Factors affecting the blood concentration of ionized magnesium in patients in the acute phase of myocardial infarction.

Magnesium is physiologically active in its free state (Mg2+). In the present study, we attempted to clarify factors affecting blood concentrations of Mg2+ in the acute phase of myocardial infarction (AMI). Subjects were 84 consecutive patients with AMI. Blood samples were collected at the time of admission, 24h after admission, and 1 week after admission, to measure blood concentration of Mg2+ and noradrenaline (NA). Furthermore, to assess daily Mg intake the hardness of local drinking water was determined, and a survey was conducted regarding dietary preferences and habits. Based on the results of this survey, the patients were defined as having a low Mg intake (L Group) or not. In addition, based on chronological shifts in blood Mg2+ concentrations, subjects were divided into the following four groups: Normal group, blood concentration of Mg2+ within normal range at all measurement points; Early recovery group, low at time of admission, but normalized on the next day; Delayed recovery group, low at time of admission, but normalized 1 week after admission; and Unrecovered group, below normal range at all measurement points. The mean blood Mg2+ concentration on admission was 0.52 +/- 0.06 mmol/l, significantly lower than the normal range (P < 0.05). A negative correlation between blood Mg2+ and NA concentrations on admission was observed (r = 0.49, P < 0.005). As a result, blood Mg2+ concentrations were normalized in 94% of subjects by 1 week after admission. Mean blood Mg2+ concentration on admission in the L Group was 0.47 +/- 0.05 mmol/l, significantly lower than that found in other subjects (0.52 +/- 0.05 mmol/l, P < 0.01). Eighty percent of the patients classified into the Unrecovered group belonged to the L Group. These findings suggest that lower blood concentrations of Mg2+ and higher plasma NA levels may be a result of serious AMI. However, chronic Mg intake deficiency may play a partial role in patients whose blood concentrations of Mg2+ remain low for long periods of time.