Effects of Calcium Channel Blockers on In Vitro Platelet Function in Whole Blood Using Single Platelet Counting

The effects of various calcium channel blockers on in vitro platelet aggregation were studied using whole blood platelet counting. Diltiazem and verapamil inhibited aggregation caused by adrenaline 5 μM and collagen 2 μg/ml, but only at concentrations far in excess of those seen in clinical use. Nifedipine and nimodipine also inhibited aggregation to these agonists, but this seemed to be due to the solvent used. The solvent for these dihydropyridines contains 15% ethanol, 15% polyethylene glycol and 70% water, and the ethanol component is the most likely to have caused an antiaggregatory effect. Other studies showing an antiaggregatory effect of dihydropyridines may not have taken account of this solvent effect.

Current epidural practice--results of a survey of military anaesthetists

OBJECTIVES

As epidurals are now used for pain relief on deployment a survey was conducted to look at the current epidural practice of U.K. military anaesthetists. The aim was to identify any potential issues with regard to equipment and training to allow future development ofpre-deployment training.

METHODS

An Internet based survey was carriedout. All military anaesthetistswere sent an e-mail containing a link to the survey and the results of those who responded were analysed.

RESULTS

A total of 49 surveys were completed. 78% of respondents carried out epidurals more than once a month, in a wide range of specialities. There was considerable variation in methods of securing epidurals and in drug choice amongst respondents.

CONCLUSIONS

The results of this survey show that whilst epidurals are commonly carried out amongst military anaesthetists during their U.K. practice, there is significant variation within the practice. Areas have been identified for development of educational courses, for example methods of securing epidurals, and these have already been acted upon.

Mechanism and clinical significance of precordial ST depression in inferior myocardial infarction: evaluation by contrast-enhanced dynamic myocardial perfusion magnetic resonance imaging

We elucidated the mechanism and clinical significance of precordial ST depression in patients with an inferior myocardial infarction using first-pass, contrast-enhanced, myocardial perfusion magnetic resonance imaging (MRI). Forty-seven patients with acute inferior myocardial infarction underwent first-pass contrast-enhanced MR studies within 2-6 days postinfarction. Patients were followed-up for a minimum of 1 year after infarct (range, 12-32 months). Total perfusion deficit scores derived qualitatively from MRIs were compared in patients with (group 1, n = 30) and without (group 2, n = 17) ST depression precordially. Perfusion remote from the infarct zone was also compared. The combined end points of adverse clinical events and/or the need for further intervention were assessed for each group. Total perfusion deficit scores were significantly higher in group 1 than group 2 (medians 9.7 versus 4.5, p < 0.005). Posterolateral basal extension of hypoperfusion was greater in group 1 versus group 2 (1.23 versus 0.42, p < 0.02), with no evidence of remote anterior perfusion abnormalities. There were more patients with an adverse clinical end point in group 1 versus group 2 (18 versus 1, p < 0.01). Furthermore, in patients with ST depression (group 1), there was a significant increase in number of adverse clinical end points in patients with a global deficit score > 15 versus 0-5 (7/7 versus 1/7, p < 0.01). MRI shows that precordial ST depression in inferior myocardial infarction is a marker for a larger global perfusion abnormality with posterolateral basal extension and an increase in adverse clinical end points. Furthermore, the magnitude of the perfusion deficit correlates with an increase in the number of adverse clinical end points, highlighting the potential of MRI perfusion studies as a research and clinical tool in myocardial infarction.

T-ceIl recognition of discrete regions of the thrombolytic drug streptokinase

Streptokinase (SK) is a bacterial protein used clinically as a thrombolytic agent in humans. Administration of SK causes a rapid increase in the frequency of anti-SK T cells and the titre of specific anti-SK antibodies that, on subsequent administration of SK, may neutralize the activity of the drug or elicit allergic-type reactions. By locating and modifying the immunogenic T-cell epitopes within the SK protein, it is possible that an agent with reduced immunogenicity but equal efficacy may be produced. We have investigated the T-cell epitopes within SK using nine non-overlapping, recombinant peptide fragments of SK. We investigated the proliferative T-cell response of peripheral blood mononuclear cells obtained from patients before and 6 days after administration of SK for myocardial infarction. We also examined the response of cultured anti-SK T-cell lines derived from patients 6 days after treatment with SK. Before administration of SK, peripheral blood mononuclear cells from six of nine patients showed a proliferative response to SK. The response was significantly higher 6 days after administration of SK (P = 0.0004). Cultured T-cell lines showed similar proliferative responses to clinical-grade SK and recombinant SK. Marked differences in T-cell responses were apparent in response to each recombinant SK fragment (P = 0.04). The mean proliferative response exceeded background to only two peptides, peptide 2 (P = 0.04) and peptide 3 (P = 0.009). Peptide 3, representing amino acids 100-150 of mature SK, was recognized preferentially in the majority of assays. Marked variation in the T-cell response to SK following treatment with this agent was observed between subjects. Despite these differences, peptides 2 and 3 induced T-cell proliferation at a level significantly above background in the majority of subjects. These epitopes may represent a region of enhanced immunogenicity within SK.

Pathogenicity of avian malaria in experimentally-infected Hawaii Amakihi

The introduction of avian malaria (Plasmodium relictum) and mosquitoes (Culex quinquefasciatus) to the Hawaiian Islands (USA) is believed to have played a major role in the decline and extinction of native Hawaiian honeycreepers (Drepanidinae). This introduced disease is thought to be one of the primary factors limiting recovery of honeycreepers at elevations below 1,200 m where native forest habitats are still relatively intact. One of the few remaining species of honeycreepers with a wide elevational distribution is the Hawaii Amakihi (Hernignathus virens). We measured morbidity and mortality in experimentally-infected Hawaii Amakihi that were captured in a high elevation, xeric habitat that is above the current range of the mosquito vector. Mortality among amakihi exposed to a single infective mosquito bite was 65% (13/20). All infected birds had significant declines in food consumption and a corresponding loss in body weight over the 60 day course of the experiment. Gross and microscopic lesions in birds that succumbed to malaria included enlargement and discoloration of the spleen and liver and parasitemias as high as 50% of circulating erythrocytes. Mortality in experimentally-infected amakihi was similar to that observed in Apapane (Himnatione sanguinea) and lower than that observed in Iiwi (Vestiaria coccinea) infected under similar conditions with the same parasite isolate. We conclude that the current elevational and geographic distribution of Hawaiian honeycreepers is determined by relative susceptibility to avian malaria.

Humoral and cellular immune responses up to 7.5 years after administration of streptokinase for acute myocardial infarction

AIMS

Administration of streptokinase results in an immunological response which may lead to increased risk of anaphylactic reaction or reduced thrombolytic efficacy on repeat administration. For these reasons current recommendations suggest that streptokinase should not be given up to 1 year after first administration. We sought to define the profile of both the circulating antibody and T-cell response to streptokinase in patients who had received streptokinase up to 7.5 years previously following acute myocardial infarction.

METHODS

Neutralizing anti-streptokinase antibody and total anti-streptokinase IgG were measured in 219 patients who had suffered acute myocardial infarction between 12 and 90 months previously and had received streptokinase. T-cell response to streptokinase was assessed by in-vitro proliferation of peripheral blood mononuclear cells (n=234). Data on all parameters were available in 184 patients. Controls (n=22) had suffered acute myocardial infarction between 73 and 84 months previously but had not received thrombolytic therapy.

RESULTS

Compared to controls, anti-streptokinase antibodies were elevated at all time periods from 12 to 90 months after streptokinase treatment. Total anti-streptokinase titres showed the expected correlation with neutralizing anti-streptokinase antibodies (P<0.0001). Peripheral blood mononuclear cells showed a vigorous in-vitro proliferative response to streptokinase 6 days after treatment (P=0.05 vs pre-treatment), but this was not detectable at 6 weeks or subsequently.

CONCLUSION

There is as yet no evidence of a time limit beyond which administration of streptokinase on a second occasion can be regarded as safe and likely to be effective. Measurement of neutralizing anti-streptokinase or total anti-streptokinase IgG titre appear to provide equivalent information regarding the antibody status of a population. Further studies are required regarding the apparent lack of peripheral blood mononuclear cells responsiveness in patients previously exposed to streptokinase.

Long-term endoscopic management of variceal bleeding

Recurrent hemorrhage from esophageal varices is a major source of morbidity and mortality in patients with portal hypertension. Esophageal sclerotherapy (EST) and more recently esophageal band ligation (EVL) can obliterate varices in 3-6 treatment sessions. Multiple band ligators make the use of overtubes unnecessary and make the procedure faster and more tolerable for the patient. EVL has several advantages, including fewer complications, fewer treatment sessions to obliteration, lower rebleeding rates, and lower mortality as compared to EST; the other advantages of EVL make it the treatment of choice for bleeding varices and long term management. The recommendations and rational for long term EST and EVL are presented and combination therapy and EUS guided EVL are discussed.

Influence of endoscopic biopsy forceps characteristics on tissue specimens: results of a prospective randomized study

BACKGROUND

A large variety of endoscopic biopsy forceps are commercially available. However, little is known regarding the influence of forceps characteristics such as disposability, size, shape, and presence of a needle on the adequacy of the specimens for histologic diagnosis. Our aim was to analyze in a prospective, randomized, pathologist-blinded study the performance of different biopsy forceps.

METHODS

Twelve biopsy forceps were tested, 6 each at upper endoscopy and colonoscopy. Two biopsy specimens were obtained with each forceps, for a total of 12 specimens per patient. The tissue samples were examined for the following parameters: weight (mg), size (mm3), depth, crush artifact, sheering effect, and adequacy of the specimens for histologic information (0 = inadequate, 1 = suboptimal, and 2 = adequate).

RESULTS

Fifty-five patients undergoing routine upper or lower gastrointestinal endoscopy were included in the study, and a total of 624 tissue samples were available for analysis. Overall, disposable forceps provided specimens of greater size and depth. At upper endoscopy, alligator-shaped forceps improved the depth of the sample as did the absence of a needle within the cup. These factors, however, had no impact on the specimens obtained at colonoscopy. When the adequacy of the specimens was assessed for histologic diagnosis, no significant difference was noted between any of the individual forceps, although collectively oval-shaped forceps were superior to alligator-shaped forceps at colonoscopy.

CONCLUSIONS

The biopsy forceps currently available in the market are equally efficient in providing histologic diagnosis. The primary consideration when selecting an endoscopic biopsy forceps, therefore, should be the cost and ease of use and not any perceived advantage in performance.

Utilisation of thrombolytic therapy in older patients with myocardial infarction

Empirical evidence from many countries, obtained from sampling populations of patients admitted to hospital with acute myocardial infarction, has confirmed that elderly patients are significantly less likely to receive thrombolytic therapy. This difference persists after controlling for confounding factors such as admission delay and contraindications to thrombolysis. However, evidence supporting the efficacy of thrombolysis in reducing mortality after acute myocardial infarction is less clear cut in patients aged 75 years or above than in younger patients. These older patients are substantially under-represented in the clinical trials although they constitute one third of the clinical population. Observational studies indicate that older patients are at slightly higher risk than younger patients of experiencing haemorrhagic stroke after thrombolysis. It is, however, unlikely that efficacy and tolerability considerations alone account for the low use of thrombolytics in the elderly as similar trends are seen for other modalities of treatment of acute myocardial infarction. Since older patients have the highest mortality risk after myocardial infarction, they have the greatest potential gain from thrombolytic treatment, assuming a uniform treatment effect across age. The estimated cost effectiveness (cost per quality-adjusted life-year gained) improves with increasing age. It is concluded that patient age should not influence the treatment decision concerning thrombolysis. To ensure that elderly patients receive maximum benefit from this therapeutic advance requires attention to referral patterns from the community, speed of assessment in hospital and a clear treatment policy without age constraints. The effectiveness of these measures should be routinely audited.

Ontogeny of prolactin-secreting cells during chick embryonic development: effect of vasoactive intestinal peptide

It was previously reported that prolactin (PRL)-containing cells differentiate by days 15 to 19 of embryonic development and that vasoactive intestinal peptide (VIP) increased plasma PRL concentrations and pituitary PRL protein and mRNA levels in vivo. In the present study, anterior pituitaries derived from day 15, 16, 17, 18, and 19 embryos were subjected to reverse hemolytic plaque assays (RHPA) for chicken PRL to determine the ontogeny of lactotrophs. We found that PRL secreting cells were first consistently detected on day 17 of embryonic development, indicating that lactotroph differentiation during normal development occurs by this age. However, extended treatment in the RHPA with VIP exposed lactotrophs as early as day 15, suggesting that a lactotroph precursor population was present earlier. Next, primary cultures of embryonic anterior pituitary cells from day 12, 13, 14, 15, 16, and 17 embryos were incubated for 0, 2, or 4 days in serum-free medium or medium supplemented with 10 nM VIP. After the culture periods, cells were subjected to RHPAs for chicken PRL. PRL-secreting cells differentiated spontaneously by 2 days in culture for day 15 and 16 cells and by 4 days in culture for all embryonic ages tested, except day 17. Culturing with VIP for 2 days did not increase PRL-secreting cells at any embryonic age tested, whereas VIP treatment for 4 days increased lactotroph numbers at all ages except day 12. Cells from days 15, 16, and 17 were responsive to VIP in the RHPA after 2 days in untreated cultures, but after 4 days only day 17 cells continued to respond to VIP in the RHPA. Treatment with VIP in culture for 4 days maintained VIP responsiveness in the RHPA for cells derived from embryos as early as day 14. We conclude that lactotroph differentiation during normal chicken development occurs by embryonic day 17. Moreover, our results indicate that responsiveness to VIP is an early event in PRL cell development and that lactotroph differentiation may be stimulated in vitro by VIP as early as embryonic day 13.

Use of coronary angiography and revascularization procedures following acute myocardial infarction. A European perspective

AIMS

There is little evidence to inform routine practice in the use of coronary angiography and revascularization procedures after acute myocardial infarction. Large differences in the uptake of these procedures have been reported but representative data are scarce. Outcome studies have produced opposing conclusions concerning the impact of the high rate of these cardiac procedures.

METHODS AND RESULTS

A population-based patient sampling approach was utilized to identify routine practice in representative samples from 11 European countries. Data were collected retrospectively on treatment in the 6 months following acute myocardial infarction (n=2807). There was wide variation in utilization of coronary angiography and revascularization procedures. Even after restricting the analysis to patients <65 years (n=1262), there remained a 6 13 fold variation in the use of these procedures. A decreased likelihood of undergoing these procedures was associated with older age. In addition, there was an independent and negative association between female sex and utilization of coronary angiography and coronary artery bypass grafting (CABG).

CONCLUSION

The effect on patient outcome of the observed variation in use of these procedures is not known but has important cost and resource implications for the health services. Outcome research is needed to define patient selection criteria and to measure the cost-utility of different angiography and revascularization rates.

Beta-blockers and antithrombotic treatment for secondary prevention after acute myocardial infarction. Towards an understanding of factors influencing clinical practice. The European Secondary Prevention Study Group

AIMS

Long-term beta-blockade reduced mortality after acute myocardial infarction by about a quarter in a series of published trials. Representative data on beta-blocker use for secondary prevention are scanty but indicate wide variations. We have analysed European practice, and sources of variation, by regional sampling of acute myocardial infarction patients admitted to hospital in 11 countries during the period January 1993-June 1994.

METHODS AND RESULTS

Treatment data for 4035 representative patients were collected for the hospital phase and 6 months after discharge. A logistic regression model was developed to describe the predictors of beta-blocker use. In the 11 regional samples, 6-38% (20% overall) of patients had no recorded contraindications but were discharged without a beta-blocker. In the absence of perceived contraindications, there was a strong, independent negative association between age and odds of treatment (P < 0.001), and women were less likely to be treated than men (adjusted odds ratio 0.76, 95% CI 0.58-0.99). Discontinuation of beta-blocker treatment by 6 months was significantly less likely in regions where the proportion given such treatment at discharge was high. In contrast, use of antithrombotic agents in the samples was consistently high.

CONCLUSIONS

There is persisting low use of beta-blocker secondary prophylaxis, particularly in the elderly and in women, not attributable to perceived contraindications or intolerance. Considerable regional variations persist despite shared trials evidence. Discharge treatment strongly influences long-term medication.

Tenderizing spent fowl meat with calcium chloride. 4. Improved oxidative stability and the effects of additional aging

The goal of these experiments was to determine the effects of CaCl2 and NaCl injections on spent fowl meat tenderness and oxidative stability. Two hundred spent Leghorn hens were used in this two-part study. In the first experiment, breast fillets from 160 spent Leghorn hens were harvested immediately after death, injected with 0.3 M CaCl2 or H2O, vacuum tumbled, and either cooked immediately after tumbling or aged at 1 C for 23 h prior to cooking. Although the CaCl2 injection reduced shear values without aging, additional tenderization occurred during the aging period. In the second experiment, breast fillets from 40 spent Leghorn hens were harvested immediately after death, injected with 0.3 M CaCl2, 0.6 M NaCl, 0.15 M CaCl2 + 0.3 M NaCl, or H2O, vacuum tumbled, and then aged at 1 C for 23 h before cooking. The three salt injection treatments reduced shear values to a similar extent, but the sarcomeres were significantly longer for the NaCl treatment than the CaCl2 or combination treatments. Panelists preferred the CaCl2 + NaCl fillets over the CaCl2 fillets. Replacing some of the CaCl2 with NaCl maintained the tenderizing effect, and panelist comments indicated that the slight aftertaste of the 0.3 M CaCl2 treatment was reduced. The sodium contribution of the 0.6 M NaCl treatment would also be reduced by the CaCl2 + NaCl treatment.

First myocardial infarction in patients of Indian subcontinent and European origin: comparison of risk factors, management, and long term outcome

OBJECTIVE

To compare long term outcome after first myocardial infarction among British patients originating from the Indian subcontinent and from Europe.

DESIGN

Matched pairs study.

SETTING

Coronary care unit in central Leicester.

SUBJECTS

238 pairs of patients admitted during 1987-93 matched for age (within 2 years), sex, date of admission (within 3 months), type of infarction (Q/non-Q), and site of infarction.

MAIN OUTCOME MEASURES

Incidence of angina, reinfarction, or death during follow up of 1-7 years.

RESULTS

Patients of Indian subcontinent origin had a higher prevalence of diabetes (35% v 9% in patients of European origin, P < 0.001), lower prevalence of smoking (39% v 63%, P < 0.001), longer median delay from symptom onset to admission (5 hours v 3 hours, P < 0.01), and lower use of thrombolysis (50% v 66%, P < 0.001). During long term follow up (median 39 months), mortality was higher in patients of Indian subcontinent origin (unadjusted hazard ratio = 2.1, 95% confidence interval 1.3 to 3.4, P = 0.002). After adjustment for smoking, history of diabetes, and thrombolysis the estimated hazard ratio fell slightly to 2.0 (1.1 to 3.6, P = 0.02). Patients of Indian subcontinent origin had almost twice the incidence of angina (54% v 29%; P < 0.001) and almost three times the risk of reinfarction during follow up (34% v 12.5% at 3 years, P < 0.001). The unadjusted hazard ratio for reinfarction in patients of Indian subcontinent origin was 2.8 (1.8 to 4.4, P < 0.001). Adjustment for smoking, history of diabetes, and thrombolysis made little difference to the hazard ratio. Coronary angiography was performed with similar frequency in the two groups; triple vessel disease was the commonest finding in patients of Indian subcontinent origin and single vessel disease the commonest in Europeans (P < 0.001).

CONCLUSIONS

Patients of Indian subcontinent origin are at substantially higher risk of mortality and of further coronary events than Europeans after first myocardial infarction. This is probably due to their higher prevalence of diffuse coronary atheroma. Their need for investigation with a view to coronary revascularisation is therefore greater. History of diabetes is an inadequate surrogate for ethnic origin as a prognostic indicator.

A meta-analysis of the association of the deletion allele of the angiotensin-converting enzyme gene with myocardial infarction

BACKGROUND

The ACE gene is characterized by a polymorphism based on the presence (insertion [I]) or absence (deletion [D]) within intron 16 of a 287-basepair alu repeat sequence, resulting in three genotypes (DD and II homozygotes and ID heterozygotes). In 1992, the DD genotype was reported to be associated with an increased risk of myocardial infarction (MI). Subsequent studies have produced conflicting findings. To further evaluate the association of the ACE I/D genotype with MI risk, we carried out a meta-analysis of all the published studies.

METHODS AND RESULTS

In total, 15 studies containing 3394 MI cases and 5479 control subjects were analyzed. The overall distribution of genotypes in the control subjects was 22.7% II, 49.0% ID, and 28.3% DD. The mean odds ratio for MI for DD versus ID/II genotypes across all studies was 1.26 (95% CI, 1.15, 1.39; P < .0001). Pairwise odds ratios were 1.36 (95% CI, 1.19, 1.55) for DD and II, 1.24 (95% CI, 1.11, 1.38) for DD and ID, and 1.09 (95% CI, 0.96, 1.23) for ID and II. The relative risk appeared to be increased in Japanese populations (2.55; 95% CI, 1.75, 3.70).

CONCLUSIONS

Within the limitations of the available data, the meta-analysis therefore supports an association of the ACE D allele with MI risk and strengthens the justification for further evaluation in appropriately powered studies.

Insertion/deletion polymorphism in the angiotensin-converting enzyme gene and risk of and prognosis after myocardial infarction

OBJECTIVES

We sought to prospectively investigate whether genetic variation at the angiotensin-converting enzyme gene locus defined by an insertion (I)/deletion (D) polymorphism influences the risk of myocardial infarction or prognosis after infarction, or both.

BACKGROUND

It has been suggested that the deletion allele of the angiotensin-converting enzyme gene, and specifically the DD genotype, may increase the risk of myocardial infarction, although previous studies have produced conflicting reports. No studies have yet examined the effect of I/D polymorphism on survival after infarction.

METHODS

Angiotensin-converting enzyme genotypes in 684 patients with myocardial infarction recruited at the time of the acute event through coronary care units in two centers were compared with those of 537 control subjects recruited from the base populations. All patients were followed up to assess the impact of the angiotensin-converting enzyme genotype on prognosis.

RESULTS

We found no difference (p = 0.89) in the genotype distribution between patients and control subjects (patients DD 31%, ID 47%, II 22%; control subjects DD 30%, ID 48%, II 22%). The odds ratio for myocardial infarction for DD compared with II/ID genotype adjusted for age, gender and center was 1.16 (95% confidence interval [CI] 0.82 to 1.65, p = 0.44). The study had 90% power to detect a 1.5-fold increase in risk of myocardial infarction associated with the DD genotype. For one center, data were available for other risk factors (hypertension, diabetes, angina, previous myocardial infarction, smoking, body mass index, total and high density lipoprotein cholesterol) in both patients and control subjects. In a stepwise logistic regression analysis the odds ratio for DD versus ID/II genotypes remained nonsignificant (1.44, 95% CI 0.84 to 2.46, p = 0.20) for these subjects. Over a median follow-up period of 15 months (range 3 to 22), 155 patients (22.7%) died. There was no difference in mortality between subjects with the DD genotype and those with ID/II genotypes. (21.8% vs. 23.1%, p = 0.25). Likewise, there was no difference in the distribution of survival times in the two groups (p = 0.62). The study had 70% power to detect a 1.5-fold increase in mortality during follow-up associated with the DD genotype.

CONCLUSIONS

We conclude that in the groups studied, genetic variation at the angiotensin-converting enzyme gene locus defined by I/D polymorphism does not significantly influence either the risk of or the short- to medium-term prognosis after myocardial infarction.

Reproducibility and automatic measurement of QT dispersion

This study investigated interobserver (two observers) and intrasubject (two measurements) reproducibility of QT dispersion from abnormal electrocardiograms in patients with previous myocardial infarction, and compared a user-interactive with an automatic measurement system. Standard 12-lead electrocardiograms, recorded at 25 mm.s-1, were randomly chosen from 70 patients following myocardial infarction. These were scanned into a personal computer, and specially designed software skeletonized and joined each image. The images were then available for user-interactive (mouse and computer screen), or automatic measurements using a specially designed algorithm. For all methods reproducibility of the RR interval was excellent (mean absolute errors 3-4 ms, relative errors 0.3-0.5%). Reproducibility of the mean QT interval was good; intrasubject error was 6 ms (relative error 1.4%), interobserver error was 7 ms (1.8%), and observers' vs automatic measurement errors were 10 and 11 ms (2.5, 2.8%). However QTc dispersion measurements had large errors for all methods; intrasubject error was 12 ms (17.3%), interobserver error was 15 ms (22.1%), and observers' vs automatic measurement were errors 30 and 28 ms (35.4, 31.9%). QT dispersion measurements rely on the most difficult to measure QT intervals, resulting in a problem of reproducibility. Any automatic system must not only recognize common T wave morphologies, but also these more difficult T waves, if it is to be useful for measuring QT dispersion. The poor reproducibility of QT dispersion limits its role as a useful clinical tool, particularly as a predictor of events.

How accurate is the determination of blood in gastric juice? Comparison of peroxidase and porphyrin methods

BACKGROUND

Mucosal bleeding is frequently used as a measure of gastric mucosal integrity. We compared the orthotolidine method for quantifying haemoglobin in gastric juice with a method based on measurement of fluorescent porphyrins extracted from haem. We also investigated whether acid or pepsin had a deleterious effect on the results of either method.

METHODS

We compared the effects of pH (2 or 7), time (up to 180 min), haemoglobin concentration and the addition of pepsin (2.5, 5 or 7.5 kU/mL hog pepsin) on the accuracy of the two methods.

RESULTS

With the orthotolidine method there was a time-dependent decline in detectable haemoglobin concentration (P < 0.02) at pH 2 that was not seen at pH 7. The time- and pH-dependent decline in detectable haemoglobin was not seen using the porphyrin assay.

CONCLUSION

The widely used orthotolidine method for determination of blood in gastric juice is less reliable than the porphyrin method as it is more likely to be influenced by acidic conditions in the stomach.

Use of lead adjustment formulas for QT dispersion after myocardial infarction

OBJECTIVE

To determine whether lead adjustment formulas for correcting QT dispersion measurements are appropriate in patients after myocardial infarction.

DESIGN

Retrospective analysis of QTc dispersion measurements in 461 electrocardiograms (ECGs). Data are presented as uncorrected QTc dispersion "adjusted" for a number of measurable leads and coefficient of variation of QTc intervals for ECGs in which between six and 12 leads had a QT interval that could be measured accurately.

PATIENTS

Patients were drawn from the placebo arm of the second Leicester Intravenous Magnesium Intervention Trial. Some 163 patients who subsequently died and an equal number of known survivors had ECGs recorded on day 2 or 3 of acute myocardial infarction. ECGs were also available in 135 of these patients from at least 1 month postinfarct.

RESULTS

The most common lead in which a QT interval measurement was omitted was aVR (n = 176), the least common lead was V3 (n = 13). The longest QTc interval measured was most usually in lead V4 (n = 72) and the shortest in lead V1 (n = 67). As the number of measurable leads decreased there was a small, nonsignificant increase in QTc dispersion from 12 lead to eight lead ECGs (mean (SD) 100 (35.5) v 109.5 (47.9) ms). Lead adjusted QTc dispersion (QTc dispersion/square root of the number of measurable leads) showed a large, significant increase when the number of measurable leads decreased from 12 to eight (28.9 (10.3) v 38.7 (16.1) ms, P < 0.001). A similar trend was seen for coefficient of variation of QTc intervals (standard deviation of QTc intervals/mean QTc interval 64.3 (2.19) v 8.45 (3.94)%, P < 0.001).

CONCLUSIONS

Lead adjustment formulas for QT dispersion are not appropriate in patients with myocardial infarction. Large differences in lead adjusted QTc dispersion are produced, dependent on the number of measurable leads, for very small differences in QTc dispersion. It is recommended that QT dispersion is presented as unadjusted QT and QTc dispersion, stating the mean (SD) of the number of leads in which a QT interval was measured.

Three-lead measurement of QTc dispersion

INTRODUCTION

QTc dispersion has traditionally been calculated from all 12 leads of a standard electrocardiogram (ECG). It is possible that alternative, quicker methods using fewer than 12 leads could be used to provide the same information.

METHODS AND RESULTS

We have previously shown a difference in QTc dispersion from ECGs recorded at least 1 month after myocardial infarction between patients who subsequently died and long-term survivors. In the current study, we recalculated QTc dispersion in these ECGs using different methods to determine if the observed difference in QTc dispersion measurements between the two groups, as calculated from 12-lead ECGs, persisted when using smaller sets of leads. QTc dispersion was recalculated by four methods: (1) with the two extreme QTc intervals excluded; (2) from the six precordial leads; (3) from the three leads most likely to contribute to QTc dispersion (aVF, V1, V4); and (4) from the three quasi-orthogonal leads (aVF, I, V2). For each of the 270 12-lead ECGs examined, a mean of 9.9 leads (SD 1.5 leads) had a QT interval analyzed; the QT interval could not be accurately measured in the remaining leads. Using the standard 12-lead measurement of QTc dispersion, there was a difference in the fall in QTc dispersion from early to late ECG between the groups: 9.1 (SD 60.8) msec for deaths versus 34.4 (55.2) msec for survivors (P = 0.016). This difference in QTc dispersion between early and late ECGs was maintained using either three-lead method (quasi-orthogonal leads: -2.6 [56.2] msec for deaths vs 26.9 [54.3] msec for survivors [P = 0.003]; "likeliest" leads: 8.6 [64.9] msec vs 29.5 [50.2] msec [P = 0.05]), but not when using the other two methods (precordial leads: 19.1 [55.5] msec vs 22 [50.8] msec [P = 0.76]; extreme leads removed: 9.2 [50.1] msec vs 21.8 [42] msec [P = 0.13]).

CONCLUSION

QTc dispersion calculated from three leads may be as useful a measurement as QTc dispersion calculated from all leads of a standard ECG. Its advantages over the standard measurement are its simplicity and the lack of problems with lead adjustment.

Mega-trials and management of acute myocardial infarction

Clinical management of acute myocardial infarction has been strongly influenced by large, simple trials (mega-trials) with unrestrictive protocols and limited data collection. The design has been adopted to increase statistical power to a maximum. Its validity rests on an effective randomisation procedure and intention-to-treat analysis of deaths. Experience has shown that mega-trials tend to generate effect-estimates nearer the null than those from conventional trials or meta-analyses. When a small or absent observed treatment effect (or subgroup effect) in a mega-trial contrasts with the results of conventionally designed trials, it is necessary to assess both null bias and failure to increase the true treatment effect to a maximum in the mega-trial. Null bias will arise when the contrast between treatment and no-treatment, or between subgroups, is blunted either by non-protocol therapy or by inaccuracy of data, including misclassification between subgroups. Each is more likely with an unrestrictive design. To increase the true treatment effect to a maximum, trial conditions must be specified with insight into mechanism, dose-dependence, and time-dependence. The mega-trial design is therefore unsuited to an exploratory role. These issues are illustrated by the examples of nitrates, angiotensin-converting-enzyme inhibitors, and magnesium in acute myocardial infarction but have general relevance to the validity and generalisability of simple trials.

Selection factors for the use of thrombolytic treatment in acute myocardial infarction: a population based study of current practice in the United Kingdom. The European Secondary Prevention Study Group

OBJECTIVES

To identify and rank the factors that currently limit the use of thrombolytic treatment in patients admitted to hospital with acute myocardial infarction.

DESIGN

Weighted sampling study with retrospective data retrieval from clinical records.

SETTING

All hospitals within the Trent region providing acute general medical services.

PATIENTS

Random sample of 420 patients admitted during February-April 1993 who had acute myocardial infarction as the main discharge diagnosis.

MAIN OUTCOME MEASURES

Treatment odds ratios (and 95% confidence intervals (CI)) for the use of thrombolysis in patient groups defined by relevant clinical characteristics.

RESULTS

The patient population was older and less likely to have ST segment elevation on the initial electrocardiogram than patients entered into the randomised trials of thrombolysis. Thrombolytic treatment was given to 49% of patients (SE 2.4%). After controlling for negative associations with a history of stroke (treatment odds ratio 0.18 (95% CI 0.04 to 0.53)) and peptic ulcer (odds ratio 0.52 (95% CI 0.26 to 1.01)) use of thrombolysis decreased with increasing patient age. This was particularly noticeable for those aged > 74 years (odds ratio 0.17 (95% CI 0.05 to 0.51)) relative to those aged < 65 years. Thrombolysis was less likely to be used in patients with ST depression (odds ratio 0.22 (95% CI 0.11 to 0.41)) or bundle branch block (odds ratio 0.18 (95% CI 0.07 to 0.44)) than in those with ST elevation on the initial electrocardiogram. Delay from symptom onset to admission was more than 12 h in 15% of patients.

CONCLUSIONS

The patient population admitted to hospital with acute myocardial infarction differs in several respects from the samples that have been included in the trials of thrombolysis. The main factors limiting wider use of thrombolysis are diagnostic uncertainty at admission and delayed presentation. Perceived clinical contraindications to treatment are of lesser importance. There is evident reluctance to use thrombolytic treatment in older patients, who were substantially under-represented in the clinical trials.

32P-postlabelled DNA adducts in liver obtained from women treated with tamoxifen

32P-Postlabelling of DNA extracted from the livers obtained from seven women receiving tamoxifen (20 mg either once or twice daily) was compared with liver DNA from seven individuals not receiving this drug. In all but one of the treated women, tamoxifen and its N-desmethyltamoxifen metabolite could be detected in liver extracts by high performance liquid chromatography; none was detected in control samples. The total level of 32P-postlabelled DNA adducts extracted from the tamoxifen treated women ranged between 18-80 adducts/10(8) nucleotides. The pattern of 32P-postlabelled adducts was not the same as those seen in rats dosed with this drug. There was no significant difference in the level of DNA damage between the tamoxifen treated and control groups. Although only a small number of subjects has so far been examined it appears that women are less susceptible to liver DNA damage caused by tamoxifen than rats.

QT dispersion and mortality after myocardial infarction

QT dispersion may serve as a measure of variability in ventricular recovery time and may be a means of identifying patients at risk of arrhythmias and sudden death after acute myocardial infarction. We investigated this possibility on electrocardiograms (ECGs) recorded 2 or 3 days after infarction (early) and at least 4 weeks later (late). 163 patients who died between 1 day and 5 years after infarct were compared with an equal number of survivors matched for age and sex. 53 of the patients who died and 82 survivors also had late ECGs. There was no difference in early QT dispersion between the patients who died and the survivors (mean QTc dispersion 112.1 [SD 44.4] vs 109.9 [42.7] ms1/2). QTc dispersion fell significantly from early to late ECGs in survivors (110.9 [48.5] to 76.5 [28.8] ms1/2), but not in patients who died during follow-up (108.0 [51.0] to 98.9 [43.1] ms1/2). The difference between the groups in the mean change was significant (34.4 [55.2] vs 9.1 [60.8] ms1/2, p = 0.016). QT dispersion measured on an ECG recorded 2 or 3 days after acute myocardial infarction does not predict mortality during the next 5 years. Increased QT dispersion on ECGs recorded at least 4 weeks after infarct may be associated with subsequent mortality, but this finding must be confirmed in a prospective trial.

Agism and provision of thrombolysis

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Wildlife disease and conservation in Hawaii: pathogenicity of avian malaria (Plasmodium relictum) in experimentally infected iiwi (Vestiaria coccinea)

Native Hawaiian forest birds are facing a major extinction crisis with more than 75% of species recorded in historical times either extinct or endangered. Reasons for this catastrophe include habitat destruction, competition with non-native species, and introduction of predators and avian diseases. We tested susceptibility of Iiwi (Vestiaria coccinea), a declining native species, and Nutmeg Mannikins (Lonchura punctulata), a common non-native species, to an isolate ofPlasmodium relictumfrom the island of Hawaii. Food consumption, weight, and parasitaemia were monitored in juvenile Iiwi that were infected by either single (low-dose) or multiple (high-dose) mosquito bites. Mortality in both groups was significantly higher than in uninfected controls, reaching 100% of high-dose birds and 90% of low-dose birds. Significant declines in food consumption and a corresponding loss of body weight occurred in malaria-infected birds. Both sex and body weight had significant effects on survival time, with males more susceptible than females and birds with low initial weights more susceptible than those with higher initial weights. Gross and microscopic lesions in malaria fatalities included massive enlargement of the spleen and liver, hyperplasia of the reticuloendothelial system with extensive deposition of malarial pigment, and overwhelming anaemia in which over 30% of the circulating erythrocytes were parasitized. Nutmeg Mannikins, by contrast, were completely refractory to infection. Our findings support previous studies documenting high susceptibility of native Hawaiian forest birds to avian malaria. This disease continues to threaten remaining high elevation populations of endangered native birds.

Long-term outcome after intravenous magnesium sulphate in suspected acute myocardial infarction: the second Leicester Intravenous Magnesium Intervention Trial (LIMIT-2)

The second Leicester Intravenous Magnesium Intervention Trial (LIMIT-2) examined the effect of an intravenous regimen of magnesium sulphate in 2316 patients with suspected acute myocardial infarction. Treatment, according to a double-blind randomised protocol, was started with a loading injection, before any thrombolytic therapy, and continued with a maintenance infusion for a further 24 h. Cause-specific mortality of randomised patients has now been examined over 1.0-5.5 (mean 2.7) years of follow-up. Mortality rate from ischaemic heart disease was reduced by 21% (95% CI 5-35%, p = 0.01) and all-cause mortality rate reduced by 16% (2-29%, p = 0.03) in magnesium-treated patients. Magnesium protects the contractile function of the myocardium from reperfusion injury ("stunning") in experimental models; this observation accords with the 25% (7-39%, p = 0.009) reduction in early left ventricular failure in the magnesium group of LIMIT-2. For such protection to occur, magnesium must be raised by the time of reperfusion since the injury is immediate. In the clinical context the timing of magnesium treatment in relation to thrombolytic therapy or spontaneous reperfusion is likely to be critical. The early benefits of this simple and safe intervention are reflected in improved long-term survival.

Investigation of the effects of intravenous magnesium sulphate on cardiac rhythm in acute myocardial infarction

OBJECTIVE

To examine the effect of doubling serum magnesium concentration on the incidence of arrhythmias in patients with suspected acute myocardial infarction.

DESIGN

Randomised double blind clinical trial.

SETTING

Coronary care unit of a teaching hospital.

PATIENTS

Clinical data were collected on 2316 randomised patients with suspected acute myocardial infarction. Holter monitoring was performed in a subgroup of 70 patients and analysed in 48 patients in whom acute myocardial infarction was confirmed.

INTERVENTIONS

By random allocation, patients received either an intravenous loading dose of 8 mmol magnesium sulphate over five minutes plus 65 mmol over the next 24 hours, or equal volumes of saline.

MAIN OUTCOME MEASURES

(a) Clinically documented arrhythmias; (b) use of antiarrhythmic treatments, cardioversion, and insertion of a pacemaker; (c) incidence of all abnormal rhythms during Holter monitoring.

RESULTS

In the main trial the incidence of rhythm disturbance while in the coronary care unit (expressed as the odds ratio (OR) for magnesium: placebo and its 95% confidence interval) was not significantly different between treatment groups for ventricular fibrillation (OR 0.74; 0.46 to 1.20), ventricular tachycardia (OR 0.87; 0.63 to 1.20), supraventricular tachycardia (OR 0.69; 0.38 to 1.26), atrial fibrillation (OR 0.92; 0.69 to 1.23), or heart block of any degree (OR 1.17; 0.83 to 1.65). Sinus bradycardia was significantly more common in the magnesium group (OR 1.38; 1.03 to 1.85; p = 0.02). These findings were corroborated by the use of treatments for rhythm disturbance and the data from Holter monitoring.

CONCLUSION

The regimen of intravenous magnesium sulphate used here had no significant effect on arrhythmia in acute myocardial infarction. The reduction in mortality that has been shown with this form of treatment is not attributable to suppression of life threatening rhythm disturbances.

A scoring system to predict rebleeding after endoscopic therapy of nonvariceal upper gastrointestinal hemorrhage, with a comparison of heat probe and ethanol injection

We prospectively and randomly compared heat probe and ethanol injection in 80 patients with major nonvariceal upper gastrointestinal hemorrhage who were bleeding actively or had endoscopic stigmata associated with a high risk for rebleeding. We also attempted to predict which patients would rebleed within 72 h after successful endoscopic therapy, using a three-component scoring system. Heat probe and ethanol injection proved to be similar in efficacy and safety. Active bleeding was controlled with equal success with heat probe and ethanol injection (92% vs. 82%), and there was no difference in the rebleeding rate (11% vs. 13%). The scoring system was useful in predicting which patients would rebleed. Significant differences were seen in the mean values of all three scores, and specific cut-offs in the pre-endoscopy and post-endoscopy scores predicted patients who rebled. High likelihood ratios and post-test probabilities for rebleeding were found for the number and severity of concurrent illnesses, but not for endoscopic stigmata, implying that the excess risk associated with stigmata is eliminated after effective endoscopic therapy, and clinical factors become the primary determinants of rebleeding.

Impact of clinical trials on clinical practice: example of thrombolysis for acute myocardial infarction

Little is known about incorporation of new knowledge from randomised clinical trials into clinical practice. Thrombolytic therapy was shown to reduce the mortality of acute myocardial infarction in several large trials published during 1986-88. To examine the effect of these data on clinical practice, we analysed the supply of thrombolytic drugs in a representative English region (population 4.7 million) in 1987-92. During the study period there were over 10,000 hospital admissions per year in the region for acute myocardial infarction. From a very low initial level, thrombolytic drug use rose slowly for several years after publication of the trial results and reached a plateau in 1991-92. Rates of use per 1000 patients admitted with myocardial infarction varied almost six-fold between districts in 1989-90 and over two-fold in 1991-92. Level of use attained by districts in the latter period was strongly associated with the extent of their previous participation in multicentre trials of thrombolysis (p = 0.003); we estimate that 35-50% of patients admitted with acute myocardial infarction were receiving thrombolytics. The full potential of thrombolytic treatment has still not been achieved in routine care and the limiting factors need to be defined.

Disease variations in Asians in Leicester

The epidemiological study of ethnic groups provides valuable information for physicians in a number of ways. First, it assists in the diagnostic approach in individual patients, especially for doctors unfamiliar with patients of a particular ethnic background. Second, it provides population data to assist in health care planning and provision for the present and future in districts where ethnic minorities are resident in significant numbers. Third, it may provide pointers for the study of pathogenic mechanisms. Fourth, changing epidemiology in migrant ethnic minorities may help to distinguish the degree of influence of genetic and environmental pathogenic factors. These studies are particularly valuable when minority populations are of a size which allows meaningful data to be collected on uncommon conditions. Furthermore the contrasts between migrant and indigenous populations are most clearly seen if migration has occurred over a restricted period. For these and other reasons the study of the migrant population from the Indian subcontinent (defined as India, Pakistan and Bangladesh) which has settled in Leicester since the mid-1960s has proved particularly rewarding. This report summarizes the distinctive epidemiological features of these people now living in Leicester.

Modification of the circadian rhythm of onset of acute myocardial infarction by long-term antianginal treatment

OBJECTIVE

To elucidate the mechanism of the circadian pattern of onset of acute myocardial infarction by examining the effects of prior antianginal treatment upon it.

DESIGN

Retrospective analysis of clock time of the onset of acute myocardial infarction by linear modelling to define the circadian distribution of hourly onset rates and to examine the deviation of treated groups of patients from this distribution.

SETTING

Coronary care unit in a general hospital taking unselected acute admissions from a district of 0.9 million people.

PATIENTS

A series of 2231 patients with confirmed acute myocardial infarction.

RESULTS

A major 24 h cycle and smaller 12 h and 6 h cycles were present in patients not taking antianginal medication. Onset rates varied twofold over the day, with maxima around 10.00 am and 10.00 pm. This pattern was unchanged in patients on prior treatment with regular nitrates, but in those who had been taking a beta blocker or a calcium antagonist the 24 h cycle was absent.

CONCLUSIONS

These results are best explained by the shared property of beta blockers and calcium antagonists to reduce blood pressure and myocardial oxygen demand. The mid-morning peak of the onset of myocardial infarction is attributable to the physiological increase in sympathetic drive and cardiac work at that time. The data are not consistent with the triggering of the 24 h periodicity by fluctuations in coronary tone or haemostatic activity.

Cerebrovascular carbon dioxide reactivity and failure of autoregulation in preterm infants

Changes in cerebral blood flow velocity (CBFV) in response to a rise in arterial carbon dioxide tension (PaCO2) in 94 ventilated preterm infants were determined using Doppler ultrasound to assess whether the nature of this change might predict subsequent neurological injury. Concomitant changes in mean arterial pressure (MAP) were recorded. Both CBFV and MAP rose significantly in response to the rise in PaCO2, the response being significantly less in the first 24 hours. Analysis indicated that the change in CBFV in the first day of life in infants less than or equal to 30 weeks' gestation was dependent to a great extent on the concomitant change in MAP. Similar dependence also occurred after administration of pancuronium to infants whose CBFV response was previously independent of changes in MAP. This dependency lasted for the duration of paralysis. Changes in CBFV after a rise in PaCO2 did not predict subsequent neurological injury. The influence of pancuronium on cerebrovascular regulation warrants further study.