József Tenczer

Rate-dependent patterns of modulated ventricular parasystole

The effects of ventricular pacing on the arrangement of ventricular parasystolic beats were studied in 14 patients. By analyzing the effects of various pacing rates and modalities, it was found that both rate and pattern of manifest parasystolic beats were intimately related to the rate and coupling interval of the paced rhythm. Our findings indicate that fixed coupling of ectopic beats is not incompatible with parasystole; modulated parasystole may manifest as fixed rate classic parasystole; a parasystolic pacemaker can be entrained by a wide range of driving rates both above and below the intrinsic rate of the parasystole; and with different driving rates, these rate-dependent patterns can be observed in the same patient. Our observations suggest that spontaneous or drug-induced changes in the heart rate can lead to major alterations in the frequency and patterns of ventricular parasystole.

Early proarrhythmia during intravenous amiodarone treatment

We present a case of early (within the first 24 hours) development of malignant torsades de pointes (TdP) associated with intravenous amiodarone tberapy. After correction of predisposing factors (heart failure, hypokalemia, digoxin) amiodarone again resulted in torsades. This observation suggests that in patients who have experienced amiodarone‐induced proarrhythmia, amiodarone administration under different, more stable clinical conditions may still be hazardous.

A study of modulated ventricular parasystole by programmed stimulation

To analyze the phase-dependent sensitivity of the parasystolic pacemaker to nonparasystolic beats, 11 patients with modulated ventricular parasystole were studied using the ventricular extrastimulus method. The intrinsic parasystolic cycle lengths ranged from 1,100 to 1,800 ms. Premature stimuli altered the duration of the parasystolic cycle lengths by amounts that depended on timing of the test impulses within the parasystolic cycles. Premature impulses delivered during the first part of the parasystolic cycles prolonged the parasystolic cycle lengths to 107 to 151% of the intrinsic parasystolic cycle lengths and impulses applied during the second part abbreviated them to 70 to 81% of the intrinsic parasystolic cycle lengths. In 10 patients the accelerating effects were of greater magnitude than the decelerating effects. Transition from the accelerating to slowing phases was progressive or unstable in 9 patients and abrupt in 2. Changes induced by individual stimuli were short-lived and the parasystolic pacemakers returned immediately to their original rates. In 1 patient the biphasic sensitivity of parasystole to premature stimuli was shown to sustain for 21 days.

Atrial reentry in chronic repetitive supraventricular tachycardia

Atrial reentrance as a mechanism of the tachycardia was demonstrated in a 28-year-old patient suffering from chronic repetitive supraventricular tachycardia. Criteria for diagnosis included the following: (1) Repetitive supraventricular tachycardia was induced and terminated by properly timed atrial extrastimuli. (2) Return cycles of all atrial extrastimuli not abolishing the tachycardia were fully compensatory. (3) A-H prolongation was not a prerequisite to induce the tachycardia. (4) The contours of P and A waves during tachycardia differed from those in sinus rhythm, but atrial activation remained antegrade. (5) A concealed anomalous pathway could not be proved.

Electrophysiologic Study of Tachycardia-Dependent Paroxysmal His Bundle Block in Man

Electrophysiologic sludy was performed in a potienl with tachycardia‐dependent paroxysmal atrioventricular block. The site of block was within the His bundle. The effective refractory period of the His bundle was markedly prolonged and it was comparable to the critical atrial cycle length producing type II His bundle block. The most likely mechanism of paroxysmal atrioventricular block was repetitive concealed penetration of the blocking zone by nonconducted impulses that reached the proximal His bundle. Enhancing the blocking ratio at the atrioventricular nodal level resulted in improvement of overall atrioventricular conduction.

Unusual effect of adenosine

We report the occurence of bundle branch block following the termination of supraventricular tachycardia by adenosine.

Alternation of Right Bundle Branch Block with Beats Showing Normal Conduction and with a Less Complete Right Bundle Branch Block Pattern

We report the case of an 80‐year‐old man with a preexistent right bundle branch block (RBBB) who underwent dobutamine stress echocardiography. As the sinus cycle length gradually decreased during the stress test, he first developed a 2:1 RBBB pattern alternating with beats showing normal conduction and then an alternating 2:1 less complete and more complete RBBB pattern. An elucidation of the potential mechanism of the latter very rare phenomenon is provided.

More about adenosine and arrhythmias

We read with great interest the review by Mubagwa and w x co-workers 1 on the effects of adenosine on the cardiovascular system. In this review the diagnostic effects of adenosine in arrhythmias were discussed. We would like to present some additional, clinically important effects and adverse effects of adenosine, focusing on arrhythmias. 1. Adenosine can not only unmask pre-excitation but in some cases can abolish pre-excitation due to the direct inhibitory effect on decremental pathway conduction conw x taining AV node-like structure 2 . 2. The therapeutic and diagnostic role of adenosine in wide-complex tachycardia was described in the review, but it may also be added that it could cause life-threatening conditions by precipitating atrial fibrillation in the Wolffw x Parkinson-White syndrome 3 . 3. Adenosine is a very useful drug in distinguishing between ventricular and supraventricular tachycardias and among the different forms of supraventricular tachycardias. In addition, adenosine may provoke potentially dangerous arrhythmias by accelerating the heart rate due to enhanced w x Ž . sympathetic tone in atrial flutter 4 Fig. 1 . 4. Another possibly important clinical value of adenosine is help in distinguishing between ventricular extrasystole and parasystole by causing temporary SA or AV w x Ž . block, or by terminating parasystolic activity 5 Fig. 2 .

Escape-capture bigeminy in rate dependent (phase 3) block of atrioventricular conduction.

Escape-capture bigeminy is a bigeminal rhythm in which each escape beat is followed by a conducted beat. Bradley and Marriott (1958) were the first to describe this interesting electrocardiographic pattern in a case of sinoatrial block. Schamroth and Dubb (1965) reported cases of escape-capture bigeminy resulting from sinoatrial block, atrioventricular block, and a second degree Wenckebach type atrioventricular block ending in an atrial echo beat. A fourth mechanism was published by Dubb and Schamroth (1975) in which escapecapture bigeminy was caused by blocked atrial extrasystoles. We present a case of escape-capture bigeminy caused by a specific, hitherto unpublished mechanism.

New interactive arrhythmia processing system

Software designed to meet the varied and changing medical requirements of real-time arrhythmia analysis, data storage, and scientific reanalysis was developed. The incorporated define function allows the specification of various rhythm patterns and relationships (e.g. ventricular parasystole), which can be analyzed by the system. The results suggest that the program is capable of detecting complex clinical arrhythmias.<<ETX>>