All-artery multigraft coronary artery bypass grafting with only internal thoracic arteries possible and safe: a randomized trial.

BACKGROUND: The internal thoracic artery (ITA) bypass to the left anterior descending coronary artery is of proven benefit in multigraft coronary artery bypass. Total ITA grafts, if reoperation is averted by avoiding saphenous vein grafts (SVGs), are attractive. The safety of the total ITA graft operation (all-ITA) is a concern. METHODS: A randomized trial of multiple-ITA bypass graftings with the use of bilateral sequential ITA without SVGs was performed. Control patients received 1 ITA plus SVG. Inclusion criteria were those used in the Coronary Artery Surgery Study, extended to age 76 years, and any angina class, except emergent. One hundred sixty-two patients were randomized (81 patients per group) from January 1, 1990, to December 31, 1994. RESULTS: Baseline traits were similar as were cross-clamp times, pump times, and number of arteries bypassed (average, 4.3 arteries). Patients who received multiple ITA grafts had no myocardial infarctions, per reference laboratory. One patient died, and 2 patients returned for bleeding. The ITA-SVG group had similar results. The all-ITA group experienced successful completion in 93% of cases. Complications did not differ from control patients. CONCLUSIONS: Early and 5-year outcomes were not different between the all-ITA group and the ITA with SVGs group. We believe experienced surgeons can safely extend the ITA to multibypass coronary artery bypass without use of SVG to achieve an all-ITA operation.

Relation between magnesium and potassium concentrations in myocardium, skeletal muscle, and mononuclear blood cells.

Potassium and magnesium were measured in 26 cardiac surgery patients (right atrial appendage), 23 autopsy subjects (right atrial appendage, left ventricular free wall, and skeletal muscle), and 9 healthy volunteers (mononuclear blood cells) to determine whether there was a relation between these two ions in the tissues measured. In the cardiac surgery patients, the potassium and magnesium concentrations were 46.35 +/- 3.89 and 4.40 +/- 0.58 (mean +/- SD, mumol/g wet weight tissue), respectively, and were significantly correlated (r = 0.54, P = 0.005). In the autopsy group, the respective concentrations were: for right atrial appendage, 30.54 +/- 10.18 and 3.66 +/- 0.70 mumol/g (r = 0.38, P = 0.14); left ventricular free wall, 60.69 +/- 17.93 and 7.74 +/- 1.73 mumol/g (r = 0.92, P = 0.0001); and skeletal muscle, 93.05 +/- 20.49 and 8.64 +/- 2.06 mumol/g (r = 0.91, P = 0.0001). In the healthy volunteer group, the results for potassium and magnesium in mononuclear blood cells were 42 +/- 9.9 and 3.99 +/- 0.70 fmol/cell, respectively (r = 0.94, P = 0.0001). Thus, potassium and magnesium concentrations were significantly correlated in all the tissues measured.

Can the magnesium content of mononuclear blood cells be altered by oral magnesium supplementation?

A randomized, double-blind, placebo-controlled trial was performed on a rigorously defined group of normal subjects to see if magnesium (Mg) supplementation could affect serum Mg levels or Mg content of mononuclear blood cells. Forty-nine subjects were randomized to either placebo, tablets containing 90% United States recommended daily allowance (USRDA) of Mg, or tablets containing 180% USRDA of Mg. We were unable to demonstrate a statistically significant increase in Mg content of mononuclear blood cells.

ROC curve analysis: an example showing the relationships among serum lipid and apolipoprotein concentrations in identifying patients with coronary artery disease.

Clinical accuracy, defined as the ability to discriminate between states of health, is the fundamental property of any diagnostic test or system. It is readily expressed as clinical sensitivity and specificity, and elegantly represented by the receiver operating characteristic (ROC) curve. To demonstrate the use of ROC curves, we reexamine a study of the ability of serum lipid and apolipoprotein measures to discriminate among degrees of coronary artery disease in patients undergoing coronary angiography. ROC curve analysis reveals that none of these indexes is highly accurate, but demonstrates a modest increase in the accuracy of apolipoprotein over lipid indexes.

Magnesium deficiency: recognition and treatment in the emergency medicine setting.

Magnesium deficiency and its clinical manifestations are common in patients presenting to the emergency department. Assessment of the total body magnesium status of a patient is problematic since the serum magnesium concentration, the only readily available clinical test for this condition, may not be accurate in predicting the intracellular magnesium concentration. Therefore, empiric magnesium therapy should be considered in high-risk patients. Since magnesium participates in numerous metabolic processes in the body, a deficiency can affect multiple organ systems and present clinically in a variety of ways. Magnesium deficiency is reviewed in this paper with regard to therapeutic implications; specific treatment guidelines are given including dose, infusion rate, and magnesium preparation. Magnesium is also reviewed with regard to its homeostasis and metabolic role in the body. Special mention is made regarding precautions for use of magnesium in the setting of renal insufficiency.

Clinical correlates of the molecular and cellular actions of magnesium on the cardiovascular system.

Magnesium is a ubiquitous element that participates in metabolic processes essential for life. Magnesium acts as a metallic cofactor in more than 300 enzymatic reactions; notably it is essential for all reactions requiring ATP. Magnesium also functions as a transmembrane and intracellular modulator of other ions. Altered magnesium homeostasis, particularly a deficiency, can cause alterations in metabolic functions that result in clinically recognizable events. Recognition of magnesium deficiency is problematic, since there is no test that will reliably and consistently detect this condition. A high index of suspicion for magnesium deficiency is necessary and treatment should be given when indicated. This article reviews the molecular and cellular actions of magnesium and correlates these basic scientific findings with clinically recognized cardiovascular events in humans. In addition, management guidelines are delineated.

Magnesium metabolism: a case report and literature review.

Magnesium has been shown to play an important role in the body. In the critical care setting of particular concern is the role of Mg++ in the treatment of malignant tachydysrhythmias such as ventricular tachycardia and ventricular fibrillation. Research is being conducted to determine appropriate methods of assessing Mg++ status, the relationship of altered Mg++ states to clinical manifestations, and the treatment of the abnormalities associated with Mg++ deficiency. Safe and effective forms of parenteral and oral Mg++ supplements are currently available.

Myocardial magnesium: relation to laboratory and clinical variables in patients undergoing cardiac surgery.

Magnesium concentration was measured in the right atrial appendage of 100 patients undergoing cardiac surgery and associations with serum and mononuclear blood cell magnesium, other laboratory values and patient clinical variables were studied. In addition, magnesium was measured in the right atrial appendage and left ventricular free wall in 23 autopsy subjects to determine whether there was a proportional relation between right atrial appendage and left ventricular free wall magnesium. The mean left ventricular free wall/right atrial appendage magnesium ratio was 2.13 +/- 0.39 (r = 0.67, p = 0.0009). In the group with cardiac surgery, the right atrial appendage magnesium concentration correlated inversely with age (r = -0.54, p = 0.001). The mean right atrial appendage magnesium concentration (micrograms/g wet weight tissue) was lower in patients with postoperative cardiac arrhythmia than in those without arrhythmia (103 +/- 13 versus 111 +/- 10, p = 0.009) and in diabetic than in nondiabetic patients (103 +/- 13 versus 109 +/- 12, p = 0.02). The right atrial appendage magnesium concentration also tended to be lower in patients receiving potassium/magnesium-losing diuretics, although this difference did not achieve statistical significance (105 +/- 14 versus 109 +/- 11, p = 0.16). Right atrial appendage magnesium concentration correlated positively with serum creatinine concentration (r = 0.31, p = 0.002) and negatively with serum calcium concentration (r = -0.29, p = 0.013). Serum magnesium did not correlate with right atrial appendage or mononuclear blood cell magnesium concentration or clinical variables. There was a statistically significant correlation between mononuclear blood cell and right atrial appendage magnesium concentrations in some subgroups of patients.

Magnesium metabolism.

Magnesium is the second most abundant intracellular cation in the human body and is necessary as a cofactor in more than 300 enzymatic reactions. The generation and use of adenosine triphosphate is dependent on the presence of magnesium. The assessment of the magnesium status of a patient is problematic because there are no easily performed tests that reliably predict the intracellular concentration. There are recognized molecular and cellular actions of magnesium that explain clinically recognizable problems when a magnesium deficiency or excess is present. Guidelines for therapy of magnesium deficiency are given. Future directions in research are given.

Apolipoproteins A-I and B as predictors of angiographically defined coronary artery disease.

Apolipoprotein A-I and B concentrations were measured in 502 patients undergoing diagnostic cardiac catheterization to assess the predictive power of apolipoproteins B and A-I to discriminate between patients with coronary artery disease and those with normal coronary arteries as defined by coronary arteriography. The strength of the associations was compared with that of the associations between traditional risk factors (eg, smoking status, cholesterol levels) and coronary artery disease. The study population consisted of 154 women (mean age, 62.9 years) and 348 men (mean age, 59.6 years). The apolipoprotein A-I concentration averaged (+/- SD) 124 +/- 25 mg/dL and the apolipoprotein B concentration, 98 +/- 24 mg/dL. In all cases, the apolipoprotein measures showed a larger univariate difference between the "normal" (no coronary artery disease) group (66 patients) and the group with coronary artery disease (436 patients) than did the corresponding standard lipoprotein measures. The variable with the strongest association with coronary artery disease was the ratio of apolipoprotein A-I to apolipoprotein B, followed by apolipoprotein B level. These findings were confirmed using logistic regression, adjusting for other coronary artery disease risk factors. Fasting status did not affect apolipoprotein A-I or B concentrations. We conclude that the use of apolipoprotein A-I and B concentrations gives additional information to that supplied by lipoprotein measures to help predict the presence of coronary artery disease. Since traditional lipid measures may be changed by a meal, apolipoproteins A-I and B might be more useful measures when the fasting status of a patient is in question.

Effect of intravenous magnesium sulfate on blood magnesium parameters.

Magnesium sulfate was administered intravenously (0.6 mEq/kg body weight over 10 min) to 13 patients with hypertrophic cardiomyopathy undergoing electrophysiologic testing. Total serum, ultrafilterable and protein-bound serum, mononuclear blood cell (MBC) content and concentration, and red blood cell (RBC) concentration of Mg were measured at the following intervals: (1) baseline (before Mg infusion), (2) at the end of infusion, and (3) approximately 40 min after the end of infusion. The total serum, ultrafilterable, and protein-bound fractions rose immediately after infusion and fell by 40 min. The RBC Mg rose and fell less sharply than the serum parameters after Mg infusion. In contrast, the MBC Mg content continued to rise significantly at 40 min after Mg infusion, and MBC concentration showed a continued trend to rise, although this was not statistically significant.

Magnesium metabolism. A review with special reference to the relationship between intracellular content and serum levels.

Magnesium (Mg++) is a ubiquitous element in nature, playing a role in photosynthesis and many metabolic functions in humans. All enzymatic reactions that involve adenosine triphosphate have an absolute requirement for Mg++. Levels of Mg++ are controlled by the kidneys and gastrointestinal tract and appear closely linked to calcium, potassium, and sodium metabolism. The clinical manifestations and causes of abnormal Mg++ status are protean. Testing for altered Mg++ homeostasis is problematic. Serum levels, which are those generally measured, reflect only a small part of the total body content of Mg++. The intracellular content can be low, despite normal serum levels in a person with clinical Mg++ deficiency. Future directions in research related to intracellular content of Mg++ are discussed. Treatment of altered Mg++ status depends on the clinical setting and may include the addition of a potassium/Mg++-sparing drug to an existing diuretic regimen. Guidelines for therapy are given.

Intracellular magnesium of mononuclear cells from venous blood of clinically healthy subjects.

Measurement of intracellular magnesium (Mg2+) may have advantages over serum Mg2+ measurements in the assessment of Mg2+ homeostasis in patients. An accurate and reproducible method of measuring the Mg2+ content of mononuclear cells (lymphocytes and monocytes) from the venous blood of human subjects utilizing commonly available reagents and equipment is described. A well-defined clinical population of 88 subjects (48 males and 40 females) was used as the normal population. The mean mononuclear cell Mg2+ content was 67.8 +/- 13.8 (SD) fg/cell giving a 95% confidence interval normal range of 40-95 fg/cell which compared favorably to the empirical 95% limits of 44-94 fg/cell. The serum Mg2+ measured at the same time was 0.90 +/- 0.06 (SD) mmol/l. No significant correlation was found when comparing serum and mononuclear cell Mg2+ concentrations. Additionally, no significant differences were found when serum and intracellular Mg2+ were analyzed for sex and age with the exception that intracellular Mg2+ tended to be slightly higher in the younger age groups. The routine performance of this assay may require as little as 7 ml of venous blood and was done with a coefficient of variation of 3.0-3.6%.

Hypomagnesemia in patients entering the ICU.

Serum magnesium was measured in 102 consecutive patients admitted to a medical ICU. Twenty percent of these patients had hypomagnesemia and 9% had hypermagnesemia. There were no other laboratory tests or clinical features suggesting hypomagnesemia. Of all ion levels measured routinely in these patients, serum magnesium had the highest prevalence of abnormal values.