Magnesium and acute myocardial infarction. Transient hypomagnesemia not induced by renal magnesium loss in patients with acute myocardial infarction

Association between low serum magnesium level and major adverse cardiac events in patients treated with drug-eluting stents for acute myocardial infarction

Objectives

We investigated the association of serum magnesium (Mg) levels and major adverse cardiac events (MACEs) after drug-eluting stent (DES) implantation.

Background

Mg depletion plays a key role in the pathphysiologic features of diabetes mellitus, hypertension, thrombosis, arrhythmias and coronary artery disease. Whether the depletion is related to the long-term prognosis of DES implantation is not known.

Methods

From 2008 to 2011, we enrolled 414 consecutive patients <50 years old who underwent DES implantation for acute coronary syndrome. Serum Mg level was analyzed and patients were followed up for a median of 24 months (interquartile range 14–32 months) for the occurrence of MACEs defined as death, myocardial infarction, stroke, and any revascularization.

Results

For patients with unstable angina, no significant association between serum Mg level and MACEs was found in the multivariate model. For patients with myocardial infarction, after adjusting for age, positive family history, smoking status, hypertension, hypercholesterolemia, and diabetes at baseline, the risk was 8.11-fold higher for patients with quartile 1 than 4 Mg level (95% confidence interval 1.7–38.75; P<0.01). In addition, when tested as a continuous variable, serum magnesium was a significant predictor for MACEs of acute myocardial infarction (HR [per 0.1 mM increase], 0.35 [95% CI, 0.19–0.63], p< 0.01), after adjustment for other confounders.

Conclusions

Low serum level of Mg may be an important predictor of MACEs with DES implantation for acute myocardial infarction. Further research into the effectiveness of Mg supplementation for these patients is warranted.

Magnesium causes nitric oxide independent coronary artery vasodilation in humans

OBJECTIVE

To determine how magnesium affects human coronary arteries and whether endothelium derived nitric oxide (EDNO) is involved in the coronary arterial response to magnesium.

DESIGN

Quantitative coronary angiography and Doppler flow velocity measurements were used to determine the effects of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) on magnesium induced dilation of the epicardial and resistance coronary arteries.

SETTING

Hiroshima University Hospital a tertiary cardiology centre.

PATIENTS

17 patients with angiographically normal coronary arteries.

INTERVENTIONS

Magnesium sulfate (MgSO(4)) (0.02 mmol/min and 0.2 mmol/min) was infused for two minutes into the left coronary ostium before and after intracoronary infusion of L-NMMA.

MAIN OUTCOME MEASURES

Diameter of the proximal and distal segments of the epicardial coronary arteries and coronary blood flow.

RESULTS

At a dose of 0.02 mmol/min, MgSO(4) did not affect the coronary arteries. At a dose of 0.2 mmol/min, MgSO(4) caused coronary artery dilation (mean (SEM) proximal diameter 3.00 (0.09) to 3.11 (0.09) mm; distal 1.64 (0.06) to 1.77 (0.07) mm) and increased coronary blood flow (79.3 (7.5) to 101.4 (9.9) ml/min, p < 0.001 v baseline for all). MgSO(4) increased the changes in these parameters after the infusion of L-NMMA (p < 0.001 v baseline).

CONCLUSIONS

Magnesium dilates both the epicardial and resistance coronary arteries in humans. Furthermore, the coronary arterial response to magnesium is dose dependent and independent of EDNO.

Magnesium deficiency in patients with recent myocardial infarction and provoked coronary artery spasm

This study sought to clarify the relationship between magnesium (Mg) deficiency and coronary artery spasm provoked by pharmacologic agents in patients with a recent acute myocardial infarction (AMI). Twenty-three consecutive patients suffering from AMI were investigated with a Mg retention test (Mg: 0.1 mmol/kg for 4 h) in both the acute phase (within I week (3+/-2 days) of onset) and the subacute phase (3-4 weeks (24+/-6 days) of the onset). Early coronary arteriography was performed in all patients. Coronary stenosis in the infarct-related artery was less than 90% in all patients in the subacute phase. The spasm provocation test was performed in the subacute phase and coronary spasm was defined as transient subtotal or total occlusion in association with angina or electrocardiographic ST-segment deviation. Coronary artery spasm was provoked in only 13 of the 23 patients. Compared with the control subjects (12 patients without coronary artery disease or coronary spasm), the 24-h Mg retention was significantly higher in patients with AMI (acute phase: 78+/-27%, subacute phase: 66+/-32%, vs control: 48+/-12%, p<0.05). In the subacute phase, the 24-h Mg retention decreased in patients without coronary spasm (43+/-26%), but a high level of Mg retention was still observed in patients with coronary spasm (84+/-25%). There was no difference in the serum concentrations of Mg, calcium and phosphorus between the 2 groups on both phases. In conclusion, both Mg deficiency and provoked coronary artery spasm were noted in more than half of the Japanese patients with a recent AMI, suggesting a close association between Mg deficiency and AMI.

Magnesium in disease: a review with special emphasis on the serum ionized magnesium

This review deals with the six main clinical situations related to magnesium or one of its fractions, including ionized magnesium: renal disease, hypertension, pre-eclampsia, diabetes mellitus, cardiac disease, and the administration of therapeutic drugs. Issues addressed are the physiological role of magnesium, eventual changes in its levels, and how these best can be monitored. In renal disease mostly moderate hypermagnesemia is seen; measuring ionized magnesium offers minimal advantage. In hypertension magnesium might be lowered but its measurement does not seem relevant. In the prediction of severe pre-eclampsia, elevated ionized magnesium concentration may play a role, but no unequivocal picture emerges. Low magnesium in blood may be cause for, or consequence of, diabetes mellitus. No special fraction clearly indicates magnesium deficiency leading to insulin resistance. Cardiac diseases are related to diminished magnesium levels. During myocardial infarction, serum magnesium drops. Total magnesium concentration in cardiac cells can be predicted from levels in sublingual or skeletal muscle cells. Most therapeutic drugs (diuretics, chemotherapeutics, immunosuppressive agents, antibiotics) cause hypomagnesemia due to increased urinary loss. It is concluded that most of the clinical situations studied show hypomagnesemia due to renal loss, with exception of renal disease. Keeping in mind that only 1% of the total body magnesium pool is extracellular, no simple measurement of the real intracellular situation has emerged; measuring ionized magnesium in serum has little added value at present.

Acute exogenous elevation of plasma free fatty acids does not influence the plasma magnesium concentration

OBJECTIVE

Plasma non-esterified (free) fatty acid concentrations rise as a consequence of stimulated endogenous lipolysis and are inversely related to the plasma magnesium concentration when plasma adrenaline concentration is increased. The aim of the study was to test whether high plasma non-esterified fatty acid concentration after infusion of non-esterified fatty acids decreases plasma magnesium concentration.

METHODS

Twelve healthy subjects received 500 ml Intralipid or saline in a randomised, cross-over, double-blind design. Infusion of Intralipid results in an isolated elevation of plasma non-esterified fatty acid concentration. Plasma magnesium concentration was determined at baseline and every 30 minutes; plasma non-esterified fatty acid and triglyceride concentrations at baseline and after 120 minutes.

RESULTS

Initial plasma magnesium, non-esterified fatty acid, and triglyceride concentrations were similar in both groups. A significant increase in plasma non-esterified fatty acids (2.42 +/- 0.96 mmol/l vs 0.58 +/- 0.23 mmol/l, p = 0.00013) and triglyceride (median and 95th percentile 5.36 (7.35) mmol/l vs 1.18 (1.92) mmol/l, p = 0.003) concentrations was seen with Intralipid. Plasma magnesium concentration increased significantly after Intralipid (0.89 +/- 0.09 mmol/l vs 0.81 +/- 0.06 mmol/l, p = 0.007). No significant changes were seen with saline. A positive association was found between the change in plasma magnesium and triglyceride concentrations (r = 0.85, p = 0.001).

CONCLUSION

Acute infusion of non-esterified fatty acids from an exogenous source does not result in a fall in plasma magnesium concentration, indicating that the circulating non-esterified fatty acids play no part in a decrease in plasma magnesium concentration. The high circulating non-esterified fatty acid levels and the fall in plasma magnesium concentration are both a consequence of intracellular lipolysis.

The role of signal averaged P wave duration and serum magnesium as a combined predictor of atrial fibrillation after elective coronary artery bypass surgery

OBJECTIVE

To investigate the role of low serum magnesium as a trigger for atrial fibrillation in patients with a substrate for the arrhythmia (assessed by signal averaged P wave duration).

DESIGN

A case-control study.

SETTING

A regional referral cardiac centre.

PATIENTS AND INTERVENTIONS

105 consecutive patients undergoing elective coronary artery bypass surgery had signal averaged P wave recordings before operation. Serum electrolytes were analysed preoperatively and on days 1, 2, and 5 after surgery.

MAIN OUTCOME MEASURES

Any episode of electrocardiographically recorded atrial fibrillation was taken as a study end point.

RESULTS

Of 102 patients discharged, 27 (26%) had documented episodes of atrial fibrillation at a mean of 2.7 days after surgery. A combination of P wave duration > 155 ms and serum magnesium on the first postoperative day of < 0.7 mmol/l had a sensitivity of 75% and specificity of 80% for predicting atrial fibrillation. Duration of hospital stay (7.9 v 6.8 days) was longer in the atrial fibrillation group (P < 0.01). Stepwise regression showed age, serum magnesium < 0.7 mmol/l on the first postoperative day (both P < 0.001), angiotensin converting enzyme inhibitor withdrawal (P < 0.02), and signal averaged P wave duration (P = 0.04) to be independent predictors.

CONCLUSIONS

The combination of signal averaged P wave duration and low serum magnesium on the first postoperative day identified the majority of patients with atrial fibrillation after coronary artery bypass surgery. Early identification and pharmacological treatment for selected patients may reduce the incidence of postoperative atrial fibrillation.

Changes of ionized magnesium and free fatty acids in serum after acute myocardial infarction

The most feared early complications after an acute myocardial infarction are ventricular arrhythmias. These may be initiated by changed concentrations of catecholamines and electrolytes. The present study shows a reduction of total serum magnesium after acute myocardial infarction which is normalized within a few days. Further, it could be shown that a more significant decrease of ionized Mg2+ (iMg2+) takes place at the day of acute myocardial infarction in the total group of myocardial infarction patients (n = 36). A closer investigation reveals that iMg2+ was considerably decreased in one third of the patients, whereas two thirds showed minor changes of iMg2+ in both directions. The pronounced decrease of iMg2+ in the first sub-group can be explained by the time course of free fatty acids in serum. On the day of the myocardial infarction free fatty acids in serum were increased. This is probably caused by beta-adrenergic-induced lipolysis due to catecholamines released by the stressful situation of an acute myocardial infarction. The increased free fatty acids in serum bind Mg2+, thus reducing iMg2+. As long as a beneficial effect of a general Mg infusion in all acute myocardial infarction patients is controversial, iMg2+ should be measured and Mg infusion therapy should be applied only in patients with low iMg2+.

Influence of oral magnesium supplementation on cardiac events among survivors of an acute myocardial infarction

OBJECTIVE

To investigate the effect of long term oral magnesium treatment on incidence of cardiac events among survivors of an acute myocardial infarction.

DESIGN

Double blind, placebo controlled parallel study in which patients were randomised to treatment or placebo.

SETTING

Two coronary care units and corresponding outpatient clinics.

SUBJECTS

468 survivors of an acute myocardial infarction (289 men and 178 women) aged 31-92.

INTERVENTIONS

One tablet of 15 mmol magnesium hydroxide or placebo daily for one year.

MAIN OUTCOME MEASURES

Incidences of reinfarction, sudden death, and coronary artery bypass grafting in one year.

RESULTS

There was no significant difference between treatment and placebo groups in the incidence of each of the three cardiac events, but when the events were combined and drop outs were excluded from calculations there was a significantly higher incidence of events in the treatment group (56/167 v 33/153; relative risk 1.55 (95% confidence interval 1.07 to 2.25); p = 0.02). When the timing of events was incorporated by means of a Kaplan-Meier plot the treatment group showed a significantly higher incidence of events whether drop outs were included or excluded (p < 0.025).

CONCLUSION

Long term oral treatment with 15 mmol magnesium daily doses not reduce the incidence of cardiac events in survivors of an acute myocardial infarction and, indeed, seems to increase the risk of developing a cardiac event. Consequently, this treatment cannot be recommended as secondary prophylaxis for such patients.

Effects of intravenous magnesium in suspected acute myocardial infarction: overview of randomised trials

OBJECTIVE

To investigate the effect of intravenous magnesium on mortality in suspected acute myocardial infarction.

DESIGN

Systematic overview of all available randomised trials in which patients were allocated to receive either intravenous magnesium or otherwise similar treatment without magnesium.

SETTING

Coronary care units of several hospitals.

PATIENTS

1301 patients in seven randomised trials.

MAIN OUTCOME MEASURE

Short term mortality.

RESULTS

Considering the seven trials collectively there were 25 (3.8%) deaths among 657 patients allocated to receive magnesium and 53 (8.2%) deaths among 644 patients allocated control, generally during hospital follow up. This represents a 55% reduction in the odds of death (p less than 0.001) with 95% confidence intervals ranging from about one third to about two thirds. 70 of 648 patients allocated magnesium compared with 109 of 641 controls had serious ventricular arrhythmias, suggesting that magnesium reduces the incidence, though the definition varied among trials. Other adverse effects were rare in the limited number of patients for whom this data were available.

CONCLUSION

Despite the limited number of patients randomised this overview suggests that intravenous magnesium therapy may reduce mortality in patients with acute myocardial infarction. Further large scale trials to confirm (or refute) these findings are desirable.

Magnesium therapy in ventricular arrhythmias

Magnesium (Mg) is the known activator of 300 enzymes which govern energy utilization, cell permeability, and ionic membrane currents in the cardiac conducting cells. This may explain the antiarrhythmic efficacy of Mg in specific clinical settings, despite its only modest electrophysiological effects. This review summarizes the effect of Mg administration in four clinical conditions: in digitalis toxicity; in drug-induced torsade de pointes; in patients with chronic diuretic therapy; and in acute myocardial infarction. Mg effectively abolished ventricular tachyarrhythmias associated with digitalis intoxication. This effect of Mg is related to the activation of sodium-potassium ATP-ase, which is inhibited by digitalis. Drug-induced torsade de pointes was promptly abolished by Mg sulfate in the clinical setting. Experimental studies showed that Mg suppresses the early afterdepolarizations and the triggered activity responsible for occurrence of the arrhythmia. In diuretic-treated hypertensives, potassium depletion has been associated with increased ventricular ectopy and sudden death. Mg has been found to be an important adjuvant for intracellular repletion of potassium in these patients. Several randomized, double-blind studies in patients with acute infarction showed that Mg administered on admission improved survival or reduced the incidence of complex ventricular arrhythmias. Thus, Mg should be employed as first-line therapy in digitalis intoxication and drug-related torsade de pointes, and should be considered an important adjuvant therapy in hypertensives treated with diuretics and patients with acute myocardial infarction.

The influence of elevated Mg2+ concentrations on cardiac electrophysiologic parameters

This study was performed to evaluate the direct effects of magnesium ions on cardiac conduction velocities and on refractoriness using a modified Langendorff perfusion system and a special ECG recording and stimulation technique. An increase of the MG2+ concentration to 2.3 mM had no detectable effects. Higher concentrations of up to 4.6 mM decreased the spontaneous sinus rate and the conduction velocity through the AV node and the His bundle in a concentration-dependent manner. During stimulation with premature beats, in the presence of 4.6 mM of Mg2+, the effective and relative refractory periods (ERP, RRP) of sinoatrial, AV nodal, and His bundle conduction and the ERP of the ventricular myocardium were significantly prolonged, whereas the ERP of the atrial myocardium remained unaffected. The refractoriness of sinoatrial, AV nodal, and His bundle conduction, and of the ventricular myocardium, were also prolonged during pacing with a stepwise increased pacing rate. These observations suggest a marked rate-dependent inhibitory effect of magnesium on the refractoriness of the His-bundle conduction and of the ventricular myocardium, which might be an important factor in the antiarrhythmic effectiveness of magnesium in ventricular tachyarrhythmias.

A comparison of plasma magnesium values in patients with acute myocardial infarction and patients with chest pain due to other causes

Plasma magnesium concentrations were monitored daily in 86 patients who were admitted to a coronary care unit with a provisional diagnosis of acute myocardial infarction. Twenty-six patients had suffered a myocardial infarction, while the remainder had angina or non-cardiac chest pain. Magnesium levels were also obtained daily for five consecutive days in five normal subjects, who served as the control group. Calculations of the 95% confidence intervals on the differences between Day 1, Day 2 and individual subjects' mean plasma magnesium concentrations for the group with acute myocardial infarctions versus the group that did not have an acute myocardial infarction, the group with acute myocardial infarctions versus the reference group, and the group that did not have an acute myocardial infarction versus the reference group, and analysis of variance for the data from the three subject groups revealed no significant difference between the plasma magnesium levels of patients with an acute myocardial infarction and those with chest pain due to other causes or the normal reference population.