Beat-to-beat changes in AV nodal refractory and recovery properties during Wenckebach cycles

American Journal of Physiology-Heart and Circulatory Physiology

2009

Tadros R, Billette J. Rate-dependent AV nodal refractoriness: a new functional framework based on concurrent effects of basic and pretest cycle length. Am J Physiol Heart Circ Physiol 297: H2136-H2143, 2009. First published October 9, 2009 doi:10.1152/ajpheart.00712.2009.-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 ϭ A2H2 ϩ H2A3 and FRPN ϭ H2A3 ϩ A3H3, where A is atrium and H is His bundle) with S 1S2S3 protocols in six rabbit heart preparations. At control BCL, PTCL shortenings prolonged ERPN (113 Ϯ 12 vs. 101 Ϯ 14 ms, P Ͻ 0.01) as a net result of prolonged A2H2 and curtailed H2A3. At control PTCL, BCL shortenings increased ERPN (127 Ϯ 20 vs. 101 Ϯ 14 ms, P Ͻ 0.01) by prolonging A 2H2. FRPN did not vary with BCL but decreased (163 Ϯ 6 vs. 175 Ϯ 10 ms, P Ͻ 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 H 2A3 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 THE ATRIOVENTRICULAR (AV) node generates a delay between atrial and ventricular activation and filters atrial impulses during tachyarrhythmias. Hence, optimal filtering of atrial impulses through pharmacological modulation of AV nodal function has become a cornerstone of atrial fibrillation therapy (22). Underlying intrinsic rate-dependent AV nodal refractory properties are commonly assessed in clinical or drug studies with the effective (ERPN) and functional (FRPN) refractory period determined with premature protocols performed at different basic rates (12,18,19,24,32,34). However, resulting data remain puzzling in several respects. First, and for as-yet unclear reasons, ERPN increases with rate (11,12,27,36),16,17,24). Second, these effects vary much with subjects, age, and species and often depart from the main trend (7,8,12,13,26,35,38). Third, a fast rate induces both cumulative and noncumulative effect...

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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

American Journal of Physiology-Heart and Circulatory Physiology

2009

“…This is a dynamic process that evolves until a new constant conduction time is reached. There is also evidence that nodal recovery time changes from beat‐to‐beat despite constant AA and a constant level of fatigue, particularly during Wenckebach cycles 3,18,20–22 …”

Section: Discussionmentioning

confidence: 99%

Dependence of AV Nodal Function Curves on the Selected Recovery Index: Pivotal Role of Pretest Conduction Time

Lavallée

Cardiovasc electrophysiol

2007

“…For instance, these properties account for transient responses to linear ramp increase and decrease in cycle length inducing hysteresis in AV nodal conduction time (12,75). These properties also quantitatively account for a variety of other rate-induced AV nodal responses including Wenckebach cycles (54,62,68,74). A recent study also provides analytical and modeling data supporting their involvement in human supraventricular tachyarrhythmias (46).…”

Section: Physiology and Assessment Of Transient Av Nodal Responsesmentioning

confidence: 92%

Integrated rate-dependent and dual pathway AV nodal functions: principles and assessment framework

American Journal of Physiology-Heart and Circulatory Physiology

2014

The atrioventricular (AV) node conducts slowly and has a long refractory period. These features sustain the filtering of atrial impulses and hence are often modulated to optimize ventricular rate during supraventricular tachyarrhythmias. The AV node is also the site of a clinically common reentrant arrhythmia. Its function is assessed for a variety of purposes from its responses to a premature protocol (S 1S2, test beats introduced at different cycle lengths) repeatedly performed at different basic rates and/or to an incremental pacing protocol (increasingly faster rates). Puzzlingly, resulting data and interpretation differ with protocols as well as with chosen recovery and refractory indexes, and are further complicated by the presence of built-in fast and slow pathways. This problem applies to endocavitary investigations of arrhythmias as well as to many experimental functional studies. This review supports an integrated framework of rate-dependent and dual pathway AV nodal function that can account for these puzzling characteristics. The framework was established from AV nodal responses to S 1S2S3 protocols that, compared with standard S 1S2 protocols, allow for an orderly quantitative dissociation of the different factors involved in changes in AV nodal conduction and refractory indexes under rate-dependent and dual pathway function. Although largely based on data from experimental studies, the proposed framework may well apply to the human AV node. In conclusion, the rate-dependent and dual pathway properties of the AV node can be integrated within a common functional framework the contribution of which to individual responses can be quantitatively determined with properly designed protocols and analytic tools. atrioventricular node; functional assessment; conduction; refractory period; pretest cycle length; recovery; facilitation; fatigue THE ATRIOVENTRICULAR (AV) node generates a delay between atrial and His bundle activation that helps optimize ventricular filling and blood pumping. The AV node also has rate-dependent conduction and refractory properties accounting for the filtering of atrial impulses during supraventricular tachyarrhythmias. The optimization of this filtering to control the ventricular rate constitutes a cornerstone of atrial fibrillation therapy (3). Another consistent feature of the normal AV node is its built-in fast pathway (FP) and slow pathway (SP) (29,36,45,50,60,73). In some human hearts, SP and FP interplay to result in a clinical arrhythmia known as AV nodal reentrant tachycardia, the most common form of paroxysmal supraventricular tachycardia that can now be successfully cured by ablation therapy (24,34,59,61). These properties are obviously sensitive to autonomic tone (54 -57), itself modulated by conditions such as rest, exercise, pregnancy, stress, diseases, drugs, etc. However, the basic AV nodal physiology and its assessment tools remain debated. Their understanding is the primary goal of this review.The understanding of AV nodal function remains indeed challenging. Zip...