Endovascular cryotreatment catheter

Abstract

A catheter is attached to an elongated catheter body adapted for endovascular insertion with a balloon assembly at its distal end. Coolant injected through the catheter body may, in different embodiments, directly cool tissue contacting the balloon, or may cool a separate internal chamber. In the first case, the coolant also inflates the balloon, and spent coolant is returned to the handle via a return passage extending through the body of the catheter. A valve may regulate back pressure in the return passage to coordinate the flow of coolant into and out of the balloon so as to both inflate the balloon and achieve cryogenic cooling at the surface of the balloon. The coolant is biologically safe, and may be liquid carbon dioxide. Plural balloons may be provided adjacent the cooling segment, and one balloon may be shaped to treat the ostium of a vessel. Preferably, thermal conductivity of the balloon wall is enhanced by inclusion of thermally conductive material, such as metal, which may be introduced as a component of a composite elastomer material, or as a patterned metal layer that defines a pattern of thermally conductive treatment regions of the balloon surface. Patterns formed by printing, lithography or other means with copper, silver or other highly thermally conductive material enhance through-conduction characteristics of the wall so icing preferentially occurs to stimulate tissue destruction and vascular regeneration. Suitable patterns include spirals, dots, arrays of separated segments, or meandering curves which allow expansion of the balloon body without introducing delamination, localized stress cracking or separation of the balloon material. The conductive patterns may include patterns such as waffle-iron or other arrays of small lesions that are effective to treat the endovascular wall. When separate media are used for cooling and for balloon expansion, the cooling chamber may have a large diameter, and the balloon may form a thin shell or cuff. In that case, the balloon may be quickly inflated with a medium such as a saline to provide a quickly deployed and compliant contact structure of excellent conductivity.