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Functional dissociation of cellular activation as a mechanism of Mobitz type II atrioventricular block.

Abstract：

BACKGROUND:Several mechanisms have been advanced to explain Mobitz type II atrioventricular block in the ischemically damaged His-Purkinje system. Only recently, however, has an animal model been developed to study this form of conduction defect in vivo and in vitro. METHODS AND RESULTS:Conduction defects were induced in anesthetized dogs by ischemic damage to the proximal His-Purkinje system after anterior septal artery ligation. Stable 2:1 atrioventricular block, localized within the His bundle or in the proximal bundle branches, was obtained in each dog by atrial pacing at an average rate of 239 +/- 20 beats per minute (n = 12). In vitro studies were then performed from the same hearts. Action potentials and electrograms were simultaneously recorded from the His bundle and the proximal right bundle branch at the site of damage. At slow rates of pacing (40-60 beats per minute), the action potential amplitude was 85 +/- 4 mV, and some cells (10 +/- 3%) showed dissociation from the electrical activity in the bundle. At fast rates (149 +/- 11 beats per minute), during 1:1 conduction, the frequency of cellular dissociation increased to 57 +/- 6% (p < 0.001), and the action potential amplitude decreased (-31 +/- 4%, p < 0.001). The frequency of dissociation closely correlated with the reduction in action potential amplitude (r = 0.87, p < 0.001). These changes were markedly attenuated once 2:1 block developed. The site of block was not constant but rather showed a dynamic behavior with spatial shifting in response to changes in pacing rate or the introduction of extrastimuli. CONCLUSIONS:These results indicate that in the ischemically damaged proximal His-Purkinje system, an increase in rate leads to reduced and asynchronous cellular activation before 2:1 block. The latter provides a more stable activation pattern, because the frequency of dissociation is markedly reduced.

journal_name

Circulation

journal_title

Circulation

authors

Gonzalez MD,Scherlag BJ,Mabo P,Lazzara R

doi

10.1161/01.cir.87.4.1389

subject

Has Abstract

pub_date

1993-04-01 00:00:00

pages

1389-98

issue

eissn

0009-7322

issn

1524-4539

journal_volume

pub_type

杂志文章

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Functional dissociation of cellular activation as a mechanism of Mobitz type II atrioventricular block.