatively (Reimer et al. Pulsus paradoxus may be noted on the physical examina-
2004). tion, evidenced by an increased femoral arterial pulse
Congenital pericardial cysts are rare in dogs and have strength during expiration and decreased pulse intensity
not been reported in cats; however, the physiologic on inspiration. It is defined by a drop of >10 mmHg in
implications are similar to those of pericardial effusion arterial pulse pressure with inspiration compared to Pericardial Diseases
(see below). Thus, the expected history, clinical signs, expiration and occurs due to blood pooling within the
and pathophysiology would be similar to those described great vessels in the thorax and away from the heart during
below, but in a young animal. Diagnosis historically was inspiration when the intrathoracic pressure is most neg-
made using pneumopericardiography in dogs; however, ative, which is subsequently pumped back into the heart
echocardiography has largely supplanted this technique. during expiration. Most often arterial pulse strength is
Surgical removal of the cyst and partial pericardiectomy weak and pulses may be difficult to locate in severely
results in an excellent prognosis. affected, hypotensive patients. Hepatomegaly may be
detected with abdominal palpation.
ACQUIRED PERICARDIAL DISEASES Pericardial effusion is the most common pericardial
abnormality in cats, but it rarely causes cardiac tampon-
Pathophysiology ade or secondary right sided heart failure. However, the
Pericardial effusion (PE) can develop for a variety of clinical signs described above should prompt astute clini-
reasons and as it accumulates, intrapericardial pressure cians to consider cardiac tamponade in their feline
increases. If the pericardial pressure increases above patients since there have been sporadic reports of feline
right ventricular diastolic pressure, cardiac tamponade patients with cardiac tamponade. In cats, PE is most often
ensues, resulting in increased diastolic intracardiac pres- present in small volumes in conjunction with congestive
sures, reduced ventricular filling, and reduced cardiac heart failure. Congestive heart failure can lead to mild or
output. As right atrial pressure increases, systemic moderate pericardial fluid accumulation, through a
venous pressure also becomes elevated. As fluid contin- similar mechanism to the formation of pleural effusion,
ues to accumulate in the pericardium, pericardial and but tamponade due to heart failure-associated PE should
right atrial and ventricular diastolic pressures rise not be possible. Unlike in dogs, CHF is the most common
together. Eventually, they can equalize with left ventricu- cause of PE in cats, followed by neoplasia (see Chapters
lar diastolic pressure. At this stage, there is a marked 1 and 16). Contrary to the prevalence noted in dogs,
decline in cardiac output, and compensatory measures chemodectomas have only been sporadically reported in
such as activation of the sympathetic nervous system are cats (George and Steinberg 1989). However, a case of