Cyanotic Congenital Heart Disease

1. Cyanotic Congenital Heart Disease Done by: Dr.Abdulhalim Shamout Moderator: Dr.Ali AlHalabi

2. Pathophysiology of left to right shunts • When an abnormal connection exists between the systemic and pulmonary circulations, the potential exists for an excess volume of blood to flow from the systemic (left side) circulation to the pulmonary circulation (right side).

3. Multiple factors influence the extent of flow through the shunt and its physiologic effects.

4. Shunt size  • The extent of extra flow is assessed as the ratio of measured pulmonary blood flow (Qp) to systemic blood flow (Qs). • In the normal case, where no connection exists, the ratio Qp:Qs is 1:1. • Left-to-right shunting results in a Qp:Qs >1 • Right-to-left shunting results in a Qp:Qs <1 • For example, a Qp:Qs of 2:1 indicates that the pulmonary blood flow is twice that of systemic blood flow.

5. Cont……………Shunt size  • The overall effect of a left-to-right shunt is the recirculation of already oxygenated pulmonary venous blood through the pulmonary vasculature. • This excess pulmonary blood flow results directly or indirectly in almost all of the significant clinical features that characterize heart failure in infants and children.

6. Pulmonary effects  • Lung mechanics are often abnormal in children with large left-to-right shunts and increased pulmonary blood flow. • The tidal volume and lung compliance were lower and expiratory airway resistance was higher in infants with congenital heart disease and left-to-right shunts than in healthy controls.

7. Cont……….. Pulmonary effects • The mechanism of abnormal pulmonary mechanics is thought to be due to: • -increased extravascular lung water, which appears to be directly related to the increase in Qp. • The increased extravascular lung water results from transudation of fluid under increased pressure across capillary walls at rates greater than can be accommodated by lymphatic drainage.

8. Cont……….. Pulmonary effects • If Qp and pulmonary venous pressure are extremely elevated, transudation of fluid into the lungs may result in clinical and radiographic findings of pulmonary edema. • Pulmonary function abnormalities resolve after surgical repair and normalization of Qp.

9. Neurohumoral activation • The sympathetic nervous system and the renin-angiotensin system are highly activated in patients with left-to-right shunts. • Patients with a significant left-to-right shunt had increased levels of BNP, with the increase positively correlated with shunt volume.

10. Neurohumoral activation • In one Study of children with Acyanotic congenital heart disease, plasma norepinephrine(NE) concentration was higher. • In another study of infants with left-to-right shunts, NE concentration and plasma renin activity were more closely associated with clinical signs of heart failure, such as tachypnea, than conventional hemodynamic measurements of the volume of shunting, such as Qp:Qs.

11. Metabolic effects • Acute and chronic malnutrition are common in children with heart failure, occurring in 60 percent of hospitalized children with left-to-right shunts. • This is due to elevated metabolic expenditures associated with increased respiratory effort and myocardial work, leading to decreased nutritional intake and/or increased catabolism.

12. Pulmonary hypertension • The increased pulmonary blood flow caused by left-to-right shunting often is associated with sustained elevation of pulmonary artery pressure, sometimes at systemic levels.

13. Pulmonary hypertension • Initially, there is overgrowth of vascular smooth muscle as well as intimal proliferation, causing gradual effacement of the pulmonary arterioles. • These changes lead to loss of the normal reactivity of the pulmonary vascular bed and ultimately result in fixed pulmonary hypertension and irreversible pulmonary vascular disease.

14. CLINICAL MANIFESTATIONS • Patients with increased pulmonary blood flow due to left-to-right shunting can be asymptomatic or have tachypnea or respiratory distress. • In general, left-to-right shunts with Qp:Qs >2:1 have significant homodynamic consequences.

15. CLINICAL MANIFESTATIONS • Tachypnea due to interstitial edema. • Tachycardia and diaphoresis due to increased release of catecholamines from the adrenal glands and myocardium. • Poor weight gain resulting from increased caloric demands and myocardial oxygen demands. • Affected patients also may develop hepatomegaly.

16. CLINICAL MANIFESTATIONS • The most sensitive and specific signs and symptoms of heart failure were a: • History of poor feeding (<3.5 ounces/feed) • Tachypnea (respiratory rate >50/min), • An audible gallop, and hepatomegaly.

17. Pulmonary infections • Children with large left-to-right shunts have increased vulnerability to viral infections that affect the lower respiratory tract, especially respiratory syncytial virus (RSV). • In these patients, RSV infection is associated with increased mortality and prolonged hospitalization, compared to unaffected children.

18. Poor growth • The increased work of breathing combined with poor intake contribute to poor growth in infants, even when caloric intake appears adequate. • Growth may be affected even when the shunt is small and patients are otherwise asymptomatic.

19. Time of presentation  • Because PVR is elevated, little left-to-right shunting occurs immediately after birth in term newborns, even those with large communications due to VSDor PDA. • Shunting typically increases as PVR declines during the first postnatal weeks. • Clinical manifestations may develop as shunting increases.

20. Time of presentation  • Symptoms may be exacerbated by anemia because oxygen carrying capacity is reduced and cardiac output increases. • In contrast, the increased viscosity associated with higher hemoglobin concentration may slightly elevate PVR and decrease shunting.

21. Cont… • In premature infants, PVR decreases more rapidly and accelerates the time course for development of left-to-right shunting through a PDA.

22. CHARACTERISTICS OF SPECIFIC SHUNTS  • ASD • VSD • PDA

23. ATRIAL LEVEL SHUNTS • Lesions at the atrial level that cause left-to-right shunting include ASDs of all types and anomalous pulmonary venous drainage. • The principal determinant of shunting at this level is the relative compliance of the right and left ventricles.

24. ATRIAL LEVEL SHUNTS • The right ventricle is normally much thinner-walled and more compliant than the thick-walled left ventricle. • As a result, blood flows preferentially through the tricuspid valve during diastole. • In the presence of an ASD, the more rapid emptying of the right atrium results in left-to-right shunting. .

25. ATRIAL LEVEL SHUNTS • The increased pulmonary venous return to the left atrium further favors left-to-right shunting across the atrial communication • Atrial level shunts often result in enlargement of the right ventricle, which is known as right ventricular volume overload.

26. Cont…. • Newborns with ASDs may have right-to-left shunting. • This is due to hypertrophy and decreased diastolic compliance of the right ventricle at birth, resulting from exposure to systemic pressures during fetal development. • As PVR gradually declines postnatally, right ventricular compliance slowly increases and is accompanied by increasing atrial left-to-right shunting.

27. Cont…. • Thus, most infants with ASDs do not present early. • An exception is the infant with an ASD who also has obstruction of the mitral valve. • In this case, resistance to left ventricular filling is so impaired that blood is forced left-to-right across the defect to fill the right ventricle.

28. VENTRICULAR LEVEL SHUNTS • Ventricular level shunts result from all types of VSDs, including membranous and muscular defects, AV canal, and conoventricular defects. • The pathophysiologic changes associated with a VSD depend upon the size of the defect and the resistance to flow distal to the lesion.

29. VENTRICULAR LEVEL SHUNTS • Shunts at the atrial level lead to isolated increases in right ventricular and pulmonary blood flow; pressures are usually normal. In VSD : • Increased pulmonary blood flow originates from the left as well as the right ventricle. • This left ventricular volume overload may result in hypertrophy and increased end-diastolic pressure, which in turn may cause increased pulmonary venous pressure.

30. VENTRICULAR LEVEL SHUNTS • Unrestrictive VSDs often result in significant pulmonary hypertension, with pulmonary arteries facing systemic or near systemic pressures.

32. The size of the defect influences its effect. • Small VSDs — Small VSDs restrict left-to-right shunting by providing direct resistance to flow. • They usually result in a small left-to-right shunt, with normal PVR, normal pulmonary artery and right ventricular pressures, and little increase in ventricular stroke work. • Symptoms and signs of heart failure are rare.

33. Moderate VSDs • Some limitation of shunting occurs. • However, if PVR is low, a significant left-to-right shunt may develop. • This results in volume overload of the left atrium and ventricle and signs and symptoms of heart failure. • In these patients, PVR, right ventricular pressures, and pulmonary artery pressures may remain low or be moderately elevated.

34. Large VSDs • Large VSDs are unrestrictive; ie, they provide no effective resistance to flow between the right and left ventricles. • As a result, pressures in the two ventricles are approximately equal throughout the cardiac cycle. • The overall amount of left-to-right shunt is dependent upon the resistance of the pulmonary and systemic vascular beds.

35. Associated lesions • Associated stenotic lesions of the right and/or left ventricular outflow tracts modify the flow across a large VSD. • For example, tetralogy of Fallot typically includes a large, unrestrictive VSD caused by malalignment of two components of the ventricular septum. • However, the amount of left-to-right shunting in this disorder is determined by the degree of obstruction of the right ventricular outflow tract.

36. Associated lesions • Obstruction to left ventricular outflow, such as subvalvar and valvar aortic stenosis or obstructive lesions of the aortic arch, favor left-to-right shunting.

37. Cont…………..Large VSDs • In the presence of large defects, the normal postnatal decline in PVR may be delayed for several months. • This reduces the extent of left-to-right shunting and limits the development of left ventricular volume overload and signs and symptoms of heart failure. • Thus, newborns with large VSDs may sometimes have a relatively symptom-free ("honeymoon") period before PVR falls.

38. Cont…………..Large VSDs • However, as PVR decreases, pulmonary blood flow increases, leading to left atrial and ventricular volume overload. • As left ventricular and left atrial pressures rise, pulmonary venous hypertension develops, contributing to pulmonary edema and diminished pulmonary compliance.

39. Cont…………..Large VSDs • Paradoxically, the absence of signs of heart failure in an infant with a large VSD may be an ominous sign, as it may suggest the early development of irreversible pulmonary vascular disease.

40. ARTERIAL LEVEL SHUNTS • Connections between the aorta and the pulmonary artery include: • PDA • Aortopulmonary collaterals • Surgically placed aortopulmonary shunts.

41. ARTERIAL LEVEL SHUNTS • Similar to a shunt at the ventricular level, the size of a left-to-right shunt at the arterial level depends upon: • The size of the communication • The relative resistances of the systemic and pulmonary vascular beds.

42. ARTERIAL LEVEL SHUNTS • In contrast to atrial level shunts, which occur primarily during ventricular diastole, and ventricular level shunts, which occur primarily during ventricular systole. • The arterial level shunts typically occur throughout the cardiac cycle. • This is because the capacitance of the large arteries maintains a pressure during diastole that is greater than the simultaneous pressure in the pulmonary arteries.

43. ARTERIAL LEVEL SHUNTS • Large arterial level communications with significant left-to-right shunting may result in widening of the pulse pressure due to runoff of arterial pressure into the pulmonary arteries.

45. Increased PVR • PVR may increase in response to excessive pulmonary blood flow, particularly in the face of the high pulmonary arterial and venous pressures often associated with large ventricular and arterial level shunts.

46. Changes with Increased PVR • These changes are irreversible and include fibrous and muscular proliferation in the pulmonary microvasculature and gradual obliteration of the pulmonary vascular bed. • The resultant reversal of the shunt to right-to-left causes cyanosis, and is known as Eisenmenger's syndrome.

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