Abstract:
A system for providing medical electrical stimulation includes a pulse generator coupled to a lead having two electrodes for placement in the right atrium or for placement of one in the right atrium and one in the coronary sinus or coronary vein. In the preferred embodiment the surface area of the first electrode is smaller than that of the second electrode so that the sensed signal from the first electrode is less than that from the second. The system provides dual site pacing with essentially single site sensing without the use of extra switches, connectors, or adaptors.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to medical electrical stimulation, and more particularly, to a lead system for providing medical electrical stimulation to either two locations in a single atrium or to a site in each of the two atria of a patient&#39;s heart. 
     BACKGROUND OF THE INVENTION 
     Electrical stimulation of body tissues and organs is often used as a method of treating various pathological conditions. Such stimulation generally entails making electrical contact between body tissue and an electrical pulse generator through one or more stimulation leads. Various lead structures and various techniques for implanting these lead structures into body tissue and particularly the heart have been developed. For example, a transvenous endocardial lead is passed through a vein, with the assistance of a fluoroscope, into the heart where it may be held in electrical contact with the endocardium of the right atrium or ventricle. 
     The left chambers of the heart are presently not available for the implantation of long term transvenous leads due to risk of thrombus or clot formation. In particular, blood flows through the right side of the heart, through the lungs, through the left side of the heart and then through the rest of the body, including the brain, before returning again to the right side of the heart. Implanted objects often cause minor blood clots and thrombus to form in the blood. These may, on occasion, dislodge and be released into the bloodstream. Because the blood circulates directly from the left atrium and ventricle to the brain, any clots could have serious consequences if they were to reach the brain, e.g. a stroke. In contrast, any clots released from an object implanted in the right side of the heart would simply travel to the lungs, where they would lodge without any serious risk. Thus at present, chronic transvenous leads may not be safely implanted within the left side of the heart. 
     In spite of the difficulties, there remains a great need to be able to electrically stimulate the left side of the heart. As a result, transvenous lead placement into the coronary sinus (CS) or deeper into the great cardiac vein (GCV) or other coronary vein has recently become an important technique for cardiac pacing and defibrillation electrode implantation to gain electrical access to the left side of the heart. U.S. Pat. No. 4,932,407 to Williams; U.S. Pat. No. 5,099,838 to Bardy; and U.S. Pat. Nos. 5,348,021; 5,433,729; and 5,350,404 to Adams et al., incorporated herein by reference, describe inserting a lead through the right atrium and CS into one of the coronary veins. To implant a lead made in conformance with the present invention, the implanter passes the lead through a guide catheter, or introducer, until it is in or near the CS. This is done using a standard technique of stiffening the lead with a stylet, guiding the stiffened lead by hand through the right atrium (RA) and into or near the CS, aided by fluoroscopy. Following proper placement, any stiffening stylets or guide catheters are retracted. 
     As an example of placing leads into the CS, dual site right atrial pacing and biatrial pacing with the left atrium paced from the CS are being studied to reduce the incidence of paroxysms of atrial fibrillation. In a recent publication (Daubert et al., “Biatrial Synchronous Pacing: A New Approach to Prevent Arrhythmias in Patients with Atrial Conduction Block,” from  Prevention of Tachyarrhythmias with Cardiac Pacing , Futura Publishing Company, Inc., Armonk, N.Y., 1997, p. 111), dual site pacing has been done by pacing the RA cathodically and the LA anodically, using a Y adaptor. This composite dual atrial lead configuration detects three successive intracardiac signals: the RA electrogram, the LA electrogram, and a far field R wave sensed in the CS and corresponding to LV depolarization. If the pacemaker misinterprets these LV signals as originating in the atria, inappropriate inhibition or inappropriate triggering may occur, possibly creating a pacemaker-mediated tachycardia (PMT). In U.S. Pat. No. 5,514,161 to Limousin, a Y adaptor is used as described above, and software is used to deal with the ventricular signals in order to avoid such a PMT. It would be desirable to provide dual site pacing without requiring a Y adaptor or added connectors, and sensing only one atrial bipolar signal while rejecting ventricular signals. 
     As another example of placing leads into the CS or deeper, defibrillation electrodes within the CS have been shown to reduce atrial and ventricular defibrillation thresholds. U.S. Pat. No. 5,476,498 to Ayers shows an example of a lead having an atrial defibrillation electrode for implantation within the CS. 
     As yet another example of placing leads through the CS and deeper into a coronary vein, pacing the left ventricle (LO from within a coronary vein appears to improve hemodynamics in certain disease states such as heart failure. For example, in patients with dilated cardiomyopathy, electrical stimulation of both the right side and the left side of the heart has been shown to be of major importance to improve the patient&#39;s well-being and manage heart failure. See, for example, Cazeau et al., “Tour Chamber Pacing in Dilated Cardiomyopathy.” PACE, November 1994, pp. 1974-79. 
     The functions desired of pacemakers and pacemaker/defibrillators currently require a large number of electrodes, a large number of lead connectors, and a large header with a large number of connector cavities. A solution is needed to provide needed features while not increasing device size and hardware to a clinically unacceptable level, and while still using standard (IS-1 and DF-1) connectors. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide a lead or lead system that paces two sites simultaneously while sensing from essentially only one. 
     It is a further object of this invention to provide a lead or lead system that uses standard connectors. 
     It is a further object of this invention to reduce the hardware required without a reduction in desired features. 
     It is a further object of this invention to provide a lead system that does not require any adaptors. 
     It is a further object of this invention to provide a lead system for which no extra switches are required for switching between electrodes for pacing and sensing. 
     Briefly, the above and further objects and features of the present invention are realized by providing a system that uses one connector for both dual site pacing and single site sensing. In a first embodiment of the invention, the first pacing site is an RA location, and the second site is a second RA site near the CS os. In an alternative embodiment, the second site is an LA site through the CS. In one embodiment, a CS (LA) pacing electrode at the second site is electrically coupled to an RA electrode at the first site, with each acting as the cathode in its respective chamber. The anode for both is a second RA electrode, which may be either a dedicated ring electrode or a defibrillation electrode. 
     The present invention may include a CS defibrillation electrode, and the second site pacing electrode may be located either proximal or distal of the CS defibrillation electrode. If located distal of the CS defibrillation electrode, the electrode paces the LA; if proximal, the electrode may be positioned to pace the LA or a second site in the RA. 
     In the preferred embodiment, the lead is preshaped to encourage contact of the electrodes with the endocardium. For example, a curve in the portion of the lead to be positioned in the RA may be used to force the RA electrodes in contact with the RA endocardium. Likewise, one or more angles on the distal end of the CS lead may be used to force the LA electrode in contact with the CS oriented toward the LA. See for example U.S. Pat. No. 5,683,445 to Swoyer, which is incorporated herein by reference. 
     By keeping the LA (CS) pacing electrode very small, its current density can be kept high for pacing, while getting very little sensed signal from it (compared with the RA electrode). Increasing the impedance of the LA electrode as compared with the RA electrodes will accomplish this. Besides keeping the macroscopic surface area small, the microscopic surface area should also be kept small. In one embodiment of the invention, a smooth platinum or platinum iridium alloy tip is used to accomplish this in a lead that is stable within the CS in which sensing is not desirable. The RA electrodes are preferably porous to optimize sensing. In an alternative embodiment, one of the RA electrodes is replaced by an RA/SVC defibrillation electrode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a first embodiment of the cardiac lead of the present invention as implanted within the heart and with an electrode in the coronary sinus; 
     FIG. 2 is a schematic illustration of the cardiac lead shown in FIG. 1; 
     FIG. 3 is a block diagram of the electrical connections cardiac lead and pulse generator shown in FIG. 1; 
     FIG. 4 is a schematic illustration of an alternative embodiment of the cardiac lead of the present invention; and 
     FIG. 5 is a block diagram of the cardiac lead shown in FIG. 4 as connected to a pulse generator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a human heart  1  with the cardiac lead  10  of the present invention passing through the superior vena cava (SVC)  2 , the right atrium (RA)  3 , the coronary sinus os (CS os)  7  and into the coronary sinus (CS)  8  so that a first electrode  11  on lead  10  is implanted within the CS  8  and so that a second electrode  12  and a third electrode  13  are implanted within RA  3 . Lead  10  is connected to pulse generator  18  using a coaxial bipolar connector  30 . When positioned as shown, electrode  11  can be used to apply a stimulating pulse to the LA without the need of being in the left atrial chamber. Electrode  12  can be used to apply a stimulating pulse to the RA and electrodes  12  and  13  can be used to sense the electrical activity of the RA  3 . 
     FIG. 2 shows in greater detail the structure of cardiac lead  10  shown in FIG.  1 . As shown in FIG. 2, lead  10  includes an elongated body having a proximal end  19  and a distal end  20 . Electrode  11  is shown as a tip electrode positioned at distal end  20  and is electrically coupled to a first conductor  21 . Conductor  21  is, in turn, electrically coupled to a first contact  31  of coaxial bipolar connector  30 . Electrode  11  may, alternatively be a ring electrode. Second electrode  12  is shown as a ring electrode and is electrically coupled to a second conductor  22 , which is in turn electrically coupled to first contact  31 . As shown, conductor  21  is coupled to first contact  31  via conductor  22 , thereby saving space by not running parallel conductors. Alternatively, conductor  21  could extend all the way from first electrode  11  to first contact  31  without directly attaching to second electrode  12 , and second conductor  22  could be completely separate from first conductor  21 . This would, however, require more space. Electrode  12  preferably is spaced from electrode  11  along lead  10  by at least 20 mm so that pacing pulses will stimulate tissue in the vicinity of each electrode separately. Electrode  13  is shown as a ring electrode and is electrically coupled to a third conductor  23 , which, in turn, is electrically coupled to a second contact  33  of coaxial bipolar connector  30 . Electrode  13  may alternatively be a very large surface area electrode suitable for atrial and/or ventricular defibrillation as will be described in connection with FIG. 5 below. Electrode  13  preferably is spaced from electrode  12  by 2 mm to 15 mm such that bipolar signals obtained between electrodes  12  and  13  are optimum for sensing. As shown, connector  30  is a standard connector type, IS-1 BI, wherein first contact  31  is a pin that is typically used to couple to a pacemaker cathode, and second contact  33  is a ring that is typically used to couple to a pacemaker anode. 
     It is desirable to make the profile of the distal end of a lead implanted in a coronary vein as small as possible to limit occlusion of flow through the blood vessel when the lead is in place and to limit damage to the vessels. As shown in FIG. 2, lead  10  may be angled at distal end  20  to stabilize the lead within the CS and to bring electrode  11  in close contact with the tissue. 
     FIG. 3 is a block diagram showing lead  10  connected to pulse generator  18 . Pulse generator  18  includes a microprocessor  48 , pacing circuits  49 , and sensing circuits  50  as are well known in the art. Pulse generator  18  also includes first pacing output  40 , second pacing output  41 , first sense amplifier input  42 , and second sense amplifier input  43 . When connector  30  is inserted into the connector port (not shown) of pulse generator  18 , first contact  31  is electrically coupled to first pacing output  40  and to first sense amplifier  42 , and second contact  33  is electrically coupled to second pacing output  41  and to second sense amplifier  43 . In this way, electrodes  11  and  12  become coupled to first pacing output  40  and to first sense amplifier  42 , and electrode  13  becomes coupled to second pacing output  41  and to second sense amplifier  43 . In the embodiment shown in FIG. 3, first contact  31  is a pin coupled to the pacing output cathode, and second contact  33  is a ring coupled to the pacing output anode. 
     It is advantageous to pace from both electrode  11  and electrode  12 . However, the pacing threshold is generally higher when pacing the LA through the CS as compared with pacing the RA. Therefore, it is desirable to keep the current density higher at electrode  11  than at electrode  12  to even out the pacing thresholds. Furthermore, no stimulation is desired at electrode  13 . Still further, in order to avoid sensing ventricular signals, it is desirable to have all sensed signal come from electrodes  12  and  13 , with as little as possible from electrode  11 . By keeping the LA (CS) pacing electrode very small, its current density can be kept high for pacing, while getting very little sensed signal from it (compared with the RA electrodes). This can be done by increasing the impedance of the LA electrode as compared with the RA electrodes. One effective method for doing this is to make both the macroscopic surface area and the microscopic surface area smaller than that of electrodes  12  and  13 . A smooth platinum tip is preferred for this application if the lead is already stable within the CS and sensing is not desirable. It will also be easier to remove than a porous tip, should the need arise. The RA electrodes  12  and  13  are preferably porous to optimize sensing. 
     FIG. 4 shows an alternative embodiment of lead  10 ′ that provides additional functions as compared to the embodiment of FIGS. 1-3. As in the previously described embodiment, electrodes  11  and  12  are coupled to first contact  31  of connector  30  via conductors  21  and  22 . Electrode  12  preferably is spaced from electrode  11  along lead  10 ′ by at least 20 mm so that pacing pulses will stimulate tissue in the vicinity of electrode  11  and electrode  12  separately. Electrode  11  is positioned on lead  10 ′ to pace the LA from within the CS. Electrode  12  is positioned on lead  10 ′ to pace the RA. Alternatively, electrodes  11  and  12  may be positioned to pace different parts of the RA. 
     Electrode  13  is shown as a large surface area electrode for placement within the RA and/or SVC and suitable for atrial and/or ventricular defibrillation as well as for a “reference electrode” for pacing and sensing. Electrode  13  is electrically coupled a first high voltage connector  34  via low resistance conductors  23  and  24 . In this case connector  34  is shown as a standard DF-1 connector. Low resistance conductor  24  is an extension of low resistance conductor  23 ; alternatively, low resistance conductor  24  may be a separate conductor coupled to low resistance conductor  23 . Low resistance conductor  23  is coupled also to second contact  33  of connector  30  via a high resistance conductor  32  (shown schematically as a resistor). 
     Even more electrodes and conductors can be added for sensing, pacing or defibrillating as desired. For example, a large surface area defibrillation electrode  14  for implantation within the CS or great cardiac vein is shown on the distal portion of lead  10 ′. Preferably, defibrillation electrode  14  has a shape that stabilizes lead  10 ′ within the CS. The distal portion  20  of lead  10 ′ that is intended for placement through the CS os preferably has a smaller diameter than the proximal portion  19 . Defibrillation electrode  14  is coupled to a second high voltage connector  35  via a low resistance conductor  25 . Alternatively or additionally, lead  10 ′ includes one or more pacing or sensing electrodes for implantation within the CS for pacing the LV. 
     FIG. 5 is a block diagram showing lead  10 ′ of FIG. 4 connected to pulse generator  18 ′. Pulse generator  18 ′ includes a microprocessor  48 , pacing circuits  49 , sensing circuits  50 , and defibrillation circuits  51  as are well known in the art. Pulse generator  18 ′ also includes first pacing output  40 , a second pacing output  41 , a first sense amplifier input  42 , a second sense amplifier input  43 , a first defibrillation output  44 , and a second defibrillation output  45 . When connector  30  is inserted into the connector port (not shown) of pulse generator  18 ′, first contact  31  is electrically coupled to first pacing output  40  and to first sense amplifier  42 , and second contact  33  is electrically coupled to second pacing output  41  and to second sensing input  43 . Furthermore, when first high voltage connector  34  is inserted into the first high voltage connector port (not shown) of pulse generator  18 ′, third electrode  13  is electrically coupled to first defibrillation output  44 . When second high voltage connector  35  is inserted into the second high voltage connector port (not shown) of pulse generator  18 ′, fourth electrode  14  is electrically coupled to second defibrillation output  45 . Defibrillation outputs  44  and  45  may be of opposite polarity, or may be of the same polarity to be used in conjunction with other defibrillation electrodes. 
     Electrode  13  is electrically coupled to a first high voltage connector  34  via low resistance conductors  23  and  24 . Low resistance conductor  23  is coupled also to second contact  33  of connector  30  via a high resistance conductor  32 . The resistance that is added in the pacing/sensing leg by high resistance conductor  32  protects the pacing and sensing circuits during defibrillation. 
     The foregoing discussion is intended to illustrate various preferred arrangements for meeting the objectives of the present invention. For example, more than two sites may be paced simultaneously. Those skilled in the art can make modifications and variations without departing from the invention. Accordingly, the invention is limited only by the scope of the following claims.