Giuseppe Oreto, MD(*1) Antonino Don...

Giuseppe Oreto, MD(*1) Antonino Donato, MD;(*2) David Blumsohn MB F.C.C.P.;([unkeyable]) Keith Segal, M.B.;([unkeyable]) Neil Maresky, M.B.;([unkeyable]) Leo Schamroth, M.D.([unkeyable])

We ready a case of atrioventricular (AV) junctional parasystole manifesting with ventricular fusion beats suitable 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 come to one's minds because the ectopic AV junctional impulse is guarded through the His bundle, whereas the sinus impulse is carriageed to the ventricles through the Kent bundle

An AV junctional parasystole is the expression of a fostered and thus independent, pacemaker that is situated within the AV junction. The arrhythmia is usually diagnosed in the nearness of: (a) premature ventricular complexe of AV junctional origin, which manifest with variable coupling intervals; (b) mathematically related interectopic intervals; and (c) absence of ventricular fusion beats.[1] This report deals with a case of AV junctional parasystole where ventricular fusion beats do flash on the mind This is due to the concomitant personality of an accessory AV conduction pathway.

The ECG (Fig 1 prefered strips of standard leads 1 2 and 3) was recorded from a 40-year-old man affected by way of mild hypertension. The following is evident: (1) The basic number is sinus bradycardia, at a rate ranging from 42 to 54 (2) The P-R interval of waysed sinus beats is 0.11 s A marked initial slurring of the R wave, a delta wave, is also evident in lead 2 The QR duration of sinus beats is 011 s (3) There are several QR complexe of ectopic origin. They differ in configuration from the basic sinus complexe The ectopic beats deliberate the following features that are absent in the sinus beats: (a) small q waves in leads 2 and 3; (b) small s waves in lead 1. The frontal plane QR axis of ectopic complexe is +60 [degrees] This is true different from the QRS axis of administrationed sinus complexes, which is about 0 [degree] Furthermore, no delta wave is evident in the ectopic complexe the duration of which is 009 s (4) The ectopic beats are at times dissociated from the near-synchronous sinus P waves (for example, the next to the first QRS complex in the top strip), whereas in other instances a retrograde P' wave chases the premature beats, being partially hidden in the QR complicated (for example, the penultimate beat in the next to the first strip). (5) Several fusion beats, labeled F are also evident in lead 3 They muse an intermediate configuration between the "pure" ectopic complexe and the sinus complexe (6) The coupling intervals of the ectopic beats are variable, and range from 103 to 142 s The interectopic intervals are mathematically related: the short intervals range from 240 to 245 s while the long intervals are multiples of 237 to 250 s

DISCUSSION

A form of AV junctional parasystole, associated with the Wolff-Parkinson-White (WPW) syndrome is evident from this tracing. The AV junctional origin of the ectopic rhyme results from the narrow configuration and normal duration of the ectopic complexe It is evident that the impulse delivered from the AV junctional focus has no access to the Kent pack being conducted to the ventricles by means of the normal AV pathway barely This accounts for the difference between the sinus and the ectopic QR complexes: the sinus beats resulting, in fact, from a fusion between the impulse simultaneously managemented by the Kent bundle and the normal AV pathway.

The parasystolic mechanism is evident, since the coupling intervals of ectopic beats are variable, and the interectopic intervals are mathematically related. The rather out of the way finding in this tracing is the nearness of ventricular fusion beats, which ensue from simultaneous ventricular activation by the agency of both the sinus and the parasystolic impulse. Ventricular fusion beats are impossible in uncomplicated AV junctional parasystole, since the conduction to the ventricles of the two sinus and parasystolic impulses hangs on a single pathway.[1] Therefore, whenever this pathway (the AV node and the His bundle) is jot downed and depolarized by one (sinus or ectopic) impulse, a near-synchronous impulse delivered by means of the other pacemaker cannot be careered Furthermore, if the couple impulses would succeed in entering the AV node simultaneously, they would necessarily immerge within the conduction pathway, in such a manner that the final result would be a normal QR composite and never a fusion beat.

It is worth noting, however, that atrial fusion beats are still possible in AV junctional parasystole. In the at hand case, ventricular fusion beats arise whenever a sinus P wave immediately take the lead ofs a parastystolic complex. The sinus impulse, however, is managemented to the ventricles by the Kent packet only (Fig 2).

(*) Istituto di Clinica Medica e Terapia Medica, Cattedra di Malattie Cardiovascolari, Universita di Messina, Messina, Italy.