Chapter 8

    This frequent heart disease which constitutes from 8% to 15% of the congenital cardiac problems has been more prevalent among women than men and in high altitude countries like Mexico, Peru and many areas of Asia.
    During the fetal life the ductus arteriosus delivers approximately 30% of the blood flow from the pulmonary artery to the aorta and placenta. The high pulmonary vascular resistance of fetal life favors this situation.
    After birth, the pulmonary vascular resistance diminishes rapidly in a few hours with a simultaneous elevation of the peripheral resistance and inversion of the blood flow direction (left to right shunt).
    Then in a few hours, days, or even a few months, the ductus wall collapses and closes, due to both hemodynamic and neuroendocrine reasons (See Prostaglandins uses in PDA patients).

ANATOMY

    In the majority of patients the ductus links the left branch of the pulmonary artery with the aorta, immediately below the origin of the left subdavian artery. In few cases the ductus arises from the right pulmonary artery branch.
    Aside from the patent ductus arteriosus existence, the most typical anatomical findings are the left atrium and ventricular hypertrophy due to volume overload resulting in recirculation of blood flow. Moderate hypertrophy of the pulmonary artery can be seen with normal right sided chambers, unless the patient develops pulmonary hypertension.

PHYSIOLOGY

    Unless severe pulmonary hypertension appears, these patients have a left to right shunt.
    There are two main factors controlling the hemodynamics in a patient with PDA:

1. Shunt volume and size of the PDA
2. Pulmonary vascular resistance

    As in case of ASD and VSD, many patients will develop pulmonary hypertension, and, as in these malformations, with increase of the pulmonary pressure the shunt volume will decrease. In the patient with systemic pulmonary hypertension (Eisenmenger Syndrome), the shunt will be bidirectional and finally predominantly from left to right.
    In cases of pulmonary hypertension due to PDA, two categories of patients exist. The first are infants where the physiological drop of pulmonary artery pressure never occurred (persistence of the fetal hemodynamic pattern). The second is the one where, after a period of relatively normal pressure, a progressive pulmonary hypertension supervenes.
    When compared with VSD, these patients develop frequently less severe pulmonary hypertension but, more often than in ASD.
    PDA brings an increase of the blood pulmonary flow with volume overload of the left heart, due to blood recirculation.

CLINICAL PICTURE

    Four categories can be recognized in relation to the shunt volume, alterations on the left heart anatomy (hypertrophy) and pulmonary vascular resistance.

GRADE I

    Most of the children with PDA are asymptomatic, having normal growth and development. The physical examination, other than for the murmur, can be totally normal with no chamber enlargement and no recognizable pulmonary increase of circulation. The electrocardiogram and roetgenogram will be normal.

GRADE II

    Patient may show frequent respiratory tract infections with otherwise normal physical growth. Congestive failure is rare and cyanosis is absent even during exercise.
    Functional aerobic capacity can be moderately diminished with easy fatigability.
    Mild pulmonary hypertension may occur with mild left ventricular hypertrophy and moderate increase in the pulmonary flow in the chest x-ray.
    A systolic thrill may be palpable in the second and third left intercostal space with a continuous murmur audible in the same area. This murmur is usually harsh of "machinery type", louder in late systole and radiated toward the left clavicle. The second sound can practically disappear behind the murmur in many cases. The apical impulse can be hyperactive in many of these patients.
    Many patients will remain in this stage, but the majority of them will evolve eventually toward the third and fourth stages with a pace which is particular for each patient.

GRADE III

    Frequent respiratory tract infections. Dypsnea is almost permanent and increases with exertion.
    Defective growth in infants and congestive failure is frequent, during the first weeks of life, if the ductus is large. The failure can be severe producing rapid hearth growth with consequent cardiomegaly. Pulmonary edema is not rare. However, after the patient is a few months old, failure is rather unusual and the development of cardiomegaly and pulmonary hypertension will act as protective barriers against CHF.
    Moderate cyanosis with exertion can be seen. The murmur is typically only systolic with a late systolic accentuation. These murmurs are of lower location than in the previous case (third and fourth left intercostal spaces). Bounding pulses will be seen. Paradoxical splitting of S₂ can be proved by the phonocardiogram. The physical exam, electrocardiogram and roentgenogram will demonstrate left atrial and ventricular volume overload with moderate right ventricular hypertrophy.
    The pulmonary hypertension in this stage (usually higher than 60 mm Hg) will lead to the palpation of the pulmonary artery and the second sound.

GRADE IV (EISENMENGER SYNDROME)

    Both the pulmonary vascular and peripheral resistance are equal or very similar. The patient has a bidirectional shunt with mild cyanosis and physical findings of systemic pulmonary hypertension.
    It should be emphasized that in Eisenmenger Syndrome, regardless of the basic congenital disease, the findings, symptoms and hemodynamic situation are almost the same. As a matter of fact, at this level (Grade IV) an accurate diagnosis of the underlying congenital disease is almost impossible without cardiac catheterization.
    The major complications of PDA are congestive heart failure and pulmonary hypertension.
    CHF usually complicates young infants with PDA but it is a rather unusual problem as soon as protective pulmonary hypertension develops.
    Pulmonary hypertension can be a problem since birth, or, more commonly, it appears with time after several years of almost asymptomatic disease.
    Another major complication is bacterial endocarditis which can appear in any patient with PDA regardless of the diseases' stage.
    The differential diagnosis must be done with other situations leading to the appearance of continuous murmurs as the venous hum which is occasionally present in youngsters, most frequently in the right supraclavicular fossa. Other pathologies, as rupture of a sinus of valsalva, arteno-venus fistulas, coronary artery fistula and multiple stenosis of the pulmonary artery branch should be ruled out. All of them may produce continuous types of murmurs.
    It should be remembered that in persons with pulmonary hypertension and infants until one year of age, the murmur may be only systolic in most cases.

ELECTROCARDIOGRAM

    The electrocardiogram does not show characteristic changes in this disease but it is useful attempting the evaluation of the hemodynamical condition of the patient.
    If the left to right shunt is significant (PDA Grade II and Grade III), the electrocardiogram will show changes of left ventricular hypertrophy and left atrial overload.
    Biphasic P wave with a longer than normal duration may be seen attimes in leads I, II and V₁. These P wave changes are important in differential diagnosis with the ventricular septal defect where the QRS configuration and axis rotation over the frontal and horizontal plane can be similar, but the P wave configuration is different.
    Left ventricular hypertrophy is frequent in Grade II and III patent ductus arteriosus. Diastolic left ventricular overload will be present with V₅ and V₆ deep Q wave, with tall R wave and narrow and higher than usual T wave. ST segment can be at times moderately elevated, which is typical of certain cases of left diastolic overload (volume overload). Leads V₁ and V₂ will show deep S waves with R waves of different amplitude depending on the degree of left ventricular overload.
    If pulmonary hpertension is present (Grade IV), the electrocardiographic signs of left ventricular hypertrophy will be associated to the proper ones of right ventricular systolic overload.
    As mentioned in other chapters, the typical electrocardiographic changes of right ventricular systolic overload will appear with a pulmonary artery pressure over to 50 mm Hg. In these cases of pulmonary hypertension, the P wave, as previously mentioned, will have an amplitude and duration higher than normal in leads I and V₁. Biphasic Rs complex of relatively high amplitude from leads V₁ to V₆ (Rs complex from leads V₁ to V₃, RS complex from V₄ to V₆), are seen.
    The right ventricular hypertrophy and systolic overloads are the preponderant electrocardiographic findings in patients with systemic pulmonary hypertension, with left ventricular diastolic overload masqueraded from right ventricular enlargement.

ROETGENOGRAM

ECHOCARDIOGRAM IN PDA

    The visualization of the patent ductus is not possible. However, the left atrium size and gross diameter of the aorta can be evaluated. Several authors claim that the ratio of dividing the atrial diameter by the aortic, can be useful information in assessing the magnitude of the shunt. It is our personal opinion that this data still lacks practical use and can be misleading.
    Echocardiography however, is useful in assessing left ventricular performance in this patient.

CARDIAC CATHETERIZATION AND ANGIOGRAPHY

    Many centers do not advise routinely catheterizing all patients with PDA before surgery, reserving such studies for only atypical cases.
    Actually, however, in most of the cases, right catheterization is almost a routine before surgery, which is useful in evaluating not only the hemodynamic siutation and confirming the diagnosis, but in ruling out associated malformations.
    Indications for catheterization in PDA:

1. Patient below one year of age.
2. Atypical physical findings in PDA.
3. Cases with significant pulmonary hypertension.
4. When another associated malformation is thought to be present.

    The definite diagnosis will result from passing the catheter from the pulmonary artery to the descending aorta confirmed by oximetry, catheter position and finally by the typical pull back pressure recording (aorta-ductus pulmonary artery-right ventricular curves).
    If systemic pulmonary hypertension is severe, 100% oxygen can be given to the patient for a few minutes. If the pulmonary pressure diminishes it indicates that the arterial lesion is not definitive and that the patient may still be a candidate for surgical repair (before indicating surgery, a bidirectional shunt should prove to change to a left to right type with the 100% oxygen test).
    Angiography is rarely necessary unless other associated malformations are suspected. When the shunt is left to right, contrast should be injected in the ascending aorta and the dye will fill the pulmonary artery branches.

MEDICAL AND SURGICAL TREATMENT

    The basics of the medical treatment consist in:

1. Prevention of bacterial endocarditis with antiobiotics.
2. Treatment of the congestive heart failure
3. Still experimental is the use of prostaglanding antagonists as Idomethacin, to facilitate the closing of a PDA when the infant is approximately 20 days old. If at 20 days of life the ductus is still patent, there is a good possibility for it to remain patent. Prostaglandin E₁ may facilitate for the patent foramen to remain open. E₁ antagonist as aspirin and Indomethacin tend to close the patent ductus.

    Otherwise, all patients with PDA should probably be operated on regardless of the clinical grade (I, II, III). However if systemic pulmonary hypertension is present, and no response in the pulmonary pressure is seen with 100% oxygen, surgery is contraindicated.
    The pulmonary hypertension otherwise after surgery tends to normalize slowly during several months.
    Bacterial endocarditis is a relative surgical contraindication. Ideally the patient should be older than one year, although this criterion is flexible if severe congestive failure endangers the patient's life. The optimal age for surgery is 1 to 2 years of life.
    The operative mortality in a good center doing pediatric cardiac surgery should be negligible.
    The ductus at surgery must be clamped and cut appropriately and both ends sutured with silk.

Electrocardiogram of a 13 year-old boy with Stage II of PDA. The pulmonary artery pressure (MPA) was 29/4 mm Hg.

Patent Ductus Arteriosus. Eighteen year-old boy from Mexico.

Diagrammatic representation of the anatomy and hemodynamic findings in patent ductus arteriosus. There is an oxygen saturation step up at pulmonary artery level.
    The Indocyanine green dye dilution curves indicate early appearance of the colorant in the pulmonary artery when injected in the aorta. When the injection is done in the pulmonary artery the recirculation pattern obtained in the femoral artery indicates that the shunt is at the level of the ductus arteriosus.