For a perspective, in the normal heart, blood flowing in the right sided chambers (atrium and ventricle) is completely separated from the left sided chambers by the atrial septum. When there is a hole in this "wall", blood from the left atrium flows through the hole into the right side. Left to right shunting (blood flow) occurs because the pressure of blood in the left atrium is higher than in the right, and we know, any fluid, including blood, will flow from a place with high pressure to one with a lower pressure.
There can be irregularity in the rhythm of the heart. Since it handles a large volume of blood, the right atrium enlarges. This causes a disturbance in the heart's electrical activity, causing it to beat faster - a disorder called ATRIAL FIBRILLATION. All of these problems are common in LARGE ASD's.
Smaller ASD's are less dangerous than the large ones. But there is one other problem which may occur in both large and small ASD's - PARADOXICAL EMBOLISM.
Paradoxical embolism happens as blood flow in the veins is normally slow and sluggish, and some small clots may form. CLOTS are small pieces of hardened blood. In a normal person, these clots may pass from the veins, through the heart and into the lungs. Here, they are "filtered" and prevented from entering the ARTERIES along with the purified blood. When there is an ASD, however, the clot, on entering the right atrium, may pass across the ASD into the left atrium. Along with the "pure" blood, it can then pass into the arteries, and from here to the brain. In the brain, it may block a blood vessel, preventing blood flow to a part of the brain. This causes a STROKE. A stroke is an injury to the brain. It may cause weakness or paralysis of an arm or leg, or inability to speak or unconsciousness. It can be a very serious problem, sometimes. It's because of this risk of stroke that doctors advise that even small ASD's be closed, by surgery or other methods.
"Recently, some alternatives to surgery have emerged. These are experimental", in the sense that their effectiveness in the long run has not been proved. The advantages with these new procedures is that they are less painful, make hospital stay shorter, and avoid a scar of a surgical incision.
One of these is TRANS-CATHETER CLOSURE. A catheter is a special thin tube passed into the blood vessels through a small "needle-stick" in the groin or forearm. Through this catheter, a special device similar to an umbrella - called a "clamshell device" - is passed into the heart. The "umbrella" device is pushed across the ASD and opened. The hole is now blocked by the umbrella, which is then fixed in place.
Another method makes use of the idea of MINIMALLY INVASIVE HEART SURGERY. Through 3 or 4 small "puncture" holes in the chest, specially designed instruments are passed into the chest and used to repair the ASD".