The GDC coil system was developed by Target Therapeutics, Fremont California. The device provides the interventionalist the ability to insert a coil into an aneurysm or blood vessel, assess its position, and withdraw it if the result is less than satisfactory. Other coil systems are not detachable but rather pushed or injected into position. Once these coils leave the catheter, they are difficult if not impossible to retrieve.

In order to treat an aneurysm with GDC coils the interventionalist must first place a micro catheter into the aneurysm fundus. Once properly positioned a coil is inserted through the catheter and into the aneurysm. If the operator does not like the coils configuration he or she can remove it and reposition it or choose another size coil.

The GDC system consists of a soft platinum coil soldered to a stainless steel delivery wire. When the coil is properly positioned within the fundus a 1 mA current is applied to the delivery wire. The current dissolves the stainless steel delivery wire proximal to the platinum coil by means of electrolysis. At the same time, the positively charged platinum theoretically attracts the negatively charged blood elements such as white and red blood cells, platelets, and fibrinogen thus inducing intra-aneurysmal thrombosis. Once electrolysis occurs the delivery wire can be removed leaving the coil in place. Another coil can now be introduced into the fundus. The process is continued until the aneurysm is densely packed with platinum and no longer opacifies during diagnostic contrast injections.

The mechanism by which GDC coils occlude aneurysms is still debated. We have made observations at surgery on recently coiled aneurysms that lead us to question the theory that the positive charge within the aneurysm during electrolysis induces significant thrombus formation. Coils likely provide immediate protection against rehemmorhage by reducing blood pulsations within the fundus, and sealing the weak portion of the wall or hole. Eventually organized thrombus does form within the aneurysm and the aneurysm is excluded from the parent vessel by the formation of an endothelialized layer of connective tissue that covers the neck's ostium. This has been demonstrated in experimental dog models and in human autopsy studies.

While the indications for the GDC coils is continually expanding as interventionalists become more skillful in their placement, they tend to be most successful in cases of aneurysms with small necks or necks that are smaller in diameter than the maximal aneurysm diameter and aneurysms without significant intrafundal thrombus. Nevertheless, decisions concerning their applications are made on a case by case basis and few dogmatic rules exist.

Basilar tip aneurysm pre-embolization (L) and post-embolization (R)
with GDC coils.

Outcomes

In 1995 the USA Multicenter GDC Study Groups results with 753 aneurysms treated in 715 patients. Complete occlusion of small aneurysms with small necks occurred in 62% of cases while complete occlusion in small aneurysms with wide necks was 33%. Large aneurysms with small necks and giant aneurysms with thrombus each had a 37% occlusion rate and giant aneurysms alone had 35% occlusion rates. Technical complications occurred in 11% of cases and included aneurysm perforation (1.5%), parent artery narrowing (0.5%), parent artery occlusion (3.8%), embolization (3.7%), and coil migration (1.1%). Complications that had permanent clinical implications, however, occurred in only 4.4% of the cases. The procedure related mortality rate was 1.12% and the overall mortality rate for the entire study population was 5.2%. The post embolization aneurysm hemorrhage rate was 1.26%. Aneurysm recanalization occurred in 7.7% of small aneurysms, 15% of large aneurysms, 29% of giant aneurysms, and 31% of giant/partially thrombosed lesions. Since 1994, results have improved as newer sized and less traumatic coils were introduced into the market. These advances allow for denser fundus packing and improved obliteration rates with reduction in delayed recanalization.

Conclusion

Aneurysm embolization using the GDC system offers an alternative to traditional surgical clipping in selected cases. Decisions must be made on a case by case basis. At our institution considerations include patient age, medical condition, aneurysm geometry and location. While the particular surgeon's and interventionalist's skills are not as relevant at institutions where both disciplines are practiced at the highest level, such considerations are relevant where discrepancies exist.