In the rapidly advancing field of neurointervention, precision and stability are paramount. Among the array of sophisticated tools used by neurointerventionists, the Distal Access Catheter(DAC) has become an indispensable workhorse. It plays a critical role in enabling safe and effective treatments for conditions like ischemic stroke, cerebral aneurysms, and arteriovenous malformations(AVMs).
What is a Distal Access Catheter?
A Distal Access Catheter is an intermediate-length, large-bore catheter designed to provide stable support deep within the neurovasculature. It acts as a stable "platform" or "rail" through which microcatheters, stent retrievers, coils, and other devices are delivered to the target lesion.
Think of it as an extension of the guiding catheter. While the guiding catheter secures a stable position in the proximal great vessels (e.g., the internal carotid or vertebral artery), the DAC is advanced further distally, navigating the tortuous curves of the skull base to reach the intracranial vessels (e.g., the M1 segment of the Middle Cerebral Artery or the basilar artery).
Key Characteristics and Design Features
The effectiveness of a DAC hinges on a carefully balanced set of engineering properties:
1. Trackability and Pushability: A DAC must be flexible enough to navigate tight, tortuous anatomy without causing vasospasm or dissection (trackability), while also being stiff enough to be pushed from its proximal end without kinking (pushability). This is often achieved through complex, multi-layer braided designs.
2. Distal Flexibility with Proximal Support: The catheter tip is typically very soft and flexible to minimize trauma to delicate vessels. This flexibility gradually transitions to a stiffer, more supportive shaft along its length.
3. Large Inner Diameter (Luminal Size): A large inner diameter (or bore) is crucial. It allows for:
A. The passage of various microcatheters and devices.
B. Efficient aspiration during thrombectomy procedures (ADAPT technique).
C. Contrast injection for roadmapping and angiography.
4. Hydrophilic Coating: Most DACs have a hydrophilic coating on their outer surface, which becomes extremely slippery when wet. This significantly reduces friction during navigation and advancement.
5. Kink Resistance: The internal braiding prevents the catheter from collapsing or kinking when navigating sharp bends, ensuring an uninterrupted lumen for device delivery and aspiration.
How is a DAC Used? The "Tri-Axial" System
1. Sheath: A short introducer sheath placed in the femoral or radial artery provides initial vascular access.
2. Guiding Catheter: A long guiding catheter is advanced over a wire and positioned in a proximal great vessel (e.g., the cervical Internal Carotid Artery).
3. Distal Access Catheter (DAC): The DAC is then advanced over a microcatheter/microwire combination ("co-axial" technique) deep into the intracranial circulation. Once the DAC is in a stable position, the microcatheter can be advanced through it to the precise target.
This system creates a stable "highway" from the access point to the lesion, minimizing friction and maximizing control.