1/30. 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) |
2/30. Premature depolarization concealed in two pulmonary veins.A case is presented in which a premature depolarization emanated from a partially activated left inferior pulmonary vein, activated the entire left superior pulmonary vein, but did not activate the atria ("concealed"). The site of conduction block between each vein and the left atrium was the anatomic atriovenous junction. At times, the same depolarization would activate the atria and initiate atrial fibrillation. The shortest depolarization coupling interval that activated the atria was significantly longer than the atrial fibrillation cycle length recorded in either vein. Observations in this case support two concepts: (1) the existence of myocardial "tracts," extending into and between pulmonary veins; and (2) a "mismatch" between pulmonary vein activation ingress and egress.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
3/30. Differentiation between parasystole and reentry in concealed bigeminy.There are two different theories to explain the mechanism of concealed bigeminy: one is '2:1 concealed reentry'; the other is 'irregular parasystole.' Two exemplary cases of the even-number variant of concealed bigeminy are presented. In case 1, the mechanism can be explained by an irregular parasystole due to a modulated parasystole; however, findings during temporary sinus arrest caused by vagal stimulation indicate that this case is not governed by a parasystole, but by a 2:1 concealed reentry. In case 2, the mechanism can be explained by a 2:1 concealed reentry without parasystole; however, findings during temporary sinus arrest indicate that this case is governed by an irregular parasystole due to a type-I second-degree entrance block. Thus, in cases of concealed bigeminy without pure ectopic cycles, it does not seem easy to explain the mechanism of concealed bigeminy on the theory of a modulated parasystole.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
4/30. Failure of parasystolic impulses to appear on schedule. Exit block due to concealed conduction of sinus impulses.A 45-year-old patient free of any heart disease was admitted to the hospital with an electrocardiographic pattern of ventricular parasystole. The parasystolic rhythm was relatively fast, such that several consecutive ectopic complexes manifested. A later tracing reflected only isolated parasystolic complexes with long and fixed coupling intervals. The interectopic intervals, however, were once more in multiple of the parasystolic cycle as directly measured during the phases of undisturbed parasystolic rhythm. In the latter tracing, several scheduled parasystolic impulses did not yield a response, despite calculation suggesting that these impulses occurred outside the refractory period. In other words, an exit block was present. Analysis of the tracing suggests that the exit block was caused by concealed penetration of the sinus impulses into the ectopic-ventricular junction. That is, any sinus impulse penetrates into the junction and renders it refractory, in such a way that only parasystolic impulses that are relatively late within the sinus cycle may be conducted to the surrounding myocardium and result in a parasystolic complex.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
5/30. Mechanism of bradycardia-dependent appearance of manifest extrasystoles in concealed bigeminy. A theoretical model derived from the concepts of longitudinal dissociation and multilevel block in the reentrant pathway of extrasystoles.A case of bradycardia-dependent appearance of manifest extrasystoles in concealed bigeminy is presented. To explain the mechanism of such bradycardia-dependent appearance, a theoretical model is derived from the concepts of "longitudinal dissociation" and "multilevel block" in the reentrant pathway of extrasystoles. In the theoretical model, functional longitudinal dissociation divides the reentrant pathway into dual pathways F and S. When manifest extrasystoles are not found for a long time, alternate sinus impulses pass through both pathways F and S, but become concealed extrasystoles because of insufficient conduction delay in the pathways. The other alternate sinus impulses are blocked in the pathways; in pathway F, the impulses are blocked at the entrance, while in pathway S, the impulses are blocked at a more distal level. When sinus cycles gradually lengthen, one of such alternate sinus impulses passes through the entrance of pathway F and, traveling very slowly, is blocked at a more distal level. The next sinus impulse is blocked at the entrance of pathway F; namely, 3:2 Wenckebach block occurs at the entrance of pathway F. Thus this sinus impulse enters only pathway S and passes through pathway S with enough conduction delay to become a manifest reentrant extrasystole.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
6/30. Atrioventricular nodal reentry in the wolff-parkinson-white syndrome.Although supraventricular tachycardia in the Wolff-Parkinson-White (WPW) syndrome is generally due to atrioventricular reentry, the presence of the accessory pathway does not preclude other mechanisms of tachycardia. We observed AV nodal reentry in three of 95 consecutive patients (3.1%) referred for assessment of arrhythmias associated with WPW syndrome. The unique observation of spontaneous transition from atrioventricular reentry to AV nodal reentry at a similar cycle length was observed in one patient and is the subject of this report.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
7/30. Alternating left and right bundle branch block aberration of atrial extrasystoles in bigeminal rhythm.We report two cases of atrial extrasystolic bigeminy manifesting with alternating right and left bundle branch block aberration. The manifestation is explained on the basis of cycle-dependent variations of the bundle branch refractory period with alternate resetting of bundle branch refractoriness.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
8/30. Periodic changes in cycle length of ventricular tachycardia: a Wenckebach type exit block?A 55-year-old female developed ventricular tachycardia (VT) which showed a Wenckebach periodicity in cycle length. She had had a myocardial infarction about ten years previous and, at age 51, felt fatigability and palpitations. The ECG showed VT. Thereafter, she had had palpitations of short duration two to three times a year. On the last admission she developed fatigability; the ECG showed VT. lidocaine (100 mg i.v.) did not terminate VT. procainamide (600 mg) could not terminate the VT, but the rate became slower. Programmed stimulation was given at bedside which effectively terminated VT. Electrophysiologic study induced VT in a reproducible manner. Ventricular tachycardia showed initial fluctuation in cycle length which stabilized at 270 msec. disopyramide therapy (400 mg/day p.o.) was begun and electrophysiologic study was repeated one week later. VT was again induced but the cycle length was a little longer. A periodic change in cycle length from 328 to 442 msec was repeated. The change in cycle length was uniformly found in surface leads (I, II, V1) and intracardiac electrograms from the right ventricular apex and the His bundle region. No change in QRS complex was found and the periodicity was unrelated to atrial activity. A Wenckebach type exit block was therefore suggested; disopyramide might be responsible for the development of the block. We could not find another such case in the literature.- - - - - - - - - - ranking = 9keywords = cycle (Clic here for more details about this article) |
9/30. tachycardia- and bradycardia-dependent atrioventricular block: observations regarding the mechanism of block.A case of paroxysmal bradycardia- and tachycardia-dependent atrioventricular (AV) block is described in a patient with right bundle branch block. The His bundle recordings demonstrated the site of the AV block to be distal to the His bundle recording site (probably in the left bundle branch). Whereas AV block distal to the His bundle occurred at an atrial paced cycle length of 700 ms, intact ventriculoatrial (VA) conduction was present up to a ventricular paced cycle length of 400 ms. Resumption of AV conduction was dependent on a critical HH or RH (in case of escapes) interval. These findings suggest that the bradycardia-dependent block is related to a time-dependent decrease in the amplitude of the current intensity of the proximal segment during late diastole. Spontaneous diastolic depolarization during late diastole resulted in impaired anterograde (AV) conduction but facilitated retrograde (VA) conduction. These findings are consistent with experimental "in vitro" observation in the sucrose gap model of AV block.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
10/30. Concealed ventricular quadrigeminy linked to atrial quadrigeminy: a manifestation of modulated parasystole.Analysis of a long electrocardiographic recording including many atrial and ventricular extrasystoles shows that when atrial extrasystoles are in a quadrigeminal distribution, the ventricular extrasystoles also manifest a quadrigeminal distribution or reflect a distributional pattern of concealed quadrigeminy. Conversely, when atrial extrasystoles are other than in a quadrigeminal distribution, the ventricular extrasystoles do not occur in a quadrigeminal or concealed quadrigeminal distribution. This pattern is explained on the basis of modulated parasystole. A biphasic phase-response curve explains the observed phenomena on the basis of variations of the parasystolic cycle length due to the modulating effect of supraventricular beats.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
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