The normal heart
The normal heart has a right and left atrium (filling chambers) and a right and left ventricle (pumping chambers). The valves of the heart are the aortic valve, mitral valve (sometimes referred to as bicuspid), pulmonary valve and tricuspid valve. These valves are one-way "gates" that allow blood to flow into an area but not to flow back into the area it has just left.
The normal circulation of the heart
Blood returns to the heart from the body via two large veins. The upper body's blood returns via the superior vena cava, and the lower body's blood returns via the inferior vena cava. Both of these vessels return blood to the right atrium.
From the right atrium, blood passes through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary valve into the pulmonary artery, and right and left arteries feed the blood into the right and left lungs.
The lungs remove carbon dioxide from and add oxygen to the blood. The lungs normally have a low pressure/low resistance, so the blood flows easily throughout.
Next, the blood returns to the heart via the pulmonary veins into the left atrium. From the left atrium, the blood passes through the mitral (or bicuspid) valve into the left ventricle.
The left ventricle is the powerhouse or muscle of the heart. The left ventricle is very strong, thick and muscular to pump the blood out through the aortic valve into the aorta and, ultimately, to the rest of the body.
Normally there is no direct communication between the right and left side of the heart. The right side handles blood that does not carry oxygen. The left side handles blood that carries oxygen.
The normal circulation of a fetus while in the uterus follows a slightly different path than after a baby is born. While in the uterus, the placenta acts as the lungs, therefore less blood passes into the actual fetal lungs. There are two structures within a fetal heart that allow this "bypass." One is the patent ductus arteriosus, or PDA. The PDA allows blood mixing between the pulmonary artery and the aorta, as it is a passageway between these two major vessels. The other is the patent foramen ovale, or PFO. The PFO is a hole between the two atriums. It allows mixing of blood between the right and left atrium. The PDA and PFO allow a right-to-left flow, which directs blood away from the lungs and directs this more-oxygenated blood to travel to the body.
The pressure in the lungs of a fetus is higher than that in the body. This increased pressure also encourages the right-to-left flow. After a baby is born, the pressure in the lungs decreases as the vessels in the lungs begin to relax. The pressure in the body increases after birth. This change in the pressure allows more blood to flow into the lungs. These changes in pressure are what cause the PDA and PFO to eventually close. The final closure usually takes several days.
Keeping the PDA open
Some congenital heart diseases are dependent upon fetal circulation remaining intact and the PDA remaining open to allow the mixing of oxygenated with unoxygenated blood. To keep the PDA open, we can give prostaglandins (PGE).
This medication can cause negative side effects. However, the benefit of the medication far outweighs the risks of the side effects. Some side effects of PGE may include:
- Apnea (long delay in breathing)
- Thickened secretions
If your baby should develop a fever, we will draw blood to look for an infection because fever can also be a sign of infection. Once the blood has been drawn, we will start antibiotics as a precaution.
If apnea becomes significant, there are a couple things that help. The first thing to try is the medication caffeine. This will stimulate your baby and encourage him or her to breathe more regularly. If caffeine is not enough to control the apnea and the heart rate is being affected, the next treatment would be intubation and ventilation.
Intubation means a special tube is placed in your baby's windpipe to help with breathing. This tube is called an endotracheal tube or ETT. A ventilator would be attached to this tube to help the baby breathe. The ETT triggers production of secretions, so the nursing staff will suction the tube to keep it open because thickened secretions is another side effect of prostaglandins.
Keeping the PFO open
Some congenital heart diseases are dependent on the fetal circulation remaining intact and the PFO remaining open to provide mixing of oxygenated with unoxygenated blood. To make sure the PFO remains open in babies with these conditions, surgeons will perform a balloon atrial septostomy. This is a surgical procedure done in the NICU. It would be done shortly after birth.
While observing via ultrasound, the surgeon would insert a special catheter, or tube, into a major vessel in the groin area. Then he or she would thread the catheter through the vessel to the heart via the inferior vena cava.
Then the surgeon would pass the catheter through the PFO and inflate a balloon. This inflated balloon is pulled back through the PFO, which will "tear" open the PFO and make it larger. This larger hole allows for more mixing between the two sides of the heart.