Page 1507 - Cote clinical veterinary advisor dogs and cats 4th

Patent Ductus Arteriosus 765

ASSOCIATED DISORDERS through the PDA is from the aorta to the • Packed cell volume (PCV) to determine
• Arrhythmias pulmonary artery (left-to-right type), causing presence of anemia or erythrocytosis
VetBooks.ir • Pulmonary hypertension circulation, left atrium, left ventricle, and Advanced or Confirmatory Testing Diseases and Disorders
increased flow through the pulmonary
• Congestive heart failure (CHF)
• Two-dimensional echocardiography (p. 1094)
ascending aorta, resulting in enlargement of
• Erythrocytosis (right-to-left shunting PDA)
Clinical Presentation these chambers and left ventricular hyper- to determine chamber sizes, wall thickness,
trophy (eccentric). Established left-to-right
systolic ventricular function, presence of any
DISEASE FORMS/SUBTYPES types rarely develop enough pulmonary concurrent cardiac defects, and an approxi-
• Clinical/gross classification: type 1 = small hypertension to cause reversed PDA flow mate measurement of ductal diameter in
PDA, type 2 = medium PDA, type 3A (right-to-left type). anticipation of device-based surgical closure
= large PDA, type 3B = large PDA with • In animals with a large PDA and pulmonary • Color Doppler echocardiography to verify
CHF, type 4 = large PDA with pulmonary hypertension (type 4, persistent fetal circula- turbulent blood flow in the pulmonary artery
hypertension and right-to-left or bidirectional tion), there is right ventricular hypertrophy, • Spectral Doppler echocardiography to
shunt and blood flows through the ductus pre- determine flow velocity in the PDA and
• Angiographic classification of PDA mor- dominantly from the pulmonary artery to estimate the aorta/pulmonary artery pressure
phology: type 1 (5%) = gradual tapering the aorta (as in the fetus), resulting in caudal gradient. If tricuspid or pulmonic insufficien-
from aorta to pulmonary artery, type IIa cyanosis and secondary erythrocytosis. cies are present, respective estimates of right
(most common, 54%) = gradual tapering ventricular systolic and pulmonary artery
from aorta to pulmonary artery plus abrupt DIAGNOSIS diastolic pressures can be made.
taper at pulmonary artery insertion, type IIb
(32.5%) = parallel walls of PDA plus abrupt Diagnostic Overview TREATMENT
tapering at pulmonary arterial insertion, type The diagnosis is made easily by auscultating
III (8%) = walls of PDA are parallel for the a continuous murmur over the left heart base Treatment Overview
length of the PDA (tubular) (types 1-3) and palpating a precordial thrill PDA closure is recommended for all left-to-
(types 2 and 3). Chest radiographs reveal the right cases (types 1-3) but contraindicated in
HISTORY, CHIEF COMPLAINT degree of cardiomegaly and the urgency of right-to-left cases (type 4). In type 4 cases,
• Varies with PDA diameter and age PDA closure. phlebotomy and/or chemotherapy is used to
• Most often recognized as an incidental heart reduce and maintain hematocrit at 60%-65%,
murmur in a young animal presented for Differential Diagnosis which improves blood flow characteristics.
vaccination and not showing overt clinical • Combined abnormalities producing systolic
signs and diastolic heart murmurs such as a ven- Acute General Treatment
• When clinical signs are present, they include tricular septal defect and aortic insufficiency • Type 3B: for large PDA, preoperative diuretic
exercise intolerance, failure to thrive, and due to an unsupported aortic valve leaflet and cage rest to alleviate CHF and then
signs of CHF (p. 408). • Aorticopulmonary window closure of PDA are indicated.
• Arteriovenous fistula • Types 1-3: surgery or transarterial coil or
PHYSICAL EXAM FINDINGS Amplatz duct occluder to occlude PDA (see
Varies with PDA diameter (see classification Initial Database Video)
systems above) • Thoracic radiographs to assess heart and lung • Type 4: phlebotomy to reduce erythrocytosis.
• Type 1, small: characteristic focal continuous vessel size and lung parenchyma Goal is PCV of 60%-65%; volume removed
murmur at left heart base • Electrocardiogram (p. 1096) to identify varies, but 10 to 15 mL/kg (with or without
• Type 2, medium: type 1 signs plus continu- cardiac arrhythmias and findings supportive crystalloid volume replacement) is reasonable
ous murmur audible at apex and precordial of ventricular hypertrophy initially.
thrill at left heart base
• Type 3A, large: types 1 and 2 signs plus
bounding pulses, prominent cardiac impulse
at left apex, and systolic murmur of mitral
regurgitation at left apex
• Type 3B, large with CHF: types 1, 2, and A A
3A signs and signs of CHF (e.g., dyspnea,
pulmonary crackles, ascites [occasionally]); D
arrhythmias, especially atrial fibrillation, P D
possible
• Type 4, large PDA with pulmonary hyper-
tension: no heart murmur; prominent right
apical impulse, split second heart sound, P
caudal cyanosis (differential cyanosis),
hindlimb collapse with exercise

Etiology and Pathophysiology
• The principal cause of PDA in dogs is site-
specific hypoplasia of ductus smooth muscle,
coupled with reciprocal excess elastic tissue in A B
the wall of the ductus. To varying degrees, the
hypoplastic smooth muscle does not encircle PATENT DUCTUS ARTERIOSUS A, Postmortem photograph of the heart, aorta (A), and pulmonary artery
(P) of a 4-month-old dog with a PDA (D) and ductal-aortic aneurysm (arrows). B, Sagittal section photograph
the lumen, and muscle contraction does not of the great vessels and a ligature demonstrates PDA ligation at surgery (thoracotomy). Most of the PDA lies
completely constrict the lumen postpartum. within the wall of the aorta in dogs and constitutes a ductal-aortic aneurysm commonly referred to as a ductus
• Typically, pulmonary vascular resistance diverticulum. The typical ridge at the pulmonary artery opening (at the level of the ligature in this image) limits
decreases after birth and postnatal blood flow PDA diameter and determines blood flow through the PDA.

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