Importance

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Abstract

In an endocardial, active fixation, screw-in lead of the type having a fixation helix adapted to be rotated in a first, advancement direction out of an electrode head chamber and into cardiac tissue by rotation of a lead connector end and attached lead conductor with respect to an insulating sheath in the first direction and retracted into the chamber by rotation of the lead connector in the opposite, retraction direction, a retraction stop mechanism for preventing over rotation of the helix in the retraction direction. The rotational motion of the lead conductor is transmitted to the helix by a connecting assembly and is translated into axial advancement and retraction of the helix by a guide cooperating with the helix turns. A retraction stop mechanism stops rotation of the helix in the retraction direction upon full retraction of the helix into the chamber and allows rotation of helix in the advancement direction. The retraction stop mechanism includes a fixed stop formed of a plurality of fixed cam and axial stop surfaces surrounding a proximal end bore of the chamber through which the lead conductor passes and a movable stop formed in the connecting mechanism of a like plurality of rotatable cam and axial stop surfaces aligned to face the fixed cam and axial stop surfaces adapted to engage in a locked relation of the stop surfaces upon full retraction of the fixation device into the chamber.

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First Claim