Page 136 - Small Animal Internal Medicine, 6th Edition

108 PART I Cardiovascular System Disorders

pulmonary trunk. Right atrial (RA) dilation from secondary region sometimes is narrow and difficult to clearly visual-
tricuspid insufficiency and high RV filling pressure predis- ize. Poststenotic dilation of the main pulmonary trunk is
VetBooks.ir poses to atrial tachyarrhythmias and right-sided CHF. The expected. Ascites or pleural effusion accompany secondary
right-sided CHF. Doppler evaluation along with anatomic
combination of PS and a patent foramen ovale or ASD can
findings provide an estimate of PS severity. The pressure
allow right-to-left shunting at the atrial level.
A single anomalous coronary artery has been described gradient between the RV and PA is estimated by measur-
in some Bulldogs and other brachycephalic breeds with PS ing peak blood flow velocity across the valve. PS gener-
and is thought to contribute to the outflow obstruction. In ally is considered mild if the Doppler-derived gradient is
such cases, palliative surgical procedures and balloon valvu- <50 mm Hg, moderate if pressure gradient is 50 to 80 mm
loplasty can cause death secondary to transection or avulsion Hg, and severe if it is >80 mm Hg. Cardiac catheterization
of the major left coronary branch that wraps circumferen- and angiocardiography also can be used to assess the pres-
tially around the stenotic pulmonic valve annulus. sure gradient across the stenotic valve, diameter of the valve
annulus, and other anatomic features. Doppler-estimated
Clinical Features systolic pressure gradients in unanesthetized animals usually
Many dogs with PS are asymptomatic when diagnosed, are 40% to 50% higher than those recorded during cardiac
although some have right-sided CHF or a history of exercise catheterization.
intolerance or syncope. Clinical signs might not develop
until the animal is several years old, even in those with severe Treatment and Prognosis
stenosis. Physical examination findings characteristic of Balloon valvuloplasty is recommended for palliation of
moderate to severe stenosis include a prominent right pre- severe (and sometimes moderate) stenosis, especially if
cordial impulse and a systolic ejection murmur heard best infundibular hypertrophy is not excessive. This proce-
high at the left heart base, with or without precordial thrill. dure can reduce or eliminate clinical signs and improves
The murmur can radiate cranioventrally and to the right in long-term survival in severely affected animals. Balloon
some cases but usually is not heard over the carotid arteries. valvuloplasty, done in conjunction with cardiac catheter-
An early systolic click sometimes is identified; this is prob- ization and angiocardiography, involves passing a specially
ably caused by abrupt checking of a fused valve at the onset designed balloon catheter across the valve and inflating the
of ejection. A murmur of tricuspid insufficiency or arrhyth- balloon to enlarge the stenotic orifice. Pulmonary valves
mias can be heard in some cases. Femoral pulses are typically with mild to moderate thickening and simple fusion of
normal and mucous membranes usually pink. Ascites, the leaflets with normal annulus size are likely to be easier
jugular venous distension or pulsation, and other signs of to effectively dilate. Dysplastic valves with annular hypo-
right-sided CHF are present in some cases. Occasionally, plasia can be more difficult to dilate effectively, but good
cyanosis accompanies right-to-left shunting through a con- results are possible in some cases. Successful balloon val-
current atrial or VSD. vuloplasty is generally defined as at least 50% reduction in
prevalvuloplasty pressure gradient or reduction to pressure
Diagnosis gradient of less than 50 mm Hg. Various surgical proce-
Radiographic findings typically seen with PS are outlined in dures also have been used to palliate moderate to severe
Table 5.2. Marked RV hypertrophy shifts the cardiac apex PS in dogs, including pulmonary arteriotomy for valvulot-
dorsally and to the left. The heart can appear as a “reverse omy and patch grafting, or placement of a valved RV-PA
D” shape on a DV or ventrodorsal (VD) view. A variably conduit. Balloon valvuloplasty usually is attempted before
sized pulmonary trunk bulge (poststenotic dilation) is best a surgical procedure because it is less risky. Animals with
seen at the 1 o’clock position on a DV or VD view (Fig. 5.6). a single anomalous coronary artery generally should not
The size of the poststenotic dilation does not necessarily undergo balloon or surgical dilation procedures because
correlate with the severity of the pressure gradient. Diminu- of increased risk of death, although conservative balloon-
tive peripheral pulmonary vasculature and/or a dilated ing reportedly has been palliative in a few cases. Placement
caudal vena cava may be apparent. ECG changes are more of a valved RV-PA conduit to bypass the pulmonic valve
common with moderate to severe stenosis. These include an could be an option for such patients. Coronary anatomy can
RV hypertrophy pattern, right axis deviation, and sometimes be evaluated initially using echocardiography, but defini-
an RA enlargement pattern or tachyarrhythmias. tive diagnosis of coronary artery anomalies may require
Echocardiographic findings characteristic of moder- either aortic root angiography or computed tomography
ate to severe stenosis include RV concentric hypertrophy with angiography.
and enlargement. The interventricular septum appears flat- Exercise restriction is advised for animals with moderate
tened when pressure in the RV exceeds that in the LV and to severe stenosis. β-blocker therapy could be helpful in
pushes it toward the left; paradoxical septal motion may cases of moderate to severe PS, especially in those with
occur. Secondary RA enlargement is common as well, espe- prominent RV infundibular hypertrophy and a dynamic
cially with concurrent tricuspid regurgitation (TR). A thick- component to their right ventricular outflow tract (RVOT)
ened, asymmetric, or otherwise malformed pulmonic valve obstruction. β-blockade also decreases myocardial oxygen
usually can be identified (see Fig. 5.7), although the outflow demand and arrhythmias, improves coronary perfusion, and