Page 158 - Small Animal Internal Medicine, 6th Edition

130 PART I Cardiovascular System Disorders

comfort. Other strategies for intensifying home therapy are CMVD can develop worsened pulmonary edema after initial
discussed in Chapter 3, p. 74. sildenafil treatment, especially at higher doses; rapid reduc-
VetBooks.ir PULMONARY HYPERTENSION tion in pulmonary vascular resistance with an increase in
pulmonary blood flow is thought to be the cause in these
The development and severity of PH associated with high
and other respiratory signs is warranted when beginning
pulmonary venous pressure (so-called postcapillary PH) cases. Therefore close monitoring for increasing RRR, cough,
increases with advancing CMVD severity. It is most common sildenafil therapy. An increase in dose and/or frequency of
in dogs with stage C disease. Usually, PH associated with pimobendan administration is another strategy that could
CMVD is of mild to moderate severity, although a minority enhance pulmonary vasodilation.
of dogs with CMVD has severe PH. Although PH seen with
CMVD usually is related to chronic pulmonary venous ARRHYTHMIAS
hypertension, increased precapillary vascular resistance The onset or worsening of paroxysmal or sustained tachyar-
from hypoxia-induced pulmonary arteriolar vasoconstric- rhythmias can precipitate weakness, syncope, and congestive
tion can occur with pulmonary edema or concurrent pulmo- signs in a previously stable patient. The arrhythmia may be
nary disease. Reactive pulmonary vascular remodeling can evident on physical examination and further identified on
contribute to PH, especially in dogs with severe disease. resting ECG; however, ambulatory ECG monitoring may be
Moderate and severe PH increases right heart strain, pro- needed for definitive diagnosis and to guide antiarrhythmic
motes RV dilation (and hypertrophy), and contributes to therapy. Conversely, an intermittent bradyarrhythmia may
tricuspid annulus dilation and worsening TR. Dogs with underlie episodic weakness in syncope in some dogs. See
CVMD and moderate to severe PH are likely to have worse Chapter 4 for management.
outcomes.
Dogs with mild to moderate PH can be asymptomatic RUPTURED CHORDAE TENDINEAE
or have some degree of exercise intolerance or other clini- Affected animals tend to be older, male small-breed dogs,
cal signs consistent with CMVD. Especially with severe although chordal rupture also occurs in females. Rupture of
PH, clinical signs can include cough, respiratory difficulty, a primary (marginal) chorda tendineae often provokes acute
R-CHF signs (ascites, pleural effusion), lethargy, weak- pulmonary edema, and prognosis can be poor in such cases.
ness, syncope, prerenal azotemia, and cyanosis. Concurrent Rupture of a minor (second- or third-order) chorda some-
arrhythmias can exacerbate these signs. On auscultation, the times is an incidental finding on echocardiogram or at nec-
animal’s systolic murmur might be louder over the tricuspid ropsy. Factors that influence the clinical outcome include the
region, with or without a loud or split S 2 sound. Pulmonary size and location of the ruptured chord, the degree of valve
crackles can relate either to pulmonary edema or concur- regurgitation, LA compliance, and LV function.
rent chronic lung disease in these dogs. The diagnosis of
PH is generally made by echocardiography, although radio- LA RUPTURE
graphs can be suggestive (see Chapters 2 and 10, pp. 30 Older, male Miniature Poodles, Cocker Spaniels, Cavalier
and 191). King Charles Spaniels (CKCS), Dachshunds, and Shetland
Management of CVMD with PH first centers on standard Sheepdogs are thought to have higher prevalence of LA
CHF therapy to reduce pulmonary venous pressure by con- tearing, but mixed breed and other dogs also are affected.
trolling pulmonary edema and improving forward cardiac Full-thickness tearing of the LA wall is an uncommon but
output. Pimobendan, besides supporting myocardial func- devastating complication of CMVD. Acute intrapericardial
tion and systemic vasodilation, also has some pulmonary bleeding generally causes rapid onset of cardiac tamponade
vasodilating effect via phosphodiesterase (PDE)-3 inhibi- (see Chapter 9) and often is fatal. Acute weakness or collapse
tion. Additional therapy with a PDE-5 inhibitor (such as is typical; other signs could include cough, dyspnea, and
sildenafil) generally is reserved for dogs with PH that have respiratory or cardiac arrest. Most of these dogs have
persistent signs of R-CHF or syncope. Sildenafil (1-3 mg/ advanced CMVD, with severe LA enlargement, atrial jet
kg q8h) usually is started at a lower dose q(8-)12h then lesions, and often ruptured first-order chordae tendineae.
titrated upward over several days to a week based on clini- Pericardial effusion, usually with tamponade, is seen on
cal response. Concurrent administration of an L-arginine echocardiography in almost all cases. There may be clots in
supplement (100 mg/kg q8h PO) is thought to enhance the fluid. Echocardiography also may show an intraluminal
sildenafil’s efficacy, because this amino acid is a substrate thrombus attached to the LA wall, with either a partial or
for nitric oxide production. Doppler (TR maximum veloc- full thickness tear. In rare cases, an LA tear occurs in the
ity) and other echo observations can help assess the effect interatrial septum rather than the lateral LA wall.
of sildenafil treatment, although a decrease in TR Vmax In dogs with tamponade, a cautious attempt at pericardio-
or smaller RV is not always documented despite clinical centesis might relieve the tamponade, although the decrease
improvement. Systemic BP should be monitored, especially in intrapericardial pressure could trigger further bleeding,
in patients receiving another vasodilator along with an ACEI, especially if a clot seal is disturbed. Prognosis generally is
even though sildenafil primarily affects the pulmonary vas- poor in these cases, even with aggressive supportive care and
culature. Occasionally, dogs with severe PH and advanced immediate surgical attempt to close the rupture. However, if