Hypomagnesemia and refractory cardiac arrhythmia in a nondigitalized patient

Proton pump inhibitor-induced hypomagnesemia complicated with serious cardiac arrhythmias

Introduction: Magnesium is the third most common intracellular ion after potassium and calcium and is an important element in the functions of the body, since it participates in more than 300 enzyme systems. It also, plays a significant role in the transport of calcium and potassium across the cell membranes and protects against cardiac arrhythmias and is useful for their treatment due to hypomagnesemia induced from the proton pump inhibitors (PPIs). Areas covered: PPIs are used for the treatment of peptic ulcer disease (PUD) and gastroesophageal reflux disease (GERD), but have been associated with hypomagnesemia with serious cardiac arrhythmias including torsades de pointes (TdP). To better understand the magnitude of this problem, a Medline search of the English language literature was conducted from 2010 to 2018 and 35 papers with pertinent information were selected. Expert commentary: The review of these papers suggests that PPIs cause hypomagnesemia, which could be associated with serious cardiac arrhythmias including TdP. However, its incidence is not very common considering the millions of people taking PPIs, but the FDA has advised the physicians to be watchful about this serious adverse effect of PPIs and check the magnesium levels before initiation of PPI treatment.

Role of magnesium in the prevention of postoperative arrhythmias in neonates and infants undergoing arterial switch operation

The objectives of the study were to measure magnesium levels in neonates and infants undergoing arterial switch operation and to ascertain the role of magnesium supplementation in the prevention of postoperative arrhythmias. Group I (n=25): magnesium was administered in the dose of 30 mg/kg over 10 minutes in normal saline (5 ml) immediately after cessation of cardiopulmonary bypass (CPB). Group II (n=25): normal saline (5 ml) was administered over 10 minutes immediately after cessation of CPB. Samples of arterial blood were collected at four time points: 1) after induction of anaesthesia; 2) 10 minutes after initiation of CPB; 3) at rewarming during CPB; and 4) 4 hours after shifting the patient to the intensive care unit. Samples were measured for ionized magnesium (iMg), blood gases, haematocrit level, electrolytes, ionized calcium and glucose. Continuous ECG rhythm analysis and documentation of arrhythmias was performed for 24 hours after surgery. The mean preoperative iMg levels were below the normal level in both the groups. A significant increase in iMg levels (P=0.00) was seen in both groups during rewarming. There is no statistically significant difference in the incidence of arrhythmias between the magnesium supplemented group (4%) and the control group (20%) in the postoperative period, a tendency towards reduction in arrhythmias was only observed in the magnesium supplemented group.

Magnesium deficiency. Etiology and clinical spectrum

Magnesium deficiency may complicate many diseases. The causes include the following: inadequate intake during starvation or increased requirement during early childhood, pregnancy, or lactation; excessive losses of magnesium as a result of malabsorption from the gastrointestinal tract or from the kidneys during use of diuretics; and to a combination of the two, as in alcoholism. Most often the etiological factors have been operative for a month or more. Acute hypomagnesemia can occur without previous Mg deficiency after epinephrine, cold stress and stress of serious injury or extensive surgery. The clinical manifestations depend on the age of the patient and may begin insidiously or with dramatic suddenness, or there may be no overt symptoms or signs. The manifestations can be divided into the following categories: totally non-specific symptoms and signs ascribable to the primary disease; neuromuscular hyperactivity including tremor, myoclonic jerks, convulsions, Chvostek sign, Trousseau sign (rarely), spontaneous carpopedal spasm (rarely), ataxia, nystagmus and dysphagia; psychiatric disturbances from apathy and coma to some of all facets of delirium; cardiac arrhythmias including ventricular fibrillation and sudden death; hypocalcemia which is responsive only to Mg therapy; and hypokalemia which is not easily nor completely corrected without Mg therapy. The diversity of etiologies and the multiplicity of manifestations result in confusion and controversy. The documentation of normal renal function is absolutely necessary for maximum doses. The order of magnitude of dose is 1.0 meq Mg/kg on day 1, and 0.3 to 0.5 mEq/kg per day for 3 to 5 days. In emergencies such as convulsions or ventricular arrhythmias, a bolus injection of 1.0 gm (8.1 meq) of MgSO4 is indicated. Therapy of Mg deficiency in the presence of renal insufficiency requires smaller doses and frequent monitoring. Complete repletion occurs slowly.

Serum magnesium in acute myocardial infarction. Relation to arrhythmias

During 1 1/2 years, 768 patients-905 admissions, 342 with acute myocardial infarction (AMI), 563 with other diagnoses-were treated in the CCU at Serafimerlasarettet. On admission, both the AMI and the non-AMI group had significantly lower serum magnesium levels than a reference group. The incidence of serious VEBs, VT and VF on admission was significantly higher in the hypomagnesemic patients with AMI. AV blocks and SVB were more frequently observed in the hypermagnesemic patients, both in the AMI and in the non-AMI group. The incidence of AF and SVT was higher in the hypomagnesemic patients.

Magnesium deficiency in critical illness

Magnesium (Mg) deficiency commonly occurs in critical illness and correlates with a higher mortality and worse clinical outcome in the intensive care unit (ICU). Magnesium has been directly implicated in hypokalemia, hypocalcemia, tetany, and dysrhythmia. Moreover, Mg may play a role in acute coronary syndromes, acute cerebral ischemia, and asthma. Magnesium regulates hundreds of enzyme systems. By regulating enzymes controlling intracellular calcium, Mg affects smooth muscle vasoconstriction, important to the underlying pathophysiology of several critical illnesses. The principle causes of Mg deficiency are gastrointestinal and renal losses; however, the diagnosis is difficult to make because of the limitations of serum Mg levels, the most common assessment of Mg status. Magnesium tolerance testing and ionized Mg2+ are alternative laboratory assessments; however, each has its own difficulties in the ICU setting. The use of Mg therapy is supported by clinical trials in the treatment of symptomatic hypomagnesemia and preeclampsia and is recommended for torsade de pointes. Magnesium therapy is not supported in the treatment of acute myocardial infarction and is presently undergoing evaluation for the treatment of severe asthma exacerbation, for the prevention of post-coronary bypass grafting dysrhythmias, and as a neuroprotective agent in acute cerebral ischemia.

The effects of magnesium prime solution on magnesium levels and potassium loss in open heart surgery

In this study, we examined the effects of magnesium supplementation in the cardiopulmonary bypass (CPB) prime solution on pediatric patients' magnesium levels and potassium loss with open heart surgery. Forty pediatric patients undergoing heart surgery were randomly assigned either magnesium sulfate (magnesium group, n = 20; 0.25 mmol/kg) or saline (placebo group; n = 20) supplementation to the prime solution. Ionized magnesium (IMg) and urinary magnesium and potassium were measured at defined time points during and after CPB. In the magnesium group, IMg concentration was larger during CPB but not after CPB. IMg decreased in the early stages of CPB in the placebo group and decreased to an even smaller level 24 h after CPB. Urinary magnesium levels in the magnesium group were larger than those in the placebo group during and after CPB, and urinary potassium concentrations reached significantly smaller levels 24 h after CPB (44.2 +/- 2.9 versus 60.9 +/- 2.6 mmol/L; P < 0.01). We conclude that the addition of magnesium into prime solution maintains normal IMg levels and prevents potassium flux during the perioperative period.

IMPLICATIONS

In our study, we demonstrate that a magnesium prime solution can prevent hypomagnesemia during and after cardiopulmonary bypass (CPB) and decrease the urinary potassium loss after CPB in pediatric patients undergoing open heart surgery.

Woman with postpartum ventricular tachycardia and hypomagnesemia

A 28-year-old Japanese woman who had received continuous intravenous infusion of magnesium sulfate from 24 weeks of pregnancy until delivery underwent cesarean section at 30 weeks and gave birth to twins. Serum magnesium sharply declined to a subnormal level of 1.5 mg/dL on postpartum day 4. The patient exhibited sinus bradycardia (48 b.p.m.) with intermittent supraventricular contraction on postpartum day 2, intermittent ventricular bigeminy on postpartum day 3, and frequent selfterminated polymorphic ventricular tachycardia on postpartum day 4. The electrocardiogram (ECG) disclosed that the patient had prolonged QTc of 0.45-0.67. Correction of serum magnesium improved ECG findings promptly, resulting in the disappearance of arrhythmias. Hypomagnesemia due to postpartum diuresis may have played a role causing ventricular tachyarrhythmia in this patient.

Does magnesium have a role in the treatment of patients with coronary artery disease?

Hypomagnesemia is common in hospitalized patients, especially in elderly patients with coronary artery disease (CAD) and/or those with chronic heart failure. Hypomagnesemia is associated with increased all cause mortality and mortality from CAD. Magnesium supplementation improves myocardial metabolism, inhibits calcium accumulation and myocardial cell death; it improves vascular tone, peripheral vascular resistance, afterload and cardiac output, reduces cardiac arrhythmias and improves lipid metabolism. Magnesium also reduces vulnerability to oxygen-derived free radicals, improves endothelial function and inhibits platelet function, including platelet aggregation and adhesion, which potentially confers upon magnesium physiologic and natural effects similar to adenosine-diphosphate inhibitors such as clopidogrel. However, data regarding the use of magnesium in patients with acute myocardial infarction (AMI) are conflicting. Although some previous relatively small randomized clinical trials demonstrated a remarkable reduction in mortality when intravenous magnesium was administered to relatively high risk AMI patients, two recently published large-scale randomized clinical trials (the Fourth International Study of Infarct Survival [ISIS 4] and Magnesium in Coronaries [MAGIC]) were unable to demonstrate any advantage of intravenous magnesium over placebo. Nevertheless, the theoretical benefits of magnesium supplementation as a cardio-protective agent in CAD patients, promising results from animal and human studies, its relatively low-cost and ease of handling requiring no special expertise, together with its excellent tolerability, gives magnesium a place in treating CAD patients, especially in those at high risk, such as CAD patients with heart failure, the elderly and hospitalized patients with hypomagnesemia. Furthermore, magnesium therapy is indicated in life-threatening ventricular arrhythmias such as torsades de pointes and intractable ventricular tachycardia.

Magnesium supplementation in the prevention of arrhythmias in pediatric patients undergoing surgery for congenital heart defects

BACKGROUND

The efficacy of magnesium in the prevention of arrhythmias in pediatric patients after heart surgery remains unknown. Therefore we prospectively examined the effect of magnesium treatment on the incidence of postoperative arrhythmias in pediatric patients undergoing surgical repair of congenital heart defects.

METHODS AND RESULTS

Twenty-eight pediatric patients undergoing heart surgery with cardiopulmonary bypass were prospectively, randomly assigned in a double-blind fashion to receive intravenous magnesium (magnesium group, n = 13; 30 mg/kg) or saline (placebo group, n = 15) immediately after cessation of cardiopulmonary bypass. Magnesium, potassium, and calcium levels were measured at defined intervals during surgery and 24 hours after surgery. Continuous electrocardiographic documentation by Holter monitor was performed for 24 hours after surgery. Magnesium levels were significantly decreased below the normal reference range for patients in the placebo group compared with the magnesium group on arrival in the intensive care unit and for 20 hours after surgery. Magnesium levels remained in the normal range for patients in the magnesium group after magnesium supplementation. In 4 patients in the placebo group (27%), junctional ectopic tachycardia developed within the initial 20 hours in the intensive care unit. No junctional ectopic tachycardia was observed in the magnesium group (P =.026).

CONCLUSIONS

Although this study was originally targeted to include 100 patients, the protocol was terminated because of the unacceptable incidence of hemodynamically significant junctional ectopic tachycardia that was present in the placebo group. Thus low magnesium levels in pediatric patients undergoing heart surgery are associated with an increased incidence of junctional ectopic tachycardia in the immediate postoperative period.

[Magnesium deficiency and magnesium substitution. Effect on ventricular cardiac arrhythmias of various etiology]

During recent years there has been an increasing but still controversial discussion on the antiarrhythmic effects and overall benefit of magnesium when directed to patients with various types of ventricular tachyarrhythmias. While magnesium is considered to be a simple, safe and cost-effective approach and many casuistic and empiric reports have indicated antiarrhythmic properties of magnesium in patients with suspected or manifest ventricular arrhythmias, controlled studies proving the antiarrhythmic and overall benefit and justifying a broader use of magnesium in treating various types of ventricular arrhythmias are missing or rare. At present, antiarrhythmic properties and clinical benefit of magnesium application has only been established in patients with torsade de pointes and digitalis-induced ventricular tachyarrhythmias. In perioperative patients at risk for ventricular tachyarrhythmias and in patients suffering from manifest heart failure, data may also indicate some antiarrhythmic properties of magnesium, however, in this case with a wide consensus that the prevention of magnesium deficit is more effective and preferred in most patients over the therapeutic application of magnesium. Another group of patients who may profit from such a therapeutic approach are patients with frequent ventricular arrhythmias and stable underlying heart disease, in whom a recently published double-blind, randomized study documented an antiarrhythmic effect of a 3 week treatment with potassium and magnesium. For all other types of ventricular tachyarrhythmias, the therapeutic use of magnesium can be considered as not harmful, but also as not proven to be effective.

The influence of cardiopulmonary bypass on ionized magnesium in neonates, infants, and children undergoing repair of congenital heart lesions

The purpose of this study was to measure the ionized magnesium (iMg) concentrations in children undergoing the correction of congenital heart defects. iMg levels were measured in 115 consecutive patients at five sample periods: prebypass, onset of bypass, during rewarming, immediately postbypass, and 1 h postbypass using an ion-selective electrode of the NOVA-CRT 8 (Nova Biomedical, Watham, MA). The incidence of dysrythmias was noted. Patients were divided into two groups: those who received Plegisol as the cardioplegic solution and those who did not. This study demonstrates that iMg decreases with the onset of cardiopulmonary bypass (CPB) in patients who weigh < 10 kg. In the Plegisol group, all subgroups of patients demonstrated statistically higher iMg during the rewarming phase of CPB, immediately post-CPB, and 1 h post-CPB, when compared with control values. The probability of dysrhythmias in the Plegisol group was almost twice that of the non-Plegisol group. However, this did not reach statistical significance (P = 0.22). The results of our study demonstrate that the use of CPB on pediatric patients produces alterations in the iMg. The changes differ depending on both patient weight and the use of a magnesium-containing cardioplegic solution, exemplified here by Plegisol. The role of these changes in iMg on dysrhythmias could not be further evaluated.

Significance of magnesium in congestive heart failure

Electrolyte balance has been regarded as a factor important to cardiovascular stability, particularly in congestive heart failure. Among the common electrolytes, the significance of magnesium has been debated because of difficulty in accurate measurement and other associated factors, including other electrolyte abnormalities. The serum magnesium level represents < 1% of total body stores and does not reflect total-body magnesium concentration, a clinical situation very similar to that of serum potassium. Magnesium is important as a cofactor in several enzymatic reactions contributing to stable cardiovascular hemodynamics and electrophysiologic functioning. Its deficiency is common and can be associated with risk factors and complications of heart failure. Typical therapy for heart failure (digoxin, diuretic agents, and ACE inhibitors) are influenced by or associated with significant alteration in magnesium balance. Magnesium therapy, both for deficiency replacement and in higher pharmacologic doses, has been beneficial in improving hemodynamics and in treating arrhythmias. Magnesium toxicity rarely occurs except in patients with renal dysfunction. In conclusion, the intricate role of magnesium on a biochemical and cellular level in cardiac cells is crucial in maintaining stable cardiovascular hemodynamics and electrophysiologic function. In patients with congestive heart failure, the presence of adequate total-body magnesium stores serve as an important prognostic indicator because of an amelioration of arrhythmias, digitalis toxicity, and hemodynamic abnormalities.

Magnesium deficiency: pathophysiologic and clinical overview

Magnesium is an essential cation, involved in many enzymatic reactions, as a cofactor to adenosine triphosphatases. It is critical in energy-requiring metabolic processes, as well as protein synthesis and anaerobic phosphorylation. Serum Mg concentration is maintained within a narrow range by the kidney and small intestine since under conditions of Mg deprivation both organs increase their fractional absorption of Mg. If Mg depletion continues, the bone store contributes by exchanging part of its content with extracellular fluid (ECF). The serum Mg can be normal in the presence of intracellular Mg depletion, and the occurrence of a low level usually indicates significant Mg deficiency. Hypomagnesemia is frequently encountered in hospitalized patients and is seen most often in patients admitted to intensive care units. The detection of Mg deficiency can be increased by measuring Mg concentration in the urine or using the parenteral Mg load test. Hypomagnesemia may arise from various disorders of the gastrointestinal tract, conditions affecting Mg renal handling, or cellular redistribution of Mg. The gastrointestinal causes include the following: protein-calorie malnutrition, the intravenous administration of Mg-free fluids and total parenteral nutrition, chronic watery diarrhea and steatorrhea, short bowel syndrome, bowel fistula, continuous nasogastric suctioning, and, rarely, primary familial Mg malabsorption. The renal causes include Bartter's and Gitelman's syndrome, post obstructive diuresis, post acute tubular necrosis, renal transplantation, and interstitial nephropathy. Many therapeutic agents cause renal Mg wasting and subsequent deficiency. These include loop and thiazide diuretics, aminoglycosides, cisplatin, pentamidine, and foscarnet. Magnesium deficiency is seen frequently in alcoholics and diabetic patients, in whom a combination of factors contributes to its pathogenesis. Hypomagnesemia is known to produce a wide variety of clinical presentations, including neuromuscular irritability, cardiac arrhythmias, and increased sensitivity to digoxin. Refractory hypokalemia and hypocalcemia can be caused by concomitant hypomagnesemia and can be corrected with Mg therapy. The dose and route of administration of Mg in the treatment of hypomagnesemia is dictated by the clinical presentation, the degree of Mg deficiency, and the renal function.

Maximizing benefits of therapies in acute myocardial infarction

Major advances in the management of acute myocardial infarction have been achieved by a combination of careful experimental work and development of effective pharmacologic and interventional strategies in conjunction with the conduct of large, reliable randomized trials. Current trials indicate that a combination of thrombolytic therapy, aspirin, and intravenous followed by oral beta blockers reduces mortality. There are a number of additional promising interventions, such as intravenous magnesium, nitrates, and the newer antithrombin agents. However, before these agents are used widely in clinical practice, clear proof of benefit and adequate safety should be available from the ongoing randomized trials. Following discharge from the hospital, long-term therapy with aspirin and beta blockers should be considered in all patients. In patients with heart failure and low ejection fraction, angiotensin-converting enzyme (ACE) inhibitors have been shown to reduce mortality, reinfarction, and the need for further hospitalizations for heart failure. Therefore, these therapies, in conjunction with risk factor modification (cessation of cigarette smoking, treatment of hypercholesterolemia, treatment of hypertension), should be considered in all appropriate patients. A number of new strategies for the prevention of atherosclerosis and its complications are currently being evaluated in prospective randomized trials. These include the natural antioxidant vitamins, estrogen replacement therapy, tamoxifen therapy, and ACE inhibitors in patients without evidence of heart failure or left ventricular dysfunction.

Ventricular arrhythmias late after myocardial infarction are related to hypomagnesemia and magnesium loss: preliminary trial of corrective therapy

It has been well established that in acute myocardial infarction (MI) many patients display low serum magnesium (Mg). This is associated with complex ventricular arrhythmias. The question arises whether predischarge arrhythmias occurring late after MI might also be related to Mg imbalance. In 118 patients subjected to heart rhythm 24 h Holter monitoring in the second or third week after MI, we investigated (1) the relationship between serum Mg, urinary Mg loss, and ventricular arrhythmias, and (2) the effect of Mg supplementation on heart rhythm disturbances. In patients with undisturbed rhythm or monomorphic ventricular ectopic beats (VEB) (Lown 0-2; n = 84), mean serum Mg level (mg% +/- SD) was 1.83 +/- 0.21, whereas in patients with multifocal VEB, pairs, or nonsustained ventricular tachycardia (VT) (Lown 3-4; n = 34) serum Mg was decreased to 1.68 +/- 0.27 (p < 0.01). Serum Mg normal range in our laboratory is 1.7-2.6 mg%. The lowest serum Mg reaching 1.55 +/- 0.27 was found in nonsustained VT (Lown 4 b) subgroup (n = 14). Urinary Mg loss measured in 81 patients was more pronounced in those with Lown 3-4 arrhythmias (n = 26) than with Lown 0-2 (n = 55). The daily values were 73 +/- 22 and 54.4 +/- 26 mg, respectively (p < 0.001). Thirteen patients with complex arrhythmias and low serum Mg received Mg supplementation (MgSO4, 8 g in 500 ml 5% glucose intravenously during 24 h). This resulted in restoration of almost undisturbed rhythm in 10 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of magnesium versus verapamil on supraventricular arrhythmias

Magnesium has previously been used in the treatment of various arrhythmias, but few randomized and prospective studies are available. In a single-blind study, the efficacy and safety of intravenous magnesium sulfate (bolus doses of 5 + 5 mmol followed by infusion of 0.04 mmol/min) versus verapamil (5 + 5 mg followed by 0.1 mg/min) was evaluated in 57 patients with supraventricular arrhythmias (supraventricular tachycardia, atrial fibrillation, and atrial flutter) of recent onset (less than 1 week). Fifteen (58%) of the patients receiving magnesium (n = 26) converted to sinus rhythm within 4 h, and 16 (62%) within 24 h. Verapamil caused a lower ventricular rate, but only six (19%) of the patients (n = 31) converted to sinus rhythm within 4 h (p < 0.01) and 16 (52%) within 24 h (NS). No side effects were observed during magnesium infusion, whereas six patients receiving verapamil had to be withdrawn from further study medication due to symptomatic side effects (hypotension in three, cardiac failure in three). Magnesium appears to be an effective and safe drug for the treatment of supraventricular arrhythmias. The overall efficacy for conversion to sinus rhythm is at least as effective as with verapamil, and its action is more rapid.

Magnesium: clinical considerations

Magnesium is gaining recognition as a clinically important electrolyte. Hypomagnesemia has been associated with a variety of disorders including seizures, malignant ventricular dysrhythmias, and sudden death. The emergency department patients who are most likely to be magnesium deficient include alcoholics, patients who take diuretics, and those in diabetic ketoacidosis. Hypokalemia and hypocalcemia may represent unrecognized hypomagnesemia. Clinical trials and case reports also document increasing interest in magnesium as an effective therapeutic agent for potentially life-threatening problems such as torsade de pointes, digitalis toxicity, bronchospasm, and alcohol withdrawal. We present an overview of hypomagnesemia, review the current literature, and focus on the role of magnesium in the acute care setting and the implications for the emergency physician.

Myocardial magnesium depletion associated with prolonged hypomagnesemia: a longitudinal study in heart transplant recipients

OBJECTIVES

This study was carried out to establish prospectively the incidence and relation of hypomagnesemia and myocardial magnesium depletion after heart transplantation.

BACKGROUND

No serial in vivo study of the relation of serum with tissue magnesium has been described. Myocardial magnesium depletion is associated with intracellular calcium overload, an increased incidence of cardiac arrhythmia and changes in coronary vasculature similar to those seen in the accelerated atherosclerosis that compromises graft survival after transplantation.

METHODS

In a prospective study in 19 consecutive patients, serum and myocardial magnesium content were measured serially for 9 months after heart transplantation. Blood cyclosporine was assayed simultaneously.

RESULTS

The incidence of hypomagnesemia was 100% during the 9-month study period, with lowest levels at 3 months (mean 0.80 vs. 0.64 mmol/liter, p less than 0.002). Myocardial magnesium depletion developed in 94% and was persistent in 55%; the lowest levels occurred at 6 months (mean 33.6 vs. 30.1, mumol/g, p less than 0.04). Hypomagnesemia predated decreases in myocardial magnesium by 2 to 6 weeks. Peak cyclosporine levels correlated positively with the decrease in serum magnesium. Clinical events were rare.

CONCLUSIONS

This is the first report of serial measurement of tissue magnesium. Persistent hypomagnesemia is invariably accompanied by myocardial magnesium depletion in the transplanted heart. Reciprocal calcium overload and adverse changes in coronary vasculature would be expected from previous studies and merit further investigation. Should the implications of this study extend to the native heart, myocardial magnesium depletion may contribute to the high incidence of fatal arrhythmic events observed in patients with heart failure, who commonly have persistent hypomagnesemia.

Magnesium deficiency and diabetes mellitus. Causes and effects

A large body of evidence demonstrates the prevalence and adverse clinical consequences of magnesium deficiency in patients with diabetes mellitus. It would be prudent for physicians who treat these patients to consider magnesium deficiency as a contributing factor in many diabetic complications and in exacerbation of the disease itself. Repletion of the deficiency or prophylactic supplementation with oral magnesium may help avoid or ameliorate such complications as arrhythmias, hypertension, and sudden cardiac death and may even improve the course of the diabetic condition.

Effects of secretagogues on intracellular free calcium and magnesium concentrations in rat pancreatic acinar cells

1. Rat pancreatic acinar cells were loaded with Fura 2 AM or Magfura AM and levels of cytosolic Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) were observed. 2. Addition of acetylcholine (ACh) evoked a transient rise in [Ca2+]i. The component of the rise dependent on extracellular Ca2+ sources, but not intracellular sources, was seen to be enhanced when both ACh and 5 mM Ca2+ were present in the medium. In the presence of elevated extracellular Mg2+ (10 mM) and ACh both components of the Ca2+ transient were inhibited. 3. Both GTP gamma S and fluoroaluminate, which can directly stimulate G-proteins, evoked a transient rise in [Ca2+]i in acinar cells. These responses were inhibited in the presence of elevated Mg2+. 4. Resting [Mg2+]i was seen to be 1.36 mM +/- 0.08 (n = 29) for cells in normal medium, 1.8 mM +/- 0.08 (n = 6) in elevated Mg2+ medium and 0.93 mM +/- 0.02 (n = 5) in cells bathed and Mg(2+)-free medium. Addition of ACh led to reductions in [Mg2+]i in cells bathed in normal medium and Mg(2+)-free medium but not elevated Mg2+ medium. 5. It is concluded that levels of extracellular Mg2+ strongly influence [Mg2+]i and [Ca2+]i mobilization during ACh-evoked responses. Mg2+ does not appear to be exerting its effects by influencing receptor-agonist interactions or by competing with Ca2+ at extracellular sites of Ca2+ uptake.

Is hypomagnesemia arrhythmogenic?

An understanding of the role of magnesium in cardiac conduction is complicated by the multiplicity of intracellular events coordinated by the magnesium ion. Several reports have cited magnesium deficiency as the cause of a variety of ventricular and supraventricular arrhythmias. On further inspection, the circumstances of each report strongly suggest the coexistence of significant potassium depletion; isolated hypomagnesemia as a cause of arrhythmia is not reported. This discussion brings together new data from basic science with that of clinical research to refute the suggestion that isolated hypomagnesemia is arrhythmogenic. However, there is sufficient evidence to indicate that hypomagnesemia will significantly exacerbate the proarrhythmic effect of hypokalemia, particularly if occurring in the presence of digoxin toxicity. Potassium and magnesium depletion are commonly concomitant, and simultaneous repletion of both ions in the presence of hypokalemia-induced arrhythmia would be both logical and effective. The beneficial effects of intravenous magnesium in the acute control of ventricular tachyarrhythmia are concluded to occur as a result of a separate antiarrhythmic action, quite independent of underlying magnesium balance.

Electrophysiologic and antiarrhythmic effects of magnesium in patients with inducible ventricular tachyarrhythmia

Intravenous magnesium is reported to be effective in the treatment of ventricular arrhythmias associated with hypomagnesemia, digitalis toxicity, or prolongation of the QT interval. In most previous reports, magnesium was added to conventional antiarrhythmic drugs that had failed. There are few data on the antiarrhythmic efficacy of magnesium as monotherapy in patients without these associated abnormalities. Ten patients with life-threatening ventricular arrhythmia and inducible ventricular tachyarrhythmia by programmed electrophysiologic testing were treated with intravenous magnesium. Following magnesium infusion, all patients still had inducible ventricular tachyarrhythmia. Moreover, magnesium therapy was not associated with significant changes in ventricular refractory period or in the morphology, cycle length, or hemodynamic response to induced ventricular tachycardia. These data suggest that intravenous magnesium has no significant electrophysiologic or antiarrhythmic effects in patients with life-threatening ventricular arrhythmia and inducible ventricular tachyarrhythmia.

Metabolic, hemodynamic, and electrocardiographic responses to increased circulating adrenaline: effects of pretreatment with class 1 antiarrhythmics

In order to study the effects of treatment with class 1 antiarrhythmics on the metabolic, hemodynamic, and electrocardiographic responses to adrenaline, 12 healthy volunteers were infused on four occasions, after pretreatment with placebo, disopyramide, mexiletine, and flecainide, respectively, with adrenaline at a rate producing serum adrenaline concentrations comparable with those seen in acute myocardial infarction. After pretreatment with placebo adrenaline caused significant falls in serum potassium, serum magnesium, serum calcium, and serum phosphate and a significant increase in blood glucose. Adrenaline also caused a significant increase in heart rate and systolic blood pressure and a significant fall in diastolic blood pressure. On the electrocardiogram a significant prolongation of QTc duration and a flattening of the T-wave amplitude were seen. Pretreatment with disopyramide had no effect on the hemodynamic response to adrenaline but caused a significant prolongation of Qtc duration before the adrenaline infusion. Pretreatment with mexiletine was associated with a significantly greater fall in serum potassium during adrenaline infusion, and pretreatment with flecainide with a greater fall in serum magnesium, as compared with placebo pretreatment Flecainide also caused a significant prolongation of the QRS duration before adrenalin infusion, and after all the active pretreatments a prolongation of QRS duration was seen during adrenaline infusion. The metabolic and hemodynamic changes during adrenaline infusion may not only reduce the antiarrhythmic efficacy of antiarrhythmics but may also increase the risk of proarrhythmic effects in a clinical setting. These results may help to explain why treatment with antiarrhythmics seems to be without beneficial effect on mortality in post-myocardial infarction patients.

Prophylaxis of atrial fibrillation with magnesium sulfate after coronary artery bypass grafting

Ninety-nine consecutive consenting patients were prospectively entered into a randomized, double-blind, placebo-controlled trial to determine the efficacy of postoperative magnesium therapy on the incidence of cardiac arrhythmias after elective coronary artery bypass grafting. No patient had documented or suspected arrhythmias preoperatively. Forty-nine patients received 178 mEq of magnesium given over the first 4 postoperative days, and 50 patients received only placebo. The clinical characteristics of both groups were similar. The preoperative mean serum magnesium concentration was similar in both study (1.90 mEq/L) and placebo (1.90 mEq/L) groups. The mean postoperative serum magnesium concentration in study patients was significantly elevated over postoperative days 1 through 4 when compared with preoperative levels (p less than 0.001). The postoperative mean serum magnesium concentration in control patients declined and remained significantly depressed through postoperative day 3 (p less than 0.001), but increased to preoperative levels by postoperative day 4. The mean serum magnesium concentration was significantly greater in the study patients as compared with the control patients over postoperative days 1 through 4 (p less than 0.001). Although there was no significant difference between groups with respect to episodes of ventricular arrhythmias, there was a significant decrease in the number of episodes of atrial fibrillation in the group receiving magnesium therapy (p less than 0.02). There were no recognized adverse effects of magnesium therapy. Prophylactic magnesium administration seems to lessen the incidence and severity of atrial fibrillation after coronary artery bypass grafting.

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

Digitalised patients with chronic atrial fibrillation (AF) have a high prevalence of ventricular premature beats (VPB); magnesium deficiency may be a contributory factor. We have used a magnesium loading-test to examine the relationship between ventricular ectopy and magnesium status in 14 digitalised patients with chronic AF. Among seven patients with infrequent VPB (less than 250 24 h-1; mean 107 24 h-1) mean magnesium retention was 10.1% and four subjects retained no significant quantities of magnesium, indicating magnesium repletion. Among the remaining seven patients, mean magnesium retention was significantly higher (33.1%, P less than 0.02) and all patients retained 20% or more of the load given. There was an overall relationship between Mg retention and numbers of VPB (rs = 0.54; P less than 0.05). Magnesium deficiency may be determinant of ventricular ectopy in digitalised patients with chronic AF.

Beneficial effect of magnesium sulfate in acute myocardial infarction

The effects of magnesium on the incidence of arrhythmias and on mortality were evaluated in 103 patients with documented acute myocardial infarction (AMI) in a randomized, double-blind, placebo-controlled study. Fifty patients received a magnesium infusion for 48 hours and 53 received only the vehicle (isotonic glucose) as placebo. The baseline characteristics of the population were similar in the 2 groups. Tachyarrhythmias requiring drug therapy were recorded in 32% of the patients in the magnesium group and in 45% of the placebo group. Conduction disturbances were found in 23% of the placebo group as compared to 14% in the magnesium group. The intrahospital mortality was 2% (1 patient) in the magnesium group, compared to 17% (9 patients) in the placebo group (p less than 0.01). No adverse effects were observed during and after the magnesium infusion. These data support a possible protective role of magnesium in patients with AMI.

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.

Metabolic, electrocardiographic, and hemodynamic responses to increased circulating adrenaline: effects of selective and nonselective beta adrenoceptor blockade

Twelve healthy male volunteers were given adrenaline infusions, 0.05 microgram/kg body weight/minute over one hundred twenty minutes (min), in order to achieve serum adrenaline concentrations comparable with those seen in acute myocardial infarction. The infusions were given on three occasions, at intervals of at least four weeks. Before the infusions the subjects were given, in random order, two days' pretreatment with placebo, a beta-1-selective adrenoceptor blocker (atenolol), or a nonselective beta blocker (propranolol) with each subject receiving each pretreatment. Six of the volunteers also had a fourth adrenaline infusion, after two days' pretreatment with a beta-2-selective beta blocker, ICI 118551. Adrenaline increased heart rate by 11 beats/min, increased systolic blood pressure by 10 mmHg, and decreased diastolic blood pressure by 15 mmHg. These changes were partly prevented by atenolol. Propranolol and ICI 118551 partly prevented the rise in systolic blood pressure but differed from atenolol in their effects on heart rate and diastolic blood pressure, causing falls in heart rate by 7 beats/min and 12 beats/min respectively, secondary perhaps to increases in diastolic blood pressure by 13 mmHg and 17 mmHg respectively. Adrenaline caused a prolongation of QTc duration by 0.03 second and a flattening of the T-wave amplitude by 1.04 mm. These changes in cardiac repolarization were partly inhibited by atenolol, but the effects of propranolol and ICI 118551 were greater, each causing a reduction of QTc and an increase in T-wave amplitude. During adrenaline infusion S-potassium declined by 0.60 mmol/L, S-magnesium by 0.05, S-calcium by 0.10, and S-phosphate by 0.24, but S-free fatty acids increased nearly threefold. All these changes were statistically significant and were presumably mediated mainly by the beta-2-adrenoceptor, for they were blocked more effectively by the beta-2-adrenoceptor blockers than by the selective beta-1-adrenoceptor blocker. B-glucose increased by 4.1 mmol/L, the increase being practically unaffected by the different pretreatments. These adrenaline-induced hemodynamic, electrocardiographic, and metabolic changes may predispose to arrhythmias and impair cardiac performance after a myocardial infarction. Nonselective beta blockers may be more effective in blocking the electrocardiographic and metabolic effects, but beta-1-selective beta blockers may have hemodynamic advantages.

Prospective evaluation of parenteral magnesium sulfate in the treatment of patients with reentrant AV supraventricular tachycardia

This study prospectively assessed the electrophysiologic effects of parenteral magnesium sulfate administration on paroxysmal atrioventricular (AV) reentrant supraventricular tachycardia and the efficacy of magnesium to terminate these arrhythmias. Eleven normomagnesemic patients, seven with orthodromic reentrant supraventricular tachycardia that used an accessory AV pathway, and four with typical AV nodal reentry were examined. All patients had a history of sustained supraventricular tachycardia requiring pharmacologic therapy or electrical cardioversion for termination of tachycardia. After baseline electrophysiologic study, including documentation of sustained supraventricular tachycardia that was reproducibly induced, parenteral magnesium sulfate (a bolus of 0.3 mEq/kg of elemental magnesium infused over a 10-minute period followed by a maintenance infusion of 0.2 mEq/kg/hr) was administered during sustained supraventricular tachycardia. The serum magnesium concentration increased from (mean +/- standard deviation) 1.9 +/- 0.2 mg/dl to 4.0 +/- 0.6 mg/dl (p = 0.0001). Except for flushing and mild diaphoresis during infusion of the magnesium sulfate bolus, and dry heaves in one patient, there were no untoward effects or significant changes in systolic blood pressure. During administration of magnesium, the tachycardia cycle length increased from 319 +/- 39 msec to 348 +/- 43 msec (p = 0.0001). Slowing of the tachycardia occurred predominantly in the antegrade limb of the circuit at the level of the AV node with the AH interval increasing from 171 +/- 66 msec to 197 +/- 68 msec (p = 0.0001), whereas there was no significant change in the HV interval (43 +/- 3 msec to 43 +/- 4 msec, p = NS) or the VA interval (106 +/- 43 msec to 110 +/- 47 msec, p = NS) during tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

S-Mg does not change inversely to S-FFA during acute stress situations

The apparently divergent changes in serum magnesium (S-Mg) and serum free fatty acids (S-FFA) in stress situations associated with elevated levels of circulating adrenaline were studied experimentally in 12 healthy volunteers, who were each given three adrenaline infusions (0.05 micrograms/kg bw/min over one hundred twenty minutes). Before the adrenaline infusions the volunteers were treated for three days with either a non-selective beta-blocking agent (propranolol) or a beta-1-selective agent (atenolol) or with placebo. Six of the volunteers underwent a fourth adrenaline infusion after pretreatment with a beta-2-selective beta-blocking agent (ICI 118551). S-Mg and S-FFA were determined every fifteen minutes. After pretreatment with placebo, adrenaline infusion caused an increase in S-FFA from 0.22 +/- 0.20 mmol/L (mean +/- SD) to max 0.59 +/- 0.39 mmol/L after thirty minutes of adrenaline infusion (p less than 0.001). At one hundred twenty minutes S-FFA had decreased to 0.35 +/- 0.26 mmol/L. Thirty minutes after cessation of the adrenaline infusion, S-FFA had returned to the same level as before the infusion. S-Mg before the adrenaline infusion was 0.83 +/- 0.05 mmol/L, rose to 0.85 +/- 0.05 at fifteen minutes, and then decreased to 0.78 +/- 0.05 at one hundred thirty-five minutes (p less than 0.05). Pretreatment with atenolol did not change this pattern, although the changes in S-FFA and S-Mg were of a smaller magnitude but still statistically significant.

Cardiovascular consequences of magnesium deficiency and loss: pathogenesis, prevalence and manifestations--magnesium and chloride loss in refractory potassium repletion

Dietary magnesium (Mg) deficiency is more prevalent than generally suspected and can cause cardiovascular lesions leading to disease at all stages of life. The average American diet is deficient in Mg, especially in the young, in alcoholic persons, and in those under stress or with diseases or receiving certain drug therapies, who have increased Mg needs. Otherwise normal, Mg-deficient diets cause arterial and myocardial lesions in all animals studied, and diets that are atherogenic, thrombogenic and cardiovasopathic, as well as Mg-deficient, intensify the cardiovascular lesions, whereas Mg supplementation prevents them. Diuretics and digitalis can intensify an underlying Mg deficiency, leading to cardiac arrhythmias that are refractory unless Mg is added to the regimen. Potassium (K) depletion in diuretic-treated hypertensive patients has been linked to an increased incidence of ventricular ectopy and sudden death. K supplementation alone is not the answer. Mg has been found to be necessary to intracellular K repletion in these patients. Because patients with congestive heart failure and others receiving diuretic therapy are also prone to chloride loss leading to metabolic alkalosis that also interferes with K repletion, the addition of Mg and chloride supplements in addition to the K seems prudent.

The electrophysiological effects of intravenous magnesium on human sinus node, atrioventricular node, atrium, and ventricle

The effects of intravenously (IV) administered magnesium chloride (MgCl) on electrophysiologic and electrocardiographic variables were studied in 13 patients undergoing a routine electrophysiologic assessment for clinical indications. An infusion of 12 mmol of MgCl was given during a 10-min period and relevant electrophysiologic variables were determined before and after the infusion. Serum Mg levels increased from 0.78 +/- 0.03 (mean +/- SEM) before to 1.52 +/- 0.08 ms after the infusion (p less than 0.0001). Magnesium treatment caused a significant prolongation in PR interval (from 151 +/- 8 to 174 +/- 8 ms, p less than 0.001) as well as in QRS duration (from 90 +/- 4 to 101 +/- 6 ms, p less than 0.05). Likewise, intra-atrial (PA) as well as atrioventricular (AV) nodal (AH) conduction times were significantly prolonged (from 33 +/- 3 to 46 +/- 3 ms, p less than 0.01, and from 85 +/- 6 to 94 +/- 6 ms, p less than 0.05, respectively). Mean effective and functional atrial refractory periods increased (from 228 +/- 8 to 256 +/- 10 ms, p less than 0.01 and from 292 +/- 9 to 320 +/- 11 ms, p less than 0.01, respectively), as did mean AV node functional refractory period (from 399 +/- 29 to 422 +/- 27 ms, p less than 0.02). No significant change occurred with regard to sinus node function (as estimated from heart rate, sinus node recovery time, and calculated sinoatrial conduction time) or ventricular refractoriness. It is concluded that IV Mg has several electrophysiologic effects that may be beneficial in the treatment/prevention of supraventricular tachyarrhythmias.

Electrophysiologic effects of intravenous magnesium in patients with normal conduction systems and no clinical evidence of significant cardiac disease

Parenteral magnesium has been used for several decades in the empiric treatment of various arrhythmias, but the data on its electrophysiologic effects in man are limited. We evaluated the electrophysiologic effects of magnesium sulfate (MgSO4) administration in eight normomagnesemic patients with normal mononuclear cell magnesium content, who had no clinically significant heart disease and had normal baseline electrophysiologic properties. After administration of intravenous MgSO4, serum magnesium rose significantly from 1.9 +/- 0.1 to 4.4 +/- 1.7 mg/dl (p less than 0.02). During a maintenance magnesium infusion, we observed significant prolongation of the ECG PR interval (145 +/- 18 to 155 +/- 26 msec, p less than 0.05), AH interval (77 +/- 27 to 83 +/- 26 msec, p less than 0.002), antegrade atrioventricular (AV) nodal effective refractory period (278 +/- 67 to 293 +/- 67 msec, p less than 0.05), and sinoatrial conduction time (60 +/- 34 to 76 +/- 32 msec, p less than 0.02). No significant effect was observed on sinus cycle length, sinus node recovery time, intra-atrial or intraventricular conduction times, QRS duration (during both sinus rhythm and ventricular pacing), QT interval, HV interval, paced cycle length resulting in AV nodal Wenckebach block, AV nodal functional refractory period, retrograde ventriculoatrial (VA) effective refractory period, or atrial and ventricular refractory periods. These findings, in conjunction with the demonstrated ability of magnesium to block slow channels for sodium movement, may provide an explanation of the mechanism by which magnesium exerts its effect in the treatment of atrial and junctional arrhythmias.

Magnesium levels in cardiac arrest victims: relationship between magnesium levels and successful resuscitation

Multivariate analysis was performed to evaluate significant differences between electrolytes, serum magnesium, and successful resuscitation in cardiac arrest victims in a prospective controlled study. Twenty-two cardiac arrest victims having ventricular fibrillation or tachycardia, electromechanical dissociation, or asystole were compared with 19 matched controls with no ventricular arrhythmias. Of the control group, one was hypermagnesemic (5%), 17 normomagnesemic (90%), and one hypomagnesemic (5%). In the arrest group, eight were hypermagnesemic (36%), nine normomagnesemic (41%), and five hypomagnesemic (23%). Thirteen of 22 cardiac arrest victims (59%) had an abnormal serum magnesium level. All hypermagnesemic and hypomagnesemic patients expired (100%). In the normomagnesemic group, four out of nine (44%) were successfully resuscitated. A positive correlation was identified between normomagnesemia and successful resuscitation (P less than .01). There was no correlation between other electrolytes and successful resuscitation (P greater than .05).