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At least 433 records · Page 24Linked to original sources
PubMed2006

Anticonvulsive effects of carbenoxolone on penicillin-induced epileptiform activity: an in vivo study.

Epilepsy is an important problem in neurological disorders. Recent studies claimed that gap junctions have a critical role in epileptic neuronal events. The aim of present study is to investigate the effects of gap junction blocker carbenoxolone on penicillin-induced experimental epilepsy. For this purpose, 4-month-old male Wistar rats were used in the present study. Permanent screw electrodes allowing EEG monitoring from conscious animals and permanent cannula providing the administration of the substances to the brain ventricle were placed into the cranium of rats under general anesthesia. At the end of the postoperative recovery period, epileptiform activity was generated by injecting 300 IU crystallized penicillin through the ventricular cannula. Epileptiform activity monitored from a digital recording system, when it reached its maximum intensity, carbenoxolone (100, 200, 500 nmol) was applied in the same way with penicillin. Effects of carbenoxolone on epileptiform activity were assessed by both electrophysiological and behavioral analysis. Carbenoxolone suppressed epileptiform activity by decreasing the amplitude and frequency of epileptiform spikes and by attenuating the epileptiform behavior. The results of this study suggest that the blockade of electrical synapses may contribute to the prevention and amelioration of epileptic activity.

Animals↗
PubMed2003

Digital image analysis in dental research applied for treatment of fissures on occlusal surfaces of premolars.

The aim of this paper was to quantitatively assess caries changes of teeth by using digital image analysis. Digital images of stained sections of crowns of teeth were acquired with a computer-assisted light microscope. In each image, spots representing the main and total demineralization of enamel were segmented to determine their area. The area of total demineralization was significantly different between premolars with sealed fissures and unprotected premolars as indicated by the Mann-Whitney test. Fissures on occlusal surfaces of premolars were characterized by their width, height, and distance from the bottom of the fissure to the enamel-dentin junction. This distance was also significantly different between protected and unprotected teeth. The results of our in vitro studies of enamel lesions allow us to plan an effective diagnosis, prophylaxis, and treatment of early caries changes in in vivo conditions.

Adolescent↗
PubMed2006

Efficacy of sealing proximal early active lesions: an 18-month clinical study evaluated by conventional and subtraction radiography.

This study assessed the efficacy of sealing proximal lesions on adult patients using a split-mouth design. Eighty-two 15- to 39-year-olds from the Dental Faculties in Copenhagen and Bogotá participated, each having 2 or more proximal lesions in the following radiographic stages: (1) lesion restricted to the outer half of enamel; (2) lesion from the inner half of enamel including the enamel dentine junction, and (3) lesion restricted to the outer third of dentine. Standardized geometrically aligned baseline and follow-up radiographs were obtained. One randomly selected lesion (test) in each patient was sealed with 1 of 2 resins. The patients were instructed to floss all the proximal lesions 3 times per week. The baseline to 18 months difference in caries lesion progression status was assessed using 3 methods: (1) radiographs were independently assessed visually; (2) radiographs were read in pairs, and (3) using subtraction radiography of digitized images. A total of 72 subjects finished the study (12.2% dropout). The compliance concerning flossing was poor (15%). For the repeated examinations kappa was 0.84 for the visual examination, 0.44 for the paired readings and 0.84 for the subtraction examination. Two test lesions and 1 control lesion were restored. For the independent radiograph assessment method 10 and 26% progressed in the test and control group, respectively (p > 0.05); with the paired radiograph method the corresponding data were 22% in the test and 47% in the control groups (p < 0.01). By subtraction radiography 44% of the test group and 84% of the control were judged to have progressed (p < 0.001). The sealing technique was superior to instructing patients to floss, and subtraction radiography appeared to be the most sensitive method for assessing lesion progression.

Adolescent↗
PubMed2004

Guided tissue regeneration in intrabony periodontal defects following treatment with two bioabsorbable membranes in combination with bovine bone mineral graft. A clinical and radiographic study.

AIM: Comparison of two bioabsorbable barriers (collagen and polylactic acid (PLA) membranes) combined with a bovine bone mineral (BBM) graft, with an access flap procedure (AFP) alone for treating intrabony defects. MATERIAL AND METHODS: Thirty-four subjects participated in this prospective, controlled clinical trial. Baseline clinical examination (probing depth (PD), clinical attachment level (CAL)) of selected sites was performed 2 months after completion of conservative treatment in conjunction with hard-tissue measurements to ascertain the depth of the defect (cementoenamel junction to the bottom of the defects). After randomly dividing patients into three groups (two membrane groups, one control group), full thickness flaps were elevated and exposed root surfaces planed before filling defects with bone graft and positioning a barrier membrane covering the defect. The control group was treated identically except for the barrier and bone graft placement. Clinical treatment outcomes were finally evaluated 12 months after surgery for changes of PD and CAL. Radiographs at baseline and 12 months were compared using non-standardized digital radiography. RESULTS: A mean reduction in PD value of 5.08 mm and mean CAL gain of 4.39 mm occurred in the collagen-BBM group. Corresponding values for the PLA-BBM group were 4.72 and 3.71 mm, while access flap procedure (AFP) sites produced values of 2.50 and 2.43 mm. All improvements in clinical parameters were statistically significant (p<0.001) within groups for all variables. Both membranes produced statistically greater PD reduction and CAL gain compared with AFP treatment (p<0.05). Comparison between barrier groups failed to reveal any statistically significant difference in probing pocket depth reduction (p=0.56) or in CAL gain (p=0.34). CONCLUSION: Placement of the two barrier membranes used in the present study in combination with BBM graft significantly improved clinical and radiographic parameters of deep intrabony pockets and proved superior to access flap alone.

Adult↗
PubMedDate not supplied

Homologous plasma-stored tendon grafting in equids--gross and histomorphological observations.

The efficacy of homologous plasma-stored tendon grafting in the superficial digital flexor tendon severed in the mid-metacarpal region was evaluated in 10 donkeys. Experimental tenectomies were performed, followed by grafting using plasma-stored tendon and human amniotic membrane encasement in group I (n=8) but no grafting or encasement in group II (control) (n=2). Gross observations in group I showed no peritendinous adhesions, except in one animal, while control animals showed thick fibrous adhesions and thickening at both the cut ends. Histologically, in the grafted tendon there was normal healing tissue at the junctional sites with negligible collagen fibre and mild regressing inflammatory reaction by day 15. By day 30 there were a great number of blood vessels but without any inflammatory reaction. The healing tissue at the grafted site and the adjoining paratenon was more mature. The fibroblastic activity appeared to be both extrinsic and intrinsic in origin. By day 60 fibroblastic activity was negligible and the healing tissue at the distal graft and host tendon junction site was at a more advanced stage of maturation and showed early fasciculi/bundle formation. Healing tissue at three months showed collagen fibres fasciculi/bundle comparable to normal tendon architecture. Tendon appeared histologically normal at four months after grafting.

Amnion↗
PubMed1989

Retinoic acid application to chick wing buds leads to a dose-dependent reorganization of the apical ectodermal ridge that is mediated by the mesenchyme.

Local application of retinoic acid to wing buds of chick embryos leads to dose- and position-dependent changes in the pattern of cellular differentiation. Early effects of retinoid treatment on the apical ectodermal ridge coordinate pattern changes and morphogenesis. The length of the apical ridge increases when additional digits will form but decreases when digits are lost. These changes in length can be understood in terms of a threshold response to the local retinoid concentration that results in either disappearance or maintenance of the ridge (Lee & Tickle, J. Embryol. exp. Morph. 90, 139-169 (1985)). Here, we have analysed the mechanisms involved in ridge disappearance by locally applying retinoic acid to the apex of stage 20 chick wing buds. With this treatment regime, low doses give duplicated digit patterns and higher doses truncations. The height of the apical ridge is progressively reduced with increasing doses of retinoid and the time course of ridge flattening indicates that the height of the ridge is correlated with bud outgrowth. With high doses of retinoic acid, the typical ridge, a pseudostratified epithelium in which the columnar cells are tightly packed, disappears and the epithelium at the tip of the bud consists of loosely packed cuboidal cells. Shortly after treatment, there is a decrease in the number of gap junctions between ridge cells. This early change in cell contacts suggests that gap junctions may be involved in maintaining epithelial morphology. When treated epithelium is recombined with untreated mesenchyme, an apical ridge is reestablished and distal structures can be generated. In contrast, when treated mesenchyme is recombined with the epithelium from normal buds, only proximal structures are formed. Therefore, retinoids can lead to a reorganization of the apical ectodermal ridge which is mediated and maintained by the mesenchyme.

Animals↗
PubMed1990

Localizing the site of magnetic brain stimulation in humans.

Magnetic stimulation of the human brain is performed in clinical and research settings, but the site of activation has not been clearly localized in humans or other species. We used a set of magnetic stimulus coils with different field profiles to isolate movement of single digits at motor threshold and to calculate corresponding electric field strengths at various distances beneath the scalp. Two coils could produce the same electric field intensity at only 1 point. Thus, we could estimate the depth of stimulation by finding the intersection of the electric field plots, which were then superimposed on MRIs of the underlying brain. In each of 3 subjects the field plots intersected at the crown of a gyrus, in the region of the central sulcus, an near the level of the gray-white junction. This position and the electric field orientation support localization to layer VI of cerebral cortex.

Adult↗
PubMedDate not supplied

A case of extrahepatic portal vein aneurysm accompanying lupoid hepatitis.

Portal vein aneurysm, especially that of the extrahepatic portal vein, is a very rare entity. We recently observed a case of aneurysm at the junction of the superior mesenteric vein and the splenic vein which accompanied lupoid hepatitis. Abdominal ultrasonography, color Doppler ultrasonography, abdominal computed tomography (CT), magnetic resonance imaging (MRI), and angiography revealed a portal vein aneurysm that increased in size after a period of about 10 months.

Aneurysm↗
PubMed2004

Cross-modal temporal order memory for auditory digits and visual locations: an fMRI study.

A function of working memory is to remember the temporal sequence of events, often occurring across different sensory modalities. To study the neural correlates of this function, we conducted an event-related functional magnetic resonance imaging (fMRI) experiment with a cross-modal memory task. Subjects were required to recall auditory digits and visual locations either in mixed order (cross-modality) or in separate order (within-modality). To identify the brain regions involved in the memory of cross-modal temporal order, we compared the blood oxygenation level-dependent (BOLD) response between the mixed and the separate order tasks. As a control, cortical areas sensitive to the memory load were mapped by comparing the 10-item condition with the 6-item condition in the separate order task. Results show that the bilateral prefrontal, right premotor, temporo-parietal junction (TPJ) and left superior parietal cortices had significantly more activation in the mixed task than in the separate task. Some of these areas were also sensitive to the memory load, whereas the right prefrontal cortex and TPJ were relatively more sensitive to the cross-modal order but not the memory load. Our study provides potential neural correlates for the episodic buffer, a key component of working memory as proposed previously [Baddeley. Trends Cogn Sci 2000;4:417-423].

Acoustic Stimulation↗
PubMedDate not supplied

A novel GJA 1 mutation in oculo-dento-digital dysplasia with curly hair and hyperkeratosis.

Oculo-dento-digital dysplasia (ODDD) is a rare autosomal dominant congenital disorder mainly affecting the development of the face, eyes, skeletal system, heart and dentition. ODDD has been mapped to chromosome 6q22-q24 and germline mutations have been identified in the connexin 43 gene, GJA1. Abnormalities of the skin, hair, and nails have been recognized in ODDD but are often easily overlooked. We report an ODDD patient with curly hair, early trichorrhexis nodosa and discrete keratoderma. Molecular genetic studies revealed a novel GJA1 mutation affecting the amino terminus of the gap junction protein alpha-1 (Cx43). In the light of the cutaneous findings in our patient and based on recent ectodermal dysplasia classification systems, we propose to include ODDD in the group of ectodermal dysplasias.

Abnormalities, Multiple↗
PubMed1991

Matching focal and non-focal magnetic coil stimulation to properties of human nervous system: mapping motor unit fields in motor cortex contrasted with altering sequential digit movements by premotor-SMA stimulation.

Possible classifications of effects of magnetic coil (MC) stimulation are discussed, with the conclusion that the most useful is focal versus non-focal excitation. The mode of excitation of peripheral motor axons by the longitudinal-orthogonally orientated round MC is deduced from the insignificant latency shift in motor unit response when the current direction is reversed either by rotating the coil or by a switching device. A hypothesis is advanced of how peak membrane current entry and exit could occur only 1-3 nodes apart. The mode of excitation of cerebral cortex is more complex. Related to the orientation of the round MC, corticospinal neurons are: (1) directly excited and; or (2) indirectly excited through stimulation of corticocortical and other presynaptic inputs. Although the round MC can directly excite monkey corticospinal neurons at two sites, i.e. the initial segment and the node, the node is believed to be the main target in humans. The meaning of 'focality' of excitation is discussed as applied to MC stimulation of peripheral nerve and cerebral cortex. A potential conflict exists between focality and magnitude of response to MC excitation. However, by appropriately orientating the round MC, activation of all motor axons in one nerve (e.g., the median nerve at the wrist) can be achieved without coactivation of another (e.g., the ulnar nerve). By contrast, no orientation of the round MC, or use of a specially designed MC (e.g., double coil) over motor cortex permits all members of a defined set to be activated in isolation. Nevertheless, some members of the set can be activated in isolation with the MC over motor cortex. Response properties of individual motor units in the extensors of the digits when focally stimulating motor cortex with the figure '8' MC include: (1) Responses are variable to a given stimulus a little above threshold. Comparing responses by individual motor units with that of the population, or with other simultaneously recorded units revealed both coherent and independent sources of variability. (2) The scalp field from which the motor units could be driven by suprathreshold stimulation was of the order of 4-6 cm2. The fields were elongated in the antero-posterior axis, possibly related to the similar orientation of the junction region of the figure '8' MC. (3) Motor units initially excited by threshold MC stimulation were typically recruited early during voluntary contraction (confirming Hess et al. 1987).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2001

Cisapride decreases gastroesophageal reflux in preterm infants.

OBJECTIVE: Gastrointestinal prokinetic agents, such as cisapride, are commonly used in pediatric practice to improve gastric emptying, to decrease emesis, to improve lower esophageal sphincter tone, and to improve irritability and feeding aversion associated with gastroesophageal reflux (GER). Although cisapride seems to be effective in infants from 2 months to 14 years old, data for younger and preterm infants are not available. Whether reflux is a significant cause of reflex apnea or feeding intolerance in the preterm infant is controversial. The objective of this 1-year prospective study, started in 1998, was to determine the efficacy of cisapride for treatment of reflux and reflux-associated apnea (RAAP) in preterm infants. Before this study, the diagnosis of reflux was often made clinically and the effect of therapy on reflux or the decision to increase the dose of cisapride was made empirically. The clinical bias was that persistent apnea, not responding to caffeine, was caused by GER. We reasoned that a systematic approach to the diagnosis and treatment of reflux would improve the care of preterm infants and reduce the risk of toxicity, especially if an increased dose of cisapride showed no improvement in reflux or apnea. STUDY DESIGN: Twenty-four preterm infants (24-36 weeks' gestational age) had clinical apnea/pH studies when they were referred by the attending neonatologist for suspected GER. These infants were born at 28.8 +/- 3.1 weeks with birth weight of 1169 +/- 387 g (range: 631-2263 g). Each infant was studied before and 8 days after starting cisapride treatment. Cisapride dose was 0.09 to 0.25 mg/kg every 6 hours enterally. Treatment decisions regarding dose of cisapride were the responsibility of the attending neonatologist. The pH was recorded continuously for 24 hours at 0.25 Hz and was analyzed using EsopHogram software. A single sensor pH catheter was inserted to ~2 cm above the esophageal gastric junction. GER was defined as a drop in esophageal pH below 4.0 for a least 5 seconds, or pathologic GER was defined as a reflux index (RI) >2 standard deviation (SD) from the mean based on published norms for term infants. The following parameters were calculated from the pH recording: number of reflux events per 24 hours, duration of the longest episode, number of episodes >5 minutes per 24 hours, and RI, ie, percentage of time with pH <4.0. Each study had a combined time-lapse video recording and multichannel digital recording. Recorded parameters were: continuous pulse oximetry, electrocardiogram, respiratory effort (piezo sensor), and airflow (temperature sensor at nostrils and mouth). The recording was scored for central apneas of 10 to 14 seconds and >/=15 seconds (prolonged) and >/=10 seconds for obstructive and mixed apneas. RAAP was scored when an apnea (irrespective of the type) occurred within 1 minute of a GER event. Baseline, after cisapride, and follow-up electrocardiograms were performed because of concern about prolonged QTc and cardiac arrhythmias. The infants were 35.6 +/- 4.5 weeks postconceptional age when first studied. Twelve infants (mean birth weight: 1821 +/- 749 g; gestational age: 32 +/- 2 weeks; postconceptional age: 35.6 +/- 2.6 weeks) were identified retrospectively as controls because their baseline GER parameters were within the normal range using Vandenplas' criteria. RESULTS: Overall, cisapride treatment significantly improved the RI from 16.6 +/- 15.2 to 9.1 +/- 8.4 SD. The number of reflux episodes >/=5 minutes was reduced from 7.1 +/- 5.8 to 4.3 +/- 4.4 SD. No significant effect was seen on the total number of refluxes (/24 hours). Eight infants (33%) had no decrease in the RI after a week of treatment. Three of these infants improved after cisapride dose was increased from 0.09 to 0.25 mg/kg/dose every 6 hours. Although 0.09 mg/kg/day is the minimum effective dose, 67% of our infants did respond to this low dose. Cisapride was discontinued in 3 infants because of prolonged QTc >/=0.450 seconds (0.473 in 1 and 0.470 in 2). More data about the effect of cisapride on QTc interval are reported in Pediatrics in a separate article. Only 1 infant showed no improvement with increased dose. Caffeine treatment had no effect on the baseline or follow-up GER values. Although apnea indexes for central and obstructive apnea were similar before and after cisapride, mixed apnea was less during treatment. There was a significant decrease (0.32 +/- 0.40 to 0.12 +/- 0.17/hour) in RAAP when the one infant who had increased reflux on increased dose of cisapride was excluded as an outlier. The statistical difference, before and after cisapride, for the group is significant with the outlier omitted. The clinical significance is unclear because ~50% of the infants had minimal changes in their apnea indexes. Furthermore, ~40% of infants did not have RAAP. (ABSTRACT TRUNCATED)

Cisapride↗
PubMedDate not supplied

Errors in the differential diagnosis of incompetence of the popliteal vein and short saphenous vein by Doppler ultrasound.

Doppler Ultrasound is now routinely used to demonstrate valvular reflux in the venous system. Incompetence detected at the back of the knee is located either in the short saphenous vein or in the popliteal vein. Whether the incompetence is in the deep or superficial venous system can be differentiated by digital compression over the short saphenous vein in the upper calf; if reflux is abolished then the incompetence is assumed to be in the superficial vein but if it is not prevented it must be in the popliteal vein. Sometimes the reflux is not controlled when the deep system is normal. This has been shown to be due to variations in the anatomy of the short saphenous vein and especially the pattern of its termination. Examples with venography are given, showing that in the presence of incompetence at the sapheno-popliteal junction there may be no reflux in the short saphenous vein; instead the proximal tributaries are involved and reflux in these veins is not controlled by pressure over the short saphenous vein. This explains the false positive diagnosis of valvular incompetence in the popliteal vein.

Adult↗
PubMed2006

Digital moiré interferometric investigations on the deformation gradients of enamel and dentine: an insight into non-carious cervical lesions.

OBJECTIVES: The objective of this study was to evaluate the biomechanical basis of non-carious cervical lesions by examining the patterns of deformation (strain) in the enamel and dentine. METHODS: The digital moiré interferometry is optics based non-destructive, whole-field experimental technique that provides whole-field strain information. Diffraction gratings (with a frequency of 1200 lines/mm) were transferred onto sagittal sections of human teeth, which were subsequently loaded compressively for loads ranging from 10 to 200 N at the incisal edge of the tooth. The acquired digital moiré fringe patterns were used to determine the in-plane deformation pattern in the enamel and the dentine in the direction parallel to the long axis (axial direction) and in the direction perpendicular to the long axis (lateral direction) of the tooth. RESULTS: It is observed that the enamel displayed marked strain gradients in the lateral direction, while the coronal dentine experienced marked strain gradients in the axial directions during compression. With the increase in applied loads, the strains in the enamel increased at the cervical edge (above the cemento-enamel junction) on the facial side, while the strains in the dentine increased below the cemento-enamel junction on the facial side. CONCLUSION: The enamel and dentine displayed unique in-plane deformation patterns in the axial and the lateral directions of the tooth. These experiments support the hypothesis that occlusal loading will contribute to cervical loss of dental hard tissues.

Compressive Strength↗
PubMedDate not supplied

Iliotibial band tenodesis: a new strategy for attachment.

We investigated the changes in distance between Gerdy's tubercle on the tibia and points on the posterior two thirds of the lateral surface of the lateral femoral condyle and adjacent lateral femoral shaft in 15 cadaveric knees. A three-dimensional digitizer was used to quantify motion of the knee during flexion ranging from full extension to 120 degrees of flexion. Four load states were applied: internal, external, and neutral rotation, and quadriceps muscles loads based on one third of values in the literature for maximal isometric quadriceps muscles moments. The femoral location most isometric to Gerdy's tubercle was found to be strongly influenced by the load state. A 1.0 cm wide iliotibial band tenodesis was modelled by five straight lines arising from Gerdy's tubercle and attaching to a simulated washer at the junction of the lateral femoral condyle and shaft. Using this model and the motion data obtained from the cadavers, we investigated the effects of quadriceps muscles loading and external rotation of the knee on changes in the distances between these tibial and femoral attachments for each of the five lines. A 180 degrees twist modelled into the tenodesis significantly reduced the range of changes in distance (difference between the largest and smallest changes in distance among the lines for a given angle of flexion) for both of these load states. Therefore, a 180 degrees twist in the tenodesis can enhance isometry among the fibers of the tenodesis. This implies that a 180 degrees twist can enhance load sharing among the fibers of the tenodesis and, therefore, enhance the overall strength of the tenodesis.

Adult↗
PubMed1998

Dentin demineralization inhibition at restoration margins of Vitremer, Dyract and Compoglass.

PURPOSE: To examine the in vitro caries inhibition of a resin-modified glass ionomer cement (Vitremer-3M) and two compomers (Dyract-Dentsply; Compoglass-Ivoclar). MATERIALS AND METHODS: Standardized Class V preparations were placed in 40 molars, the gingival margin placed below the cementoenamel junction. Randomly, 10 Vitremer, 10 Dyract and 10 Compoglass restorations were placed according to manufacturer's instructions, in 30 teeth. Ten teeth received P-50 composite resin (3M) restorations and acted as the control. All teeth had an acid-resistant varnish placed to within 1 mm of restoration margins and they were then placed into artificial saliva for 4 weeks, the saliva being replenished every 48 hours. All teeth were subjected to an artificial caries challenge (pH 4.4) for 5 days. Sections of 100 microns were obtained, photographed under polarized light microscopy, and then digitized to quantitate demineralized areas adjacent to the restoration. RESULTS: The mean (+/- S.D) area (microns 2) demineralization 100 microns from the dentin/gingival margin was: Vitremer 4965 +/- 841, Compoglass 4981 +/- 2209, Dyract 5375 +/- 516, P-50 8088 +/- 2083. ANOVA and Duncan's (P < 0.05) indicated all three fluoride-releasing materials examined in this study had significantly less demineralization adjacent to restoration margins than the P-50 composite resin control. Seventy percent of glass ionomer cement restorations demonstrated adjacent dentin inhibition zones, while no dentin inhibition zones were demonstrated with the compomer restorations.

Analysis of Variance↗
PubMed1984

Ureteropelvic junction obstruction in adults.

Ureteropelvic junction obstruction (UPJ) in adults is more common than generally appreciated. It may mimic other diseases and may be associated with abdominal pain, hypertension, and recurrent pyelonephritis. Diagnosis and surgical correction were frequently delayed with an average duration of symptoms of 3.2 years for 31 adult patients. Only 4 adults (13%) were diagnosed at the time of their initial onset of symptoms. Nephrectomies were performed on 24 per cent of renal units. Accessory lower pole renal vessels were found in 52 per cent of the adults with UPJ obstruction, twice the rate found in children. Intravenous digital subtraction angiography and diuretic radionucleotide renography should be considered in the evaluation of an adult patient with a UPJ obstruction because of the high rate of accessory vessels. If accessory vessels are present on the contralateral side, especially postnephrectomy, there is heightened concern for the remaining kidney and close follow-up with ultrasonography is recommended.

Adolescent↗
PubMed1978

Multicentric origin of the atrial depolarization wave: the pacemaker complex. Relation to dynamics of atrial conduction, P-wave changes and heart rate control.

In studies to ascertain the basis of dynamic changes in the P wave, bipolar epicardial potentials were recorded from multiple atrial electrodes in dogs. One hundred to 120 activation times were displayed by a digital computer and used to construct atrial isotemporal activation sequence maps. Changes in heart rate or beat-to-beat cycle length were induced by vagal stimulation or infusion of autonomic mediating drugs. Changes in cycle length were associated with dynamic changes in the atrial activation sequence and surface P-wave. A conspicuous finding was that epicardial atrial depolarization began at three widely separated locations. These three points were consistently present in all animals and were generally located at the 12, 3, and 6 o'clock positions of the superior vena cava-right atrial junction. The dynamic changes in P waves and atrial activation sequence which accompanied the changes in cycle length were due to sudden shifts in the point of earliest activity between the three early sites. Asymmetric atrial depolarization with more rapid conduction along the crista terminalis, superior interatrial band, and pectinate muscles was present in all dogs. Although the anisotropic atrial geometry played an important role in the asymmetric conduction, the widely distributed onset of activity contributed significantly to the uneven spread. The multiple points of origin of the atrial wavefront might be explained by either a trifocal, distributed pacemaker or the epicardial exits of three specialized pathways conducting an impulse emanating from a single focus. These data explain the dynamic variation in P-wave morphology in normal hearts and also imply a relationship between the altered origin of atrial depolarization, atypical P waves, brady- or tachyarrhythmias, and heart rate control.

Action Potentials↗