A comparison of calcitonin gene-related peptide effects on coronary flow and cardiac conduction system in the guinea pig.
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The purpose of this study was to examine the effects of calcitonin gene-related peptide (CGRP) on coronary flow and various parts of cardiac conduction system (CCS) in the isolated guinea pig heart by recording the cardiac electrogram and His bundle activity simultaneously. The coronary flow (CF) was measured and the right atrium was paced at incremental frequencies periodically. Perfusing heart with CGRP at the concentrations of 3 30 nmol/L increased CF strikingly and dose-dependently. CGRP (30 nmol/L) caused a moderate and significant increase in the spontaneous heart rate, but failed to influence the atrioventricular nodal and His bundle-Purkinje fiber conduction time and the longest atrial pacing cycle length inducing 3 2 Wenckebach and 2 1 AV nodal conduction. The results indicate that CGRP in the guinea pig heart might act mainly on coronary vessels and then the sinus node, but did not affect the conductivity and refractoriness of the AV conduction system. (+info)
Quantification of interventricular asynchrony during LBBB and ventricular pacing.
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The quantification of mechanical interventricular asynchrony (IVA) was investigated. In 12 dogs left bundle branch block (LBBB) was induced by radio frequency ablation. Left ventricular (LV) and right ventricular (RV) pressures were recorded before and after induction of LBBB and during LBBB + LV apex pacing at different atrioventricular (AV) delays. Four IVA measures were validated using computer simulations on experimentally obtained pressure signals. The most robust measure for IVA was the time delay between the upslope of the LV and RV pressure signals (DeltaT(up)), estimated by cross correlation. The induction of experimental LBBB decreased DeltaT(up) from -6.9 +/- 7.0 ms (RV before LV) to -33.9 +/- 7.6 ms (P < 0.05) in combination with a significant decrease of LV maximal first derivative of pressure development over time (dP/dt(max)). During LV apex pacing, DeltaT(up) increased with decreasing AV delay up to +20.9 +/- 14.6 ms (P < 0.05). Interventricular resynchronization (DeltaT(up) = 0 ms) significantly improved LV dP/dt(max) by 15.1 +/- 5.9%. QRS duration increased significantly after induction of LBBB but did not change during LV apex pacing. In conclusion, DeltaT(up) is a reliable measure of mechanical IVA, which adds valuable information concerning the nature of asynchronous activation of the ventricles. (+info)
Effects of heart rate and atropine on 'dual AV conduction'.
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In patients with evidence of dual AV conduction, a premature atrial depolarization is normally conducted via a fast conducting pathway with a long refractory period. At a critically timed coupling interval, the effective refractory period is reached and now the impulse is conducted over a pathway with a slow conduction velocity and a short effective refractory period. At this moment in the His bundle electrocardiogram, a sudden increase in the AH interval occurs which is called the 'break' phenomenon. This phenomenon was studied in 14 patients, with a history of supraventricular paroxysmal tachycardia, at the patient's own heart rate, at different paced heart rates, and after the administration of atropine. In 11 patients the 'break' phenomenon could be elicited during sinus rhythm,; in 3 when the heart rate was accelerated. The effective refractory period of the fast conducting pathway was prolonged in 9 patients, remained unchanged in 3, and was shortened in 2 when the heart rate was increased. The effective refractory period of the slow conduting pathway was reached when block occurred proximal to the His bundle. This parameter was increased in 8 patients, remained unchanged in 3, and was decreased in 1 patient with augmentation of the heart rate. This effective refractory period was not measured in 2 patients. Atropine led to a shortening of the refractory period of both pathways in 8 patients studied. Atrial echo phenomena indicating the beginning of a re-entry circuit occurred at an AH prolongation that was not always identical to that measured at the point of 'break'. Widening, as well as narrowing, of the echo zone was found, indicating that the re-entry circuit was in a state of labile equilibrium. In cases where shortening of the pathways involved in the re-entry circuit was found, structures other than nodal may exist; therefore paranodal bypass must be considered. (+info)
Delay and block of cardiac impulse caused by enhanced phase-4 depolarization in the His-Purkinje system.
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The underlying mechanism of bradycardia-dependent bundle-branch and paroxysmal atrioventricular block appears to be enhancement of phase-4 depolarization in a branch or in a natural or acquired monofascicular pathway. Clinical records of these forms of impaired conduction occurring in the bundle-branches, with either longer or shorter cardiac cycle lengths, are presented and analysed. These also include the combination of Mobitz typw I atrioventricular block with variable degrees of bundle-branch block, as a representative example of narrow ventricular escape beats firing in the zone where prominent diastolic depolarization is present. (+info)
Reversed remodelling of dilated left sided cardiomyopathy after upgrading from VVIR to VVIR biventricular pacing.
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AIMS: To show reversed remodelling of the left ventricle and left atrium after upgrading to biventricular pacing in a patient with worsening heart failure due to VVIR pacing. To review the literature concerning reversed remodelling after upgrading to biventricular pacing. METHODS AND RESULTS: In a 61-year-old man, with cardiomyopathy and worsening heart failure and mitral insufficiency following conventional pacing after His-bundle ablation, upgrading to biventricular pacing showed left sided reversed remodelling of the heart with decrease in mitral regurgitation in 6 months. The literature is reviewed by a Medline search between 1966-2001. CONCLUSION: The occasionally observed progressive heart failure after right ventricular pacing following His-bundle ablation can be reversed by upgrading to VVIR biventricular pacing and under these circumstances upgrading should be considered. (+info)
Demonstration of a left atrial input to the atrioventricular node in humans.
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BACKGROUND: During right atrial stimulation, the anterior and posterior approaches provide inputs to the atrioventricular (AV) node. The purpose of the present study was to determine how activation proceeding from the left atrium reaches the AV node. METHODS AND RESULTS: We studied AV nodal conduction during right and left atrial (coronary sinus) stimulation in 46 patients (27 women and 19 men; mean age, 46+/-4 years) who had structurally normal hearts. At an identical cycle length (600 ms), left atrial stimulation resulted in shorter A-H intervals than right atrial stimulation (73+/-3 ms versus 99+/-3 ms; P<0.05). In addition, atrial electrograms recorded close to the His bundle changed from near to far field potentials when stimulation was shifted to the left atrium. The A-H interval prolonged as the site of pacing was progressively moved from the distal to the proximal coronary sinus. During constant pacing from the distal coronary sinus, atrial activation close to the His bundle could be advanced by late extrastimuli delivered at the anterior and posterior approaches (up to 11+/-2 ms and 9+/-1 ms, respectively), without altering His bundle activation time. In contrast, late extrastimuli delivered at the inferoparaseptal mitral annulus advanced both the A and H electrograms in 19 of 20 patients, which is consistent with a left-sided input to the AV node. Right and left atrial stimulation resulted in similar AV nodal function. CONCLUSION: The mitral annulus provides a left atrial input to the human AV node. (+info)
Monitoring the progression of the atrial electrical remodeling in patients with paroxysmal atrial fibrillation.
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It is important to clarify how electrical remodeling develops in clinical cases of paroxysmal atrial fibrillation (PAF), because it has been suggested that this electrophysiological phenomenon promotes an increase in the frequency of PAF. In the present study, the f-f interval during PAF was analyzed from the ambulatory ECG recordings of 21 patients with PAF (total PAF duration >2/24 h with normal atrial size) to monitor the atrial electrophysiological changes. The patients were clinically followed-up for 6 months without any antiarrhythmic drugs. Before and after the follow-up period 24-h Holter monitoring was carried out and the duration of both the PAF and the f-f intervals during the PAF episode were evaluated. In selected cases, the atrial effective refractory period (ERP) was evaluated in an electrophysiologic study before and after the follow-up period. The total PAF duration was prolonged from 187+/-50 to 223+/-79 min (p=0.034) and the f-f interval was shortened from 0.14+/-0.03 to 0.12+/-0.02 ms (p=0.003). There was an inverse relationship between the changes in total PAF duration and f-f interval (p=0.027). The ERP was shortened from 214+/-15 to 194+/-5 ms (n=5, p=0.025) and there was a direct correlation between the changes in ERP and f-f interval (p=0.048). In clinical cases, the prolongation of the PAF was related to the shortening of the f-f interval during the PAF episodes and to the shortening of the atrial ERP. Electrical remodeling plays a role in promoting the development of the atrial fibrillation in patients with PAF. (+info)
Intercellular coupling in the atrioventricular node and other tissues of the rabbit heart.
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1. A fluorescent tracer dye, sodium fluorescein (mol.wt. 332), was used to assess the relative degree of intercellular coupling in various tissues of the rabbit heart. 2. Dye was injected intracellularly by micro-iontophoresis. Subsequent movement into contiguous cells was monitored by video microscopy. From these data the permeability of the intercellular boundaries was computed. 3. The values of boundary permeability were consistent with those expected from previous studies with tracers whose molecular weights bracketed that of fluorescein. 4. In the atrium, ventricle, Purkinje strands and His bundle, the relative magnitude of the boundary permeability correlated reasonably well with the relative profusity of gap junctional area on the intercalated disk, the latter estimated from published data. 5. The rate of passage of dye between N cells of the atrioventricular, AV, node was at least three orders of magnitude lower than between cells of the other tissues studied; this result is consistent with published reports indicating few gap junctions between cells within the region of slow conduction. 6. Quantitative considerations based on these data indicate that N cells may not be sufficiently well coupled to permit impulse propagation through the AV node by intercellular current flow, alone. (+info)