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Ann Thorac Surg 1979;27:63-69
© 1979 The Society of Thoracic Surgeons

Articles

Myocardial Stimulation Impedance: The Effects of Electrode, Physiological, and Stimulus Variables

G. Frank O. Tyers, M.D.*, Robert R. Brownlee, M.S.E.E., Howard C. Hughes, Jr., V.M.D., Carolyn W. Shaffer, M.D., Edward H. Williams, M.D., Race L. Kao, Ph.D.

Division of Cardiovascular and Thoracic Surgery, Department of Surgery, The University of Texas Medical Branch, Galveston, TX.

Accepted for publication January 17, 1978.

* Address reprint requests to Dr. Tyers, Division of Cardiovascular and Thoracic Surgery, The University of Texas Medical Branch, Galveston, TX 77550.

With exposed metal at the electrode tissue interface (8 mm2, 28 mm2, 57 mm2), myocardial threshold stimulation impedance increased as pulse duration was lengthened, with left ventricular intramyocardial stimulation, and with the smaller surface area electrode. An 0.5 mm2 differential-current-density electrode, which eliminated direct metal-to-tissue contact at the electrode-myocardial interface, was associated with notably higher impedances than each of the three metal tip electrodes and did not show increasing impedance levels with changes in pulse duration, confirming the minimization of polarization energy losses with this device. The majority of electrode, electrode tissue interface, and myocardial variables that are characterized by high threshold stimulation impedance are associated with low threshold energy requirements for pacing and reduced pacemaker power source drain. No accurate information about sensing impedances can be derived from current knowledge of pacing impedance.






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