Abstract:
Apparatus is disclosed for providing a practitioner the ability to switch from one cardiac pacing mode to another cardiac pacing mode when treating a patient suffering from heart failure due to discoordinate ventricular contraction. Also disclosed are methods of providing different modes of cardiac pacing to a cardiac pacing patient using the apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit under Title 35, United States Code, §119(e)(1) of U.S. provisional application Ser. No. 60/277,447, filed Mar. 21, 2001. 

   TECHNICAL FIELD 
   This invention relates to therapeutic medical devices, and more particularly to cardiac pacing apparatus. 
   BACKGROUND 
   Patients with dilated cardiomyopathy occasionally undergo coronary artery bypass or valvular surgery. Heart failure, characterized by discoordinate ventricular contraction and non-uniform electrical activation, may be present temporarily following a myocardial infarction or a surgical insult. At the conclusion of an operative procedure when other modalities have failed to improve cardiac function, temporary cardiac pacing can be employed to improve hemodynamics. 
   For temporary cardiac pacing, fine gage insulated cardiac pacing leads are commonly attached to the cardiac patient&#39;s heart. One type of lead placement frequently done in conjunction with open-heart surgery is transthoracic lead placement. Such placement is normally performed when the patient is on full cardiopulmonary support after cardiac surgery. With transthoracic lead placement, positive and negative cardiac pacing leads are usually placed on the right ventricular epicardium, often by means of a surgical needle. If unipolar (single-conductor) leads are placed, they will be spaced apart from one another in order to include ventricular tissue within the intended electrical circuit. In cases in which a bipolar (dual-conductor) coaxial pacing lead is selected for use in cardiac pacing, only one lead will be placed, since such a lead contains two discrete electrodes, spaced apart for adequate electrical performance. The cardiac pacing lead(s) are then threaded through the skin and are cut. Commonly the leads will then be tested for adequate electrical threshold. 
   Equipment used to conduct temporary cardiac pacing in conjunction with internally implanted cardiac pacing leads includes an external pulse generator, also known as a temporary pulse generator, and a pacing cable. Temporary pulse generators are electronic devices packaged in the typical box-like enclosures, are generally powered by mercury (alkaline) batteries, and when in use are typically pinned to the patient&#39;s gown so the unit will not be dislodged when the patient shifts position, stands or sits. Examples of temporary pulse generators which have been used by practitioners include the Medtronic Single-Chamber Model 5348 External Pulse Generator, and the Medtronic Dual-Chamber Model 5388 External Pulse Generator. Temporary pulse generators provide controlled electrical pulses to the heart of a pacing patient which stimulate the heart to beat in concert with the pulses provided. Accordingly, such pulse generators will provide paired negative and positive terminals, which are integrated within an externally accessible connector port. 
   A pacing cable is used to connect the pulse generator with the pacing leads extending from the heart and through the skin of the patient. The pacing cable will have a connector to mate with above-mentioned connector port of the temporary pulse generator, and when the connector and the connector port are mated thereby, a positive lead in the pacing cable is electrically connected to the positive terminal of the connector port, and a negative lead in the pacing cable is electrically connected to the negative terminal of the connector port. The conductors within the cable will typically be made of copper, surrounded by flexible material to provide electrical insulation, flexibility, and toughness. Typically the positive and negative leads within the pacing cable will pass through the cable without branching, and will simply terminate at the other end of the cable in terminals designed to accept and connect to the fine gage cardiac pacing leads. One type of connection used is a clip connection, commonly called an ‘alligator clip.’ Another type of connection commonly used involves a threaded cylinder-type terminal, in which the pacing lead is inserted into an aperture in the cylinder, and the threaded portion of the terminal is screwed downward, securing the pacing lead within the terminal. Once the wiring is in place, temporary pacing can begin. 
   Traditionally, when cardiac patients have required post-operative temporary cardiac pacing, right ventricular pacing has been performed, in which cardiac pacing leads including a positive electrode and a negative electrode are attached to the right ventricle of the heart. Recently, however, practitioners have found certain patients will benefit when cardiac pacing is performed in concert upon on the right and left ventricle, and have responded by reconfiguring temporary pacing apparatus to provide ‘biventricular pacing’, i.e., a pacing regimen in which both the right and left ventricles are subjected to electrical pulses intended to stimulate simultaneous contraction. In such instances, a left negative cardiac pacing lead is placed on the left ventricular epicardium, generally equidistant from the septum (LAD) when compared to the right negative cardiac pacing lead, and the negative cardiac pacing leads are usually combined at the point they attach to the pacing cable (i.e., the alligator clip or threaded cylindrical terminal). Positive leads are usually similarly combined when biventricular pacing is provided. 
   Other practitioners have also recently found that some patients, such as those who suffer from left bundle branch block, may benefit when left ventricular pacing, as distinguished from right ventricular or biventricular pacing, can be provided after surgery. However, the temporary pulse generators and pacing cables which are commercially available are designed to provide pulse generation for single-site (generally the right ventricle) ventricular pacing, and will provide biventricular pacing only when cardiac pacing wires are doubled up at the terminal interfaces of the pacing cable. As a result, a practitioner concerned with providing his patients the fastest post-operative recovery possible will find presently available pacing apparatus incapable of providing him the flexibility to select from among the alternative modes of ventricular pacing described above in a quick fashion commensurate with efficient clinical care. 
   SUMMARY 
   Herein I have disclosed details of a pacing cable, which when used in conjunction with a cardiac temporary pulse generator, such as a Medtronic models 5348 and 5388, will provide temporary cardiac pacing. The pacing cable described in the present application allows for switching between multiple modes of ventricular pacing, including left ventricular, right ventricular, and biventricular pacing, and provides the capacity for the caregiver to switch between cardiac pacing modes easily in an effort to improve the clinical outcome. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  shows four cardiac pacing leads placed in mechanical and electrical connection with a patient&#39;s heart at the time of surgery in accordance with the present application. 
       FIG. 2  shows a pacing cable in accordance with the present application. 
       FIGS. 3A ,  3 B and  3 C show wiring diagrams of pacing cables in accordance with the present application. 
       FIG. 4  shows three cardiac pacing leads placed in mechanical and electrical connection with a patient&#39;s heart at the time of surgery in accordance with the present application. 
       FIG. 5  shows a pacing cable in accordance with the present application. 
       FIGS. 6A ,  6 B and  6 C show wiring diagrams of pacing cables in accordance with the present application. 
       FIG. 7  shows a pacing cable in accordance with  FIG. 2  and the present application connected to a standard temporary pulse generator. 
       FIG. 8  shows a pacing cable in accordance with  FIG. 5  and the present application connected to a standard temporary pulse generator. 
       FIG. 9  shows a temporary pulse generator in accordance with the present application. 
       FIG. 10  shows a temporary pulse generator in accordance with the present application. 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   With regard to  FIG. 1 , transthoracic placement of four cardiac pacing leads is shown, two on the right ventricular epicardium, and two on the left ventricular epicardium. Lead  101  is the positive pacing lead for the right ventricle, and lead  102  is the negative pacing lead for the right ventricle. Lead  103  is the negative pacing lead for the left ventricle, and lead  104  is the positive pacing lead for the left ventricle. Pacing leads  101 ,  102 ,  103 , and  104  are lead away from the heart and through the skin of the patient, in order to provide the conductive path necessary for temporary cardiac pacing. 
   The features of a pacing cable in accordance with the present application will be shown with reference to  FIGS. 2 ,  3 A,  3 B, and  3 C. Some terminals mentioned below are not visible in  FIG. 2  because they are enclosed within the pacing cable  200 , but all terminals are depicted, either by solid or dashed lines, in the pacing cable wiring diagrams  301 ,  302 , and  303  shown in  FIGS. 3A ,  3 B, and  3 C respectively. The pacing leads  101 ,  102 ,  103  and  104  shown in  FIG. 1  are attached, respectively, to terminals  201 ,  202 ,  203  and  204  of the pacing cable  200 . Terminal  201  is at the end of positive lead  211 , which passes directly through the pacing cable, ending at terminal  231  within the pulse generator connector  250 . Terminal  204  is at the end of positive lead  214 , which also passes directly through the pacing cable and ends at terminal  231  within the pulse generator connector. In this way a branched positive return lead is created within the pacing cable. Terminal  202  is at the end of negative lead  212 , which passes through the cable, ending at terminal  222  within the cable. Terminal  203  is at the end of negative lead  213 , which passes through the cable, ending at terminal  223  within the cable. Terminal  225  is within the cable at the end of negative lead  215 , which passes through the cable, ending at terminal  235  within the pulse generator connector  250 . 
   Toggle switch region  210  has three mode selection buttons  242 ,  243  and  244 , which are adapted to be selectably manipulated so as to configure the pacing cable to provide the desired mode of pacing. Toggle switches are shown and were used in an embodiment, but any suitable switching mechanism known to those with skill in the art may be used for this purpose. As an example of the manner in which the toggle switch mechanism of  FIG. 2  functions, the abstract wiring diagram  301  of  FIG. 3A  demonstrates that when mode selection button  242  is depressed, an electrical connection between terminals  222  and  225  is provided by terminal  225  being moved into contact with terminal  222 , and that an electrical isolation of terminal  223  is provided at the same time, since terminal  225  has been moved away from it. Such an arrangement would permit right ventricular pacing. Alternatively, the abstract wiring diagram  302  of  FIG. 3B  demonstrates that when mode selection button  243  is depressed, an electrical connection between terminals  223  and  225  is provided by terminal  225  being moved into contact with terminal  223 , and that an electrical isolation of terminal  222  is provided at the same time, since terminal  225  has been moved away from it. Such an arrangement would permit left ventricular pacing. Finally, the abstract wiring diagram  303  of  FIG. 3C  demonstrates that when modes selection button  244  is depressed, a simultaneous electrical connection between terminals  222 ,  223 , and  225  is provided, resulting in a branched negative lead within the pacing cable, as shown in wiring diagram  303  of  FIG. 3C . Such an arrangement would permit biventricular pacing. 
   With regard to  FIG. 4 , transthoracic placement of three cardiac pacing leads is shown, two on the right ventricular epicardium, and one on the left ventricular epicardium. Lead  401  is a positive pacing lead, lead  402  is the negative pacing lead for the right ventricle, and lead  404  is the negative pacing lead for the left ventricle. Pacing leads  401 ,  402  and  403  are lead away from the heart and through the skin of the patient, in order to provide the conductive path necessary for temporary cardiac pacing. It has been observed that one positive pacing lead placed on the heart on either ventricle will provide an adequate return path for right ventricular, left ventricular, and biventricular pacing. 
   The features of another pacing cable in accordance with the present application will be shown with reference to  FIGS. 5 ,  6 A,  6 B, and  6 C. Some terminals mentioned below are not visible in  FIG. 5  because they are enclosed within the pacing cable  500 , but all terminals are depicted, either by solid or dashed lines, in the pacing cable wiring diagrams  601 ,  602 , and  603  shown in  FIGS. 6A ,  6 B, and  6 C respectively. The pacing leads  401 ,  402  and  403  shown in  FIG. 4  are attached, respectively, to terminals  501 ,  502  and  503  of the pacing cable  500 . Terminal  501  is at the end of positive lead  511 , which passes through the cable, ending at terminal  531  within the cable. Terminal  502  is at the end of negative lead  512 , which passes through the cable, ending at terminal  522  within the cable. Terminal  503  is at the end of negative lead  513 , which passes through the cable, ending at terminal  523  within the cable. Terminal  525  is within the cable at the end of negative lead  515 , which passes through the cable, ending at terminal  535  within the pulse generator connector  550 . 
   Toggle switch region  510  has three mode selection buttons  545 ,  543  and  544 , which are adapted to be selectably manipulated so as to configure the pacing cable to provide the desired mode of pacing. Toggle switches are shown and were used in an embodiment, but any suitable switching mechanism known to those with skill in the art may be used for this purpose. As an example of the manner in which the toggle switch mechanism of  FIG. 5  functions, the abstract wiring diagram  601  of  FIG. 6A  demonstrates that when mode selection button  642  is depressed, an electrical connection between terminals  522  and  525  is provided by terminal  525  being moved into contact with terminal  522 , and that an electrical isolation of terminal  523  is provided at the same time, since terminal  525  has been moved away from it. Such an arrangement would permit right ventricular pacing. Alternatively, the abstract wiring diagram  602  of  FIG. 6B  demonstrates that when mode selection button  543  is depressed, an electrical connection between terminals  523  and  525  is provided by terminal  525  being moved into contact with terminal  523 , and that an electrical isolation of terminal  522  is provided at the same time, since terminal  525  has been moved away from it. Such an arrangement would permit left ventricular pacing. Finally, the abstract wiring diagram  603  of  FIG. 6C  demonstrates that when modes selection button  544  is depressed, a simultaneous electrical connection between terminals  522 ,  523 , and  525  is provided, resulting in a branched negative lead within the pacing cable, as shown in wiring diagram  603  of  FIG. 6C . Such an arrangement would permit biventricular pacing. 
   As may be seen with reference to  FIG. 7 , pulse generator connector  250  of the pacing cable  200  may be connected to the connector port  760  at the ventricular position of a standard temporary pulse generator  700  such as the Medtronic model 5388. Positive terminal  231  connects with the positive terminal  731  of the connector port  760 . Negative terminal  235  connects with the negative terminal  735  of the connector port  760 . By means of selective operation of its mode selection feature as described above, the pacing cable  200  may be combined with a standard temporary pulse generator to provide three modes of cardiac pacing: right ventricular pacing (standard), left ventricular pacing, and biventricular pacing. 
   As may be seen with reference to  FIG. 8 , pulse generator connector  550  of the pacing cable  500  may be connected to the connector port  860  at the ventricular position of a standard temporary pulse generator  800  such as the Medtronic model 5388. Positive terminal  531  connects with the positive terminal  831  of the connector port  860 . Negative terminal  535  connects with the negative terminal  835  of the connector port  860 . By means of selective operation of its mode selection feature as described above, the pacing cable  500  may be combined with a standard temporary pulse generator to provide three modes of cardiac pacing: right ventricular pacing (standard), left ventricular pacing, and biventricular pacing. 
   As may be seen with reference to  FIG. 9 , the switching function performed by pacing cable  200  in accordance with the present application may be incorporated within a temporary pulse generator itself. A temporary pulse generator  900  in accordance with the present application is shown in  FIG. 9 . The ventricular position has four terminals  901 ,  902 ,  903  and  904  within its connector port  960 . These four terminals may be connected, respectively, to the pacing leads  101 ,  102 ,  103  and  104  of  FIG. 1  by means of a simple, four lead pacing cable (not shown). Switch  940  at the ventricular position of the temporary pulse generator permits the practitioner to select between position  941 , providing right ventricular pacing through terminals  901  and  902 ; position  942 , providing left ventricular pacing through terminals  903  and  904 ; and position  943 , providing biventricular pacing through all four terminals. A dial switch is shown in the embodiment, but any suitable switching mechanism known to those with skill in the art may be used for this purpose. Furthermore, any suitable arrangement of electronics and wiring within the temporary pulse generator may be employed by those with skill in the art to support the switching function shown. 
   As may be seen with reference to  FIG. 10 , the switching function performed by pacing cable  500  in accordance with the present application may be incorporated within a temporary pulse generator itself. A temporary pulse generator  1000  in accordance with the present application is shown in  FIG. 10 . The ventricular position has three terminals  1001 ,  1002  and  1003  within its connector port  1060 . These three terminals may be connected, respectively, to the pacing leads  401 ,  402  and  403  of  FIG. 4  by means of a simple, three lead pacing cable (not shown). Switch  1040  at the ventricular position of the temporary pulse generator permits the practitioner to select between position  1041 , providing right ventricular pacing through terminals  1001  and  1002 ; position  1042 , providing left ventricular pacing through terminals  1001  and  1003 ; and position  1043 , providing biventricular pacing through all three leads. A dial switch is shown in the embodiment, but any suitable switching mechanism known to those with skill in the art may be used for this purpose. Furthermore, any suitable arrangement of electronics and wiring within the temporary pulse generator may be employed by those with skill in the art to support the switching function shown. 
   It will be understood that various modifications may be made to the apparatus described in the present application without departing from the spirit and scope of the invention. For example, coaxial-type pacing leads may be used where the use of single-conductor pacing leads are described in the present application. Accordingly, other embodiments are within the scope of the following claims.