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Similar recovery properties in fast and slow atrioventricular nodal pathways
Journal of Electrocardiology Vol. 29 Supplement
Similar Recovery Properties in Fast and Slow Atrioventricular N o d a l P a t h w a y s
Ming-Lon Young, MD,* Vikas Kohli, MD,* Chi-Tai Kuo, MD,-tand Grace S. Wolff, MD*
Objective
the m i n i m u m HA at which a conducted AH is registered (effective refractory period). AH~i~ is the AH interval after an infinite long recovery time. The shortest AH interval was taken as the fast pathway AHmin (AHmin {fast)). The shortest recognizable slow pathway conducted AH interval was taken as AHnin {slow). In order to compare F-F and S-S curves and their @values, the difference (8) of AHmin {sIow/ and AHmin (fast) was obtained in each case to correct the slow pathway curve and its @value ((Jislow)c= @tsto~)+ 8).
The purpose of this study was to determine w h e t h er fast and slow atrioventricular (AV) nodal pathways have the same time-dependent recovery properties.
Background Atrioventricular nodal recovery properties are studied by delivering atrial extrastimuli coupled to basic atrial beats and plotting nodal coupling intervals against nodal conduction time. In patients with dual nodal pathways, the resultant curves will include fast-to-fast (F-F) and fast-to-slow (F-S) pathways coupled curves. While fast pathways recovery property can be represented by the former, slow pathway recovery property will require assessment by studying the slow-to-slow (S-S) pathways coupled curve.
Results In patients with dual pathways, while the S-S curve was markedly deviated upward and leftward from the FF curve, it became close to or superimposed on the F-F curve w h e n it was righward and downward translocated by 8 value (the difference of time constants for F-F ['CF-F 88 --+ 28 ms] and S-S curves ['Cs_s 100 _+ 55 ms] was not significant). While the @{f~s*/ (232 _+ 49 ms) was longer than the @(slow) (20 _+ 75 ms) (P < .001) in patients with dual pathways, w h e n @(siow/was corrected by the 8 value (187 _+ 66 ms), it became close to the @ of the control patients (170 _+ 62 ms).
Methods In nine patients with dual nodal pathways, F-E F-S, S-F, and S-S curves were obtained by pacing protocols. In eight patients without dual nodal pathways, F-F and FIs)-F curves (atrial extrastimuli coupled to a preceding slowly conducted fast pathway beat) were obtained. Atrioventricular nodal recovery properties were obtained by the equation AH = AHmin + exp (~z - HA/z), for HA _>@, where AH is the AH interval at any given HA coupling interval, c~ is a constant, ~ is the time constant of the curve, and @is
Conclusion and Speculation Our results of a similar t i m e - d e p e n d e n t recovery property for the fast and slow AV nodal pathways and a longer fast p at h w ay effective refractory period than that of the slow p at h w ay (which, in turn, is close to the effective refractory period of the normal AV node) suggest that in patients with dual pathways, w h e n the fast p at h w ay effective refractory period is reached, block occurs at its input tract and the conduction is continued via the slow pathway to traverse the same AV node. W h e n the slow pathway effective refractory period is finally reached, the conduction block occurs at the node proper.
From the *Department of Pediatrics, University of Miami, Miami, Florida, and ~First Division of Cardiology, Chang Gung Memorial Hospital, Taipei, Taiwan. Reprint requests: Ming-Lon Young, MD, University of Miami School of Medicine, Division of Pediatric Cardiology, PO Box 016960 (R-76), Miami, FL 33101.
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Similar Recovery Properties in Fast and Slow Atrioventricular N o d a l P a t h w a y s
Ming-Lon Young, MD,* Vikas Kohli, MD,* Chi-Tai Kuo, MD,-tand Grace S. Wolff, MD*
Objective
the m i n i m u m HA at which a conducted AH is registered (effective refractory period). AH~i~ is the AH interval after an infinite long recovery time. The shortest AH interval was taken as the fast pathway AHmin (AHmin {fast)). The shortest recognizable slow pathway conducted AH interval was taken as AHnin {slow). In order to compare F-F and S-S curves and their @values, the difference (8) of AHmin {sIow/ and AHmin (fast) was obtained in each case to correct the slow pathway curve and its @value ((Jislow)c= @tsto~)+ 8).
The purpose of this study was to determine w h e t h er fast and slow atrioventricular (AV) nodal pathways have the same time-dependent recovery properties.
Background Atrioventricular nodal recovery properties are studied by delivering atrial extrastimuli coupled to basic atrial beats and plotting nodal coupling intervals against nodal conduction time. In patients with dual nodal pathways, the resultant curves will include fast-to-fast (F-F) and fast-to-slow (F-S) pathways coupled curves. While fast pathways recovery property can be represented by the former, slow pathway recovery property will require assessment by studying the slow-to-slow (S-S) pathways coupled curve.
Results In patients with dual pathways, while the S-S curve was markedly deviated upward and leftward from the FF curve, it became close to or superimposed on the F-F curve w h e n it was righward and downward translocated by 8 value (the difference of time constants for F-F ['CF-F 88 --+ 28 ms] and S-S curves ['Cs_s 100 _+ 55 ms] was not significant). While the @{f~s*/ (232 _+ 49 ms) was longer than the @(slow) (20 _+ 75 ms) (P < .001) in patients with dual pathways, w h e n @(siow/was corrected by the 8 value (187 _+ 66 ms), it became close to the @ of the control patients (170 _+ 62 ms).
Methods In nine patients with dual nodal pathways, F-E F-S, S-F, and S-S curves were obtained by pacing protocols. In eight patients without dual nodal pathways, F-F and FIs)-F curves (atrial extrastimuli coupled to a preceding slowly conducted fast pathway beat) were obtained. Atrioventricular nodal recovery properties were obtained by the equation AH = AHmin + exp (~z - HA/z), for HA _>@, where AH is the AH interval at any given HA coupling interval, c~ is a constant, ~ is the time constant of the curve, and @is
Conclusion and Speculation Our results of a similar t i m e - d e p e n d e n t recovery property for the fast and slow AV nodal pathways and a longer fast p at h w ay effective refractory period than that of the slow p at h w ay (which, in turn, is close to the effective refractory period of the normal AV node) suggest that in patients with dual pathways, w h e n the fast p at h w ay effective refractory period is reached, block occurs at its input tract and the conduction is continued via the slow pathway to traverse the same AV node. W h e n the slow pathway effective refractory period is finally reached, the conduction block occurs at the node proper.
From the *Department of Pediatrics, University of Miami, Miami, Florida, and ~First Division of Cardiology, Chang Gung Memorial Hospital, Taipei, Taiwan. Reprint requests: Ming-Lon Young, MD, University of Miami School of Medicine, Division of Pediatric Cardiology, PO Box 016960 (R-76), Miami, FL 33101.
226