Cases reported "Parasystole"

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1/3. 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.
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2/3. 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.
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3/3. Mechanism of atrial escape-capture bigeminy: second-degree sinoatrial exit and entrance block.

    Two women with atrial escape-capture bigeminy were reported in whom sinus P waves and escape P waves alternated with each other. Their electrocardiographic findings showed that, during the bigeminal rhythm, 2:1 exit block of sinus impulses associated with entrance block of escape impulses occurred in the sinoatrial junction. Three phenomena are suggested to explain the observations. (1) Seeming bradycardia-dependent sinoatrial exit block may have occurred, probably as a result of phasic changes in vagal tone due to respiration, with decreased vagal tone depressing conductivity in the sinoatrial junction to a greater degree than automaticity in the sinus node. (2) In case 1, type II second-degree entrance block in the sinoatrial junction may have occurred, reflecting the presence of sinus parasystole with incomplete entrance block. (3) Sinus escape also may have occurred, especially in case 2. These phenomena have never been reported before.
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