Diagnosing and treating common congenital heart defects (Proceedings)

Congenital heart diseases are an important cause of morbidity and mortality in pediatric veterinary patients. The incidence of such defects is listed below.

Congenital Heart Diseases:

North American Study (canine) 0.46%-0.85%

• PDA 31.7% (female predominance 2:1)

• SAS 22.1%

• PS 18.3%

• VSD 6.6%

• PRAA 4.5%

• ToF 2.7%

• TVDys 2.4% (male predominance)

• ASD 0.7%

North American Study (feline) 0.2-1.0%

• AV septal defects 23% (male predominance)

VSD,ASD,AV canal

• M&TVDys 17%

• PDA 11%

• AS 6% (male predominance)

• ToF 6%

• PS 3%

Patent Ductus Arteriosus:

Is the most common congenital defect in dogs. It is a L- R shunting defect resulting from failure of closure of the left sixth aortic arch. If left untreated it results in left sided congestive heart failure. Clinically animals present with a Continuous (Machinery) Murmur at the left heart base with Hyperkinetic Femoral Pulses. A systolic murmur of mitral regurgitation may also be ausculted secondary to annular dilation from volume overload of the left ventricle.

Signalment: toy breeds (Corgi, Poodle, Maltese), German Shepard, Rottweiller are common large breeds affected. There tends to be a female:male (2:1) ratio.

Thoracic radiographs: Left ventricular enlargement, +/- L atrial enlargement, pulmonary overcirculation, "Ductus bump" (dilatation of the descending aortic), +/- pulmonary edema

Treatment – Multiple options to close the ductus now exist. Surgical closure has been the gold standard however interventional closure has overtaken surgery as the most common method in cardiology centers. Three devices have been studied and proven successful in our patients, Gianturco coil, Amplatz Plug, and the Canine ductal occluder.

Subaortic Stenosis:

Subaortic stenosis (SAS) is the second most common congenital defect in canine patients. It results in significant pathology and may cause sudden death. A fibrous, muscular or fibromuscular narrowing is formed just below the aortic valve in the LVOT that may involve the base of the aortic valve and the anterior leaflet of the mitral valve and anterior leaflet of the mitral valve since the annulus of these two structures is formed contiguously. The lesion may not be present at birth, can worsen over the first few months of life. MV dysplasia commonly associated.

Pathophysiology stenotic ring induces increase in LV afterload pressure overload→ concentric hypertrophy associated coronary arterial changes reduce coronary flow increased wall tension especially in subendocardial regions (↑ MVO2) → ischemia/arrhythmias.

Signalment : It is most commonly seen in large breed dogs such as Newfoundland, Golden Retriever, Rottweiller, Boxer, German Shepard; exact genetics unknown, suspect autosomal dominant with modifying genes or polygenic.

Clinical signs

Exercise intolerance, syncope, sudden death, L-CHF (unusual) may all be present however a number of patients will present perfectly normal. Physical exam Cardiac auscultation often reveals an Ejection-type systolic murmur around left heart base (3rd - 4th ICS) of variable intensity radiates craniad and to the right, up the carotids and calvarium in some circumstances. The quality of the femoral pulses gives a strong physical exam clue as the severity of the stenosis. Reduced and late rising Pulses parvus et tardus suggest more severe disease.

Treatment – B-blockers, balloon dilation not as productive as the narrow often returns in about 6 months. If necessary however given the relative non-invasiveness of ballooning it can be performed at multiple times.

Pulmonic Stenosis:

Pulmonic stenosis results from malformation (dysplasia) or fusion of the pulmonic valve. Our patients tend to have a combination of both types. This results in obstruction to blood flow from the right ventricle. Signalment Breed predisposition Bulldog, Boxer, Labrador, Beagle (polygenetic), Mastiff, terriers, many others.

Pathophysiology: stenosis induces increase in RV afterload; pressure overload→ concentric hypertrophy; associated coronary arterial changes reduce coronary flow; increased wall tension especially in subendocardial regions (↑ MVO2) → ischemia/arrhythmias reduced coronary flow increased heart rate (↓ diastolic filling time, (↑ MVO2) → critical stenosis can lead to ( CO and syncope

Physical exam Cardiac auscultation Ejection-type systolic murmur around left heart base (3rd ICS) of variable intensity radiates dorsally. Femoral pulses may be reduced if critical PS but usually NORMAL Jugular pulses may display a Prominent a-wave (RVH) distension if R-CHF

ECG RVE, +/- RAE TREATMENT: β-blockers (atenolol) to ↓HR, ↓MVO2, ↓ ischemia and risk of arrhythmias. Balloon valvuloplasty is used best with thin fused valve excellent results with little morbidity/mortality even in apparently dysplastic valves. However the

Ventricular Septal Defect:

Ventricular septal defects are common defects especially seen in cats and not uncommon in dogs that often results in left to right shunting of blood. Generally they are placed in two broad categories:

"Restrictive" VSD small hole with large pressure gradient from LV→ RV high on IVS L→ R shunt directly into the RVOT/PA Volume overload of the L heart

"Non-restrictive" VSD large defect with equilibration of LV and RV pressures if RV afterload is normal, L→ R shunt with L-CHF or biventricular failure. Increased RV afterload (PS, pulmonary hypertension) may result in either bidirectional or R→ L shunting. Signalment Dogs (breed predisposition) Bulldog, Springer Spaniel, Keeshonds (autosomal recessive) Cats. Clinical signs Often asymptomatic exercise intolerance, coughing, poor growth, syncope, exercise intolerance, cyanosis (R→ L VSD) Physical exam Pansystolic murmur over the right cranial sternal border, +/- ejection-type systolic murmur left heart base (3rd ICS) of variable intensity (relative PS), Split S2 Diastolic decrescendo over left heart base (AI, PI), S3 gallop, Clinical management Most are asymptomatic; congestive heart failure usually develops early in life unlikely to develop after 6 months of age. Medical management could include Diuretics, positive inotropes, ACE inhibition, +/- afterload reducers. Surgical therapy is either definitive closure (cardiopulmonary bypass) ; or PA banding Create supravalvular PS to reduce the amount of L→ R shunting. There are interventional devices that are available to close ventricular septal defects however, due to perimembranous location of most VSD's in veterinary patients, placement of available devices may result in disruption of atrioventricular (AV) valve function.

Tetralogy of Fallot

Is a defect that results from 4 changes in the heat. Ventricular septal defect, Overriding aorta, pulmonic stenosis, and right ventricular hypertrophy. Cranial deviation of the infundibular septum is responsible for all 4 defects of Tetralogy. Direction of VSD flow is primarily dependent upon the severity of RV obstruction; RV pressures must be suprasystemic to get R→ L shunting; Mild to complete atresia of the PA "pink" tetralogy.

Desaturation of arterial blood causes ↑erythropoietin which leads to polycythemia. cyanosis of entire body R→L shunting worsens with exercise ↓ systemic arterial resistance ↑ in RV obstruction (dynamic) return of more desaturated mixed venous blood to R heart Systemic bronchial collaterals form tortuous network that supplies blood flow from aorta to lungs Can participate in gas exchange Physical exam: ejection-type systolic murmur left heart base (3rd ICS) of variable intensity (RV obstruction). On rare occasions one may hear no murmur. The mucous membranes may be cyanotic, especially with exertion or normal. Thoracic radiographs Normal to small "club-shaped" cardiac silhouette MPA is not dilated (compared to PS with intact IVS) Pulmonary Undercirculation. Clinical management Medical: β-blockers (reduce exercise-induced R→L shunting), periodic phlebotomy, crystalloid fluid replacement moderate to severe exercise restriction, hydroxyurea; Surgical: Create L→R shunt, Blalock-Taussig shunt (left subclavian→PA), Potts shunt (ascending aorta→PA Waterston-Cooley shunt (descending aorta→PA).

Other common defects include:

Vascular Ring Anomalies

• Most common are associated with regurgitation in puppies

• Abnormal embryological development

Persistent Right Aortic Arch

• Persistence of the R 4th aortic arch instead of L 4th aortic arch

• Left 6th aortic arch (ductus) remains which forms a constrictive band around the esophagus at the heart base

• Ductus can be patent or a ligamentum

Atrial Septal Defects

Defect in formation of IAS 2 septa Septum secundum is to the right of septum primum Clinical findings are usually limited depending on the size of the defect. A soft murmur of relative pulmonic stenosis may also be ausculted at the left heart base with larger defects that are cause hemodynamic changes. Signalment Boxers, standard poodles; cats. Treatment: Larger defects may be amendable to closure via catheter based delivery of an Amplatz Ductal Occluder.

Reference available upon request.