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PubMed1977

[Incorporation of 3H-thymidine into the cells of the heart conduction system (sinoatrial and atrioventricular nodes, bundle of His) during cardiogenesis in mice].

The number of DNA synthesizing myocytes in the conductive system, as compared with the working myocardium, was determined by means of light autoradiography. At the same time the number of mitosing cells was counted. The indices of labelled nuclei in the sinoatrial and atrioventricular nodes of the embryos after the single and repeated 3H-thymidine injections were significantly lower than in the working ventricle and atrium. During the postnatal development (3-11 days) only in the sinoatrial node the index of labelled nuclei was significantly lower than in the working ventricle. The proliferative activity in all the myocardium parts fell markedly by the 13th day of development. Following 10 3H-thymidine injections with 12 hrs intervals, the indices of labelled nuclei varied from 0.03 to 0.67% in the working ventricle and atrium and from 0.13 to 1.0% in the conductive system of adult mice. During the embryogenesis the index of labelled nuclei in the sinoatrial node was significantly higher than in the atrioventricular one and during the postnatal development-vice versa.

Animals↗
PubMed1992

Physiology of "atypical" atrioventricular junctional reentrant tachycardia occurring following radiofrequency catheter modification of the atrioventricular node.

The physiology of atypical atrioventricular junctional reentrant tachycardia (AVJRT) occurring following catheter modification of the AV node is poorly defined. Six patients undergoing radiofrequency current catheter modification of the AV node had inducible atypical AVJRT before or after AV nodal modification. Typical AVJRT was differentiated from atypical AVJRT by a ventriculoatrial (VA) time < 60 msec in the His-bundle electrogram recording. Five of six patients had typical AVJRT and two had atypical AVJRT prior to AV nodal modification. Following anterior approach AV nodal modification, previously undetected atypical AVJRT was induced in four patients. Earliest retrograde atrial activation in the posterior septum was documented in all patients with atypical AVJRT prior to modification and in three of four patients with atypical AVJRT following modification. The AH intervals during tachycardia were 320 +/- 52 msec in typical AVJRT, 88 +/- 33 msec in the premodification atypical AVJRTs, and 172 +/- 12 msec in the postmodification atypical AVJRTs (P = 0.0001). The AH/HA ratios were 4.1 +/- 0.9 in typical AVJRT, 0.5 +/- 0.2 in the premodification atypical AVJRTs, and 0.9 +/- 0.2 in the postmodification atypical AVJRTs (P = 0.0001). Two patients with postmodification atypical AVJRT underwent further posterior approach AV node modification that resulted in VA block. One patient with postmodification atypical AVJRT had further anterior approach AV nodal modification that resulted in heart block. The retrograde limb of the atypical AVJRT seen following anterior approach AV nodal modification is a posterior, slow pathway.

Atrioventricular Node↗
PubMed1999

Role of the differential bombardment of atrial inputs to the atrioventricular node as a factor influencing ventricular rate during high atrial rate.

OBJECTIVES: The role of the atrial inputs for the conduction through the atrioventricular node (AVN) at slow rates and during reentrant tachycardia is well acknowledged, although still controversial. However, the relationship between the sequence and rate of atrial engagement of the AVN inputs and the resulting ventricular rate during high atrial rate remains unclear. This study provides quantitative description of complex AVN input-output correlations determining the ventricular rate during random high atrial rate. METHODS AND RESULTS: 12 rabbit heart preparations were used to evaluate the ventricular rate during programmed regular high atrial rate pacing or random pacing from eight atrial sites. Electrograms were recorded at the posterior (P) and anterior (A) AVN inputs, and at the bundle of His along with nodal cellular action potentials. Lorenz-plots and input-output-rate correlations were used to quantify the ventricular rate under different pacing protocols. Small alternations in the sequence of activation of P and A resulted in substantial changes of the organization of the intranodal cellular responses and the ventricular rate. The ventricular rate was shown to be significantly dependent on the site of high rate pacing (P < 0.01) and on the resulting mean rate of inputs activation. Furthermore, the asymmetry between P- and A-bombardment was an important determinant, so that high ventricular rate was associated with large difference between the inputs rates and vice versa (P < 0.05). CONCLUSIONS: The prevailing ventricular rate during high atrial rate is a complex dynamic parameter that depends not only on the global mean atrial rate but, in a major part, on the differential bombardment of the AVN inputs and on the site of initiation of the atrial wave fronts.

Action Potentials↗
PubMed2006

Randomized study of propofol effect on electrophysiological properties of the atrioventricular node in patients with nodal reentrant tachycardia.

BACKGROUND: Atrioventricular nodal reentrant tachycardia (AVNRT) is probably the most common form of paroxysmal supraventricular tachycardia. Percutaneous catheter ablation is a technique to interrupt cardiac conduction pathways selectively. The anesthetist is challenged to provide a safe anesthetic which takes into account the electrophysiologist's requirements for minimal cardiac conduction interference. Propofol is an ideal drug. However, previous studies have shown that the infusion of propofol has sometimes been associated with bradyarrhythmias or conversion of arrhythmias to sinusal rhythm. The purpose of this report is to verify the interferences of propofol in the electrophysiological properties of the atrioventricular (AV) node conduction system in patients with AVNRT. METHODS: Patients were randomly assigned to receive either a placebo or propofol at sedative doses. An electrophysiological study was performed consisting of measuring the anterograde (AERPFP) and retrograde effective refractory period of the fast (RERPFP) and the anterograde effective refractory period of the slow (AERPSP) AV nodal pathway. Reciprocating tachycardia was induced and the cycle length (CL) and atrial-His (AH), His-ventricular (HV), and ventriculoatrial (VA) intervals were measured. RESULTS: Propofol did not cause alteration (P > 0.05) in the AERPFP or RERPFP and the AERPSP AV nodal pathway. The AH, HV, and VA intervals were not affected. Sustained reciprocating tachycardia could be induced in the all patients. All slow pathways were successfully identified and ablated. CONCLUSION: Propofol has no effect on the electrophysiological properties of the AV node conduction system. It is thus a suitable anesthetic agent for use in patients undergoing ablative procedures.

Adult↗
PubMed1988

Membrane actions of quinidine sulfate in the rabbit atrioventricular node studied by voltage clamp method.

The effects of quinidine (0.01-20 micrograms/ml) on spontaneous action potentials and membrane current systems of the rabbit atrioventricular node were studied. At therapeutic concentrations, this drug decreased the action potential amplitude, the maximal diastolic potential, the threshold potential as well as the maximal rate of depolarization and showed a negative chronotropic action. Quinidine, at 5 micrograms/ml, decreased the peak slow inward current by 30.2%, increased its time constant of inactivation by 27.3%, shifted the steady-state inactivation curve toward more negative membrane potentials by 2.8 mV and decreased its fully activated current. Quinidine exerted not only resting but also use-dependent blocking actions on the slow inward current. The depression of the action potential upstroke can thus be explained by the reduction in this current. The outward K+ tail current was decreased by 65.4% and its deactivation time constant was increased by 19.0%. These effects may have contributed to the prolongation of the action potential duration, the reduction in the maximal diastolic potential and the slowing of diastolic depolarization. Quinidine shifted the steady-state activation curve for this K+ current toward hyperpolarization by as much as 7.8 mV. It decreased the hyperpolarization-activated inward current by 16.3% and increased its activation time constant by 10.1%, but this current appeared to play a small role in reducing the rate of diastolic depolarization. These observations indicate that, depending upon dose, quinidine has the potential to decrease all of the time- and voltage-dependent ionic currents in atrioventricular nodal cells.

Action Potentials↗
PubMed1992

Developmental cellular electrophysiologic effects of propafenone on the rabbit atrioventricular node.

Transmembrane recordings and surface electrograms were used to evaluate the influence of propafenone on the cellular electrophysiology of isolated neonatal and adult rabbit atrioventricular node (AVN) preparations. An automatic interval of 863 +/- 82 ms (mean +/- SEM, n = 14) in neonates was found to be significantly shorter than the 1510- +/- 205-ms (n = 12) automatic interval observed in adults. Propafenone in a concentration of 5 x 10(-6) M significantly increased the automatic interval of neonatal pacemakers but not that of the adult preparations. These changes in automaticity produced by propafenone were not dependent on the adrenergic receptor-blocking action of the drug. The pacemaker escape time after overdrive pacing was also shorter in the neonate than in the adult. Propafenone prolonged the escape time of the neonatal tissues but not those of the adult. AVN refractory period, A-H interval, and antegrade Wenckebach rate were comparably increased in a concentration-dependent manner in both age groups. The maximum diastolic potential was decreased by propafenone in the neonatal atrionodal tissue but not in other regions of the AVN and not in any region of the adult AVN. Action-potential duration was increased in all regions of the AVN in both age groups. Action-potential amplitude and maximum upstroke velocity were decreased by propafenone in both age groups. Unlike other excitable tissues of the heart, the action-potential duration of AVN nodal cells increased with decreasing pacing intervals as the pacing interval approached the Wenckebach interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1997

Ion channel and exchange currents in single myocytes isolated from the rabbit atrioventricular node.

OBJECTIVE: To review findings from the authors' laboratory in studies of electrophysiological properties of single rod- and spindle-shaped myocytes from rabbit atrioventricular node (AVN). DESIGN: Single cells were isolated from the AVN of the rabbit heart with the use of enzymatic and mechanical dispersion. For recording, cells were superfused with a Tyrode's solution at 33 to 37 degrees C, and recordings were made with microelectrodes or patch pipettes under 'current' or voltage' clamp conditions. Results are expressed as mean +/- SEM. RESULTS: AVN cells had a mean membrane capacitance of 40 +/- 3.9 pF and membrane resistance of 565 +/- 167 M omega (n = 9). Spontaneously active cells exhibited pacemaker activity showing a clear diastolic depolarization and overshooting action potential (AP) with a relatively slow upstroke velocity (7.4 +/- 0.9 V/s, n = 6) and a maximum diastolic potential of -70.5 +/- 2.9 mV. Under voltage clamp conditions, depolarizing pulses from 40 mV elicited L-type calcium currents sensitive to inhibition by nifedipine and managanese or cadmium ions, which could also block spontaneous APs. Depolarizing pulses also activated delayed rectifier potassium current (IK). IK showed rapid activation, and IK 'tails' in AVN cells were blocked by 5 microM E4031, consistent with the rapidly activating subtype of IK (IKr). IK was similar in AVN and ventricular myocytes, except for the time-course of deactivation, which was faster in AVN cells. In 80% to 90% of cells, hyperpolarizing voltage steps activated a small time-independent current. Ten per cent to 20% of cells showed the hyperpolarization-activated current (I(f)), but I(f) amplitude was only significant at potentials more negative than the pacemaker potential. AVN cells showed an apparent absence of inwardly rectifying potassium current. CONCLUSIONS: The high membrane resistance of AVN cells suggests that only small changes in ionic currents could significantly affect membrane potential. L-type calcium current is important in generating the AP upstroke, and IKr may play a role in both AP repolarization and diastolic depolarization. The ionic basis underlying spontaneous activity is not yet clear, but in some cells I(f) is not required because cells without I(f) can generate spontaneous APs.

Animals↗
PubMed1987

Morphological study of sarcoplasmic reticulum in the atrioventricular node and bundle cells in guinea pig hearts.

The osmium-ferrocyanide method for staining of the sarcoplasmic reticulum (SR) was used for a morphological investigation of the various components of the SR in the atrioventricular node and bundle (AVNB) cells of guinea pig hearts. On the basis of light microscopic observations, the AVNB tissue in guinea pig hearts can be divided into five regions: atrionodal junction, midnode, proximal bundle, distal bundle, and bundle branches. Electron microscopic observations revealed two types of junctional SR (j-SR) saccules in the cells from all the regions of AVNB tissue. One is similar to that seen in the working cardiac cells, i.e., flattened saccules with junctional granules. The second type is dilated and contains electron-dense granular material throughout its lumen. The flattened type is seen more often than the dilated type in atrionodal junctional cells and midnode cells, whereas the dilated type occurs more often in distal bundle cells and bundle branch cells. In most cells from the atrionodal junction and midnode regions, the j-SR saccules are apposed more often to sarcolemmal areas associated with nonspecialized regions of intercellular junctions than to other sarcolemmal areas. This distribution was not found in the distal bundle and bundle branch cells. Free SR tubules around the myofilament bundles are poorly developed in the midnode cells, generally in accord with the extent of development of myofibrils. Z-tubules are found in cells from all regions but are poorly developed in midnode cells. Corbular SR vesicles are found in cells from all the regions of AVNB tissues but are rare in midnode cells. Thus, each of the regions in the AVNB tissue has a different, characteristic distribution of SR components. Because of their possible relationship to the regulation of the intracellular concentrations of calcium, these differences in SR morphology may contribute to the diverse physiological properties of the different regions of the AV node and bundle.

Animals↗
PubMed2000

[Papillary fibroelastoma of the aortic valve coincident with a cystic tumor of the atrioventricular node].

We describe a rare case of a papillary fibroelastoma of the aortic valve occurring simultaneously with a cystic tumor (a so-called mesothelioma) of the atrioventricular nodal region. At autopsy the tumor was found to prolapse into and occlude the right coronary ostium, leading to an acute, recurring myocardial infarction. Histological examination of the grossly unremarkable conduction system of the heart revealed a cystic tumor in the region of the atrioventricular node. To our knowledge, this is the first report of co-existence of these two rare cardiac tumors.

Aged↗
PubMed2000

Effects of a novel vesamicol receptor ligand, m-(iodobenzyl)trozamicol, on the canine isolated, blood-perfused atrioventricular node preparation.

m-(Iodobenzyl)trozamicol (MIBT) is a recently discovered vesamicol analogue. It has been shown that radiolabelled [125I]MIBT can be used as a marker of cholinergic innervation in the heart as well as in the brain. The purpose of this study was to analyze the direct effects of MIBT on the atrioventricular and intraventricular conduction in addition to the coronary blood flow using the canine isolated, blood-perfused atrioventricular node preparation. Intracoronary administration of MIBT suppressed the atrioventricular and intraventricular conduction, while it increased the coronary blood flow. The effect and duration of action on the intraventricular conduction was less pronounced compared with other effects. Moreover, the doses of MIBT needed to cause negative dromotropic and coronary vasodilator effects in this study was much greater than those needed for imaging the cardiac cholinergic innervation. Pretreatment of the preparations with a muscarinic receptor antagonist, atropine, did not block these effects of MIBT, suggesting that MIBT may possess muscarinic receptor-independent ion channel activity in the cardiac conduction system and coronary arteries.

Animals↗
PubMed1995

Mechanisms of conduction time hysteresis in rabbit atrioventricular node.

The functional origin of atrioventricular nodal hysteresis was studied in isolated rabbit heart preparations. This hysteresis is characterized by asymmetric changes in nodal conduction time (NCT) occurring for symmetric changes in cycle length. The respective contribution of the nodal properties of recovery, facilitation, and fatigue to the beat-to-beat changes in NCT observed during paired symmetric ramps of decreasing and increasing cycle length was determined with specifically design stimulation protocols. Nodal hysteresis was found to be entirely accounted for by variations in the contribution of nodal recovery and fatigue properties observed at corresponding cycle lengths. The study establishes how this contribution varies on a beat-to-beat basis as a result of cycle length history. This holds true for the numerous changes in hysteresis observed in response to changes in the sequence and slope of the ramps. Facilitation clearly affected NCT during these responses but did not contribute to the hysteresis. Moreover, the study demonstrates that there is no inherent change in the characteristics of nodal function with the direction of the ramp that could account for the hysteresis. Thus nodal hysteresis arises from nodal functional properties of recovery and fatigue but does not constitute a distinct independent intrinsic property of the node.

Animals↗
PubMed1999

Implications of marked fatty infiltration around and in the atrophic atrioventricular node in elderly patients with permanent pacemaker implantation for symptomatic sick sinus syndrome.

The present study undertook an extensive analysis of the histopathological findings of the atrioventricular conduction system in 14 elderly patients treated with permanent pacemakers for sick sinus syndrome (SSS). Special attention was given to the lowest Wenckebach block points of atrioventricular conduction during rapid atrial pacing, and ventricular rate or duration of ventricular pause during chronic atrial fibrillation. An electrophysiological study (EPS) was conducted under sinus rhythm in 13 patients and under junctional escape rhythm in 1 patient. Three of the 14 cases showed a lower Wenckebach block point of 130 beats/min or less. Two of these 3 cases showed excessive fatty infiltration around the atrionodal junction area and into the atrophic atrioventricular node (AVN) itself. Of the 6 patients who had chronic atrial fibrillation after pacemaker implantation, 2 cases showed a slow ventricular response of less than 60 beats/min and/or a long ventricular pause of 3.3 s. One of the 2 cases showed a lower Wenckebach block point of 130 beats/min at the time of EPS. The other, who later progressed to idiopathic atriomegaly, also showed marked fatty infiltration around the AVN. This fatty lesion was closely associated with diffuse disruption of the muscular fibers connecting the atrophic AVN with the atrium. In addition, most of the remaining cases also had an atrophic AVN. In conclusion, a sparse or absent atrionodal connection and an atrophic AVN due to excessive fatty infiltration in the atrionodal transitional area should be investigated in atrioventricular conduction disturbances in the elderly with SSS.

Aged↗
PubMed1984

Anatomical variants of sinoatrial and atrioventricular node arteries.

The authors investigated on 70 hearts taken from deceased subjects of either sex, aged 19 to 75 years, anatomical variants of sinoatrial (SAN) and atrioventricular node (AVN) arteries. As regards the branching of the SAN artery from the right and left coronary artery (RCA, LCA), they found altogether 14 variants of connection with the anterior atrial sulcus and the orifice of the superior vena cava. As regards the branching of the AVN from the RCA and the LCA, they identified altogether 6 variants of connection with the venous sinus orifice and the base of the interventricular septum. Problems of surgical interventions on SAN and AVN arteries and mechanisms of possible traumatization in the course of these operations are discussed. Surgical lesions can be prevented by thorough analysis of coronarograms and by taking into account anatomical variants of SAN and AVN arteries.

Adolescent↗
PubMed1997

Spontaneous accelerated junctional rhythm: an unusual but useful observation prior to radiofrequency catheter ablation for atrioventricular node reentrant tachycardia in young patients.

Between May 1990 and March 1995, 5 of 29 young patients (ages 4.2-25 years; median 14.1 years) undergoing RF ablation for atrioventricular node reentrant tachycardia (AVNRT) presented with spontaneous accelerated junctional rhythm (AJR) (CL = 500-750 ms), compared to 0 of 58 age matched controls undergoing RF ablation for a concealed AV accessory pathway (P = 0.004). In 3 of the 5 patients with AVNRT and AJR, junctional beats served as a trigger for reentry. During attempted slow pathway modification in the five patients with AVNRT and AJR, AVNRT continued to be inducible until the AJR was entirely eliminated or dramatically slowed. These 5 patients are tachycardia-free in followup (median 15 months; range 6-31 months) with only 1 of the 5 patients continuing to experience episodic AJR at rates slower than observed preablation. Episodic spontaneous AJR is statistically associated with AVNRT in young patients and can serve as a trigger for reentry. Successful modification of slow pathway conduction may be predicted by the elimination of AJR or its modulation to slower rates, suggesting that the rhythm is secondary to enhanced automaticity arising near or within the slow pathway.

Adolescent↗
PubMed1990

Congenitally corrected transposition with normally positioned atria, straddling mitral valve, and isolated posterior atrioventricular node and bundle.

A heart is described with congenitally corrected transposition of the great arteries, normally positioned atria, and a straddling mitral valve. Instead of an anteriorly positioned atrioventricular node, a regularly positioned posterior node and bundle were observed. This observation has important clinical and surgical implications and underlines that close inspection of the alignment of atrial and ventricular septa during operations is mandatory.

Atrioventricular Node↗
PubMed1997

Electrophysiologic characteristics and radiofrequency catheter ablation in atrioventricular node reentrant tachycardia with second-degree atrioventricular block.

INTRODUCTION: Detailed electrophysiologic study of AV nodal reentrant tachycardia (AVNRT) with 2:1 AV block has been limited. METHODS AND RESULTS: Six hundred nine consecutive patients with AVNRT underwent electrophysiologic study and radiofrequency catheter ablation of the slow pathway. Twenty-six patients with 2:1 AV block during AVNRT were designated as group I, and those without this particular finding were designated as group II. The major findings of the present study were: (1) group I patients had better anterograde and retrograde AV nodal function, shorter tachycardia cycle length (during tachycardia with 1:1 conduction) (307 +/- 30 vs 360 +/- 58 msec, P < 0.001), and higher incidence of transient bundle branch block during tachycardia (18/26 vs 43/609, P < 0.001) than group II patients; (2) 21 (80.8%) group I patients had alternans of AA intervals during AVNRT with 2:1 AV block. Longer AH intervals (264 +/- 26 vs 253 +/- 27 msec, P = 0.031) were associated with the blocked beats. However, similar HA intervals (51 +/- 12 vs 50 +/- 12 msec, P = 0.363) and similar HV intervals (53 +/- 11 vs 52 +/- 12, P = 0.834) were found in the blocked and conducted beats; (3) ventricular extrastimulation before or during the His-bundle refractory period bundle could convert 2:1 AV block to 1:1 AV conduction. CONCLUSIONS: Fast reentrant circuit, rather than underlying impaired conduction of the distal AV node or infranodal area, might account for second-degree AV block during AVNRT. Slow pathway ablation is safe and effective in patients who have AVNRT with 2:1 AV block.

Aged↗
PubMed1990

Clinical efficacy of radiofrequency current in the treatment of patients with atrioventricular node reentrant tachycardia.

Eight women (mean age 41 years, range 24 to 62) with drug-resistant atrioventricular (AV) node reentrant tachycardia underwent radiofrequency catheter ablation. Radiofrequency energy was delivered in a unipolar mode with use of a back paddle as the anode placed between the two scapulae. The total applied energy was 2,233 +/- 1,919 J. The AH interval increased from 87 +/- 13 to 113 +/- 17 ms (p less than 0.05) and the PQ interval increased from 141 +/- 15 to 169 +/- 34 ms (p less than 0.05). The anterograde Wenckebach cycle length increased from 300 +/- 41 to 320 +/- 42 ms (p less than 0.05). Retrograde conduction was abolished in five patients. Atrioventricular node tachycardia was still inducible in three patients. During a follow-up period of 9 +/- 3 months, four patients remained clinically asymptomatic without drug therapy and four patients had recurrent symptoms. Three of the latter responded to previously unsuccessful antiarrhythmic drugs and the fourth patient underwent surgical cure for persistence of tachycardia. Right bundle branch block occurred in five patients; it was permanent in four and transient in one. In conclusion, radiofrequency catheter ablation represents a valuable but still investigational therapy in patients with drug-refractory AV node reentrant tachycardia.

Adult↗