The protective effect of magnesium on acute catecholamine cardiotoxicity in the neonate

Propranolol ameliorates and epinephrine exacerbates progression of acute and chronic viral myocarditis

Recent studies point to important interactions between proinflammatory cytokines and neurohumoral mediators in heart failure. Here we investigate the influence of the β-adrenergic system on cytokines and neurohumoral factors and the sequelae of viral myocarditis. In an experimental model with virus-infected BALB/c mice, we studied the acute and chronic effects of epinephrine and propranolol on myocardial morphology, cytokine gene expression, and survival. BALB/c mice were inoculated with the encephalomyocarditis virus (EMCV) or sham inoculated with saline and followed for 30 days. Epinephrine increased the severity of inflammatory cell infiltration and myocardial necrosis induced by EMCV. Gene expression of TNF-α, IL-6, and IL-10 was markedly enhanced by epinephrine in EMCV-inoculated mice. Survival rate after 30 days was reduced to 40% in epinephrine-treated EMCV-inoculated mice compared with 70% in untreated EMCV-inoculated mice ( P < 0.05). Treatment with the β-blocker propranolol significantly decreased mortality, myocardial necrosis, and infiltration of inflammatory cells in EMCV-inoculated mice. Propranolol also suppressed gene expression of TNF-α, IL-6, and IL-10. A single dose of epinephrine 120 days after EMCV inoculation caused sudden death in 70% of infected mice; propranolol significantly reduced incidence of death to 33%. These results indicate that acute and chronic stages of viral myocarditis are modulated by the β-adrenergic system and its interactions with proinflammatory cytokines.

Clinical symptoms of mitral valve prolapse are related to hypomagnesemia and attenuated by magnesium supplementation

Mitral valve prolapse syndrome (MVP) is a frequent disorder characterized by a number of complaints which lessen the quality of life. The pathogenesis of MVP symptoms has not been fully elucidated. Hyperadrenergic activity and magnesium deficiency have been suggested. This study was designed to verify the concept that heavily symptomatic MVP is accompanied by hypomagnesemia and to elucidate whether magnesium supplementation alleviates the symptoms and influences adrenergic activity. We assessed serum magnesium in 141 subjects with heavily symptomatic primary MVP and in 40 healthy controls. Decreased serum magnesium was found in 60% of patients and in 5% of controls (p <0.0001). Patients with low serum magnesium were subjected to magnesium or placebo supplementation in a double-blind, crossover fashion. Typical symptoms of MVP (n = 13), intensity of anxiety, and daily excretion of catecholamines were determined. After 5 weeks, the mean number of symptoms per patient decreased from 10.4 +/- 2.1 to 5.6 +/- 2.5 (p <0.0001), and a significant reduction in weakness, chest pain, dyspnea, palpitations, and anxiety was observed. Increased noradrenaline excretion before and after magnesium was seen in 63% and 17% of patients, respectively (p <0.01). Mean daily excretion of noradrenaline and adrenaline was significantly diminished after magnesium. It is concluded that many patients with heavily symptomatic MVP have low serum magnesium, and supplementation of this ion leads to improvement in most symptoms along with a decrease in catecholamine excretion.

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.

Ethanol intake, plasma catecholamine levels, and ST-segment changes without myocardial injury in rats with short-term ethanol consumption

The authors studied the effect of short-term ethanol consumption on the ST-segment and the association between ST-segment changes and the amount of daily ethanol intake and levels of plasma catecholamines. The study used 63 rats (control group n = 20, study group n = 43). The rats in the study group were exposed for 6 days to progressively larger doses of ethanol followed by 15 days of continuous exposure to ethanol. At baseline an electrocardiogram (ECG) was recorded, and on day 25 the ECG was repeated and plasma catecholamine levels were measured. The animals' hearts were removed and processed for histologic study. Repolarization abnormalities were observed in 68% of the ethanol-consuming rats. Two factors differentiated the subgroup of ethanol-consuming rats with ST-segment changes from the subgroup without ST-segment changes: amount of daily ethanol intake (0.0077 +/- 0.02 mL/g/d vs 0.0058 +/- 0.019 mL/g/d) and plasma epinephrine levels (3,881 +/- 733 pg/mL vs 1,478 +/- 406 pg/mL). No myocardial damage was detected. Our results suggest that in ethanol-consuming rats, high-volume daily ethanol intake and increased plasma catecholamines may mediate changes in the ST-segment.

Magnesium flux during and after open heart operations in children

Hypomagnesemia and depletion of the body's magnesium stores is known to be associated with an increased incidence of both cardiac arrhythmias and neurological irritability. In a two-part prospective study we have evaluated whether magnesium deficiency is a significant occurrence in children treated in the intensive care unit after open heart operations, and subsequently have sought to identify how intraoperative metabolic changes were related to the resultant findings. In 41 children studied after operation the plasma magnesium concentration showed a significant decrease from 0.92 mmol/L (10th to 90th centile, 0.71 to 1.15 mmol/L) immediately after operation to 0.77 mmol/L (0.65 to 0.91 mmol/L) on the following morning. The subsequent change in grouped values was not significant but 14 (34.2%) and 7 (17.1%) possessed values of less than 0.7 mmol/L and 0.6 mmol/L, respectively. The occurrence of cardiac arrhythmias was not statistically related to the occurrence of hypomagnesemia. In 21 children perioperative changes in extracellular and tissue magnesium, potassium, and calcium content were measured. It was found that hemodilution with a prime low in magnesium caused a reduction from a median of 0.81 mmol/L to 0.61 mmol/L (p < 0.01). Plasma potassium level, however, was elevated from 3.7 mmol/L to 4.15 mmol/L (p < 0.05) and the ionized calcium content from 1.17 mmol/L (1.07 to 1.25 mmol/L) to 1.49 mmol/L (1.25 to 2.56 mmol/L) (p = 0.0009). The myocardial content of magnesium did not change significantly but skeletal muscle content was depleted from 6.75 mumol/g (2.85 to 8.35 mumol/g) to 5.65 mumol/g (2.45 to 7.2 mumol/g) (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Magnesium flux caused by coronary artery bypass operation: three patterns of deficiency

We undertook a study to evaluate the patterns of magnesium deficiency that may develop during and following coronary artery bypass operation without cardioplegia. In 18 patients intraoperative measurements of plasma magnesium and potassium concentrations and measurements of cardiac and skeletal muscle content of these ions were taken. The changes in plasma concentrations and excretion were evaluated postoperatively. Hemodilution at initiation of cardiopulmonary bypass caused a 17.3% decrease in plasma magnesium concentration (p < 0.01), which persisted until the first postoperative day. By the fifth postoperative day the level was 19.5% greater than the preoperative value. Urinary excretion of magnesium reflected changes in plasma magnesium concentration. Cardiac muscle content of magnesium decreased by 13.3%. Plasma potassium concentration was elevated by hemodilution (p < 0.01), and muscle potassium was not depleted. We conclude that three patterns of magnesium depletion occur: hemodilution, intraoperative cellular depletion, and postoperative cellular depletion. The findings support the need for magnesium supplementation during and after cardiac operation.

Effects of magnesium sulphate and nitric oxide in pulmonary hypertension induced by hypoxia in newborn piglets

AIM

To examine the haemodynamic effects of intravenous magnesium sulphate on an animal model of neonatal pulmonary hypertension induced by hypoxia.

METHODS

The cardiac index (Q), pulmonary arterial pressure (PAP), systemic arterial pressure (SAP), and pulmonary (PVRI) and systemic (SVRI) vascular resistance indices were measured in nine newborn piglets (including three controls). Pulmonary hypertension was induced by lowering the FIO2 to 0.12-0.14, after which there was a significant increase in PAP and PVRI (37% and 142%, respectively; p < 0.01) and a significant fall in SAP and Q (30% and 33%, respectively; p < 0.01).

RESULTS

Magnesium sulphate was infused intravenously as four doses of 25 mg/kg, 15 minutes apart, which resulted in a significant mean (SD) increase in serum magnesium (0.83 (0.07) mmol/l to 1.82 (0.19) mmol/l; p < 0.01). After the initial dose SAP, SVRI, PAP and PVRI decreased, but not significantly. Each subsequent dose of (50, 75, 100 mg/kg) was accompanied by further significant reductions in these variables from control baseline (p < 0.05). The PVRI:SVRI ratio remained unchanged throughout. Inhaled nitric oxide (NO) 40 ppm was administered after the last dose of magnesium sulphate. The PVRI:SVRI significantly decreased (p < 0.05), indicating that reversible pulmonary hypertension remained after a maximum dose of magnesium sulphate.

CONCLUSIONS

Unlike NO, magnesium sulphate is not a selective pulmonary vasodilator and may lead to deleterious effects on systemic pressures in critically ill newborns.