300 ABSIRACTS

quadrupolar contribution could not be removed by origin shifting.

R. Plonsey

Mashima, S. On the determination and expressions of equivalent quadrupole of the cardiac generator. IEEE Trans. Biomed. Engr. 16: 69, 1968. (Second Dept. Int. Med., Univ. of Tokyo, Tokyo, Japan)

This paper comprises certain theoretical considera- tions and the proposal of a lead system which seem to be valuable for the determination of the equivalent dipole and quadrupole of the isolated heart. The first section gives the geometrical analysis of the quadrupole field. The quadrupole is represented by a rhombus with equal sides and Taylor components are utilized throughout in order to describe properties of the field graphically and to define necessary parameters. In the second section, a practical lead system is introduced which gives dipole and quadrupole components of the isolated heart directly, provided that octupolar and �9 higher order terms are negligible. The modification which makes the lead system insensitive to the octupole is also given.

R. Plonsey

Downs, T. D. and Liebman, J. Statistical methods for vectorcardiographie directions. IEEE Trans. Biomed. Engr. 16: 87, 1968. (Case Western Reserve Univ. School of Med., Cleveland, Ohio)

Current statistical methods for treating vector- cardiographic directions are invalid because they treat the directions as points on a line or plane. It is more appropriate to consider the directions as points on a circle or sphere; the direction toward the center of gravity of such points is then a measure of the prevalent direction, and the distance from the center of the circle or sphere to the center of gravity is a measure of precision. The precision is a measure of how closely the directions cluster about the prevalent direction. The Fisher distribution is suggested as a probability model for spatial directions, and its use- fulness is illustrated by 1) a test statistic for determining whether two samples of directions came from the same population, 2) the construction ofa"confidence circle" for the spatial prevalent direction, and 3) a method for obtaining planar prevalent directions and prccisions from the spatial ones.

R. Plonsey

C A R D I A C PACING

Jaron, D., Schwan, H. P. and Geselowitz, D. B. A mathematical model for the polarization impedance of cardiac pacemaker electrodes. Biomed. Eng. 6: 579, 1968. (Biomed. Engin. Dept., Univ. of Pennsylvania, Philadelphia, Penna.)

A mathematical model for the linear properties of �9 the polarization impedance of cardiac pacemaker �9 electrodes i s presented. This model reproduces fre- quency and time domain behavior of the electrodes in physiological saline. The model chosen is a special case of a more general model used to describe dielectric relaxation behavior. Equations are presented for the dependence on frequency of polarization resistance, capacitance and for the tano inductance, potential difference across the interface vs. time in response to a current step. Frequency domain measurements were made with constant current pulses delivered to the electrodes immersed in saline. The experimental results exhibit the same behavior a s predicted from the . . . .

model, with good agreement between theory and exper- iment. Features proposed by this model are also exhibited by other metal electrodes.

R. Plonsey

Bay, G. Artificial pacemakers in the treatment of heart block (Norweg.). Tid. Norsk Laegefor. No. 7, 617, 1968. (Rikshospital, Oslo 1, Norway.)

The indications for cardiac pacing are outlined and the different modes of pacing are mentioned. In the authors opinion, transvenous pacing of the right ventricular endocardial surface is the method of choice. The complications of pacing and their treatment are described. Patients with artificial pacemakers are advised to control their pulse rate frequently and to go to the doctor every third month. If symptoms of failure of the pacemaker are discovered, the patient should be admitted to hospital immediately for correction.

G. Tibblin

Hollingsworth, J., Muller, W . , Beckwith, J. and McGuire, L. Patient selection for permanent cardiac pacing. Ann. Intern. Med. 70: 263, 1969. (School Med., Univ. Virginia, Charlottesville, Va.)

This is a report of a 3-year foll0w-up of 26 patients with heart block in whom permanent pacing was deferred at the time of initial evaluation. These patients were either asymptomatie or had minor and rare syncopal attacks, or showed electrocardiographic evidence of improvement in A-V conduction. Nine of these patients had to be paced eventually because of recurrence of Adams-Stokes episodes. Twelve (46.5 N) have remained almost symptom-free. However, five patients (19~) died suddenly from five days to 18 months after recognition, of the conduction defect; these deaths were considered secondary to fatal arrhythmias. In contrast, a follow-up of 33 patients who underwent permanent pacing at the onset showed only a 6 ~ mortality (2 patients); these deaths also resulted from fatal arrhythmias. In the first group those who died suddenly had characteristic premonitory features which could be be helpful in the prognosis: 1) increasing episodes of dizziness or syncope and 2) appearance of variable ventricular irritability.

L. Lemberg

Harthorne, J. J., DeSanctis, R. W., Sulit, Y. Q. M., Sanders, C. A. and Austen, W. G. Epieardial versus endoeardial pacemakers. Ann. Thorae. Surg. 6: 417, 1968. (Massachusetts Gen. Hosp., Boston, Mass.)

Follow-up study of 109 patients with heart block who had undergone implantation of electronic pace- maker systems showed a survival of 7 6 ~ with epicardial pacemakers followed up after an average of 29 months, versus 857o survival with endocardial pacemakers followed up after an average of 9 months. Implantation of epicardial pacemakers was associated with relatively high initial hospital morbidity and mortality as compared to endocardial placement. Electrode failure was a major complication of both systems, being frequent in the first 24 months after insertion but unusual thereafter. Ventricular perfora- tion, loss of electrode position, or rise in stimulation threshold generally appeared in the first month, rarely after that. The late survival results appeared to be similar in both techniques. The treatment of choice, therefore, was endocardial pacing because of ease, safety and reliability.

R. E. London