This invention relates to a percutaneous transcatheter delivery system for a medical device, particularly an occlusion device, which allows a physician to deliver the device and observe its position without the tissue contortion caused by a stiff catheter or delivery device while the device remains tethered to the system. 
Current medical technology provides for the percutaneous implantation of medical devices, delivered through a catheter, which gives individuals an option to traditional surgery in a variety of medical situations. 
Generally this procedure begins by inserting a guidewire into a major blood vessel and advancing it through the body to the treatment location.  Next, a catheter is advanced over the guidewire until it reaches the treatment location, so that the guidewire can then be removed.  A medical device is then attached to a delivery device (also called a delivery forceps) which is used to advance the medical device through the catheter to the treatment location.  Once the medical device is properly positioned it is released from the delivery device. 
For example, permanently repairing cardiac apertures in adults and children normally requires open heart surgery which is a risky, expensive, and painful procedure.  To avoid the risks and discomfort associated with open heart surgery, modern occlusion devices have been developed that are small, implantable devices capable of being delivered to the heart through a catheter to occlude the aperture.  This procedure is performed in a cardiac cathlab and avoids the risks and pain associated with open heart surgery. 
To deliver an occlusion device, a guidewire and a catheter are inserted into a major blood vessel and advanced, through the body, to the treatment site.  To allow for proper control and maneuvering, each item of the delivery system, including the guidewire, catheter, and delivery device, must be sufficiently stiff to maneuver to the desired location despite resistance caused by contact with the surface of the vasculature and turns in the body.  At the same time, guidewires, catheters, and delivery devices must also be flexible enough to navigate the numerous turns in the body's vasculature.  The necessary stiffness of the guidewire, catheter, and delivery device may distort the tissue on the way to and at the site of the defect, making it difficult to optimally position the occlusion device. 
One difficulty in implanting occlusion devices is ensuring that the occluder conforms to the contours of the defect.  Poor conformation to the defect results in poor seating of the occlusion device which decreases the ability of the occlusion device to occlude the defect.  Ensuring the proper seating of an occlusion device once it has been deployed poses a continuing challenge given the uneven topography of the vascular and septal walls of each patient's heart.  The challenge in correctly positioning an occluder so that it conforms to the uneven topography is compounded by the fact that the contours of each defect in each individual patient are unique. 
Distortion of tissue surrounding the defect caused by the stiffness of the guidewire, catheter, or delivery device adds to the seating challenge.  If the surrounding tissue is distorted by the catheter, it is difficult to determine whether the occlusion device will be properly seated once the catheter is removed and the tissue returns to its normal state.  If the occlusion device is not seated properly, it may have to be retrieved and re-deployed.  Both doctors and patients prefer to avoid retrieval and re-deployment because it causes additional expense and longer procedure time.  Worse yet, if the occlusion device embolizes or is improperly deployed, retrieval of the device may require open heart surgery. 
Releasing the occlusion device from the delivery device also poses challenges to treatment.  Currently, a variety of release mechanisms are used to release an occlusion device from the delivery device.  Some release mechanisms work by pulling or twisting a handle of the delivery device in order to release the occlusion device.  This pulling on or twisting of the delivery device may make the delivery device very stiff due to the tension created by the release mechanism.  The tension may add to tissue contortion. 
One example of a current release system is a delivery device with a small jaw on the end which grasps the occlusion device.  The small jaw is connected to a long wire.  Pulling on the wire opens the jaw and releases the occlusion device.  A drawback to this design is the tension that is created when the wire is pulled.  When the wire must be pulled to release the occlusion device, the delivery device becomes very stiff, particularly at the end of the device closest to the occlusion device.  This stiffness near the occlusion device distorts the tissue at the location where the occlusion device is to be deployed.  As a result, it is difficult to judge whether or not the occlusion device is properly placed, or whether or not it will remain properly placed once released from the device and the tissue returns to normal. 
Thus, there is a need in the art for a delivery system that allows physicians to observe the placement of an internal medical device without tissue contortion that also allows for easy release and retrieval.