Single photon emission computed tomography of the thyroid

Single photon emission computed tomography (SPECT) entails imaging at multiple positions along an arc and computed-assisted reconstruction of transaxial, coronal, and sagittal images. To determine if SPECT imaging of the thyroid augments information provided by planar imaging, both SPECT and pinhole planar scans were performed in 52 patients with thyroid disease. After 123I (n = 45), Tc99m (n = 5), or thallium-201 (n = 2) administration, images were acquired at 30 intervals along a 180 degree arc. Nodules that were hypofunctioning on planar scans (n = 4) were equally well shown on SPECT images. SPECT analysis of 123I uptake by 5 palpable nodules with completely normal 123I planar scans demonstrated the nodular tracer uptake was increased (n = 1), equivalent (n = 3), or decreased (n = 1) in comparison with that of extranodular tissue. In 6 of 12 multinodular goiters, transaxial SPECT images showed tracheal compression, which was confirmed by neck x-ray, flow volume loops, or surgery. A neck phantom study was performed to assess the accuracy of SPECT-determined functional thyroid volume. SPECT-estimated volumes (30-173 mL; n = 11) correlated well with true volumes (r = 0.996; P less than 0.001). Our observations suggest that SPECT is a useful adjunct to planar imaging in 1) estimating functional volume for 131I dosimetry; 2) evaluating the size, extension, and tracheal compression of multinodular goiter; and 3) determining the functional properties of palpable nodules with normal 123I planar pinhole images.

Detection of activated double-stranded RNA-dependent protein kinase in 3T3-F442A cells

We have previously reported that cultured mouse 3T3-F442A cells exhibit a transient, double-stranded RNA (dsRNA)-dependent phosphorylation of the dsRNA-dependent eIF-2 alpha kinase (eIF-2 alpha, alpha-subunit of the eukaryotic initiation factor 2) (dsI). When dsI is activated by low levels of dsRNA, it is a potent inhibitor of protein synthesis. The transient expression of dsI is due to an autocrine effect of interferon at specific stages of growth and differentiation, and it may represent a mechanism for regulating cell growth and differentiation in 3T3-F442A cells. In this report, the purification of dsI from 3T3-F442A cell cultures by a two-step procedure is described. A specific immune serum to dsI was prepared by immunizing a rabbit with highly pure preparations. Immune precipitation studies demonstrate that the serum reacts with phosphorylated dsI both in vitro and in vivo and with de novo synthesized dsI after induction with interferon. We find that dsI of 3T3 cells can undergo phosphorylation in vitro without the addition of dsRNA and in vivo in the absence of viral infection. These results are consistent with a physiologic role for dsI in the growth and differentiation of these cells.

Iodine-123 SPECT of the thyroid in multinodular goiter

Iodine-123 single photon emission computed tomography (SPECT) imaging of the thyroid was performed in two patients with multinodular goiter and swallowing difficulty to provide the functional and anatomic orientation of the goiter in relation to the airway. Transaxial slices showed the retrolaryngeal extension of the enlarged thyroid and the tracheal compression by the goiter in both patients. Sagittal and coronal sections confirmed the posterior extension of the goiter. Tracheal displacement was confirmed by roentgenography of the neck in both patients. Vocal cord paralysis demonstrated by fiberoptic laryngoscope and esophageal compression shown by esophagography were found in a patient with toxic multinodular goiter with coexisting papillary carcinoma of the thyroid. In this patient, both the tracheal compression noted in SPECT imaging and the tracheomalacia suggested by the flow volume loop pattern in pulmonary function test were confirmed at the time of thyroidectomy. Our observation suggests that SPECT imaging of large multinodular goiter may be useful in preoperative delineation of the functional anatomy and the extension of goiter in relation to the airway.

Analysis of the idiotypic network in tumor immunity

Herein we have analyzed the expression of idiotopes associated with a monoclonal anti-tumor-associated antigen (TAA) antibody in DBA/2 mice which have progressively growing tumors or resist tumor growth. A panel of eight monoclonal antiidiotypic antibodies raised against a monoclonal antibody which reacts with a mouse mammary tumor virus cross-reactive qp52 envelope protein (TAA) of the L1210/GZL lymphoma was used to measure the expression of idiotopes in sera from different treatment groups. Significant correlations between the expression of certain idiotopes and the growth of the tumor or the establishment of anti-tumor immunity are seen. 1) Idiotypes detected by anti-idiotype D11 are high in anti-idiotype immunized progressor or tumor-susceptible mice and low or absent in regressor mice, i.e., the mice immunized with the protective 2F10 anti-idiotype; 2) the 3A4-detected idiotypes are less frequent or absent in irradiated tumor-immunized regressor mice than in untreated mice challenged with live tumor or progressor mice; 3) no difference in the anti-TAA titers is seen in mice in which the tumor growth is inhibited and in mice in which the tumor grows; 4) no difference in 11C1 idiotype + anti-TAA titer was observed between regressor and progressor mice; and 5) mice with normal or accelerated tumor growth have higher titers of idiotypes detected by a polyclonal anti-idiotype. These findings provide evidence for a regulatory idiotype network induced by the growing L1210/GZL tumor or by anti-idiotypic immunization. The titer of anti-TAA antibody does not correlate with the biology of tumor growth, but certain idiotopes correlate with either progressive or regressive tumor behavior. Therefore, the target of the idiotype regulation is likely to be anti-tumor T effector cells. Effective idiotype therapy of tumors must deal with the complexity of idiotype regulation induced by the tumor itself and is unlikely to be successful if anti-idiotypes are used only as internal mimicry of a TAA.

Analysis of the idiotypic network in tumor immunity

Herein we have analyzed the expression of idiotopes associated with a monoclonal anti-tumor-associated antigen (TAA) antibody in DBA/2 mice which have progressively growing tumors or resist tumor growth. A panel of eight monoclonal antiidiotypic antibodies raised against a monoclonal antibody which reacts with a mouse mammary tumor virus cross-reactive qp52 envelope protein (TAA) of the L1210/GZL lymphoma was used to measure the expression of idiotopes in sera from different treatment groups. Significant correlations between the expression of certain idiotopes and the growth of the tumor or the establishment of anti-tumor immunity are seen. 1) Idiotypes detected by anti-idiotype D11 are high in anti-idiotype immunized progressor or tumor-susceptible mice and low or absent in regressor mice, i.e., the mice immunized with the protective 2F10 anti-idiotype; 2) the 3A4-detected idiotypes are less frequent or absent in irradiated tumor-immunized regressor mice than in untreated mice challenged with live tumor or progressor mice; 3) no difference in the anti-TAA titers is seen in mice in which the tumor growth is inhibited and in mice in which the tumor grows; 4) no difference in 11C1 idiotype + anti-TAA titer was observed between regressor and progressor mice; and 5) mice with normal or accelerated tumor growth have higher titers of idiotypes detected by a polyclonal anti-idiotype. These findings provide evidence for a regulatory idiotype network induced by the growing L1210/GZL tumor or by anti-idiotypic immunization. The titer of anti-TAA antibody does not correlate with the biology of tumor growth, but certain idiotopes correlate with either progressive or regressive tumor behavior. Therefore, the target of the idiotype regulation is likely to be anti-tumor T effector cells. Effective idiotype therapy of tumors must deal with the complexity of idiotype regulation induced by the tumor itself and is unlikely to be successful if anti-idiotypes are used only as internal mimicry of a TAA.

Tumor-specific idiotype vaccines. III. Induction of T helper cells by anti-idiotype and tumor cells

In a previous report, we have demonstrated the induction of tumor-specific immunity by monoclonal anti-idiotype antibodies generated against a monoclonal anti-tumor antibody, 11C1, that also cross-reacts with mouse mammary tumor virus envelope glycoprotein gp52. Also, we showed that whereas one anti-idiotype antibody, 2F10, could induce protective immunity, another anti-idiotype antibody, 3A4, induced nonprotective immunity. Here we demonstrated the existence of T helper cells which recognize anti-idiotypes that exert differential controls on tumor growth. The qualitative nature of idiotype recognizing T cells generated in response to 2F10, 3A4, irradiated tumor, and progressively growing tumor was compared. The reactivity pattern of idiotype recognizing T cells obtained from 2F10 and irradiated tumor immunized mice were similar in nature in the sense that Lyt-2- T cells obtained from these immunized mice responded to both 2F10 and 3A4 as antigen, although T cells from tumor immunized mice responded better to 3A4 antigen. On the other hand, the idiotype-recognizing T cells obtained from 3A4-immunized mice showed a similar reactivity pattern to T cells isolated from mice during the early phase of tumor growth (within day 4 to 5 after the inoculation of 10(4) live tumor cells). Lyt-2- T cells isolated from mice immunized with 3A4 or during the early phase of tumor growth responded only to 3A4 antigen. The inability of Lyt-2- T cells, isolated from 4- to 5-day-old tumor in mice, to cooperate with 2F10-TNP is not due to the absence of 2F10 idiotype recognizing T cells as 2F10 id recognizing T cells are present when examined at the precursor level. These data on the idiotype specificity of T helper cells show a correlation with the presence of anti-tumor immunity. This information will help in the design and application of idiotype vaccine in tumor immunotherapy.

Tumor-specific idiotype vaccines. III. Induction of T helper cells by anti-idiotype and tumor cells

In a previous report, we have demonstrated the induction of tumor-specific immunity by monoclonal anti-idiotype antibodies generated against a monoclonal anti-tumor antibody, 11C1, that also cross-reacts with mouse mammary tumor virus envelope glycoprotein gp52. Also, we showed that whereas one anti-idiotype antibody, 2F10, could induce protective immunity, another anti-idiotype antibody, 3A4, induced nonprotective immunity. Here we demonstrated the existence of T helper cells which recognize anti-idiotypes that exert differential controls on tumor growth. The qualitative nature of idiotype recognizing T cells generated in response to 2F10, 3A4, irradiated tumor, and progressively growing tumor was compared. The reactivity pattern of idiotype recognizing T cells obtained from 2F10 and irradiated tumor immunized mice were similar in nature in the sense that Lyt-2- T cells obtained from these immunized mice responded to both 2F10 and 3A4 as antigen, although T cells from tumor immunized mice responded better to 3A4 antigen. On the other hand, the idiotype-recognizing T cells obtained from 3A4-immunized mice showed a similar reactivity pattern to T cells isolated from mice during the early phase of tumor growth (within day 4 to 5 after the inoculation of 10(4) live tumor cells). Lyt-2- T cells isolated from mice immunized with 3A4 or during the early phase of tumor growth responded only to 3A4 antigen. The inability of Lyt-2- T cells, isolated from 4- to 5-day-old tumor in mice, to cooperate with 2F10-TNP is not due to the absence of 2F10 idiotype recognizing T cells as 2F10 id recognizing T cells are present when examined at the precursor level. These data on the idiotype specificity of T helper cells show a correlation with the presence of anti-tumor immunity. This information will help in the design and application of idiotype vaccine in tumor immunotherapy.

Analyses of two-way chronic studies

This paper proposes a method for analyzing tumor data from chronic studies when the experimental design includes combinations of two factors, for example, sex and dose. Both main effects and combined-effect (interaction) hypotheses are considered. A stratified log-rank statistic is presented for tests of no column or row (main) effects. The paper shows that when the numbers of animals in the cells are unequal and disproportional, the null distribution of the unstratified log-rank statistic does not have a chi-square distribution. Two simple models, additive and multiplicative, for representing the combined effect of row and column are considered under the proportional hazards model. A simple conservative statistic is proposed for testing the additivity of the row and column effects. A simulation experiment to examine the behavior of the null distribution of the combined-effect test statistic under the additive model and the power of the test against the multiplicative model is reported. The procedure is illustrated by analyzing mammary tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) in yellow and agouti F1 female mice from a laboratory experiment.

Tumor-specific idiotype vaccines. II. Analysis of the tumor-related network response induced by the tumor and by internal image antigens (Ab2 beta)

In this study the tumor-specific immuneresponse induced by irradiated tumor cells (L1210/GZL) and by anti-idiotype antibodies was analyzed. The anti-idiotype antibodies (Ab2) were made against the paratope of a monoclonal antitumor antibody (11C1) that recognizes a tumor-associated antigen which cross-reacts with the mouse mammary tumor virus-encoded envelope glycoprotein 52. Two Ab2, 2F10 and 3A4, induced idiotypes expressed by the monoclonal antitumor antibodies 11C1 and 2B2. Cytotoxic T cells, generated by immunization with irradiated tumor cells, lyse 2F10 and 3A4 hybridoma cells. Furthermore, immunization with Ab2 induces tumor-specific cytotoxic T lymphocytes. The frequency of tumor-reactive cytotoxic T lymphocyte was found to be similar in mice immunized with Ab2 or irradiated tumor cells when examined at the precursor level. However, only 2F10 induces protective immunity against the growth of L1210/GZL tumor cells. The depletion of a L3T4+ T cell population from 2F10 immune mice was found to increase the effectiveness of transferred T cells to induce inhibition of tumor growth. The inability of 3A4 to induce antitumor immunity could be correlated with the presence of a population of Lyt2+ regulatory T cells. Collectively, these results demonstrate the existence of a regulatory network controlling the expression of effective tumor immunity. Our results demonstrate that selection of binding site-related Ab2 may not be a sufficient criteria for the development of an idiotype vaccine. A better understanding of the regulatory interactions induced by anti-idiotypes is needed for the design of effective antitumor immunotherapy.

Tumor-specific idiotype vaccines. II. Analysis of the tumor-related network response induced by the tumor and by internal image antigens (Ab2 beta)

In this study the tumor-specific immuneresponse induced by irradiated tumor cells (L1210/GZL) and by anti-idiotype antibodies was analyzed. The anti-idiotype antibodies (Ab2) were made against the paratope of a monoclonal antitumor antibody (11C1) that recognizes a tumor-associated antigen which cross-reacts with the mouse mammary tumor virus-encoded envelope glycoprotein 52. Two Ab2, 2F10 and 3A4, induced idiotypes expressed by the monoclonal antitumor antibodies 11C1 and 2B2. Cytotoxic T cells, generated by immunization with irradiated tumor cells, lyse 2F10 and 3A4 hybridoma cells. Furthermore, immunization with Ab2 induces tumor-specific cytotoxic T lymphocytes. The frequency of tumor-reactive cytotoxic T lymphocyte was found to be similar in mice immunized with Ab2 or irradiated tumor cells when examined at the precursor level. However, only 2F10 induces protective immunity against the growth of L1210/GZL tumor cells. The depletion of a L3T4+ T cell population from 2F10 immune mice was found to increase the effectiveness of transferred T cells to induce inhibition of tumor growth. The inability of 3A4 to induce antitumor immunity could be correlated with the presence of a population of Lyt2+ regulatory T cells. Collectively, these results demonstrate the existence of a regulatory network controlling the expression of effective tumor immunity. Our results demonstrate that selection of binding site-related Ab2 may not be a sufficient criteria for the development of an idiotype vaccine. A better understanding of the regulatory interactions induced by anti-idiotypes is needed for the design of effective antitumor immunotherapy.

Carcinogenic risk assessment: comparison of estimated safe doses for rats and mice

Data from the National Cancer Institute/National Toxicology Program (NCI/NTP) carcinogenesis bioassays were examined to compare cancer risks in rats and mice. Only those bioassays where chemicals were administered orally were used. The ratios for rats to mice of the virtually safe dose (VSD) levels associated with a risk of 10(-6) were compared. Comparisons of the ratios were made for those chemicals that NCI/NTP determined to be carcinogenic in at least one species and that showed a dose response trend in the same sex at the same tissue/organ site in the other species. In all, 69 comparisons from 38 carcinogens were performed. The overall geometric mean of the VSD ratios is 1.27 in terms of concentration (ppm); the mean and the standard deviation in logarithm are 0.24 and 1.83, respectively. The VSD ratios vary from 1:51 to 49:1. Without the restriction of the same sex and site, the geometric mean of the minimum VSDs is 1.38, and the standard deviation in logarithm is 1.79. By directly comparing the VSDs for rats and mice (as they are performed for risk assessment), this study showed a probability of 0.10 that the ratio of VSDs is greater than 10, and the ratio is greater than 20 with a probability of 0.05 when a chemical is carcinogenic in both species.

Euthyroid pretibial myxedema

Pretibial myxedema is typically associated with clinical hyperthyroidism, diffuse goiter, and ophthalmopathy in patients with Graves' disease. A case of biopsy-proved pretibial myxedema was encountered in a clinically euthyroid woman who had neither diffuse goiter nor exophthalmos. Although serum total and free thyroxine hormone concentrations were normal, the thyroid-stimulating hormone response to thyrotropin-releasing hormone was absent. This case illustrates that pretibial myxedema may present without other more common manifestations of Graves' disease. In patients with suspect pretibial skin lesions, the thyrotropin-releasing hormone stimulation test may be required to establish the presence of subtle underlying thyroid gland autonomy and the diagnosis of euthyroid pretibial myxedema.

Hypothalamic involvement in the hyperglycemia and satiety actions of somatostatin in rats

To determine whether the anorexic and the hyperglycemia actions of somatostatin were mediated through the hypothalamic nuclei, rats were infused with somatostatin and normal saline through previously implanted hypothalamic cannulae. Administration of somatostatin (0.5-1.5 microgram in 1.0 microliter) into the lateral hypothalamus, but not the ventromedial or the anterior hypothalamus, caused a reduction in food consumption without affecting relative water intake (or water-to-food ratio) in conscious rats in a freely moving state. On the other hand, administration of somatostatin into the lateral hypothalamus, but not the anterior or the ventromedial hypothalamus, caused an increase in blood glucose level in rats. This hyperglycemia was antagonized by vagotomy, but not by spinal transection or adrenalectomy. The data indicate that the lateral hypothalamus is the most sensitive site of the somatostatin-induced anorexia and the action of somatostatin on the lateral hypothalamus-vagus efferent activity is also a possible mechanism mediating hyperglycemia in rats.

Somatostatin potentiation of insulin-induced glucose uptake in normal individuals

The ability of somatostatin (SRIF) to enhance insulin-stimulated glucose uptake was evaluated during clamp studies in normal individuals and patients with non-insulin-dependent diabetes mellitus (NIDDM). The results demonstrated that glucose uptake at insulin levels of approximately 100 microU/ml was significantly greater (P less than 0.001) in normal individuals in response to insulin plus SRIF as compared with insulin alone. In contrast, SRIF did not enhance insulin-stimulated glucose uptake in patients with NIDDM. Measurements were also made of the relative ability of insulin as compared with insulin plus SRIF to suppress C-peptide and glucagon concentrations during the clamp studies. The results of these experiments showed that SRIF did not potentiate the ability of insulin to suppress C-peptide concentrations in normal subjects but did in patients with NIDDM. However, plasma glucagon levels were reduced to a greater degree when SRIF was added to insulin in both normal and diabetic individuals.

Standardized tumor rates for chronic bioassays

If crude experimental proportions of animals with tumors from chronic bioassays for carcinogenicity are used for low-dose extrapolation in a risk analysis, different dose-specific patterns of mortality due to competing risks can bias the results. In order to adjust tumor rates for differential mortality across dose groups, Farmer, Kodell, and Gaylor (1982, Risk Analysis 2, 27-34) recommended using nonparametric estimates of probability distributions of times to onset of tumors, with competing causes of death removed, when performing a risk analysis. This paper extends the approach of Farmer et al. by proposing a method for adjusting tumor rates to reflect lifetime or near-lifetime tumor incidences that would be obtained if all dose groups experienced the control mortality rate from causes other than the tumor of interest. Thus, natural mortality due to competing risks is explicitly included, rather than removed. The proposed standardized tumor rates are calculated as a summation of adjusted age-specific probabilities of dying with a tumor during the course of an animal bioassay for carcinogenicity plus the probability of being alive with a tumor at the terminal sacrifice.

Susceptible and resistant subgroups in genetically identical populations: response of mouse liver neoplasia and body weight to phenobarbital

Following 17-19 months of feeding 500 p.p.m. sodium phenobarbital (PB) in the diet to yellow Avy/A and agouti A/a (C3H X VY) F1 hybrid male mice, two subgroups differing in responsiveness to PB with respect to promotion of hepatocellular adenomas and body weight gain were observed within each genotype. In untreated mice of both genotypes, the presence of an adenoma at necropsy was associated with decreased body weight gain during this study. However, PB treatment inverted this association. In treated mice the presence of an adenoma at necropsy was preceded by a greater increase in body weight during the study than when no tumor was present. This increase in average body weight gain was more pronounced among the yellow mice (44%) than among the agouti mice (21%). Among yellow mice PB treatment had no effect on body weight gain unless an adenoma was present at necropsy. However, in those yellow mice in which an adenoma was found, body weight was greater than in untreated yellow controls throughout the study beginning at week 27. The mean body weight curve of treated yellow mice bearing one adenoma was slightly higher than that of treated yellow mice in which no adenoma was found. The mean body weight curve of treated yellow mice bearing multiple adenomas was significantly higher than those of yellow mice with no or only one adenoma.

Amplified response to phenobarbital promotion of hepatotumorigenesis in obese yellow Avy/A (C3H x VY) F-1 hybrid mice

Mottled yellow Avy/A and agouti A/a (C3H x VY) F-1 hybrid male mice were fed untreated control diet or diet with a target dose of 500 p.p.m. sodium phenobarbital (PB) for 17-19 months. No differences in prevalence of hepatocellular adenomas or carcinomas were found between untreated yellow and agouti mice. PB treatment increased prevalence of adenomas but decreased prevalence of carcinomas. No difference in enhancement of adenoma formation by PB was observed between yellow and agouti mice bearing single adenomas. However, the proportion of PB-treated yellow mice bearing multiple adenomas (66%) was much greater than the proportion of analogous agouti mice (18%). Fatty changes in the periportal area of the liver and focal cytoplasmic vacuolization were induced to a much greater extent in PB-treated yellow mice than among treated agoutis. PB increased the prevalence and severity of focal areas of chronic inflammation in the liver considerably more in agouti than in yellow mice. The possible relation of this finding to the altered immune responses of obese yellow mice remains to be determined. The results of this study suggest that the use of yellow Avy/A and agouti A/a (C3H x VY) F-1 hybrid mice in carcinogenicity assays make make it possible to differentiate between weak and strong promoters as well as between promoters and complete carcinogens. Weak promoters should induce hepatocellular adenomas in yellow mice even if they fail to do so in agouti mice. Promoting substances which act similarly to PB may be identified in this system by simultaneously increasing adenoma prevalence and decreasing carcinoma prevalence. Complete carcinogens should increase carcinoma prevalence in the yellow mice even at low dose levels.

Influence of age on induction of mammary tumors by diethylstilbestrol in C3H/HeN mice with low murine mammary tumor virus titer

C3H/HeN female mice with low murine mammary tumor virus titer (MTV-) were fed diets containing a targeted concentration of 640 ppb diethylstilbestrol [(DES) CAS: 56-53-1; 4,4'-(1,2-diethyl-1,2-ethenediyl)bis-phenol]. Mice were started on DES at 3, 5, 7, or 9 weeks of age. Some continued on the diet throughout the rest of their life-spans, whereas others were killed as soon as they had been fed DES for 2, 4, 6, 8, 10, or 12 weeks. Controls were also examined throughout the study. Among mice killed early, the only observation significantly influenced by age at the start of DES treatment was the presence or absence of corpora lutea (CL). DES did not prevent CL from appearing in mice started on DES at 7 or 9 weeks of age, but it did prevent their appearance in about 25% of the mice started at 5 weeks and in up to 75% of the mice started at 3 weeks of age. In the life-span-exposure groups, CL either disappeared or were never formed in 88% or more of the mice, regardless of age at the start of treatment. Neoplastic or presumptive preneoplastic lesions apparently influenced by DES in the life-span-treatment groups included ovarian tubular adenomas; granulosa cell tumors and luteomas; pituitary cystoid degeneration, hyperplasia, and adenomas; uterine adenocarcinomas and cervical adenosis; mesotheliomas; and mammary hyperplastic alveolar nodules (HANs) and adenocarcinomas. Luteoma and granulosa cell tumor incidences were reduced by DES, regardless of age at the start of treatment. Influence of age at the start of treatment was minimal or not apparent for mesotheliomas, uterine adenocarcinomas, or pituitary adenomas; however, pituitary cystoid degeneration and hyperplasia and cervical adenosis occurred in higher frequency and/or with shorter duration of DES exposure the earlier that treatment was started. A delay in the start of DES treatment was associated with a remarkable delay in HAN and mammary adenocarcinoma development. This was especially apparent in young mice (3-7 wk old) in which a 2-week delay in treatment resulted in a 20-week delay in HAN or tumor onset. Age at the start of treatment was a major factor in susceptibility of C3H/HeN-MTV- female mice to DES-induced mammary tumorigenesis.

Terminal cardiac electrical activity in adults who die without apparent cardiac disease

Prolonged electrocardiographic (Holter) recording was performed to analyze terminal electrical events in 23 hospitalized adults who died without apparent cardiac disease. Most patients showed a gradual slowing of heart rate with shifting of cardiac pacemaker downward from the sinus node or atria to the atrioventricular junction and ventricles, resulting in cardiac asystole. Dominant bradyarrhythmia was more common than ventricular tachyarrhythmia (83 vs 17%). Agonal ST-segment elevation was not uncommon (26%). These terminal electrical events became manifest from 1 to 450 minutes (mean 62) before cessation of cardiac electrical activity. Forty-eight percent of the patients continued to show deteriorating sinus or atrial activity up to the last moment. The mechanism of bradycardiac asystole in patients with no apparent cardiac disease may be attributed to generalized anoxic and toxic depression of the sinus node and subsidiary pacemakers, together with neurogenic suppression of these structures.