Characterization of the excitable gap in a functionally determined reentrant circuit. Studies in the sterile pericarditis model of atrial flutter

BACKGROUND

Single premature beats were introduced in the reentrant circuit during stable atrial flutter in the canine sterile pericarditis model to test the hypotheses that (1) despite the fact that the reentrant circuit is functionally determined, there is a fully excitable gap; (2) the excitable gap in the reentrant circuit is not uniform; and (3) inhomogeneities of conduction in the reentrant circuit explain the effects of premature beats.

METHODS AND RESULTS

A multiplexing system was used to record 190 unipolar electrograms from the right atrial free wall during 18 atrial flutter episodes in 9 dogs. In all 18 episodes, premature stimuli captured the atrial flutter reentrant circuit. At the longest coupling intervals, the return cycle at the site closest to the pacing site did not prolong. As the coupling interval of the premature stimulus decreased, the return cycle then progressively increased, associated with changes in conduction in the reentrant circuit that were not uniform. The result was that coupling intervals associated with introduction of the premature beat also were not constant. The mean duration of the total (ie, fully plus partially) excitable gap was 12 +/- 4 ms in areas of slow conduction, and it was always shorter than the total excitable gap in other areas (22 +/- 6 ms, P < .001). The mean duration of the fully excitable gap based on analysis of the return cycle was 4 +/- 1 ms in the reentrant circuit. In 13 of 18 atrial flutter episodes, a premature stimulus terminated atrial flutter by causing block of the orthodromic wave front of the premature beat in an area of slow conduction. The mean coupling interval that caused orthodromic block was 113 +/- 5 ms (recorded at the site just proximal to the area of block), and it was always longer than the delivered stimulus coupling interval at the pacing site (96 +/- 8 ms, P < .001).

CONCLUSIONS

We conclude that in this functionally determined atrial flutter reentrant circuit in the canine sterile pericarditis model, (1) a fully excitable gap is present in at least part of the reentrant circuit; (2) the duration of the excitable gap in the reentrant circuit is shortest in areas of slow conduction; and (3) when a premature beat encounters the partially excitable gap of the reentrant circuit, it results in changes in conduction such that the coupling intervals are not uniform throughout in the reentrant circuit.

Mechanism of interruption of atrial flutter by moricizine. Electrophysiological and multiplexing studies in the canine sterile pericarditis model of atrial flutter

BACKGROUND

Moricizine is said to have potent effects on cardiac conduction but little or no effect on cardiac refractoriness.

METHODS AND RESULTS

The effects of moricizine (2 mg/kg IV) on induced atrial flutter were studied 2 to 4 days after the creation of sterile pericarditis in 11 dogs. Ten episodes of stable atrial flutter before and after the administration of moricizine were studied in 9 dogs in the conscious, nonsedated state, and 7 episodes were studied in 6 dogs in the anesthetized, open chest state. In the conscious state, the effects of moricizine on atrial excitability, atrial effective refractory period, and intra-atrial conduction times were studied by recording during overdrive pacing of sinus rhythm from epicardial electrodes placed at selected atrial sites. Moricizine prolonged the atrial flutter cycle length in all the episodes, from a mean of 133 +/- 9 to 172 +/- 27 milliseconds (P < .001), and then terminated 7 of the 10 episodes. Moricizine increased the atrial threshold of excitability from a mean of 2.3 +/- 1.4 to 3.3 +/- 2.2 mA (P < .01) and prolonged intra-atrial conduction times (measured from the sulcus terminalis to the posteroinferior left atrium) from a mean of 58 +/- 6 to 64 +/- 5 milliseconds (P < .005). Prolongation of the atrial effective refractory period from 166 +/- 20 to 174 +/- 24 milliseconds (P < .05) was observed only at the sulcus terminalis site. In the open chest studies, administration of moricizine prolonged the atrial flutter cycle length from a mean of 150 +/- 15 to 216 +/- 30 milliseconds (P < .001) and then terminated the atrial flutter in all 7 episodes. As demonstrated by simultaneous multisite mapping from 95 bipolar sites on the right atrial free wall, the atrial flutter cycle length prolongation was either due to further slowing of conduction in an area of slow conduction in the reentrant circuit of the atrial flutter (5 episodes) or further slowing of conduction in an area of slow conduction plus the development of a second area of slow conduction (2 episodes). The change in conduction times in the rest of the reentrant circuit was negligible (10.9 +/- 8.7% of the total change). In all 7 episodes, the last circulating reentrant wave front blocked in an area of slow conduction.

CONCLUSIONS

Moricizine (1) prolongs the atrial flutter cycle length, primarily by slowing conduction in an area of slow conduction in the reentrant circuit, (2) terminates atrial flutter by causing block of the circulating reentrant wave front in an area of slow conduction of the reentrant circuit, and (3) effectively interrupts otherwise stable atrial flutter in this canine model. The reason for these effects of moricizine are not readily explained by its effects on global atrial conduction times and refractoriness studied during sinus rhythm. Local changes in conduction in an area(s) of slow conduction are responsible for both cycle length prolongation and atrial flutter termination rather than the traditional wavelength concept of head-tail interaction.

Mapping the conversion of atrial flutter to atrial fibrillation and atrial fibrillation to atrial flutter. Insights into mechanisms

It is not generally believed that there is a relation between atrial flutter, thought to be due to a single reentrant circuit, and atrial fibrillation, thought to be due to simultaneously circulating multiple-reentrant wave fronts. However, there are many reasons to suggest that these rhythms are more closely related than previously thought. To test the hypothesis that the length of an area of functional block in the right atrial free wall is critical to the conversion of atrial flutter to atrial fibrillation and of atrial fibrillation to atrial flutter, we studied spontaneous and ATP-induced conversion of stable atrial flutter to sustained atrial fibrillation and spontaneous conversion of sustained atrial fibrillation to stable atrial flutter. We studied 13 episodes of the conversion of stable atrial flutter to sustained atrial fibrillation and sustained atrial fibrillation to stable atrial flutter in seven dogs with sterile pericarditis. Six episodes were spontaneous and seven were ATP related. All episodes were studied by using a multisite mapping system to record 190 unipolar electrograms (converted in the software to 95 bipolar electrograms) from the right atrial free wall along with ECG lead II. Atrial flutter induction was attempted by atrial stimulation (S1S2 or S1S2S3) or by rapid atrial pacing for > or = 20 beats from selected sites at selected rates. For both the spontaneous and the ATP-related episodes, stable atrial flutter was defined as any episode of > or = 5 minutes, and sustained atrial fibrillation was any episode of > or = 1 minute. During all the episodes of stable atrial flutter, a line of functional block with a mean length of 24 +/- 4 mm was localized on the right atrial free wall. When the previously stable line of functional block decreased to a mean of 16 +/- 3 mm (P < .05), either spontaneously or after ATP administration (40 mg i.v.), the new line of functional block was not long enough to maintain stable atrial flutter, and conversion to atrial fibrillation resulted. This shortened line of functional block continued to change and migrate over the right atrial free wall throughout sustained atrial fibrillation. These observations were similar for both spontaneous and ATP-induced conversions. When sustained atrial fibrillation evolved to stable atrial flutter, there was reformation of a long line of functional block, long enough (> or = prior length) to create a stable reentrant circuit, which then captured the right atrial free wall and subsequently both atria.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of the antidepressant drug tianeptine on plasma and platelet serotonin of depressive patients and healthy controls

We have examined the effects of a single 12.5 mg dose and of 12 weeks treatment up to 37.5 mg daily with tianeptine, a new antidepressant drug that potentiates in vivo the uptake of serotonin (5-HT). On day 0, tianeptine reduced plasma 5-HT concentration. This acute effect occurred also on subsequent examination days. However, long-term treatment tended (P < 0.06) to increase basal plasma 5-HT concentrations, in covariation with decreases of MADRS (Montgomery-Asberg Depression Rating Scale) and HARS (Hamilton Anxiety Rating Scale). Platelet 5-HT increased only in elderly patients, probably due to the higher plasma concentration of the drug in this group than in younger patients. These results show that the acute effects of therapeutic doses of tianeptine are consistent with an enhancement of the 5-HT uptake. However, long-term treatment does not result in a decreased plasma 5-HT, as might be expected from the acute effects of the drug.

Mechanism of spontaneous termination of stable atrial flutter in the canine sterile pericarditis model

BACKGROUND

We tested the hypotheses that spontaneous termination of stable atrial flutter is directly related to spontaneous beat-to-beat cycle length oscillations and that block of the circulating reentrant wave front occurs in an area of slow conduction.

METHODS AND RESULTS

We studied 30 episodes of spontaneous termination of stable atrial flutter induced by atrial stimulation in 11 conscious, nonsedated dogs with sterile pericarditis. Additionally, in 5 dogs, 14 episodes of spontaneous termination of stable atrial flutter were studied with a multisite mapping system to record simultaneously from 190 right atrial electrodes. In the conscious-state studies, atrial flutter cycle length oscillations began 6 +/- 1 (mean +/- SEM) beats before termination in 26 episodes, stable atrial flutter evolved into atrial fibrillation in 3 episodes, and no cycle length change occurred before termination in 1 episode. In the open-chest studies, in all instances, spontaneous oscillations began 7 +/- 1 beats before termination. The only consistent oscillation pattern occurred for the last two beats: a long cycle length (149 +/- 9 milliseconds) followed by a much shorter cycle length (110 +/- 6 milliseconds) (P < .01). Activation maps demonstrated that all cycle length oscillations were explained by changes of conduction in an area(s) of slow conduction in the reentrant circuit. In two instances, the last (short) cycle length was associated with disappearance of an area of slow conduction. In all episodes, the last circulating reentrant wave front blocked in an area of slow conduction in the reentrant circuit. Although not tested, during the last beat, the very early arrival of the circulating reentrant wave front at an area of slow conduction suggests an important role for refractoriness, with head and tail interactions, resulting in block.

CONCLUSIONS

Spontaneous termination of stable atrial flutter in the sterile pericarditis model (1) is preceded by beat-to-beat cycle length oscillations that result from changes in conduction in areas of slow conduction in the reentrant circuit and (2) results from block of the circulating reentrant wave front in an area of slow conduction.

Randomized trial comparing three forms of pelvic floor repair for neuropathic faecal incontinence

A randomized controlled trial in women with neuropathic faecal incontinence compared total pelvic floor repair (n = 12) with anterior levatorplasty and sphincter plication alone (n = 12) and postanal repair alone (n = 12). Review at 6 and 24 months indicated that results were significantly better for total pelvic floor repair than either of the other procedures. Complete continence was achieved in eight of the 12 patients 2 years after total pelvic floor repair. Only total repair significantly elongated the anal canal. Both total pelvic floor repair and anterior levatorplasty improved sensation in the upper anal canal.

[Mucinous adenocarcinoma of the urachus. Apropos of a case]

This report present one case of mucinous adenocarcinoma of the urachus, a very uncommon tumour with eccentric clinical behaviour. It includes a brief description of both its macro and microscopic appearance, establishing the differential diagnosis both with adenocarcinoma of the vesical dome and the metastatic tumours which can affect the bladder. Also, there is a brief comment on the main anatomo-clinical characteristics of these tumours.

Propylthiouracil (PTU)-induced agranulocytosis treated with recombinant human granulocyte colony-stimulating factor (G-CSF)

Two premenopausal female patients with Graves' hyperthyroidism and propylthiouracil (PTU)-induced agranulocytosis are presented. The first patient, age 47, received 300 mg of PTU per day and developed agranulocytosis within 6 weeks of the commencement of therapy. There were no granulocytes in the peripheral smear and a bone marrow biopsy demonstrated an absence of the entire myeloid cell line as well as the presence of many granulomas. The second patient, age 39, received PTU 1600 mg per day for two and half weeks and then 2 days of methimazole, 200 mg per day. She developed complete agranulocytosis on peripheral smear within 3 weeks of the initiation of therapy. Her bone marrow biopsy demonstrated maturation arrest of the granulocytic cell line at the myelocyte stage. In addition to discontinuing their antithyroid drugs, both patients were treated with G-CSF subcutaneously. The first patient received 300 micrograms of G-CSF on days 2 and 4 after discontinuing PTU with the appearance of 4.7 x 10(9)/L granulocytes and granulocyte precursors on day 4. The second patient received 575 micrograms of G-CSF for 2 days and 300 micrograms for 1 additional day beginning on the third day after discontinuing antithyroid drugs. On the second treatment day there were 5.8 x 10(9)/L granulocytes and granulocyte precursors on the peripheral smear. A comparison to previously published cases on antithyroid drug induced agranulocytosis suggests that the use of G-CSF decreased the amount of time required for marrow recovery after the cessation of the offending drug.

[Gammagraphic findings in hepatic focal nodular hyperplasia]

Two cases, of focal nodular hyperplasia (FNH) are presented which were detected by chance and in which the gammagraphic study was the only parameter which indicated the changes that occurred in the hyperplasia revealing a hypervascular mass, colloid capture and 99mTc-DISIDA retention in the later image. These liver masses are now seen more frequently given the wide use of echography and the gammagraphic studies could be useful in the orientation of their nature in a non aggressive manner.

Cation-induced aggregation and fusion of N-acyl-N-methyl-phosphatidylethanolamine vesicles

Aggregation and fusion of unilamellar vesicles consisting of N-acyl-N-methylphosphatidylethanolamine were studied as a function of mono- and divalent cation concentrations. The aggregation reactions were irreversible processes, as demonstrated by changes in monovalent ion concentrations and by the addition of ethylenediaminetetraacetic acid (EDTA) to chelate divalent cations, suggesting the possibility of some cation-induced vesicle fusion. An increase in the NaCl ionic strength of the vesicle suspension solutions diminishes the threshold concentration for Li+ and K+ and increases that corresponding to Mn2+, Mg2+ and Ca2+. However NaCl concentrations above 300 mM yield smaller threshold values for the divalent cation-induced processes, probably due to the increased size of phospholipid vesicles as the ionic strength of the medium increases.

Effects of monoamine uptake inhibitors on extracellular and platelet 5-hydroxytryptamine in rat blood: different effects of clomipramine and fluoxetine

1. The concentration of 5-hydroxytryptamine (5-HT) in rat platelet-free plasma increased significantly 30 min after a single i.p. injection (10 mg kg-1) of each of six inhibitors of the high-affinity 5-HT uptake (fluvoxamine, fluoxetine, alaproclate, paroxetine, sertraline and clomipramine). The increases ranged from 226% to 776% of control values. In contrast, imipramine, desipramine and femoxetine had no significant effect. The increase elicited by paroxetine was dependent on the dose (1, 5 and 10 mg kg-1) and returned to control values after 4 h. That observed after clomipramine was also transient and paralleled the plasma concentration of the drug (Spearman-rank correlation r = 0.43). 2. In vivo, the rat pulmonary vascular endothelium removed trace amounts (8.8 nmol in a bolus) of intravenously injected [14C]-5-HT. Paroxetine pretreatment (10 mg kg-1, 30 min before-hand) reduced this uptake by 73%. 3. Repeated fluoxetine treatments reduced rat whole blood 5-HT concentration (ca. -60% after daily 2 x 5 mg kg-1, i.p. during 14 days). However, plasma (extracellular) 5-HT was not increased. 4. Various repeated treatments with clomipramine (i.p. injections or osmotic minipumps, up to 30 mg kg-1 day-1), failed to decrease rat whole blood 5-HT concentrations. Platelet-free plasma 5-HT was also unchanged, even after treatments yielding plasma clomipramine levels 2.7 times higher than those that increased it acutely. 5. These results indicate that the extracellular pool of 5-HT in rat blood (measured in the platelet-free plasma) is physiologically under the control of high-affinity 5-HT uptake systems.The sustained 5-HT uptake inhibition does not result in an increase of 5-HT in platelet-free plasma, suggesting that adaptative mechanisms are triggered. The distinct long-term effects of the two antidepressants clomipramine and fluoxetine on rat whole blood 5-HT suggest a differential in vivo action on the rat 5-HT uptake.

Total pelvic floor repair for the treatment of neuropathic fecal incontinence

Long-term results of postanal repair are poor. Many patients with neuropathic incontinence have evidence of anterior pelvic floor weakness. A more comprehensive surgical repair has therefore been developed that involves postanal repair, anterior levatorplasty, and external sphincter plication. Primary total pelvic floor repair was performed in 22 women with neuropathic fecal incontinence. Fourteen patients who remained incontinent after conventional postanal repair underwent secondary anterior levatorplasty and external sphincter plication (two stages). Neither resting nor squeeze anal pressures were influenced by any of these procedures. However, pelvic floor descent at rest and straining was significantly decreased following primary total pelvic floor repair and secondary pelvic floor repair (p less than 0.05) but not by postanal repair. Complete continence for liquids, solids, and flatus was achieved in 41% of patients after primary total pelvic floor repair and in 14% after secondary anterior levatorplasty and external sphincter plication, but in only 4% after postanal repair. Only one patient after primary total pelvic floor repair and one after secondary anterior levatorplasty and external sphincter plication had persistent incontinence compared with 18 (38%) after postanal repair.

Post-Chernobyl accident radioactivity measurements in the Comunidad Autonoma de Valencia, Spain

Increased atmospheric radioactivity after the accident in Chernobyl was first detected on air filters. Measurements were begun in Valencia on May 2, 1986, with the maximum activity being observed around May 3-4, 1986. As a consequence of this accident, annual campaigns of measurements on migrating birds (several species of aquatic birds and song-thrushes) were started. The data corresponding to the campaign immediately after the accident (1986/87) show a generalized contamination (approximately 50% of the measured specimens). Significant levels of 134Cs, 137Cs and 110Agm were found. It is important to note that 110Agm is only present in Aythya ferina. In the successive campaigns in 1988/89 and 1989/91 few samples were found to be contaminated and only 137Cs was identified. Strontium-90 was measured and identified in some specimens, mainly in their bones.

How reliable is measurement of the anorectal angle by videoproctography?

The anorectal angle can be determined either by constructing a straight line along the lower border of the rectum (Method A) or by using the central longitudinal axis of the lower rectum (Method B). We have used a computer program to derive the centroid of the rectum for Method B. The coefficients of variation for angles measured at rest, during maximum pelvic floor contraction, and during attempted defecation were 0.616, 0.351, and 0.358, respectively, compared with 0.993, 0.972, and 0.968 for Method B. The presence of a rectocele had no influence on the measurement of the anorectal angle in incontinence, but there was a significant difference in assessment of the angle between constipated patients (P less than 0.05) and controls (P less than 0.05). Posterior indentation of the rectum had no significant influence on measurement of the angle in any group. These data indicate that a computer-derived centroid is more reliable for measurement of angles, but a correction factor for anterior rectocele is needed in constipated patients and controls.

[Therapeutic usefulness of antioxidant drugs in experimental intestinal reperfusion syndrome]

The intestinal reperfusion injury has been studied in Sprague-Dawley rats weighing 200 g. Intestinal ischemia has been induced by clamping the Superior Mesenteric Artery (SMA) for 120 minutes. In order to parallel clinical situations, free radical scavengers (allopurinol [ALLO]) and superoxide-dismutase [SOD] were inoculated at a low perfusion rate through the femoral vein during the last 20 minutes of the ischemic period. Both drugs have decreased the mortality rate (from 70% in control group, to 40%) and the mean percentage of damaged intestine (30.89% vs. 23.84% and 24.70%). Histologically, ALLO was less effective than SOD (12.54 control; 8.40 SOD; 11.54 ALLO). The modification of glucose, SGOT, SGPT and LDH found in all the ischemic animals shows the hepatocellular injury induced by intestinal reperfusion.

Effects of the antidepressant drug tianeptine on plasma and platelet serotonin concentrations in the rat

The antidepressant drug tianeptine increased rat plasma 5-hydroxyindoleacetic (5-HIAA) concentrations after single and repeated treatment for 14 days. This effect was not due to an increase in 5-hydroxytryptamine (5-HT) synthesis, as measured by the accumulation of 5-hydroxytryptophan in plasma and brain. A concurrent decrease in platelet-free plasma 5-HT concentrations occurred after subchronic treatment. Tianeptine attenuated the large increase in 5-HT concentrations in platelet-free plasma elicited by the specific 5-HT uptake inhibitors citalopram and paroxetine. These data are compatible with the reported 5-HT uptake-enhancing activity of this antidepressant drug.

The effect of age on pelvic floor dynamics

Anorectal function is known to be influenced by age but there is only scanty information about the effect of ageing on pelvic floor dynamics. Pelvic floor movements were assessed by videoproctography in two groups of ten control females (mean age of 30.5 and 60.7 years, respectively). A significantly lower pelvic floor position was found at rest in the older group (p = 0.02), but younger controls showed an increased pelvic floor descent during straining (p = 0.01). These results suggest that the pelvic floor is affected by progressive denervation but descent during straining tends to decrease with advancing age.

[Zinc deficiency caused by postgastrectomy fistula with high flow in a patient undergoing prolonged parenteral nutrition]

A case is presented of a 57-year-old male patient who underwent total gastrectomy due to gastric adenocarcinoma. During the postoperative period the patient required long-term parenteral nutrition due to a high-debit GI fistula (over 700 ml/day) and sepsis. Two months after parenteral nutrition was started, the patients presented irritability, mucocutaneous lesions and progressive bolding. Serum alkaline phosphatase and zinc levels were lower than normal, although a supplemental 0.03 mg/k/day of zinc was administered. Faced with this zinc deficiency picture, 10 mg zinc sulfate was administered parenterally on a daily basis. The deficiency picture improved markedly over a week's period, and serum zinc and alkaline phosphatase levels returned to normal. The importance of zinc balance control in patients under long-term parenteral nutrition and high fluid debit through GI fistulas is highlighted.

[Echocardiographic diagnosis of accessory leaflet of mitral valve]

The accessory mitral valve leaflet is a rare cardiac congenital anomaly usually associated to complex cardiac congenital malformations. It also represents a rare cause of left ventricular outflow tract obstruction. Its diagnosis has often been ignored by conventional diagnostic methods. This fact may represent a cause for relative surgical failure, when operations for cardiac complex anomalies are performed. Echodopplercardiography is the choice and more accurate method for its diagnosis. In our case, parasternal and apical long axis planes, allowed an unmistakable visualization of a parachute shape fibrous structure, with its concave surface turned up towards the aortic valve. Chordae tendinae proper to the anomalous accessory mitral valve tissue were connected to chordae or to papillary muscles of the mitral valve. A careful echodopplercardiographic study will allow us, not only to diagnose this malformation, as well as to differentiate it from other conditions like tumors, vegetations or other types of subaortic obstruction.