Go Konishi

Atrioventricular wenckebach periodicity in athletes: Influence of increased vagal tone on the occurrence of atypical periods

In 37 athletes with atrioventricular (AV) Wenckebach periodicity, the relationship between PP and RR intervals was investigated. In most athletes, when PP intervals gradually lengthened, RR as well as PR intervals usually also gradually lengthened until a blocked P wave occurred, resulting in the occurrence of an atypical Wenckebach period with prolongation of the last RR interval (variant I). In 20 athletes, sudden marked prolongation of a PR interval occasionally occurred, which was usually followed by a blocked P wave (variant II). In five athletes, once sudden marked prolongation of a PR interval occurred, markedly long PR intervals were maintained for some time, and then a PR interval suddenly shortened without a blocked P wave (variant III). It appeared that the above findings were caused by spontaneous variations in vagal tone. It was suggested that longitudinal dissociation and concealed reentry in the AV node occurred in atypical Wenckebach periods of variants II and III, but not in the other periods.

Bradycardia- and tachycardia-dependent termination of ventricular bigeminy: Mechanism of ventricular extrasystoles with fixed coupling

Fourteen men with intermittent ventricular bigeminy were selected for this study because coupling intervals of the extrasystoles were considerably long and usually fixed, and bradycardia-dependent (10 cases) and/or tachycardia-dependent (12 cases) termination of bigeminy occurred. In all cases, when the heart rate ranged between two certain values, ventricular bigeminy with fixed-coupled extrasystoles was sustained. In all cases showing bradycardia-dependent termination, bigeminy was suddenly terminated with no changes in coupling of the preceding extrasystoles when the heart rate was decreased below a certain lower value. In all cases showing tachycardia-dependent termination except one, when the heart rate increased beyond a certain higher value, coupling intervals gradually lengthened until bigeminy was terminated. These findings strongly suggest the possibility that, in a considerably large number of clinical cases, ventricular extrasystoles with fixed coupling are caused by longitudinal dissociation of conduction in the reentrant pathway of extrasystoles.

Mechanism of irregular parasystole: Differentiation of second-degree entrance block from electrotonic modulation

Experts had believed for a long time that the parasystolic rhythm is regular and independent of sinus rhythm. In 1974, Kinoshital reported a case of ventricular parasystole in which when a sinus impulse fell late in the parasystolic cycle, it hastened the next ectopic discharge. Since then, many cases of such “irregular” parasystole have been reported,2-14 and it has been shown that in most clinical cases of parasystole, such hastening of the ectopic discharge can be observed.15, l6 There are two theories to explain hastening of the ectopic discharge: one, which was postulated by Kinoshita et a1.,l-12, 15* I6 is type I second-degree entrance block; the other, which was postulated by Jalife and Moe,17 is electrotonic modulation. According to both theories, the parasystolic cycle can be divided into the early period and the late period, and only when nonparasystolic impulses fall in the late period do they hasten the next ectopic discharge. Thus the coupling intervals of ectopic QRS complexes to the preceding sinus QRS complexes have a discontinuous distribution; that is, there is a gap in distribution bet,ween the coupling intervals to early intervening sinus QRS complexes and those to late intervening sinus QRS complexes. The upper limit of the gap is seen when a sinus QRS complex occurs at the terminal portion of the early period; the lower limit of the gap is seen when it occurs at the initial portion of the late period. At the site of entrance block, the length of the early period is invariable according to both theories. Although these characteristics resemble each other, their mechanisms are quite different.

Mechanisms of atypical atrioventricular Wenckebach periodicity

Abstract To explain the mechanisms of atypical atrioventricular (AV) Wenckebach periodicity, a model of the AV node was theoretically derived from the concepts of “inhomogeneous excitability” and “electrotonically mediated conduction”. The theoretical model of the AV node has the following characteristics: (1) increased vagal tone depresses excitability in the AV node, (2) depressed excitability in the AV node is inhomogeneous in both transverse and longitudinal directions, and (3) electrotonically mediated conduction occurs across inexcitable gaps in the AV node. Many features in atypical AV Wenckebach periodicity are explained by the use of this model. Delayed AV conduction is caused mostly by electrotonically mediated conduction across a much-depressed region in the AV node, and thereafter AV conduction is blocked at the same region, resulting in the occurrence of an AV Wenckebach period with gradual lengthening of PR intervals. Occasionally, longitudinal dissociation and concealed reentry in the AV node occur in the part below (distal to) the above depressed region, resulting in the occurrence of an AV Wenckebach period with sudden marked lenthening of a PR interval. The sinus impulse following such suddenly delayed AV conduction is usually blocked in the AV node as the result of concealed reentry of the preceding impulse.

Mechanism of ventricular extrasystoles with fixed coupling: A theoretical model derived from the concept of longitudinal dissociation in the reentrant pathway of extrasystoles

An electrocardiogram taken from a 29-year-old man with old myocardial infarction is presented as an exemplary case of ventricular extrasystoles with fixed coupling. To explain the mechanism of ventricular extrasystoles with fixed coupling, a theoretical model is derived from the concept of longitudinal dissociation in the reentrant pathway. In the model, functional longitudinal dissociation divides the reentrant pathway into dual pathways F and S. When a sinus impulse is blocked in pathway F and passes only through pathway S, it becomes a manifest reentrant extrasystole because of marked conduction delay in pathway S. When the sinus rate does not exceed a certain value, such an impulse always becomes a manifest extrasystole with fixed coupling. Part of the impulse passing through pathway S enters pathway. F retrogradely. In some cases, thereafter, it reenters pathway S and initiates ventricular reentrant tachycardia. When, on the other hand, a sinus impulse passes through both of pathways F and S, it becomes a concealed reentrant extrasystole because of insufficient conduction delay in the pathways.

‘Stereovectorcardiogram’ Made by Stereolithography

A method for making directly a single solid vectorcardiogram is reported. A solid vectorcardiogram was made by employing an apparatus for production of three-dimensional objects by stereolithography. Stereolithography is a computer-aided manufacturing technique that is practiced in conjunction with computer-aided design and engineering. To design the solid vectorcardiogram, voltages in the X, Y and Z axes obtained according to the Frank lead are memorized in the computer-aided design system. By use of the stereolithography apparatus, the designed solid vectorcardiogram is formed in a vat filled with liquid plastic. In the vat, the plastic changes rapidly from liquid to solid in the presence of ultraviolet light so that a solid vectorcardiogram made of solid plastic may be formed.

Protection of the Ventricular Parasystolic Focus due to Interference of Sinus and Parasystolic Impulses in the Ventricular-Ectopic Junction

A 50-year-old man with intermittent ventricular parasystolic bigeminy is reported in whom the parasystolic focus was protected from late intervening sinus impulses. This is the first report to suggest the presence of protection due to interference in parasystolic bigeminy. The findings in this case suggest that when a sinus impulse falls in a late period of the parasystolic cycle, it travells so slowly along the ventricular-ectopic junction that it is unable to reach the parasystolic focus before the spontaneous occurrence of the next parasystolic impulse; as a result, the sinus impulse interferes with the next parasystolic impulse in the ventricular-ectopic junction. Thus it is suggested that the parasystolic focus is protected from the sinus impulse because of the interference and not because of an entrance block. This reinforces the concept of a second-degree entrance block as a mechanism of parasystole.

Type A Alternating Wenckebach Periodicity in the Reentrant Pathway of Interpolated Ventricular Extrasystoles

A 67-year-old man with interpolated ventricular extrasystoles is reported in whom alternate sinus QRS complexes were followed by interpolated ventricular extrasystoles with progressively lengthening coupling intervals until one of these alternate sinus complexes failed to be followed by an extrasystole. This is the first report to suggest the presence of type A alternating Wenckebach periodicity in the reentrant pathway of interpolated ventricular extrasystoles. It is suggested that 2:1 block occurred at a proximal level in the reentrant pathway, while Wenckebach block occurred at a distal level in the pathway.

Intermittent ventricular bigeminy as an expression of two-level Wenckebach periodicity in the reentrant pathway of extrasystoles.

A patient with intermittent ventricular bigeminy is reported in whom the presence of two‐level Wenckebach periodicity in the reentrant pathway of extrasystoles is suggested. When sinus arrest was caused by vagal stimulation, no ectopic QRS complex occurred. This indicated that ventricular bigeminy was not parasystolic bigeminy but ordinary extrasystolic bigeminy. Observations of the electrocardiogram suggested that Wenckebach block occurred at two different levels in the reentrant pathway of ventricular extrasystoles. When extrasystoles were noninterpolated, Wenckebach block occurred at the distal level of the pathway and caused termination of ventricular bigeminy. On the other hand, when extrasystoles were interpolated, Wenckebach block occurred at the proximal level of the pathway. This is the first report to suggest the presence of two‐level Wenckebach periodicity in a reentrant pathway of extrasystoles.

Mechanism of concealed atrial trigeminy

Abstract In concealed trigeminy, the number of sinus QRS complexes intervening between 2 successive manifest extrasystoles is generally 3n − 1, where n is any positive integer. This phenomenon was originally reported in 1960 by Satoh et al1 in a case of ventricular extrasystoles. Since then, concealed ventricular trigeminy has been reported in many patients, whereas concealed atrial trigeminy appears only once, in a case reported by Levy et al.2 In the present report, another case of concealed atrial trigeminy is presented, in which the presence of 3:2 Wenckebach periodicity in the pathway of extrasystolic impulses is suggested as a new mechanism of concealed trigeminy.