Atriyal Septal Defekt

The heart contains two atria, right and left, and two ventricles. An atrial septal defect (ASD) is a congenital defect: an opening in the atrial septum, the wall that separates the right atrium from the left atrium.

Types of ASD

• Ostium secundum ASD – 80% of all ASDs; located in the region of the fossa ovalis and its surroundings. This is the type of ASD that is suitable for closure without surgery.
• Ostium primum ASD – 15%; also termed partial atrioventricular septal defect (AVSD) or partial atrioventricular (AV) canal defect; located near the crux of the heart. The AV valves are typically malformed, resulting in varying degrees of regurgitation.
• Superior sinus venosus defect – 5%; located near the entry of the superior vena cava (SVC); associated with partial or complete connection of the right pulmonary veins to the SVC or the right atrium (RA).
• Inferior sinus venosus defect – less than 1%; located near the entry of the inferior vena cava (IVC).
• Unroofed coronary sinus – less than 1%; characterized by partial or complete absence of separation from the left atrium (LA).

The left atrium is the chamber in which oxygenated blood returning from the lungs collects, whereas the right atrium is the main structure that receives deoxygenated blood from the body. When a defect is present in the atrial septum separating the two atria, part of the oxygenated blood arriving from the lungs crosses the defect and mixes with the deoxygenated blood in the right atrium. The volume of this shunt is directly proportional to the size of the defect.

When the ASD is large in particular, blood that has already been oxygenated but has crossed into the right atrium through the defect is pumped to the lungs to be oxygenated once again, and this places an additional workload on the lungs. If the defect remains unrecognized and stays open, it may lead in later life to enlargement of the right heart chambers, severe heart failure and pulmonary hypertension. As pulmonary vascular pressure and resistance rise, the shunt that was initially left-to-right may reverse and become right-to-left, so that deoxygenated rather than oxygenated blood is delivered to the body. Paradoxical embolism, severe arrhythmias and death in the patient’s fifties may also result.

As noted above, the most common ASD in the general population is the ostium secundum type, which accounts for 80% of cases. In the past, the only treatment for an ASD was open surgery, in which a patch was sutured over the defect. Today, in children and in adults alike, we are able to close ostium secundum ASDs by the percutaneous transcatheter route in the catheterization laboratory, using dedicated closure devices and without open surgery. For the other, less common types of ASD we continue to recommend surgical repair.

How is the diagnosis made?

In the past, the diagnosis of an ASD rested on physical examination and electrocardiographic findings alone. Today the diagnosis can be established readily with echocardiography, a highly advanced form of ultrasound imaging. Transthoracic echocardiography, performed simply by placing an ultrasound probe on the front of the chest, provides the probable diagnosis; the definitive diagnosis is made by transesophageal echocardiography (TEE), in which the probe is swallowed and positioned in the esophagus.

Once color Doppler flow across the atrial septum has been demonstrated on two-dimensional TEE (2D-TEE), real-time three-dimensional TEE (3D-TEE) usually confirms the definitive diagnosis. It also shows the location and the number of the defects and whether the rims of the defect are adequate to support a closure device, which allows us to decide whether the defect can be closed without surgery and to determine the number and the size of the devices to be used. TEE is today accepted as the gold standard both for establishing the diagnosis and for selecting the treatment method in ASD. In our clinic, 3D-TEE is performed in every patient in whom an atrial septal defect is suspected.

How is percutaneous transcatheter closure performed?

The veins of the groin return deoxygenated blood from the legs and the lower body to the right heart through the large vein known as the inferior vena cava. In the catheterization laboratory, the femoral vein is punctured with a fine needle and a sheath is placed into the vein.

Through this sheath, atraumatic guidewires and catheters (fine tubes) that do not injure the vessel are advanced into the right atrium, then across the defect between the two atria into the left atrium, and onward into the pulmonary veins that drain into it.

A support guidewire is positioned within a pulmonary vein, and a balloon is advanced over this wire to the site of the defect. The balloon is inflated to perform balloon sizing of the defect and is then withdrawn. The delivery system that holds and carries the closure device is advanced over the support wire left in the pulmonary vein and is positioned in the left atrium.

Under two- or three-dimensional echocardiographic guidance, the closure device – which may be pictured as a double-disc occluder – is deployed: its left disc is opened in the left atrium, its waist segment sits exactly within the defect, and its right disc is opened in the right atrium, so that the defect is closed completely.

Once a dedicated maneuver has confirmed that the device is seated precisely across the defect, it is released from the delivery cable and left in place. Within approximately 6 months to 1 year after the procedure, the surfaces of the device are covered spontaneously by endothelium, the body’s own lining tissue – a process known as endothelialization. Angiographic images and a video recording of the transcatheter ASD closure procedures performed in our clinic are presented below.

Does the transcatheter method or the closure device carry any risks?

Compared with open heart surgery, the complications of this treatment are far less frequent. The complications that may arise during open surgery – major bleeding, the complications of prolonged anesthesia, and injury to vessels and cardiac structures – are not commonly encountered with the transcatheter approach. Because the chest is not opened and access is obtained with no more than a small needle puncture and a sheath in the groin, the cosmetic advantage of the transcatheter procedure is also clear.

Most of these devices are manufactured from nitinol, a special shape-memory metal alloy. No side effect of the devices has been reported other than in patients with nickel allergy, and platinum-coated closure devices are also available to us. However, in procedures performed by operators without dedicated training and experience in this field, the device may dislodge and embolize into the cardiac chambers if the defect has not been measured appropriately or an appropriate device has not been selected. Even in that event, dedicated snares have been developed with which a device can be retrieved from within the body, and the device is captured with these snares and removed without difficulty. Bleeding, air embolism, and pericardial effusion or tamponade (a collection of blood around the heart) may also occur during the procedure, although only very rarely; such complications are extremely infrequent compared with open heart surgery.

For these reasons, both the American Heart Association and the European Society of Cardiology recommend transcatheter closure as the first-line treatment option for the closure of an atrial septal defect.

Images of the closure procedure