I. Richard Zucker

Idioventricular Rhythm in Acute Myocardial Infarction

An ectopic ventricular rhythm (IVR) with a rate of 60 to 100/min was detected in 36 of 100 consecutive patients with acute myocardial infarction by constant monitoring of the electrocardiogram. This mechanism was not apparent clinically and was usually transient, lasting 4 to 30 beats. It was frequently associated with inferior myocardial infarction and usually occurred during sinus bradycardia or the slow phase of sinus arrhythmia. Unlike true paroxysmal ventricular tachycardia (PVT), IVR did not progress to ventricular fibrillation and did not influence the prognosis adversely. Recognition of IVR is important in order to avoid unnecessary and perhaps dangerous treatment with cardiosuppressive drugs and electrical cardioversion.

Prediction of impending pacemaker failure in a pacemaker clinic

A pacemaker clinic has been established for the detection of impending pacemaker failure. Over a two year period, there were 121 operations on 87 patients, comprising a third of our living patients. Of the 93 pacemaker replacements evaluated, 77 (83 percent) were for failure of the pulse-forming circuit and 16 (17 percent) for wire dislogment, heart perforation on lead fracture. Sixty-four percent of the pacemakers were replaced electively as a result of changes detected in the electrical impulses or the electrocardiogram. Only 10 percent of replacements were elective in patients not attending the clinic. On the basis of observed defects in the pacemakers, a maximal yield of 83 percent elective pacemaker replacements could have been anticipated from the test procedures of the clinic. The most significant changes observed were decreases in the artifact amplitude and in rate, especially if found together or in conjunction with alteration in pulse width or impulse configuration. Absolute indications were uncommon but included rounding of the square wave of Electrodyne units and loss of synchronization of any unit with a sensing circuit (standby and synchronous pacemakers). A computer simplified the clinic procedure by providing real-time rapid analysis of the data and a neat, concise report for the records. However, the computer was not necessary for preparing and evaluating the tests although it will be used for analog to digital conversion in further development of the clinic. The clinic provides close follow-up of all patients and gives them and their physicians the assurance that trouble will usually be spotted before it occurs. We believe that premature and emergency replacement of pacemakers can be avoided with this semiquantitative method.

A REVIEW OF INTRACARDIAC PACING WITH SPECIFIC REFERENCE TO THE USE OF A DIPOLAR ELECTRODE.

Summary Insertion of a dipolar electrode has been successfully performed on 47 occasions in 35 patients, and the heart rate was controlled in 46 of these. This electrode produces an effective, consistent ventricular response at exceedingly low voltage levels. Threshold stimuli do not tend to rise when the clectrode is used for periods of a few weeks. The dipolar electrode is of particular value in preparation and maintenance of patients with A-V block who are to have general anesthesia, for emergency control of the heart rate in patients with frequent Adams-stokes seizures, for interim pacing in situations where a return to regular sinus rhythm might be anticipated, and in evaluating patients for contemplated insertion of a permanent pacemaker. The dipolar electrode is superior to the unipolar because it requires no skin wire, needs no contact with the endocardium, and produces consistent ventricular response with low voltage requirements. It also is preferable to medical therapy in cases of frequent Adams-Stokes seizures because it provides absolute control of cardiac rate without need for monitoring. Although complications do occur, they are almost always of a minor nature, and most have been eliminated altogether with improvements in equipment and technique. Two major complications occurred: one was probable perforation of the coronary sinus; this should be avoidable with careful catheterization techniques. The other was a death during the procedure, when attempts were made to salvage a hopelessly moribund individual. In contrast, seven other patients in very critical condition were resuscitated. It is our opinion that, without electric pacing, all of them would have died within a matter of hours. Successful experience with the dipolar electrode justifies its continued use in a variety of clinical situations. Present and potential indications for the use of the electrode have been discussed.

THE POTENTIALITY OF THE USE OF BIOLOGIC ENERGY AS A POWER SOURCE FOR IMPLANTABLE PACEMAKERS

The fact that “permanent” implantable pacemakers, containing their own power packs, require replacement every few years prompted a search for biologic energy sources that might serve as a permanent power source. The results of our work have shown, in fact, that such energy is available in sufficient amounts to produce stimulation of the dog’s heart. A number of techniques were considered before ultimately settling on piezoelectric energy sources. Intravascular turbines, thermocouples, interstitial o r intragastric batteries, and magnetostriction were discarded because they were impractical or too bulky, or because there was potential destruction of body tissues. It appeared most logical to use the movement of some part of the body that under most daily circumstances would continue to move. This would include the heart and major arteries and the diaphragm and ribs. After consideration of these, the pulsations of the aorta and the movements of the diaphragm seemed most practical. It was planned to use this mechanical energy to bend or strike ceramic piezoelectric crystals that in turn would produce electric energy by the piezoelectric effect. The electricity thus developed would have to be altered in some way to produce a properly timed and shaped impulse for stimulation of the heart. It was hoped that an electric impulse of 1.6 milliseconds duration and at least 1 volt amplitude could be obtained. Efforts to devise self-energizing pacemakers are pertinent, both because favorable experience with battery-powered implantable units attest to the feasibility of long-term implantation of foreign materials and because many patients with complete A-V block have hearts that are apparently healthy enough to sustain life for many years as long as adequate heart rates are maintained.

Permanent Pacemaker Insertion: A Five-Year Appraisal

uring the past five years, 115 permanent pacemakers have been implanted in 93 patients at the Newark Beth Israel Hospital. D An analysis of this experience has suggested what seem to be safe surgical techniques that can be used under a variety of circumstances. The choice of one method over another has become a complex matter because of the continuous development of new surgical techniques and new and improved equipment. This report will summarize the results of the past five years and will suggest what appears to be a sensible approach to surgical management of complete heart block and Stokes-Adams syndrome. The figures presented, it will be seen, are quite similar to those reported by others [2-4, 13-15].

Antiarrhythmic drugs in the prevention of ventricular arrhythmias related to paired pacing

Abstract Lidocaine, quinidine and diphenylhydantoin proved ineffective in preventing pacer-induced ventricular fibrillation in dogs in which paired pacing was attempted after coronary artery ligation. p]Propranolol prevented ventricular fibrillation in 11 of 14 animals, but only in a dose (5 mg/kg) that significantly reduced heart rate and myocardial contractility. Bretylium (5 mg/kg) protected 9 of 10 dogs against pacer-induced ventricular fibrillation and produced none of the negative chronotropic and inotropic effects observed with propranolol. These data suggest that administration of bretylium before paired pacing may be of value in the cardiogenic shock-low output failure syndrome related to acute myocardial infarction in man.

The Effect of Carotid Sinus Nerve Stimulation On Cardiovascular Dynamics in Man

Electrical stimulation of the carotid sinus nerve (CSNS), sometimes called baropacing, has been proposed as a treatment of uncontrolled essential hypertension.l,2 2 Although the method has been applied clinically, relatively few studies on cardiac performance during CSNS have been reported. The role of the carotid sinus in the regulating of systemic blood pressure was first described by Hering in 1923.3 The carotid sinus &dquo;baroreceptors&dquo; are stretch receptors which are stimulated by an increase in mean arterial pres-

CLINICAL USE OF A NEW TRANSVENOUS ELECTRODE

Recently we described a new type of transvenous electrode that displayed remarkably low thresholds for electrical stimulation of the heart and minimal polarization effects.I3 This electrode, called a differential current density (DCD) electrode, is constructed of a helical coil of platinum-iridium or Elgiloy, widened at its tip to form a cylinder with a surface area of more than 1 cm2. It is encapsulated in a silicone-rubber housing. The cylinder is opened at the very tip through the Silastic capsule where contact with the endocardium is made (FIGURE 1). When a current is applied, it passes through the hole at the tip so that the current density is low at the metal and high at the hole. The metal cyPnder is sufficiently large so that polarization effects are minimal at current densities needed for stimulation. At the same time, the effective area of the hole at the electrodemyocardial interface is so small that there is a high current density and therefore an extremely low excitation threshold. The concept of using a hole to increase current density was originally suggested by M a ~ r o . ~ Preliminary studies with various models of the DCD electrode in dogs revealed that excitation thresholds were ten to 20 times lower than those seen with standard metal electrodes. Moreover, it appeared that the transvenous model was sufficiently stable to warrant clinical trial.

Telemetric monitoring of arrhythmias in acute myocardial infarction

Abstract A relay telemetric system has been developed for the continuous monitoring and recording of the electrocardiogram in patients with acute myocardial infarction. The results in the first 6 cases are described. The monitor demonstrated arrhythmias in all the cases, with episodes of ventricular tachycardia in 4 of the 6. Most of the disturbances in rhythm were not detected on frequent clinical examinations and conventional electrocardiograms. Continuous electrocardiographic monitoring provides for immediate recognition of arrhythmias and also serves as an important investigative tool for study of the electrogenesis of these potentially fatal complications of myocardial infarction.

Coexisting paroxysmal ventricular tachycardia and idioventricular rhythm in acute myocardial infarction

Summary Two patients with acute myocardial infarction (AMI) and coexisting paroxysmal ventricular tachycardia (PVT) and idioventricular rhythm (IVR) are described. Accurate diagnosis of these arrhythmias requires elimination of the possibility that a single ventricular mechanism exists with abrupt rate changes due to varying degrees of exit block. Management of coexisting PVT and IVR includes cardio-acceleration by atropine or pacing; cardiosuppressive agents should be used only in the presence of a pacing device, since they may increase the underlying bradycardia.