For about ten years we have studied radio-frequency as a means of transmitting pulses for heart stimulation from an external source.l*p The most immediate and simplest solution appeared to be the epicardial application of a passive receiver, leading the stimulus to the heart by means of two electrodes. The electrical pulses, in the form of radio-frequency wave trains, were produced by an external tran~mitter.~*~ With this system, we attempted to resolve the problem of breakage of the wire electrodes used in most pacemakers at that time. A total of 38 patients were treated in this manner.This system was abandoned because of the electrophysiological factors that quickly produced fibrosis formation around the pacing electrodes, thus causing their electrical insulation (FIGURE 1 ) . However, the good results obtained with catheter electrodesSl0 prompted us to connect one of these catheters, of the bipolar type, to a radio-frequency receiver of the type previously used, and to implant this unit subcutaneously in the thoracic wall (FIGURE 2). An external transmitter with an annular antenna (FIGURE 3) was placed upon the receiver but outside the thorax.11-13 The transmitter power supply was furnished by rechargeable nickel-cadmium batteries, charged every five days.Catheter use has the notable advantage that thoracotomy is not necessary, and trauma is minimized. Moreover, the following properties of the first system were retained: (1) the ability to change the stimulus energy and to stop the stimulation whenever necessary; (2) the ability to change the cardiac frequency;(3) the ability to modify or replace the pulse transmitter, without a new surgical operation (FIGURE 4 ) . The characteristics of this radiopacemaker, which we have named model RFlZ/C, compared with those of our other models, are reported in TABLE 1.To date, 46 pacemakers of this model have been implanted, since October, 1966. The first 33 were implanted with the United States Catheter & Instrument Co. catheter 5651, which was the only one available at that time in Italy. Although we were aware that this type of catheter was designed by its manufacturer for temporary pacing, we were encouraged to use it for long-term stimulation after our own successful experience and that of others with it. However, we noticed that after a period of time varying from two to 21 months, the woven Dacron insulator between the coaxial conductors, of which the catheter is formed, tended in several cases to absorb organic fluids. This led to a gradual short circuit of the catheter, making the stimulation ineffective.In the meantime, the Medtronic catheters for long-term stimulation became available, and we substituted them for the old catheters in the patients who showed signs of short circuiting. In addition, we encountered one case of receiver failure; two cases of transmitter failure, one of which was due to the batteries; and one case of catheter displacement that could not be overcome with an increase 846
Twenty patients with advanced AV block and normal sinus node function underwent pacemaker implantation, randomly receiving a CPI 910 ULTRA II model VDD pacemaker. The first 13 patients received the implantation of a single lead with a screw-in positive ventricular fixation tip and a unipolar ring floating atrial electrode spaced 13 cm from the tip. A subsequent group of seven patients received a conventional porous tinned-tip lead with a pair of unipolar ring floating electrodes. The second solution was adopted because the best atrial signal was not always in the high or mid-high atrium portion, but sometimes in the middle or mid-low position. With the modified double-electrode lead, the floating atrial electrode that detects the best signal can be selected, cutting out the pin of the one not used. The comparisons between minimal atrial slew rate and maximal ventricular slew rate, as well as those between minimal P wave amplitude and maximal R wave amplitude, show a highly significant range difference, as large as P less than 0.01. Surface electrocardiograms, stress tests, and 24-hour Holter monitoring showed the correct functioning of the system with an average sensing failure from 0.05 to 1%. In conclusion, VDD stimulation is feasible with a single unipolar lead and a floating atrial electrode in conjunction with a pacemaker generator (CPI 910 ULTRA II) originally designed for permanent twin-lead implantation.
The use of programmed electrical stimulation in the long term treatment of re-entry tachycardia offers encouraging perspectives. Among the others proposed, the "scanning" system seems to be the most effective. However, an implantable stimulator with these features is not yet available and, thus, a temporary external lead is required. These difficulties have been overcome by utilizing radiofrequency to synchronize and stimulate. An implantable device was therefore designed which is triggered by the patient and automatically searches the interruption zone of the tachycardia by exploring the R-R cycle. The external transmitter, which can produce one or two synchronized impulses, is programmed to scan the R-R cycle with progressive steps of 5 or 10 ms; when tachycardia is interrupted, further stimulation is inhibited. The implanted module connected to an endocavitary lead does not have any power supply and, therefore, is very small. The efficacy of this method has been demonstrated in 4 patients with supraventricular tachycardia (3 with WPW syndrome) resistant to conventional pharmacologic therapy.
The treatment of ventricular fibrillation (VF) by means of automatic implantable cardioverter defibrillators (AICD) poses many severe problems and limitations at the present time. In order to overcome these problems, we propose a totally new way to terminate VF or ventricular sustained tachycardia (VST). Our proposal consists of replacing the electric shock, which is dangerous, delayed, and sometimes ineffective, with a "chemical" shock: i.e., a chemical bolus retroperfused in the coronary sinus (CS) immediately after VF arises. The possible device is hypothesized and preliminary investigations in animals, performed to verify the theoretical assumption, are presented. In rabbits, and in larger animals (sheep and swine). Drugs were perfused in the coronary bed: lidocaine was used in 86% and bretylium tosylate in 14% of the animals. The results were: lidocaine immediately terminated VF in 100% and sinus rhythm was restored in rabbits; lidocaine terminated VF in VST in sheep; and in swine, bretylium immediately produced sinus rhythm in one case; in another one, only delayed sinus rhythm was achieved but lasted a short time; in the last case ventricular tachycardia at 128 beats/min appeared. Because new drugs, which are really "defibrillating" drugs, are available (bretylium tosylate, bethanidine, clofilium, tricyclic antidepressants, phenotiazine derivatives), we plan to investigate these defibrillating drugs in isolated hearts, found in suitable animals like dogs (sheep and swine are difficult to defibrillate) and in humans during routine electropharmacological studies.
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