Atrioventricular junctional parasystole with ventricular fusion beats due to complicating Wolff-Parkinson-White syndrome.

We present a case of atrioventricular (AV) junctional parasystole manifesting with ventricular fusion beats due to the presence of an accessory AV conduction pathway. Ventricular fusion beats are usually impossible in AV junctional parasystole. In the reported case the ventricular fusion occurs because the ectopic AV junctional impulse is conducted through the His bundle, whereas the sinus impulse is conducted to the ventricles through the Kent bundle.

Trifascicular block with asynchronous intraventricular recovery and "supernormal" AV conduction.

The authors present a case of trifascicular block: complete right bundle branch block, tachycardia-dependent left anterior hemiblock, and bradycardia-dependent left posterior hemiblock. There is, in addition, a complicating independent AV junctional rhythm that is in most instances not affected by the conducted sinus impulses. Occasionally, however, this focus is discharged by very early sinus impulses that are unexpectedly conducted to the ventricles (a manifestation of "supernormal" conduction). A complex electrocardiographic pattern results from the interplay of the aforementioned mechanisms.

Concealed ventricular hexageminy.

The authors report a case of concealed ventricular hexageminy in which, with a few exceptions, extrasystoles were separated by sinus beats conforming to the formula 6n - 1. Whenever an exception to this formula occurs, the intervening beats are not all of sinus origin, but include also a ventricular extrasystole that is different from those occurring in hexageminal distribution. The pattern is explained by a parasystolic rhythm modulated by sinus impulses, assuming a 3:1 ratio between the parasystolic cycle and the sinus cycle. Such a ratio would have to be associated with a trigeminal or concealed trigeminal distribution. There is, however, a 2:1 ectopic-ventricular block, leading to a change of the ectopic distributional pattern from the expected concealed trigeminy to that of the concealed hesageminy.

Mobitz type II delay.

Mobitz type II second-degree block manifests with several consecutive impulses conducted with a constant conduction time that are followed by block. This study reflects an entirely new concept of the Mobitz type II phenomenon, wherein consecutive impulses have constant conduction times, but instead of being followed by a block of conduction, are in fact followed by a conduction delay. The diagnosis of this manifestation at the atrioventricular (AV) junction is made by the appearance of an unexpected prolonged PR interval followed by a shorter PR interval. The recognition of this manifestation at the sinoatrial junction is suggested when, during regular sinus rhythm with manifest episodes of Mobitz type II sinoatrial block, the sinus rhythm is at times also complicated by a sudden unexpected prolongation of a P-P interval, which is followed by an shortened P-P interval. This new phenomenon is termed by Mobitz type II delay.

Concealed ventricular bigeminy with exceptions due to time-dependent modulation of an ectopic rhythm.

This presentation reflects a case of atypical concealed bigeminy, where some interectopic intervals contain even numbers of sinus beats. Exceptions to the rule of concealed bigeminy only occur during slowing of the sinus node. The pattern is explained on the basis of modulated parasystole, by drawing a phase-response curve which explains all the interectopic intervals on the basis of the modulating effect exerted by the sinus impulses upon a parasystolic focus.

"Irregular" ventricular parasystole: the influence of sinus rhythm on a parasystolic focus.

Fifteen cases of ventricular parasystole were analyzed to determine whether the interectopic intervals were regular, as expressed by long intervals being exact multiples of the short ones, or not. The regularity of the interectopic intervals was assessed by means of the variation index: the ratio of the maximal difference between various measurements of the parasystolic cycle length and the mean parasystolic cycle length. Three out of 15 cases had a variation index less than 5, and were classified as "regular parasystole." Twelve cases were associated with a variation index greater than 7.5, and were classified as "irregular parasystole." The cases of irregular parasystole were then analyzed to determine whether the variability of the interectopic intervals was casual or dependent on action of the sinus beats. A parasystolic resetting by critically timed sinus impulses (a form of intermittent parasystole) was evident in three cases. The irregularity in the remaining nine cases was due to modulation (viz., due to electrotonic influence exerted by the sinus beats on the parasystolic focus). In every case of modulated parasystole a phase-response curve was constructed, which enabled an analysis of all the interectopic intervals on the basis of a time-dependent effect exerted by the sinus impulses on an otherwise rhythmic parasystolic focus.

Bigeminal and trigeminal distribution of ventricular extrasystoles as an expression of "atypical" concealed bigeminy.

This report reflects a case of bigeminal and trigeminal ventricular extrasystoles where bigeminal extrasystoles are associated with short coupling intervals, while trigeminal extrasystoles manifest long coupling intervals. The arrhythmia is interpreted as an "atypical" form of concealed bigeminy.

Torsade de pointes due to coxsackie B3 myocarditis.

Viral myocarditis may present with a variety of electrocardiologic aberrations. Torsade de pointes, a potentially malignant ventricular arrhythmia associated with prolongation of the QT interval has not been described in patients with acute viral myocarditis. This report details this finding in a patient with coxsackie B3 myocarditis in whom symptomatic torsade de pointes was documented.

The localization of bypass tracts in the Wolff-Parkinson-White syndrome from the surface electrocardiogram.

The bypass tracts of the WFW syndrome may be situated anywhere along the AV ring. Accurate localization of such tracts has in the past been largely effected by electrophysiologic studies, particularly epicardial mapping. During recent years, however, criteria for localization of the bypass tracts from the conventional 12-lead ECG have become increasingly apparent. The preceding presentation constitutes a review and state of the art governing these rapidly developing diagnostic principles.