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PubMed1990

Vasoactive intestinal polypeptide facilitates atrioventricular nodal conduction and shortens atrial and ventricular refractory periods in conscious and anesthetized dogs.

Our study was designed to determine the cardiac electrophysiological influence of vasoactive intestinal polypeptide (VIP) in conscious dogs. Dogs (n = 8) were chronically instrumented with arterial and venous catheters, cervical vagal cooling coils, and right atrial and right ventricular bipolar epicardial pacing and recording electrodes. After autonomic blockade (10 mg/kg i.v. hexamethonium, 0.11 mg/kg i.v. atropine, and vagal cold blockade), VIP (50 and 100 pmol/kg/min i.v.) or isoproterenol (ISO) (250 and 500 pmol/kg/min i.v.) increased heart rate (maximum increases: VIP, 81.1 +/- 4.2 beats/min; ISO, 61.3 +/- 8.5 beats/min), decreased the atrial-ventricular interval (during constant atrial pacing) (VIP, -41.9 +/- 6.3 msec; ISO, -34.6 +/- 7.4 msec), shortened the atrial effective refractory period (VIP, -24.4 +/- 2.1 msec; ISO, -30.6 +/- 4.4 msec) and ventricular effective refractory period (VIP, -4.2 +/- 0.7 msec; ISO, -10.0 +/- 2.4 msec), and decreased mean arterial pressure (VIP, -51.9 +/- 4.0 mm Hg; ISO, -26.1 +/- 2.4 mm Hg). beta-Adrenergic blockade with propranolol (1 mg/kg i.v.) eliminated the positive chronotropic and atrioventricular nodal dromotropic responses to bolus doses of ISO (30, 100, 300, and 1,000 pmol/kg i.v.) but did not affect the responses to VIP (10, 30, 100, and 300 pmol/kg i.v.). Comparable blood pressure decreases produced by sodium nitroprusside caused only minimal changes in heart rate, atrial-ventricular conduction times, and atrial and ventricular refractory periods. In three additional anesthetized dogs, after vagotomy and beta-adrenergic blockade (1 mg/kg i.v. propranolol), VIP (100 pmol/kg/min i.v.) shortened the atrial-His interval but did not alter intra-atrial, intraventricular, or His-Purkinje conduction. Our findings combined with the demonstration by others of VIP-immunoreactive nerves innervating canine sinus nodal cells, atrioventricular nodal cells, and atrial and ventricular myocardial cells suggest that endogenous VIP may directly alter the electrical properties of the heart.

Anesthesia↗
PubMedDate not supplied

[Evaluation of the sinoauricular conduction time: comparison of the recording of the sinus potential and Narula's method].

The sino-atrial conduction time, measured by Narula's method (SACTN) is compared to the direct sino-atrial conduction time measured by recording the sinus potential (SACTD) in 55 patients, 20 with normal sinus function and 35 with sinus dysfunction. In the absence of sinus dysfunction, SACTN and SACTD are not significantly different and a significant but mediocre correlation (r = 0.57) is observed between the two parameters. Major discordances between the two methods are seen in 4 patients. In cases with sinus dysfunction, there was no correlation between SACTD and SACTN; SACTN is close to SACTD in 12 patients, but much shorter in 11 patients and much longer in 10 patients. These discordances raise the problem of the penetration of the sinus node by the extrastimulus in Narula's method. This method does not seem capable of giving a reliable evaluation of the duration of sino-atrial conduction.

Adolescent↗
PubMed2006

Clinical and electrophysiological characteristics of binodal disease.

BACKGROUND: Although coexistence of atrioventricular conduction disturbances with sick sinus syndrome (SSS), so-called binodal disease (BND), is a frequently encountered disorder, its clinical significance and electrophysiological characteristics remain unknown. METHODS AND RESULTS: One hundred and seven patients with SSS were divided into BND (n=30) and N-BND groups (n=77). Sinus cycle length, sinus node recovery time (SRT), sino-atrial conduction time (SACT), the number of isolated sinus node electrograms, atrio-His (AH) interval, His-ventricular (HV) interval, intra-atrial conduction time (PA intervals) and QRS width were measured. In addition, the prevalence of bundle-branch block was obtained. The parameters of sino-atrial and intra-atrial conduction were significantly longer in the BND group: SRT (5,070+/-2,628 vs 3,122+/-1,856 ms, p<0.05), SACT (115+/-30 vs 87+/-21 ms, p<0.05), PA intervals (56+/-13 vs 41+/-8 ms, p<0.05). The BND group was more likely to have atrial fibrillation than the N-BND group (83.3% vs 53.2%, p<0.01). HV interval, QRS width and the prevalence of associated bundle-branch block did not differ between the 2 groups. CONCLUSION: BND patients not only had sino-atrial and atrioventricular node dysfunction, but also widespread atrial conduction disturbances. Thus, in the clinical setting BND should be categorized as severe SSS.

Aged↗
PubMed1998

Mechanisms of pharmacologic cardioversion of atrial fibrillation by Class I drugs.

INTRODUCTION: We recently developed a goat model of sustained atrial fibrillation (AF) in which repetitive induction of AF by burst pacing shortened the atrial effective refractory period (AERP) (electrophysiologic remodeling) and progressively prolonged the paroxysms of AF to become sustained (24 hours) within 1 to 3 weeks (atrial fibrillation begets atrial fibrillation). The aim of the present study was to study the effect of Class I drugs in this animal model of chronic AF. METHODS AND RESULTS: The effects of hydroquinidine (HQ) on seven chronically fibrillating goats and of flecainide (Fl) on nine goats were studied. Both drugs were infused intravenously until sustained AF was cardioverted or adverse drug effects occurred. HQ and Fl restored sinus rhythm in 86% and 67% of the cases. Adverse drug effects occurred in 14% and 56%, respectively. The average atrial cycle length of AF (AFCL) was prolonged to a different degree. Just before restoration of sinus rhythm, the two drugs had increased AFCL by 72% and 50%. The duration of the QRS complex was prolonged 17% by HQ and 50% by Fl. The RR interval was not affected by HQ and was prolonged slightly by Fl. Directly after restoration of sinus rhythm, the AERP during pacing with an interval of 400 msec was 92 +/- 29 (HQ) and 66 +/- 10 msec (Fl) (control value: 149 +/- 10 msec). Intra-atrial conduction velocity was 83 +/- 7 and 86 +/- 11 cm/sec (control value: 116 +/- 10 cm/sec). Although both drugs were effective in terminating AF, after cardioversion the atrial vulnerability was still very high and a single premature stimulus reinduced AF in 100% of the animals. As a result of the short AERP by the AF-induced remodeling and the depressed intra-atrial conduction by the Class I drugs, directly after cardioversion the atrial wavelength was abnormally short (between 5.7 and 7.5 cm). This explains the still high atrial vulnerability to AF directly after cardioversion by Class I drugs. Surprisingly, the prolongation of AFCL by either Class I drug was not due to lengthening of the functional refractory period but rather to a widening of the excitable gap during AF. CONCLUSION: In a goat model of chronic AF, infusion of Class IA and Class IC drugs restored sinus rhythm in 67% to 86% of the cases. However, due to the short AERP and the depressed intra-atrial conduction directly after cardioversion, the atrial vulnerability was still very high and a premature beat easily reinduced AF.

Animals↗
PubMed2002

Supervulnerable phase immediately after termination of atrial fibrillation.

INTRODUCTION: Recent studies with the implantable atrial cardioverter have shown that atrial fibrillation (AF) recurs almost immediately after successful cardioversion in about 27% of cases. In the present study, we determined the electrophysiologic properties of the caprine atrium immediately after spontaneous termination of AF both before and after 48 hours of AF-induced electrical remodeling. METHODS AND RESULTS: In eight goats, atrial effective refractory period (AERP), intra-atrial conduction velocity, and atrial wavelength were measured during sinus rhythm both before (t = 0) and after 48 hours (t = 48) of electrically maintained AF (baseline). After baseline, a 5-minute paroxysm of AF was induced, during which the refractory period (RPAF) was determined. AERP, conduction velocity, and atrial wavelength also were measured immediately after spontaneous restoration of sinus rhythm (post-AF values). Both in normal and remodeled atria, immediately after AF, AERP and conduction velocity were markedly decreased compared with baseline (P < 0.01). In normal atria, post-AF AERP (107+/-14 msec) gradually prolonged from its AF value (114+/-17 msec) to its baseline value (138+/-13 msec). Conduction velocity decreased from 130+/-9 cm/sec to 117+/-9 cm/sec. After 48 hours of AF, AERP had shortened to 74+/-8 msec. RPAF was 89+/-9 msec. Surprisingly, immediately after termination of AF, AERP shortened further to 58+/-6 msec (P < 0.01). Post-AF conduction velocity decreased from 136+/-11 cm/sec to 122+/-10 cm/sec (P < 0.01). As a result, the post-AF atrial wavelength became as short as 7.1+/-1 cm. These changes were transient, and all parameters gradually returned to baseline within 1 to 2 minutes after conversion of AF. CONCLUSION: Due to a combined decrease in AERP and conduction velocity, marked shortening of the atrial wavelength occurs during the first minutes after conversion of AF. In electrically remodeled atria, this results in a transient ultrashort value of AERP (<60 msec) and atrial wavelength (7.1 cm). These observations imply a highly vulnerable substrate for reentry immediately after termination of AF. During this supervulnerable phase, both early and later premature beats reinitiated immediate recurrences of AF.

Animals↗
PubMed1999

Reversal of atrial electrical remodeling following cardioversion of long-standing atrial fibrillation in man.

BACKGROUND: In animal studies, atrial fibrillation has been shown to shorten the atrial refractory period and impair its rate adaptation. However, little is known about the effects of chronic atrial fibrillation on atrial electrophysiology and its recovery course in humans. METHODS AND RESULTS: Nineteen patients, mean age 64 +/- 14 years, with chronic atrial fibrillation of more than six months duration were included in this study. All of them were successfully converted to sinus rhythm with an external defibrillator. Atrial effective refractory periods at right atrial appendage and distal coronary sinus were determined with five pacing cycle lengths (300, 400, 500, 600 and 700 ms) at 30 min after cardioversion and once a day for four days. The atrial conduction properties, including P wave duration of surface ECG, and right and left atrial conduction times, were also measured at the same time interval. Twenty age-matched patients without a history of atrial tachyarrhythmia were evaluated as controls. In comparison with controls, chronic atrial fibrillation significantly shortened the atrial effective refractory period, impaired its rate adaptation response, especially at distal coronary sinus, and depressed the conduction properties of atria. The atrial conduction properties did not change during the four-day follow-up period; however, the atrial effective refractory period was gradually prolonged and its rate adaptation response improved after restoration of sinus rhythm. CONCLUSIONS: In humans, chronic atrial fibrillation significantly shortened the atrial effective refractory period, and impaired its rate adaptation response. Restoration and maintenance of sinus rhythm could reverse these electrophysiological changes.

Aged↗
PubMed1989

Electrophysiologic spectrum of concealed intranodal conduction during atrial rate acceleration in a model of 2:1 atrioventricular block.

Concealed anterograde penetration of the atrioventricular (AV) node has been used to explain a wide variety of electrocardiographic findings. The effects of atrial rate acceleration on this phenomenon remain undefined. To examine the dynamic interrelations between conducted and nonconducted beats at different atrial rates, a unique atrial pacing protocol of functional 2:1 AV block was used in 10 patients. The pacing protocol involved abrupt transitions from 2:1 to 1:1 AV conduction and enabled quantification of conduction delay produced by nonpropagated impulses over extremes of atrial rate. Stable 2:1 AV conduction was maintained over a mean range of atrial paced cycle lengths of 289 +/- 29.6 to 223 +/- 33.0 msec, respectively. The mean AV conduction time during 2:1 and corresponding 1:1 drives at the longest atrial paced rates were 169 +/- 33.5 and 136.5 +/- 26.9 msec, respectively--revealing a significant effect of nonpropagated impulses on subsequent conduction. Surprisingly, at the shortest atrial paced rates, the mean AV conduction times were 191.5 +/- 31.8 and 161.0 +/- 23.3 msec, respectively. The lack of significant changes in conduction time between 2:1 and 1:1 drives at the extremes of atrial rate (32.5 vs. 30 msec, p = NS) suggests that the effect of concealed conduction is "fixed" and independent of rate. Clinical implications and postulated electrophysiologic mechanisms are discussed.

Adult↗
PubMedDate not supplied

[Actions of chlorpheniramine and its isomers on the auricular fibers of the mammalian heart].

The effects of the antihistaminic agent, chlorpheniramine and its optical isomers, were studied on the transmembrane potentials of specialized atrial conducting tissue and ordinary auricular muscle fibers. On atrial myocardium fibers, both isomers increase the duration of the action potential to a different degree and they also reduce the maximum rate of rise of phase O or dV/dt. In specialized conducting atrial tissue, the levo isomer increase the duration of the action potential in a larger proportion than the dextro compound. This occurs at the expense of the repolarization process. The l-compound produces only minimal changes in the dV/dt. The effects observed on both types of atrial tissues leads us to conclude: 1) Either type of tissue responds differently to each optical isomer of chlorpheniramine; 2) the results confirm the participation of specialized conduction pathways in atrial flutter; 3) the levo isomer may be considered as a possible candidate for clinical trial in patients with atrial flutter.

Animals↗
PubMed1995

Intermittent preexcitation and mesothelioma of the atrioventricular node: a hitherto undescribed entity.

This is the first documented case of spontaneous intermittent preexcitation associated with mesothelioma of the atrioventricular (AV) node. A 66-year-old male with recurrent atrial arrhythmias, palpitations, heart failure, and marked intra-atrial conduction defect that required a pacemaker died during sleep. Electrophysiologic study revealed left free-wall bypass tract with marked intra-atrial conduction defect and prolonged conduction across the bypass tract. With atrial pacing, high degrees of block were noted in the bypass tract. Serial section of the conduction system and both AV rims revealed two left posterior and lateral bypass pathways with patchy areas of fibrosis. A large mesothelioma (benign AV nodal tumor) almost completely replaced the AV node. In addition, there was marked fatty infiltration of the atria. In summary: (1) the intermittent preexcitation with prolonged conduction across the bypass tract and block with atrial pacing were probably related to the incomplete patchy degenerative changes in the bypass tract, and/or almost complete replacement of the AV node by the tumor; (2) the intra-atrial conduction defect was probably related to the replacement of the AV node by mesothelioma and/or the fatty infiltration of the atria; and (3) the paroxysmal atrial arrhythmias probably reflect the marked atrial pathology.

Aged↗
PubMed2004

Concurrent multiple left atrial focal activations with fibrillatory conduction and right atrial focal or reentrant activation as the mechanism in atrial fibrillation.

OBJECTIVE: We examined the atrial activation during atrial fibrillation to validate the rationale behind simplified surgical procedures. METHODS: Intraoperative mapping of the entire atrial epicardium was performed in 21 patients with permanent atrial fibrillation and mitral valve disease using a 256-channel, 3-dimensional dynamic mapping system. RESULTS: Concurrent multiple repetitive activations arose from the posterior left atrium adjacent to the pulmonary veins or the left atrial appendage in all patients. The fastest activation propagated toward the right atrium conducting through Bachmann's bundle, leaving the other activations confined to a small atrial region. As the activation propagated toward the right atrium, there was a progressive conduction delay or block in the pathway. As a result, the activation in the right atrium desynchronized with the left atrial activation and became irregular and complex. The average cycle length measured at the right atrial appendage was significantly longer than that at the left atrial foci (206 +/- 32 milliseconds vs 175 +/- 23 milliseconds, P <.001). In addition to the passive activation, a focal activation and reentrant activation were also observed in the right atrium in 5 and 6 patients, respectively. The number of wave fronts in the right atrium was significantly greater than that in the left atrium (2.9 +/- 0.8 vs 0.6 +/- 0.7, P <.001). CONCLUSIONS: Multiple left atrial focal activations with fibrillatory conduction and right atrial focal or reentrant activations are the mechanism in permanent atrial fibrillation associated with mitral valve disease. Intraoperative mapping would facilitate the indication for simplified procedures confined to the left atrium or the pulmonary veins.

Atrial Fibrillation↗
PubMed1976

Sinoventricular conduction in atrial standstill.

Sinoventricular rhythm implies preserved sinus node function with conduction of impulses to the A-V junction without generalized atrial excitation. Impulse propagation in such cases is presumably via specialized internodal tracts. In this present case, synchronized but localized activation from an area of the right atrium preceded each QRS, without generalized atrial depolarization. These recordings are offered as further evidence for the clinical occurrence of sinoventricular rhythm in humans.

Aged↗
PubMed2004

Age- and sex-related atrial electrophysiologic and structural changes.

Age and gender dependence of the 3 major variables--left atrial (LA) dimension, effective refractory period (ERP), and atrial conduction--that govern the development of atrial fibrillation (AF) were examined in 76 women and 39 men without structural heart disease. A significant positive correlation was found between age and LA dimension, mainly because of a strongly positive correlation in women not taking hormone replacement therapy but not in women on hormone replacement therapy. Men had a significantly greater average LA dimension than women. Neither ERP nor atrial conduction estimated by normalized P-wave duration demonstrated any significant correlation with either age or gender. It was concluded that LA size is greater in the elderly and in men, which may increase their risk for AF.

Adult↗
PubMed2001

Lengthening of intraatrial conduction time in atrial fibrillation and its relation with early recurrence of atrial fibrillation.

Intraatrial conduction delay in atrial fibrillation (AF) that is considered a component of atrial electrical remodeling has been demonstrated previously in experimental models and it is considered an important factor for the induction or stabilization of AF. However, it is not known if this phenomenon exists in human AF. The present study aimed to compare intraatrial conduction time (IACT) in patients with chronic atrial fibrillation who were converted to sinus rhythm and a matched control group, and to investigate its relation with early AF recurrence. Seventeen patients with chronic AF (mean duration of 20.71+/-16.35 months) were enrolled in the study (7 males, 10 females, 63+/-8 years). An age and sex matched control group (n=12) consisted of patients with sinus rhythm who underwent electrophysiological study (EPS). None of the patients were on any antiarrhythmic treatment during the procedures. Cardioversion was performed via external DC cardioversion. Eight patients in the control group were delivered a DC shock because of induced ventricular tachycardia during EPS. IACT was defined as the interval between the onset of P wave surface ECG and the beginning of A wave at high right atrium (IACT 1) and low right atrium (IACT 2). Additionally, the interval between A wave at high right atrium and low right atrium was measured (IACT 3). Patient characteristics such as age, sex and echocardiographic variables were not different between the AF group and the control group. Heart rate after cardioversion was found to be similar between the two groups. Total delivered energy was significantly higher in the AF group than in the control group (464.47+/-165.82 joules vs. 315.00+/-27.77 joules, p<0.001). IACT 1 (15.30+/-7.61 msec vs 8.50+/-5.29 msec, p<0.02 ), IACT 2 (45.25+/-836 msec vs 26.44+/-10.45 msec, p<0.001) and IACT 3 (26.9+/-8.26 msec vs. 18.67+/-10.05, p<0.05) significantly lengthened in the AF group after maintenance of sinus rhythm compared to the control group. There were 6 early AF recurrences during the 1 week follow-up period. Multivariate analysis, revealed IACT 2 and IACT 3 were significantly different between the control group, the patient with recurred AF and the patients with maintained sinus rhythm. Post-hoc analysis revealed that IACT 2 and IACT 3 significantly lengthened in the patients with recurred AF compared to both the control group and patients with maintained sinus rhythm. On the other hand, only IACT 2 patients with maintained sinus rhythm were found to be higher than those of the control group. The present study indicated that intraatrial conduction was disturbed in patients with AF, a finding which is consistent with those of previous experimental studies. Additionally, such a phenomenon may be a risk factor for the early recurrence of AF after cardioversion to sinus rhythm.

Atrial Fibrillation↗
PubMed1991

Electrophysiologic evaluation of cardiovascular agents in the isolated intact rabbit heart.

A modification of the Langendorff perfused rabbit heart is described. This model can be used to perform electrophysiologic studies in the isolated heart and is ideally suited for acute pharmacologic evaluation. His bundle electrograms were measured with a plunge electrode and allowed atrioventricular (AV) nodal physiology to be directly and precisely evaluated. Atrial conduction and refractoriness, atrioventricular node conduction and refractoriness, His-Purkinje conduction, and ventricular conduction and refractoriness could be accurately measured. Verapamil had a depressant effect on AV nodal conduction and refractoriness without affecting His--Purkinje conduction or myocardial refractoriness. Flecainide prolonged atrial conduction and His-Purkinje conduction with less effect on AV nodal physiology. The use of this isolated perfused rabbit heart model is an inexpensive and reliable technique for the evaluation of the electrophysiologic effects of pharmacologic agents on the conduction system of the heart. A major advantage of the isolated heart model is the absence of autonomic reflexes, which can confound studies performed in intact animals.

Animals↗
PubMed1981

[A new method of recording spike potentials of the atria from the body surface].

A new method of recording spike potentials (rapid deflections) of the heart conductive system (sinus node, atrial conductive tracts, His' bundle)from the body surface was developed using differential magnifying 50 to 250 times and yielding frequencies 30-110 Hz with special filters. The curves with differentially amplified spike potentials (DASP) of the heart conductive system were recorded in 249 patients with various cardiac arrhythmias; the control group consisted of 60 healthy persons. By means of synchronous recording of intracardiac ECG and DASP curves on the latter well recognizable points for the determination of the excitation spreading rate in certain areas of the conductive system were distinguished. The recording of DASP-curves allowed the determination of intraatrial conduction disturbances, atrial overloading and distinguishing of retrograde conduction in atria, sinoventricular conduction, ectopic prefibrillatory activity and differentiation of paroxysmal tachycardias. The new method of recording of spike potentials of the atria from the body surface allows the diagnosis of the conduction disturbances and cardiac arrhythmias, including life threatening ones, which were previously determined using exclusively intracardiac ECG. The application of our method enables to increase the possibilities of the investigation of cardiac arrhythmias and conductive disturbances and allows a multiple examination and evaluation of the influence of drugs on the heart conductive system.

Arrhythmias, Cardiac↗
PubMed1981

One to one atrioventricular conduction during atrial pacing at rates of 300/minute in absence of Wolff-Parkinson-White Syndrome.

One to one atrioventricular (A-V) or atrio-His bundle (A-H) conduction occurred during right atrial pacing at rates of 300/min in two patients with short P-R (and A-H) intervals, narrow QRS complexes and recurrent supraventricular tachyarrhythmias. Patient 1 had episodes of reciprocating A-V tachycardia and of atrial fibrillation with very fast rates (270 to 290/min) that were slowed to 100 to 135/min after administration of intravenous verapamil. Enhanced A-V (A-H) conduction was exposed only during stimulation from the high right atrium, but not from the low lateral right atrium or coronary sinus. Patient 2 had episodes of atrial flutter with 1:1 A-V conduction and rates of 290/min. The H-V interval was short (25 ms) during sinus rhythm and atrial pacing presumably because conduction occurred through an atrio-"distal" His bundle (atriofascicular) tract. In contrast, the H-V interval was normal (40 ms) in echo beats or when the "proximal" His bundle was stimulated. In these two patients, having as "common denominators" short P-R (and A-H) intervals, narrow QRS complexes and recurrent supraventricular tachyarrhythmias, enhanced A-V (A-H) conduction was (1) possible due to different electrogenetic mechanisms; (2) pacing-site dependent; (3) manifested, during atrial fibrillation and atrial flutter, by extremely fast ventricular rates; and (4) unrelated to the rate of reciprocating A-V tachycardias because the latter was predominantly a function of anterograde conduction through the "slow" nodal pathway.

Adolescent↗