Thomas N. James

Characterization of atrial flutter. Studies in man after open heart surgery using fixed atrial electrodes.

Studies were performed using bipolar atrial wire electrodes to record atrial electrograms and to pace the atria in 27 patients who developed atrial flutter after open heart surgery. Two types of atrial flutter, classic or type I atrial flutter, and type II atrial flutter, were identified. Both types of atrial flutter were characterized by uniformity of the beat-to-beat atrial cycle length, morphology, polarity, and amplitude of the recorded bipolar atrial electrogram. Both types sometimes manifested a beat-to-beat electrical alternans, which in turn was sometimes associated with an alternans in beat-to-beat cycle length. The initial basis of separation of types I and II atrial flutter was that type I atrial flutter was always influenced by rapid atrial pacing from the high right atrium, and type II atrial flutter was not. Two additional observations suggested that types I and II atrial flutter were different, although related, rhythms: 1) In four patients, type II atrial flutter was present after termination of rapid atrial pacing used to treat type I atrial flutter; 2) in two patients, type II atrial flutter changed to type I atrial flutter in a one-step fashion. The range of rates of the two types of atrial flutter were also different type I atrial flutter was slower (range 240–338 beats/min) than type II (range 340–433 beats/min). We concluded that type II atrial flutter is a distinct rhythm which may be intermediate between classic, or type atrial flutter and atrial fibrillation

Transient entrainment and interruption of the atrioventricular bypass pathway type of paroxysmal atrial tachycardia. A model for understanding and identifying reentrant arrhythmias.

We studied transient entrainment and interruption of atrioventricular (AV) bypass pathway-type paroxysmal atrial tachycardia in 15 patients during overdrive pacing from selected atrial sites. Overdrive atrial pacing at less than a critically rapid rate for interruption transiently entrained the tachycardia. Transient entrainment was due to repeated early entrance of the wave front from the pacing impulse into the reentry loop in both antidromic and orthodromic directions. The antidromic wave front of each pacing impulse was repeatedly blocked as it collided with the orthodromic wave front of the previous beat, in effect extinguishing the tachycardia. However, the early entrance of the orthodromic wave front of each pacing impulse repeatedly reset the tachycardia. The result was that during transient entrainment, the tachycardia rate increased to the pacing rate. Interruption of the tachycardia occurred when overdrive pacing produced block within the reentry loop of both the antidromic and orthodromic wave fronts of the same pacing impulse, the block occurring either at separate sites within the reentry loop or at the same site. Atrial fusion beats were demonstrated during transient entrainment in nine patients and resulted from intraatrial collision of the antidromic wave front from the pacing impulse with the orthodromic wave front of the previous beat. The presence offusion beats depended critically on the relationship of the pacing site to the reentry loop and the duration of conduction around the reentry loop, particularly through the area of slow conduction.The data from this study suggest that (1) if one can demonstrate constant fusion beats during transient entrainment of a tachyarrhythmia except for the last transiently entrained beat; or (2) if during transient entrainment of a tachyarrhythmia at two or more different pacing rates, one can demonstrate constant fusion at each of the different pacing rates, but different degrees of fusion at the different rates; or (3) if interruption of a tachyarrhythmia by overdrive pacing is associated with localized conduction block to a site followed by activation of that site by the next pacing impulse from a different direction and with a shorter conduction time, then the underlying mechanism of the arrhythmia can be best explained by reentry.

Neural effects on sinus rate and atrioventricular conduction produced by electrical stimulation from a transvenous electrode catheter in the canine right pulmonary artery.

We studied the effects on sinus rate and atrioventricular (AV) conduction of electrical stimulation from a 12-polar electrode catheter advanced into the right pulmonary artery of 21 anesthetized dogs. In each experiment, the distal tip of the electrode catheter was positioned at a standard fluoroscopic site, and a sequence of bipolar electrograms was recorded during sinus rhythm from the 11 adjacent catheter electrode pairs using a standardized technique. Within each sequence of electrograms, a characteristic change in the polarity of the atrial complexes was identified at a site in the proximal right pulmonary artery. This recording site was labeled the site of initial polarity transition. Stimulus-strength response testing was performed from each catheter electrode pair during spontaneous sinus rhythm and during atrial fibrillation sustained by rapid atrial pacing. The least stimulus strengths required to slow sinus rate or to depress AV conduction were obtained using an electrode pair at a proximal right pulmonary artery site identified as the optimal stimulation site. This stimulation site was at, or immediately proximal to, the recording site of initial polarity transition. Stimulation distal to the site of initial polarity transition precipitated atrial fibrillation using stimulus strengths which were very low compared to stimulus strengths required to precipitate atrial fibrillation at more proximal sites. Negative chronotropic and negative dromotropic effects persisted throughout 5-minute periods of stimulation from the optimal stimulation site and could be modulated by varying stimulus parameters. Using neurophysiological and neuropharmacological techniques, we demonstrated that these effects were produced by stimulation of preganglionic parasympathetic efferent nerve fibers. Circ Res 46: 48-57, 1980

Atrial excitability and conduction during rapid atrial pacing.

Using temporary atrial wire electrodes placed at selected atrial sites, rapid atrial pacing at rates of up to 368 beats/min was used to study atrial excitability and conduction in seven patients who underwent open heart surgery. The threshold for atrial pacing was found to be an exponential function of pacing rate (r = 0.55, p < 0.01), increasing threefold when the fastest pacing rates were compared with the slowest pacing rates (p < 0.005). Atrial conduction times (measured from pacing to recording sites), prolonged during rapid atrial pacing both for studies conducted before institution of cardiopulmonary bypass (p < 0.005) and for those done 7 days postoperatively (p < 0.05). However, prolongation of conduction times always depended on achievement of a critically rapid pacing rate. During rapid atrial pacing, we observed a high incidence of alternans of the atrial electrogram (17 of 42 studies). Thus, human atrial excitability, conduction and electrogram morphology are not constant during pacing at rapid rates. Rather, at rapid pacing rates, there is depression of atrial excitability, prolongation of atrial conduction times and alternation in electrogram morphology. These findings have clinical relevance and theoretical implications for the understanding and treatment of rapid atrial rhythms.

De subitaneis mortibus. XV. Hereditary stenosis of the His bundle in Pug dogs.

Syncope and sudden death occurs in certain purebred Pug dogs which have been found to have intermittent sinus pauses and paroxysmal second degree heart block on electrocardiographic (ECG) study. We have established a colony of such dogs to study this problem and here report the results of histological examination of the cardiac conduction system in twenty-one of them. These include a dam which may be considered the proband, three of her offspring (two littermates) and three fetal pups in an unborn litter of one of these; three of the four adult dogs died suddenly and unexpectedly. Two groups of puppies descendants of these lines were also studied after they all died within three days of birth. The first group of puppies (8) did not have suitable ECG studies but the second group (6) did and showed ECG changes similar to those in the adult dogs. In all 21 dogs the sinus node was anatomically normal, but in every one there was significant stenosis of the midportion of the His bundle. There was no abnormality of the atrioventricular (A-V) node or of the bundle branches, and the cardiac valves and coronary arteries were normal. Two pups had ventricular septal defects and one of these had an atrial defect as well. All the dogs were of the normal fawn color, had a normal physical appearance and no visible evidence of associated extracardiac abnormalities. The adult dogs were able to hear normally but the puppies died too early to test their hearing. The paroxysmal heart block may in part be attributable to the abnormality in the His bundle, but other factors possibly leading to heart block and long sinus pauses are discussed. Stenosis of the midportion of the His bundle appears to be a heritable trait in these purebred Pug dogs.

Distribution of 13 trace metals in pig heart tissue

Abstract The concentrations of 13 trace metals in 17 discrete anatomic sites of 11 pig hearts have been determined by emission spectrometry. The metals determined were copper, manganese, molybdenum, zinc, chromium, nickel, cesium, barium, strontium, cadmium, aluminum, tin, and lead. Anatomic sites sampled included aorta, main pulmonary artery, right superior vena cava, tricuspid valve, mitral valve, pulmonary valve, aortic valve, right atrium, left atrial appendage, right ventricle (free wall), left ventricle (free wall), left ventricle-papillary muscle, interventricular septum, crista supraventricularis, sinus node, atrioventricular node and His bundle, and left bundle branch. Statistical analysis of the data incorporated a multivariate analysis of variance and a Duncan analysis. The results showed that certain tissues of the cardiovascular system have distinctive trace metal contents.

Novel classification scheme of cardiovascular tissues using trace metal compositions

Abstract Statistical methods of pattern recognition have been employed to characterize the trace metal profiles created by the concentrations (the geometric means of 11 determinations) of 13 trace metals for 17 anatomic regions of pig heart tissue. Metals analyzed were zinc, copper, tin, aluminum, lead, cadmium, manganese, molybdenum, nickel, strontium, barium, cesium and chromium. Anatomic sites sampled included main pulmonary artery, aorta, mitral valve, tricuspid valve, aortic valve, pulmonary valve, right superior vena cava, right atrium, sinus node, crista supraventricularis, left bundle branch, atrioventricular node and His bundle, left ventricle-papillary muscle, right ventricle (free wall), left ventricle (free wall), interventricular septum, and left atrial appendage. Both techniques of pattern recognition used, namely cluster analysis and discriminant analysis, recognized similar relationships among the tissues, including differences between: (1) arterial and venous tissues; (2) semilunar and atrioventricular valves; and (3) tissues derived from ordinary and specialized myocardium and those derived from blood vessels and heart valves. The pulmonary valve was found to concentrate many trace metals relative to other anatomic sites. The differences among the tissues were sufficiently striking that, using the profiles, 65% of the specimens analyzed were correctly classified with respect to their anatomic origin.

Distribution of 9 trace metals in 17 anatomic sites of dog heart tissue and their classification using pattern recognition

The concentrations (geometric means of 11 determinations) of 9 trace metals in 17 anatomic regions of dog heart tissue and blood vessels were determined. The relationships recognized within the set of trace metal profiles were comparable to those reported earlier for the cardiovascular systems of pig [J. Mol. Cell Cardiol 6, 383 (1974)] and those of beef [Bioinorg, Chem. (in press)]. These included differences in trace metal concentrations that allowed differentiation of the following tissues from each other: (1) ordinary and specialized myocardium from blood vessels and heart valves, (2) blood vessels from heart valves and (3) arterial from venous tissues.

Differential modulation of autonomic activity by ethmozin and ethacizin (analog of ethmozin) on the canine sinus node and atrioventricular junction

The chronotropic and dromotropic actions of ethmozin and its diethylamine analog ethacizin were studied in the presence and absence of combined muscarinic, beta- and alpha-adrenoreceptor blockade in the intact canine heart in situ (n = 38). Injections of ethacizin, 5, 10 and 25 micrograms/ml, into the sinus node artery caused an immediate and significant (p less than 0.001) sinus bradycardia of 2, 6 and 11%, respectively. Injection of 25 and 50 micrograms/ml of ethacizin into the atrioventricular (AV) node artery significantly (p less than 0.001) prolonged AV conduction time with occasional second degree heart block. Conduction delay was located exclusively during the AH interval of the His bundle electrogram. Autonomic blockade did not alter the negative chronotropic or negative dromotropic effects of ethacizin. Ethacizin, 25 micrograms/ml, injected into the sinus node artery immediately reduced the sinus node response to vagal stimulations by 30% and the effect of acetylcholine, 0.1 micrograms/ml, injected into the sinus node artery by 50%. Ethacizin, 25 micrograms/ml, injected into the AV node artery immediately reduced the duration of complete AV block elicited by vagal stimulation or intranodal acetylcholine, 0.5 micrograms/ml, by 90%. Ethacizin caused a minor reduction in sinus node response to right stellate stimulations without, however, altering the sinus node response to intranodal norepinephrine. Ethmozin injections of up to 50 micrograms/ml into the sinus and AV node arteries had no chronotropic or dromotropic effects. Ethmozin had a minor and variable vagolytic action but significantly (p less than 0.05) reduced the sinus node response to sympathetic nerve stimulation. Hence, ethacizin, in contrast to ethmozin, has a direct depressing action on both the sinus node and the AV junction.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of pattern recognition to classify beef cardiovascular tissues on the basis of their trace metal compositions

The pattern recognition procedure of discriminant analysis has been used to characterize the trace metal profiles created by the concentrations of 8 trace metals in 15 anatomic sites of beef heart tissue. Metals analyzed were copper, tin, lead, molybdenum, strontium, cesium, barium, and aluminum. Anatomic sites sampled included main pulmonary artery, aorta, mitral and tricuspid valves, left and right coronary arteries, os cordis, right atrium, left atrial appendage, crista supraventricularis, left bundle branch, free wall of the right and left ventricles, interventricular septum, and papillary muscle of the left ventricle. The striking features of the data were: (1) All specimens of the mitral valve, tricuspid valve, and os cordis were ambiguously described by their trace metal profiles; (2) the four blood vessels constituted two groups of two tissues each (aorta, main pulmonary artery; left and right coronary arteries); (3) tissues derived from ordinary and specialized myocardium were quite different from blood vessels, heart valves and os cordis. Using these profiles, 85% of the specimens analyzed were correctly classified by discriminant analysis with respect to their anatomic origin.