Relationships between refractoriness and conduction and the likelihood of obtaining results from these tests have not been reported in detail in patients undergoing clinically indicated electrophysiologic testing. Therefore, attempts were made in 100 such patients to determine the effective and functional refractory periods (ERP, FRP) of the atrium, atrioventricular (AV) node, and specialized ventricular conduction system during sinus rhythm and atrial pacing. Conduction was tested using incremental ramp atrial pacing. To facilitate comparison of conduction and refractoriness, effective and functional conduction periods (ECP, FCP) were defined: ECP = longest pacing cycle length failing to conduct and FCP = shortest conducted cycle length. One or more determinations of atrial refractoriness were possible in 95 subjects, but no measurable atrial conduction end points were attained. In contrast, AV nodal ERPs or FRPs could be determined in only 47, using the extrastimulus technique, in spite of multiple atrial drive pacing rates. AV nodal ECPs and FCPs could be determined in all 100 patients using ramp pacing. Comparison of atrial ERPs and FRPs in patients in whom AV nodal refractoriness could and could not be determined showed no significant differences. Patients in whom it was not possible to determine AV nodal ERPs and FRPs had shorter ECPs and FCPs than other patients. Thus, inability to determine AV nodal refractory periods was caused by prior atrial refractoriness (atrial FRP longer than AV nodal ERP). Block or refactoriness in the atrium or AV node prevented detailed evaluation of the ventricular specialized conduction system in all but a few subjects. AV nodal ECPs correlated with ERPs, but were longer; FCPs also correlated but were shorter than the FRPs. The maximum AV node delay (AH interval) was the same with ramp pacing and extrastimulus testing during atrial pacing. In the high right atrium, refractory period testing is more useful than rapid pacing. For evaluation of AV nodal function, particularly in large groups of patients such as those undergoing drug studies, conduction testing will provide more nearly universal data than testing for refractoriness. Neither method is able to provide routine assessment of the ventricular specialized conduction system.
|Original language||English (US)|
|Number of pages||15|
|Journal||Journal of Electrophysiology|
|State||Published - Jan 1 1988|
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine