Page 272 - Clinical Small Animal Internal Medicine

240 Section 3 Cardiovascular Disease

of these tests in animals with CHD, though evidence in Therapy
VetBooks.ir human cardiology suggests that these markers are often Medical Therapy
elevated in children with severe CHD. At this time, no
guidance can be given for or against the utility of cardiac
biomarkers in screening animals for CHD. Asymptomatic Disease
Treatment of asymptomatic CHD depends on the
Echocardiography specific underlying disease and its severity, so definitive
History, physical examination, thoracic radiography, and diagnosis is essential. In general, diseases of moderate to
ECG are all useful diagnostic tests for determining the severe outflow tract obstruction causing concentric
presence of CHD, but are less capable of making a defini- hypertrophy (e.g., SAS and PS) are treated by the author
tive diagnosis, assessing disease severity, or ruling out with beta‐blockers such as atenolol. Atenolol is typically
the presence of multiple or complex congenital lesions. uptitrated in dose over 4–8 weeks, starting at 0.2–0.5 mg/
In veterinary medicine, echocardiography with Doppler kg (0.1–0.2 mg/lb) q12h PO and increasing to a target
is the noninvasive gold standard for definitive diagnosis dose of 1–1.5 mg/kg (0.4–0.7 mg/lb) q12h PO. The
of CHD. All animals with a high suspicion of CHD should rationale for such therapy is that beta‐blockers help to
ideally have a detailed echocardiogram performed by a reduce the force of myocardial contraction, thereby
veterinarian trained in the diagnosis of CHD. reducing myocardial oxygen demand and protecting the
Echocardiography allows for the detection of specific diseased/hypertrophied myocardium. The antiarrhyth-
types of CHD, the presence of concomitant defects, and mic properties of atenolol are also believed to be of
assessment of disease severity, risk for complications, benefit as these patients are at risk for life‐threatening
direction of cardiac shunting, estimate of intracardiac arrhythmias. Atenolol is often chosen given its low cost,
pressures, and likelihood of congestive heart failure. appropriate size tablets, and ease of administration.
Echocardiography is also necessary in assessing the need Therapy for asymptomatic diseases of volume over-
for therapy as well as for planning interventional or sur- load such as moderate to severe mitral or tricuspid
gical options. Figure 24.4 provides representative two‐ regurgitation and left‐to‐right shunting defects like PDA,
dimensional images of common CHD seen in the dog prior to development of CHF, is controversial. However,
and cat by echocardiography. the addition of angiotensin converting enzyme (ACE)
inhibitors such as enalapril at 0.5 mg/kg (0.2 mg/lb) q12h
Angiography PO is common if there is severe ventricular dilation,
Nonselective or selective angiography with fluoroscopic impaired cardiac output, and atrial enlargement suggest-
visualization of cardiac structures was historically the ing high risk for development of CHF.
definitive test for CHD prior to the advent of echocardiog-
raphy. For some defects, angiography is still utilized, par- Symptomatic Disease
ticularly for lesions of the great vessels that are not easily Medical therapy of symptomatic CHD depends on the
appreciated by ultrasound. Figure 24.5 shows a nonselec- type of lesion and developing clinical signs. Diseases
tive, digitally subtracted angiogram of a right‐to‐left of outflow tract obstruction (SAS, PS) commonly cause
shunting PDA in a cat, while Figure 24.6 shows a right ven- exercise intolerance and syncope related to reduced
triculogram from a dog with PS. In practice, angiography cardiac output, inappropriate baroreceptor activation,
is used most commonly at the time of interventional ther- and/or ventricular arrhythmias. Life‐threatening or
apy to confirm the diagnosis, visualize the defect to be symptomatic ventricular arrhythmias are treated with
addressed, and guide intervention with balloon or device, antiarrhythmic agents. Sotalol at a dose of 1–2 mg/kg
as discussed in the interventional therapy section. (0.4–0.9 mg/lb) q12h PO is typically the first‐line antiar-
rhythmic of choice so long as ventricular function is not
Cross‐Sectional Imaging severely depressed. Syncope that occurs without ventric-
Cardiac computed tomography and magnetic resonance ular arrhythmias (presumed to be reflex‐mediated
imaging allow three‐dimensional reconstructions of the syncope whereby the cardiac hypertrophy stimulates an
heart and great vessels. Such imaging modalities are exaggerated baroreceptor response) is typically treated
commonly employed in human medicine to evaluate with beta‐blockade. Modification of exercise level with
children with CHD and case reports of their use in vet- avoidance of high‐level intense or burst activity will also
erinary medicine are present in the literature. Figure 24.7 commonly reduce this clinical sign.
shows a three‐dimensional reconstruction of a com- Diseases of left‐sided volume overload will com-
puted tomographic angiogram in a dog with PS. The monly cause symptoms of cough in the dog prior to the
benefit of cross‐sectional imaging is likely greatest in onset of CHF due to severe left atrial enlargement and
instances of complex CHD where the cardiac anatomy resultant left bronchial compression. Bronchial com-
can be viewed from multiple perspectives in situ. pression in the absence of CHF may be treated with