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Patent Ductus Arteriosus

Patent Ductus Arteriousus and A/P Septal Defect

1. Patent Ductus Arteriosus Definition

A. Communication between upper descending aorta and proximal (L) PA
B. Result of patency of fetal ductus arteriosus
C. Derived from distal part of 6th aortic arch
D. May connect to subclavian/innominate artery
E. Bilateral/absent

2. Morphology of closure 2 stages of post-natal closure*

A. First Stage
1) Complete 10-15 hrs
2) Smooth muscle contraction
3) Intimal cushion apposition
B. Second Stage
1) Complete at 2-3 weeks
2) Fibrous proliferation of intima
3) Necrosis of inner layer of media
4) Hemorrhage into wall
5) * Closure begins at PA and towards aorta - Ductal bump/DIVERTICULUM

3. Ductal Closure

A. 8 weeks - 88% closed
B. If delayed - prolonged patency
C. If failed - persistent patency
D. Mediation
E. Vasoactive substances
F. pH
G. PGE1 / PGE2 / Prostacyclin (relax)
H. PaO2 (closure)
I. * Different sensitivity in mature fetus vs. immature (insensitive)

4. PDA as coexistent anomaly

A. Ductus delivers 55% of combined output to descending aorta - angle of insertion acute
B. Duct dependant circulation - angle of insertion obtuse (R) sided arch - Left sided PDA more common
C. PDA from aortic diverticulum / aberrant subclavian artery (L) vascular ring formed

5. Aneurysms of the Ductus (Rare)

A. 2 Types
B. Spontaneous infantile
1) Entire length of ductus
2) Occlusion of PA end
3) Narrow / patent aortic end
4) Regress spontaneously - thrombosis
C. Childhood / Adult type
1) May be patent at both ends
2) Usually PA end closed
3) Greater tendency for growth / rupture

6. Clinical Features

A. Essentially consequence of (L) to (R) shunting
B. Magnitude of shunt
C. Size of PDA
D. PVR
E. Presentation - shunt magnitude
F. Natural History
1) 5-10% congenital heart disease
2) 2x common females
3) Rubella in first trimester
4) (Multiple peripheral artery stenosis/renal artery stenosis)

7. Operation - Persistent patency

A. Surgical
1) (L) Thoracotomy
2) Thorascopic
B. Non-surgical
1) Percutaneous (Rashkind umbrella)
C. Surgical Complications
1) Phrenic nerve
2) Recurrent laryngeal nerve
3) Chylothorax

8. PDA in premature infants

A. Patency increased with decreased gestational age and birth weight
B. Surgical intervention
1) Respiratory distress
2) Large PDA
3) Failure of 2 courses of indomethacin
4) NEC
5) Intracranial hemorrhage

9. Aortopulmonary Septal Defect

B. Definition
1) Opening between ASCENDING AORTA and Pulmonary artery
2) Separate aortic and pulmonary valves
C. Morphology
1) Single orifice (may be fenestrated)
2) Situated (L) lateral wall of ascending aorta
3) Proximity to LCA ostium
4) More distal AP window - between aorta and RPA

10. Associations : (30-50% have associated abnormality)

A. AP window and anomalous origin of RPA from ascending aorta
1) APW may open between RPA and aorta
2) RPA may straddle AP window
3) RPA may originate from aorta communicating with
4) LPA via APW
B. Lethal combination
1) APW downstream/RPA from aorta, IVS, PDA and interrupted arch/coarctation
C. Type A interruption
D. VSD
E. SAS
F. TOF

11. Clinical features and diagnosis

A. Dependant upon (L) to (R) shunt
1) Size of window
2) PVR
3) Infants develop CCF
4) Similar to large PDA / VSD
5) Continuous murmur
6) * Cardiac cath to exclude associated lesions and to quantify the PVR

12. Operative intervention

A. Routine CPB (snare RPA and LPA)
B. Patch closure of defect
C. Correction of associated defects
D. Mortality depends on
E. Age at operation
F. PVR
G. Diagnosis indication for operation
H. Repair before 3 months of age

13. Morphologic Considerations

A. Anomalous Origin of the Right PA
1) Usually arises from the right or posterior aspect of the ascending aorta
2) Usually within 1-3 cm of aortic valve
3) Isolated lesion 20% of the time
4) Most common co-existing lesion is PDA in 50% of cases
B. Anomalous Origin of the Left PA
1) Rare condition
2) Usually associated with right aortic arch
3) Most commonly associated lesion is Tetralogy of Fallot

14. Clinical Features and Diagnostic Criteria

A. Infants
1) Respiratory distress
2) CHF
3) May have cyanosis
4) Bounding pulses
5) Cardiomegaly on chest x-ray with globular heart
6) Diagnosis established with ECHO and cardiac cath

15. Natural History and Operative Results

1) Anomaly rare
2) Lethal without operation
3) When an isolated lesion, can be low-risk procedure

EXTENDED OUTLINE

1. Patent Ductus Arteriosus

A. Derived from the left sixth aortic arch
B. Equal in diameter to the descending aorta
C. Normally originates from the pulmonary confluence as a continuation of the main pulmonary artery and terminates into the left descending aorta a few millimeters from the left subclavian artery
D. Composed primarily of smooth muscle which is sensitive to prostaglandins (relaxation) and oxygen (vasoconstriction); mucoid lakes in the junction between intima and media
E. Of note, the fetal PVR is high—most of the RV outflow is through the ductus
F. At birth the ductus closes, this is secondary to the release of histamine, catecholamines, bradykinin, and acetylcholine. Decreases in fetal endogenous and placental prostaglandins also play an important role. The greatest stimulus for closure appears to be an increase in oxygen tension brought about by breathing—the wider availability of O2 increases the synthesis of ATP, triggering smooth muscle contraction within the ductus.
G. There are two phases:
1) early (reversible)—smooth muscle contraction of ductal wall; first hours of life
2) late (irreversible)—ductal fibrosis; period of a few weeks
H. Pathophysiologic effects are related to the associated L > R shunt
1) the size of the shunt (diameter and length)
2) difference between PVR and SVR
3) small shunts are restrictive—low volume/high velocity; patient susceptible to endocarditis; minimal hemodynamic effects
4) moderate shunt—evidence of LV overload, usually good end organ perfusion; some pulmonary congestion
5)large shunts are non-restrictive; thus as PVR decreases in the neonatal period, the L > R shunt increases dramatically
I. Pulmonary edema, alveolar gas exchange compromised
J. Diastolic shunt—widened pulse pressure with decreased end organ perfusion
1) persistent fetal circulation—PVR remains at fetal levels and exceeds systemic circulation; R > L shunt; systemic hypoxia

2. Persistent Pda

A. This term applied if fails to close by 3 months of age (88% are closed by 8 weeks)
B. 1/2000 infants
C. Twice as common in females as in males
D. Other factors: high altitudes, hypoxia, RDS, maternal rubella(affects the development of elastic and fibrous tissue), inheritance, low gestational age, associated cardiac malformations
E. Premature infant
F. Approximately 30% overall > 30 weeks; 28-30 weeks ~ 80%
G. Ductus not as sensitive to O2 and more sensitive to prostaglandins which are increased in prematurity
H. Often these patients have RDS

3. Anatomy

A. As stated, it is an extension of the main PA joining the aorta a few millimeters from the origin of the subclavian artery—segment of aorta between subclavian artery and ductal junction is termed the isthmus
B. Recurrent laryngeal nerve separates from the vagus lateral to the ductus, curves caudally underneath, and then courses medially and superiorly toward the tracheo-esophageal groove
C. Variations possible from the pulmonary or arterial end
D. Right arch:
1) PA to mirror image left innominate artery
2) RPA to R descending aorta
3) PA >> behind esophagus>>R descending aorta
4) PA to retroesophageal left subclavian artery
E. Tetrology of Fallot: usually absent ductus—may originate from a varied arterial site and enter the pulmonary circulation via branch pulmonary arteries
F. Aneurysms are rare
1) infantile—spontaneous regression-usually resolve without therapy
2) usually involve the central portion;
3) pulmonary end closed with marked narrowing of the aortic end childhood—aortic end patent
4) potential for rupture and death

4. Presentation

A. Based on the size of the shunt
1) small ductus may be discovered incidentally
2) moderate size ductus will present with heart failure/pulmonary infection
B. Physical findings-related to LV volume overload and increased pulmonary blood flow
1) hyperactive precordium with an increased LV impulse
2) upper left sternal border thrill
3) bounding peripheral pulses
4) hepatomegaly / JVD
5) machinery murmur
C. EKG—LV hypertrophy
D. CXR—cardiac enlargement, increased pulmonary vascular markings
E. Echocardiography—method of choice for evaluation
F. Cardiac catheterization—usually reserved for patients suspected of having increased PVR (If PVR equals SVR, flow across the ductus may be minimal and color flow echocardiography may not describe it well) or if findings suggest pulmonary hypertension. In most patients there will be normal right heart pressures and a step up in oxygen saturation at the pulmonary artery level.
G. MRI—If echo inconclusive may employ this modality (patient usually large)

5. Natural History

A. Spontaneous closure is rare in term infants, but common in premature infants
B. SBE occurs primarily in children with a small PDA; it used to be responsible for 50% of the deaths in the pre-antibiotic era—now, deaths are rare due to this
C. Respiratory infections are common
D. Increased blood flow can lead to pulmonary endothelial injury—pulmonary HTN results; Eisenmenger’s syndrome can result in as short as 12 months
E. CHF accounts for 30% of deaths in children with an untreated PDA; death from heart failure in patients with a moderate sized ductus and chronic volume overload occur most often in the third and fourth decade of life

6. Treatment

A. Initial tx is focused on symptoms:
1) digoxin
2) diuretics
3) vetillatory support—if necessary
4) inotropes—if necessary
5) antibiotics if presenting symptom is endocarditis
B. Premature infant—indomethacin 0.1-0.2 mg/kg Q8H for 3 doses; may be repeated one or two more times. Contraindicated in the presence of renal dysfunction, hyperbilirubinemia, and bleeding disorders. In addition, the presence of severe CHF, sepsis, inadequate tissue perfusion, or organ failure is a strong relative contraindication to indomethacin.

7. Surgery

A. A PDA in and of itself is an indication for closure—a term infant > 3 months old should be electively closed; if symptomatic, control symptoms with medication and then close
B. A small ductus in a premature infant can be followed; if CHF develops, the ductus should be closed promptly
C. Surgical risk is <1%--those at higher risk are generally older with chronic heart and/or lung disease, or an older fragile PDA. Should not be closed in those with severe pulmonary hypertension and cyanosis due to reversal of flow.
D. Technique
1) Left posterolateral thorocotomy
2) 3rd/4th intercostal space
3) identify vagus, phrenic, LPA, LSA
4) expose the ductus (vagus and recurrent laryngeal lie just medial to the pleura)
5) Hemoclip (premature infants) or ligatation (older infants)
6) Older infants are ligated/divided to prevent the risk of recanalization
E. Open method—usually reserved for adults with calcified/friable ducts.
1) Patch or direct closure of the duct using CPB
F. Horocoscopic closure
G. Transarterial catheter closure
1) Rashkin PDA occluder/Lock clamshell device/gianturco coils
2) Best results if <3mm; up to 10mm acceptable
H. Complications:
1) left vocal cord paralysis
2) phrenic nerve injury
3) Horner’s syndrome
4) Chylothorax
5) Recanalization—may be as high as 23% in single ligature/hemoclip techniques
6) False aneurysm formation

8. Aortopulmonary Septal Defect

A. AP window is a defect of conotruncal development in which there is incomplete separation of the aorta and pulmonary arteries—there is a direct communication (“window”) between the two great vessels.
B. Rare ~ 0.2% of CHD
C. L to R shunt>>increased pulmonary blood flow>>LV volume overload and failure; most defects are large and allow equalization of pressures between the aorta and PA
D. Presentation is much like a PDA and depends on size of the defect, the PVR, and other associated malformations. Cyanosis is frequently absent unless severe pulmonary disease has developed; failure to thrive and frequent respiratory infections are common.
E. Diagnostic study of choice is echo; cardiac cath also helpful to evaluate associated abnormalities
F. Systolic murmur on examination
G. Type I defects are simple, nearly circular between the proximal ascending aorta and the main pulmonary artery; they begin in/near the sinus of Valsalva and end before the origin of the RPA; Right or Left coronary arteries (more often the Right) may be associated with the proximal rim of the defect.
H. Type II defects are helicoid in shape and extend in a more cephalad direction; frequently extend to the origin of the RPA
I. Type III defects often have no discernible posterior rim and can extend to involve the RPA and the posterior wall of the ascending aorta; RPA may seem to arise from the aorta
I. Associated defects
1) isolated lesion
2) PDA, ASD, right aortic arch-10% of patients
3) Interruption of the aortic arch (Type A), hypoplastic arch, coarctation--30-50% of patients.

Aortic arch obstruction impedes systemic blood flow and promotes shunting to the pulmonary system, causing further hemodynamic embarrassment; usually aortic interruption is associated with a more complicated type of AP septal defects involving the RPA, and the size of the aorta may decrease abruptly above the defect

9. Management

A. Medical stabilization
1) diuretics and digoxin
2) transfusion and antibiotics as necessary
3) prostaglandins if a coincident aortic arch obstruction exists avoid oxygen
B. Closure undertaken at the time of diagnosis because of the risk of developing pulmonary vascular disease—patients with a large APW will not survive infancy uncorrected
C. Surgical technique
D. Median sternotomy and cardiopulmonary bypass control of pulmonary arteries necesssary defect is exposed through an aortotomy(Type II/III) or ?transpulmonary(Type I) approach closed with a patch which avoids the coronary ostia
1) usually a routine post op course, in some cases sudden, severe pulmonary hypertension may occur—increased PA pressures, hypoxia, hypotension. Tx with high dose O2/possibly ECMO
2) mortality 10%--outcome generally depends on the PVR at the time of repair