Barouh V. Berkovits

Comparison of alternating current with direct current electroshock across the closed chest

I T IS BECOMING increasingly recognized that ventricular fibrillation is an important cause of sudden death. The treatment of this arrhythmia is by electrical countershock delivered to the heart either directly or indirectly through the intact chest wall. From the onset of ventricular fibrillation only a few minutes are available for restoring an integrated cardiac mechanism. Until recently the successful use of countershock has been largely limited to the operating room where this brief time could be prolonged by the prompt institution of direct cardiac massage. The demonstration by Kouwenhoven and co-workers1 that in the arrested heart pressure on the lower sternum maintains blood flow to vital organs has greatly extended the time available for effective use of electrical defibrillation. Recently it has been shown2-4 that electrical countershock across the closed chest will abolish cardiac arrhythmias other than ventricular fibrillation. It is therefore pertinent to determine whether alternating current, widely accepted for inducing countershock, is indeed the best available method. The present study compared the action on the heart of alternating current and three types of direct current both during ventricular fibrillation and during normal sinus rhythm.

Dynamic characterization of premature ventricular beats and ventricular tachycardias

Abstract The contraction patterns induced by ectopic ventricular premature beats and ventricular tachycardias occurring in man during left ventriculography were analyzed. These were compared with contraction patterns induced by ventricular premature beats and tachycardias produced in five dogs by epicardial left ventricular apical or basilar stimulation. Two patterns of contraction observed in the animals corresponded to two patterns observed in man. Apically stimulated left ventricular beats produced an “hourglass” type of contraction pattern and were hemodynamically more effective than beats arising from basilar stimulation, which produced an inverse “teardrop” pattern. The same patterns were reproduced by experimental ventricular tachycardias. These observations stress the importance of a normal sequence of ventricular contraction to optimal cardiac function in man and warn against the hazards of misinterpretation of the left ventricular contraction pattern if the beat originates ectopically during ventriculography.

Clinical experiences with a new implantable demand pacemaker

Abstract There is a need for a demand type of implantable pacemaker that imitates the natural escape mechanism of the heart. Such an instrument has been developed and has undergone laboratory evaluation. Successful use of this implantable demand pacemaker in 6 patients is reported. With commercial availability, additional uses will undoubtedly be clarified.

Variations in discharge rate of demand pacemakers not due to malfunction

Demand pacemakers may have variations in discharge rate which are not due to malfunction. Physiologic changes of intraventricular conduction can cause implanted ventricular units to sense earlier or later during the QRS interval and therefore discharge so as to produce a different R-R interval. Furthermore, if the patients own ventricular rate exceeds the pacers escape rate, demand pacing will not occur. Because of such features, demand units should be regularly tested in a continuous (fixed-rate) mode produced by application of an external magnet. The rate of the induced continuous mode will always by design exceed the escape rate in the demand mode. External demand pacers discharge more slowly in the demand than in the fixed-rate mode as a function of the interval from the pacemaker spike to the peak of the corresponding R wave which is sensed by the demand pacemaker circuit. The decreased heart rate is particularly striking with temporary atrial pacing, where the beat to beat interval is lengthened by the interposition of the P-R segment. Electrocardiograms from illustrative cases are presented to demonstrate these phenomena. The physician should be aware that variations in pacer discharge rate in the demand mode and between demand and continuous pacing are not necessarily due to pacemaker malfunction, but are rather inherent features of normal demand pacemaker operation.

Hemodynamic effects of glucagon and intraaortic balloon counterpulsation in canine myocardial infarction

Abstract The hemodynamic effects of glucagon (50 μg/kg) and intraaortic balloon counterpulsation were investigated in open chest anesthetized dogs after production of myocardial infarction and cardiogenic shock. Glucagon produced striking increases in arterial pressure, cardiac output and maximal left ventricular dp/dt together with a reduction in left ventricular end-diastolic pressure and systemic vascular resistance. The condition of most animals was stabilized at a viable level with 1 or more doses of glucagon. The effects of counterpulsation during severe cardiogenic shock were slight, although good counterpulsation was always achieved during control studies with normal pressure. When counterpulsation was instituted in combination with glucagon therapy there was an increase in mean arterial pressure together with a reduction in maximal left ventricular dp/dt and peak systolic pressure. Thus, counterpulsation tended to reduce the increased oxygen cost of the inotropic effects of glucagon. We suggest that an appropriate combination of counterpulsation and inotropic support (as with glucagon) may be better than either method alone.

PACEMAKER‐INDUCED CARDIAC RHYTHM DISTURBANCES

Continuous stimulation of the heart has been used successfully in the treatment of symptomatic atrioventricular conduction disturbances. However, recent reports have stressed the possible Occurrence of pacemaker-induced repetitive firing during coaction of natural and artificial rhythms. A review of the subject can be found in a recent textbook by Siddons and Sowton.’ Repetitive firing* (FIGURE 1) has been observed fourteen times in our department: (a ) during intermittent paired electrical stimulation, three cases, one requiring countershock;2 (b ) at the onset of pacing during complete atrioventricular block, five case^,^^^ two of them unreported; (c ) during coaction of sinus rhythm and continuous asynchronized pacers (chronic block, three (unreported) cases, in two of which the spikes that triggered repetitive firing fell on an extrasystolic T-wave; (d ) in acute myocardial infarction during coaction of supraventricular and continuous pacemakers, three cases,4 one requiring countershock. Stimuli fell on the T-waves of supraventricular complexes. It is for precisely this purpose that other forms of pacing have been developed. The present report deals with the electrocardiographic changes produced by one of the pacemakers used to prevent this potentially hazardous complication.

Effects of AV Sequential Versus Asynchronous AV Pacing on Pulmonary Hemodynamics

We studied the effects of various pacing modes on cardiac hemodynamics and pulmonary gas alterations in chronic heart blocked dogs. Changing the pacing mode from an atrioventricular interval of 100 ms (AV100) to a ventriculo‐atrial interval of 100 ms (VA100) caused a significant fall in left ventricular pressure (117.64 ± 11.91 to 95.60 ± 16.58 mmHg) and cardiac output from 2.18 ± 0.24 to 1.46 ± 0.20 L/min. Following the change in pacing mode from AV100 to VA 100, there was an increase in the alveolar‐arterial O2 gradient from 23.28 ± 6.97 to 28.74 ± 8.43 mmHg and a decrease in the arterial CO2 tension from 32.42 ± 3.22 to 29.42 ± 3.22 mmHg. There was also a decrease in arterial CO2 tension when the AV100 pacing mode was compared to asynchronous ventricular pacing (32.42 ± 3.22 versus 30.56 ± 2.82 mmHg). The minute volume of O2 also decreased when the pacing mode was changed from AV100 to asynchronous ventricular pacing (0.134 ± 0.01 versus 0.126 ± 0.01 L/min) and decreased further at VA100 to 0.114 ± 0.01 L/min. Other significant changes were also observed: the percent of expired CO2 decreased when the pacing mode was changed from AV100 to VA100 (3.68 ± 0.13 versus 3.37 ± 0.26%) or to asynchronous ventricular pacing (3.40 ± 0.31%). The end‐expiratory O2 increased and CO2 decreased when the pacing mode was changed from AV100 to VA100. The breath‐by‐breath correlation of end‐expiratory O2 and CO2 with left ventricular systolic pressure showed an almost immediate increase in O2 and reduction in CO2 concentration associated with decreasing systolic pressure. The decrease in pulmonary gas exchange appeared in part related to alterations in cardiac hemodynamics and particularly to the fall in cardiac output. It is speculated but not proven by these studies that alterations could be further explained by a fall in O2 consumption or reflex shunting of blood in vascular beds due to the fall in cardiac output. However, the additional deleterious effects of atrial contraction against a closed AV valve on pulmonary gas exchange and hemodynamics were also apparent. Notably, these studies could provide a physiologic basis for some symptoms associated with the pacemaker syndrome produced by the absence of AV synchrony.

Repetitive Firing Produced by Pacemaker Stimuli Falling After the T Wave

Abstract Multiple responses secondary to pacemaker stimuli falling after the end of the T wave (ventricular diastole) were seen in 3 patients. In 1 of them, the induced QRS deflections were identical to those seen during a previously present spontaneous ventricular tachycardia. Another patient had two areas of repetition, one in late systole (Q-spike intervals ranging between 0.25 and 0.33 sec) and the other in early diastole (Q-spike intervals between 0.32 and 0.43 sec). A third patient with a malfunctioning pacemaker unit showed stimulation during the supernormal phase after variable periods of pacemaker failure. Capture during the supernormal phase was followed either by bursts of spontaneous multiple responses or by a series of effective pacemaker stimuli. These unusual arrhythmias were abolished, respectively, by the administration of lidocaine, after a change to a demand mode of operation, and by pacemaker replacement. It is believed that a Wedensky-like effect best explains the genesis of diastolic repetition. However, the presence of two areas of vulnerability, one for ventricular fibrillation and the other for ventricular tachycardia, cannot be definitely excluded in Case 1.

Treatment of Drug Resistant A‐V Reciprocating Tachycardias with Multiprogrammable Dual Demand A‐V Sequential (DVI,MN) Pacemakers

Programmable dual A‐V sequential demand (DVI,MN) pacemakers were implanted in eight patients with recurrent or incessant, drug‐refractory, A‐V reciprocating tachycardias. This was done after intracardiac studies had identified a variety of electrogenetic mechanisms which include tachycardias involving Kent bundles, (manifest or concealed Wolff‐Parkinson‐White syndrome), nodoventricular (Mahaim) fibers, enhanced A‐V node pathways (Lown‐Ganong‐Levine syndrome), and dual intranodal pathways. The antitachycardia features of the pacemaker were evaluated during the electrophysiological studies. No immediate postoperative complications occurred after implantation. Furthermore, during the follow‐up periods (4 to 20 months), clinical assessment, ambulatory (Holter) monitoring and invasive (as well as noninvasive) evaluations have confirmed continuous effectiveness in recognizing and automatically terminating the tachycardias. Late pacemaker system malfunction has not occurred. The frequency of the tachycardias and the dosage of concomitantly‐administered antiarrhythmic medications were significantly reduced. Furthermore, preliminary studies performed in our laboratory suggest that DVI,MN pacemakers may also be useful in certain types of intra‐atrial reentry tachycardias coexisting with sinus node dysfunction.

Systolic and diastolic pacemaker induced repetitive firing in the human heart: Analysis of 23 cases

Summary Twenty-three tracings obtained from patients showing pacemaker-induced repetitive firing were reviewed. This complication was manifested as single extra beats, ventricular tachycardia and ventricular fibrillation. Cases in which a definite relation between pacemaker stimuli and multiple responses could not be established were excluded from this series. Systolic repetition was observed in 17 patients. This phenomenon, which was attributed to ventricular vulnerability occurred during chronic block (12 cases) as well as during acute myocardial infarction (5 cases). There were 5 instances of diastolic repetitive firing in patients with digitalis intoxication and recent myocardial infarction. It was postulated that a Wedensky-effect best explained the genesis of diastolic repetition. Knowledge regarding the types and possible mechanisms of the different types of repetitive firing can be applied for the safer use of continuous, demand and ventriculo-synchronized pacemakers.