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. Apparent bradycardia-dependent right bundle branch block associated with atypical atrioventricular Wenckebach periodicity as a possible mechanism.The Holter monitor electrocardiogram was taken from a 15-year-old male athlete. Intermittent right bundle branch block frequently occurred at rest. When sinus cycles gradually lengthened, sinus impulses were conducted to the ventricles with right bundle branch block (RBBB) in succession. When, thereafter, sinus cycles gradually shortened, sinus impulses were conducted without RBBB. However, it seems that these findings do not show true bradycardia-dependent RBBB. Atypical atrioventricular Wenckebach periodicity was occasionally found in which sudden shift from the period of comparatively short PR intervals to the period of long PR intervals occurred. In the Wenckebach periodicity, when a QRS complex occurs after a much longer pause, RBBB was not found, while when it occurs after a much shorter period, RBBB was found. This suggests that this case may be apparent bradycardia-dependent RBBB, namely, a form of tachycardia-dependent RBBB. This is the first report suggesting apparent bradycardia-dependent bundle branch block associated with gradual lengthening of sinus cycles, as a possible mechanism.- - - - - - - - - - ranking = 3keywords = cycle (Clic here for more details about this article) |
3/8. First-degree trifascicular block unmasked by sinus arrhythmias. Report of a case studied with intracardiac electrocardiography.A case is presented in which first-degree block in all three fascicles of the intraventricular conduction system results in a QRS complex with no specific features of fascicular block. During spontaneous sinus arrhythmia the typical features of RBBB and LAH appear at the longest sinus cycles. This is associated with shortened P-R and H-Q intervals. During shorter sinus cycles, near equalization of delay in each fascicle is associated with delay in His-Purkinje conduction but loss of the typical features of bifascicular block as the ventricular myocardium becomes activated more synchronously. documentation of the changing patterns of ventricular activation is provided by His bundle electrocardiography.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
4/8. Underdrive suppression of the sinus rhythm in man.This report demonstrates unusual responses of the sinus rhythm to atrial pacing. The sinus rhythm failed to become manifest when the heart was driven at a rate slower than the inherent sinus rate. Sinus rhythm returned only after termination of underdrive pacing with the recovery time longer than twice the cycle length of the control sinus rhythm. The largest difference between underdrive and sinus cycle lengths measured 600 msec. To the best of our knowledge, underdrive suppression of the sinus rhythm has not been previously reported in man.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
5/8. Autonomic sinus node dysfunction and its treatment.The clinical, electrocardiographic, pharmacologic, electrophysiologic and Holter monitoring findings are described in four patients with autonomic sinus node dysfunction and one patient with autonomic binodal disease. All showed cerebral symptoms, and had attacks of dizziness, weakness, near-syncope or syncope. After a pharmacologic autonomic blockade with propranolol and atropine, all patients had normal intrinsic heart rates. Electrophysiological studies revealed normal corrected intrinsic node recovery time (less than or equal to 240 msec) a gradual return to the basic cycle length in the secondary postpacing cycles after autonomic blockade, and no intrinsic paroxysmal atrioventricular block. Continuous ECG monitoring (1-3 X 24 hours) revealed severe sinus bradycardia, SA-block, severe sinus arrest, cardiac standstill, atrial fibrillation and in two patients associated AV-block. Autonomic blockade with electrophysiological studies exclude the intrinsic involvement of the sinoatrial and atrioventricular node. Holter monitoring is the best method for assessing the autonomic neurovegetative component of dysrhythmias. Therapy regarding isolated autonomic sinus node dysfunction depended on the pathomechanisms of rhythm disorders: two patients received permanent pacemakers, antiarrhythmic drugs were applied in the case of two patients, and etiological treatment in the case of one. During the follow-up, all patients became symptom-free.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
6/8. Alternating sinus rhythm and intermittent sinoatrial block induced by propranolol.Alternating sinus rhythm and intermittent sinoatrial (S-A) block was observed in a 57-year-old woman, under treatment for angina with 80 mg propranolol daily. The electrocardiogram showed alternation of long and short P-P intervals and occasional pauses. These pauses were always preceded by the short P-P intervals and were usually followed by one or two P-P intervals of 0.92-0.95 s representing the basic sinus cycle. Following these basic sinus cycles, alternating rhythm started with the longer P-P interval. The long P-P intervals ranged between 1.04-1.12 s and the short P-P intervals between 0.80-0.84 s, respectively. The duration of the pauses were equal or almost equal to one short plus one long P-P interval or to twice the basic sinus cycle. In one recording a short period of regular sinus rhythm with intermittent 2/1 S-A block was observed. This short period of sinus rhythm was interrupted by sudden prolongation of the P-P interval starting the alternative rhythm. There were small changes in the shape of the P waves and P-R intervals. S-A conduction through two pathways, the first with 2/1 block the second having 0.12-0.14 s longer conduction time and with occasional 2/1 block was proposed for the explanation of the alternating P-P interval and other electrocardiographic features seen. atropine 1 mg given intravenously resulted in shortening of all P-P intervals without changing the rhythm. The abnormal rhythm disappeared with the withdrawal of propranolol and when the drug was restarted a 2/1 S-A block was seen. This was accepted as evidence for propranolol being the cause of this conduction disorder.- - - - - - - - - - ranking = 3keywords = cycle (Clic here for more details about this article) |
7/8. Incomplete interpolation caused by sinoatrial pacemaker shift. A report of two cases.Shortened return cycles after premature atrial stimulation (PAS) are commonly referred to as sinoatrial entrance block and exit delay at the sinoatrial junction or sinus-node reentries. In the 2 reported cases PAS at critical coupling intervals was followed by shortened return cycles characterized by a changed high right electrogram (and surface P waves in 1 case) and a normal sequence of atrial activation with unaltered intraatrial conduction. These changes lasted for some beats and a concomitant shorter or longer atrial cycle length was observed. Electrophysiological events furnish indirect evidence of sinoatrial pacemaker shift as a cause of incomplete interpolation in man.- - - - - - - - - - ranking = 3keywords = cycle (Clic here for more details about this article) |
8/8. 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) |