Flexible intra-vascular aneurysm treatment stent

An intra-vascular aneurysm-treatment stent and a method for lowering pressure within an aneurysm bubble in a blood vessel. A stent coil is insertable into a blood vessel, the coil made of a material sufficiently flexible to move around curves, loops, and corners in the blood vessel. Selected portions of the stent coil, in cross-section, have substantially convex outer surfaces, and either substantially flat, or substantially concave, inner surfaces, plus upstream leading edges and downstream trailing edges. The stent coil is positioned in the blood vessel with selected stent coil portions proximate an opening into either a saccular aneurysm or a fusiform aneurysm. Blood in the lumen of the blood vessel flows past the leading edges and both over the convex outer surfaces, and under the either flat or concave inner surfaces. A portion of the blood inside the aneurysm becomes entrained with the blood flowing over the outer surfaces. At the trailing edges, the converging blood flows create eddies which result in dPs proximate the opening into the aneurysm. The dPs draw more blood out of the aneurysm and into the lumen, reducing pressure in the aneurysm.

FIELD OF THE INVENTION

The present invention relates to flexible intra-vascular stents and to flow diverters and modifiers, and more particularly to flexible wire intra-vascular stents for treatment of aneurysms in the carotid and vertebral arteries and branch blood vessels extending from the carotid and vertebral arteries into the brain.

BACKGROUND OF THE INVENTION

An aneurysm is a circumscribed dilation of a blood vessel, or cardiac chamber, in direct communication with its respective lumen, usually resulting from an acquired or congenital weakness of the wall of the blood vessel, or chamber. An aneurysm occurs when a part of the artery, other blood vessel, or cardiac chamber, swells, either due to damage to the wall or a weakness in the wall. As blood pressure builds up with each heartbeat, the wall balloons out at its weakest point, forming an aneurysm bubble. The bubble tends to fill with blood, as blood flowing through the lumen is partly diverted through the opening into the aneurysm. As the aneurysm grows, in addition to causing pain and other complications, a risk of rupture of the bubble increases. Rupture of an aneurysm in a carotid or vertebral artery in the neck, or in a branch blood vessel extending from the carotid or vertebral artery into the brain can cause a hemorrhage or stroke, which can be at best severely debilitating, and at worst deadly. For perspective, aneurysmal subarachnoid hemorrhage (SAH) occurs about 30,000 times annually in the U.S. Of these, between ⅓ and ½ of those so afflicted will not survive the trip to the hospital.

FIGS. 1 and 2depict various configurations of aneurysms. In each drawing, a generally tubular blood vessel10comprises an inner peripheral wall12, and an outer peripheral wall14. The inner peripheral wall12defines a lumen16through which blood17flows. A weak point in the wall12has an opening, called a neck,18. A portion of the blood flow17is diverted from the lumen16through the neck18to form and maintain a saccular aneurysm20. A saccular aneurysm20is shown inFIG. 1.FIG. 2shows a fusiform aneurysm20′. If the arterial wall weakness is focal, i.e., it does not extend all the way around the artery, the aneurysm is most likely to be saccular. If the weakness is circumferential, it will more likely be fusiform. In the saccular aneurysm20, its communication with the lumen16is though the aneurysm neck18. The fusiform aneurysm20′ by definition does not have a neck.

FIGS. 3A-3Bdepict a conventional attempt to treat aneurysms.FIG. 3Adepicts a wire stent30, installed in a blood vessel10with a fusiform aneurysm bubble20′. Referring toFIG. 3B, a raised strut portion32of the wire stent30depicted inFIG. 3Ais provided against the blood vessel inner peripheral wall12immediately upstream of the aneurysm neck18. It is intended that an increase in velocity of the blood flow17over the raised strut portion32will create a pressure drop (dP) at a trailing edge thereof to cause blood17in the saccular aneurysm bubble20to flow back into the lumen16of the blood vessel10.

FIG. 4explains why this conventional attempt to treat aneurysms is sometimes ineffective, even harmful. At the trailing edge of the raised strut portion32, as in the case of a trailing edge of an airplane, the flow of fluid (in this case blood17) flows across the apex of the wing and down past the trailing edge. The configuration and positioning of the strut32inFIG. 3B, however, rather than creating a pressure drop (dP), drawing blood17out of the saccular aneurysm20and into the lumen16, instead directs more blood flow17at the trailing edge into the saccular aneurysm20, thereby achieving an effect opposite of that which was intended. In fact, it can have the effect of directing high-velocity blood to strike the inflow zone of the aneurysm, a fragile, delicate part.

SUMMARY OF THE INVENTION

In accordance with the invention, a flexible intra-vascular catheter for treating an aneurysm includes an expanding coil insertable into a blood vessel, including a curving blood vessel, with coil portions positioned proximate an opening in the blood vessel wall into an aneurysm bubble, the coil portions are configured to receive blood flow in the blood vessel on their upstream side/leading edge and re-direct the blood flow back toward a central lumen of the blood vessel, thereby creating an eddy effect proximate the downstream side/trailing edge of the respective coil portions, creating a pressure drop (dP) which draws blood in the aneurysm bubble back into the lumen of the blood vessel, and collapsing the bubble, or at least substantially decreasing pressure in it.

In one embodiment, the coil portions have an arcuate upper surface proximate the inner blood vessel wall and facing the opening into the aneurysm bubble, and generally flat inner surfaces facing the lumen of the blood vessel. Blood flow on the upstream side/leading edge of each coil portion travels over and across the arcuate outer surface and is directed back down toward the lumen of the blood vessel. Proximate the opening into the aneurysm bubble, on the downstream side/trailing edge of each coil portion, this downward flow converges with the flow along the flat inner surfaces, creating an eddy, with a corresponding pressure drop (dP). The dP draws blood out of the aneurysm bubble and back into the lumen of the blood vessel, thereby collapsing the bubble, or decreasing pressure in it.

In another embodiment, the coil portions have convex outer surfaces proximate the inner wall of the blood vessel and facing the opening into the aneurysm bubble, and concave inner surfaces facing the lumen of the blood vessel. Blood flow from upstream flows over and across each convex outer surface, and also flows into each successive concave inner surface at its respective upstream/leading edge portion, and out of the concave inner face at its respective trailing edge, being redirected back toward the lumen of the blood vessel. The converging blood flows at each respective downstream/trailing edge portion, create an eddy at each downstream/trailing edge portion. Once again, each eddy creates a corresponding pressure drop dP. This dP draws blood out of the aneurysm bubble and toward the lumen of the blood vessel, thereby collapsing the bubble, or decreasing pressure in it.

DESCRIPTION OF THE EMBODIMENTS

As broadly embodied herein, referring toFIGS. 5-8B, a flexible coil intra-vascular stent40/60in accordance with the invention comprises a self-expanding or balloon-expanded generally tubular stent, flexible for going around curves, loops, and corners in blood vessels, particularly carotid or vertebral arteries in the neck, and branch blood vessels leading off the carotid arteries into the brain. It is preferred that the stent40/60be made of flexible wire, which in a preferred embodiment is formed of a memory metal such as Nitinol. In another preferred embodiment the stent40/60is formed of a non-memory metal, e.g., stainless steel.

Preferred configurations and operation of the flexible intra-vascular wire stent40/60in accordance with the invention is explained with respect toFIGS. 6A-7C.

As broadly embodied inFIG. 6A, a first embodiment of a flexible intra-vascular wire coil stent40is positioned in a generally tubular blood vessel10, the blood vessel10including a peripheral inner wall12, a peripheral outer wall14, a central lumen16, and an aneurysm neck18in the wall12, allowing blood17to flow from the lumen16into an aneurysm bubble20.

Flexible intra-vascular wire coil stent40includes a plurality of sequential coil portions42, depicted in cross-section inFIGS. 6A and 6B. As depicted inFIGS. 6A and 6B, each coil portion42includes an upstream leading edge44, an outer surface46, a downstream trailing edge48, and an inner surface50. Each outer surface46defines an arc between the leading edge44and the trailing edge48, whereas the inner surface50is substantially flat. Moreover, whereas several of the outer surfaces46face the inner wall12of the blood vessel10, and the inner surfaces50all face the lumen16of the blood vessel12, selected coil portions42′ have outer portions46′ facing the neck18into the aneurysm20.

In operation, blood flow17in the lumen16will flow past the generally flat inner surfaces50, with some blood flow17being diverted by the leading edges44′ of the selected coil portions42′ facing the neck18, across the outer surfaces46′, past the trailing edges48′ and back towards the lumen16. ComparingFIG. 6AtoFIG. 4, it can be seen that rather than directing blood flow into the aneurysm20, as was the case with the conventional art, selected coil portions42′ direct blood flow away from the aneurysm20and toward the lumen16. Some of the blood17in the aneurysm20will become entrained in the blood flow17over the outer surfaces46′ and be directed back into the lumen16. More significantly, the converging blood flow paths17at the trailing edges48′ of the selected coil portions42′ create eddies52proximate the trailing edges48′ of the selected coil portions42′. Each eddy52results in a pressure drop dP between pressure at the respective outer surface46′ and the respective trailing edge48′. The dP generated at the respective trailing edges48′ will draw blood17out of the aneurysm20and back into the blood flow17in the lumen16, thereby collapsing the bubble20, or at least decreasing it.

In the second embodiment, as depicted inFIGS. 7A and 7B, each coil portion62of a flexible wire coil intra-vascular stent60includes an upstream leading edge64, an outer surface66, a downstream trailing edge68, and an inner surface70. In the second embodiment ofFIGS. 7A and 7B, the outer surface66defines a convex surface between the leading edge64and the trailing edge68, whereas the inner surface70defines a concave surface between the leading edge64and the trailing edge68. Moreover, whereas several of the outer surfaces66face the inner wall12of the blood vessel10, and the inner surfaces70all face the lumen16of the blood vessel10, selected coil portions62′ have outer surfaces66′ facing the neck18into the aneurysm20.

In operation, blood flow17in the lumen16will flow into and out of the concave inner surfaces70, with some blood flow17being diverted by the leading edges64′ of the selected coil portions62′ proximate the neck18, across the convex outer surfaces66′, past the trailing edges68′ and back towards the lumen16. As discussed above with respect to the embodiment ofFIG. 6A, some of the blood17in the aneurysm20will become entrained in the blood flow17passing across the outer surfaces66′ and will flow back into the lumen16. More significantly, the converging blood flow paths17at the selected trailing edges68′ create eddies72proximate the trailing edges68′ of the selected coil portions62′, each eddy72resulting in a pressure drop dP between pressure at the respective convex outer surface66′ and the respective trailing edge68′. In the location of the selected coil portions62′, the dP generated at the respective trailing edges68′ will draw blood17out of the aneurysm20and back into the blood flow17in the lumen16, thereby collapsing the bubble20, or at least decreasing it.