Key result
High-rate atrial activation during atrial flutter led to decreasing conduction ratios (0.34 to 0.23; P<0.01) and reduced pattern stability at advanced block levels (64.3% to 28.3%; P<0.01).
Observational (n=10)
Intrinsic AV nodal properties, including nodal recovery, dual pathway physiology, and concealed conduction, account for the complex AV block patterns observed during regular atrial tachyarrhythmias.
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Hypothesis-generating for AV nodal dynamics in flutter; leaves open effects on management.
The genesis of complex ventricular rhythms during atrial tachyarrhythmias in humans is not fully understood. To clarify the dynamics of atrioventricular (AV) conduction in response to a regular high-rate atrial activation, 29 episodes of spontaneous or pacing-induced atrial flutter (AFL), covering a wide range of atrial rates (cycle lengths from 145 to 270 ms), were analyzed in 10 patients. AV patterns were identified by applying firing sequence and surrogate data analysis to atrial and ventricular activation series, whereas modular simulation with a difference-equation AV node model was used to correlate the patterns with specific nodal properties. AV node response at high atrial rate was characterized by 1) AV patterns of decreasing conduction ratios at the shortening of atrial cycle length (from 236.3 ± 32.4 to 172.6 ± 17.8 ms) according to a Farey sequence ordering (conduction ratio from 0.34 ± 0.12 to 0.23 ± 0.06; P < 0.01); 2) the appearance of high-order alternating Wenckebach rhythms, such as 6:2, 10:2, and 12:2, associated with ventricular interval oscillations of large amplitude (407.7 ± 150.4 ms); and 3) the deterioration of pattern stability at advanced levels of block, with the percentage of stable patterns decreasing from 64.3 ± 35.2% to 28.3 ± 34.5% (P < 0.01). Simulations suggested these patterns to originate from the combined effect of nodal recovery, dual pathway physiology, and concealed conduction. These results indicate that intrinsic nodal properties may account for the wide spectrum of AV block patterns occurring during regular atrial tachyarrhythmias. The characterization of AV nodal function during different AFL forms constitutes an intermediate step toward the understanding of complex ventricular rhythms during atrial fibrillation.
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Masè et al. (2012) conducted an observational in Atrial flutter (n=10). High-rate atrial activation was evaluated on Atrioventricular conduction patterns and pattern stability (p=<0.01). High-rate atrial activation during atrial flutter led to decreasing conduction ratios (0.34 to 0.23; P<0.01) and reduced pattern stability at advanced block levels (64.3% to 28.3%; P<0.01).
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