Abstract:
A lead for monitoring or stimulating cardiac activity is provided. The lead is adapted for implantation on or about the heart within the coronary vasculature and for connection to a signal generator. The lead body has one or more electrodes associated therewith. The lead is constructed and arranged so that when it is implanted, the electrodes are housed in the coronary vasculature and urged into intimate contact a vessel wall.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 10/431,136, filed on May 7, 2003, which is continuation of U.S. patent application Ser. No. 09/651,340, filed on Aug. 30, 2000, now issued as U.S. Pat. No. 6,584,362, the specifications of which are incorporated herein by reference.  
         [0002]     This application is also related to commonly assigned, U.S. patent application Ser. No. 09/650,568, filed on Aug. 30, 2000, now issued as U.S. Pat. No. 6,493,586, the specification of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0003]     The present invention relates to the field of leads for correcting arrhythmias of the heart. More particularly, this invention relates to leads for pacing and/or sensing the heart from the coronary vasculature.  
       BACKGROUND OF THE INVENTION  
       [0004]     A cardiac pacing system includes a battery powered pulse generator and one or more leads for delivering pulses to the heart. Current pulse generators include electronic circuitry for determining the nature of an irregular rhythm, commonly referred to as arrhythmia, and for timing the delivery of a pulse for a particular purpose. The pulse generator is typically implanted into a subcutaneous pocket made in the wall of the chest. Insulated wires called leads attached to the pulse generator are routed subcutaneously from the pocket to the shoulder or neck where the leads enter a major vein, usually the subclavian vein. The leads are then routed into the site of pacing, usually a chamber of the heart. The leads are electrically connected to the pulse generators on one end and are electrically connected to the heart on the other end. Electrodes on the leads provide the electrical connection of the lead to the heart. The leads deliver the electrical discharges from the pulse generator to the heart.  
         [0005]     The electrodes are typically arranged on a lead body in two ways or categories. A pair of electrodes which form a single electrical circuit (i.e., one electrode is positive and one electrode is negative) positioned within the heart is a bipolar arrangement. The bipolar arrangement of electrodes requires two insulated wires positioned within the lead. When one electrode is positioned in or about the heart on a lead and represents one pole and the other electrode representing the other pole is the pulse generator, this arrangement is known as a unipolar arrangement. The unipolar arrangement of electrodes requires one insulated wire positioned within the lead.  
         [0006]     Some patients require a pacing system having multiple sites in one chamber of the heart for detecting and correcting an abnormal heartbeat. In the past, a common practice for a patient requiring multi-site pacing within one or more chambers of the heart, would be to provide two separate and different leads attached to the particular chamber of the heart. One lead would be implanted at one site in the chamber. Another lead would be implanted at another site in the same chamber, or another chamber. Typically, the single chamber of the heart receiving multi-site pacing would be the right atrium.  
         [0007]     Having two separate leads is undesirable for many reasons. Among these are the complexity of and time required for the implantation procedure for implanting two leads as compared to that of the procedure for implanting one lead. In addition, two leads may mechanically interact with one another after implantation which can result in dislodgement of one or both of the leads. In vivo mechanical interaction of the leads may also cause abrasion of the insulative layer along the lead which can result in electrical failure of one or both of the leads. Another problem is that as more leads are implanted in the heart, the ability to add leads is reduced. If the patient&#39;s condition changes over time, the ability to add leads is restricted. Two separate leads also increase the risk of infection and may result in additional health care costs associated with re-implantation and follow-up.  
         [0008]     It is well understood that the heart functions with two sides. The right side of the heart receives blood from the body and pumps it into the lungs to exchange gases. The left side of the heart receives the oxygenated blood from the heart and pumps it to the brain and throughout the body. As currently practiced, endocardial pacing and defibrillation leads are positioned within the right chambers of the heart. A major reason that this is typically practiced is that the risk of severe cerebral accidents during endocardial, left heart procedures is greater than that encountered during endocardial right side heart procedures. Although it is safer for the patient to position leads within the right heart, numerous difficulties are encountered when it is desired to sense and pace the left heart endocardially.  
         [0009]     There is a need for an endocardial lead that can reliably perform pacing and sensing of the heart without being placed in the left side of the heart.  
       SUMMARY  
       [0010]     A lead is provided which includes a lead body adapted to carry signals to and from a heart, where the lead body has a proximal portion and a distal portion. The lead further includes a connector located at a proximal end of the lead. The lead is adapted for connection to a signal generator for monitoring or stimulating cardiac activity, and is constructed and arranged for implantation within a coronary vein. A portion of the distal portion of the lead body has a preformed radius of curvature substantially the same as or slightly smaller than a coronary sinus and geometrically shaped to hug a wall of the coronary sinus upon implantation therein. In addition, the lead further includes at least one electrode coupled with the lead body.  
         [0011]     Several options for the lead are as follows. For example, the lead is constructed and arranged for implantation within the coronary sinus. In another option, the at least one electrode includes a first electrode associated with the distal portion of the lead body, and the first electrode includes a first electrode contact area. The at least one electrode further includes a second electrode associated with the distal portion of the lead body, and the second electrode includes a second electrode contact area. The distal portion of the lead is constructed and arranged to urge the first and second electrodes toward a wall of the coronary sinus. In yet a further option, the first electrode and the second electrode are spaced in close proximity to one another. Optionally, the lead further comprises at least one atrial pacing electrode. In yet another option, the distal portion of the lead body further includes a helical portion having the at least one electrode thereon, and the helical portion is constructed and arranged to urge the at least one electrode toward a myocardial wall. In a further option, the distal portion of the lead body further includes at least one arched tine located opposite the first electrode, and at least one arched tine located opposite the second electrode, where the tines are constructed and arranged to urge the electrode contact area of the first and second electrodes toward a myocardial wall of the coronary sinus. In another option, the distal portion of the lead body further comprises a double bias configuration constructed and arranged to urge the at least one electrode toward a myocardial wall of the coronary sinus. Other options include an external steroid collar disposed in close proximity to one electrode, or at least a portion of the lead body having a shape memory material. Still further, a distal portion of the lead body optionally has a tapered outer diameter.  
         [0012]     In another embodiment, a lead is provided which includes a lead body adapted to carry signals to and from a heart, where the lead body has a proximal portion and a distal portion. The lead further includes a connector located at a proximal end of the lead. The lead is adapted for connection to a signal generator for monitoring or stimulating cardiac activity, and is constructed and arranged for implantation within a coronary vein. The distal portion of the lead body has a helical portion adapted to be implanted within a coronary vein. At least one electrode coupled with the helical portion of the lead body. Optionally, a plurality of electrodes are disposed on the helical portion, and the plurality of electrodes are spaced about 120 degrees apart along the helical portion.  
         [0013]     Other optional features are as follows. For instance, the lead further includes apical electrodes, mid ventricular electrodes, and ventricular electrodes on the helical portion. In another example, at least a portion of the lead body comprises a shape memory material.  
         [0014]     In yet another embodiment, a lead is provided which includes a lead body adapted to carry signals to and from a heart, where the lead body has a proximal portion and a distal portion, and an intermediate portion therebetween. The lead further includes a connector located at a proximal end of the lead. The lead is adapted for connection to a signal generator for monitoring or stimulating cardiac activity, and is constructed and arranged for implantation within a coronary vein. At least one electrode is coupled with the lead body. In addition, the distal portion of the lead body has a tapered outer diameter, and the outer diameter includes a first diameter at the intermediate portion and a second diameter at the distal portion, and the first diameter is greater than the second diameter.  
         [0015]     Several options for the lead are as follows. For instance, the distal portion of the lead body further includes a helical portion which has the at least one electrode thereon, and the helical portion constructed and arranged to urge the at least one electrode toward a myocardial wall. As a further option, a plurality of electrodes are disposed on the helical portion, and the plurality of electrodes are spaced about 120 degrees apart along the helical portion. In yet another option, the lead further comprises apical electrodes, mid ventricular electrodes, and ventricular electrodes coupled with the lead body. Another example of an option is the distal portion of the lead body further includes at least one arched tine located opposite the at least one electrode. In yet another option, the at least one arched tine comprises a pliable, thin arched tine which extends from a first end to a second end, and the first end and the second end are coupled with the lead body.  
         [0016]     A method for a cardiac vein lead is also described herein. The method includes providing any of the above coronary vein leads, inserting the coronary vein lead into the coronary sinus, advancing the lead from the coronary sinus toward the left atrium, and rotating the coronary vein lead. Optionally, the method further includes sensing and/or pacing the heart via the coronary vein lead.  
         [0017]     In another method embodiment, a method includes providing any of the above coronary vein leads, where the coronary vein lead includes two or more electrodes, inserting the coronary vein lead into the coronary sinus, advancing the lead from the coronary sinus toward the left atrium. In one option, the method includes inserting a stylet into the coronary vein lead prior to inserting the coronary vein lead into the coronary sinus, and removing the stylet after inserting the coronary vein lead into the coronary sinus. In yet another option, the method further includes advancing the lead from the coronary sinus toward the left atrium and into a coronary branch vein. Another option includes pacing and sensing only the left atrium and/or the left ventricle.  
         [0018]     In another method embodiment, a method includes providing any of the above coronary vein leads, where the coronary vein lead includes two or more electrodes, inserting the coronary vein lead into the coronary sinus, advancing the lead from the coronary sinus toward the left atrium. In one option, the method further includes placing a guide catheter into the coronary sinus, threading a guide wire into the coronary vein, and pushing the lead over the guide wire and into the coronary vein. In yet another option, the method further comprises hugging an interior wall of the coronary vein with the lead body.  
         [0019]     In another method embodiment, a method includes providing any of the above coronary vein leads, where the coronary vein lead includes two or more electrodes, inserting the coronary vein lead into the coronary sinus, advancing the lead from the coronary sinus toward the left atrium. In one option, the method further comprises placing a guide catheter into the coronary sinus, threading a guide wire into the coronary sinus, pushing the coronary sinus lead over the guide wire and into the coronary sinus; and providing left sided sensing and pacing of the heart via the coronary sinus lead in its implanted site in the coronary sinus.  
         [0020]     The leads advantageously provide the ability to sense and pace the heart using leads positioned within the cardiac vasculature, and further the leads provide the ability to pace and/or sense the left heart. It has been found that by placing a therapeutic lead near the atrium, but not in the atrium, higher amplitude electrograms may be detected as compared to a standard endocardial lead. Further, it has been found that left sided pacing may help suppress atrial arrhythmias, particularly those originating near the left atrium. Still further, it has been found that the ability to critically control the timing between pacing the atria and ventricles of the heart is of utility in optimizing pacing therapies. The leads described herein involve geometries that utilize the shape of the local vasculature, the shape of the heart, or both, to help insure that an optimally positioned lead will remain in that position well beyond the time of implant. The lead designs discussed herein yield reliable and optimal performance in sensing and pacing of the heart. New coronary lead configurations are provided which can provide dual chamber pacing and/or defibrillation on a single lead body.  
         [0021]     These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims and their equivalents. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0022]      FIG. 1A  is a side view of a coronary vein lead constructed in accordance with one embodiment;  
         [0023]      FIG. 1B  is a side view of a coronary vein lead constructed in accordance with another embodiment;  
         [0024]      FIG. 2  is an enlarged view of the lead of  FIG. 1A , taken along circle  2 - 2  of  FIG. 1 ;  
         [0025]      FIG. 3A  is side view of a coronary vein lead constructed in accordance with one embodiment, shown positioned in a coronary vein;  
         [0026]      FIG. 3B  is side view of a coronary vein lead constructed in accordance with another embodiment, shown positioned in a coronary vein;  
         [0027]      FIG. 3C  is side view of a coronary vein lead constructed in accordance with another embodiment, shown positioned in a coronary vein;  
         [0028]      FIG. 4A  is a side view of a coronary vein lead constructed in accordance with one embodiment;  
         [0029]      FIG. 4B  is a side view of a coronary vein lead constructed in accordance with one embodiment  
         [0030]      FIG. 4C  is a side view of a coronary vein lead constructed in accordance with one embodiment  
         [0031]      FIG. 4D  shows lengths and diameters of a coronary vein lead constructed in accordance with one embodiment;  
         [0032]      FIG. 4E  shows radii of a coronary vein lead constructed in accordance with one embodiment; vein geometry  
         [0033]      FIG. 5A  is a side view of a portion of a coronary vein lead constructed in accordance with one embodiment;  
         [0034]      FIG. 5B  is an end view of a coronary vein lead constructed in accordance with one embodiment;  
         [0035]      FIG. 5C  is a side view of a portion of a coronary vein lead constructed in accordance with one embodiment;  
         [0036]      FIG. 5D  is a side view of a portion of a coronary vein lead constructed in accordance with one embodiment;  
         [0037]      FIG. 6A  is a side view of a coronary vein lead constructed in accordance with one embodiment;  
         [0038]      FIG. 6B  is a side view of a coronary vein lead constructed in accordance with one embodiment;  
         [0039]      FIG. 6C  is an enlarged cross section of a portion of the lead as shown in  FIG. 6B ;  
         [0040]      FIG. 6D  is an enlarged cross section of a portion of the lead as shown in  FIG. 6B ;  
         [0041]      FIG. 6E  is an enlarged cross section of a portion of the lead as shown in  FIG. 6B ;  
         [0042]      FIG. 6F  is an enlarged cross section of a portion of the lead as shown in  FIG. 6B ;  
         [0043]      FIG. 6G  is an enlarged cross section of a portion of the lead as shown in  FIG. 6B ;  
         [0044]      FIG. 7  is a side view of a coronary vein lead constructed in accordance with one embodiment;  
         [0045]      FIG. 8  is a side view of an electrode constructed in accordance with one embodiment of the coronary vein lead;  
         [0046]      FIG. 9  is a side view of a coronary vein lead constructed in accordance with one embodiment;  
         [0047]      FIG. 10A  is a side view of a coronary vein lead constructed in accordance with one embodiment; and  
         [0048]      FIG. 10B  is a side view of a coronary vein lead constructed in accordance with one embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0049]     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.  
         [0050]      FIG. 1A  is a side view of one example of a coronary vein lead  100 . The lead  100  has a proximal end  102  and a distal end  104  and includes a connector terminal  110  and a lead body  120 . The lead  100  attaches to a pulse sensor and generator  140 . In one embodiment, the lead  100  is constructed and arranged for insertion into the coronary sinus, as discussed further below. The lead body  120  has a number of electrodes  122  in its distal end  104  which is implanted in a coronary vein. The connector terminal  110  electrically connects the various electrodes and conductors within the lead body  120  to a pulse sensor and generator  140 . The pulse sensor and generator  140  contains electronics to sense various pulses of the heart and also produce pulsing signals for delivery to the heart. The pulse sensor and generator  140  also contains electronics and software necessary to detect certain types of arrhythmias and to correct for them.  
         [0051]     The lead  100 , in one option, operates similarly to a bipolar lead having positive and negative portions of a circuit located in the lead body  120 . It should be noted that this lead may also be made a unipolar lead. In other words, one electrode or both electrodes of the lead body  120  can be pacing/sensing electrodes, or one electrode can be a pacing/sensing electrode and the anode can be the pulse generator.  
         [0052]     The lead body  120  is a tubing material formed from a polymer biocompatible for implantation, and preferably the tubing is made from a silicone rubber polymer. Alternatively, the lead body  120  may be made of a biocompatible material having shape memory characteristics such that it will return to its preformed shape once implanted and a stylet or guidewire is removed. An example of such a material is polyether polyurethane. In addition, the lead body  120  optionally has portions which have shape memory characteristics, comprising either a shape memory polymer or a shape memory metal. The lead body contains several electrical conductors. The electrical conductors are made of a highly conductive, highly corrosion-resistant material. The electrical conductors carry current and signals between the pulse sensor and generator  140  and the electrodes located at the distal end  104  of the lead  100 . Electrical conductors are shown, for example, at  472  and  473  of  FIGS. 4B and 4C , and at  672  and  673  of  FIGS. 6C, 6E  and  6 G.  
         [0053]     The lead body  120  optionally has a helical portion  130  at the distal end  104 . After implantation, the helical portion  130  will be located in a coronary vein, as shown, for example, in  FIG. 1B . Referring to  FIG. 1B , a coronary vein  124  is shown which includes a free wall  126  and a myocardial wall  128 . The free wall  126  is disposed away from the heart  125 , and the myocardial wall  128  abuts the heart  125 .  
         [0054]     The helical portion  130  of the lead body  120  is optionally made of a biocompatible material having shape memory characteristics such that it will return to its preformed helical shape once implanted and a stylet or guidewire is removed. An example of such a material is polyether polyurethane. In addition, the lead body may have portions which have shape memory characteristics, comprising either a shape memory polymer or a shape memory metal. The diameter of the helical portion is about 0.25 cm-2 cm. The pitch of the helix ranges from 0.5 cm-2.5 cm. As mentioned above, the helical portion  130  includes electrodes  122 . In one option, the electrodes  122  are evenly spaced at about 120 degrees apart, which increases the opportunity for the electrodes  122  to make contact with the myocardial wall  128 . In a further option, pairs of electrodes  122  are evenly spaced about 120 degrees apart along the lead body  120 . The electrodes  122  are electrically coupled with one conductor, or are electrically coupled with separate conductors.  
         [0055]     The helical portion  130  facilitates placement of the electrodes against the myocardial wall  128  of the coronary vein  124  during and/or after implantation. The helical shape of the lead  100  provides large lead/vessel wall area interface to produce reliable, long term stability. When implanted, the helical shape of the lead  100  produces subtle lateral forces between the electrodes  122  and myocardial wall  128 , resulting in low pacing thresholds.  
         [0056]     Referring to  FIGS. 1A and 2 , the distal end  104  of the lead  100  includes several electrodes  122 , and in one example has two electrodes  132 ,  134 . The first electrode  132  is generally referred to as the distal electrode. A second electrode  134  is located near the distal electrode and proximally thereof and can be used as a counter electrode for electrode  132  or for defibrillation therapy. The lead  100  may be generally described as a tachycardia (tachy) lead, although it is not limited thereto. The electrodes  132 ,  134  are of an electrically conductive material such as an alloy of platinum and iridium which is highly conductive and highly resistant to corrosion. The electrodes  132 ,  134  optionally include a passive fixation portion. Electrodes  132  and  134  are masked or otherwise insulated on the inside radius  142  of the distal end  104  of the lead  100 . This decreases electrode area and provides desired increase in impedance. The bipolar electrode pair spacing between electrodes  132  and  134  is shown at line A of  FIG. 2  to be from about 1-5 mm. With such close electrode spacing, increased rejection of problematic far field (ventricular) signals is accomplished. Optionally, the electrode surfaces  136 ,  138  are raised beyond the body  120  of the lead  100 . Electrodes designed in this fashion increase the chances of achieving intimate tissue-electrode contact thereby resulting in lower thresholds.  
         [0057]      FIG. 3A  shows an alternative embodiment of a coronary vein lead  200  which has a helical distal end  230 , where the heart  10 , left ventricle  22 , right ventricle and apex  24  of the heart  10  are shown. It should be noted that the helical distal end  230  can be combined with any of the embodiments discussed below. The left coronary artery  25  branches into the circumflex artery  26  and the anterior descending artery  27 . The coronary sinus  28  branches into the coronary branch vein  29 . Placing the lead  200  in the coronary branch veins, for example, on the left ventricle has been found to be a suitable means for delivering pacing therapy to patients suffering from congestive heart failure.  
         [0058]     Referring to  FIG. 3B , the lead  200  is adapted to be used within the coronary artery  25  and also within the coronary branch vein  29 . A coronary vein lead  200  with a helical distal portion  230  is shown located in an implanted site. The coronary vein lead  200  includes a mid ventricular electrode pair  246  (electrodes  232  and  234 ). The electrodes  232 ,  234  are shown in intimate contact with the vessel wall  108  of the branch vein  29 , where the electrodes  232 ,  234  contact the myocardial wall, as discussed above. The coronary vein lead  200  optionally includes a mid ventricular electrode pair  246  (electrodes  232  and  234 ) and further optionally includes an apical electrode pair  250  (electrodes  252  and  254 ). The helical portion  230  and the spacing of the electrodes positions the electrodes  232 ,  234  against the myocardium to reduce pacing thresholds. The helix diameter is such that a vein of any size will reduce the diameter of the helix so that at least one electrode will be pressed against the myocardial wall. The lead  200  optionally has a fixation mechanism  240 , as shown in  FIGS. 3A and 3C .  
         [0059]     In one embodiment shown at  FIG. 3B , multiple smaller electrodes  232 ,  234 ,  242 ,  244  are strategically placed along the helix  230  thereby increasing the probability of direct electrode contact on the myocardial wall of the vein versus the free wall. For example, multiple electrodes are spaced apart along the helix  230  to span from the apex  24  to the base  18  of the heart  10 . Electrodes  232 ,  234  form a midventricular electrode pair  246  and electrodes  242 ,  244  form a basal electrode pair  248 , so designated by their proximity to a particular region of the heart when the lead  200  is in its implanted site in the heart  10 . In one embodiment, lead  200  has an apical electrode pair  250  formed of electrodes  252 ,  254  which have a proximity to the apex  24  of the heart  10  when implanted. The portion of the lead  200  including the apical electrode pair  250  optionally includes a helical portion. In another option, instead of pairs, single electrodes, or more than two electrodes can be included in that discussed above.  
         [0060]     In an embodiment where multiple electrodes are connected to the same conductor, the electrode with the best tissue contact will serve as the stimulating electrode. In one embodiment, the lead  200  has multiple electrodes and conductors, and the electrodes which are the cathodes or anodes are selected depending on the thresholds acquired at each stimulation site. As an example, in a bipolar lead, optimal therapy may be achieved by choosing the tip or ring (such as are shown, for example, at  750  and  734  of  FIG. 7 ) as cathode or anode depending on the different thresholds. In the embodiments shown at  FIGS. 3A and 3B , multiple electrode capacity is provided in the left ventricular vein. These electrodes are capable of pacing together, or alternatively with only a pair of the electrodes pacing together. Further, the electrodes optionally pace with a delay between them or sequentially.  
         [0061]     Referring to  FIG. 3C , a steroid is optionally used to ensure pacing at the cathodal site. The steroid is located in close proximity of the cathode electrode, for example, electrode  234 , and not in close proximity of the anode electrode. The steroid is provided by way of steroid collar  256  loaded with the desired drug which is then time released. The steroid collar  256  is external to the lead body  220 , and adjacent to the electrode. The drug has a very localized effect, thereby requiring close proximity to the cathode. Steroid release in close proximity to the anode electrode is not critical, but may be allowed. This placement of the steroid collar  256  ensures that the cathode electrode paces first, and before the anode electrode. An example of such a drug is dexamethasone acetate. In another option, a steroid collar or a steroid coating, for example, is provided as a generally cylindrical component adjacent one or both sides of an electrode of any lead described herein.  
         [0062]     Another option for the leads described herein involves the use of local drug elution, for example a steroid, in the vicinity of the electrodes. In many applications, desired low chronic pacing thresholds can be achieved through the local release of at least one pharmacologically active agent. This can be easily accomplished by compounding agents into polymeric components positioned adjacent to the electrodes. A pharmaceutical agent typically used in pacing applications is one possessing anti-inflammatory action. Dexamethasone, dexamethasone sodium phosphate and dexamethasone acetate have been used in commercially released devices. Other agents with other actions are other options. For example, steroidal anti-inflammatory agents other than dexamethasone, nonsteriod anti-inflammatory agents, as well as antiarrhythmic, antibiotic, anticoagulative, thrombolytic and other agents known to improve biocompatibility and/or electrical therapies are optionally used.  
         [0063]     For steroid release to be therapeutic, it must occur in very close proximity to the electrode. As such, in one embodiment, the steroid is released from the interior of an electrode and subsequently delivered directly to the heart tissue contacting the electrode. This is accomplished by first compounding a biocompatible polymer (such as silicone) with a steroid substance (such as dexamethasone) and then molding the polymer-drug matrix into a small component than can finally be positioned within a porous electrode. Alternatively, a polymer-drug matrix is molded into a generally cylindrical component that can be subsequently positioned adjacent to one or both sides of a generally cylindrical electrode. Another alternative is to apply a thin coating of the polymer-drug matrix to the completed lead body construction in locations consistent with the needed close proximity to the electrode. In yet another option, a steroid collar is used, as discussed above.  
         [0064]     In one embodiment, the lead is constructed and arranged for fixation in the coronary sinus and has specific biases to facilitate placement and retention in the coronary sinus. Referring now to  FIGS. 4A , a double-bias lead  400  constructed and arranged for fixation in the coronary sinus is shown. It should be noted that the double-bias lead  400  can be combined with embodiments discussed above and below. The lead  400  includes a first bias  402  and a second bias  406 , although an additional bias is optionally further provided with the lead  400 . The first bias  402  is disposed in a direction that is different than the second bias  406 .  
         [0065]     At  FIG. 4A , a lead  400  is shown include half ring electrodes  432 ,  434  which are biased against the vessel wall by a biased portion  460  of the lead  400 . In one embodiment, the electrodes  432 ,  434  are spaced about 10 mm apart along the lead  400 , and the length of the biased portion  460  is about 30 mm. In one embodiment, the lead  400  is constructed and arranged so a first plane including a surface  438  of the electrode  434  is spaced about 10 mm from a second plane including a surface  436  of the electrode  432 . The lead  400  in one embodiment is an over the wire lead with an open distal end, as shown in  FIG. 4B . A distal portion  404  near distal end  490  has a diameter of about 0.66 inch (5 French).  
         [0066]     The lead  400  has a length which fits within the coronary sinus/great cardiac vein. The bias portion  460  pushes the electrode up against the vein wall. The bias portion  460  is constructed and arranged to fit within the area of the coronary sinus/great cardiac vein around the mitral valve. The lengths and diameters of the coronary sinus/great cardiac vein are shown at  FIG. 4D . The coronary sinus has a length of about 37 mm and the great cardiac vein has a length of about 43 mm, for a combined length of about 80 mm. The diameter of the proximal end of the coronary sinus at the thebesian valve is about 10 mm. Where the coronary sinus and the great cardiac vein meet at the distal end of the coronary sinus and the proximal end of the great cardiac vein at the valve of vieussens, the diameter is about 5 mm. The distal portion of the great cardiac vein has a diameter of about 3 mm.  
         [0067]     The mitral valve may have a radius (R) between about 9.5 mm-42 mm. In general the radius is about 30 mm. In one embodiment, the biased lead portion  460  shown at  FIG. 4A  has a radius between about 9.5 mm to about 42 mm. In one embodiment, the biased portion has a radius of about 30 mm. The biased portion  460  of lead  400  urges electrodes  432 ,  434  against the vein wall. The diameter of the bias portion  460  of lead  400  is between electrodes  432  and  434  is larger than the diameter of the vein to provide a snug fit. In one embodiment the diameter is about 10 mm. Subtle lateral forces on vessel wall produce reliable long term stability. Lateral forces between electrode and vessel wall result in low pacing thresholds. In one embodiment, the distal end of the lead  400  has a diameter of about 0.066″.  
         [0068]     Referring to  FIG. 4B , in one embodiment the lead  400  has an atraumatic tip  490  having an outer diameter of about 5 French (0.066 inch) and an inner diameter of about 0.038 inch. The interior space between coils  472  has a diameter of about 0.018 inch. Atraumatic tip  490  in one embodiment comprises silastic tubing extending beyond the coils  472  to avoid bruising the vasculature during implantation therein. At  FIG. 4C  the transition  476  from a portion of lead body  420  which has two coils to the distal portion having one coil  478  is shown. In one embodiment, the distal portion having one coil  478  has an outer diameter of about 0.066 inch. In one embodiment the distal portion  404  has a ring electrode  474 . In one embodiment the lead has an outer diameter of about 0.067 inch at the point where electrode  474  is located.  
         [0069]     Because the lead  400  of  FIG. 4A  is designed to be implanted inside the coronary sinus/great cardiac veins (CS/GCV), the size of the lead in relation to the veins is very important. The leads described herein are designed to be held in place by wall tension, i.e. by the force of the lead against the heart wall. The lead  400  must be small enough to slide into place and not damage the walls by excess forces. The lead bias or holding mechanism must not be too small or the lead  400  may become dislodged and fall out. The biased portion  460  must not be too long or it will extend into the atrium. Referring to  FIG. 4D , the length of the coronary sinus and great cardiac veins together is 80 mm. If the pacing electrodes are desired to sit in the middle of that vein when the tip  470  of the lead  400  is located at the end of the great cardiac veins, the electrode should be placed about 43 mm proximal to the tip. The diameter of the vein averages at 10 mm at the os (entrance) and goes down to an average of 3 mm at the end of the great cardiac veins. As such, the intended position in the implanted site, or the final lead position, is considered in the lead design so that in its final position the lead  400  is wedged or held in the appropriate place. The outer diameter of the portion that is being wedged in place would be about 20 to 30% larger than the inner diameter of the blood vessel. For example, referring to  FIG. 4A , the dimension  462  of the biased portion  460  is 10 mm. This would wedge into a portion of the vein that is about 7 mm in diameter, which is near the end of the coronary sinus near the beginning of the great cardiac veins.  
         [0070]     In one embodiment, the lead body  420  may be made of a biocompatible material having shape memory characteristics such that it will return to its preformed shape once implanted and a stylet or guidewire is removed. An example of such a material is polyether polyurethane. In addition, the lead body may have portions which have shape memory characteristics, comprising either a shape memory polymer or a shape memory metal.  
         [0071]      FIGS. 5A-5D  show a lead  500  constructed and arranged for fixation in the coronary sinus, where the lead  500  includes any of the above and below discussed leads. The silicone arches  540 , in one option, are attached to and extend from a lead body  520  opposite the contact area  536  of electrode  532 . The arches  540  provide spring forces to position the electrode  532  against the vessel wall, and help to reduce dislodgement and keep pacing thresholds lower. The arches  540  also reduce complications arising in the event that the lead  500  must be removed. Referring to  FIG. 5C , in one option, the arch or arches  540  are part of a molded part of the lead  500 . In another option, as shown at  FIG. 5D , the arches  540  are straight silicone rubber cylinders affixed to the lead body  520  wall by glue in two locations that force the cylinders to assume an arched configuration. Alternatively, molded components in the shape of an arch are positioned on the lead body  520 , as shown at  FIGS. 5A and 5B .  
         [0072]     The arches  540  straddle the electrode  532 , as shown in  FIGS. 5A, 5C , and  5 D. In operation, any of the above mentioned arches  540  provide a side thrust to the lead body  520  when that lead body  520  is advanced into a narrow vessel with an inner diameter less than the combined distance of the lead body outer diameter (d, as shown at  FIG. 5B ) and the maximum height (h, as shown at  FIG. 5B ) of the arch. The side thrust will force the electrode  532  against the vessel wall in a position opposite of the arches  540 . These arches  540  are provided to reduce the rate of two types of complications. First, during implantation of a lead body  520  having arches  540 , that lead body  520  could be manipulated back and forth in the vessel. Second, and consistent with the first advantage, repositioning or removal of a subchronic or chronic lead will be easier than if the lead had free ended springs (like tines) entangling tissues when manipulation in at least one direction is needed. In an alternative embodiment, the lead  500  also comprises a helical portion as shown at  FIGS. 1-2  and  3 A- 3 C. In one embodiment, the lead body  520  may be made of a biocompatible material having shape memory characteristics such that it will return to its preformed shape once implanted and a stylet or guidewire is removed. An example of such a material is polyether polyurethane. In addition, the lead body may have portions which have shape memory characteristics, comprising either a shape memory polymer or a shape memory metal.  
         [0073]      FIGS. 6A-6G  show a lead  600  adapted for implantation and fixation in the coronary sinus.  FIG. 6A  shows the entire lead  600 , and  FIGS. 6B-6G  illustrate a portion of the lead  600 . The lead body  620  is generally shaped with the same or smaller radius of curvature as the coronary sinus, so that it hugs the anatomy of the coronary sinus when the lead  600  is implanted. The shape of the lead body  620  hugging the myocardial wall of the coronary sinus urges the electrodes  632 ,  634  against the wall of the coronary sinus. Because of this geometry compatibility, the lead  600  will have good long term stability with relatively small forces on the lead body  620  and vessel walls. By distributing forces along the extent of the lead body  620 , the possibility of lead or vessel wall damage is reduced.  FIG. 6B  shows the distal portion of one embodiment of lead  600  in greater detail. The radii of curvature and angles along different portions of the lead body are shown. In one option, the lead body  620  is made of a biocompatible material having shape memory characteristics such that it will return to its preformed shape once implanted and a stylet or guidewire is removed. An example of such a material is polyether polyurethane. In addition, the lead body may have portions which have shape memory characteristics, comprising either a shape memory polymer or a shape memory metal. In another option, the lead body  620  is preformed such that is has a shape adapted to hug the heart while the lead  600  is disposed in the coronary sinus. It should be noted that the hugging shape of the lead body  620  can be combined with any of the above and below discussed embodiments.  
         [0074]      FIG. 6C  shows the side cross section of one embodiment of the lead  600  along line C-C of  FIG. 6B . The lead  600  optionally has two sets of coils  672 , 673  at this portion.  FIG. 6D  shows a pacing electrode  632  in greater detail. The electrode  632  optionally is partially masked with the contact portion  636  facing outward, so that in an implanted site, the electrode  632  contacts the vascular tissue adjacent the myocardial wall.  FIG. 6E  shows the side cross section of the lead along line E-E of  FIG. 6B , of a lead portion having one set of coils  672 .  FIG. 6F  shows one embodiment of electrode  634  in greater detail, showing a partially masked electrode  634  with the contact portion  638  facing inward.  FIG. 6G  shows the side cross section of the lead  600  along line G-G of  FIG. 6B  showing the end tip  690  of the lead  600 .  
         [0075]      FIG. 7  illustrates another option for a cardiac vein lead, for example, a multiple polar lead  700  adapted for use in a cardiac vein. In one option, a third electrode  750  is added to a bipolar configuration, and the lead  700  can be used to pace and sense both the atrium and the ventricle. This configuration would allow the middle electrode  732  to be used as a common anode for both an atrial and ventricular bipole. This configuration would result in a lead utilizing the advantages of two bipole pairs with only three electrodes. In another option, the electrode  734  is electrically common with the electrode  750 .  
         [0076]     The lead  700  has a proximal end (as shown at  102  of  FIG. 1 ), and attaches to a pulse sensor and generator (as shown at  140  of  FIG. 1 ). The lead body  720  is cylindrical in shape and includes one or more electrical conductors. The electrical conductors are made of a highly conductive, highly corrosion-resistant material. The one or more electrical conductors carry current and signals between the pulse sensor and generator and the electrodes  732 ,  734  and  750 . In one embodiment, the electrode  734 , for example, a full ring electrode, serves as ground. The electrode  732  is a half ring electrode and serves as an atrial electrode. In another option, the electrode  750  is a PICOTIP (TM) electrode, and also comprises a ventricular electrode.  
         [0077]      FIG. 8  shows a miniaturized high impedance PICOTIP (TM) electrode  850  constructed and arranged to be a side mounted electrode, which can be used with any of the leads discussed herein. This miniaturized electrode  850  increases electrode impedance by using a smaller exposed area. Electrode  850  comprises an electrode mesh  852  which increases chronic lead stability by providing local tissue ingrowth into the electrode mesh. In another embodiment, the PICOTIP (TM) electrode protrudes from the lead body to enhance intimate wall contact.  
         [0078]     A lead according to the coronary vein leads described herein is implanted in any suitable manner, for example, as follows. Venous access is obtained via the subclavian, cephalic or jugular vein. A standard stylet is inserted into the lead to straighten it and provide stiffness for insertion of the lead into the vasculature. The coronary vein lead will then be guided into the coronary sinus/great cardiac vein. Once the coronary vein lead is positioned, the stylet will be removed. The preferred position for coronary vein lead placement is, in one option, to place the tip of the coronary vein lead near the origin of the great cardiac vein just proximal to the point where it originates from the interventricular vein. This will position the pacing electrodes near the end of the coronary sinus.  
         [0079]     The lead is tested for P-wave, P/R ratio and atrial and ventricular threshold. The lead will be manipulated and repositioned to maximize P-Wave and P/R ratios, and minimize atrial voltage threshold. Target thresholds will be below 2.0 volts with a P-wave above 2 mVolts and a P/R ratio above 2. An optional method for implanting these leads is to use an “over the wire” method. This involves (1) placing a guide catheter into the coronary sinus (2) threading a guide wire into the coronary veins, and (3) pushing the lead over the guide wire.  
         [0080]     Two other design features are described herein which improve the implantability and the chronic performance of leads. First, it was found that a slender distal tubing or stylet/conductor coil section was instrumental in improving the ability of the medical personnel to position these leads. It is believed that this feature provided the distal portion of the lead with a guiding means that easily followed the vasculature. This was accomplished only when the diameter of this guiding section was considerably less than that of the vasculature. In one embodiment shown at  FIG. 9 , a lead body  920  having a tapered flexible distal tip  990  at its distal end  904  is shown which allows for easier access to distal veins. The outer diameter  980  of the lead body  920  tapers from the proximal portion  902  to the distal end  990  of the distal portion  904 . The tapered lead body provides a smaller outer diameter at the distal end  990 , and allows more easy access to the distal veins, which have a decreasing inner diameter, and can be more complex.  
         [0081]     Referring to  FIG. 10A , a lead is shown generally at  1000 . The lead  1000  provides ventricular pacing and sensing with or without atrial pacing and sensing. In another option, the lead  1000  provides atrial pacing and sensing with or without ventricular pacing and sensing. In yet another option, the lead  1000  provides ventricular pacing and sensing with or without sided defibrillation. The lead  1000  has a proximal end shown generally at  1002  and a distal end shown generally at  1004 . The lead  1000  has a connector terminal  1010  at its proximal end and a lead body  1020 , and is constructed and arranged for insertion into the coronary sinus. The lead  1000  attaches to a pulse sensor and generator  1040 . The lead body  1020  has multiple electrodes. Proximal ring electrodes  1006  and  1008  are provided for atrial or ventricular sensing and distal electrodes  1012  and  1014  are provided for ventricular sensing and pacing. Connector terminal  1010  electrically connects the various electrodes and conductors within the lead body to the pulse sensor and generator  1040 . The pulse sensor and generator  1040  also contains electronics to sense various pulses of the heart and also produce pulsing signals for delivery to the heart. The pulse sensor and generator  1040  also contains electronics and software necessary to detect certain types arrhythmias and to correct for them. Physicians are able to program the pulse sensor and generator to correct a particular arrhythmia that the patient may have. It should be noted that there are numerous types of connector terminals which connect to a pulse sensing and generating unit  1040 .  
         [0082]     In use, the distal end  1004  of the lead  1000  is placed far enough into the coronary venous system to stimulate the ventricle, as shown for example, in FIG.  3 B. This stimulation may occur at the base of the ventricle, the middle ventricle or the apex of the ventricle.  
         [0083]     In one embodiment, the lead  1000  is instantiated only for pacing and sensing purposes, and the lead  1000  may have a unipolar or bipolar distal electrodes. Referring to  FIG. 10B , in one embodiment, the lead  1000  has multiple pairs of distal electrodes for multisite ventricular pacing. Electrodes  1046  and  1048  form an electrode pair located in the coronary sinus/great cardiac vein, and electrodes  1050  and  1052  form an electrode pair located in the ventricular portion of the lead  1000 , implanted in the coronary venous system. Electrodes  1054  and  1056  also form an electrode pair located on the ventricular portion of the lead  1000  implanted in the coronary venous system. The embodiment shown at  FIG. 10B  may have a lead body  420  made of a biocompatible material having shape memory characteristics such that it will return to its preformed shape once implanted and a stylet or guidewire is removed. An example of such a material is polyether polyurethane. In addition, the lead body may have portions which have shape memory characteristics, comprising either a shape memory polymer or a shape memory metal.  
         [0084]     In one embodiment, the lead  1000  has proximal electrodes, shown at  1006  and  1008  of  FIG. 10A , which are either bipolar or unipolar, for sensing and/or pacing of the atrium. In one embodiment, multiple pairs or multiple sets of electrodes may be used for bi-atrial pacing. An optional distal electrode  1014  of the lead  1000  serves as a distal shocking electrode for the purpose of delivering a high energy shock greater than about 0.01 Joule to the ventricle. This distal shocking electrode may be added to any of the lead configurations disclosed herein.  
         [0085]     The leads described herein provide several advantages over previous leads. The leads provide, in one option, the ability to sense and pace the heart using leads positioned within the cardiac vasculature, and further the leads provide the ability to pace and/or sense the left heart. It has been found that by placing a therapeutic lead near the atrium, but not in the atrium, higher amplitude electrograms may be detected as compared to a standard endocardial lead. Further, it has been found that left sided pacing may help suppress atrial arrhythmias, particularly those originating near the left atrium. Still further, it has been found that the ability to critically control the timing between pacing the atria and ventricles of the heart is of utility in optimizing pacing therapies. The leads described herein involve geometries that utilize the shape of the local vasculature, the shape of the heart, or both, to help insure that an optimally positioned lead will remain in that position well beyond the time of implant. The lead designs discussed herein yield reliable and optimal performance in sensing and pacing of the heart. New coronary lead configurations are provided which can provide dual chamber pacing and/or defibrillation on a single lead body.  
         [0086]     Further provided herein is a method for placing a lead into a coronary vein to provide sensing and pacing of the heart, for example, the left side of the heart. In one embodiment, a lead is provided that is a right side lead and is placed within the coronary sinus, and is then advanced from the coronary sinus toward the left atrium to provide left sided sensing and pacing.  
         [0087]     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. It should be noted that embodiments discussed in different portions of the description or referred to in different drawings can be combined to form additional embodiments of the present invention. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.