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At least 451 records · Page 25Linked to original sources
PubMed2000

Determination of refractory periods and conduction velocity during atrial fibrillation using atrial capture in dogs: direct assessment of the wavelength and its modulation by a sodium channel blocker, pilsicainide.

OBJECTIVES: The purposes of this study were to measure the atrial refractory period and the conduction velocity (CV) during atrial fibrillation (AF) and to explore the antiarrhythmic mechanism of a sodium channel blocker, pilsicainide, during AF. BACKGROUND: Sodium channel blockers not only decrease the CV, but also prolong the atrial refractory period, particularly during rapid excitation. Because these effects on the wavelength are counteractive and rate dependent, it is critical to measure these parameters during AF. METHODS: In eight dogs, after AF was induced under vagal stimulation, a single extra-stimulus was repeatedly introduced from the left atrium and its capture was statistically determined for each coupling interval. The local CV was also measured during constant capture of the fibrillating atrium by rapid pacing. The same procedure was repeated after pilsicainide administration. RESULTS: Pilsicainide significantly increased the mode of AF intervals from 81 +/- 10 to 107 +/- 16 ms (p < 0.01). While the CV was decreased from 0.9 +/- 0.1 to 0.7 +/- 0.1 m/s (p < 0.02), the effective refractory period during AF was increased from 69 +/- 11 ms to 99 +/- 17 ms (p < 0.01). As a result, the wavelength was significantly increased by pilsicainide from 6.6 +/- 0.9 to 7.6 +/- 1.2 cm (p < 0.05). CONCLUSIONS: During AF, whereas the sodium channel blocker pilsicainide decreases CV, it lengthens the wavelength by increasing the refractory period, an action that is likely to contribute to the drug's ability to terminate the arrhythmia. The direct measurement of refractoriness and CV during AF may provide new insights into the determinations of the arrhythmia and antiarrhythmic drug action.

Animals↗
PubMed2001

Attenuation of interatrial conduction using right atrial septal catheter ablation.

OBJECTIVES: We sought to characterize a method of attenuating interatrial conduction using radiofrequency ablated lesions applied to the right atrial septum. BACKGROUND: Interatrial conduction occurs in specific zones. Recent data suggest that interatrial conduction can be important in triggering and sustaining atrial fibrillation. Therefore, a method for attenuating interatrial conduction may have therapeutic value. METHODS: In 13 healthy pigs, interatrial conduction was evaluated before and after sequential ablation of the right atrial septum, targeting interatrial conduction zones. In six animals, zone 1 (crista terminalis and limbus) was ablated first, followed by ablation of zone 2 (fossa ovalis and coronary sinus ostium). In the other seven animals, the order of ablation was reversed. Electrophysiologic and pathologic findings were correlated. RESULTS: After ablation of zone 1, interatrial conduction was slowed, but there was no block. After ablation of zone 2, conduction was unchanged. After ablation of both zones, complete block was observed in four animals, and there was left atrial quiescence. In the remaining nine animals, incomplete block was observed, with marked conduction slowing or block during sinus rhythm and pacing. Ablation did not adversely affect atrioventricular node conduction, nor did it facilitate sustenance of an atrial arrhythmia. Pathologic analysis revealed that complete interatrial conduction block was associated with confluent ablation of both targeted zones. CONCLUSIONS: Catheter ablation of the right atrial septum attenuated interatrial conduction without disturbing atrioventricular conduction.

Animals↗
PubMed1988

Cardiac electrophysiology of the antiarrhythmic agent recainam (Wy-42,362) in anesthetized dogs: relation to plasma and myocardial concentrations.

The present study was undertaken to characterize the cardiac electrophysiologic effects of the investigational class I antiarrhythmic agent recainam (Wy-42,362) on the canine heart in situ, and to determine the possible relationship between these effects and the concentration of drug in plasma and myocardium. Cardiac conduction times and refractory periods were measured at a paced cycle length of 300 ms in open-chest anesthetized dogs by recording atrial, ventricular, and His bundle electrograms. Recainam was infused intravenously (as a loading + maintenance dose) at either (a) 7.5 mg/kg/20 min + 5 mg/kg/60 min (low-dose group) or (b) 15 mg/kg/20 min + 10 mg/kg/60 min (high-dose group). Samples of plasma and ventricular myocardium were removed at selected times for subsequent analysis. At the end of the maintenance infusion, low-dose recainam produced a plasma concentration of 4.1 +/- 0.5 micrograms/ml and significantly increased atrial conduction time only. Plasma levels with high-dose recainam reached 9.4 +/- 3.5 micrograms/ml at end infusion, and produced significant increases in all measured electrophysiologic parameters except ventricular refractory period. Myocardial levels of recainam were undetectable in the low-dose group, but increased linearly with plasma concentration in the high-dose group with a myocardium/plasma ratio of nearly 1:1. Changes in ventricular conduction time, H-V interval, atrial and ventricular refractory periods, and Wenckebach cycle length correlated significantly with recainam concentration in plasma. In addition, drug levels in the ventricle correlated with the observed changes in both ventricular conduction time and ventricular refractory period. The data suggest that recainam plasma levels may serve as a useful guide in monitoring electrophysiologic response to this agent.

Anesthesia↗
PubMed2004

P wave separation after atrial compartment operation for atrial fibrillation.

Surgically induced abnormalities in atrial conduction could result in unusual P wave changes. A 31-year-old woman underwent concomitant mitral valve surgery and atrial compartment operation for mitral stenosis and atrial fibrillation (AF). After operation, the AF was successfully converted to sinus rhythm, whereas an unusual electrocardiogram (ECG) with a discrete negative deflection before the T wave in V1 was noted. Electrophysiological study showed a marked conduction delay from the high right atrium (HRA) to the right atrial appendage (RAA) compartment, which resulted in a separation of P waves. The P wave preceding the QRS complex represented the activation of sinus node and the left atrial compartments, and the P at the vicinity of T wave represented the activation of RAA compartment. The conduction from HRA to RAA was worsened on HRA pacing at a faster rate, and improved after isoproterenol infusion. This report demonstrated that conduction across a surgically created isthmus in the atrium could be severely impaired and result in unusual P wave separation.

Adult↗
PubMed1987

Periodic occurrence of premature atrial beats inducing alternation during supraventricular tachycardia in a case of pre-excitation syndrome.

During orthodromic atrioventricular reciprocating tachycardia (AVRT) in a patient with pre-excitation syndrome, 2:1 to 9:1 cycle length alternation was observed. The alternation was induced by the development of premature atrial beats (PABs) recurring in every three to ten AVRT beats. An electrophysiologic study revealed that: 1) PAB developed periodically during atrial/ventricular tachy-pacing (at a rate of 140-170 times/min), during atrial/ventricular extrastimulus study, and during electrically induced AVRT. 2) The PAB had a constant coupling interval to the preceding atrial complex, probably an atrial echo beat, and was associated with no His bundle or ventricular deflection. 3) An intensive search failed to reveal any third ventriculo-atrial conduction pathway. The PABs may have been induced by intra-atrial reentry or by triggered activity in the atrium.

Anti-Arrhythmia Agents↗
PubMed1982

[Effect of etmozin on the atrioventricular conduction system function of the heart in paroxysmal subventricular tachycardia].

With the aid of intracavitary electrophysiological investigation in hospital the influence of ethmosin, an antiarrhythmic agent, on the function of atrio-ventricular conducting system was studied in 52 patients with paroxysmal supraventricular tachicardias. It was established that the drug depresses significantly the electrophysiological values of Kent's bundle, the His-Purkinje system and atrioventricular node (mainly in the retrograde conduction): and also prolongs considerably the time of the intra-atrial conduction. Ethmosin exerts practically no influence on the refractory periods of the atria and on the function of the atrioventricular node for the anterograde conduction. These data suggest that ethmosin may be an effective antiarrhythmic agent in treating patients with certain forms of paroxysmal disorders of the cardiac rhythm in whom the atrioventricular node and Kent bundle are involved in the re-entry.

Adolescent↗
PubMed1976

Intraatrial conduction disturbances: vectorcardiographic patterns.

Frank P loop vectorcardiograms were recorded in 30 normal subjects and in 40 patients who had intraatrial conduction disturbances alone or in association with cardiac disease. High magnification of the P loop (0.1 mv = 3 cm) permitted accurate measurement of the P loop duration, magnitude and direction. High-frequency recordings allowed optimal evaluation of the notches, bites and conduction delays in the PsE loop. Four vectorcardiographic patterns have been selected as counterparts of the four types of enlarged P waves seen in electrocardiograms of patients with atrial conduction disturbances. When intraatrial conduction disturbances coexisted with left atrial enlargment, the PsE loop was larger and smoother. The role of partial or complete block in the specific internodal or interatrial pathways is discussed. High magnification, high-frequency vectorcardiography of the P loop seems to be the best available method for determing a specific pattern of intraatrial conduction disturbance.

Adult↗
PubMed1975

[Examination of sinoatrial conduction through premature atrial stimuli via the esophagus].

Sinoatrial (SA) conduction can be tested in man by premature atrial stimuli. The difference between the post-extrasystolic pause and the spontaneous sinus cycle is a sign of the sinoatrial delay. Extern atrial stimuli provoked over the esophagus showed analogous results to intracardiac tests. The sinoatrial conduction time estimated by the esophagus method is about 20 ms higher. In 30 normal persons it was 95 +/- 36 ms (x +/- 2 SX). 7 patients with sick sinus syndrome showed aberrations as in the intracardiac test. Different types of sinoatrial block should be distinguished. Type I measured by the esophagus method had a "SAE time" over 130 ms. Type II always had compensating postextrasystolic pauses due to higher SA delay. Type III of other authors could not be observed; there are doubts about the rightness of this type. In 2 patients SA blocks over several sinus cysles could be induced by premature stimuli. This feature osberved for the first time has been declared as type IV. In 28 patients with different diseases of the heart type I could be found 12 times and type II 6 times; SA block was not known previously. The calculation of the SA time by atrial stimuli via the esophagus offers a riskless and simple method for the further differential diagnosis of disturbances of the cardiac rhythm.

Adult↗
PubMed1993

Vagal-mediated atrial premature beats: a computer model.

A computer algorithm is described that used experimental data to model the arrhythmogenic interaction of phasic vagal stimuli and atrial ectopic pacemakers. The model consisted of a dominant sinus node and a single ectopic pacemaker center separated by conducting atrial tissue. Its primary operation was to predict the timing and incidence of atrial premature beats resulting from transient escape of ectopic automatic impulses when vagal-induced entrance block of the sinus impulse was simulated near the ectopic focus. These predictions were based on a series of experimentally derived phase-response and corrected recovery time curves, describing the modulation of ectopic pacemaker periodicity by vagal input and overdrive suppression, respectively. Depending on the combination of curves tested, the model predicted premature beats to develop only with critically timed vagal stimuli. The coupling intervals of vagal-induced premature beats were > 300 ms and varied as a function of vagal timing and sinus cycle length. The model suggests therefore that phasic vagal stimuli within the atrium may transiently protect ectopic pacemaker foci from conducted sinus impulses and mediate the genesis of atrial extrasystoles with long coupling intervals.

Animals↗
PubMedDate not supplied

Antiarrhythmic effects of flecainide against canine ventricular arrhythmias induced by two-stage coronary ligation and halothane-epinephrine.

We studied the electrophysiologic effects of flecainide on noninfarcted and infarcted dog hearts and in dogs anesthetized with halothane and administered intravenous epinephrine. Flecainide demonstrated no effect on atrial conduction times, but significantly (p less than 0.05) increased ventricular conduction times in noninfarcted, infarcted, and halothane-epinephrine-exposed dog hearts. Atrial and ventricular effective refractory periods (ERPs) were significantly (p less than 0.05) increased by flecainide. The increase in ERP was more pronounced in infarcted than in noninfarcted dog hearts. Flecainide significantly (p less than 0.05) decreased the echo zone for two or more repetitive ventricular responses in infarcted dog hearts and eliminated all ventricular arrhythmias observed at 48 h after coronary artery ligation. The dose of epinephrine required to induce ventricular arrhythmias in dogs anesthetized with halothane was significantly increased (p less than 0.05) by flecainide. Acute intravenous administration of flecainide to dogs with infarcted hearts produced sinus arrest, transient third-degree heart block, inability to pace, right bundle branch block, and torsade des pointes. Our results provide evidence that flecainide produces its antiarrhythmic effects by increased ventricular ERP and ventricular conduction time. Caution is advised when administering flecainide to patients with previous history of myocardial infarction.

Animals↗
PubMed1975

[Atrioventricular conduction in the Lown-Ganong-Levine syndrome].

In 18 patients with LGL-syndrome His bundle electrography and atrial pacing were performed. In all cases the atrial conduction time was normal, the H-V interval within the lower limit (36 msec). The A-H interval was significantly shortened (58 msec). During rapid atrial pacing four different patterns of reaction could be distinguished: 1) A-H interval unchanged (1 case). 2) Sudden prolongation of the A-H interval at a critical rate (4 cases). 3) Continuous prolongation of the A-H time according to the driving frequency (9 cases). 4) Marked delay and block (4 cases). Verapamil had only little or no effect on the A-H interval in these patients. The results indicate, that only in a few cases with LGL-syndrome the shortened A-H time is due to a James bundle bypassing completely the A-V node.

Adolescent↗
PubMed2006

SCN5A mutation associated with cardiac conduction defect and atrial arrhythmias.

INTRODUCTION: We aimed at identifying the molecular defect underlying the clinical phenotype of a Finnish family with a cardiac conduction defect and atrial arrhythmias. METHODS AND RESULTS: A large Finnish family was clinically evaluated (ECG, 24-hour ambulatory ECG, echocardiography). We performed linkage analysis with markers flanking the SCN5A gene and subsequently sequenced the SCN5A gene. Five family members had atrial arrhythmias and intracardiac conduction defects, and due to bradycardia needed a pacemaker when adolescents. No heart failure or sudden cardiac death was observed. Left ventricle dilatation was seen in one individual and three individuals had a slightly enlarged right ventricle. Premature death due to stroke occurred in one subject during the study, and two other members had suffered from stroke at young age. Linkage analysis favored the role of the SCN5A gene in disease pathogenesis, and direct sequencing disclosed D1275N mutation. This alteration was present not only in all six affected individuals, but also in two young individuals lacking clinical symptoms. CONCLUSIONS: Cardiac conduction defect and atrial arrhythmias in a large Finnish family appear to result from the SCN5A D1275N mutation. Although no sudden cardiac death was recorded in the family, at least three affected members had encountered brain infarction at the age of 30 or younger.

Atrial Fibrillation↗
PubMed2002

Use of global atrial fibrillation organization to optimize the success of burst pace termination.

OBJECTIVES: The purpose of this study was to determine if burst atrial pacing would have an effect on terminating atrial fibrillation. BACKGROUND: We hypothesized that frequency domain analysis of a filtered wide bipolar atrial electrogram describes the global organization of atrial fibrillation (AF) and should vary over time. Timing burst pacing to periods of high organization of AF should promote regional atrial conduction block and terminate AF. METHODS: Nine dogs were conditioned with rapid atrial pacing for 48 h. Electrogram recordings were made from a wide right atrium (RA) to left atrium (LA) bipole and digitally filtered. A fast-Fourier transform was performed every 0.5 s on a sliding 2-s window, and the organization index (OI) was calculated as a ratio of the area of the first four harmonic peaks to the total power of the spectrum. Organization indexes >0.5 indicated more organized AF activity. Right atrium and LA burst pacing (burst) (cycle length 50 ms, 9.9 ms, 9.9 mA, 1 to 4 s) was performed through decapolar catheters. Burst was either random or synchronized to OI >0.5. RESULTS: Burst termination was attempted 1,814 times (889 OI sync, 925 random) and succeeded in seven of nine dogs. Burst had an overall success rate of 11.1% versus 6.3% for random (p < 0.0003). Biatrial pacing had the highest efficacy for terminating AF, with a success rate of 16.5% for OI sync versus 8.2% for random (p < 0.0001). CONCLUSIONS: Timing the delivery of the burst pace when the OI is >0.5 increases the efficacy of burst pace termination of AF. Biatrial pacing is more effective than either RA or LA pacing alone.

Animals↗
PubMed2003

The results of pacing trials for the prevention and termination of atrial tachyarrhythmias: is there any evidence of therapeutic breakthrough?

Atrial fibrillation (AF) is now recognized as the most prevalent sustained cardiac arrhythmia and it is associated with considerable mortality and morbidity. The demand for effective therapeutic strategies for AF has always been high and is anticipated to further increase. Anticoagulation and pharmacologic antiarrhythmic therapy or radiofrequency catheter ablation remain the mainstay of treatment for AF. Among the wide range of nonpharmacologic options which are presently being investigated, only ablation in or around the pulmonary veins and the surgical maze procedure have been shown to accomplish the aim of the curative treatment of the arrhythmia. Preventative atrial pacing and antitachycardia pacing may offer an attractive alternative option for the management of AF by either eliminating the triggers and/or by modifying the substrate of the arrhythmia. The results of several recent trials have shown a significant increase in the time to first AF recurrence, a decrease in atrial conduction time, and a trend towards reduction in AF burden, suggesting that atrial pacing may prevent AF due to improved synchronization of atrial depolarization. The recognition of potential triggers of AF, such as atrial premature complexes, short-long sequence, and bradycardia, has encouraged the development of novel atrial pacing algorithms designed to prevent the initiation of the arrhythmia on an individual basis. Observations of AF often starting with regular atrial activity consistent with atrial tachycardia have supported the hypothesis that early antitachycardia pacing may prevent progression to AF. The concept of "hybrid therapy" based on the combination of several different therapeutic strategies suggests that antitachycardia pacing therapy, integrated with an atrial defibrillator and preventative atrial pacing modes, may act synergistically to prevent AF. Dual chamber cardioverter-defibrillators with capacity to prevent and interrupt AF may offer more comprehensive and successful treatment for patients with advanced heart disease, frequent paroxysms of AF, and the risk of proarrhythmia.

Algorithms↗
PubMed1996

Unravelling the electrical mysteries of atrial fibrillation.

Animal experiments have confirmed that a short but variable excitable gap is present during induced atrial fibrillation. The existence of this gap allows atrial fibrillation to be locally captured by rapid pacing. An area of up to 4 cm in diameter can be activated by uniform wave fronts propagating away from the site of stimulation, although the size of this area may be limited by intra-atrial conduction block or by collision with fibrillation waves. Rapid pacing can accelerate atrial fibrillation by inducing local re-entry circuits with a cycle length shorter than the pacing interval. During pacing-induced atrial fibrillation in patients undergoing surgery for Wolff-Parkinson-White syndrome, three types of atrial activation have been identified, which vary in their degree of complexity and in the length of their fibrillation intervals. It appears that the spectrum of varying cycle lengths during atrial fibrillation might be explained by a mixture of different sorts of atrial re-entry patterns, comprising purely functional intra-atrial re-entry, random re-entry, anatomical re-entry, and nodal re-entry.

Animals↗
PubMed1980

Impulses of S-A block area.

Micro-electrode studies in 13 excised rabbit preparations were done to determine the site of S-A block. Previously the fastest S-A conduction occurred in the area connecting the sinus node and the right branch of the crista terminalis. When a small cut was made in this area, 5 of the 13 hearts showed the first degree S-A block. Two hearts exhibited the second degree S-A block of the Wenckebach phenomenon and 3 showed the third degree block after cutting the same area. All blocks were transient and, within 1 hour after cutting, they were of the first degree. When the caval area was subsequently cut in these 10 hearts, all of them developed the complete S-A block. Three other hearts showed the complete S-A block by cutting only the connectable area of the sinus node with the right branch of the crista terminalis. The first cutting of the caval area surrounding the sinus node excepting the above mentioned connection did not change the S-A conduction time. Conclusions from these experiments reveal that the dominant sino-atrial conduction occurs through the connectable area of the sinus node with the right branch of the crista terminalis. Functional impairment to this region is essential and necessary to the development of any degree of S-A block.

Animals↗
PubMedDate not supplied

[The influence of frequency and blockade of the autonomic nervous system on the functional behaviour of the human conduction system. Part A: Conduction velocity (author's transl)].

32 patients were studied by His-bundle recordings to examine the extent to which frequency and autonomic nervous system influence the conduction velocity in the subdivisions (atrium, AV-node, His-Purkinje system) of the normal PR-interval. The measurements were performed during sinus rhythm and three electrically induced atrial frequencies before and after intravenous administration of 1 mg Atropine (15 patients) and 0.4 mg Visken (17 patients). In influencing the atrial conduction velocity frequency dominates the blockade of both components of the autonomic nervous system. Increase in frequency lengthens the intraatrial conduction time. Blockade of parasympathicus and sympathicus does not significantly influence the changes in intraatrial conduction velocity induced by increase of frequency. Patients with prolonged intraatrial conduction respond in the same way to cycle length shortening and blockade of the autonomic tone as patients with normal conduction. The results are discussed with respect to acetylcholine and catecholamine influence on the electrophysiological properties of the atrial myocardium. The AV-node is the part of the conduction system most sensitive to the influence of both cycle length shortening and blockade of the autonomic nervous system. Artificially induced cycle length shortening prolongs the intranodal conduction time to a different individual level for each patient. Blockade of the parasympathicus not only shortens this interval but also reduces the steepness of the AH-time induced by atrial pacing. Blockade of the sympathicus has the opposite effect. The most likely explanation for these results is the abolishing of the functional dissociation within the AV-node by blocking the autonomic influence on this structure. The conduction velocity in the His-Purkinje system is influenced neither by atrial pacing nor by blockade of both components of the autonomic nervous system.

Adrenergic beta-Antagonists↗
PubMed1987

[Study of electrophysiological effects of betaxolol].

Betaxolol is a new cardioselective beta-blocker without any intrinsic sympathomimetic activity. A study of the cardiac electrophysiological effects of this molecule used intravenously was carried out in 20 patients. Betaxolol prolongs the sinus cycle (+ 25%, p 0.001), prolongs the sino-atrial conduction time (+ 20.1%) and atrio-hissian conduction time (+ 10.8%, p 0.001), and prolongs the refractory periods at all levels: atrial (+ 8%), nodal (+ 20.8%), right ventricular (+ 4.3%). These findings confirm the electrophysiological characteristic effects of the beta-blockers series; however, the moderate but significant increase of the refractory ventricular period, seems to provide this molecule with a certain degree of originality in this therapeutic class.

Adrenergic beta-Antagonists↗