581 Views Posted on 03-Mar-2011 under Features

By Dr. Kow Entsua-Mensah
Surgeon, National Cardiothoracic Centre
Heart diseases are an important cause of morbidity and mortality in our society today. It is not infrequent to see a frail child soliciting for funds to have life saving surgery at the Cardiothoracic Centre in Accra.

But this is just a fraction of the problem of heart disease. There are many adults out there who also have heart disease requiring equally urgent attention, medically and surgically.

Thus heart disease may be classified as congenital or acquired. A congenital heart disease is a structural defect of the heart and the proximal parts of the great vessels present at birth, whereas an acquired heart disease is a disease of the heart arising in a previously normal heart.

Our focus for the next few weeks will be on congenital heart disease; starting with one of the simplest conditions known as a patent ductus arteriosus.

Patent ductus arteriosus (PDA) is a congenital disorder in the heart where a newborn's ductus arteriosus fails to close after birth.

Importance of the ductus arteriosus
In the developing foetus, the ductus arteriosus is the vascular connection between the major vessel carrying blood to the lung, the pulmonary artery and the major artery carrying blood from the heart, the aorta. This allows most of the blood from the right ventricle to bypass the foetus’s fluid-filled and compressed lungs. During the development of the foetus, this shunt protects the right ventricle from pumping against the consequent high pressure in the lungs, which can lead to right ventricular failure if the ductus arteriosus closes in-utero, i.e. before the child is born.
When the newborn takes its first breath, the lungs open and results in a fall of the pressure in the blood vessels of the lungs. The lungs also produce chemicals that cause the wall of the ductus arteriosus to narrow and reduce blood flow through it. The ductus completely closes usually within the first few weeks of life. In most newborns with a patent ductus arteriosus, the blood flow is reversed from that of in utero flow, i.e. the blood flow is from the higher pressure aorta to the now lower pressure pulmonary artery.
In the normal newborn, the ductus arteriosus is substantially closed within 12–24 hours after birth, and is completely sealed after three weeks. The driving stimulus for the closure of the ductus is the increase in oxygen concentration of the newborn’s blood. Withdrawal of certain chemicals that help maintain patency which are obtained from mother’s bloodstream also contributes to ductal closure. Upon closure, a fibrous cord, called ligamentum arteriosum, is what remains in the ductus in the normal adult heart.

Associated conditions
A patent ductus arteriosus may be isolated without an obvious identifiable cause, or secondary to another condition. Some common contributing factors in humans include:
· Preterm birth
· Congenital rubella syndrome
· Chromosomal abnormalities such as Down syndrome
Causation of problems
When the ductus arteriosus remains patent, oxygenated blood flows abnormally from the higher pressure aorta to the low pressure pulmonary artery. If this shunt is substantial, the newborn becomes short of breath: the additional fluid returning to the lungs increases lung pressure to the point that the newborn has greater difficulty inflating the lungs. Breathing requires more energy than normal and often interferes with feeding in infancy. The lungs are congested with fluid, resulting in congestive heart failure.
In certain complex congenital heart diseases, ductal patency is essential to keep the newborn alive. In such conditions, prostaglandins are artificially administered to keep the ductus arteriosus open until the newborn can be helped.
Symptoms
While some cases of PDA are asymptomatic, common symptoms include:
· Rapid heart beat
· respiratory problems
· shortness of breath
· Poor growth
Examination by the doctor will yield the relevant physical signs.
Without treatment, the disease may progress from left-to-right (noncyanotic heart) shunt to right-to-left shunt (cyanotic heart) called Eisenmenger syndrome. When this happens the life expectancy of the infant is severely curtailed.
Diagnosis
Following the history and examination by the doctor, he may order for a series of investigations to confirm the presence of the PDA and to determine its characteristics. Electrocardiogram (ECG), a recording of the electrical activity of the heart, is usually the first investigation carried out. A chest X-ray may be taken next, which reveals the overall size of the newborn's heart. The x-ray also gives an idea of the blood flow to the lungs and confirms a chest infection. Echocardiography, in which reflected sound waves are used to capture the motion of the heart, together with associated Doppler studies are the main methods of detecting a PDA. The exact size of the PDA and its flow characteristics are determined. Supporting blood investigations are also required.

Treatment
Newborns without adverse symptoms may simply be monitored as outpatients, while symptomatic PDA can be treated with both surgical and non-surgical methods.
Surgically, the PDA may be closed by opening through the left chest to tie it off using sutures or clips. It may also be tied or clipped and then divided completely.

Non-surgical methods involve the use of drugs or minimally invasive percutaneous procedures.
Because Prostaglandin E2 is responsible for keeping the ductus patent, inhibitors of prostaglandin synthesis such as indomethacin, have been used to help close a PDA. This is an especially viable alternative for premature infants.
More recently, PDAs can be closed by percutaneous interventional methods. These methods permit closure without formal surgery. Using the big artery or vein of the groin, a platinum coil can be deployed via a catheter, which induces the formation of a clot to block the ductus.. Alternatively, a PDA occluder device composed of nitinol mesh, is deployed from the pulmonary artery through the PDA.
Prognosis
Prognosis is excellent. Risk of surgery or percutaneous intervention is very minimal indeed. Once ligated or occluded, the child is expected to live a normal life.
By Dr. Kow Entsua-Mensah