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This Article Full Text Full Text (PDF) Supplemental Table Buy All Versions of this Article: 297/6/H2136    most recent 00712.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Tadros, R. Articles by Billette, J. PubMed PubMed Citation Articles by Tadros, R. Articles by Billette, J.

Rate-dependent AV nodal refractoriness: a new functional framework based on concurrent effects of basic and pretest cycle length

Département de physiologie, Faculté de médecine, Université de Montréal, Montreal, Canada

Submitted July 30, 2009 ; accepted in final form October 4, 2009

The atrioventricular (AV) node filters atrial impulses. Underlying rate-dependent refractory properties are assessed with the effective (ERPN; longest nonconducted atrial cycle length) and functional (FRPN; shortest His bundle cycle) refractory period determined with premature protocols at different basic rates. Fast rates prolong ERPN and shorten FRPN, but these effects vary with subjects, age, and species. We propose that these opposite and variable effects reflect the net sum of concurrent cumulative and noncumulative effects associated with basic (BCL) and pretest cycle length (PTCL), respectively. To test this hypothesis, we assessed selective and combined effects of five BCL (S₁S₁) and six PTCL (S₁S₂) on ERPN, FRPN, and their subintervals (ERPN = A₂H₂ + H₂A₃ and FRPN = H₂A₃ + A₃H₃, where A is atrium and H is His bundle) with S₁S₂S₃ protocols in six rabbit heart preparations. At control BCL, PTCL shortenings prolonged ERPN (113 ± 12 vs. 101 ± 14 ms, P < 0.01) as a net result of prolonged A₂H₂ and curtailed H₂A₃. At control PTCL, BCL shortenings increased ERPN (127 ± 20 vs. 101 ± 14 ms, P < 0.01) by prolonging A₂H₂. FRPN did not vary with BCL but decreased (163 ± 6 vs. 175 ± 10 ms, P < 0.01) with PTCL that curtailed H₂A₃. Equal BCL and PTCL shortenings as in standard protocols prolonged ERPN but left FRPN unchanged. Notably, ERPN and FRPN significantly correlated through their H₂A₃ subinterval. In conclusion, BCL and PTCL are both important determinants of AV nodal refractoriness and together account for rate-induced changes in ERPN and FRPN observed during standard premature protocols. ERPN and FRPN are related variables. Similar functional rules may govern nodal refractory behavior during supraventricular tachyarrhythmias.

atrioventricular node; heart rate; effective refractory period; functional refractory period; rate dependence