Title of Invention: IMPLANTABLE MEDICAL DEVICE LEAD Abstract: An implantable lead including a lead body including an outer surface, a proximal end, a distal end, and at least one electrode; an electrically insulating member that extends axially over a first portion of the outer surface of the lead body between the proximal end and distal end, the electrically insulating member defining at least one aperture that exposes a first portion of the at least one electrode when in a first position over the lead body; and a reinforcement member formed at least partially of a different material than the insulating member and coupled to the insulating member, the reinforcement member extending axially over the outer surface of the lead body between the insulating member and proximal end. The reinforcement member may be configured to transfer at least one of a radial or axial force from a proximal portion of the reinforcement member to the insulating member, wherein the at least one of radial or axial force transferred to the insulating member is sufficient to move the insulating member over the outer surface of the lead body. In some examples, the lead may further include a deployable lobe member configured to anchor the reinforcement member and insulating member adjacent a tissue site within a patient. Detailed Description: This application claims the benefit of U.S. Provisional Application No. 61/221,960, entitled, “IMPLANTABLE MEDICAL DEVICE LEAD,” and filed on Jun. 30, 2009, the entire content of which is incorporated herein by reference. TECHNICAL FIELD The disclosure relates to medical devices and, in particular, implantable medical devices configured to deliver electrical stimulation therapy to a patient. BACKGROUND A wide variety of implantable medical devices (“IMD”) that deliver therapy to or monitor a physiologic condition of a patient have been clinically implanted or proposed for clinical implantation in patients. Some implantable medical devices may employ one or more elongated electrical leads and/or sensors. Such implantable medical devices may deliver therapy or monitor the heart, muscle, nerve, brain, stomach or other organs. In some cases, implantable medical devices deliver electrical stimulation therapy and/or monitor physiological signals via one or more electrodes or sensor elements, which may be included as part of one or more elongated implantable medical leads. Implantable medical leads may be configured to allow electrodes or sensors to be positioned at desired locations for delivery of stimulation or sensing electrical depolarizations. For example, electrodes or sensors may be located at a distal portion of the lead. A proximal portion of the lead may be coupled to an implantable medical device housing, which may contain electronic circuitry such as stimulation generation and/or sensing circuitry. For example, implantable cardiac devices, such as cardiac pacemakers or implantable cardioverter defibrillators, provide therapeutic stimulation to the heart by delivering electrical therapy signals such as pulses or shocks for pacing, cardioversion or defibrillation pulses via electrodes of one or more implantable leads. In some cases, an implantable cardiac device may sense intrinsic depolarizations of the heart, and control the delivery of therapeutic stimulation to the heart based on the sensing. When an abnormal rhythm of the heart is detected, such as bradycardia, tachycardia or fibrillation, an appropriate electrical therapy (e.g., in the form of pulses) may be delivered to restore the normal rhythm. For example, in some cases, an implantable medical device may deliver pacing, cardioversion or defibrillation signals to the heart of the patient upon detecting ventricular tachycardia, and deliver cardioversion or defibrillation therapy to a patient's heart upon detecting ventricular fibrillation. SUMMARY In general, the disclosure is directed to medical systems including at least one medical lead, e.g., an implantable medical lead, for delivering electrical stimulation therapy to a patient. The implantable lead may be adapted to be placed within a patient proximate a tissue site targeted for electrical stimulation, and the electrical stimulation may be delivered to the patient via one or more electrodes arranged on a distal a portion of the implantable lead positioned proximate the target tissue site. The implantable lead includes an insulating member, e.g., a tubular sleeve formed of an electrically insulating material, configured to surround a portion of the outer surface of the lead body adjacent one or more of the lead electrodes. The insulating member may define one or more aperture such that the insulating sleeve may be positioned over the outer surface of the lead body to selectively expose all or portions of the lead electrode(s) by actuating the member in an axial and/or radial direction. The lead may further include a reinforcement member coupled to the insulating member to facilitate the movement of the insulating member over the lead body, e.g., during the positioning of the insulating member over the lead body within a patient. For example, the reinforcement member may include a tubular sleeve formed of braided structure, such as, e.g., a braided wire structure, that extends from the insulating member positioned near the distal end of a lead to the proximal portion of lead body configured to connect to an implantable medical device (“IMD”). In some examples, the reinforcement member may be configured to shield the lead body from RF fields generated during magnetic resonance imaging (MRI) and/or to provide protection to the lead against compressive forces that may result in lead crush. In some examples, the lead may further includes a deployable lobe member configured to anchor the reinforcement member and insulating member adjacent a tissue site within a patient. In one example, the disclosure is directed to an implantable lead including a lead body including an outer surface, proximal end, a distal end, and at least one electrode; an electrically insulating member that extends axially over a first portion of the outer surface of the lead body between the proximal end and distal end, the electrically insulating member defining at least one aperture that exposes a first portion of the at least one electrode when in a first position over the lead body; and a reinforcement member formed at least partially of a different material than the electrically insulating member and coupled to the insulating member, the reinforcement member extending axially over the outer surface of the lead body between the insulating member and proximal end, wherein the reinforcement member is configured to transfer at least one of a radial or axial force from a proximal portion of the reinforcement member to the insulating member, and wherein the at least one of radial or axial force transferred to the insulating member is sufficient to move the insulating member over the outer surface of the lead body. In another example, the disclosure is directed to a method comprising delivering electrical stimulation therapy to a tissue site of a patient from a medical device via a first portion of at least one electrode of a lead, wherein the lead includes a lead body including an outer surface, a proximal end, a distal end, and the at least one electrode; an electrically insulating member that extends axially over a first portion of the outer surface of the lead body between the proximal end and distal end, the electrically insulating member defining at least one aperture that exposes the first portion of the at least one electrode when in a first position over the lead body; and a reinforcement member formed at least partially of a different material than the electrically insulating member and coupled to the insulating member, the reinforcement member extending axially over the outer surface of the lead body between the insulating member and proximal end, wherein the reinforcement member is configured to transfer at least one of a radial or axial force from a proximal portion of the reinforcement member to the insulating member, and wherein the at least one of radial or axial force transferred to the insulating member is configured to move the insulating member over the outer surface of the lead body. In another example, the disclosure is directed to an implantable lead comprising a lead body including an outer surface, a proximal end, a distal end, and at least one electrode; means for electrically insulating the at least one electrode extending axially over a first portion of the outer surface of the lead body between the proximal end and distal end, wherein the means for electrically insulating includes a means for defining at least one aperture that exposes a first portion of the at least one electrode when in a first position over the lead body; and means for transferring at least one of radial or axial force to the means for electrically insulating the at least one electrode, wherein the means for transferring at least one of radial or axial force is formed at least partially of a different material than the means for electrically insulating the at least one electrode, and wherein the at least one of radial or axial force is sufficient to move the means for electrically insulating the at least one electrode over the outer surface of the lead body. The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a conceptual diagram illustrating an example therapy system that includes an example implantable medical device (IMD) configured to deliver electrical stimulation heart of the patient. FIGS. 2A-2C are conceptual diagrams illustrating an example lead including an example reinforcement member and example insulating member. FIG. 3 is a conceptual diagram illustrating a distal portion of an example lead including an example reinforcement member and example insulating member. FIG. 4 is another conceptual diagram illustrating a distal portion of an example lead including an example reinforcement member and example insulating member. FIGS. 5A and 5B are conceptual diagrams illustrating an example lead including an example reinforcement member and example insulating member. FIG. 6 is a conceptual diagram illustrating a proximal portion of an example lead. FIGS. 7A and 7B are conceptual diagrams illustrating a distal portion of an example lead. FIG. 8 is a conceptual diagram illustrating an example lead having a distal portion positioned within the heart of a patient. FIGS. 9A-9C are conceptual diagrams illustrating an example insulating member. FIG. 10 is a conceptual diagram illustrating an example insulating member. FIGS. 11A and 11B are conceptual diagrams illustrating an example insulating member. FIGS. 12A and 12B are conceptual diagrams illustrating an example insulating member. DETAILED DESCRIPTION In general, the disclosure is directed to medical systems including at least one medical lead for delivering electrical stimulation therapy to a patient. For example, the medical lead may be an implantable lead adapted to be positioned within a patient adjacent to one or more tissue sites. The implantable lead may deliver electrical stimulation generated by an implantable medical device (IMD) to the target tissue via one or more electrodes arranged on a distal portion of the lead body. The implantable lead may include an insulating member, e.g., a tubular sleeve formed of an electrically insulating material, surrounding a portion of the lead body adjacent one or more of the lead electrodes. The insulating member may define one or more apertures such that the insulating sleeve may be oriented relative to the lead body to selectively expose all or portions of the lead electrode(s) by actuating the member in an axial and/or radial direction. The implantable lead further includes a reinforcement member coupled to the insulating member to facilitate the movement of the insulating member over the lead body, e.g., during the positioning of the insulating member over the lead body within a patient. For example, the reinforcement member may include a tubular sleeve formed of braided metal wire that extends from the insulating member positioned near the distal end of a lead to the proximal portion of lead body configured to connect to an implantable medical device (“IMD”). In such a configuration, the reinforcement member may be moved radially and/or axially near the proximal portion of the lead body to position the insulating member over the distal portion of the lead body. In some examples, the reinforcement member may be configured to electromagnetically shield the conductors with the lead from RF fields generated during magnetic resonance imaging (MRI) and/or to provide protection to the lead against crush. In some examples, an implantable lead may be utilized to provide cardiac rhythm management therapy generated by an implantable medical device to the heart of a patient. The proximal end of the implantable lead may connect to an IMD including a therapy module configured to generate one or more electrical stimulation signals. As part of the cardiac therapy, electrical stimulation signals, such as, e.g., pacing, cardioversion and/or defibrillation signals, generated by a therapy module of an IMD may be delivered to the heart of the patient via one or more electrodes arranged on a distal portion of the implantable lead. To deliver the electrical stimulation generated by the therapy module of the IMD to the heart of the patient, the one or more implantable leads can be positioned within the patient such that one or more of the lead electrodes on the distal portion of the lead are adjacent to the target cardiac tissue site while the proximal end of the lead is coupled to the IMD. The one or more lead electrodes on the distal portion of the lead body may be distributed axially along the lead body. In some examples, an implantable lead may include an insulating member, such as, e.g., as insulating sleeve, that surrounds a distal portion of the lead body proximate to one or more of the lead electrodes. The insulating member defines one or more apertures sized to allow at least a portion of the one or more electrodes to be partially exposed to a target tissue site when the insulating member occupies certain positions on the lead body. By moving the insulating member axially and/or radially over the lead body, electrodes may be selectively exposed and covered from the tissue adjacent the electrode surface based on the position of the insulating member relative the lead body. Such a relationship may be utilized by a clinician during adjust the electrical stimulation delivered be the lead to a patient. For example, once an implantable lead is positioned within the heart of a patient, a clinician may move the insulating sleeve over the lead body until the orientation of the insulating member relative the distal portion of the lead body produces the desired electrical stimulation to the heart of the patient. A clinician may move the insulating sleeve in the radial direction and/or axial direction to direct the electrical stimulation field delivered by the lead electrode(s) to the cardiac tissue of the patient. Depending the location of the implantable lead within a patient, a clinician may only have limited access to the distal portion of the lead body on which the one or more electrodes are arranged, and the ability of the clinician to move the insulating member in the axially and/or radial direction over the distal portion of the lead as described may be limited. For example, when an implantable lead is positioned within the heart of a patient, e.g., within the left ventricle, a clinician may not have direct access to the distal portion of the lead. Rather, the clinician may control the position of the distal portion of the lead by moving the proximal portion of the lead, which may be more easily accessed by the clinician based on the location of the IMD within the patient. Similarly, the ability of the clinician to move an insulting member in a radial and/or axial direction over the distal portion of the lead body when the distal portion of the lead is positioned within the heart of a patient is limited. In some examples, an insulating member may be configured to extend axially over a substantial portion the lead body to allow a clinician to access the insulating member over a proximal portion of the lead body. However, the composition and structure of the insulating member may prevent or inhibit the remote movement of the distal portion of the insulating member through movement of the proximal portion, at least to the extent that relatively precise control over the proximal end of the insulating member is required. For example, the ability of insulating sleeve to transfer torque from the proximal to distal portion when rotational force is applied to the sleeve at the proximal portion of the lead body may be insufficient to actuate the distal portion of the insulating sleeve of the distal portion of the lead body with the precision required to selectively expose and cover electrodes on the distal end of the lead. In some cases, the insulating member may store the rotational force over the length of the insulating member causing the insulating sleeve to periodically and undesirably rotate after the distal portion of the insulating sleeve has been desirably positioned radially relative to one or more electrode on the lead. Moreover, if an implantable lead is initially positioned within a patient without the insulating member positioned over the distal portion of the lead body, a clinician may be required to slide the insulating member over the lead body from the proximal end of the lead to the distal portion while the implantable lead is positioned within the heart. Again, the composition and structure of the insulating member may prevent or inhibit a clinician from sliding the proximal portion of the insulating member from a proximal portion to a distal portion of the lead body, especially in situations in which the lead body follows a relatively tortuous path, e.g., as with an left ventricle lead. As will be described in further detail below, an implantable lead may further include reinforcement member that is coupled to the insulating member. The reinforcement member may be configured to couple to the insulating member at or near the distal portion of a lead body and extend to the proximal portion of the lead body. The reinforcement member may be formed at least in part (e.g., partially or substantially entirely) of a different material than that of the insulating member. The composition and structure of the reinforcement member provides suitable transfer of rotational force applied the reinforcement member over the proximal portion of the lead body to the insulating member positioned over the distal portion of the lead body. For example, the reinforcement member may be formed with a wire braid structure configured to provide adequate transfer of radially force to position the insulating member in the radial direction over the distal portion of the lead body from the proximal portion of the lead. Additionally, the composition and structure of the reinforcement member may increase the transfer of axial force applied to the reinforcement member over the proximal portion of the lead body to the insulating member positioned over the distal portion of the lead body. In some example, the reinforcement member may be configured to protect the lead against one or more undesirable side-effects from magnetic resonance imaging (MRI). For example, the reinforcement member may be formed of an electrically conductive material to shields conductors within a lead body from electromagnetic fields and/or radio frequency fields associated with an MRI scan. Additionally, the reinforcement member may protect the lead body against crush. The systems and devices described in the disclosure may include at least one insulating member configured to surround at least a portion of an implantable lead body and a reinforcement member coupled to the insulating member. While examples of the present disclosure are described with regard to electrical stimulation therapy systems configured to deliver cardiac rhythm management therapy, e.g., pacing, cardioversion, and/or defibrillation signals, to the heart of a patient, examples are not limited to such an application. Examples of the disclosure may also be applicable to implantable leads used for delivering neurostimulation therapy to one or more tissue sites of a patient, such as the vagal nerve stimulation or spinal cord stimulation. In some cases, examples of the present disclosure may include implantable leads used to deliver deep brain stimulation to a patient, or implantable leads configured to deliver electrical stimulation therapy to a patient to treat urinary incontinence, e.g., by directionally stimulating one or more nerve sites and not the surround muscle. FIG. 1 is a conceptual diagram illustrating an example therapy system 10 that may be used to provide therapy to patient 12. Patient 12 ordinarily, but not necessarily, will be a human. Therapy system 10 includes implantable medical device (IMD) 14, lead 16, and programmer 28. IMD 14 may generate and deliver electrical stimulation to heart 18 via electrodes (not shown) carried by lead 16 in order to manage a cardiac rhythm of heart 18. Accordingly, IMD 14 may include a therapy module (not shown) configured to generate at least one of pacing, cardioversion, or defibrillation therapy. The pacing therapy may include, for example, antitachyarrhythmia pacing (ATP) and pacing therapies designed to prevent ventricular tachycardia, ventricular fibrillation, atrial tachycardia, and/or atrial fibrillation. In some examples, IMD 14 may deliver pacing pulses, but not cardioversion or defibrillation pulses, while in other examples, IMD 14 may deliver cardioversion or defibrillation pulses, but not pacing pulses. In addition, in further examples, IMD 14 may deliver pacing, cardioversion, and defibrillation pulses. In the example shown in FIG. 1, lead 16 extends through one or more veins (not shown), the superior vena cava (not shown), and right atrium 22, and into right ventricle 20. Although not shown in FIG. 1, therapy system 10 may additionally or alternatively include a left ventricular (LV) coronary sinus lead that extends through one or more veins, the vena cava, right atrium 22, and into the coronary sinus to a region adjacent to the free wall of left ventricle 26 of heart 18. Therapy system may also additionally or alternatively include an atrial (RA) lead that extends through one or more veins and the vena cava, and into the right atrium 22 of heart 18. In other examples, IMD 14 may deliver stimulation therapy to heart 18 by delivering stimulation to an extravascular tissue site in addition to or instead of delivering stimulation via electrodes of intravascular lead 16. An extravascular tissue site may be outside of heart 18 and outside of arteries, veins, or other vasculature of patient 12. In some examples, lead 16 may be positioned epicardially to deliver electrically stimulation to heart 18 of patient 12. IMD 14 may sense electrical signals attendant to the depolarization and repolarization of heart 18 via electrodes (not shown) coupled to lead 16. In some examples, IMD 14 may provide pacing pulses to heart 18 based on the electrical signals sensed within heart 18. The configurations of electrodes used by IMD 14 for sensing and pacing may be unipolar or bipolar. IMD 14 may also provide defibrillation therapy and/or cardioversion therapy via electrodes located on lead 16. IMD 14 may detect arrhythmia of heart 18, such as fibrillation of ventricles 20 and 26, and IMD 14 may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of heart 18 is stopped. IMD 14 may detect fibrillation employing one or more fibrillation detection techniques known in the art. In some examples, IMD 14 may also be referred to as a signal generator, stimulation generator or an electrical stimulator. In some examples, lead 16 may also carry one or more sense electrodes to permit IMD 14 to sense electrical signals within patient 12. In the example of FIG. 1, IMD 14 has been implanted in patient 12 at a location that allows leads 16 to be positioned within heart 26. For example, IMD 14 may be subcutaneously or submuscularly implanted in the body of a patient 12 (e.g., in a chest cavity, lower back, lower abdomen, or buttocks of patient 12). The components for generating and delivering the pacing, cardioversion and/or defibrillation therapy via leads 16 may be substantially contained within housing 30 of IMD 14. Proximal end 16A of lead 16 is mechanically and electrically coupled to IMD 14 via lead connection header 32 either directly or indirectly (e.g., via a lead extension). In particular, conductors disposed in the lead body of lead 28 may electrically connect stimulation electrodes (and sense electrodes, if present) of lead 28 to IMD 14. In some examples, IMD 14 may include one or more housing electrodes, which may be formed integrally with an outer surface of hermetically-sealed housing 28 of IMD 14 or otherwise coupled to housing 28. In some examples, the housing electrode may be defined by an uninsulated portion of an outward facing portion of housing 28. Other divisions between insulated and uninsulated portions of housing 30 may be employed to define two or more housing electrodes. In some examples, such as the example shown in FIG. 1, the housing electrode may comprise substantially all of housing 30. In other examples, one or more electrodes may be embedded into an insulating casing that surrounds the outer surface of housing 30. Any of the electrodes of lead 16 may be used for unipolar sensing or stimulation in combination with the housing electrode. As shown in FIG. 1, therapy system 10 also includes programmer 28. In some examples, programmer 28 may be a handheld computing device or a computer workstation. Programmer 28 may include a user interface that receives input from a user. The user interface may include, for example, a keypad and a display, which may for example, be a cathode ray tube (CRT) display, a liquid crystal display (LCD) or light emitting diode (LED) display. The keypad may take the form of an alphanumeric keypad or a reduced set of keys associated with particular functions. Programmer 28 can additionally or alternatively include a peripheral pointing device, such as a mouse, via which a user may interact with the user interface. In some examples, a display of programmer 28 may include a touch screen display, and a user may interact with programmer 28 via the display. A user, such as a physician, technician, or other clinician, may interact with programmer 28 to communicate with IMD 14. For example, the user may interact with programmer 28 to retrieve physiological or diagnostic information from IMD 14. A user may also interact with programmer 28 to program IMD 14, e.g., select values for operational parameters for one or more of the stimulation therapies delivered by IMD 14. For example, the user may use programmer 28 to retrieve information from IMD 14 regarding the rhythm of heart 18, trends therein over time, or tachyarrhythmia episodes. As another example, the user may use programmer 28 to retrieve information from IMD 14 regarding other sensed physiological parameters of patient 12, such as electrical depolarization/repolarization signals from heart 18 (referred to as “electrogram” or EGM), intracardiac or intravascular pressure, activity, posture, respiration, or thoracic impedance. As another example, the user may use programmer 28 to retrieve information from IMD 14 regarding the performance or integrity of IMD 14 or other components of system 10 corresponding to the first stimulation therapy, such as lead 16, or a power source of IMD 14. Programmer 28 may communicate with IMD 14 via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, low frequency or radiofrequency (RF) telemetry, but other techniques are also contemplated. In some examples, programmer 24 may include a programming head that may be placed proximate to the patient's body near the IMD 14 implant site in order to improve the quality or security of communication between IMD 14 and programmer 28. As shown in FIG. 1, lead 16 includes reinforcement member 34 and insulating member 36. Insulating member 36 surrounds the body of lead 16 over distal portion 16B positioned within right ventricle 20, which includes one or more electrodes (not shown). Reinforcement member 34 is coupled to insulating member 36 and extends axially over the body of lead 16 from the insulating member 36 to a proximal portion of lead 16 located outside heart 18. Insulating member 36 defines one or more apertures (not shown) that may expose at least a portion of one or more electrodes (not shown) on lead 16 to cardiac tissue of heart 18 when in a first position on the body of lead 16. When the proximal portion of reinforcement member 34 is moved in either the axial and/or radial direction over the body of lead 16, the force applied to reinforcement member 34 is transferred to insulating member 36 thereby moving insulating member 36 over the body of lead 16 in the same manner. FIGS. 2A-2C are conceptual diagrams illustrating example lead 38 including reinforcement member 34 and insulating member 36. Reinforcement member 34 and insulating member 36 extend axially over lead body 40. Lead 38 may be an implantable lead configured to delivery electrical stimulation therapy to patient 12 from an IMD 14 (FIG. 1). In some examples, lead 38 may deliver cardiac rhythm management therapy to patient 12, and may be substantially the same or similar to lead 16 (FIG. 1). Lead 16 has an elongated lead body 40 including distal portion 40B and proximal portion 40A. The end of proximal portion 40A of lead 16 may be configured to connect to connection header 32 of IMD 14 (FIG. 1) to electrically and mechanically couple lead 16 to the therapy module (not shown) of IMD 14. Distal portion 40B of lead body may be configured to be positioned with heart 18 of patient 12 to deliver electrical stimulation signals to tissue of heart 18 adjacent to electrodes 46, 48, and/or 50. Lead body 40 may be formed of a biocompatible material such as, e.g., polyurethane. Lead body 40 may have a substantially tubular form and may define a substantially circular cross-section. Alternative shapes of lead body 40 are contemplated, e.g., lead body 40 may have an oval or square cross-section. Electrodes 46, 48, 50 are arranged on distal portion 40B of lead body 40. Electrodes 46 and 48 may form a substantially cylindrical ring of conductive material extending radially around a portion of lead body 40 and, in some cases, may be referred to as ring electrodes. Electrode 50 includes a conductive material formed on the distal end of lead body 40 and, in some cases, may be referred to as a tip electrode. Electrodes 46, 48, and 50 may each be used to deliver electrical stimulation signals, such as cardiac pacing signals, generated by the therapy module of IMD 14 to heart 18 of patient 12 (FIG. 1). For example, when lead 38 is properly connected to IMD 14, electrical stimulation signals generated by the therapy module of IMD 14 may be conducted via one or more conductors provided within lead body 40 to one or more of electrodes 46, 48, 50, which may deliver the electrical stimulation signals to heart 18 of patient 12. Lead 38 may include any suitable number of electrodes. For examples, lead 38 may include one, two, three, four, five or more than five electrodes. Insulating member 36 extends axially over a distal portion 40B of lead body 40, and defines aperture 42A and aperture 42B (collectively “apertures 42”). As shown, insulating member 36 may have a tubular shape or body which surrounds the outer surface of a distal portion of lead body 40. In some examples, insulating member may be referred in some cases as a tubular insulating sleeve. Insulating member 36 is sized such that the inner lumen defined by the inner surface of insulating member 36 receives the distal portion 40B of lead body 40. Insulating member 36 may be separate from lead body 40 to allow insulating member 36 may be moved axially and/or radially relative lead body 40 when insulating member 36 and reinforcement member 34 is not anchored relative to lead body 40. Apertures 42 are sized and shaped to expose portions of electrodes 46 and 48 carried by lead 38 to facilitate the selection of electrodes 46 and 48, and directional application of stimulation via the one or more selected electrode 46 and 48. By moving insulating member 36 over the body of lead 16 in the axial and/or radial direction via reinforcement member 34, the relationship of apertures 42 relative to electrodes 46 and 48 may be adjusted to selectively expose and/or cover portions of electrodes 46 and 48. In general, the portions of electrode 46 and 48 covered by insulating member 36 will be electrically insulated, and the portions of electrodes 46 and 48 exposed by apertures 42 will be capable of conducting electrical stimulation to the adjacent tissue within heart 18. Insulating member 36 may define any suitable number of apertures having any suitable size and configuration. For example, insulating member 36 may define one or a plurality of apertures, e.g., two, three, four or more than four apertures. In some examples, insulating member 36 may include the same number of apertures as electrodes carried by lead 38, while in others insulating member 36 may have more or less apertures than the number of electrode carried by lead 38. Insulating member 36 may be formed of any suitable material including biocompatible plastics and other insulating materials that allow insulating member 36 to electrically insulate electrodes 46 and 48, as described herein. For example, insulating member 36 may be formed from polyurethane, pellethane, copolymer made from urethane and silicone blend, or the like. In one example, insulating member 36 may include DOW 2363-55D polyurethane. Apertures 42 may be cut from or machined within a length of tubing to form insulating member 36. Alternatively, insulating member 36 can be formed by injection molding, vulcanization molding, or any other suitable know technique. In any case, insulating member 36 is configured to be positioned over distal portion 40B of lead body 40 that includes one or more electrode, such as electrodes 46 and 48. Insulating member 36 has a wall thickness that is sufficiently thin to allow for implantation within heart 18 of patient (or whichever portion of patient 12 that lead 38 is configured to be implanted), but also sufficiently thick to retain electrically insulative properties and avoid electrical breakdown when in contact with a covered portion of electrode 46 and/or electrode 48. Reinforcement member 34 is coupled to insulating member 36 positioned on distal end 40B of lead body 40. As shown, reinforcement member 34 may have a tubular shape which surrounds lead body 40 and extends axially over lead body 40 from distal portion 40B to proximal portion 40A. Reinforcement member 34 is sized to define an inner lumen that receives lead body 40. Reinforcement member 34 may be separate from lead body 40 to allow reinforcement member 34 may be moved axially and/or radially relative lead body 40 when insulating member 36 and/or reinforcement member is not anchored relative to lead body 40. As previously described, reinforcement member 34 be configured to transfer rotational and/or axial force applied to reinforcement member 34 at a location proximate the proximal portion 40A of lead body 30 to insulating member 36 positioned over the distal portion 40B of lead body 30. In this manner, an axial and/or rotational force may be applied to reinforcement member 34 relative the distal portion 40A of lead body 40 to move insulating member 36 over the distal portion 40B of lead body 40. By moving insulating member 36 via reinforcement member 34, select portions of electrodes 46 and 48 may be exposed by apertures 42 to conduct electrical stimulation to tissue, e.g., cardiac tissue, adjacent the exposed electrode portion. Such a technique may be utilized by a clinician to adjust the position of insulating member 36 relative lead body 40 when distal portion 40B is implanted within heart 18, or other implant site, of patient 12 and not directly accessible to the clinician. In some cases, lead body 40 may follow a relatively tortuous path from the proximal portion 40A to the distal portion 40B (e.g., when distal portion 40B of lead body 40 is positioned within the left ventricle 26 of heart 18). As such, reinforcement member 40 facilitates the transfer of force from a location near the proximal portion 40A of lead body 40 to insulating member 36 positioned over distal portion 40B of lead body 40. As shown, FIGS. 2A-2C illustrate the movement of reinforcement member 34 and insulating member 36 over lead body 40, e.g., based on the application of an axial force to the proximal portion of reinforcement member 34. Progressing in order from FIG. 2A to 2B to 2C, an axial force is applied toward the proximal end of lead 38, e.g., by a clinician, to a location on reinforcement member 34 near the proximal portion of lead body 40. Reinforcement member 34 transfers the axial force to insulating member 36 positioned on the distal portion 40B of lead body 40, which actuates insulating member 36 over the outer surface of lead body 40 in the proximal direction. In FIG. 2A, a portion of electrode 46 is exposed by aperture 42A of insulating member 36 and electrode 48 is entirely covered by insulating member 36. However, the movement of insulating member 36 in the proximal direction via reinforcement member 34 changes the orientation of insulating member 36 relative to lead body 40 and electrode 46 and 48. In FIG. 2B, a portion of both electrodes 46 and 48 are exposed by aperture 42A and 42B, respectfully, by moving insulating member a distance of L1 in the proximal direction over lead body 40. From that point, insulating member 36 may be moved a distance of L2 in the proximal direction over lead body 40 to exposed a portion of electrode 48 via aperture 42B and cover electrode 46. In this manner, reinforcement member 34 may transfer an applied axial force to move insulating member 36 over distal portion 40B of lead body 40 to selectively expose and cover portions of electrodes 46 and 48. In some examples, such a technique may be used to essentially vary the tip to ring spacing on a pacing lead. Although not directly illustrated in FIGS. 2A-2C, insulating member 36 may be moved in the radial direction over lead body 40 by applying a force to reinforcement member 34 in the radial direction to the proximal portion of reinforcement member 34. Reinforcement member 34 transfers the radial force to insulating member 36, which rotates insulating member 36 over lead body 40 along with reinforcement member 34. In this manner, insulating sleeve 36 may be rotated over distal portion 40B of lead body 40 via application of a force in the radial direction to a proximal portion of reinforcement member 34 to selectively expose and cover portions of electrodes 46 and 48 via apertures 42. Such a technique may facilitate to the directional delivery of electrical stimulation to a target tissue by providing for control of the stimulation in the radial direction. In cardiac applications, the directional delivery of electrical stimulation via electrodes 46 and/or 48 may be utilized to avoid phrenic nerve stimulation. Reinforcement member 34 may be formed of any suitable material and structure that provide one or more of the properties attributed to reinforcement member 34 herein. Reinforcement member 34 may be formed of a material that is different than that of the material of insulating member 36. In some examples, reinforcement member 34 may include a braided structure that provides suitable transfer of rotational and/or axial force. The braided structure may include a plurality of metal or metal alloy wires braided with one another to form a braided metallic sleeve configured fit of over lead body 40. The wires may be formed from any suitable metal and/or metal alloys, such as, e.g., titanium, stainless steel, tantalum, and the like. The diameter of individual wire strands in a braided structure may range from approximately 0.5 mils to approximately 2.5 mils, such as, e.g., approximately 0.5 mils to approximately 1.5 mils, approximately 1 mil to approximately 2.5 mils, or approximately 1.2 mils to approximately 1.7 mils. In some examples, the braided wire may be formed of cobalt chromium alloys, such as, e.g., MP35N or Elgiloy (Phynox), stainless steel, e.g., 316L VAR, or nickel-titanium alloy (Nitinol). In one example, the braided wire may be formed of a titanium alloy wire, such as, e.g., Ti 6Al4V ELI, having a diameter of approximately 1.5 mils annealed. The reinforcement member may be braided in any suitable pattern. For example, the braided structure may have approximately 60 to approximately 120 picks per inch, such as approximately 90 to approximately 100 picks per inch. The braided structure may include 12 to 48 wire strands. In one example, a 16 tow pattern, with two wires per tow, may be braided in a two over one pattern to form the braided wire structure of reinforcement member 34. The braided wire may form a braided wire sleeve defining an inner lumen that receives lead body 40. In some examples, the void spaces of the braided structure may be filled in with one or more suitable biocompatible polymeric materials, such as, e.g., polyurethane. For example, the braided wire structure may be embedded within the walls of the polymer structure to form reinforcement member 34. In this manner, a reinforcement member formed of a braided structure may define a continuous surface over lead body 40. In some examples, such polymeric structure of reinforcement member 34 may be substantially the same insulating material used to form insulating member 36. The braided structure may be embedded in the insulating material to provide suitable transfer of radial and/or axial force applied to the proximal portion of reinforcement member 34 over lead body 40 to insulating member 36 positioned over distal portion 40B of lead body 40. Additionally or alternatively, the braided structure may be bonded to the inner or outer surface of a polymeric tube. In other examples, individual strands, e.g., metallic wire strands, may be coated with a polymer material and then braided with one another to form reinforcement member 40. The braid pattern and braid material may be selected to provide desired properties of reinforcement member 34. In addition, the percentage and location of the braided structure over the overall length of reinforcement member 34 may be varied to provide desirable properties. In some examples, substantially the entire length of reinforcement member 34 includes a braided structure. Alternatively, only certain portions of the overall length of reinforcement member may include a braided structure. For example, reinforcement member 34 may include a braided structure over approximately 25 to approximately 97 percent of the overall length of reinforcement member 34, such as, e.g., approximately 85 to approximately 95 percent, approximately 25 to approximately 75 percent, or approximately 50 to approximately 97 percent of the overall length of reinforcement member 34. The remaining portions of reinforcement member 34 may be formed primary of polymeric material, e.g., a tube shaped polymer structure, without the incorporation of a braided structure. Reinforcement member 34 may include a braided structure in those portions that correspond to particularly tortuous areas along the implant path of lead 38 within patient 12 to increase the transfer of radial and/or axial force in reinforcement member 34 over such portions. The inner surface of reinforcement member 34 that defines the inner lumen which receives lead body 40 may include a lubricant that promotes the movement of reinforcement member 34 over lead body 40 when an axial and/or radial force is applied. The lubricating material may reduce frictional interaction between reinforcement member 34 and the outer surface of lead body 40 to prevent abrasion and/or fracture of either reinforcement member 34 or lead body 40. In some examples, the inner surface of reinforcement member 34 may include a lubricating layer at the interface between the outer surface of lead body 40 and reinforcement member 34 when reinforcement member 34 surrounds lead body 40. Any suitable lubricating material may be used for reinforcement member 34. For example, silicone oil, saline, PTFE coating insulation, polyacrylamide hydrophilic, Dow Corning MDX4-4159 Medical Grade Dispersion, and the like may be used for lubrication between the reinforcement member 34 and lead body 40. In some examples, a material that fills the void space of a braided structure, as described above, may be a lubricating material. In such a configuration, the material may separate the braided structure from the outer surface of the lead body, which prevents the braided structure from making direct contact with the outer surface of the lead body. Depending the material and pattern of the braided structure, such direct interaction between the braided structure and lead body can result in abrasive contact or fracture of the lead body. In some examples, the inner surface of reinforcement member 34 may undergo siloxane surface treatment to lubricate the interaction between reinforcement member 34 and lead body 40. In some examples, the outer surface of lead body 40 may include one or more sealing protrusions extending around the circumference of lead body 40 between electrode 46 and 48. The protrusion on the outer surface may be configured to electrically isolate electrodes 46 and 48 from one another by providing a fluid seal between the electrodes. Reinforcement member 34 may be configured to provide shielding to lead 38 from external alternating electromagnetic fields, e.g., such as those produced during MRI scans. As identified above, implantable leads of an IMD can be adversely affected when a patient is exposed to alternating electromagnetic fields. For example, without such shielding, alternating electromagnetic fields produced during an MRI may induce undesired currents within lead 38, which can discharge via electrodes 46, 48, and/or 50 to the adjacent tissue to patient 12. To electrically shield all or a portion of lead 38, reinforcement member 34 may include suitable electrically conductive material(s) to electrically shield the one or more conductors within lead body 40 that electrically couple electrodes 46, 48, 50 to the therapy module within IMD 14. In some examples, reinforcement member 34 may include metal and metal alloy wires that exhibit relatively high electrical conductivity. For example, wire including gold, platinum, palladium, silver, tantalum, tantalum-tungsten-niobium alloy, and the like may be used to form a braided structure for reinforcement member 34. Additionally or alternatively, reinforcement member 34 may include a non-metallic material that exhibits relatively high electrical conductivity. For example, the non-metallic conductive material may include carbon (e.g., in the form of graphite, continuous carbon fiber strands and/or polymer strands impregnated with carbon nanotubes) to provide a high conductivity reinforcement member that electrically shield lead 38 from electromagnetic and/or RF energy. Other highly conductive, non-metallic materials may also be used for reinforcement member 34. Reinforcement member 34 may have any suitable length. The length of reinforcement member 34 may depend on the position of electrode 46 and 48 on lead 38, the implant location of lead 38 within patient 12, and/or the length of insulating member 36. In general, it is desirable for reinforcement member 34 to have length that allows a clinician to directly access at least the proximal portion of reinforcement member 34, e.g., at the implant site of IMD 14 within patient 12, when apertures 42 of insulating member 36 are proximate to electrodes 46 and 48, so that the clinician may directly apply an axial and/or radial force to reinforcement member 34 to move insulating sleeve 36 over distal portion 40 B of lead body 40 even though insulating sleeve is positioned within patient 12 at a location that is not directly accessible to the clinician. As shown in FIG. 1, the length of reinforcement member 34 is such that reinforcement member 34 extends from insulating member 36 positioned over the distal portion 16B of lead 16 within right ventricle 20 of heart 18 to a point adjacent the proximal end 16A of lead 16 that connects to header 32 of IMD 14. In other examples, reinforcement member 34 may have a length that does not extend to the proximal end 16A of lead 16, but still has a length that allows a clinician to directly access a portion of reinforcement member 34 when insulating member 36 and lead 16 are desirable positioned within patient 12. In some examples, reinforcement member 34 may extend substantially the entire length of lead 16 from the distal end to the proximal end, e.g., in examples in which reinforcement member 34 shields lead from electromagnetic and/or RF fields of MRI scans. In such an example, reinforcement member 34 may extend along substantially the entire length from proximal end 16A of lead 16 (FIG. 1) which connects to the header 32 of IMD 14 (FIG. 1) to insulating member 36. In some examples, reinforcement member 34 may extend substantially the entire length of lead 16 to shield substantially all of lead 16 from electromagnetic and/or RF fields. In such cases, since insulating member 36 may or may not be positioned directly adjacent to the distal end of lead 16, reinforcement member 34 may extend
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