Mauricio B. Rosenbaum

Control of Tachyarrhythmias Associated with Wolff-Parkinson-White Syndrome by Amiodarone Hydrochloride

Abstract Amiodarone hydrochloride proved to be highly effective in preventing and treating arrhythmias of the Wolff-Parkinson-White (WPW) syndrome in 11 patients with WPW conduction and recurrent tachyarrhythmias. Paroxysmal supraventricular tachycardia (six patients), atrial fibrillation (four patients) and atrial flutter (one patient) were the most significant arrhythmias. In most patients the arrhythmia was seriously disabling because of the extremely rapid ventricular rate, adverse hemodynamic consequences and frequent recurrence and long duration of the episodes. Other known antiarrhythmic agents were ineffective. In all 11 patients amiodarone, in doses of 300 to 600 mg daily, totally, easily and safety controlled the arrhythmias for periods of 2 to 8 months. The drug was fully effective after an average of 7 days of treatment. Tolerance to amiodarone was excellent. The occurrence of corneal microdeposits of the drug was the only Important undesirable effect, but subjective ocular disturbances were not noted. The microdeposits are reversible, and can be avoided by discontinuing the drug for 7 days every 1 to 2 months. Amiodarone apparently causes a significant prolongation of refractoriness in the normal (A-V node and His-Purkinje system) as well as in the anomalous pathway, thus creating favorable conditions for prevention and Interruption of any reentry mechanism requiring participation of both pathways.

Intraventricular trifascicular blocks. Review of the literature and classification

Abstract The right bundle branch and the two divisions—anterior and posterior—of the left constitute the three main terminal fascicles of the intraventricular conduction system. Depending on whether conduction is permanently or only intermittently interrupted in these three fascicles, eight different possibilities or combinations of intraventricular and atrioventricular conduction disturbances may occur. A theoretical design covering all those possibilities is suggested, and clinical examples are bestowed for each of them. The existence of these syndromes, which we have termed altogether “trifascicular blocks”, provides one of the most valuable evidences of the anatomical and functional “trilaterality” of the human intraventricular conduction system.

Intraventricular trifascicular blocks. The syndrome of right bundle branch block with intermittent left anterior and posterior hemiblock

Abstract When conduction is interrupted in the right bundle branch and only intermittently in the two divisions, anterior and posterior, of the left, a very peculiar and as yet undescribed electrocardiographic syndrome occurs. Its main feature is the presence of two different right bundle branch block patterns, with completely opposite directions of the ÂQRS (superiorly and to the left in one; inferiorly and to the right, in the other); together with severe A-V conduction disturbances. Four cases of this singular syndrome are here described and analyzed. Such cases can be considered exceptional experiments of nature, providing most invaluable evidence for the existence of block within the anterior and posterior divisions of the left bundle branch. However, the syndrome of “right bundle branch block with intermittent left anterior and posterior hemiblock” is only one of the several possibilities of what we have named “intraventricular trifascicular blocks,” which will be considered in the second part of this paper.

Five cases of intermittent left anterior hemiblock

Abstract The first 5 cases of intermittent left anterior hemiblock (block in the anterior division of the left bundle branch) are reported. These cases can be considered exceptional experiments of nature, providing both invaluable evidence for the existence of left anterior hemiblock and useful material for studying, with great accuracy, the changes that this conduction disturbance produces on the previously normal or abnormal electrocardiogram in man. The three major electrocardiographic features of left anterior hemiblock are found to be: (1) An ÂQRS directed at approximately −60 °; (2) the presence of a Q 1 S 3 pattern, simulating a counterclockwise rotation of the heart; and (3) a QRS widening of not greater than 0.02 sec.

Wenckebach Periods in the Bundle Branches

Two cases of intermittent bundle-branch block in which Wenckebach periods could be directly visualized are reported. The conduction ratios were either 3:2 or 4:3, as are commonly seen in cases of the Wenckebach phenomenon of atrioventricular (A-V) conduction. Other groups of beats apparently showing 3:1 and 4:1 bundle-branch block were interpreted as indicating incompletely concealed Wenckebach periods in the bundle branches, with actual conduction ratios of 3:2 and 4:3, respectively.Three prerequisites are necessary for the occurrence of either direct or incompletely concealed Wenckebach periods in the bundle branches: (1) The opening beat should be normally conducted (in the affected bundle branch); (2) the second beat should be conducted with a delay of no more than 0.04 to 0.06 sec; (3) the damaged bundle branch should not be activated retrogradely in the closure beat.Wenckebach periods in the bundle branches may be completely concealed if the conduction delay lasts more than 0.04 to 0.06 sec in the opening beat. In cases of bilateral bundle-branch block, Wenckebach periods in the bundle branches may be indirectly visualized through changes in the A-V conduction.

Modulation of parasystolic activity by nonparasystolic beats.

We studied 12 patients with ventricular parasystole in whom pacemaker activity could be modulated by nonparasystolic beats (NPBs). In six patients (group 1) in whom the intrinsic parasystolic cycle length (XX interval) was obtained without interposed NPBs, we found that NPBs falling during the first half of the cycle prolonged the XRX interval (containing one NPB) and that NPBs falling during the second half of the cycle abbreviated the XRX interval; both effects were maximal when NPBs fell close to the middle of the cycle and were separated by a reversal point. However, because of mutual interference between parasystolic beats and NPBs, only 13.2–43.4% of the parasystolic cycle could be effectively scanned. We also found that the XRX and RX intervals were linearly related. This relationship served to establish that in six patients in whom the XX interval was not obtained (group 2), modulation showed a similar behavior, although neither the reversal point nor the sense of the modulation could be determined. In this report, we suggest diagnostic criteria of parasystolic modulation.

The mechanism of bidirectional tachycardia.

T he human intraventricular conduction system has always been considered bifascicular. However, this system also is and operates as trifascicular, its three main terminal fascicles being the right bundle branch and the two divisions, anterior and posterior, of the left bundle branch. Evidence for the trifascicularily of the conduction system has appeared extensively in the literature34-3g and this fact has shed new light on many aspects of everyday electrocardiography. This is especially true for the left anterior (LAH) and left posterior (LPH) hemiblocks (blocks in the anterior and posterior divisions, respectively, of the left bundle branch), either alone or combined with right bundle branch block (RBBB). Furthermore, the trifascicularity of the conduction system has also led to the discovery of: (1) the existence of a new family of electrocardiographic syndromes, the “intraventricular trifascicular blocks”34~35,38,3g; (2) the existence of a new type of “divisional” left bundle branch block (LBBB)34*3e; (3) the different manifestations of aberrant ventricular conduction of supraventricular premature beats.34-36 (4) In addition, it has rendered possible a new approach to the old problem of the determination of the place of origin of ventricular extrasystoles, and in this field, it permitted to predict and then substantiate that left ventricular extrasystoles must necessarily furnish two main, very definite and diametrically opponent AQRS directions.34l37 In this paper we shall try to show how the trifascicularity of the intraventricular conduction system also enables us to explain a curious cardiac arrhythmia, the so-called “bidirectional tachycardia” (BT), which has so far resisted every attempt at accurate interpretation. As we shall see, BT is nothing but a syndrome of paroxysmal trifascicular block, occurring during some episodes of supraventricular tachycardia.

Wenckebach Periods of Alternate Beats Clinical and Experimental Observations

Wenckebach periods of alternate beats (AW) can be described as a 2:1 atrioventricular (A-V) block in which the conducted P waves show progressive prolongation of the P-R interval of the Wenckebach type. However, while classical Wenckebach periods terminate with a single blocked P wave, AW necessarily ends with (or begins from) two consecutive blocked P waves. Five clinical cases and several experimental examples of AW are reported. Recovery curves of A-V conduction were constructed, and it was demonstrated that AW is related to a marked prolongation of both the absolute and relative refractory periods. All the cases were associated with intraventricular block. In addition, recording of His bundle potentials in one case, histological study of the conduction system in another, and the experimental observations, support the view that AW tends to occur below the A-V node, in one of the main ventricular conducting fascicles. Four of the five patients developed complete heart block and Adams-Stokes seizures.

Unmasking of ventricular preexcitation by vagal stimulation or isoproterenol administration.

Twenty-one patients were studied in whom ventricular preexcitation (VP) had been recorded in the past and had later disappeared, indicating antegrade block in the accessory pathway (AP), either spontaneously (10 patients) or under the effect of chronic treatment with amiodarone (11 patients). VP reappeared in nine cases during vagal stimulation, and in five cases during an i.v. isoproterenol infusion. Retrograde conduction over the AP was studied in four of the remaining seven patients and was found to be present in three and absent in one. Although these patients differ from the ordinary patient with concealed AP in that antegrade preexcitation had been demonstrated in the past, this study suggests that concealed VP may result from the following mechanisms: 1) an extremely prolonged refractory period in the AP, causing a ratedependent VP that can be identified during vagal stimulation; 2) a rate-independent depression of antegrade conduction that can be reversed by isoproterenol; 3) a depression of conduction that is apparently no longer reversible. Only in the latter case is a study of retrograde conduction needed to identify the concealed VP. These three mechanisms are likely to be a natural sequence of events leading to complete antegrade block in the AP.

Right Bundle Branch Block with Left Anterior Hemiblock Surgically Induced in Tetralogy of Fallot Relation to the Mechanism of Electrocardiographic Changes in Endocardial Cushion Defects

Abstract Four cases of tetralogy of Fallot in which right bundle branch block with left anterior hemiblock occurred after surgical repair are reported. In 2 cases right bundle branch block and left anterior hemiblock were present in the first postoperative tracings. In another case complete heart block was followed by “pure” right bundle branch block, and left anterior hemiblock occurred a few days later. In another case left anterior hemiblock was only transient, but right bundle branch block remained. The electrocardiographic changes were similar to those described in right bundle branch block with left anterior hemiblock occurring spontaneously in acquired heart disease. The cases presented also support the assumption that the electrocardiographic changes commonly observed in patients with endocardial cushion defects are due to the occurrence of right bundle branch block with left anterior hemiblock.