Drive assembly for facilitating deployment of an implantable medical device

1. An introducer assembly including a carrier element for carrying an implantable medical device, the carrier element including a distal end at which an implantable medical device is carried and a proximal end;

a sheath overlying the carrier element and being retractable so as to expose the distal end of the carrier element, the sheath including a distal end and a proximal end;

a handle assembly at the proximal end of the carrier element and sheath, the handle assembly including first and second handle portions, attached respectively to the proximal ends of the sheath and the carrier element, the handle assembly being manually operable to retract the sheath by pulling the first and second handle portions towards one another;

and a drive assembly coupled between the first and second handle portions and operable to provide a retraction assistance force pulling the first and second handle portions together; wherein the drive assembly includes a brake element configured to prevent the drive assembly from providing the retraction assistance force when there is no manual actuation;

a yoke fitted over the sheath;

a sprung element attached to the yoke;

a brake release element attached to the yoke and releasable engaged to the brake element;

the sprung element imparting a pulling force on the yoke, thereby placing the yoke in a tilted position relative to the sheath; and

wherein when the yoke is in the tilted position, the brake release element engages the brake element so that the brake element prevents the drive assembly from providing the retraction assistance force.

2. An introducer assembly according to claim 1 , wherein the sprung element is a spiral spring.

3. An introducer assembly according to claim 2 , wherein the spring is fitted to a spool element, the brake element being configured to act upon the spool element to prevent the spring from pulling the sheath in a retraction direction.

4. An introducer assembly according to claim 1 , wherein the brake element is operable to prevent retraction of the sheath until the sheath is manually pulled back by the user.

5. An introducer assembly according to claim 4 , wherein the brake element adopts a braking condition when there is no manual actuation of the handle assembly and a released condition when there is manual operation of the handle assembly.

6. An introducer assembly according to claim 4 , wherein the brake element acts to prevent operation of the sprung element.

7. An introducer assembly according to claim 1 , wherein the drive assembly includes a brake release mechanism operable to release the brake element upon manual pulling of the handle portions together.

8. An introducer assembly according to claim 7 , wherein the brake release mechanism operates on the basis of the speed of manual retraction.

9. An introducer assembly according to claim 1 , wherein the drive assembly provides mechanical assistance up to a threshold retraction rate.

10. An introducer assembly according to claim 9 , wherein the drive assembly includes a sprung element which has a limited return speed.

11. An introducer assembly according to claim 1 , including a speed control mechanism.

12. An introducer assembly according to claim 11 , wherein the speed control mechanism includes a friction element for applying friction to the drive assembly thereby to control its speed of movement.

13. A drive assembly and an introducer assembly including a carrier element for carrying an implantable medical device, the carrier element including a distal end at which an implantable medical device is carried and a proximal end; a sheath overlying the carrier element and being retractable so as to expose the distal end of the carrier element, the sheath including a distal end and a proximal end; a handle assembly at the proximal end of the carrier element and sheath and including first and second handle portions, attached respectively to the proximal ends of the sheath and the carrier element, the handle assembly being manually operable to retract the sheath by pulling the first and second handle portions towards one another; wherein the drive assembly is able to be coupled between the carrier element and the sheath and operable to provide a retraction assistance force in response to manual retraction of the sheath; the drive assembly including:

a brake element operable to prevent retraction of the sheath until the sheath is manually pulled back by the user and to prevent a sprung element from providing the pulling force if there is no manual actuation of the handle assembly;

a brake release mechanism operable to release the brake upon manual pulling of the handle portions together;

a yoke fitted over the sheath;

the sprung element attached to the yoke;

the sprung element imparting a pulling force on the yoke, thereby placing the yoke in a tilted position relative to the sheath; and

wherein when the yoke is in the tilted position, the brake release mechanism engages the brake element so that the brake element prevents the drive assembly from providing the retraction assistance force.

14. An introducer assembly comprising:

a carrier element having a distal end and a proximal end;

a sheath overlying the carrier element and having a distal end and a proximal end;

a first handle portion attached to the proximal end of the sheath and a second handle portion attached to the proximal end the carrier element; and

a drive assembly coupled between the first handle portion and the second handle portion and operable to provide a retraction assistance force pulling the first handle portion and the second handle portion together;

wherein the drive assembly includes:

a yoke fitted over the sheath;

a sprung element attached to the yoke;

a brake element releasably engaged to the sprung element;

a brake release element attached to the yoke and releasably engaged to the brake element;

the sprung element imparting a pulling force on the yoke, thereby placing the yoke in a tilted position relative to the sheath; and

wherein when the yoke is in the tilted position, the brake release element engages the brake element so that the brake element prevents the drive assembly from providing the retraction assistance force.

15. An introduce assembly according to claim 14 , further comprising a gripping element attached to the yoke; and

wherein pulling the gripping element places the yoke in an untilted position, allowing the drive assembly to provide the retraction assistance force.

16. An introducer assembly according to claim 14 , wherein the sprung element further comprises a spool element.

17. An introducer assembly according to claim 16 , wherein the spool element is a toothed spool; and

wherein the brake element is releasably engaged to the toothed spool.

18. An introducer assembly according to claim 14 , wherein a spring is held at one end by the yoke and at the other end against the first handle potion.

19. An introduce assembly according to claim 14 , wherein the drive assembly further comprises a speed control mechanism.

20. An introducer assembly according to claim 19 , wherein the speed control mechanism further comprises a friction element for applying friction to the drive assembly thereby to control its speed of movement.