In the fetus, the ductus arteriosus connects the pulmonary artery (PA) system with the aorta (AO), and should normally be closed after birth.
Patent ductus arteriosus (PDA) refers to persistent patency of the ductus arteriosus after birth.
Illustrations showing PDA and some aortic arch anomalies.
The first arteries to appear in the embryo are the right & left primitive aortas, each one developing as a continuation of the corresponding heart tube. They lie ventral to the foregut, and curve dorsally to continue as the right & left dorsal aortas.
As the two heart tubes fuse to form a single endocardial heart tube, the two primitive aortas fuse to from the aortic sac.
When the 6 branchial (pharyngeal) arches develop on each side, the aortic sac gives 6 branches on each side (6 pairs) called: the aortic arches; i.e. one aortic arch for each branchial arch.
Each aortic arch leaves the aortic sac, curves around the corresponding branchial arch and enters the dorsal aorta on its side.
Caudally beyond the level of the 6th pair of aortic arches, the two dorsal aortas fuse to form the single dorsal aorta.
Actually; The six pairs of aortic arches are never present together; When the 3rd pair appears, the 1st pair has already disappeared.
Fate of the aortic arches:
- First pair: A small part forms the maxillary artery, the rest disappears.
- Second pair: A small part forms the stapedial & hyoid arteries, the rest disappears.
- Third pair: forms the carotid arterial system: the common, internal & external carotid arteries on each side.
- Fourth pair: forms the aortic arch (AO arch) on the left side, and the right subclavian (RSC) artery on the right side. The left subclavian artery arises from the left seventh inter-segmental artery, which arises from the left dorsal aorta.
- Fifth pair: totally disappears.
- Sixth pair: forms the right & left pulmonary arteries (PA) and the ductus arteriosus (DA).
Thus, the ductus arteriosus is formed by: the dorsal part of left 6th aortic arch.
Fate of aortic arches
Ductal closure after birth:
Functional closure occurs by vascular smooth muscle (VSM) contraction, within 10-15 hours of birth.
The mechanisms of VSM contraction include:
- Sudden increase in O2 tension.
- Decreased formation of the vasodilator prostaglandin E2 (PG-E2) & PG-I2 (some of which are formed by the placenta).
- Release of vasoconstrictors, e.g. Acetyl-Choline & Catecholamines may also occur.
Anatomical closure occurs within 2-3 weeks after birth; by intimal disruption, hemorrhage, proliferation & fibrosis.
Anatomical ductal closure & fibrosis results in the formation of the ligamentum arteriosum.
The ligamentum arteriosum runs almost horizontally from the origin of the left PA to the aortic arch just distal to the origin of the left subclavian artery.
Anatomical relations of the ligamentum arteriosum:
- The superficial cardiac plexus of nerves lies anterior to it.
- The deep cardiac plexus of nerves lies posterior & to the right.
- The left recurrent laryngeal nerve hooks around it.
Anatomical relations of the ligamentum arteriosum
The anatomical & histological structure of a patent ductus arteriosus is different from that of the aorta and pulmonary arteries.
Instead of functional closure followed by definitive anatomical closure, the ductus arteriosus remains patent and carries blood from the aorta to the pulmonary arterial system (left to right shunt).
Secondary cardiac pathological changes:
With PDA the following secondary pathological cardiac changes may occur:
- Left atrial enlargement (LAE).
- Left ventricular enlargement (LVE).
- Right ventricular enlargement (RVE) occurs with wide ductus carrying the high aortic pressure to the PA system (hypertensive ductus).
- Ventricular septal defect (VSD).
- Coarctation of the aorta.
The following anomalies are called ductus-dependent conditions, since survival of the patient is dependen on the presence of PDA:
- Interruption of the aortic arch.
- Aortic atresia.
- Pulmonary atresia (P.at.) with intact ventricular septum.
- Some cases of P.at. with VSD.
- Some cases of mitral atresia.
- Some cases of tricuspid atresia.
- Some cases of transposition & mal-position complexes.
PDA most commonly results from:
- Infant prematurity.
- Maternal rubella.
In general; anomalies caused by Rubella include:
- Ventricular Septal Defect.
- Atrial Septal Defect.
- Patent ductus arteriosus.
- Pulmonary Stenosis.
- Tetralogy of Fallot.
- Aortic Stenosis.
- Coarctation of the aorta.
- Transposition & mal-position complexes.
- Tricuspid atresia.
Factors controlling ductal flow:
- Ductal resistance: which is determined by ductal cross sectional area & length:
- With high resistance: Small shunt, Mild LV overload, and Normal PA pressure (PAP) & pulmonary vascular resistance (RP).
- With moderate resistance: Bigger shunt, and Some increase in PAP.
- With low resistance: PAP may be equal to AO pressure, and LV failure frequently occurs, with pulmonary edema.
- Pressure gradient: between PA & AO.
- Pulmonary vascular resistance/Systemic vascular resistance ratio (RP/RS ratio).
With the passage of time:
- LV dilatation & compensation occurs.
- Pulmonary vascular obstructive disease (PVOD) develops with RV pressure overload.
- Eisenmenger’ s syndrome finally develops with differential cyanosis & differential clubbing of the lower body, which is supplied by the non-oxygenated pulmonary arterial blood shunted into the descending aorta (reversed shunt).
- The upper body, on the hand, is supplied by the ascending aortic flow and is not affected by cyanosis or clubbing.
- Symptoms occur only with large shunts, which result in congestive heart failure.
- Signs of hyper-dynamic circulation.
- Signs of LV volume overload.
- Manifestations of CHF, with peripheral cyanosis.
- In Eisenmenger’ s syndrome: differential cyanosis
- Systolic thrill over the pulmonary area & the right supra sternal area.
- RV impulse is increased in: Prematures & PHT.
- Apical rumble (Relative MS) occurs in moderate or big shunts.
- S2 is usually normal, but may be difficult to hear if the murmur is peaking at its time. It is accentuated with pulmonary hypertension ( PHT).
- Continuous machinery murmur is the characteristic sign: Peaking at or near the second sound, and best heard below the left clavicle & at the upper left sternal border.
PDA murmur is usually continuous throughout systole & diastole, due to persistent pressure gradient between the aorta and pulmonary arterial system.
The aortic pressure is higher than the pulmonary arterial pressure throughout systole and diastole.
Diastolic component of the murmur may be abbreviated in:
- Very small shunts.
- Pulmonary hypertension (PHT).
- In prematures: The diastolic component may totally disappear and the murmur is only systolic, or the whole murmur may disappear.
Chest x ray:
- With small shunt: Normal x-ray.
- With large shunt:
- Enlarged left atrium (LA), left ventricle (LV), aorta (AO) and pulmonary arteries (PA).
- Pulmonary plethora.
- With CHF: Pulmonary edema.
- With Eisenmenger’s PDA: All manifestations improve except central PA, which become markedly dilated.
- Small shunts: ECG is usually normal, but left axis deviation may be present.
- Large shunts:
- Left atrial enlargement (LAE).
- Left ventricular hypertrophy (LVH).
- Right ventricular hypertrophy (RVH); in cases of:
- Pulmonary hypertension (PHT).
- Premature infants.
- Visualization of the duct in:
- High parasternal short axis (SAX) view.
- Supra sternal SAX & long axis (LAX) views.
- Trans-esophageal Echocardiographic (TEE) views.
- Calculation of the systolic and diastolic pressure gradients between the aorta & pulmonary arterial system.
- Enlarged LA & LV may be detected.
Echocardiography, a high parasternal short axis view demonstrating a large patent duct (PDA). Colour flow demonstrates shunting from 'left to right', from the descending aorta (DAO) to the pulmonary arteries (MPA).
Left atrial (LA) enlargement signifies increased pulmonary venous return because of left-to-right ductal shunting. The reference measure is the ratio of the LA to aorta at the level of the aortic valve (the LA:Ao ratio). The aortic does not enlarge with even extremely large PDA so it is a useful measurement that allows for different sized babies. In general, a LA:Ao ratio >1.4:1 indicates a moderate shunt but is dependent on the operator and views. NWH experience suggests that the ratio needs to be greater than 2:1 to support the finding of a significant shunt.
The presence of a significant ductal shunt results in diastolic run-off to the pulmonary circulation. This will result in flow that is retrograde in the descending thoracic aorta beyond the duct during diastole. In practice, this can be a difficult view to obtain.
Cardiac catheterization is not usually needed for diagnosis, but may show the following:
- The catheter usually passes easily from PA to AO unless the ductus is very small
- O2 step up, usually in PA, but may occur in RA via FO with large shunts.
- RA & RV pressures are usually normal but may increase with large shunts.
- Pulmonary vascular resistance (RP) is usually normal in young children but increases in older children.
- Aortography will opacify the ductus & PA.
- In Eisenmenger’s PDA: O2 saturation decreases in the descending aorta.
Course is usually benign but it may be complicated with:
- CHF with significant morbidity & mortality.
- Infective endocarditis.
- Mycotic aneurysm with: rupture, septic emboli, or compression of the left recurrent laryngeal nerve.
- Irreversible pulmonary vascular obstructive (PVOD) with Eisenmenger’ s syndrome is rare below two years of age.
- Obstetric measures: to prevent rubella.
- Prevention and treatment of: anemia, CHF, infective endocarditis, and respiratory distress syndrome.
Pharmacological closure in infants:
- Presence of respiratory distress syndrome (RDS).
- Episodes of apnea.
- Episodes of bradycardia.
- Failure to grow.
Catheter or surgical PDA closure:
Indications for catheter or surgical closure:
- It is often recommended to close an isolated, clinically detectable PDA.
- Significant left-to-right shunt with uncontrolled congestive heart failure is a definitive indication for PDA closure.
Contraindications to ductal closure:
- Irreversible pulmonary vascular obstructive disease.
- Active endarteritis.
The catheter is introduced via the femoral vein and advanced to the PA then the AO to apply the device: coin, button, plug, or umbrella.
Catheter closure may replace surgery in special cases:
- Infants > 10 kg of body weight.
- Short ductus.
Results of PDA device closure:
- Catheter closure is successful in 90 % of suitable cases and re-occlusion adds 5 % more to the success rate.
- Trans-catheter closure of PDA is technically challenging.
- Angiography may be used to assess the suitability of PDA for trans-catheter closure, but echocardiographic assessment showed excellent correlation with angiography.
An echocardiogram of a coiled persisting ductus arteriosus; One can see the aortic arch, the pulmonary artery and the coil between them.
Complications of catheter closure are rare and include:
- Device embolism.
- Left PA coarctation.
Surgical ductal closure:
- Division & ligation.
- Multiple ligations.
- Metallic surgical clips.
- Dacron patch over the aortic orifice from within the aorta.
- Surgical mortality in infancy in experienced hands is nearly zero.
- Mortality may increase in adults & in those with high RP.
Video: surgical ductal closure.
Video: cardiac MRI: PDA.
Video: Echocardiography: Suprasternal long-axis view: PDA color Doppler flow.