Magnesium deficiency may be an important determinant of ventricular ectopy in digitalised patients with chronic atrial fibrillation

Gender-Related Association of Serum Uric Acid Levels with Premature Ventricular Contraction

In this study, we aim to investigate the association of serum uric acid (SUA) with the prevalence of premature ventricular contraction (PVC). The relationship between SUA and the prevalence of PVC in 98,965 subjects (79,034 male subjects, mean age: 51.9 ± 12.6 years old) in the Kailuan cohort study (n = 101,510, age range: 18-98 years) from June 2006 to October 2007 was investigated. These subjects were divided into five groups on the basis of their SUA levels. A multivariate logistic regression model was constructed to evaluate the association between SUA and the prevalence of PVC. The prevalence of PVC was 1.1% in all subjects, 1.1% in male subjects, and 1.0% in female subjects. Compared with the first quintile of SUA, the odds ratio (OR) and 95% confidence interval (95% CI) of other quintiles were 1.33 (1.05-1.69), 1.14 (0.90-1.46), 1.37 (1.08-1.74), and 1.63 (1.30-2.06) in male subjects; 1.12 (0.68-1.87), 1.27 (0.77-2.09), 1.45 (0.90-2.36), and 1.33 (0.81-2.18) in female subjects; and 1.30 (1.04-1.61), 1.20 (0.96-1.50), 1.33 (1.07-1.66), and 1.57 (1.26-1.95) for all subjects. The correlation between SUA and the prevalence of PVC was significant in all subjects and in male subjects, but not in female subjects. We demonstrated that SUA was apparently associated with the prevalence of PVC. The significant relationship between SUA and PVC identified in male subjects suggests the potential involvement of a gender-specific mechanism. Prospective studies are needed to further corroborate our results.

Drug-induced hypomagnesaemia : scope and management

Nearly 50 medications have been implicated as inducing hypomagnesaemia, sometimes based on insufficient data regarding clinical significance and frequency of occurrence. In fact, clinical effects attributed to hypomagnaesemia have been reported in only 17 of these drugs. A considerable amount of literature relating to individual drugs has been published, yet a comprehensive overview of this issue is not available and the hypomagnesaemic effect of a drug could be either overemphasised or under-rated. In addition, there are neither guidelines regarding treatment, prevention and monitoring of drug-induced hypomagnesaemia nor agreement as to what serum level of magnesium may actually be defined as 'hypomagnesaemia'. By compiling data from published papers, electronic databases, textbooks and product information leaflets, we attempted to assess the clinical significance of hypomagnesaemia induced by each drug. A practical approach for managing drug-induced hypomagnesaemia, incorporating both published literature and personal experience of the physician, is proposed. When drugs classified as inducing 'significant' hypomagnesaemia (cisplatin, amphotericin B, ciclosporin) are administered, routine magnesium monitoring is warranted, preventive treatment should be considered and treatment of hypomagnesaemia should be initiated with or without overt clinical manifestations. In drugs belonging to the 'potentially significant' category, among which are amikacin, gentamicin, laxatives, pentamidine, tobramycin, tacrolimus and carboplatin, magnesium monitoring is justified when either of the following occurs: clinical manifestations are apparent; persistent hypokalaemia, hypocalcaemia or alkalosis are present; other precipitating factors for hypomagnesaemia coexist; or treatment is with more than one potentially hypomagnesaemic drug. No preventive treatment is required and treatment should be initiated only if hypomagnesaemia is accompanied by symptoms or clinically significant relevant laboratory findings. In those drugs whose hypomagnesaemic effect is labelled as 'questionable', including furosemide and hydrochlorothiazide, routine monitoring and treatment are not required.

[Medicamentous anti-arrhythmia therapy. Is oral adjuvant therapy with electrolytes of value?]

Low serum concentrations of potassium and magnesium are proarrhythmic factors that are well established. Atrial and ventricular fibrillation are facilitated at low serum levels of these electrolytes. Loss of potassium and magnesium might be caused by diuretic therapy, gastrointestinal loss, drugs, and alcohol abuse. However, serum levels are not representative of total body content of potassium and magnesium, hence, adjuvant therapy might be indicated also in the presence of normal serum levels. This is especially true during the initial phase of antiarrhythmic therapy, which is accompanied by proarrhythmia in a significant number of cases. Patients with heart failure should routinely receive adjuvant electrolyte substitution, if renal function is not impaired. In the experimental model magnesium successfully prevented early afterdepolarizations caused by hypokalemia and antiarrhythmic drugs. In the clinical setting high dose magnesium abolished torsade-de-pointes tachycardias caused by antiarrhythmic drugs. Unfortunately, controlled studies are not available for low dose electrolyte therapy adjuvant to antiarrhythmic drug medication.

Magnesium status and digoxin toxicity

1. Eighty-one hospital patients receiving digoxin were separated into groups with and without digoxin toxicity using clinical criteria. Serum digoxin, sodium, potassium, calcium, creatinine, magnesium and monocyte magnesium concentrations were compared. 2. Subjects with digoxin toxicity had impaired colour vision (P less than 0.0001, Farnsworth-Munsell 100 hue test) and increased digoxin levels (1.89 (1.56-2.21) vs 1.34 (1.20-1.47) nmol l-1, P less than 0.01) (mean (95% confidence limits], though there was considerable overlap between two groups. 3. Subjects with digoxin toxicity had lower levels of serum magnesium (0.80 (0.76-0.84) vs 0.88 (0.85-0.91) mmol l-1, P less than 0.01) and monocyte magnesium (6.40 (5.65-7.16) vs 8.76 (7.81-9.71) mg g-1 DNA, P less than 0.01), but there were no significant differences in other biochemical parameters. A greater proportion of toxic subjects were receiving concomitant diuretic therapy (20/21 vs 37/60, P less than 0.05). 4. Magnesium deficiency was the most frequently identified significant electrolyte disturbance in relation to digoxin toxicity. In the presence of magnesium deficiency digoxin toxicity developed at relatively low serum digoxin concentrations.