Mobitz type I A-V block (Wenckebach) is usually characterized by gradual prolongation of the P-R interval prior to dropping out of the QRS complex. Incrementation of the P-R interval of more than 20 ms is generally indicative of Wenckebach A-V block. Mobitz type II A-V block is defined as dropping out of the QRS complex with no prior P-R interval prolongation. It is not clear whether P-R interval shortening of less than 20 ms after the blocked QRS complex is acceptable for Mobitz II block. Ischemia, experimental or clinical, uniformly leads to some degree of conduction delay prior to block of an impulse in the His Purkinje system. These findings are indicative of a continuum between Mobitz I and II A-V block. Mobitz type I may originate in either the A-V node or His PUrkinje system while the Mobitz type II block is restricted to infranodal locations with uncertainty, at this time, about its presence at the A-V nodal level in man. The clinical significance of type II block, as opposed to type I, lies in its propensity to deteriorate to higher degrees of A-V block. Tachycardia-dependent block is due to alterations in phase 3, whereas bradycardia-dependent block is related to at least 3 physiologic events during phase 4. In fascicular block, the conduction disturbance may be localized anywhere from the A-V node to the peripheral Purkinje-muscle junctions or working myocardium. Focal lesions in the His bundle could result in bundle branch block. This, however, would prerequisite more marked suppression of the transverse than the longitudinal connections thus enabling longitudinal dissociation.
|Original language||English (US)|
|Number of pages||9|
|State||Published - Jan 1 1979|
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine