Intravenous magnesium sulphate in suspected acute myocardial infarction: results of the second Leicester Intravenous Magnesium Intervention Trial (LIMIT-2)

The cardiovascular actions of the magnesium ion at pharmacological concentrations include coronary and systemic vasodilatation, platelet inhibition, and antiarrhythmic effects. Magnesium has also been reported to protect myocardial tissue in experimental models of ischaemia and reperfusion. Several small clinical trials in suspected acute myocardial infarction have suggested that early mortality can be reduced by intravenous infusion of magnesium salts in the acute phase, but none has been of sufficient size to be conclusive. We therefore conducted a randomised, double blind, placebo controlled study in 2316 patients with suspected acute myocardial infarction who received either intravenous magnesium sulphate (8 mmol over 5 min followed by 65 mmol over 24 h) or physiological saline. The primary outcome measure was 28-day mortality, which was ascertained in 99.3% of patients. The groups were well balanced for prognostic factors. By intention-to-treat analysis mortality from all causes was 7.8% in the magnesium group and 10.3% in the placebo group (2p = 0.04), a relative reduction of 24% (95% confidence interval 1-43%). Within the coronary care unit the incidence of left ventricular failure was reduced by 25% (7-39%) in the magnesium group (2p = 0.009). There was no significant difference between the groups in the incidence of heart block or the use of antiarrhythmic drugs, direct-current cardioversion, or temporary pacing. Myocardial infarction was confirmed in 65% of each group, with closely similar rises in cardiac enzymes. The side-effects of magnesium treatment were transient flushing, related to speed of injection of the loading dose, and an increased incidence of sinus bradycardia (2p = 0.02). Exploratory subgroup analyses of 28-day mortality did not indicate any effect modification by thrombolysis or aspirin, or by previous treatment with beta blockers, calcium antagonists, or diuretics. Intravenous magnesium sulphate is a simple, safe, and widely applicable treatment. Its efficacy in reducing early mortality of myocardial infarction is comparable to, but independent of, that of thrombolytic or antiplatelet therapy.

Cardiovascular effects of carbon dioxide in ventilated preterm infants

Sick preterm infants may, under certain conditions, demonstrate blood pressure passive cerebral blood flow in response to changes in arterial carbon dioxide tension. Blood pressure in turn depends on cardiac output and peripheral resistance. A Doppler technique for assessing cardiac output compared favourably in terms of reproducibility to a thermodilution technique in a group of infants undergoing cardiac catheterization for congenital heart disease. Doppler was subsequently used to monitor changes in cardiac output following an increase in arterial carbon dioxide tension of 1 kPa in 25 ventilated preterm infants. Blood pressure increased significantly (p = 0.006). However, heart rate did not change significantly (p = 0.16) and, in addition, both stroke and minute volume decreased (p = 0.023, p = 0.02, respectively). This suggests that accompanying changes in components of peripheral resistance exert important effects on blood pressure in the preterm neonate in response to changes in arterial carbon dioxide tension.

Intracellular metabolism of the antiherpes agent (S)-1-[3-hydroxy-2-(phosphonylmethoxy)propyl]cytosine

(S)-1-[3-Hydroxy-2-(phosphonylmethoxy)propyl]cytosine (HPMPC) is an antiviral phosphonate nucleotide analogue that displays activity against a range of herpesviruses. Anion exchange high performance liquid chromatography analysis of the 60% methanol extract from [14C]HPMPC-treated cells reveals the formation of three major metabolites. Two of these were identified as phosphorylated forms of HPMPC, HPMPC phosphate, and HPMPC diphosphate, by liberation of HPMPC upon acid digestion and coelution with synthetic standards on high performance liquid chromatography. The third metabolite, which is resistant to alkaline phosphatase cleavage but sensitive to phosphodiesterase, is proposed to be an HPMPC phosphate adduct. In herpes simplex virus-1-infected cells the same three metabolites are detected, at concentrations comparable to those in uninfected cells. When HPMPC is removed from the medium, the concentrations of the metabolites in cells decrease slowly, with half-lives of approximately 6, 17, and 48 hr for HPMPC phosphate, HPMPC diphosphate, and the HPMPC phosphate adduct, respectively. HPMPC diphosphate inhibits herpes simplex virus-1 and -2 DNA polymerases with a lower Ki than that for DNA polymerase alpha, and enzyme inhibition is competitive in each case. The formation and the persistence of HPMPC phosphates in cells and the selective inhibition of viral DNA polymerases by HPMPC diphosphate can explain why cells pretreated with HPMPC remain refractory to viral infection even long after HPMPC is removed from the medium.

The effects of demographic shift on coronary heart disease mortality in a large migrant population at high risk

Asian immigrants to the United Kingdom and elsewhere are at greater risk of mortality and morbidity from coronary heart disease (CHD) than UK whites. This predisposition has yet to be explained. More than 63,000 Asian people, a high proportion of whom are under 40, live in Leicester. Projections of the local Asian and non-Asian populations indicate that numbers of Asian people in higher-risk age groups will more than double between 1988 and 2008. In the absence of effective intervention, numbers of CHD deaths among Asian people, and the prevalence of other manifestations of CHD in this group, will rise by an equivalent amount. This predicted shift in the ethnic distribution of CHD has important implications for the planning of acute services in Leicester. Our predictions also demonstrate both a valuable opportunity and a pressing need for local research into the aetiology of CHD among Asian people, upon which preventative strategies may be based.

The effects of flosequinan on regional blood flow in normal man

1. The effects of 100 mg and 200 mg flosequinan on limb, hepatic and renal blood flow were investigated in 14 healthy male volunteers in a placebo controlled double-blind randomised three-way crossover study. 2. Heart rate, blood pressure, forearm blood flow and venous capacitance measured by volume plethysmography, were recorded sequentially over 4 h, after oral dosing. 3. Apparent hepatic and renal blood flows were estimated 2 h post-dose by indocyanine green dye clearance and clearance of 125-iodohippuran respectively. 4. Flosequinan produced dose-dependent reductions in resting diastolic blood pressure, accompanied by a rise in heart rate. 5. Forearm blood flow increased to a maximum 4 h after 200 mg and this was accompanied by a fall in forearm vascular resistance. 6. Hepatic blood flow increased, compared with placebo, after 200 mg flosequinan, accompanied by a fall in hepatic vascular resistance. Renal blood flow remained unchanged but renal vascular resistance fell significantly, compared with placebo, following both doses of the drug. 7. In normal man blood flow to the limb, hepatic and renal vascular beds is preserved despite dose-dependent reductions in blood pressure following single doses of flosequinan.

Endoscopic variceal ligation in patients who have failed endoscopic sclerotherapy

Endoscopic variceal ligation has been developed as an alternative to endoscopic sclerotherapy. We report a series of 12 men with a history of bleeding esophageal varices who were treated with endoscopic variceal ligation after they had failed sclerotherapy. Hemostasis was achieved in all 10 patients who were bleeding at the time of initial endoscopy and again in those who subsequently re-bled. Over a follow-up period of up to 22 months, varices have been and remain eradicated in five patients; in four others, a reduction in grade was noted before death (two patients), liver transplant, or loss to follow-up (one patient each); two patients died before they could be re-evaluated, while in the remaining patient, no reduction in variceal grade was noted before loss to follow-up. No complication was recorded after 35 endoscopic treatment sessions involving a total of 245 rubber band ligations. Our results indicate that endoscopic variceal ligation may be used with success in patients who fail sclerotherapy.

Reappraisal of thyroxine treatment in primary hypothyroidism

The optimum daily dose of thyroxine was calculated for 13 children aged 3-16 years with primary hypothyroidism by titrating their doses at monthly intervals. The condition of the thyroid was assessed by sensitive assay of thyroid stimulating hormone concentrations, as well as measurement of total and free thyroid hormone concentrations and systolic time interval ratios. Serum thyroid stimulating hormone concentration was found to be the most responsive to small changes in thyroxine. The calculated optimum daily replacement dose of thyroxine (102 micrograms/m2 or 3.5 micrograms/kg) was fractionally lower than that previously recommended, and was more closely related to surface area (coefficient of variation 8.2%) than to body weight (coefficient of variation 16.2%). Our results suggest that though monthly may be the optimal time interval for increases in the dose of thyroxine, any reduction in the dose should be made more gradually.

A new endoscopic method for managing food impaction in the esophagus

Previously described methods for dealing with acute food impaction in the esophagus are not uniformly efficacious, are cumbersome, and often prove dangerous. This paper describes a new technique using an endoscope which is modified such that the endoscope itself becomes a direct-vision suction device. We have successfully used the technique in seven patients with meat bolus impaction in the esophagus. The method proved quick and safe, and no complications occurred. After relieving the impaction an adequate diagnostic examination was done in all patients. In four patients with a predisposing peptic stricture and one with Schatzki's ring, treatment of the lesion was possible during the same endoscopic session.

Circulatory effects of fast ventilator rates in preterm infants

High frequency positive pressure ventilation has been suggested to result in a lower incidence of respiratory complications in preterm infants with idiopathic respiratory distress syndrome compared with ventilation at conventional rates. A possible disadvantage is compromise of the infant's cardiovascular condition secondary to inadvertent positive end expiratory pressure (PEEP). In a group of 20 such infants treated with high frequency positive pressure ventilation (rates of up to 100/minute) and analysed, changes in arterial blood pressure and cerebral blood flow velocity were largely influenced by changes in arterial blood gases, and no effect could be attributed to inadvertent PEEP. In addition, the observed fall in both arterial carbon dioxide and oxygen tensions could be readily predicted for theoretical reasons. Under certain conditions at the fastest rates used, cerebral blood flow velocity was significantly influenced by changes in blood pressure, which may indicate impaired cerebrovascular regulation. Though other factors (such as the severity of the infants' illness or the use of paralysis) may have been responsible for this apparent blood pressure passivity, the role of high frequency positive pressure ventilation in such infants warrants further study.

Accidental self administration of xylazine in a veterinary nurse

A 19 year old male veterinary nurse accidentally injected himself with 200 mg of xylazine (a muscle relaxant and sedative used in veterinary practice). He subsequently became comatose, hypotensive, bradycardic and acidotic. He required intensive supportive therapy, and made a full recovery over the next few hours. Xylazine toxicity in humans is very rare, and the effects are discussed.

Diabetes mellitus as a risk factor for acute myocardial infarction in Asians and Europeans

Ischaemic heart disease is commoner among immigrants from the Indian subcontinent than among Europeans in the United Kingdom. The excess cannot be accounted for by differences in smoking, blood pressure, or lipid concentrations. There is, however, an increased prevalence of diabetes mellitus in the Asian population. Separate estimates of the relative risk of acute myocardial infarction associated with diabetes from parallel case-control studies were made to compare the importance of diabetes as a risk factor in the two ethnic groups. For Asians the relative risk was 3.3 (95% confidence interval 1.9 to 5.8) and for Europeans 1.3 (1.0 to 1.7). Calculations of population attributable risk indicated that clinical diabetes mellitus accounts for 21% of the incidence of myocardial infarction in Asians but only 3% of the incidence in Europeans. Diabetes mellitus is of sufficient quantitative importance as a risk factor to account for the whole of the observed excess of deaths from ischaemic heart disease among Asians in the United Kingdom.

Low serum TSH with normal total thyroid hormone levels: an indicator of free T4 excess

We have studied 18 patients with low serum thyrotrophin (TSH) levels accompanied by normal thyroxine (T4) and triiodothyronine (T3) levels in order to clarify whether or not they are thyrotoxic. Serum T4, T3, free T3, free T4 and TSH were estimated three times weekly for 3-4 weeks. Thyroxine binding globulin (TBG) levels were estimated on one occasion only. Thyroid hormone data were expressed as the cumulative probability of having at least one result above the relevant normal range by the nth sample (Pn). For free T4 this probability was 61% by the 10th sample. Free T4 values were confined to the upper half of the normal range or above throughout the study. In contrast, free T3 values were distributed evenly within the normal range (P10 = 12%). For total T4 and total T3, P10 was 34 and 11% respectively. Thus, subjects with subnormal TSH levels but normal T4 and T3 levels have been shown to have elevated serum free T4 levels, an indicator of biochemical hyperthyroidism.

Cerebral haemodynamic effects of changes in positive end expiratory pressure in preterm infants

The effects of changes in positive end expiratory pressure (PEEP) on cerebral blood flow velocity, arterial blood gases, and mean arterial pressure were studied in newborn infants. In mechanically ventilated premature infants with severe respiratory disease, an increase in PEEP from 2 to 6 cm H2O was associated with an increase in cerebral blood flow velocity. There was no significant change in mean arterial blood pressure. There was a significant increase in PaO2 and PaCO2 for every stepwise rise in PEEP. Multivariate regression analysis showed that 72% of the effect on cerebral blood flow velocity was attributable to PaCO2 alone and that any change in blood pressure was not likely to contribute to these changes. There was no evidence that changes in PEEP within the commonly used range adversely affected the neonatal cardiovascular or cerebral circulations.

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 microM and collagen 2 micrograms/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.

The effects of intravenous and oral nifedipine on ex vivo platelet function

We have studied the possible anti-platelet effects of an intravenous formulation of nifedipine (0.75 mg as a bolus and an infusion of 1.2 mg.h-1 for 2 h), or equivalent volumes of the vehicle alone, or normal saline, in a double-blind crossover fashion in six healthy subjects. The effects of a standard oral formulation (20 mg sustained-release) compared to identical placebo were also studied in twelve other subjects. Platelet function was assessed by the addition of collagen, adenosine diphosphate, or adrenaline to whole blood followed by single platelet counting. Intravenous nifedipine had no effect on aggregation in response to any of the agonists, but oral nifedipine reduced aggregation caused by collagen by approximately 15%, despite similar plasma nifedipine concentrations after both formulations (18.5 ng.ml-1 after intravenous and 21.5 ng.ml-1 after oral administration). The lack of effect of intravenous nifedipine may be due to endothelial irritation caused by the vehicle. Intravenous nifedipine is unlikely to have a useful anti-platelet effect in patients who have acute coronary insufficiency.