Mapca 1

MAPCA

1. MAPCA DR RAHUL C

2. WHAT ARE MAPCAS ? Major AP collateral arteries is the term used to refer to the systemic to pulmonary collateral vessels . They have also been referred to in the literature as systemic arteries or persistent segmental arteries . Some authors suggest that MAPCAs are dilated bronchial arteries.

3. WHAT ARE MAPCAS ? The majority of major AP collateral arteries originate from the descending thoracic aorta , but have also been found coming off the aortic arch , subclavian artery , distal thoracic aorta, internal mammary artery , and the left coronary artery. Major AP collateral arteries are histologically similar to systemic arteries as they demonstrate reactivity and are prone to stenosis over time.

4. WHAT ARE MAPCAS ? Although the precise mechanisms that lead to development of MAPCAs are incompletely understood, hypoxemia, diminished global or regional pulmonary blood flow, and nonpulsatile flow in the pulmonary arteries are some of the commonly cited contributors. Indeed, MAPCAs are frequently encountered in patients with cardiac anomalies that include 1 of these abnormalities such as severe forms of tetralogy of Fallot and functional single ventricle (FSV). In the latter group, the clinical importance of MAPCAs and their optimal management have been topics of intense debate for 2 decades.

5. EMBRYOLOGY Embryological studies by Boyden suggest that major aortopulmonary collateral arteries are persistent segmental arteries, not bronchial arteries. During early fetal development the vascular plexus forming in the lung buds is connected to segmental arteries arising from the dorsal aorta. Within the lung, by the 40th day , the vascular plexus has differentiated into definitive segmental arteries and their branches,and the lung is perfused both by the right ventricle and sixth branchial arches and by segmental arteries , Segmental arteries latter disappear about 50 days after ovulation .

6. EMBRYOLOGY Findings suggest that during this time some bronchopulmonary segments or lobules are connected to the right ventricle and others to the aorta . In the normal fetus , as the lung develops it becomes entirely and exclusively supplied by central pulmonary arteries derived from the sixth branchial arches. In pulmonary atresia with ventricular septal defect, however, it appears that the normal maturation process is arrested .

7. EMBRYOLOGY The lack of antegrade pulmonary blood flow in utero leads to a range of morphologic findings in the pulmonary artery vasculature . If the ductus arteriosus (DA) is present, confluent true pulmonary arteries of variable size may develop. Without flow through the DA, MAPCAs, fetal vessels derived from the splanchnic vascular plexus, may persist after birth . These vessels connect the systemic and pulmonary arterial vasculature, thereby supplying pulmonary blood flow. MAPCAs are tortuous vessels that arise directly from the aorta or its branches.

8. MAPCAs vary in number and origin, follow circuitous routes to reach central, lobar, and segmental pulmonary arteries, and have variable areas and locations of stenosis . Their arborization pattern is unpredictable and often incomplete , leaving some lung segments with excessive or insufficient flow, and they can become narrow over time. As a result, a given segment of the lung may be supplied solely from the true pulmonary arteries, solely from the MAPCAs, or both. The morphology of the pulmonary vasculature and MAPCAs plays a critical role in determining management decisions.

9. Although their origin is controversial (3,4), evidence supports the concept that MAPCAs are the remnants of intersegmental arteries supplying the lung buds in early fetal development, before the intraparenchymal arteries reach the central pulmonary arteries. It is thought that the intersegmental arteries normally regress when the central pulmonary to intraparenchymal artery connection is established. Because of the absence of the normal right ventricle to lung vasculature connection (i.e., presence of PA), the intersegmental arteries apparently continue in confluence with the intrapulmonary vasculature and persist beyond birth (5) as MAPCAs.

10. What conditions allow an abnormal multicompartment pulmonary artery circulation to form? During primary morphogenesis the pulmonary artery circulation changes from the early multi- sited forgut source to the central true pulmonary arteries - the presence of either a patent pulmonary valve or a ductus arteriosus is necessary for this transition - if neither a PV or ductus is present , the forgut source persists and the native pulmonary arteries do not form normally.

11. MAPCA CLASSIFICATION

12. PATHOPHYSIOLOGY  Children with unrepaired TOF/PA/MAPCAs are cyanotic due to the right-to-left intracardiac shunt. The degree of cyanosis depends on the amount of pulmonary blood flow supplied by the MAPCAs and, in some cases, the ductus arteriosus (DA). Some patients may have torrential pulmonary blood flow with high oxygen saturations and, if left unrepaired for a prolonged period of time, are at risk for developing pulmonary hypertension .

13. In these patients, there is a large volume load to the left ventricle (LV), which may lead to the development of heart failure. In contrast, other patients may have very little pulmonary blood flow and present with cyanosis, which can progress over time.

14. MAPCAs The Challenges Morphology – Highly variable patterns of: 1) pulmonary artery size and arborization 2) collateral origin, number, and course 3) connections between the two Physiology – Although there is total mixing of the pulmonary and systemic circulations, there can be pulmonary overcirculation , or pulmonary undercirculation . Commonly both overcirculation and undercirculation occur simultaneously in the same patient.

15. MAPCAs VS PDA Whereas the duct (or shunt) dependant patient with a systemic saturation of 80% is clinically stable AND has healthy pulmonary hemodynamics , The MAPCAs patient with a saturation of 80% is clinically stable but likely does not have healthy pulmonary hemodynamics

16. A decision to observe the first patient is appropriate; a similar decision for the second patient is not. Delayed stabilization of blood flow to all segments of lung leads to microvascular disease. PDA and MAPCAs may be present in the same patient Rarely will PDA and MAPCAs coexist in the same lung

17. TOF WITH PULMONARY ATRESIA TYPES

18. Pulmonary Atresia with Confluent PAs Atresia of the pulmonary valve Confluence of both the left and right pulmonary arteries Blood supply to the PAs is from a PDA

19. MacDonald, Malcolm J.; Hanley, Frank L.; Murphy, Daniel J. Pulmonary Atresia with Ventricular septal defect, Cardiology.Published January 1, 2010. Volume 138, Issue 3. Pages 1495-1506. © 2010.

20. Pulmonary Atresia with Diminuitive PAs Atresia of the pulmonary valve Both left and right PAs are diminutive but still present. PAs connect to variable numbers of broncho -pulmonary segments The majority of pulmonary blood flow is supplied through MAPCA’s

21. MacDonald, Malcolm J.; Hanley, Frank L.; Murphy, Daniel J. Pulmonary Atresia with Ventricular septal defect, Cardiology. Published January 1, 2010. Volume 138, Issue 3. Pages 1495-1506. © 2010.

22. Pulmonary Atresia with Absent PAs Atresia of the pulmonary valve No main PA No right or left PA All Pulmonary blood flow is supplied via MAPCA’s

23. MacDonald, Malcolm J.; Hanley, Frank L.; Murphy, Daniel J. Pulmonary Atresia with Ventricular septal defect, Cardiology. Published January 1, 2010. Volume 138, Issue 3. Pages 1495-1506. © 2010

24. Problems over time Stenosis All MAPCAs are prone to stenosis Studies show anywhere from 40-75% develop stenosis Stenosis may be in one vessel or many Likely to require catheter intervention

25. Problems Over Time Common areas of stenosis At the site of aortic insertion At the site of intrapulmonary anastomosis

26. Problems Over Time Pulmonary hypertension Large collaterals No protective stenosis Under high pressure

27. What does this mean at the bedside? You must know the anatomy of the patient’s pulmonary blood supply to understand the physiology Will the patient be de-saturated or normally saturated? Will the patient develop symptoms of heart failure?

28. What does this mean at the bedside? The more MAPCA’s the patient has, the more variability there will be in PBF Most patients will need a surgical palliation or repair within the first days to months of life depending on the source of PBF

29. CLINICAL PRESENTATION Postnatal presentation  — Although most patients with TOF/PA present as neonates, The range of symptoms and clinical manifestations vary and are dependent on the pulmonary blood flow to systemic blood flow ratio ( Qp to Qs ratio). The clinical presentation and management decisions are based on the character of the MAPCAs and whether or not pulmonary blood flow is dependent on the presence of a patent ductus arteriosus (PDA).

30. ● If the MAPCAs are large with relatively few areas of stenosis , blood flow to the pulmonary vascular bed is typically unrestricted and patients may have mild or no evidence of cyanosis ( ie , pink). In some patients with unrestricted flow, heart failure may develop as their pulmonary vascular resistance (PVR) decreases after birth with an increased left ventricular (LV) volume load, and these patients may require medical therapy.

31. ● Patients with restrictive MAPCAS may have insufficient pulmonary blood flow and require intervention in the neonatal period. These patients have severe cyanosis.

32. ● Some newborns may have a PDA supplying blood flow to one or both lungs . These patients typically have moderate degrees of cyanosis with true, confluent pulmonary arteries and may not have extensive MAPCAs. Prostaglandin E infusion is required to maintain ductal patency and pulmonary blood flow, otherwise they become increasingly cyanotic and hypoxic as the PDA closes.

33. WHY SHOULD WE LOOK FOR MAPCA? MAPCAs can result in a number of complications including gross enlargement with erosion of bronchi resulting massive hemoptysis . Occlusion of the MAPCAs before open heart surgery is important because otherwise there is excessive return to the left heart when the aorta is cross clamped on cardiopulmonary bypass, flooding the operative field thus interfering the surg ery. MAPCAs may contribute low output throughout surgery which can lead to cerebral anoxia and renal hypoperfusion and devastating postoperative sequale .

34. If remain undetected can lead to pulmonary edema after operation and difficulty in weaning off the patient thus prolonging the stay . In the long term postoperatively patients may develop CCF refractory to medical treatment . Considering all these necessitates that all MAPCAs in patient with TOF with pulmonary stenosis should be evaluated.

35. EFFECT ON CPB During cardiopulmonary bypass (CPB), results in reduced systemic perfusion due to the lower pressure throughout the pulmonary system . The result of this is a flooded surgical field in which the surgeon will ask for reduced flow to enable visualisation of the cardiac structures; this exacerbates the reduced systemic flow and lower perfusion pressures. Intervention with vasoconstrictive agents to reverse the lower systemic pressures initiates a downward spiral of increased field flooding and reducing CPB output .

36. What Does the Surgeon Need to Know ? Echo Cath CT MR True pulmonary artery size and arborization Number , origin, exact course, and destination of every collateral Exact position and severity of all stenoses in both true pulmonary arteries and collaterals For every collateral, does it intercommunicate with true pulmonary artery: “isolated supply” or “dual supply” Relationship of collaterals to other thoracic structures: bronchial tree, pulmonary veins, esophogus Post stenotic pressure in collaterals

37. MANAGEMENT   The management of patients with TOF/PA is challenging given the wide spectrum of pulmonary artery architecture. Management of TOF/PA includes: ● Initial medical management to maintain sufficient pulmonary blood flow for survival. ● Subsequent management focused on complete separation of the pulmonary and systemic circulations. This is accomplished by restructuring pulmonary blood flow to create a low pressure system, establishing antegrade pulmonary blood flow from the right ventricle (RV), and closing the ventricular septal defect (VSD).

38. Initial medical treatment  — Initial management is focused on stabilization of cardiac and pulmonary function, and ensuring adequate pulmonary blood flow and systemic oxygenation. However, the range of interventions varies depending on the initial oxygen saturation .

39. IN PATIENTS WITH  INADEQUATE PULMONARY BLOOD FLOW (LOW OXYGEN SATURATION) Therapy is focused on increasing the pulmonary blood flow to systemic blood flow ratio ( Qp /Qs). Prostaglandin E1 ( alprostadil ) is initiated to maintain patency of the ductus arteriosus (DA) if it is present. Supportive measures include volume administration to increase preload, and maintaining the hematocrit above 40 percent with red blood cell transfusion to maximize oxygen carrying capacity. Occasionally, medical therapy with   phenylephrine  or norepinephrin is used to increase systemic vascular resistance and promote shunting through narrow MAPCAs.

40. PATIENTS WITH EXCESSIVE PULMONARY BLOOD Due to unrestricted MAPCAs may develop pulmonary congestion and heart failure , especially as pulmonary vascular resistance (PVR) declines after delivery. Medical intervention depends on the severity of symptoms, and includes the use of angiotensin converting enzyme (ACE) inhibitors and diuretics . In patients with sufficient, but not excessive, pulmonary blood flow, no intervention may be necessary in the neonatal period, as these patients may maintain acceptable oxygen saturations in the 75 to 85 percent range without medical treatment.

41. Surgical intervention The goal of subsequent management of patients with TOF/PA is to construct completely separate, in-series pulmonary and systemic circulations . The surgical steps include : Unifocalization , which involves detachment of collateral vessels from their aortic origins and anastomosis to the central pulmonary arteries, resulting in creation of a low pressure pulmonary arterial system. Reconstruction of the right ventricular outflow tract (RVOT) using an allograft valved conduit from the RV to pulmonary artery that results in antegrade pulmonary blood flow from the RV into the pulmonary vascular system. VSD closure.

42. Surgical management is tailored to the anatomy of each individual patient and depends on the presence and caliber of true pulmonary arteries and the anatomy of the MAPCAs. Management is focused on lowering post-repair RV pressure as much as possible because elevation of the right ventricle to left ventricle (RV/LV)  pressure ratio is associated with increased mortality . It is therefore of utmost importance to maximize the pulmonary vascular cross-sectional area by recruiting as many lung segments as possible and relieving any significant obstruction to blood delivery from the RV to the pulmonary microvasculature. Establishing antegrade flow as early as possible is also important to facilitate the postnatal growth of the underdeveloped pulmonary arterial tree, thereby allowing access for future interventional procedures.

43. TIMING OF VSD CLOSURE The timing of VSD closure is important, especially related to RVOT reconstruction. Closing the VSD too early may result in pulmonary hypertension (PH) and RV failure. However, delay in closing the VSD after unifocalization may result in excessive pulmonary blood flow causing pulmonary congestion and left-sided heart failure.

44. The decision to close the VSD is made based on data that predicts postoperative pulmonary artery pressure from an intraoperative flow study and cardiac catheterization . During the intraoperative flow study, if the mean pulmonary artery pressure stays consistently below 25 mmHg, the VSD can be closed , as it predicts a postoperative RV/LV pressure ratio at or below 0.5, which is associated with a good outcome . However, if it exceeds 25 mmHg, the VSD is not closed and the reconstruction of the RVOT is not performed.

45. Unifocalization refers to the process of changing an abnormal multi-compartment pulmonary artery circulation to a normal single compartment circulation using surgical reconstruction.

46. Aortopulmonary Collaterals in Single-Ventricle Congenital Heart Disease How Much Do They Count?

47. From a physiological standpoint, APCs may have both beneficial and adverse consequences. The principal advantageous effect of APCs is to improve systemic arterial oxygen saturation by increasing pulmonary blood flow leading to a higher “mixed” saturation in the ventricle. In addition, APCs may potentially inhibit the development of pulmonary arteriovenous malformations in patients with a bidirectional Glenn shunt by providing a route for hepatic venous blood to reach the lungs. Among the negative effects of APC flow is that it can compete with and limit the more effective, lower saturated blood flow to the lungs from the pulmonary arteries. Also of concern is that all APC flow returns to the single ventricle and thereby results in an additional volume load .

48. Because these patients are at risk for the development of systolic and diastolic heart failure and atrioventricular valve regurgitation, any increased work or dilation can justifiably be viewed as undesirable. APCs, by adding to pulmonary artery blood flow, may also increase pulmonary artery pressure. Because the Fontan circulation depends on passive venous flow into the pulmonary arteries, increases in pressure may be poorly tolerated and lead to decreased cardiac output, pleural effusions, hepatic congestion, peripheral edema, and protein-losing enteropathy . Flow energy dissipation effects from APC flow may incur significant energy loses and contribute further to the morbidity of Fontan patients.5 Finally, APCs that are in close association with the bronchial tree may dilate, erode into the airway, and rupture, leading to life-threatening hemoptysis .

49. Despite the numerous mechanisms by which APCs may affect single-ventricle patients, there are only a few studies that directly address this issue, and most of these have focused on the outcomes of Fontan surgery. Several centers have reported that higher APC flow was associated with an increased incidence of pleural effusions, elevated pulmonary artery pressure, and mortality. In contrast, other groups have found that APC flow was not significantly related to postoperative venous pressures, duration of pleural effusions, or resource utilization. McElhinney et al8 found that those patients with significant APCs were, in fact, less likely to have prolonged pleural effusions .

50. Given the limited and conflicting results regarding the importance of APCs in determining outcomes, it is not surprising that there are no well-established guidelines for the treatment of APCs in single-ventricle patients. Elimination of APCs is usually accomplished by transcatheter occlusion, typically with vascular coils or embolization foam. There is general agreement that large, discrete APCs should be occluded and that smaller vessels should be treated if patients are symptomatic; however, there is no consensus as to whether APCs should routinely and aggressively be identified and eliminated.

51. In summary, APCs are commonly found in patients with surgically palliated single-ventricle heart disease. Their clinical significance and the indications for occluding them are not well established. An important step toward improving our knowledge would be the development of a robust technique to quantify APC flow. MRI flow measurements as described by Grosse- Wortmann et al have the potential to meet this need but require additional validation and refinement before widespread use can be recommended.

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