1/8. Intermittent sinus bigeminy as an expression of sinus parasystole: a case report.A case of sinus parasystole is reported. The diagnosis of sinus parasystole is relatively difficult because there is no difference between the basic sinus P wave and the parasystolic wave. Sinus parasystole is diagnosed according to the following electrocardiographic criteria: (1) premature P waves having contour identical to P waves of basic beats; (2) intervals between premature P waves mathematically related. In the case reported, the coupling intervals during long phases of intermittent sinus bigeminy were nearly fixed, because there was little variability in the returning cycles, making the diagnosis of sinus parasystole difficult.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
2/8. Effects of exercise and standing on atrial parasystole: prolongation and shortening of the parasystolic cycle length.In recently reported cases of ventricular parasystole, it was shown that after exercise the parasystolic cycle length is prolonged, in contrast to a shortening of the sinus cycle length, whereas during standing the parasystolic cycle length and the sinus cycle length both shortened. In this report, to explore whether the same features as occur in ventricular parasystole are seen in atrial parasystole, effects of exercise and standing on the parasystolic cycle length were investigated in two men with atrial parasystole. The atrial parasystolic cycle length was prolonged after exercise, whereas it shortened during standing, similar to what occurs in ventricular parasystole. This is the first report to show such changes of cycle length in atrial parasystole. These findings suggest that in atrial parasystole, as in ventricular parasystole, influences on the parasystolic cycle length do not always act in the same direction as those on sinus cycle length.- - - - - - - - - - ranking = 13keywords = cycle (Clic here for more details about this article) |
3/8. Ventricular parasystolic couplets originating in the pathway between the ventricle and the parasystolic pacemaker: mechanism of "irregular" parasystole.This article explains the mechanism of "irregular" parasystole. Two theories have been suggested: "electrotonic modulation" and "type I second degree entrance block." This study attempts to clarify the mechanism of irregular parasystole in cases of true ventricular parasystole associated with ventricular parasystolic couplets. Cases associated with ventricular parasystolic couplets were selected from 37 clinical cases of true ventricular parasystole in which one or more pure parasystolic cycles with no intervening nonectopic QRS complexes were found. Of the 37 cases of true ventricular parasystole, ventricular parasystolic couplets were found in 4 cases. In none of the other 33 cases, ventricular parasystolic couplets were found. In all the cases coexisting with ventricular parasystolic couplets, the latter ectopic QRS complex of the couplet failed to reset the parasystolic rhythm. The above findings suggest that the latter ectopic QRS complex of the parasystolic couplet originated not in the parasystolic pacemaker but in the pathway between the ventricle and the parasystolic pacemaker. It seems that when a sinus impulse fell late in the parasystolic cycle, it passed through the site of second degree entrance block and that the parasystolic couplets originated from the reentrant pathway between the ventricle and the pacemaker. This strengthens our previous suggestion that the mechanism of irregular parasystole is governed by "type I second degree entrance block" and not by "electrotonic modulation."- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
4/8. His-bundle parasystole masquerading as exercise-induced 2:1 atrioventricular block.We describe a case of symptomatic pseudo-AV block due to His-bundle parasystole masquerading as exercise-induced 2:1 AV block. Electrophysiologic study revealed the presence of His-bundle parasystole, and the fluctuation of parasystolic cycle length could be explained by the concept of modulated parasystole. Modulated parasystole is a possible explanation for maintenance of stable 2:1 AV conduction at an atrial rate of specific range during exercise.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
5/8. Double atrial parasystole showing intermittent trigeminy.An extremely rare instance of atrial parasystole arising from two different ectopic atrial foci, i.e. double atrial parasystole, is presented, in which both parasystolic intrinsic cycles were found to be around 0.80-0.89 sec. Atrial parasystolic trigeminy with a positive P wave in leads II and III and interectopic intervals (IEIs) of 2.40-2.68 sec continued, then intermittent atrial parasystole with a negative P wave in leads II and III and IEIs of 2.45-2.69 sec took over. A wandering pacemaker between the sinus node and the upper atrio-ventricular (A-V) junction due to autonomic imbalance, i.e. increased vagal tone, in an elderly patient with bronchial asthma was supposed to be the underlying mechanism. Resetting of the parasystolic pacemaker by the third preceding atrial impulse or mutual entrainment and the subsequent 3:1 exit block may play a role in the development of intermittent atrial parasystole with a negative P wave in this case on account of the intrinsic ectopic cycle of 0.84 sec. Alternative explanation of IEIs 2.40-2.69 sec was a 2:1 exit block with the altered basic cycle of mainly 1.24-1.29 sec in consideration of the IEI of 1.24 sec. An explanation of manifest parasystolic cycles on the basis of the theory or cardiac resonant oscillation was put forward for the first time in this report. The IEIs take certain discrete values, which may represent a quantitized property of atrial parasystolic pacemakers as oscillating systems.- - - - - - - - - - ranking = 4keywords = cycle (Clic here for more details about this article) |
6/8. Irregular sinus parasystole due to intermittency and modulation of parasystolic activity.A case of intermittent sinus parasystole in which the parasystolic focus is protected from the dominant sinus rhythm only during the second half of its intrinsic cycle is reported. In addition, a modulating (i.e., electronic) effect is often clearly exerted from the dominant rhythm upon the focus during the protected period. Coexistence of both modulation and intermittency in sinus parasystole, as well as a modulating effect limited to the second part of the parasystolic cycle, have not been previously reported.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
7/8. Cardiac resonant oscillations in terms of finite-dimensional group representation in atrial parasystole.In order to understand the variation of the atrial parasystolic cycle lengths and mutual interactions of sinus node and atrial parasystolic pacemakers, a representation theory for finite groups of invertible linear transformation on a vector space is considered. A quantitative description of manifest atrial parasystolic cycles can be provided by the mapping in the group multiplication with the use of numerical factors of 2, 4 square root of 2 pi, 2/ 4 square root of 2 pi and 2 4 square root of 2 pi. These represent operators of a linear transformation in matrix multiplication of the similarity transformation representing an isomorphism.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
8/8. Intermittent parasystole with exit block.A 53-year-old patient had a complex ventricular arrhythmia, which most likely was an intermittent pure (nonmodulated) parasystole, due to protection limited to the first part of the cycle coexisting with exit block. However, other interpretations of the observations were possible. Foremost among these was modulated parasystole with partial protection or with an attenuated or nondetectable early delaying phase, with exit block. Interestingly, the parasystole appeared to have fulfilled the dynamic rules regarding the number of sinus beats interposed between manifest parasystolic beats, as has been reported for pure or weakly modulated parasystole. This case corroborates unusual manifestations of an arrhythmia, which because of its newly found complexities and various possible interpretations seems to be discussed with decreasing frequency in most textbooks on general cardiology.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |