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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 7, JULY 1979
and not allowing time for the sample and hold to acquire the new pulse height. The operation of hold and peak detect signals is illustrated in Fig. 4. The necessary overlap between these two signals is generated by the pulse stretcher D2, C3, and R 3. REFERENCES [11 H. E. Kubitshek, "Counting and sizing micro-organisms with the Coulter counter," in Methods in Cell Biology, J. R. Norris and D. W. Ribbons, Eds. London, England: Academic, 1969, pp. 593-610. [21 S. J. Rackham, "A pulse height analyzer for displaying particle size distributions," M.Sc. thesis, Univ. Waikato, Hamilton, New Zealand, 1977.
Proposed Cardiac Pacemaker System Combining Unipolar Stimulation with Bipolar Sensing
PHILIP HURZELER, V. DE CAPRIO, AND S. FURMAN Abstract-Present cardiac pacemaker designs use either unipolar or bipolar electrode systems. Advantages of unipolar electrodes for stimulation are listed; then arguments in favor of bipolar electrodes for sensing are cited. A proposed system combines unipolar stimulation with bipolar sensing and may be implemented by adding a differentialinput stage to the sensing amplifier.
STIMULATION In unipolar stimulation, while the cathode is in contact with the myocardium and connected to the pulse generator through an insulated lead wire, the anode forms part or all of the exterior package of the implanted pulse generator and, being relatively distant from the myocardium, is the "indifferent" electrode. The significant voltage loss that is characteristic of anodes during stimulation, is minimized by the large anodal surface area. In bipolar stimulation, where the anode is also in the heart and must be kept physically small, voltage stimulation thresholds are greater [ 11. Further advantages of unipolar stimulation are increased reliability due to absence of a lead wire, and avoidance of anode-to-myocardium contact with conceivable attendant fibrillation hazard [ 2 1.
SENSING For sensing of myocardial depolarization to achieve noncompetitive pacing, bipolar electrodes offer the advantage of improved rejection of electromagnetic and skeletal muscle artifact due to a more restricted lead field or "antenna" [3]. Chatterjee et al. [41 report greater signal-to-noise ratios for both ventricular and atrial sensing, using their new catheter with bipolar electrodes. Ongoing research at this institution also suggests that the bipolar signal is greater than the unipolar signal in amplitude, unless the bipolar axis is perpendicuManuscript received February 23, 1976; revised December 11, 1978. This work was supported in part by the United States Public Health Service under Grant HL 04666-16. P. Hurzeler is with Cardiac Datacorp, Inc., Bloomfield, CT 06002. V. De Caprio is with Becton-Dickinson, Inc., Fairfield, NJ 07006. S. Furman is with the Division of Cardiac Surgery, Montefiore Hospital and Medical Center, New York, NY 10467.
lar to the direction of propagation of the depolarization wave. However, new bipolar electrode geometries such as coaxial or tripod arrangements suggested by Siegel et al. [5] may be devised to overcome the directionality problem. A past constraint on such designs has been a minimum surface area of some 10 mm2 for the proximal electrode since it is also the stimulation anode. THE COMBINATION In the proposed system, one pole, say the tip, of an intracardiac bipolar electrode serves as both the stimulation cathode and as a sensing electrode, as in conventional systems. The other half of the bipole is connected only to the other input of the differential sensing amplifier, while an indifferent electrode serves as the stimulation anode. In this way the advantages of both systems are retained. An alternate way to effect the combination is to use the isolation afforded by an output transformer in the pulse generator in lieu of a push-pull differential stage in the input amplifier. As the second half of the bipole is no longer used as an anode, its surface area may be made as small as is convenient, and designs featuring hooks to attach catheter tips to the myocardium, such as described by Irnich [11, may be more valuable. A central tip, forming one pole, surrounded by a tripod of hooks forming the other pole, may overcome the directionality problem as well as avoiding dislodgement. This combination should be particularly helpful for atrial sensing. In conventional designs, the sensing amplifier input impedance is shunted by the OFF output impedance of the stimulator circuit, whereas in the proposed design the differential input impedance is not shunted. This further removes contraints on sensing electrode surface area. Also, the polarization voltage that persists after each stimulus pulse is conducted directly to a conventional single-ended sensing input, whereas in the proposed design the anodal portion of the polarization voltage, which Irnich [1I1 suggests is 'the larger portion in bipolar systems, appears as a common-mode input voltage. A further advantage is that a redundancy feature of the bipolar system is retained, to wit-in the event of a single lead wire fracture, the surgeon has the option of changing to a unipolar configuration to maintain pacing without implanting a new electrode. Finally, the concept need not be confined to systems which sense and stimulate from the same electrode tip. For instance, bipolar atrial sensing may be combined with unipolar ventricular stimulation. REFERENCES [1] W. Irnich, "Engineering concepts of pacemaker electrodes," in Advances in Pacemaker Technology, M. Schaldach and S. Furman, Eds. New York: Springer-Verlag, 1975.
[2] T. A. Preston, "Pacer induced ventricular tachycardia," in Modern
Cardiac Pacing, S. Furman and D. J. W. Escher, Eds. Bowie, MD: Charles Press, 1975. [31 A. R. Kahn and R. J. Schlentz, "Design and construction methods for protecting implanted cardiac pacemakers from electromagnetic interference," in Cardiac Pacing, H. J. Thalen, Ed. Assen, The Netherlands: Van Gorcum, 1973. [4] K. Chatterjee, H. J. C. Swan, W. Ganz, R. Gray, H. Loebel, J. Forrester, and D. Chunette, "Use of a balloon-tipped flotation electrode catheter for cardiac monitoring," Amer. J. Cardiol., vol. 36, pp. 56-61, 1975. [5] L. Siegel, E. B. Mahoney, J. A. Manning, and S. Stewart, "Conduction cardiograph-bundle of His detector," IEEE Trans. Biomed. Eng., vol. BME-22, pp. 269-274, July 1975.
0018-9294/79/0700-0440$00.75 © 1979 IEEE
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-26, NO. 7, JULY 1979
and not allowing time for the sample and hold to acquire the new pulse height. The operation of hold and peak detect signals is illustrated in Fig. 4. The necessary overlap between these two signals is generated by the pulse stretcher D2, C3, and R 3. REFERENCES [11 H. E. Kubitshek, "Counting and sizing micro-organisms with the Coulter counter," in Methods in Cell Biology, J. R. Norris and D. W. Ribbons, Eds. London, England: Academic, 1969, pp. 593-610. [21 S. J. Rackham, "A pulse height analyzer for displaying particle size distributions," M.Sc. thesis, Univ. Waikato, Hamilton, New Zealand, 1977.
Proposed Cardiac Pacemaker System Combining Unipolar Stimulation with Bipolar Sensing
PHILIP HURZELER, V. DE CAPRIO, AND S. FURMAN Abstract-Present cardiac pacemaker designs use either unipolar or bipolar electrode systems. Advantages of unipolar electrodes for stimulation are listed; then arguments in favor of bipolar electrodes for sensing are cited. A proposed system combines unipolar stimulation with bipolar sensing and may be implemented by adding a differentialinput stage to the sensing amplifier.
STIMULATION In unipolar stimulation, while the cathode is in contact with the myocardium and connected to the pulse generator through an insulated lead wire, the anode forms part or all of the exterior package of the implanted pulse generator and, being relatively distant from the myocardium, is the "indifferent" electrode. The significant voltage loss that is characteristic of anodes during stimulation, is minimized by the large anodal surface area. In bipolar stimulation, where the anode is also in the heart and must be kept physically small, voltage stimulation thresholds are greater [ 11. Further advantages of unipolar stimulation are increased reliability due to absence of a lead wire, and avoidance of anode-to-myocardium contact with conceivable attendant fibrillation hazard [ 2 1.
SENSING For sensing of myocardial depolarization to achieve noncompetitive pacing, bipolar electrodes offer the advantage of improved rejection of electromagnetic and skeletal muscle artifact due to a more restricted lead field or "antenna" [3]. Chatterjee et al. [41 report greater signal-to-noise ratios for both ventricular and atrial sensing, using their new catheter with bipolar electrodes. Ongoing research at this institution also suggests that the bipolar signal is greater than the unipolar signal in amplitude, unless the bipolar axis is perpendicuManuscript received February 23, 1976; revised December 11, 1978. This work was supported in part by the United States Public Health Service under Grant HL 04666-16. P. Hurzeler is with Cardiac Datacorp, Inc., Bloomfield, CT 06002. V. De Caprio is with Becton-Dickinson, Inc., Fairfield, NJ 07006. S. Furman is with the Division of Cardiac Surgery, Montefiore Hospital and Medical Center, New York, NY 10467.
lar to the direction of propagation of the depolarization wave. However, new bipolar electrode geometries such as coaxial or tripod arrangements suggested by Siegel et al. [5] may be devised to overcome the directionality problem. A past constraint on such designs has been a minimum surface area of some 10 mm2 for the proximal electrode since it is also the stimulation anode. THE COMBINATION In the proposed system, one pole, say the tip, of an intracardiac bipolar electrode serves as both the stimulation cathode and as a sensing electrode, as in conventional systems. The other half of the bipole is connected only to the other input of the differential sensing amplifier, while an indifferent electrode serves as the stimulation anode. In this way the advantages of both systems are retained. An alternate way to effect the combination is to use the isolation afforded by an output transformer in the pulse generator in lieu of a push-pull differential stage in the input amplifier. As the second half of the bipole is no longer used as an anode, its surface area may be made as small as is convenient, and designs featuring hooks to attach catheter tips to the myocardium, such as described by Irnich [11, may be more valuable. A central tip, forming one pole, surrounded by a tripod of hooks forming the other pole, may overcome the directionality problem as well as avoiding dislodgement. This combination should be particularly helpful for atrial sensing. In conventional designs, the sensing amplifier input impedance is shunted by the OFF output impedance of the stimulator circuit, whereas in the proposed design the differential input impedance is not shunted. This further removes contraints on sensing electrode surface area. Also, the polarization voltage that persists after each stimulus pulse is conducted directly to a conventional single-ended sensing input, whereas in the proposed design the anodal portion of the polarization voltage, which Irnich [1I1 suggests is 'the larger portion in bipolar systems, appears as a common-mode input voltage. A further advantage is that a redundancy feature of the bipolar system is retained, to wit-in the event of a single lead wire fracture, the surgeon has the option of changing to a unipolar configuration to maintain pacing without implanting a new electrode. Finally, the concept need not be confined to systems which sense and stimulate from the same electrode tip. For instance, bipolar atrial sensing may be combined with unipolar ventricular stimulation. REFERENCES [1] W. Irnich, "Engineering concepts of pacemaker electrodes," in Advances in Pacemaker Technology, M. Schaldach and S. Furman, Eds. New York: Springer-Verlag, 1975.
[2] T. A. Preston, "Pacer induced ventricular tachycardia," in Modern
Cardiac Pacing, S. Furman and D. J. W. Escher, Eds. Bowie, MD: Charles Press, 1975. [31 A. R. Kahn and R. J. Schlentz, "Design and construction methods for protecting implanted cardiac pacemakers from electromagnetic interference," in Cardiac Pacing, H. J. Thalen, Ed. Assen, The Netherlands: Van Gorcum, 1973. [4] K. Chatterjee, H. J. C. Swan, W. Ganz, R. Gray, H. Loebel, J. Forrester, and D. Chunette, "Use of a balloon-tipped flotation electrode catheter for cardiac monitoring," Amer. J. Cardiol., vol. 36, pp. 56-61, 1975. [5] L. Siegel, E. B. Mahoney, J. A. Manning, and S. Stewart, "Conduction cardiograph-bundle of His detector," IEEE Trans. Biomed. Eng., vol. BME-22, pp. 269-274, July 1975.
0018-9294/79/0700-0440$00.75 © 1979 IEEE
