Cases reported "Sick Sinus Syndrome"

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11/20. Chronic ventricular pacing with ventriculo-atrial conduction versus atrial pacing in three patients with symptomatic sinus bradycardia.

    Three patients with symptomatic sinus bradycardia due to sick sinus syndrome were treated with permanent ventricular pacing for periods ranging from 2.5 to 4 years. All three patients had ventriculo-atrial conduction on routine electrocardiography. Although ventricular pacing was effective, they complained of fatigue, lightheadedness, and near syncope. Hemodynamic studies revealed the presence of regular cannon waves in the right atrium as well as in the pulmonary artery wedge pressure curves. Temporary atrial pacing resulted in disappearance of the cannon waves and a significant rise in cardiac output (32-48%). After normal atrio-ventricular conduction was confirmed by rapid atrial stimulation and His bundle electrocardiography, the pacing mode was changed to permanent atrial pacing on demand. The effort tolerance of the patients markedly improved, and the previously mentioned symptoms disappeared. Control hemodynamic studies 9 to 12 months after implantation of the atrial demand pacemaker showed that the improvement in cardiac performance was maintained.
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12/20. Induced concealed dissimilar atrial rhythms.

    Electrophysiologic studies, including intra-atrial recordings and atrial stimulation, were performed in two patients with suspected sick sinus syndrome. Premature atrial stimuli induced atrial flutter in both patients. The arrhythmia was concealed, i.e., it was recordable only by intracavitary electrogram and invisible on surface electrocardiogram. In one case, simultaneous atrial fibrillation could be recorded in a segment of the right atrium. In this patient, the rhythm on the surface electrocardiogram changed during the study to "upper nodal" rhythm, though the atrial electrogram showed continuation of A waves at the same rate as before during sinus rhythm. It seems that atrial changes, which are frequently encountered in sick sinus syndrome, are a predisposing factor for spontaneous or inducible concealed atrial arrhythmias.
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13/20. Two mechanisms of arrhythmia induction by a DDD pacemaker: a case report.

    A 68-year-old man with sick sinus syndrome and a history of intermittent atrial fibrillation was treated by implantation of a DDD pacemaker. He subsequently developed recurrent episodes of shortness of breath and tachycardia. Investigation revealed two different arrhythmias, both induced by the pacemaker: (1) a tachycardia in which the dual-chamber pacemaker system provided the antegrade limb and the AV node provided the retrograde limb and (2) a triggered, ventricularly paced tachycardia caused by the pacemaker sensing atrial fibrillation waves. Both rhythms were abolished by reprogramming to the DVI mode.
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14/20. Prolonged atrial conduction.

    We describe a patient, in whom electrophysiologic study revealed a "negative" P-A interval in the His bundle electrogram, a prolonged intraatrial conduction time and a prolonged spike to the P wave interval during atrial pacing. The abnormalities were due to extensive sinuatrial disease.
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15/20. 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.
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16/20. case reports of phase 4 paroxysmal atrioventricular block.

    Four cases of PAVB were reported, 3 of which manifested third-degree AV block, while one exhibited first-degree AV block, while one exhibited first-degree AV block. The location and mechanism of establishment and disappearance of PAVB was discussed. It was speculated that, in some cases, concealed conduction of P waves could promote depolarization of the injured area which displayed Phase 4 block and thus temporarily restore 1.1 AV conduction.
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17/20. Apparent extension of the atrioventricular interval due to sensor-based algorithm against supraventricular tachyarrhythmias.

    Rapid ventricular tracking response to supraventricular tachyarrhythmia is one major limitation to DDD pacing. In a DDDR pacemaker, sensor-based algorithms have been used to control these arrhythmias. These include the use of an interim rate limit (conditional ventricular tracking limit) or a separate maximum tracking and sensor rate limits (discrepant upper rate). These algorithms limit inappropriate ventricular pacing rate during tracking of pathological supraventricular tachyarrhythmia and atrial flutter by Wenckebach-like prolongation of the AV interval. We observed that this may cause an unexpected extension of the AV interval in patients with high atrial rate and intact AV nodal conduction. This was due to P wave rate above the conditional ventricular tracking limit or maximum tracking limit, but AV paced interval prolongation was avoided by the occurrence of intrinsic conduction, albeit at an AV interval longer than the programmed AV interval. This might appear as failure of ventricular pacing on the ECG. This phenomenon is a modified form of "upper rate" behavior occurring in the AV interval, and should be recognized as a normal behavior rather than pacemaker malfunction.
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18/20. Cardiac amyloidosis presenting as sick sinus syndrome and intractable heart failure: report of a case.

    Cardiac amyloidosis, an uncommon disease, has been reported to manifest as congestive heart failure (CHF) and/or various arrhythmias. Herein, we report a case of CHF and sick sinus syndrome. The patient, a 66-year-old man, was admitted to the National taiwan University Hospital because of dizzy spells and recurrent syncope. Electrocardiogram showed a sinoatrial block, first degree atrioventricular block, right bundle branch block and low-voltage Q wave, R wave and S wave (QRS) complex. Prolonged corrected sinus node recovery time was documented by an atrial pacing study. A permanent pacemaker was implanted for the patient's bradyarrhythmia, but he developed progressive heart failure. echocardiography revealed a normal-sized ventricular chamber, concentric left ventricular hypertrophy with a "granular sparkling" appearance of the myocardium, and impaired diastolic and systolic function of the left ventricle. Despite aggressive treatment, the patient expired due to intractable heart failure. Postmortem needle aspiration revealed amyloidosis involving the heart, lung and skin. We conclude that cardiac amyloidosis should be considered in elderly patients with conduction disturbance and unexplained congestive heart failure.
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19/20. Areas of slow conduction in atrial re-entrant tachycardia: a case report and review of the literature.

    An electrophysiologic study of atrial tachycardia is presented. During tachycardia, transient entrainment and sinus rhythm, two patterns of persistent double potentials in the high right atrium and fragmented activity in the low atrial septum were observed. No activity was recorded from multiple areas of the right atrium with endocardial mapping during sinus rhythm. The observations suggest that persistent fragmented activity represents slow conduction within the circuit which could be orthodromically entrained. Persistent double potentials probably represent slow conduction orthodromically and/or antidromically activated outside the circuit. However, a wave front from pacing impulses travelling through this area could entrain the circuit.
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20/20. Internal cardioversion in two patients with atrial fibrillation refractory to external cardioversion.

    A 26-year-old man underwent an electrophysiological study for evaluation of a history of congenital heart disease, presyncope, and wide complex tachycardia. During the study the patient developed sustained atrial fibrillation with a rapid ventricular response. A 17-year-old man with a history of sick sinus syndrome developed sustained atrial fibrillation. Both patients failed four attempts at external cardioversion with a maximum delivered energy of 360 J. Low energy cardioversion was successful in both patients using biphasic waveforms and internal transvenous defibrillation electrodes. Internal cardioversion using a transvenous electrode system can be successful in patients with atrial fibrillation refractory to external cardioversion.
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