Effects of thyroid hormone on carbonic anhydrase I gene expression in human erythroid cells

Individuals with hyperthyroidism exhibit concentrations of carbonic anhydrase I (CAI) in red blood cells that reflect the integrated serum thyroid hormone concentration over the preceding few months. Furthermore, triiodothyronine T3, at a physiological free concentration, decreases the CAI concentration in both human erythroleukemic YN-1 cells and burst-forming unit-erythroid (BFU-E)-derived cells. In the present study, the effect of T3 on CAI mRNA levels in various human erythroleukemic cell lines (YN-1, HEL and KU-812) and BFU-E-derived cells was studied. Northern analysis of RNA extracted from erythroid cells revealed a CAI mRNA of 1.5 kilobases. T3 significantly decreased the levels of CAI mRNA in YN-1 and BFU-E-derived cells in a dose-dependent manner. Incubation of T3-stimulated cells with actinomycin D prevented the decrease in CAI mRNA levels. By contrast, T3 had no effect on either the concentrations of CAI or the levels of CAI mRNA in HEL and KU-812 cells. These results suggest that YN-1 and BFU-E-derived cells may be useful models for investigating T3 actions on CAI mRNA in human cells.

Successful slow pathway ablation in a patient with atrioventricular nodal reentrant tachycardia having a proximal common pathway

Radiofrequency catheter ablation was attempted in a patient with atrioventricular nodal reentrant tachycardia (AVNRT). AVNRT was easily inducible but an intermittent loss of the atrial activation was observed during AVNRT suggesting the presence of a proximal common pathway. During sinus rhythm, a relatively delayed activation that was compatible with a slow potential, was recorded anterior to the ostium of coronary sinus, and radiofrequency catheter ablation application (20 watts) to the site induced junction tachycardia. After an additional radiofrequency catheter ablation application to close the site, AVNRT became noninducible without deterioration of atrioventricular conduction through a fast pathway. This is the first case in which radiofrequency catheter ablation application to the slow potential recording site has been successful, even in AVNRT having a proximal common pathway.

Selective recognition of tandemly repeated DNA sequences by homo- and heterodimers of short peptides

The non-covalent and specific protein-protein interaction is critical to the specificity and the cooperativity of the DNA-binding by protein dimers. We have designed and synthesized three sets of peptide dimers with covalent- or noncovalent artificial dimerization modules to elucidate the structural and thermodynamic aspects for the sequence-specific DNA-binding by protein dimers. We have investigated the DNA binding of covalent dimer, noncovalent homodimer and noncovalent heterodimer with specific or nonspecific DNA sequences by gel mobility shift assay. Although the amino acid sequence of DNA-binding region of these peptide dimers are the same, the selectivity and the cooperativity of DNA binding by these peptide dimers were found to be different.

[Hemostatic evaluation of a patient with haloperidol-induced neuroleptic malignant syndrome associated with disseminated intravascular coagulation]

A 94-year-old man who had been admitted to our hospital for the treatment of senile dementia and restless behavior exhibited consciousness disturbances, acute respiratory failure, high fever, and thrombocytopenia the day after receiving haloperidol as prescribed by a psychiatrist. On the fourth day following administration of haloperidol, acute renal failure with rhabdomyolysis and disseminated intravascular coagulation (DIC) developed in the patient, who was accordingly given a diagnosis of haloperidol-induced neuroleptic malignant syndrome (NMS) associated with DIC. He was then given heparin and antithrombin III, and his DIC symptoms improved soon thereafter. Elevated plasma levels of tissue factor and tumor necrosis factor-alpha (TNF-alpha) were sustained during this therapy course. Other cytokines, including interleukin IL-1 beta, IL-2 and IL-6, were not elevated. There are activation of extrinsic coagulation and an elevated level of TNF-alpha during acute renal failure and rhabdomyolysis associated with NMS, which is thought to trigger the onset of DIC.

The usefulness of Holter monitoring in selecting pharmacologic therapy for patients with sustained monomorphic ventricular tachycardia: studies in patients in whom no effective pharmacologic therapy could be determined by electrophysiologic study

The usefulness of Holter monitoring (HM) in selecting pharmacologic therapy for patients with sustained monomorphic ventricular tachycardia (VT) was evaluated in patients in whom no effective pharmacologic therapy could be determined in an electrophysiologic study (EPS). The study population consisted of 49 consecutive patients with sustained VT who were receiving long-term pharmacologic therapy despite the fact that no pharmacologic therapy had been found to be effective in the EPS. The efficacy of the pharmacologic therapies was assessed by HM. A reduction in frequent (10/h) premature ventricular contractions (PVCs) was used as an index of treatment efficacy, with therapies achieving substantial PVC suppression (>70% of all PVCs) being considered to be effective (HM effective group). When no therapy was found to be effective when assessed by HM, a drug with any other beneficial effect, eg, reduction in VT rate, was chosen (HM ineffective group). VT recurrence and survival were compared between groups. During the follow-up period of 31+/-28 months, VT recurrence was observed in a total of 25/49 patients: 3/17 patients in the HM effective group, in 18/25 in the HM ineffective group, and in 4/7 in the HM undetermined group (p=0.0487). Sudden cardiac death occurred in a total 7/49 patients: 2/17 patients in the HM effective group, 4/25 patients in the HM ineffective group, and 1/7 patient in the HM undetermined group (p=0.2828). Among patients in whom no effective therapy could be determined by EPS, the VT recurrence rate was significantly lower in the group in whom treatment was effective as assessed by HM than among those in whom treatment was assessed by HM to be ineffective. Sudden cardiac death rate was also lowest in the HM effective group, although the difference was not statistically significant. HM assessment was considered useful in selection of pharmacologic therapy for patients in whom no effective therapy could be determined in the EPS.

Comparative electrophysiologic findings between responders and nonresponders to class III antiarrhythmic drugs among patients with ventricular tachyarrhythmia

Electrophysiologic testing was performed in 31 patients with ventricular tachycardia (21 cases) and fibrillation (10 cases) to characterize the electrophysiologic properties of patients responding or not responding to therapy with class III antiarrhythmic drugs. At the baseline, there were no differences among the patients in the monomorphic VT cycle length (CL), block CL or the width of the zone of entrainment. Ventricular tachyarrhythmias after the administration of class III drugs (sotalol: 9, amiodarone: 15 and E-4031/MS-551: 7) were inducible (non-responders) in 17 patients and non-inducible (responders) in 14 (45%). The class III drugs prolonged the sinus cycle length (SCL), QT interval and right ventricular effective refractory period (VERP), but had little effect on ventricular conduction time in the responders and non-responders. The SCL, QT interval and VERP at the three drive cycle lengths of 600, 400 and 300 msec were significantly longer in the responders than in the non-responders, but the class III drug action on VERP showed a reverse use-dependency. Isoproterenol administered to the responder did not fully reverse the class III antiarrhythmic drug-induced prolongation of QT, QTc and VERP, which remained significantly prolonged compared to the baseline values. Furthermore, when the VERP after the administration of class III drugs were greater than 270, 250 and 240 msec at the three drive cycle lengths of 600, 400 and 300 msec, respectively, it was associated with the non-inducibility of VT/VF. Though the precise mechanism of the drug efficacy is not yet known, these observations help to clarify the ability of class III drugs to prevent the induction of ventricular tachyarrhythmia.

Saphenous vein graft shrinkage as a mechanism of stenosis soon after bypass surgery

A 63-year-old man with left main coronary artery disease underwent aortocoronary bypass surgery using saphenous vein grafts. Less than 1 month later, severe narrowing occurred in the mid-portion of the vein graft to the left anterior descending coronary artery. Preintervention intravascular ultrasonography revealed prominent vein graft shrinkage. Percutaneous transluminal angioplasty failed because the stenotic lesion could not be dilated, even by high-pressure balloon inflation. Saphenous vein graft shrinkage appears to be one of the mechanisms of early saphenous vein graft stenosis, and balloon angioplasty to the vein graft stenosis with prominent shrinkage may be of only limited value.

Electrophysiologic effects of intravenous MS-551, a novel class III antiarrhythmic agent, on human atrium and ventricle

The effects of intravenous MS-551, a new class III antiarrhythmic drug, on atrium and ventricle were evaluated in 6 patients with ventricular tachyarrhythmias (4 males and 2 females; mean age 45 +/- 21 years) in an electrophysiologic study. Two patients had sustained ventricular tachycardia (VT) and 4 patients had ventricular fibrillation (VF). Electrophysiologic study was performed before and after the administration of MS-551 (loading infusion 0.3 mg/kg for 5 min + 0.01 mg/kg/min). The QT and QTc intervals were significantly prolonged by MS-551 from 359 +/- 52 to 411 +/- 63 msec (p = 0.01) and from 410 +/- 36 to 452 +/- 47 (p = 0.0172), respectively. No effect was observed on the sinus cycle length, QRS duration, or AH and HV intervals in sinus rhythm. The effective refractory periods of the right atrium (AERP) were significantly prolonged at paced cycle lengths of 600 (from 222 +/- 19 to 250 +/- 23 msec, p = 0.0009), 400 (from 207 +/- 15 to 228 +/- 15, p < 0.0001) and 300 (from 193 +/- 10 to 205 +/- 8 msec, p = 0.0127) msec. Similarly, the right ventricular ERP (VERP) were significantly prolonged at paced cycle lengths of 600 (from 240 +/- 23 to 268 +/- 23 msec, p < 0.0001), 400 (from 225 +/- 22 to 250 +/- 24 msec, p = 0.0007), and 300 msec (from 213 +/- 14 to 228 +/- 18 msec, p = 0.0071). MS-551 prolonged AERP and VERP in a "reverse" use-dependent manner without changing the conduction time in patients with ventricular tachyarrhythmias. MS-551 prevented the induction of VT in 1 patient and VF in only 1 patient in this electrophysiologic study. Further evaluation of the therapeutic potential of MS-551 using higher dosages is necessary.

Progression to moderate or severe mitral regurgitation after percutaneous transvenous mitral commissurotomy using stepwise inflation technique

Progression to moderate or severe mitral regurgitation (MR) was studied after Inoue balloon percutaneous transvenous mitral commissurotomy (PTMC) using the stepwise inflation technique, performed at increments of 1 mm of balloon diameter, in 49 consecutive patients with rheumatic mitral stenosis (aged from 32-73 years; 8 males, 41 females). The patients were classified on the basis of the degree of MR after PTMC, compared with that before PTMC, into either Group A, development of moderate or more severe (> or = grade 2) MR (n = 8) or Group B, no increase in MR or development of mild (grade 1) MR (n = 41). Progression to moderate or severe MR was significantly associated only with advanced age (60 +/- 8 vs 52 +/- 10 years, p < 0.05) and narrower mitral valve area (0.87 +/- 0.35 vs 1.11 +/- 0.29 cm2, p < 0.05), but other characteristics before PTMC were similar in both groups. There was no difference between the two groups in the total number and degree of balloon inflation. Immediately before the final inflation, the left atrial mean pressure and v wave pressure were decreased in smaller degrees in Group A compared with Group B (-2 +/- 2 vs -5 +/- 4 mmHg, p < 0.05; -2 +/- 2 vs -6 +/- 6 mmHg, p < 0.05, respectively). Thus, the stepwise inflations require careful monitoring of changes in the left atrial pressure and waveform to recognize the aggravation of MR, especially in older patients with severe stenosis. Patients who do not have a significant drop in left atrial mean pressure and v wave pressure during stepwise inflations of the balloon might be at risk of development of moderate or severe MR after further dilations.

Thyroid hormone regulates expression of shaker-related potassium channel mRNA in rat heart

Effects of thyroid hormones on cardiac function or rhythm have been known; however, the mechanism is still unclear. In the present study examined were effects of triiodethyronine (T3) on voltage-gated potassium channel gene expression in rat heart since the potassium channels were presumed to modulate cardiac functions. The mRNA expression of five voltage-gated potassium channel gene alpha subunits (Kv1.2, Kv1.4, Kv1.5, Kv2.1, and Kv4.2) in heart was examined by ribonuclease protection assay in rats which were treated with T3 or propylthyouracil (PTU). All these genes except Kv1.4 mRNA were apparently expressed in the normal rat heart ventricle. Kv1.2 mRNA expression in ventricle was markedly suppressed by T3-treatment and enhanced by PTU-treatment. Interestingly, upregulation of Kv1.4 mRNA expression and downregulation of Kv1.5 mRNA expression were concomitantly induced in the ventricle by the PTU-treatment. In addition, the downregulation of the ventricular Kv1.5 mRNA expression induced by PTU was restored by T3 replacement. No changes of Kv2.1 and Kv4.2 mRNA expression were observed in the ventricles by the T3- or PTU-treatment. In heart atrium the same findings were observed. Kv1.4 mRNA expression, which was detectable in control rat atrium, also decreased significantly by T3-treatment. In contrast, no changes of Kv1.2, Kv1.4, and Kv1.5 mRNA expression in rat brains were induced by T3-treatment. These findings suggest that thyroid hormone specifically influences mRNA expression of Shaker-related potassium channel genes in rat hearts through a common T3 receptor-mediated regulation at a transcriptional level.

Effects of class I and III antiarrhythmic drugs on ventricular tachycardia-interrupting critical paced cycle length with rapid pacing

The most common mechanism of sustained ventricular tachycardia (VT) is re-entry with an excitable gap, but the electrophysiologic properties and response to antiarrhythmic drugs in the area of slow conduction are not yet fully known. The purpose of this study was to assess the effects of a class I antiarrhythmic drug (procainamide) and class III agents (amiodarone, E-4031, and MS-551) on re-entrant VT using the width of the zone of entrainment. The cycle length (CL) of VT (VTCL), the block CL that was the longest paced CL that interrupted the VT, and the width of the zone of entrainment, defined as the difference between VTCL and block CL, were compared before and after treatment with antiarrhythmic drugs. The VTCL was prolonged significantly from 308+/-63 to 410+/-77 msec after procainamide (p<0.005) but was not changed after the administration of the class III agents: from 294+/-50 to 292+/-13 msec after amiodarone, and from 305+/-47 to 313+/-31 msec after E-4031 or MS-551 (p=NS). The block CL was prolonged from 255+/-61 to 331+/-70 msec after procainamide (p <0.01), from 256+/-20 to 260+/-25 msec after amiodarone, and unchanged after E-4031 or MS-551 (253+/-31 msec before and 270+/-43 msec after) (p=NS). The width of the zone of entrainment as a representative of the width of the excitable gap was changed from 52+/-26 to 79+/-35 msec (p<0.05) after procainamide, whereas it was unchanged after amiodarone (48+/-7 msec before and 43+/-7 msec after) and after E-4031 or MS-551 (50+/-10 msec before and 40+/-9 msec after). Therefore, amiodarone, E-4031, and MS-551 did not affect VTCL and block CL whereas procainamide increased these parameters. The excitable gap substituting as the zone of entrainment was increased by procainamide but slightly reduced by amiodarone, E-4031, and MS-551. The effects of these antiarrhythmic drugs on the excitable gap of re-entrant VT were variable and should be examined further.

Repetitive ventricular responses induced by radiofrequency ablation for idiopathic ventricular tachycardia originating from the outflow tract of the right ventricle

In 23 consecutive patients, radiofrequency (RF) ablation was used as treatment for idiopathic ventricular tachycardia (VT) originating from the outflow tract of the right ventricle. In this study, we focused on the repetitive ventricular response (> 5 consecutive QRS beats during RF application). The incidence and clinical implications of the repetitive ventricular response were examined through the results of endocardial mapping and RF ablation. VT origin was mapped as the earliest activation site during VT, and it was determined within 0.5 x 0.5 cm (narrow site) in 13 patients and wider than 0.5 x 0.5 cm (wide origin) in the other 10 patients. The repetitive ventricular response was induced during application of RF current in 14 of 23 patients (61%), and it was more frequently observed in VT from a wide origin (100%) than in the VT from a narrow site (31%). The QRS morphology of the repetitive ventricular response was identical to that of clinical VT. As RF application was continued and/or repeated, the RR interval of the repetitive ventricular response was gradually prolonged, the number of consecutive QRS complexes was decreased, and clinical VT was finally eliminated. The overall success rate of RF ablation was 96% (22/23 patients), and no complications were observed. In conclusion, a repetitive ventricular response was frequently observed in idiopathic right VT. The changing pattern of repetitive ventricular response, slowly and/or disappearing was consistent with successful RF ablation.

Effects of the ATP-sensitive K channel opener nicorandil on the QT interval and the effective refractory period in patients with congenital long QT syndrome. Investigator Group for K-Channel Openers and Arrhythmias

Congenital or idiopathic long QT syndrome is characterized by a frequently lethal ventricular arrhythmia called torsades de pointes (TdP) as well as a prolonged QT interval. The long QT interval related to an abnormal gene of the Na+ channel has been shown to be shortened by mexiletine. However, the action of K+ channel openers on the QT interval associated with abnormal genes of the K channel has yet to be studied. Seven patients of five families with long QT syndrome were included in this study, of whom six had syncope and six had documented TdP. Either long QT interval or sudden cardiac death had been observed in family members of all seven patients. At 1 to 3 weeks after admission, when TdP or frequent ventricular arrhythmia had subsided, nicorandil, an ATP-sensitive K channel opener, was administered orally at a dose of 15 mg/day in five patients and at 30 mg/day in the remaining two patients, and the effects were assessed on the third day after drug administration. In four patients, the effective refractory period was measured in the right ventricle before and after administration of K channel opener administration. The QT interval (QTc) prior to administration of the K channel opener was 0.60 +/- 0.09 ms (mean +/- SD) (0.61 +/- 0.10 second(1/2)), which was shortened to 0.54 +/- 0.05 ms (0.55 +/- 0.06 second(1/2)) on the third day of drug administration (P < .05 for both): 10.4 +/- 8.0% (8.6 +/- 5.5%). The QT interval at varying preceding R-R intervals on Holter electrocardiograms showed a shift toward the right as a result of the drug administration. The effective refractory period showed a significant prolongation, 256 +/- 26 ms versus 280 +/- 22 ms before and after drug administration, respectively (P <.05). Intravenous administration of nicorandil resulted in no significant change in heart rate or blood pressure, while QTc showed a tendency to shorten, but nonsignificantly (P = .08). However, a hump on the monophasic action potential was abolished, especially at the long preceding R-R interval induced by premature stimulation of the ventricle. It is concluded that nicorandil shortens the QT interval slightly when administered orally, whereas the effective refractory period shows a slight prolongation. The physiologic and clinical significance of these effects needs to be studied further.

Recovery from complete atrioventricular block caused by idiopathic giant cell myocarditis after corticosteroid therapy

Giant cell myocarditis (GCM) is a rapidly progressive disease that leads to ventricular tachycardia or high-grade atrioventricular (A-V) block, frequently requiring a pacemaker. A 64-year-old woman developed syncope as a result of idiopathic GCM with A-V block. She required both a temporary and a permanent pacemaker. Two-dimensional echocardiography showed severely reduced wall motion. There was no histologic or clinical evidence to suggest sarcoidosis. Despite treatment with diuretics and an angiotensin-converting enzyme inhibitor, exertional dyspnea persisted. She received prednisolone 4 months after the onset of complete A-V block in the late phase of GCM. Prednisolone improved A-V nodal conduction in spite of the fact that there was no influence from LV wall motion, and sinus rhythm has continued for more than 2 years. In this patient, prednisolone was effective in the treatment of GCM.

Intracoronary acetylcholine-induced prolongation of monophasic action potential in long QT syndrome

Two patients with long QT syndrome, who had episodes of syncope, underwent recordings of the monophasic action potential (MAP) from the right ventricle. Intracoronary administration of acetylcholine (ACh) induced prolongation of MAP duration and caused Torsade de Pointes (Tdp) in both patients. In one patient, intravenous atropine administration did not induce any change in MAP duration. In the other patient, ACh was administered after atropine. According to the results of the present study, abnormal regulation of the muscarinic receptor-mediated K-channel may be involved in the mechanism causing prolongation of MAP duration caused by ACh administration.

Reentrant ventricular tachycardia. Interpretations of electrophysiologic findings and its applications

Monomorphic sustained ventricular tachycardia (MSVT) was revisited in relation to the electrophysiologic findings and their relation to the drug efficacy. Old myocardial infarction is less common cause of MSVT in Japan, and the majority (about 2/3) of MSVT is unrelated to coronary artery disease but, the mechanism shared a common mechanism: reentry with an excitable gap as others. The reentrant mechanism was supported from the inducibility, the terminability of VT by electrical stimulation, and by the ability to entrain with rapid pacing. In MSVT associated with underlying heart diseases, diseased myocardium showed low amplitude and fragmented electrograms and the area was considered to participate as the central common pathway of reentrant circuit. The area of slow pathway showed a decremental conduction or all-or-nothing conductive property. The width of the excitable gap seemed to be determined by the maximal conductive frequency but not by the duration of action potential: effective refractory period. As to the drug efficacy, there was no baseline characteristics in predicting the efficacy. However, the significant narrowing of the width of the excitable gap was associated with the drug efficacy and VT became non-inducible after addition of the same drug. The response pattern of the excitable gap to specific drug including class III, was not predictable. Further electropharmacological studies will be warranted.

Use-dependent electrophysiologic effects of DL-sotalol and modulation by isoproterenol in the human ventricle

The interaction between dl-sotalol and isoproterenol on the ventricular effective refractory period (VERP) and conduction were examined in an electrophysiologic study of 9 patients at drug-free baseline, after 14 days of dl-sotalol administration (320 mg/day), and after the administration of isoproterenol. In all 9 patients, ventricular tachyarrhythmia could not be induced after dl-sotalol treatment. Isoproterenol was administered as a loading dosage of 0.025 microgram/kg for 5 min with a maintenance dosage of 0.0025 microgram/kg/min. The VERP and the QRS duration were determined at paced cycle lengths of 600, 400 and 300 msec. DL-sotalol and dl-sotalol + isoproterenol had no effect on ventricular conduction at the three cycle lengths. The VERP was significantly prolonged after dl-sotalol treatment at paced cycle lengths of 600 (241 +/- 16 to 302 +/- 28 msec, p < 0.001), 400 (223 +/- 21 to 280 +/- 23 msec, p < 0.001) and 300 msec (202 +/- 16 to 256 +/- 24 msec, p < 0.005), but there was a parallel shift of the VERP, suggesting the absence of use-dependent effects on the VERP. The dl-sotalol-induced VERP prolongation was partially reversed by isoproterenol, but it remained significantly prolonged above baseline values at paced cycle lengths of 600 (241 +/- 16 to 281 +/- 18 msec, p < 0.01), 400 (223 +/- 21 to 258 +/- 20 msec, p < 0.01) and 300 msec (202 +/- 16 to 247 +/- 22 msec, p < 0.01). The shortening of the VERP was greater at longer basic cycle lengths (600 and 400 msec) than at the shorter paced cycle length (300 msec, p < .05), but the percentage increase of the VERP was similar at the three basic cycle lengths of 600 (16%), 400 (15%) and 300 (20%) msec, indicating the lack of reverse use-dependency. The absence of reverse use-dependency of dl-sotalol on the VERP, even after isoproterenol administration, may be beneficial in the therapy of ventricular tachyarrhythmias and may account in part for the high efficacy of this drug.

Bifid T waves induced by isoprenaline in a patient with Brugada syndrome

A 41 year old man with incomplete right bundle branch block and persistent coved-type ST elevation in the right precordial leads during sinus rhythm had an episode of syncope while driving. He had never had syncope before and there was no family history of sudden cardiac death. Ventricular fibrillation was induced during electrophysiological study (EPS) by double extrastimuli applied to the right ventricle. Disopyramide was effective in preventing ventricular fibrillation during EPS. beta Adrenoceptor stimulation manifested bifid T waves and reduced ST segment elevation in right precordial leads. Simultaneously recorded monophasic action potential (MAP) duration at 90% repolarisation did not change in the right ventricular outflow tract, while it shortened in the left ventricular septum. These findings suggest that right precordial bifid T waves might result from relatively early repolarisation of the left ventricles. Moreover the gradient of action potential duration might explain the mechanism of ST segment abnormalities in a patient with Brugada syndrome.

Does mexiletine have a preferential action (versus healthy myocardium) on the reentrant circuit of ventricular tachycardia?

The preferential action (in diseased versus healthy myocardium) of class 1a antiarrhythmic but not class 1b agents has been demonstrated on the reentrant circuit. This study assessed the effect of mexiletine on the fragmented electrogram at the origin of ventricular tachycardia (VT) associated with underlying heart diseases. In 11 consecutive patients, VT of the same morphology was induced, and entrained with rapid pacing during, before, and after mexiletine. The width of the fragmented electrogram, VT cycle length, and the block cycle length (defined as the longest VT-interrupting paced cycle length during entrainment) were measured before and after mexiletine and the findings compared. The effective refractory period (ERP) was measured at the pacing site (normal myocardium) and at the VT origin. To assess the preferential action of mexiletine, changes in fragmented electrogram were examined in relation to QRS duration (defined as the index of global intraventricular conduction). After mexiletine, VT cycle length, block cycle length, and fragmented electrogram were prolonged significantly. The QRS duration was also prolonged significantly, but this change was significantly smaller than that in VT cycle length or in the width of the fragmented electrogram. There was no significant change in ERP either at the pacing site or at the VT origin. Mexiletine was confirmed to preferentially depress conduction in the diseased myocardium at the VT origin, and this action occurred at a higher rate during VT.

Hematopoietic cytokine-dependent differentiation to eosinophils and neutrophils in a newly established acute promyelocytic leukemia cell line with t(15;17)

We recently established an acute promyelocytic leukemia (APL) cell line (HT93) that has the capacity to differentiate into neutrophils and eosinophils in response to all-trans retinoic acid (ATRA) and human hematopoietic cytokines. The cells had a myeloblastic morphology, were positive for surface CD33, CD34, and CD56, and showed the following karyotypes: 46, XY, t(1;12)(q25;p13), 2q+, t(4;6)(q12;q13), and t(15;17)(q22;q11). When the cells were cultured with ATRA, they showed nuclear segmentation and developed secondary granules consisting in part of neutrophils and eosinophils. In the presence of ATRA and granulocyte colony-stimulating factor (G-CSF), the cells showed polymorphonuclear neutrophil differentiation accompanied by expression of surface CD11b, CD15, CD10, positive activity for neutrophil alkaline phosphatase (NAP), and NAP mRNA expression. In cultures with ATRA and granulocyte-macrophage colony-stimulating factor (GM-CSF), IL (interleukin)-3, or IL-5, HT93 showed remarkable eosinophil maturation at day 8 as determined by luxol fast blue staining, in addition to expression of eosinophil peroxidase and major basic protein. These results indicate that HT93 is an APL cell line with the ability to differentiate into neutrophils and eosinophils, and that these lineages are dependent on the CSF added. HT 93 should prove to be a useful model in analyzing the effects of hematopoietic cytokines on proliferation, differentiation, and maturation of hematopoietic progenitors.

Hyperthyroid Graves' disease and primary hypothyroidism caused by TSH receptor antibodies in monozygotic twins: case reports

A 33-year-old woman with signs and symptoms of hypothyroidism, including increased thyroid stimulating blocking antibody (TSBAb) activity, was referred for treatment by her local physician. Her monozygote twin was treated for hyperthyroid Graves' disease 10 years earlier. This case of hyperthyroidism and hypothyroidism in identical twins suggests the involvement of environmental factors in the pathogenesis of autoimmune thyroid diseases.

Polymorphism of the angiotensin I-converting enzyme gene in diabetic nephropathy in type II diabetic patients with proliferative retinopathy

Recently, deletion (D)/insertion (I) polymorphism in the Angiotensin I-converting enzyme (ACE) gene has been suggested to be related to the development of diabetic nephropathy in type I diabetes mellitus. This hypothesis, however, remains controversial. Differences in clinical states between patients, especially in glycemic control or duration of diabetes, could be responsible for these contradictory results. In this study we examined the relationship between D/I polymorphism of the ACE gene and diabetic nephropathy in type II diabetic patients who had already developed proliferative retinopathy (n = 45), and were thought to have been in a hyperglycemic state for long enough to develop microangiopathy. The patients were divided into two subgroups: 24 with nephropathy (albumin excretion rate: AER > or = 20 micrograms/min) and 21 without (AER < 20 micrograms/min). There was no difference in the duration of diabetes, HbA1c levels or average blood pressure over the previous year between these subgroups and other clinical characteristics were comparable. Patients without nephropathy exhibited allele I more often than those with nephropathy (p = .025). AER was lowest in genotype II and highest in genotype DD patients but the difference was not statistically significant (p = .07). From these findings, it was concluded that genotype II for the ACE gene could be a marker for reduced risk of diabetic nephropathy.

Role of thyroid-stimulating blocking antibody in patients who developed hypothyroidism within one year after 131I treatment for Graves' disease

OBJECTIVE

We recently reported that thyroid-stimulating blocking antibody (TSBAb) may not contribute to the development of hypothyroidism more than six years after 131I treatment. In the present study, we attempted to determine whether hypothyroidism that develops within a shorter period of time following 131I therapy is associated with TSBAb.

DESIGN

Retrospective study.

PATIENTS

Sera were obtained from 8 patients who developed hypothyroidism within 6 months after 131I therapy (Group 1), 8 patients who became euthyroid one year after 131I therapy (Group 2), and 7 patients who developed transient hypothyroidism (Group 3).

MEASUREMENTS

Thyroid stimulating antibody (TSAb) activity was measured as the amount of cyclic adenosine monophosphate (cAMP) produced by cultured FRTL-5 cells, and TSBAb activity as the inhibition of cAMP produced in response to 100 mU/l bovine TSH.

RESULTS

At about 3 months after 131I treatment, TSAb activity increased significantly in Groups 2 and 3, but did not change in Group 1. In contrast, TSBAb activity in Group 1 increased significantly and was positive in 6 patients at that time. At 12-18 months after 131I treatment, TSBAb activity tended to decrease and remained positive in 3 patients but became negative in 3 patients. It did not change in the patients in Groups 2 and 3. The patients in Group 1 were treated with levothyroxine, 75-125 micrograms/day. Levothyroxine was discontinued in the 3 patients whose TSBAb activity disappeared. Two of them remained euthyroid, and 1 became hypothyroid.

CONCLUSION

Results indicate that the hypothyroidism that develops within a short time after 131I treatment may be caused by TSBAb activity. Thyroid function may be recovered when TSBAb activity disappears.

Relation between bradycardia dependent long QT syndrome and QT prolongation by disopyramide in humans

BACKGROUND

Recent molecular biological investigations have identified abnormal genes in familial forms of long QT syndrome, but in bradycardia dependent acquired long QT syndrome, no such genetic abnormality has yet been identified.

OBJECTIVE

To investigate the relation between the responses of QT interval to pacing change and to disopyramide.

METHODS

This study included 13 patients with bradyarrhythmia who had undergone pacemaker implantation. The patients were divided into two groups: group I (n = 8), patients with QT prolongation (QT interval > or = 500 ms) during bradycardia; group II (n = 5), patients without QT prolongation (QT interval < 500 ms) during bradycardia. The responses of QT interval caused by the change of pacing rate were determined and compared with the changes of the QT interval after disopyramide administration.

RESULTS

The QT interval in group I was significantly longer than that in group II when the pacing rate was decreased from 110 to 50 beats/min: mean (SD) 451 (16) v 416 (17) ms at 90 beats/min (p = 0.0033), and 490 (19) v 432 (18) ms at 70 beats/min (p = 0.0002), respectively. The QT interval was prolonged significantly by disopyramide in both groups, but the change was more pronounced in group I than in group II: 78 (33) v 35 (10) ms (p < 0.05).

CONCLUSIONS

This study suggests that the patients showing bradycardia dependent QT prolongation are also more markedly affected by disopyramide and that abnormal potassium channel may be the underlying mechanism.

Frequency dependent shortening of conduction time through the reentrant pathway during transient entrainment of ventricular tachycardia

In a patient with nonischemic ventricular tachycardia (VT), VT was entrained and the conduction time from the pacing site to the entrained local electrogram showed a rate dependent shortening and its degree affected by the pacing site. The QRS complex, which was entrained by the last pacing stimulus, was constant and identical to that of VT and no rate dependent facilitated conduction was observed when the heart was paced at similar paced cycle lengths during sinus rhythm. As the mechanism of the shortening of the conduction time through the reentrant circuit, a shift of the entrance seems most likely.