8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. 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.
14. • 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.
15. 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.
16. 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.
19. 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.
20. • 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.
21.
22. 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.
23. 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
24. • 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
26. 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
28. 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
32. 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
33. PROBLEMS OVER TIME
Common areas of stenosis
At the site of aortic insertion
At the site of intrapulmonary anastomosis
35. 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?
36. 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
37. 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).
38. ●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.
39. ● Patients with restrictive MAPCAS may have insufficient pulmonary
blood flow and require intervention in the neonatal period.
• These patients have severe cyanosis.
40. ●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.
41. 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 surgery.
• MAPCAs may contribute low output throughout surgery which can lead to
cerebral anoxia and renal hypoperfusion and devastating postoperative
sequale .
42. • 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.
43. 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.
44. 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
45. 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).
46. 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.
47. 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.
48. 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.
49. 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.
50. • 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.
51. 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.
52. • 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.
53. Unifocalization refers to the process of changing an abnormal multi-compartment
pulmonary artery circulation to a normal single compartment circulation using
surgical reconstruction.
56. 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.
57. 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.
58. 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.
59. 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.
60. 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.
While this is not true PA/MAPCA anatomy and physiology I think it is important to know what Pulmonary atresia looks like without MAPCA’s to make a better comparison.
This diagram shows PA VSD in its most simplist form PA VSD, PDA . Go through diagram
This is PA VSD MAPCAs in its most severe form.
Again the same image blown up so that you can appreciate the discontinuity of the Pas and MAPCAs arising off of the descending aorta
Don’t go into catheter intervention, mention this will be covered later by Sharon Cheatham. Mention that some studies have shown that there is a pressure gradient of 60 mmHg or more even in those which angiography did not reveal a stenosis
.
Pulmonary hypertension- probably depends on age, those who live longer presumably have larger collateral artiers and higher PBF making them more susceptible to PHTN changes and the higher pressures that these vessels see
The most important take home point here is that if you know and understand your patient’s anatomy and source of pulmonary blood flow it will help you answer these questions at the bedside.
