a coil formed of a wire having a primary configuration in a constrained condition, the primary configuration having a proximal end and a distal end;

wherein the coil assumes a secondary configuration in a relaxed, unconstrained condition, the secondary configuration comprising:

a primary portion comprising a plurality of primary loops, each of the primary loops comprising a winding of the wire forming a closed loop of greater than 360º, the primary loops including a distal primary loop which is a distal-most loop of the primary loops, the distal primary loop having a proximal end and a distal end and a perimeter length from the proximal end to the distal end, the distal primary loop having turns lying in a first plane and planes substantially parallel to said first plane; and

a distal anchoring loop connected to the distal end of the distal primary loop, the distal anchoring loop having a substantially triangular shape, the distal anchoring loop having an overall length of 25% to 75% of the perimeter length of the distal primary loop, the distal anchoring loop positioned within a projection of the distal primary loop.