Showing 5 results for Av Node
Vahid Khori, Mohsen Nayebpour, Abbas Mirabbasi, Mona Pourabouk,
Volume 13, Issue 1 (4-2009)
Abstract
Introduction : The aim of this study is to obtain new insight into possible relation between functional properties of slow concealed pathway and rate-dependent properties of AV-node.
Methods : Rate-dependent nodal properties of recovery, facilitation, and fatigue were characterized by stimulation protocols in one groups of (N=7) isolated superfused AV-Nodal rabbits. Small miniature lesions were made by delivering constant voltage (110 V-100 s) with unipolar silver electrode.
Results : Fast pathway ablation significantly decreased facilitation and had no effect on fatigue and nodal refractoriness. The most important effect of fast pathway ablation was prolongation of minimum conduction time.
Conclusion : The FP-ablation revealed the presence of the concealed SP. Rate-dependent property of node is dependent to dynamic interaction between concealed slow with slow pathway. Fast pathway involved in the mechanism of facilitation.
Aref Salehi, Vahid Khori, Mohsen Nayebpour, Elnaz Rakhshan,
Volume 13, Issue 2 (8-2009)
Abstract
Objectives: Dual pathways have a determinant role in the occurrence of atrio nodal tachyarrhythmia (AVNRT). The aim of present study is to determine the role of slow pathway (SP) in the concealment zone and protective role of AV node during atrial fibrillation (AF).
Material &Methods: In 7 isolated nodal rabbit preparation zone of concealment and concealed conduction is quantified by Specific pacing protocols. The differences between effective refractory period of atrial and AV node in the basic cycle length and after introducing concealed beat was considered as Zone of concealment. AَF was simulated by high-rate atrial pacing with random coupling intervals. Small miniature lesions were made in superior compact node by delivering constant voltage100-110 v.
Results: FP ablation resulted in longer minimum nodal conduction time, but without change of nodal effective and functional refractory period. Zone of concealment was determined as 10±4.8 ms. After fast pathway modification nodal characteristics during AF did not change significantly (average H–H intervals, number of concealed beats and zone of concealment).
Conclusion: Fast pathway has not a determinant role in the mechanism of concealed conduction and zone of concealment. During AF, the wave fronts did not used fast pathway to conduct to ventricles.
Vahid Khori, Saed Saleki, Aref Salehi, Alimohammad Alizadeh, Mona Pourabouk, Fakhri Badaghabadi, Shima Changizi, Mohsen Nayebpour,
Volume 14, Issue 3 (10-2010)
Abstract
Introduction: Electrophysiological studies have demonstrated a relationship between aging and atrioventricular
(AV) nodal conduction and refractoriness. The aim of the present study was to determine the effects of nodal aging on
dynamic AV nodal field potential recording during atrial fibrillation (AF) in rabbit.
Methods: Two groups of male New Zealand rabbits (neonatal 2-week-olds and adult 12-week-olds, n=14 each
group) were used in this study. Field potential recordings were executed by silver electrodes with a diameter of 100 M.
Pre-defined stimulation protocols of AF, zone of concealment (ZOC) and concealed conduction for determination of the
electrophysiological properties of the AV-node were separately applied in each group.
Results: Results of the study showed that mean ventricular rate (HH) during atrial fibrillation was smaller in the
neonatal compared to the adult group (229.1 ± 8.3 versus 198.6 ± 13.1 msec, respectively). Also ventricular distribution
conduction pattern showed two peaks in the adult and one peak in the neonatal group. Analyzing the zone of
concealment in different rates and after concealed beat indicated that the zone of concealment in neonates were
significantly smaller compared with adult rabbits and increasing zone of concealment, which is accompanied with
increasing ventricular rate is abrogated in the neonatal group (5 ± 3.3, 12.2 ± 6.3 msec).
Conclusion: The results of this study showed that the electrophysiological protective dynamic behavior of the AV
node during atrial fibrillation is smaller in neonates compared to adults. Narrower zone of concealment, abrogation rate
dependent trend of the zone of concealment and shorter nodal refractoriness can account for the specific nodal
electrophysiological properties of neonatal rabbits.
Vahid Khori, Alimohammad Alizadeh, Mahsa Niknam, Hamid Reza Moheimani, Hamid Yazdi, Mona Pourabouk, Fakhri Badaghabadi, Shima Changizi, Mryam Rajaei, Mohsen Nayebpour,
Volume 15, Issue 2 (8-2011)
Abstract
Introduction: Developmental changes in atrioventricular nodal conduction time and refractoriness have been shown
in several studies. Prevalence of atrioventricular nodal reentrant tachycardia (AVNRT) is clearly age-dependent. The
purpose of this study was to determine developmental changes of basic and frequency-dependent electrophysiological
properties of the atrioventricular node (AV-node) in neonatal and adult rabbits.
Methods: In this study, the effects of increasing age on the basic and rate-dependent properties of isolated perfused
AV-node were analyzed in neonatal (2-week-old) and adult (12-week-old) New Zealand rabbits. Specific stimulation
protocols of recovery, facilitation and fatigue were separately applied in each group (n=7). Unipolar extracellular field
potential was recorded by a silver electrode (100 M).
Results: The results showed that the basic nodal properties (ERP, FRP, WBCL and AHmax) were significantly
shorter in neonates compared to the adult group. The magnitude of fatigue was also decreased in the neonatal group
compared to control (18.9 ±3.3 vs. 11.1 ± 1.2 msec). Time constant of recovery of the adult group was significantly
higher than the neonatal group (P<0.05).
Conclusion: The results of this study showed that nodal basic and frequency-dependent properties are age-related
and different developmental changes of slow and fast pathways are responsible for this behavior and may reveal the
grater susceptibility of AVNRT in young adults compared to infants.
Vahid Khori, Alimohammad Alizadeh, Ameneh Navaiyan, Mohsen Nayebpour, Mona Porabouk, Fakhri Badaghabadi, Shima Changizi, Maryam Rajaei, Hamidreza Moheimani, Hamidreza Yazdi,
Volume 15, Issue 3 (10-2011)
Abstract
Introduction: The aim of the present study was to determine direct effects of NO modulation on protective
electrophysiological properties of atrioventricular node (AV node) in the experimental model of AF in rabbit.
Methods: Isolated perfused rabbit AV nodal preparations were used in two groups. In the first group (N=7), LNAME
(50μM) was applied. In the second group (N=12), different concentrations of L - argenine (250 μM - 5000 μM)
were added to the solution. Programmed stimulation protocols were used to quantify AV nodal conduction time,
refractoriness and zone of concealment. AF protocol was executed by software with coupling intervals (ranging from 75
– 125 msec).
Results: L-NAME had depressive effects on basic AV nodal properties. L-Arginine (250μM) had direct inhibitory
effects on nodal conduction time, Wenckebach and refractoriness. Significant increases in the number of concealed
beats were induced by L-Arginine (500 μM ). Number of concealed beats were increased from 700.7 ± 33.7 to 763 ±21
msec (P<0.05). Trend of zone of concealment prolongation in a frequency-dependent model was abrogated by Larginine
(250, 5000 μM).
Conclusion: NO at low concentration (in the presence of L-NAME) had facilitatory role on AV nodal properties,
but at high concentration (in the presence of L-arginine) enhanced protective role of AV node during AF. Biphasic
modulatory role of NO may affect protective behavior of AV node during AF.
