Cardiovascular System Congenital Diseases

Cardiovascular System Congenital Diseases

• Congenital heart disease is an abnormality present at birth, potentially caused by genetic or non-genetic factors
• These abnormalities sometimes aren't detected until later in life, but were still present at birth
• Common congenital heart diseases in dogs include patent ductus arteriosus, subaortic stenosis, pulmonic stenosis, and mitral valve dysplasia
• Common congenital heart diseases in cats include ventricular septal defects, and atrioventricular valve dysplasia

Learning Objectives

• Review cardiac anatomy, foetal circulation, and cardiac imaging methods
• Understand cardiac murmur grading and recognize common murmur types
• Examine both common and uncommon congenital heart defects and their influence on blood flow patterns
• Understand and describe the pathophysiology, clinical presentation, diagnosis, treatment, management, and prognosis for common congenital cardiac conditions

Congenital Heart Disease

• Most puppies and kittens have no issues, but some experience innocent or pathological murmurs
• Additional signs include failure to grow at a normal size/rate, exertional fatigue, abdominal distension, episodic weakness, or syncope, and cyanosis
• Suspicion of congenital heart disease, client's feelings, and breeder information are all indicators for additional work-ups

Congenital Heart Disease Classification

• Volume Overload: PDA (L-R shunt), VSD (L-R shunt), ASD (L-R shunt), Mitral valve dysplasia, Tricuspid dysplasia
• Pressure Overload: Valvular pulmonic stenosis, Subvalvular aortic stenosis
• Cyanotic: Tetralogy of Fallot, Large PDA/VSD/ASD with R-L shunting

Less Common Congenital Conditions

• Right-sided aortic arch
• Atrial septal defect (ostium secundum, ostium primum, sinus venosus)
• "Reversed" R-L shunting patent ductus arteriosus
• Aortic-pulmonary window
• Ebstein's Anomaly
• Double-outlet right ventricle
• Cor triatriatum

Patent Ductus Arteriosus

• The ductus arteriosus connects the main pulmonary artery to the aorta in the fetus
• After birth, normal respiration reduces pulmonary vascular resistance, the flow reverses (L-R), and the ductus closes.
• Persistence of the ductus, due to lack of smooth muscle during closure, results in L-R shunting and causes volume overload.
• Dogs (Cavalier King Charles Spaniels, Poodles, German Shepherds, Springer Spaniels, Collies, Shetland Sheepdogs, and Pomeranians) show higher rates than other breeds, with females showing higher rates than males
• High grade, continuous murmur; hyperkinetic water hammer pulses due to increased aortic systolic pressure and decreased aortic diastolic pressure; precordial impulse area is expanded; Congestive heart failure (CHF) potentially develops within 1 year of diagnosis
• Radiographs: pulmonary overcirculation, left heart enlargement, and aortic bulge may be noted
• Echocardiography: visualization of the shunt; left atrial and ventricular enlargement; Doppler shows continuous blood flow

Treatment

• Ligation of the ductus may be performed via minimally invasive techniques using catheterization or minimally invasive thoracotomy
• Amplatz Canine Duct Occluder or thrombogenic coil devices can be used

Reverse Patent Ductus Arteriosus - R-L Shunting

• Large PDA, often without tapering.
• No murmur is common but differential cyanosis (pink MM in cranial half, cyanotic MM in caudal half) is noted.
• Closure isn't possible due to high pulmonary pressure.
• Medical management targets dilating the pulmonary artery to reduce pressure and control symptoms.

Pulmonic Stenosis

• Varying degrees of obstruction to the right ventricular outflow tract
• May be valvular, subvalvular, or supravalvular
• Common in Boxers, Beagles, Bull Mastiffs, Bulldogs, Cocker Spaniels, Miniature Schnauzers, Terriers, and Chihuahuas. Rare in Cats.
• Clinical signs vary based on severity, ranging from asymptomatic to syncope, CHF, and sudden death. Harsh systolic murmur is loudest over left heart base.
• Radiographic findings might show right atrioventricular enlargement and a post-stenotic bulge of pulmonary artery
• Echocardiography shows concentric hypertrophy of right ventricle and structural abnormalities of pulmonic valve and right ventricular outflow tract
• Severity assessed using Doppler (pressure difference between RV and PA)

Aortic Stenosis

• Varying degrees of obstruction to the left ventricular outflow tract, and may be subvalvular (most common), valvular, or supravalvular
• Common in large breed dogs (Boxers, German Shepherds, Newfoundlands, Rottweilers, and Golden Retrievers). Rare in cats.
• Clinical signs depend on severity and range from asymptomatic to syncope and CHF
• Radiographic findings are often normal, or show left ventricular enlargement, and post-stenotic dilation of aorta

Subvalvular Aortic Stenosis

• Fibrous ring of tissue located within the LVOT (left ventricular outflow tract)
• Concentric hypertrophy is proportional to the severity of stenosis, clinical findings depend on severity, from asymptomatic to syncope and CHF
• Radiographic findings are often normal, or show left ventricular enlargement, and post-stenotic dilation of aorta
• Echocardiography is essential to diagnose concentric hypertrophy, subvalvular obstructive lesions, post-stenotic dilation of the aorta, and high blood velocity across the valve

Atrial (ASD) and Ventricular Septal Defects (VSD)

• ASD common in dogs and cats (VSD more common in cats)
• Occur as components of more complex lesions like Tetralogy of Fallot
• ASD Types; ostium primum and ostium secundum
• A patent foramen ovale is not an actual ASD
• VSD almost always high septal defects
• Clinical signs vary based on defect size, with louder murmurs correlating to smaller defects and better prognoses.
• Echocardiography is the most crucial diagnostic tool for visualization of the shunt and patterns of hypertrophy, and to determine diameter

Further Reading

• Textbook/Chapters on Cardiovascular Disease (e.g., Ettinger's Textbook of Veterinary Internal Medicine)
• Notes on Cardiorespiratory Diseases (of the dog and cat)
• Small Animal Cardiovascular Medicine (Kittleson and Kienle - available online at VIN).
• BSAVA Manual of Canine and Feline Thoracic Imaging.