News Column

Researchers Submit Patent Application, "Detection/Stimulation Microlead with Enhanced Positioning", for Approval

June 5, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Regnier, Willy (Longjumeau, FR); Shan, Nicolas (Antony, FR), filed on November 13, 2013, was made available online on May 22, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "The invention relates to 'active implantable medical devices' as defined by the Directive 90/385/EEC of 20 Jun. 1990 the Council of the European Communities. This definition may include implants to continuously monitor heart rhythm and deliver, if necessary, electrical stimulation or resynchronization pulses. This invention relates more specifically to cardiac pacing leads to be implanted in the heart coronary network to allow the stimulation of a left or right cavity, a ventricle or an atrium.

"Unlike the right cavities, for which implanting endocardial leads via the right peripheral venous system is sufficient, the implantation of permanent leads in a cavity of the left heart involves significant risks, such as the risk of bubbles passing to the cerebral vasculature located downstream of the left ventricle. For this reason, when it is desirable to stimulate a left cavity, it is most often chosen not to introduce a lead into the cavity to pace, but rather in the coronary network, the lead being provided with an electrode that is applied against the epicardial wall of the left ventricle or of the left atrium. These leads thus stimulate the heart muscle via one or more point electrodes whose position is a function of the predefined trajectory of the cannulated vein. A lead of this type is, for example, the Situs LV model marketed by Sorin CRM (Clamart, France) and described in EP 0993840 A1 and its US counterpart U.S. Pat. No. 6,385,492 (Sorin CRM S.A.S., previously known as ELA Medical). The introduction of such a lead is via the coronary sinus, from its opening in the right atrium. The lead is then pushed and oriented along the network of coronary veins to the selected site. This procedure is very difficult due to the particularities of the venous system, including the gradual reduction in diameter of the veins as the lead progresses into the selected coronary vein. Once the target vein is reached, the surgeon is looking for a satisfying stimulation site, with a good electrical contact with the stimulation electrode against the epicardial tissue. Then, contact should be maintained despite various variations or stresses over time.

"A recent trend in the pacing of the left ventricle is the reduction of the diameter of the implantable portion in the coronary network, to a diameter of less than 4 French (1.33 mm), or even to less than 2 French (0.33 mm).

"The size of the lead body is indeed a factor directly related to the controlled guiding capacity of the lead in the coronary venous system in order to be able to select specific stimulation sites located in certain collateral veins.

"A lead is described in EP 2455131 A1 and US 20120130464 (Sorin CRM). It includes a lead body with a hollow sheath in which a microcable having a diameter of about 0.5 to 2 French (0.17 to 0.66 mm) slides. The micro cable can emerge to a length of 1 to 200 mm beyond the outlet of the lead body. This microcable, which forms the active part of the lead, has a plurality of exposed portions forming a succession of individual electrodes. The electrodes together form a network connected in series to increase the stimulation points in a deep area of the coronary network.

"Its very small diameter allows the introduction of the microcable in a first vein ('go' vein) and then to a second anastomosis vein ('back' vein) ascending therein. There is a very frequent presence of distal anastomosis in the coronary venous system. In other words, at the end of some veins there can be passage to another vein, with the possibility of communication between two separate veins at the anastomosis via their respective distal ends. It thus becomes possible, with a single lead, to simultaneously stimulate two relatively remote areas located in two separate veins. The double effect of both the distance of the two areas and of the multiplication of points of stimulation in each zone can provide a particularly beneficial effect for the resynchronization of the functioning of the heart.

"Another advantage of the small diameter of the active part of the lead is that it avoids the obstruction of a portion of the blood flow in the vein, which would lead to a deficiency of irrigation of the venous system downstream of the lead end.

"Reducing the diameter of the lead, however, is not without drawbacks. Indeed, when the diameter of the lead is significantly lower than that in the vein, it can be difficult to ensure continuous contact with the electrodes. The exposed portion of the microcable, which forms an electrode, can be located in an intermediate, 'floating' position in the middle of the vein, resulting in the contact points between the microcable and the wall of the vein being made in electrically isolated areas. Moreover, even in case of actual contact between the electrodes and the vein wall, this configuration may not be stable, because of a permanent heartbeat.

"This may be particularly true in the case of microcables inserted through an anastomosis. If the veins are of small diameter in the region of the anastomosis, typically less than 1 French (0.33 mm), beyond the anastomosis they may join the coronary sinus after having passed the left ventricle, and the vein diameter increases. The very thin microcable, allowing to cross the anastomosis, may then move into a region of relatively large diameter, resulting in difficulty establishing a stable contact between the electrodes and the wall of the vein in the region.

"One problem of the invention is to propose a structure of microlead ensuring continuous contact of all electrodes with the coronary veins, fixing the position of the lead in order to sustain the effectiveness of the stimulation. Another problem is the risk of displacement of the active part of the lead after it was implanted.

"EP 2455131 A1 cited above provides for a retaining mechanism, such as a helical relief formed on the end of the lead body near the end thereof, near the outlet where the microcable emerges. The end of the lead body thus has a locally increased diameter of about 7 French (2.33 mm) for the mechanical holding of the lead body into the vein.

"FR 2801510 A1 (corresponding to U.S. Pat. No. 6,549,812 B1) describes another mechanism for holding the lead in the target vein. However, this holding mechanism has the disadvantage of large size and may partially block the passage of blood flow in the vein. Moreover, although it can provide good retention of the lead body, it does not protect the portion of the lead inserted into the deep venous system. In such a case the telescopic microcable may be displaced by large movements of the patient. For example when a patient raises his arm, such movement tends to elongate the superior vena cava, with a risk of local traction applied to the lead, which traction is transmitted to the distal region implanted in the coronary network. These movements generated by the human body are thus an additional challenge relating to displacement of electrodes placed on the stimulation area."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Embodiments of the invention relate to detection/stimulation microleads for implantation in a target vessel, including a vessel of the coronary venous system for the stimulation of a heart cavity. The microlead can include a distal portion formed by an electrically conductive active microcable (e.g., of a diameter at most equal to 2 French (0.66 mm)). The microcable can be coated with an insulation layer. The insulation can include, along said active part and remote from the distal end of the microlead, one or more exposed regions forming stimulation electrode(s), intended to come into contact with a wall of the target vessel. The microlead includes a stimulation zone on the distal end of the microcable, in a region including the electrodes, and a retention zone. The retention zone is configured to abut against the wall of the target vessel.

"The microlead can further include a stretching zone, located proximal to the retention zone (e.g., at a distance therefrom of between 5 and 150 mm). The zone is defined by a shaped region of the microlead adapted to render it elastically deformable in the longitudinal direction under the effect of an axial traction/compression stress exerted on the microlead in its proximal region relative to the elongation area. The axial traction/compression stiffness of the elongation area is less than the axial traction/compression stiffness of the retention and stimulation zones.

"Thus, the axial forces exerted on the proximal portion of the lead between the stretching zone and a connector mounted at the proximal end of the lead is absorbed by deformation of the stretching area. This deformation of the extension area takes place without displacements of the retention and stimulation areas, consequently without a corresponding change in the positioning of the electrodes.

"According to various advantageous embodiments: The distal active portion is free of internal central lumen; The stimulation zone is defined by a first curved preshape of the microcable at the distal end thereof; The length of the stretching zone is, in the free state of the microlead, between 10 and 50 mm and its overall dimensions in the radial direction are in the free state of the microlead, included in a casing of an apparent diameter between 5 and 20 mm; The axial traction/compression stiffness of the elongation zone is between 1 and 2.5 N/mm.sup.2, and that of the retention and stimulation zones is between 2.5 and 5 N/mm.sup.2; and The length of the retention area is in the free state of the microlead, between 10 and 40 mm and its overall dimensions in the radial direction are in the free state of the microlead, included in a casing of an apparent diameter between 10 and 50 mm.

"According to an embodiment of the invention, a microlead includes a microcable (14) of a diameter not greater than 2 French (0.66 mm). The microlead includes, in a distal portion, exposed areas (30) forming stimulation electrodes, intended to come into contact with a wall of the target vessel. The microlead further includes a stimulation zone (ZS) defined by a first preshape of the microcable at the distal end thereof, in a region including the electrodes (30). The microlead further includes a retention zone (ZR) including a retainer shape adapted to abut against the wall of the target vessel, and a stretching zone (ZEL) proximal to the retention zone. The stretching zone may be defined by a shape adapted to make the region elastically deformable in the longitudinal direction under the effect of an axial traction/compression stress. The axial traction/compression stiffness in the elongation zone is lower than that in the retention and stimulation areas.

"In one embodiment, the elongation zone is defined by a second preshape of the microcable. The retention area and the stimulation area can be combined areas defined by a same region of the microcable. The microcable can advantageously include a layer of shape memory polymer permanently providing the first and second preshapes.

"In another embodiment, the microlead further includes a microcatheter of a diameter at most equal to 2 French (0.66 mm), from which the distal portion of the microcable emerges and the elongation zone is defined by a first preshape of the microcatheter. The retention area and the stimulation area may be separate areas, the retention zone being located proximal to the stimulation zone and the retention zone being defined by a second preshape of the microcatheter.

"One embodiment of the present disclosure relates to a microlead. The microlead includes a distal portion formed by an active microcable. The microcable further includes a stimulation zone at the distal end of the microcable. The microcable further includes a retention zone including a shape formed to abut the wall of a target vessel. The microcable further includes a stretching zone defined by a shaped region to provide elastic deformability in the longitudinal direction under the effect of an axial tension/compression stress exerted on the microlead. The axial traction/compression stiffness of the stretching zone is less than the axial traction/compression stiffness of the retention and stimulation zones.

"Another embodiment of the present disclosure relates to a microlead. The microlead includes a stimulation zone defined by a first preshape of the microlead at a distal end thereof. The stimulation zone includes electrodes. The first preshape forms a part of a retainer zone in which at least two surfaces of the microlead abut the wall of the target vessel. The microlead further includes a stretching zone proximal to the retainer zone defined by a shape which provides elastic deformability in the longitudinal direction under the effect of an axial traction and compression stress. The axial traction/compression stiffness in the stretching zone is lower than that in the retainer and stimulation zones.

BRIEF DESCRIPTION OF THE FIGURES

"FIG. 1 generally illustrates the myocardium, with the main veins of the coronary network in which a lead according to the invention was introduced for the stimulation of the left ventricle.

"FIG. 2 shows an example of a prior art configuration in which an electrode of a microcable is locally in a region of a relatively large diameter of a vein of the coronary network.

"FIG. 3 illustrates a first embodiment of a microlead according to the invention. The embodiment includes a microcable on which a stretching area and a combined retention and stimulation area were formed.

"FIG. 4 illustrates a second embodiment of a microlead according to the invention. The embodiment includes a microcable with a combined retention and stimulation area, and an elongation area formed in a region of a microcatheter housing the microcable.

"FIG. 5 illustrates another embodiment of a microlead according to the invention. This embodiment includes a microcable on which a stimulation area was formed, and a microcatheter housing that microcable and on which a retention area and a distinct elongation area were formed.

"FIGS. 6-10 illustrate various configurations of preshapes used for elongation, retention and/or stimulation zones, of the microlead according to the invention."

For additional information on this patent application, see: Regnier, Willy; Shan, Nicolas. Detection/Stimulation Microlead with Enhanced Positioning. Filed November 13, 2013 and posted May 22, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1421&p=29&f=G&l=50&d=PG01&S1=20140515.PD.&OS=PD/20140515&RS=PD/20140515

Keywords for this news article include: Patents, Surgery, Traction, Orthopedic Procedures.

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