Antonino Donato

Supernormal Conduction in the Left Bundle Branch Unmasked by the Linking Phenomenon

This presentation reflects a case of phase‐3 left bundle branch block (LBBB). Analysis reveals that relatively early QRS complexes are wide, whereas beats occurring later than a critical time are narrow. There are, however, two unexpected phenomena: (1) an overlap occurs between the range of R‐R intervals resulting in normal intraventricular conduction and the range of R‐R intervals resulting in LBBB pattern. Complexes that follow a wide beat are often wide although they are associated with relatively long R‐R intervals, whereas complexes that follow a normal beat tend to be normal even after relatively short R‐R cycles. This is due to concealed retrograde penetration of the bundle branch that is blocked in anterograde direction (the so‐called linking phenomenon). (2) Some early supraventricular impulses, paradoxically, resulted in normal intraventricular conduction. The phenomenon is a manifestation of supernormal LBB conduction, and only occurs following a wide QRS complex associated with retrograde activation of the LBB. The linking phenomenon reveals or unmasks the supernormal phase of LBB conduction. Following a retrograde and delayed activation of the LBB, the refractory period of the bundle branch is postponed, in such a way that a supraventricular impulse is allowed to occur during the early phase of supernormal conduction.

Longitudinal Dissociation within the Reentry Pathway of Ventricular Tachycardia

SATULLO, G., ET AL.: Longitudinal Dissociation within the Reentry Pathway of Ventricular Tachycardia. Two cases of nonsustained, repetitive ventricular tachycardia are analyzed. In both, the episodes of tachycardia do not contain random numbers of beats, but the complexes in each phase of tachycardia are either always in even numbers (case 1) or always in odd numbers (case 2). This indicates longitudinal dissociation within the reentry circuit: i.e., there are two functionally separate pathways in some part of the reentry circuit, and the reciprocating impulse runs alternatively through the two pathways. Tachycardia ends due to block of the impulse always in the same pathway, thus, the number of beats in each episode of tachycardia is always either in odd or even numbers. (PACE, Vol. 13, December, Part 1 1990)

Irregular Sinus Parasystole Due to Intermittency and Modulation of Parasystolic Activity

Intermittent Sinus Parasystole. A case of intermittent sinus parasystole in which the parasystolic focus is protected from the dominant sinus rhythm only during the second half of its intrinsic cycle is reported. In addition, a modulating (i.e., electrotonic) effect is often clearly exerted from the dominant rhythm upon the focus during the protected period. Coexistence of both modulation and intermittency in sinus parasystole, as well as a modulating effect limited to the second part of the parasystolic cycle, have not been previously reported.

4:2 Atrioventricular Block:

The ECG (Fig. 1, continuous tracings) recorded from a 73-year-old male patient with hyperkalemia (K+ 7.3 mEq/L) shows sinus rhythm at a rate of about 95 beats/min complicated by second-degree AV block with constant 4:2 conduction ratio. A difference between the first and the second QT interval is evident for each 4:2 succession: the second QT interval (i.e., the one following the second conducted QRS complex), is slightly—but constantly—shorter than the first one, so that the second—still conducted— P wave of each sequence can be seen on the T wave of the preceding ventricular complex, while the third P wave— nonconducted—is clearly separated from the previous T wave.

Modulated Parasystole Complicating Permanent Ventricular Pacing: The Different Influence of Spontaneous and Paced Impulses Upon the Parasystolic Rhythm

ORETO, G., et al.: Modulated Parasystole Complicating Permanent Ventricular Pacing: The Different Influence of Spontaneous and Paced Impulses Upon the Parasystolic Rhythm A case of modulated ventricular parasystole observed in a patient with a VVIM pacemaker is reported. Analysis reveals that the electrotonic influence (modulation) effected upon the parasysiolic focus hy the sinus impulses is different from that exerted by the paced impulses. Furthermore, fusion beats reflect an intermediate modulating effect according to the prevalence of the sinus or the paced wavefront.

Wide QRS Complex Tachycardia in the Emergency Setting

A wide QRS complex tachycardia can be (1) ventricular tachycardia (VT); (2) supraventricular tachycardia (SVT) with bundle branch block that may be either preexisting or due to aberrant conduction, namely, tachycardia-dependent abnormal intraventricular conduction; a further possibility is the effect of some antiarrhythmic drugs that slow down intraventricular conduction, resulting in marked QRS complex widening; and (3) supraventricular tachycardia with conduction of impulses to the ventricles over an accessory pathway (preexcited tachycardia).