Canine pulmonary hypertension, Part 2: Diagnosis and treatment - Veterinary Medicine
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Canine pulmonary hypertension, Part 2: Diagnosis and treatment
Once a death sentence, canine pulmonary hypertension no longer carries such a grave prognosis—in part, because of advanced diagnostic tools and the availability of sildenafil therapy.


VETERINARY MEDICINE


Thoracic radiography


1A. (Click photo for caption)
Thoracic radiography is not specific for pulmonary hypertension but may demonstrate findings supportive of it. Depending on the underlying cause of pulmonary hypertension, cardiomegaly, right-sided heart enlargement, or pulmonary artery dilation may be evident. In cases of congestive heart failure, pneumonia, or neoplasia, pulmonary infiltrates may be present. Pulmonary arteries may be tortuous in patients with heartworm disease (Figures 1A & 1B).

Electrocardiography


1B. (Click photo for caption)
The electrocardiogram (ECG) is a nonspecific test for pulmonary hypertension with low sensitivity. The ECG may be normal or show right axis deviation or a right-sided heart enlargement pattern.

Echocardiography

The echocardiogram is the gold standard noninvasive diagnostic tool used in veterinary medicine to diagnose pulmonary hypertension. Although tricuspid valve regurgitation maximum velocity measurement is the most common echocardiographic method used to diagnose systolic pulmonary hypertension in a clinical setting, other subjective and objective assessments are also possible. Subjective assessment of the cardiac structures and pulmonary artery velocity profiles can aid in diagnosing pulmonary hypertension, and objective assessment of pulmonary valve insufficiency can help diagnose and quantify diastolic pulmonary hypertension.


2. (Click photo for caption)
Subjective echocardiographic findings. Patients with pulmonary hypertension have increased right ventricular afterload and may develop right-sided heart changes associated with this pressure increase. Right ventricular and atrial chamber sizes may be normal or mildly to severely dilated. Right wall thicknesses may be normal, or some degree of right ventricular hypertrophy may be evident (Figure 2). Paradoxical septal motion and septal flattening support right ventricular pressure overload. Pulmonary artery dilation is often seen in patients with pulmonary hypertension, and in cases of heartworm infection, heartworms may be visualized in the right heart or right pulmonary artery.


3. (Click photo for caption)
Pulmonary artery velocity profiles may also aid in the echocardiographic diagnosis of pulmonary hypertension. Spectral Doppler echocardiography is used to measure the outflow velocity across the pulmonary valve by generating a pulmonary artery velocity profile.10 In patients with normal pulmonary arterial pressure, a type I profile is recorded with equal acceleration and deceleration times producing a symmetrical appearance. As pulmonary arterial pressures increase, an asymmetrical profile is recorded because of early rapid acceleration and an earlier peak velocity. This asymmetrical profile occurs as a result of increased rate of rise in pulmonary vascular pressures and is referred to as a type II profile. Type II profiles are associated with mild to moderate pulmonary hypertension. With severe pulmonary hypertension, a rapid acceleration with an earlier peak velocity occurs, and a midsystolic notch is also present. This is referred to as a type III profile. The midsystolic notch indicates blood flow reversal secondary to high pulmonary vascular pressures (Figure 3).


4. (Click photo for caption)
Doppler assessment of systolic pulmonary arterial pressure. Tricuspid valve regurgitation occurs during ventricular systole and can be viewed during an echocardiogram in right parasternal and left apical views (Figures 4 & 5). In these views, the tricuspid regurgitation jet is assessed by using color-flow Doppler, and spectral Doppler is placed over the tricuspid regurgitation jet to obtain tricuspid regurgitation velocity profiles. The peak of the profile indicates maximum tricuspid regurgitation velocity.


5. (Click photo for caption)
The maximum tricuspid regurgitation velocity estimates the pressure gradient across the tricuspid valve, which approximates the pressure difference between the right ventricle and right atrium. The pressure gradient can be calculated by applying the measured maximum tricuspid regurgitation velocity to the modified Bernoulli equation3:

pressure gradient = maximum tricuspid regurgitation velocity 2 x 4

When an estimated right atrial pressure is added to the calculated pressure gradient, an estimate of right ventricular pressure can be obtained. Right atrial pressures are estimated based on subjective assessment of the right atrium's size on an echocardiogram. A normal right atrium is assigned a pressure of 0 mm Hg, a mildly dilated right atrium has an estimated pressure of 5 mm Hg, a moderately dilated right atrium has an estimated pressure of 10 mm Hg, and a severely dilated right atrium has an estimated pressure of 15 mm Hg.11,12


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