1/11. 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) |
2/11. Cross-talk in a dual-chamber defibrillator presenting as pacemaker alternans.This case report highlights the occurrence of pacemaker alternans in a dual-chamber defibrillator. Pacemaker alternans occurs secondary to cross-talk. The sensing algorithm and basic timing cycles are reviewed.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
3/11. Spontaneous alternans in Brugada ECG morphology.A 23-year-old man presented with sick sinus syndrome and Brugada-like ECG pattern. Coved type ECG (type 1) converted to saddleback configuration (type 2) when R-R interval decreased and it changed to coved type pattern with increasing R-R cycle length. During stable heart rate, there was no change in Brugada ECG pattern. The R-R interval effect on these patterns can be explained by intensity or kinetics of ion currents and autonomic tone.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
4/11. Atrial pacing bigeminy: a manifestation of crosstalk.Atrial pacing bigeminy, defined as atrial pacing with alternating short and long cycle lengths, was recorded in two out of five DDD-pacemaker implants. Another fascinating feature, the lowering of the effective pacing rate after programming to a higher rate, occurred in one patient. Both phenomena can be explained by crosstalk; appropriate programming resulted in normal DDD-function in all cases. These observations in our patients have led to some interesting conclusions regarding multiprogrammability and nominal settings.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
5/11. Effects of supernormal capture on directly measured nonmodulated parasystolic cycles.Pacemaker capture during the supernormal period was seen in a case of modulated parasystole where ectopic cycles occurred without any interposed nonparasystolic beat. This contrasts with previous clinical reports, since, in the latter, the parasystolic cycle length could not be measured directly. As in experimental studies, supernormal modulation resulted in a triphasic phase response curve. Although less likely, similar electrocardiographic changes could be produced by a conceptually different phenomenon, namely full parasystolic resetting due to loss of protection occurring exclusively early in the cycle, combined with modulation in the other (late) parts of the cycle.- - - - - - - - - - ranking = 8keywords = cycle (Clic here for more details about this article) |
6/11. Unusual electrocardiographic patterns of modulated parasystole.Modulation of a parasystolic rhythm implies that the latter is affected by nonparasystolic beats in predictable ways. When modulation occurs the diagnosis of ventricular parasystole cannot be made by applying the well-known 'classical' criteria. This report deals with clinical tracings from three cases having modulated parasystole with unusual characteristics. Case 1 showed a 24-hour diurnal variability of parasystolic modulation characterized by its occurrence during only part of the period of sleep (from 1 to 5 am). In case 2, modulated ventricular parasystole produced episodes of intermittent ventricular bigeminy with fixed coupling resembling those attributed to a reentry mechanism. The proper diagnosis was made when the sinus cycle length changed abruptly. Finally, in case 3, the idionodal rhythm from a patient with complete AV block was shown to be not only parasystolic, but also modulated. In addition, the idionodal rhythm was entrained (captured) in a concealed fashion by paced beats so that the post-pacing events did not conform with those occurring during overdrive pacing of parasystolic nonmodulated, or nonparasystolic, idionodal rhythms. These findings constitute the clinical counterpart of experimental studies performed with microelectrode techniques.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
7/11. A new indirect method for measurement of sinoatrial conduction time and sinus node return cycle.We developed a new indirect method for the measurement of sinoatrial conduction time (SACT) and the sinus node return cycle (SRC) with a transvenous catheter technique. Two early premature stimuli, at intervals 50 msec longer than the effective refractory period (ERP), were given to the right atrium. These early stimuli were followed by eight constant stimuli. The interval of the constant stimuli was a little shorter than the basic cycle length (BCL). The return cycle A1Ar was measured and plotted on the abscissa; the next interval ArA3, was measured and plotted on the ordinate. This was called the "base point". A new stimulus, A2, was then added to the train of stimulations, first at a point simultaneous with Ar. It was then shifted toward the last constant stimulus at 10-20 msec intervals until A2 met the ERP. The relationship between A1A2 and A2A3 was obtained by the repetition of the procedures with various A1A2 intervals. It had two zones, compensatory and non-compensatory. We postulate that the atriosinus conduction time of the last of the eight stimuli was equal to that of A2 when the stimulus A2 first captured and reset the sinus nodal pacemaker cells, as indicated by the transition point of the two zones. Based on this supposition, SACT and SRC could be measured as the intervals from the base point to the transition point and from the transition point to the eighth stimulus, respectively.- - - - - - - - - - ranking = 7keywords = cycle (Clic here for more details about this article) |
8/11. sick sinus syndrome: the role of hypervagotonia.A 58-year-old man with persistent symptomatic sinus bradycardia (52 beats/min) showed a markedly prolonged postpacing pause (3240 msec) after atrial pacing at a cycle of 840 msec. In addition, Wenckebach block occurred following atrial pacing at a cycle length of 700 msec. After atropine (2 mg) postpacing pauses returned to normal value and type 1 second-degree AV block completely reversed to 1:1 AV conduction until paced rates greater than 140/min. It may be that in some patients marked and persistent vagal overactivity may predispose to "intrinsic" sinus node dysfunction; in later stages, sinus node function may paradoxically result unaffected by changes in autonomic tone.- - - - - - - - - - ranking = 2keywords = cycle (Clic here for more details about this article) |
9/11. A second zone of compensation during atrial premature stimulation: evidence for decremental conduction in the sinoatrial junction.125 consecutive patients with premature atrial stimulation were studied. Three demonstrated sinus node return cycles that were fully compensatory following premature atrial stimuli delivered early in diastole. This second zone of compensation was unaccompanied by significant alterations in the post-return cycle lengths or in P-wave morphology of the return cycle. To account for the occurrence of a complete compensatory pause following very early premature atrial depolarizations, we consider the possibility that retrograde conduction of the early atrial premature depolarization (APD) in the sinoatrial junction was delayed for a sufficient length of time to allow the sinus node to depolarize spontaneously on schedule. Collision between the APD and sinus beat would then occur despite the marked prematurity of the APD. Thus, the early APD had encountered the relative refractory period of the sinoatrial junction, suggesting that decremental conduction takes place within the sinoatrial region in man. These findings imply that there is the potential for reentry in the region of the human sinoatrial junction.- - - - - - - - - - ranking = 3keywords = cycle (Clic here for more details about this article) |
10/11. Clinicopathologic assessment of arrhythmias in a case of scleroderma heart disease with sudden death.Electrophysiologic and histopathologic correlation has been carried out in a patient with scleroderma heart disease, affected by syncopal seizures, who died of recorded ventricular fibrillation. The electrophysiological investigation disclosed dysfunction of sinoatrial conduction, revealed by sinoatrial blocks and by an abnormal return cycle pattern after premature atrial beats. Atrial effective and functional refractory periods were increased and an unusual 'pseudo-Wenckebach' phenomenon between artificial stimulus and atrium was observed during atrial pacing. Intra-AV nodal conduction time was at normal upper limits and Wenckebach-type AV block was obtained on pacing the atrium at 100 beats/min. HV conduction was moderately prolonged in the presence of left anterior hemiblock. The histopathologic substrates of these electrophysiologic disturbances were fibrosis of the sinus node, disrupted internodal pathways and atrio-AV nodal connections, and left bundle branch atrophy. As far as fatal tachyarrhythmia is concerned, myofibrillar degeneration may have contributed to its pathogenesis. It is suggested that both lesions of the ordinary myocardium and specialized conduction system account for the electrical instability of sclerodermic patients.- - - - - - - - - - ranking = 1keywords = cycle (Clic here for more details about this article) |
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