1/15. 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. ( info) |
2/15. 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. ( info) |
3/15. 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." ( info) |
| 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. ( info) |
5/15. A different approach to the analysis of pure ventricular parasystole. Until recently, it had not been recognized that predictions regarding the number of sinus beats interposed between two consecutive parasystolic beats could be made. In a case of perfect, pure parasystole resulting from unintentional fixed rate ventricular pacing, the following was observed: there were consistently three different values (0,2,3) for the number of interposed sinus beats; only one of these values was odd, and the sum of the two smaller values was one less than the larger value. Our findings, which are in keeping with those obtained in an mathematical model, may be of additional help in the diagnosis of this elusive arrhythmia. ( info) |
6/15. 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. ( info) |
7/15. Two cases of ventricular parasystole associated with ventricular tachycardia. In two patients, ventricular parasystole (VP) was associated with ventricular tachycardia (VT), and in one patient, catheter ablation was successful. In patient 1, with dilated cardiomyopathy, VP led to VT, which converted to ventricular fibrillation. In patient 2, VP led to symptomatic nonsustained polymorphic VT. The origin of parasystolic focus was determined by endocardial mapping, and a radiofrequency current was delivered to patient 2. Both VP and VT disappeared immediately, and no recurrence has been observed during a follow-up of 8 months. catheter ablation to the parasystolic focus was effective and a relationship between VP and VT was strongly suggested. ( info) |
| The coexistence of a parasystolic focus, tachycardia dependent right bundle branch aberrancy, and an AV accessory pathway is reported here. This condition was present in a 40-year-old man, which led to an incessant AV reciprocating tachycardia. Further electrophysiological study revealed that the parasystolic focus was located somewhere in the His bundle; endocardial mapping disclosed a right posterior accessory pathway. Radiofrequency current was delivered at the atrial level of the right posterolateral AV groove and successfully ablated the accessory pathway, leading to a dramatic improvement in cardiac function. In conclusion, the recognition of the electrophysiological mechanism of incessant supraventricular tachycardia was of crucial importance for the therapy decision. A definitive intervention using radiofrequency catheter ablation should be considered early and not postponed in patients with tachycardia-induced cardiomyopathy. ( info) |
| The cases of two patients with ventricular parasystole revealed a new depressive effect of adenosine on ventricular parasystolic activity. To the authors' knowledge, this is the first report that clearly demonstrates the disappearance of "true" parasystole. ( info) |
10/15. 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. ( info) |