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ABSTRACT: Role of dual AV nodal pathway physiology in the atrioventricular nodal (AVN) conduction during atrial arrhythmias remains unclear. By using His electrogram alternans (HEA), we have developed a functional model of the atrioventricular conduction that incorporates the dual AV nodal pathway physiology. Experiments performed on 5 rabbit atrial-AVN preparations were used to develop and test the presented AV nodal functional model. HEAs from the inferior margin of the His bundle were used to identify fast and slow wavefront propagations (FP and SP). Conduction curves were calculated by using the model and compared with the real experiments, the root mean square error of the FP and SP were 7±4 ms and 3±3 ms respectively. In addition, the model has been used for illustrating the effects of the atrioventricular node modification, which has emerged as one of the alternatives for ventricular rate control during atrial fibrillation. The presented model can help in understanding some of the unclear AV node conduction mechanisms and should be considered as a step forward in understanding the AV node and specifically its dual pathway physiology.
Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE; 10/2010
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ABSTRACT: Although we soon will be marking the 100th anniversary of the discovery of the atrioventricular (AV) node, the mysteries of this most complex of all parts of the conduction system of the heart remain. We are still battling controversies related to the precise morphology of the AV node and its atrial approaches. We are still debating the exact reentrant pathways of the AV nodal reentrant tachycardia. We are still uncertain if the so-called dual AV nodal electrophysiology encompasses two or more pathways, and what exactly makes these pathways in the absence of distinct insulated cables between the atrium and the AV node. It may be just surprising, in view of the above limitations, that current level of knowledge has nevertheless made possible some of the most spectacular successes in the modern cardiac electrophysiology. Thus, the cases of typical AVNRT are cured with a very high rate of success by radiofrequency ablations, increasing the quality of life of thousands of patients. AV nodal modifications are being performed to slow the ventricular rate during atrial fibrillation, although more progress is needed in this endeavor. The goal of the present review is to outline the major anatomic and electrophysiologic efforts in understanding the mechanisms underlying the dual pathway AV nodal propagation and to trace some novel approaches that promise to widen the horizon of the experimental and clinical fields.
Minerva cardioangiologica 03/2003; 51(1):1-14.
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P R Roberts, Y Zhang,
S Zhuan,
K A Mowrey,
D W Wallick,
D G Hills,
T R Betts,
S Allen,
J Ewert,
T N Mazgalev,
J M Morgan
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ABSTRACT: Auxiliary shocks (AS) from electrodes sutured to the left ventricle (LV) prior to primary biphasic shocks (PS) have been shown to reduce defibrillation thresholds (DFT). Two capacitors are required to generate these waveforms. We investigate delivery of AS from one capacitor using a novel waveform. The epicardial surface of the LV is accessed transvenously via the middle cardiac vein (MCV) avoiding a thoracotomy.
A defibrillation electrode was placed in the right ventricle (RV) and superior vena cava (SVC) in 12 pigs (37+/-2 kg). A 50x1.8 mm electrode was inserted in the MCV through a guide catheter. A can was placed in the left pectoral region. A monophasic AS (100 microF, 1.5 J) was delivered along one pathway before switching to deliver a biphasic waveform (40% tilt, 2 ms phase 2) along another. DFTs (PS+AS) were assessed using a binary search. Two configurations not incorporating AS acted as controls. DFTs were compared using repeated measures analysis of variance.
DFTs of the four novel configurations (AS/PS) were: RV-->Can/MCV-->Can=14.9+/-3.7 J, MCV-->Can/RV-->Can=17.2+/-5.7 J, RV-->SVC+Can/MCV-->SVC+Can=13.4+/-4.6 J, MCV-->SVC+Can/RV-->SVC+Can=17.1+/-5.9 J. Delivering AS in the RV followed by PS in the MCV reduced the DFT (RV-->Can (19.9+/-7.3 J, P<0.01) and RV-->SVC+Can (19.2+/-6.0 J, P<0.05)).
Delivering AS prior to PS in the MCV reduces the DFT by up to a third compared to conventional configurations of RV-->Can and RV-->SVC+Can. This is possible using only a single capacitor and an entirely transvenous approach to the LV.
Journal of Interventional Cardiac Electrophysiology 12/2001; 5(4):495-503. · 1.17 Impact Factor
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ABSTRACT: Although the atrioventricular node (AVN) plays a vital role in blocking many of the atrial impulses from reaching the ventricles during atrial fibrillation (AF), a rapid irregular ventricular rate nevertheless persists. The goals of the present study were to explore the feasibility of novel epicardial selective vagal nerve stimulation for slowing of the ventricular rate during AF and to characterize the hemodynamic benefits in vivo. Electrophysiological-echocardiographic experiments were performed on 11 anesthetized open-chest dogs. Hemodynamic measurements were performed during three distinct periods: 1) sinus rate, 2) AF, and 3) AF with vagal nerve stimulation. AF was associated with significant deterioration of all measured parameters (P < 0.025). The vagal nerve stimulation produced slowing of the ventricular rate, significant reversal of the pressure and contractile indexes (P < 0.025), and a sharp reduction in one-half of the abortive ventricular contractions. The present study provides comprehensive evidence that slowing of the ventricular rate during AF by selective ganglionic stimulation of the vagal nerves that innervate the AVN successfully improved the hemodynamic responses.
AJP Heart and Circulatory Physiology 10/2001; 281(4):H1490-7. · 3.71 Impact Factor
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ABSTRACT: The clinical assessment of left ventricular (LV) systolic function during atrial fibrillation (AF) is unreliable and difficult because of beat-to-beat variability. We evaluated an index for the estimation of LV systolic function in AF that is based on the relationship between the preceding (R-R1) and prepreceding (R-R2) R-R intervals. LV Doppler stroke volume (SV), ejection fraction (EF), peak aortic flow rate (AoF) and the maximum value of the first derivative of the LV pressure curve (dP/dt(max)) were evaluated in 13 healthy open-chest dogs during triggered AF. All parameters showed a significantly strong positive linear relationship with the ratio of R-R1/R-R2 (r = 0.65, 0.74, 0.75, and 0.70 for SV, EF, AoF, and dP/dt(max), respectively). The calculated value of LV systolic parameters at R-R1/R-R2 = 1 in the linear regression line showed a good relationship and an agreement with the measured average value of the parameter over all cardiac cycles (SV, 12.1 vs. 12.8 ml; EF, 49.6 vs. 51.2%; AoF, 1.37 vs. 1.48 l/min; and dP/dt(max), 2,323 vs. 2,454 mmHg/s). Using the LV systolic parameters estimated at R-R1/R-R2 = 1 in the linear regression line allows the LV contractile function to be accurately and reproducibly evaluated during AF and obviates the less-reliable process of averaging multiple cardiac cycles.
AJP Heart and Circulatory Physiology 09/2001; 281(2):H573-80. · 3.71 Impact Factor
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ABSTRACT: His electrogram (HE) amplitude and morphology changes were observed in our previous studies during transition from "fast" to "slow" atrioventricular nodal (AVN) conduction. This phenomenon and its significance for the dual-AVN electrophysiology are not well recognized and have not been studied.
Experiments were performed on 17 healthy rabbit atrial-AVN preparations during standard programmed electrical pacing. HEs were mapped along the His bundle with roving surface electrodes, along with recording of cellular action potentials (APs). HEs recorded from the superior margin of the His bundle were of greater amplitude during basic beats and decreased substantially, by 42+/-19% (P<0.01), when premature A(1)A(2) shortened to 178+/-20 ms. In contrast, the HEs from the inferior margin increased dramatically, 2.9+/-1.7 times (P<0.01), during short A(1)A(2) and remained high until AVN block occurred. In addition, during long A(1)A(2), the superior HEs consistently preceded the inferior by 1.9+/-0.7 ms. In contrast, at short A(1)A(2), the superior HEs occurred 2.7+/-0.8 ms after the inferior. Cellular AP recordings demonstrated clearly the presence of and the transition between early (fast) and late (slow) excitation wavefronts that accompanied HE alternans.
The morphological-electrophysiological evidence from the AV junction suggests that fast and slow wavefronts reach the His bundle differently, producing functional longitudinal dissociation into 2 domains. The characteristic HE alternans recorded from these domains are a new sensitive tool to determine the presence of distinctly different wavefronts and their participation in the conduction during reentrant or other arrhythmias. These findings provide further understanding of the mechanisms of dual-AVN electrophysiology.
Circulation 09/2001; 104(7):832-8. · 14.74 Impact Factor
