Node Functional Refractory Period Research Articles

Endoscopy-assisted radiofrequency ablation around the coronary sinus ostium in dogs: its effects on atrioventricular nodal properties and ventricular response during atrial fibrillation.

Radiofrequency ablation of the slow pathway can prolong atrioventricular (AV) nodal properties and RR intervals during atrial fibrillation (AF) in many patients with AV nodal reentrant tachycardia. However, it is not well elucidated whether these changes are related to the presence of dual AV nodal pathway physiology. The aim of this study was to evaluate changes of AV nodal properties and RR intervals during AF caused by ablation of two specific areas in dogs. Assisted by fiberoptic endoscopy, linear lesions were created between the coronary sinus ostium and tricuspid valve annulus (area 1) or posterior to the ostium (area 2) in 15 dogs. Three additional dogs served as controls. The measurements were made under autonomic blockade. Catheter ablation could be assisted in all dogs by means of endoscopy. Linear lesions were confirmed at autopsy. AV nodal parameters and RR intervals showed no overall changes. Individual data showed that ablation of area 1 resulted in modification of AV nodal properties in 54.5% (facilitation in 36.3% and inhibition in 18.2%), whereas ablation of area 2 induced changes in 50% (facilitation in 10% and inhibition in 40%). The RR intervals were shortened in 33.3% and 20% and prolonged in 44.5% and 40% after ablation of areas 1 and 2, respectively. The RR intervals during AF correlated well with the Wenckebach cycle length and the AV node functional refractory period before and after ablation (r = 0.78 to 0.94, P < 0.01 for each). Ablation of the two specific areas around the coronary sinus ostium was equally effective in modifying AV nodal properties and the ventricular response during AF without dual AV nodal pathway physiology. The ventricular rate to AF after ablation correlated well with the residual AV nodal properties.

Determinants of the ventricular rate during atrial fibrillation

Determinants of the ventricular cycle length during atrial fibrillation were examined in 52 patients. Thirty-three patients had structural heart disease and none had an accessory atrioventricular (AV) connection. The AV node effective and functional refractory periods, the shortest atrial pacing cycle length associated with 1:1 conduction, the AV node conduction time and indexes of concealed conduction in the AV node were measured in the baseline state (36 patients) and after modification of sympathetic tone by infusion of isoproterenol or propranolol (8 patients each). Atrial fibrillation was then induced with rapid atrial pacing, and the mean, shortest and longest ventricular cycle lengths were measured.Variables that correlated most strongly with the mean RR interval during atrial fibrillation were the AV node effective refractory period (r = 0.93; p < 0.001), AV node functional refractory period (r = 0.87; p < 0.001) and shortest atrial pacing cycle length associated with 1:1 conduction (r = 0.91; p < 0.001). The AH interval during sinus rhythm (r = 0.74; p < 0.001) and during atrial pacing at the shortest cycle length with 1:1 conduction (r = 0.52; p < 0.001) had weaker correlations. Measures of concealed conduction did not improve the prediction of the mean or longest ventricular cycle length during atrial fibrillation.In conclusion, the refractory periods and conductivity of the AV node are the best indicators of the potential of the node to transmit atrial impulses to the ventricles during atrial fibrillation. The degree of concealed conduction in the AV node is a less important determinant of the mean ventricular rate during atrial fibrillation.

Frequency-dependent effects of diltiazem on the atrioventricular node during experimental atrial fibrillation.

Calcium channel blockers depress atrioventricular (AV) nodal properties in vivo in a frequency-dependent manner, suggesting that selective drug action during supraventricular arrhythmias may result from use-dependent properties. The present study was designed to examine whether or not the rate-dependent actions of diltiazem account for its therapeutic effects during atrial fibrillation. The determinants of the ventricular response to atrial fibrillation (concealed AV nodal conduction and AV node functional refractory period, AVFRP) were evaluated at multiple cycle lengths (with extrastimulus techniques) and during electrically induced atrial fibrillation (with indirect indexes from RR interval histograms) in anesthetized dogs. In the presence of diltiazem, AVFRP increased progressively relative to control as rate accelerated. At cycle lengths comparable to sinus rhythm in humans, AVFRP increased 10%, 17%, and 32% after doses 1, 2, and 3 of diltiazem, respectively. Drug-induced increases in AVFRP were greater at basic cycle lengths just above the Wenckebach point (17%, 48%, and 81%) and were maximal during atrial fibrillation (39%, 86%, and 154% increases for doses 1, 2, and 3, respectively). Diltiazem also increased the AV conduction system effective refractory period, thereby increasing the potential zone of concealment into the AV node. Frequency-dependent increases in the zone of concealment were produced by diltiazem and were associated with marked increases in the standard deviation of RR interval histograms during atrial fibrillation (257%, 526%, and 923% increases after doses 1, 2, and 3, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac electrophysiologic properties of intravenous isradipine in patients with sick sinus syndrome

Isradipine is a new dihydropyridine calcium antagonist with powerful vasodilating properties. Although therapeutic concentrations do not affect myocardial contractility in vivo, in vitro studies have demonstrated a negative chronotropic action with only minor dromotropic influence. In humans with normal sinus and atrioventricular node function, even in the presence of beta-blockade, such a negative chronotropic effect could not be proved. No data are available on the effects of isradipine on a compromised sinus node. Therefore, the effect of intravenous isradipine at 0.3 μg/kg/minute for 30 minutes was studied in seven patients with the clinical signs of a sick sinus syndrome. Mean arterial blood pressure decreased from 126 ± 21 to 113 ± 15 mm Hg (p <0.05). Spontaneous sinus cycle length decreased from 969 ± 22 to 843 ± 161 msec (p <0.05). Changes in sinoatrial conduction time, sinus node recovery time, and corrected sinus node recovery time were not significant. Changes in atrioventricular node functional refractory period, the atrial-His interval, the His-ventricle interval, and Wenckebach point were not significant. Also, effective. Also, effective refractory periods of atrium and ventricle, and QRS duration changed but not significantly. The QT interval decreased (419 ± 45 to 405 ± 44 msec; p <0.05), and there was a slight (not significant) increase of QTc interval (429 ± 41 to 443 ± 37 msec; not significant). It is concluded that isradipine in hemodynamically effective doses has no depressant effect on sinus and atrioventricular node function in patients with sick sinus syndrome.

Atrioventricular nodal function in the immature canine heart [corrected and republished article orginally printed in Pediatr Res 1987 Nov;22(5):616-20

Previous studies have suggested that the atrioventricular nodal functional refractory period in the neonate is equal to or shorter than that of the ventricle, providing little or no protection to the ventricle against rapid atrial rates and allowing closely coupled atrial beats to fall within the ventricular vulnerable period. We evaluated atrioventricular node function in 21 mongrel neonatal puppies, 3-15 days old, and 15 adult dogs utilizing intracardiac His bundle recording and stimulation techniques. The mean atrioventricular nodal functional refractory period (173.1 +/- 20.0 ms) exceeded both the ventricular effective refractory period (139.5 +/- 14.3) and ventricular functional refractory period (163.3 +/- 14.5) in the neonates. Furthermore, the atrioventricular node was the site of limiting antegrade conduction in all neonates. No ventricular arrhythmias were induced by atrial extrastimulation in any of the neonates. The site of conduction delay during atrial extrastimulation was confined to the atrioventricular node in 15/16 neonates (94%) while 1/16 (6%) had combined nodal and infranodal delay. The neonates developed Wenckebach, at significantly faster heart rates than the adults, but both groups developed Wenckebach at approximately twice the resting heart rate. Retrograde conduction was a consistent finding in the neonates. However, antegrade Wenckebach occurred at a significantly faster heart rate than retrograde Wenckebach suggesting different functional properties. Our data suggest that in the neonatal canine, the atrioventricular node functional refractory period is longer than both the ventricular effective refractory period and ventricular functional refractory period. Furthermore, the degree of protection offered by the neonatal atrioventricular node to the ventricle appears to be comparable to that of the adult.

Atriovenous Nodal Function in the Immature Canine Heart

ABSTRACT. Previous studies have suggested that the atriovenous nodal functional refractory period in the neonate is equal to or shorter than that of the ventricle, providing little or no protection to the ventricle against rapid atrial rates and allowing closely coupled atrial beats to fall within the ventricular vulnerable period. We evaluated atriovenous node function in 21 mongrel neonatal puppies, 3-15 days old, and 15 adult dogs utilizing intracardiac His bundle recording and stimulation techniques. The mean atriovenous nodal functional refractory period (173.1 ± 20.0 ms) exceeded both the ventricular effective refractory period (139.5 ± 14.3) and ventricular functional refractory period (163.3 ± 14.5) in the neonates. Furthermore, the atriovenous node was the site of limiting antegrade conduction in all neonates. No ventricular arrhythmias were induced by atrial extrastimulation in any of the neonates. The site of conduction delay during atrial extrastimulation was confined to the atriovenous node in 15/16 neonates (94%) while 1/16 (6%) had combined nodal and infranodal delay. The neonates developed Wenckebach, at significantly faster heart rates than the adults, but both groups developed Wenckebach at approximately twice the resting heart rate. Retrograde conduction was a consistent finding in the neonates. However, antegrade Wenckebach occurred at a significantly faster heart rate than retrograde Wenckebach suggesting different functional properties. Our data suggest that in the neonatal canine, the atriovenous node functional refractory period is longer than both the ventricular effective refractory period and ventricular functional refractory period. Furthermore, the degree of protection offered by the neonatal atriovenous node to the ventricle appears to be comparable to that of the adult.

Electrophysiologic effects of theophylline in young patients with recurrent symptomatic bradyarrhythmias

In this study, both acute electrophysiologic actions of intravenously administered theophylline and clinical effects of chronic oral theophylline therapy were assessed in 10 young patients (aged 9 to 41 years) without clinically significant cardiac disease, in whom recurrent symptoms of syncope and dizziness were attributed to transient bradyarrhythmias (sinus pauses, marked sinus bradycardia or paroxysmal atrioventricular [AV] block). Intravenous theophylline infusion (serum concentration range 9.5 to 12.0 mg/liter) shortened means sinus cycle length (control 973 ± 285 ms versus theophylline 880 ± 226 ms, p <0.005) and decreased both the estimated sinoatrial conduction time (control 169 ± 56.0 ms versus theophylline 143 ± 55.3 ms, p <0.05) and the maximum corrected sinus node recovery time (control 442 ±251.0 ms versus theophylline 255 ± 146.2 ms, p <0.05). In addition, theophylline infusion shortened the minimum atrial paced cycle length with sustained 1:1 AV conduction (control 414 ± 86 ms versus theophylline 379 ± 97 ms, p <0.05) and consistently reduced AV node functional refractory periods. Subsequent chronic oral theophylline therapy (serum levels 9 to 12 mg/liter) was tolerated in 8 patients (80%). During a follow-up of 5 to 24 months, suppression of symptoms was achieved in 6 of the 8 patients. Thus, theophylline exhibits positive chronotropic and dromotropic effects in man at serum concentrations in the usual therapeutic range (10 to 15 mg/liter). Furthermore, suppression of symptoms during follow-up suggests that theophylline treatment may be a useful therapeutic consideration in some patients with recurrent symptomatic bradyarrhythmias.

Intracardiac electrophysiologic study of intravenous diltiazem and combined diltiazem-digoxin in patients

Fifteen patients without sinoatrial (SA) or atrioventricular (AV) node dysfunction underwent electrophysiologic study (EPS) before and after intravenous diltiazem: 0.20 mg/kg bolus followed by 0.0007 mg/kg/min infusion (seven patients) or 0.25 mg/kg bolus followed by 0.0012 mg/kg/min infusion (eight patients). In six patients intravenous digoxin (0.018 mg/kg) was given and 45 minutes later EPS was repeated while the diltiazem infusion continued. Diltiazem prolonged sinus cycle length (+7%, p < 0.01), lengthened AH conduction time (+22% in constant rate atrial paced rhythm, p < 0.001), prolonged AV node functional and effective refractory periods (+6%, p < 0.01 and +16%, p < 0.05, respectively), lengthened AV node Wenckebach cycle length (+13%, p < 0.001), shortened atrial functional refractory period (−3%, p < 0.05), and reduced mean arterial pressure (−8%, p < 0.005 in constant rate atrial paced rhythm). Subsequently, intravenous digoxin further prolonged sinus cycle length (+12%, p < 0.05), AH nonduction time (+17%, p < 0.05), AV node Wenckebach cycle length (+9%, p < 0.05), and AV node functional refractory period (+7%, p < 0.05), shortened atrial effective refractory period (−7%, p < 0.05) and ventricular effective refractory period (−6%, p < 0.05), and increased systolic arterial pressure (+6%, p < 0.05). Diltiazem and digoxin have additive depressant effects on SA and AV node function without significant adverse effects.

開心術後の刺激伝導障害に関する研究

The cardiac surgery has made a remarkable progress in recent years. On the other hand, various types of arrhythmias following open heart surgery have become serious clinical problems. In the present study a series of the cases of complete right bundle branch block with left anterior hemiblock (CRBBB c LAH) following a radical operation for an ventricular septal defect (VSD) and tetralogy of Fallot (TF) was analyzed in terms of the function of the coducting system.CRBBB coupled with LAH occured in 5 of 43 total cases (11.6%) following operation for VSD and TF. The percentage agrees with that reported by other authors. Measurement of the intervals of the cardiac cycle in electrocardiograms of the bundle of His (HBE) showed normal values except in 2 cases of VSD in which the H-V interval was prolonged to 55 msec. After right atrial pacing all conductions were found to retain 1 to 1 correspondence even at a maximum pacing rate of 240 per minute. The sinus node recovery time (SNRT) (460-1080 msec) corrective sinus node recovery time (CSRT) (-40 -355 msec), measured by the overdrive and suppression test, were both within the normal range. Measurements of the A-V node effective refractory period (AVN-ERP) and A-V node functional refractory period (AVN-FRP) showed normal values in all 4 cases.During an observation period of twelve to thirty-four months, all patients convalesced without any evidence of complete heart block and Adams-Stocks attack, showing normal sinus rhythm. These results are in agreement with other data recently published.