A medical device includes a coil having a longitudinal axis and a radial axis orthogonal to the longitudinal axis, formed from a wire. The wire includes a cross-section with a centroid, a moment of inertia with respect to an axis running through the centroid and parallel to the longitudinal axis of the coil, and a moment of inertia with respect to an axis running through the centroid and parallel to the radial axis of the coil. The moment of inertia with respect to an axis running through the centroid and parallel to the longitudinal axis of the coil is greater than the moment of inertia with respect to an axis running through the centroid and parallel to the radial axis of the coil.