Congenital Heart Disease

1. Patent Ductus Arteriosus (PDA)

• Pathophysiology

  • In normal fetal circulation, the ductus arteriosus is a blood vessel that diverts blood away from the non-functioning fetal lungs, allowing it to bypass the pulmonary circulation. It shunts blood from the pulmonary artery directly into the aorta.

  • This shunt is maintained by high levels of prostaglandins (PGE2 and PGI2) which keep the ductus arteriosus open (patent).

  • After birth, the increase in oxygen levels, decrease in pulmonary vascular resistance, and loss of placental prostaglandins typically triggers the closure of the ductus arteriosus. The closure begins with smooth muscle constriction and eventually leads to fibrous tissue formation, forming the ligamentum arteriosum.

  • In dogs with PDA, this closure does not occur, leading to abnormal blood flow, most commonly resulting in a left-to-right shunt that causes left-sided volume overload. In severe cases, right-to-left shunting may occur due to pulmonary hypertension (PHT), leading to cyanosis.

  • PDA can be classified into four types based on the ductus' anatomy and smooth muscle failure (I, IIa, IIb, III). German Shepherds often suffer from type III (tubular).

• Clinical Signs

  • Left-to-right PDA: Exercise intolerance, dyspnea, and increased sleeping respiratory rate due to congestive heart failure (CHF).

  • Right-to-left PDA: Signs of right-sided CHF and severe pulmonary hypertension (e.g., hindlimb collapse). Chronic hypoxia can lead to erythrocytosis and differential cyanosis (cyanosis present only in caudal mucous membranes).

• Diagnosis

  • Heart murmur: Detected on routine veterinary examination. A characteristic murmur suggests PDA.

  • X-rays: Chest radiographs can show heart enlargement and pulmonary changes.

  • Electrocardiogram (ECG): Can show arrhythmias or heart abnormalities.

  • Echocardiography: Gold standard for PDA diagnosis, showing the abnormal connection between the aorta and pulmonary artery.

• Prognosis

  • Without correction, PDA is generally not compatible with a normal lifespan.

  • Corrective closure improves the prognosis significantly.

• Treatment

  • Thoracotomy: Open-chest surgery to close the ductus.

  • Cardiac catheterization: Minimally invasive closure with coils or a ductal occluder. This option is preferred for smaller dogs and cats.

  • Early intervention is crucial to avoid further complications.

• Follow-up

  • Post-surgery, close monitoring and follow-up echocardiograms (1-3 months post-surgery) are essential.

  • Removal of sutures (7-10 days) and wound care are important to prevent infection.

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2. Ventricular Septal Defect (VSD)

• Pathophysiology

  • A VSD is a congenital defect in the interventricular septum (the wall between the heart's two ventricles). It allows blood to flow between the left and right ventricles, leading to shunting.

  • Types of VSD:

    • Perimembranous: Most common type, located below the aortic valve.

    • Muscular: Rare, located in the apical portion of the septum.

    • Supracristal: Located just below the pulmonic valve, often associated with aortic insufficiency.

    • Inlet: Located below the mitral and tricuspid valves, associated with endocardial cushion defects.

  • Small VSDs: Minimal blood shunting, typically asymptomatic, and might not cause significant hemodynamic changes.

  • Large VSDs: Significant left-to-right shunting causes left heart volume overload and can lead to pulmonary hypertension (PHT).

  • In severe cases, right-to-left shunting occurs due to elevated pulmonary resistance, causing cyanosis and possible development of Eisenmenger's syndrome.

• Clinical Signs

  • Small VSDs: Often asymptomatic, but may present with a loud systolic murmur.

  • Moderate to large VSDs: Dogs may show signs of left-sided CHF such as dyspnea, increased sleeping respiratory rate, and exercise intolerance.

  • Severe pulmonary hypertension (PHT): In cases where a right-to-left shunt occurs, clinical signs may include cyanosis, exercise intolerance, erythrocytosis, and in some cases, seizures.

• Diagnosis

  • Heart murmur: A loud systolic murmur, and possibly a diastolic murmur due to aortic insufficiency.

  • Radiographs: Can show left-sided heart enlargement and signs of CHF in moderate to large defects.

  • Echocardiography: The gold standard for diagnosis. Small defects may be difficult to visualize in 2D, but Doppler techniques help assess blood flow. Large defects are more easily visualized as an anechoic region in the septum.

  • Colour Doppler: Used to identify turbulent flow across the defect. Spectral Doppler helps assess flow velocities and pulmonary pressures.

  • Arterial blood gas: In cases with right-to-left shunting, hypoxemia can be detected.

• Treatment

  • Small VSDs: Often require no treatment. If symptoms of CHF are present, diuretics may be used.

  • Large VSDs:

    • Medical management: For left-to-right shunts, diuretics may help manage CHF.

    • Surgical closure: Open-heart surgery or minimally invasive methods using occluder devices can correct large VSDs. Surgery is not recommended for right-to-left defects as it may worsen PHT.

    • Pulmonary artery banding: Can help reduce pulmonary blood flow in certain cases to prevent worsening PHT.

    • Eisenmenger's syndrome: Management typically includes phlebotomies to reduce red blood cell mass and medications to manage complications.

• Prognosis

  • Small, left-to-right VSDs: Often asymptomatic and do not result in long-term consequences.

  • Large VSDs: Can lead to progressive CHF, pulmonary hypertension, and poor prognosis if not corrected early. Surgical closure has a good outcome if performed before severe heart remodeling occurs.

  • Right-to-left VSDs (Eisenmenger's syndrome): Generally, a poor prognosis due to severe complications like cyanosis and erythrocytosis.