Paradoxical behavior of PR interval dynamics during exercise and recovery and its relationship to cardiac memory at the atrioventricular node.

This preliminary study deals with the dynamics of the PR interval during exercise testing by using a Bruce protocol in 31 nonmedicated, normal patients with ages of 33 +/- 14 years. The behavior of the PR interval permitted its categorization into 2 groups. In Group I (27 of 31, 87.1% of patients) the PR interval showed the expected biphasic behavior with a gradual shortening with increasing exercise and a gradual lengthening during recovery. In contrast, the PR interval in Group II (4 of 31, 12.9% of patients) showed a triphasic behavior since, toward the end of recovery, there was a second decrease in duration. Because of this temporal relation to the phases of exercise, this paradoxical response, in analogy to what happened to the QT interval during exercise, could have been caused by a form of short-term memory or to varying, but normal, intergroup differences in autonomic function. However, further studies involving a greater number of patients are required to reach definite conclusions.

Identificaçäo da via lenta na reentrada nodal atrioventricular usando o intervalo atrioventricular mais curto / Slow pathway identification in AV nodal reentry using shortest atrioventricular interval

Em 10 pacientes consecutivos, realizou-se o mapeamento da parede septal do átrio direito durante taquicardia supraventricular por reentrada nodal AV, para comprovar a hipótese de que o intervalo AV mais curto identificava a área de conduçäo da via lenta. O septo atrial foi dividido em quatro zonas distintas. Em sete dos pacientes o intervalo AV anterógrado mais curto foi encontrado na zona 3; em dois, na zona 4; no último, na zona 2. A modificaçäo por radiofreqüência da via lenta foi obtida com sucesso, em todos os pacientes, na área de conduçäo AV mais curta. O intervalo AV durante ritmo sinusal permaneceu inalterado antes e após a ablaçäo. Após um seguimento de 21ñ4 meses, nenhum deles teve recorrência dos sintomas.

[Effects of intra-arterial Wenckebach's periods on the nodal and intranodal A-V 2:1 and 4:1 (their significance in the electrogenesis of the so-called alternating Wenckebach's periods)]. / Efectos de los períodos de Wenckebach intraauricular sobre el bloqueo A-V 2:1 y 4:1 nodal e infranodal. [Su importancia en la electrogénesis de los llamados períodos de Wenckebach alternantes.]

Intra-atrial Wenckebach patterns coexisting with distal, A-V nodal, and His-Purkinje blocks occurred in eight patients during high atrial stimulation at rapid rates. In two patients with 2:1 St-H block and in two patients with 4:1 St-V block, an increase in the degree of block occurred when the proximal intraatrial Wenckebach cycle was completed with the stimulus which otherwise would have been propagated to the distal levels. However, the degree of block did not increase when the intraatrial Wenckebach terminated in distally blocked stimuli. In one patient progression of 4:1 into 5:1 St-V block was due to the association of intraatrial Wenckebach with alternating 2:1 block at the A-V nodal, and His-Purkinje levels. Contrasting with most reports dealing with the mechanisms of alternating Wenckebach in a single structure, this study permitted the determination of the boundaries between proximal and more distal levels. The electrophysiology of documented two or three level block in different structures has validated previously made assumptions regarding multilevel block in a single structure.

Etiology of the electrocardiographic pattern of "incomplete right bundle branch block" in atrial septal defect: an electrophysiologic study.

His bundle and right ventricular apical endocardial electrograms were recorded in 18 patients, ages five to 17 years, of whom ten had atrial septal defect of the secundum type and eight had mild aortic stenosis. The H-RVA interval was assumed to approximate conduction time from the level of the His bundle along the RBB to the site of earliest activation in the right ventricle at the RVA. The H-V interval was normal in all patients (less than or equal to 40 msec). All patients in the ASD group had an rsR' or rSr' pattern in Vl with a mean duration of 99 +/- 9 msec (86 to 116 msec); the mean duration of the H-RVA intervals was 54 +/- 6 msec in this group. In patients with AS, the surface electrocardiograms were normal, with a mean QRS duration of 82 +/- 8 msec (70 to 95 msec); the H-RVA intervals averaged 52 +/- 6 msec. The difference in the H-RVA intervals in the two groups was not statistically significant (P greater than 0.50) despite the fact that patients with ASD had significant prolongation of QRS duration (P greater than 0.001). Moreover, when functional RBB block was induced by premature atrial stimulation in the ASD group, the prolongation of QRS duration was accompanied by an increase in H-RVA interval, indicating relatively intact function of the RBB. It is concluded that the rsR' or rSr' pattern in ASD is likely to be a manifestation of right ventricular overload rather than a true conduction delay in the RBB.

[Value of interacardiac recordings in the evaluation of positive QRS in V1 provoked by stimulation of the right ventricle]. / Valor de los registros intracavitarios en la evaluación de los complejos qrs positivos en V1 provocados for la estimulacion del ventrriculo derecho

The analysis of the common bundle and of the ventrical filtered electrograms has incrased our knowledge of the intraventricular conduction following the simulation of the PVS as well as the different types or reciprocating that can be produced by premature beats. 2. The positive QRS complexes in V1 produced from PVD by St2 can be explained as a greater degree of incomplete recuperation of the right ventricular wall than in the interventricular septum. In contrast with what happened in the basal beats, where the front took longer to reach the TSVD than the VI. 3. The refractarines of the transitional tissues that serve as the phisiological banier was longer than the banal myocardium. The intraventricular propagation, and therefore the morphology and direction of QRS, depended of this one; while the moment of arrival of activation retrogradly to the common bundle was conditioned by the transitional tissues. 4. Episodes of ventricular taquicardies with QRS positive complexes in V1 can be due to a re-entry throught the bundle branches or in (or around) an area that has been recently injured.

[Gap phenomenon in the bundle of his conduction]. / Fenómeno de "brecha" en la conducción por las ramas del haz de His

His bundle electrograms recorded during atrial stimulation with the extrastimulus technique permitted the analysis of the so called gaps in bundle branch conduction. Three different types of gaps were identified each with a distinct electrophysiological mechanism. In type I gap a CLBBB pattern disappeared at shorter coupling (A1-A2) intervals because the more premature impulses encountered a greater degree of the delay at the A-V node therefore reaching the left bundle branch after its effective refractory period had ended. During this part of the cycle the H1-H2 were longer and H2-V2 intervals shorter than when CRBBB was present. In type II gap a CRBBB pattern disappeared at shorter coupling intervals because the premature impulses met a greater delay in the proximal portions of the His-Purkinje system. In consequence, they arrived at the right bundle branch when its effective refractory period had expired. When this occurred the H1-H2 interval were shorter and the H2-V2 longer than those at which CRBBB had been present. The patient with type III gap had CLBBB. A-V conduction was possible through the right bundle branch very late in the cycle. However, it could not occur at shorter coupling intervals finally reappearing at even shorter coupling intervals. True supernormal conduction or vagal pulsatile discharges could have been present. Yet, we favor, as the most likely possibility, the existence of 2:1 phase 4 block with latent or abortive escapes not recorded in the surface leads.