Lloyd T. Iseri

Magnesium: Nature's physiologic calcium blocker

With the advent of “calcium blockers” in the treatment of cardiovascular disorders, one’s attention is drawn to the role of calcium in myocardial contractility, impulse formation, and smooth muscle tone. This increased awareness of calcium has also drawn attention to the role of magnesium, which in many situations has been shown to counter the actions of calcium. The present report attempts to show that excess magnesium will block, and that deficiency of magnesium will potentiate, the action of calcium. Clinical experiences, both recent and in the past, have also suggested the possibility that magnesium may effectively control certain cardiovascular functions. In a sense, magnesium may be considered nature’s physiologic calcium blocker. Biologic evolution of magnesium and calcium. In a recent monograph “Magnesium: Its biological significance,” Aikawal traces in a scholarly manner the origin of life on earth from the formation of the crust composed of iron-magnesium silicate and the primeval ocean rich in magnesium, to the formation of chlorophyll with magnesium in the center of the molecule, giving rise to photosynthesis and finally to the development of the animal cell containing adenosine triphosphate (ATP) with its “obligatory need for magnesium.“’ A cursory look into the biologic evolution of magnesium and calcium through development of life on earth indeed indicates that the two bivalent elements were incorporated into living cells for specific purposes, and perhaps as a check and balance on each other. Whereas magnesium was needed for energy transformation and cell metabolism, calcium appeared to be essential for structural stability (bone) and for motility of the organism through its neuromuscular activity. Biologic evolution would tend to favor the incorporation of calcium into primitive beings when movement through

Magnesium and potassium therapy in multifocal atrial tachycardia

Eight patients with multifocal atrial tachycardia received 7 to 12 gm of magnesium sulfate intravenously over a 5-hour period. Potassium supplements were given initially or added later. Initial arterial blood gases showed mean pH 7.48 +/- 0.03, PcO2 39.7 torr, PO2 72 torr, HCO-3 29.8 +/- 4.5 mEq/L, and base excess 6.84 +/- 3.78 mEq/L. Initial serum magnesium correlated well with initial serum potassium. Three patients had subnormal levels of magnesium and potassium. The level of serum magnesium rose with an intravenous injection magnesium and serum potassium levels tended to fall unless they were supplanted with potassium. There were seven patients who retained more than 20 mEq of the infused magnesium. Multifocal atrial tachycardia was successfully converted to sinus rhythm or sinus tachycardia in seven patients. Multifocal atrial rhythm (at slow rate) persisted in one patient. Two patients with falling serum potassium levels required potassium supplements. Results of this study confirm that patients with multifocal atrial tachycardia respond favorably to parenteral magnesium and potassium. We believe that serum magnesium administered together with serum potassium stabilizes the ionic balance of atrial cells and thus prevents spontaneous ectopy.

Prehospital brady-asystolic cardiac arrest.

Of 133 persons with spontaneous cardiac arrest attended by paramedics within 10 minutes, 100 (75%) had ventricular fibrillation as the initial rhythm and 33 (25%) had extreme bradycardia or asystole. The latter group of arrhythmias was characterized by sinus arrest or severe sinus bradycardia (90%) and complete A-V block (10%). Junctional escape rhythm was also absent or markedly retarded. Despite cardiopulmonary resuscitation and the administration of epinephrine, atropine, isoproterenol, and sodium bicarbonate, recovery of the sinus and junctional tissues was infrequent. Ventricular fibrillation developed in 11 cases (33%). One patient lived 12 days, but all others were dead on arrival or died in the emergency room. Among the 13 coronary causes of death proved at autopsy, 10 (77%) were due to a fresh thrombus and seven (54%) to an occluded proximal right coronary artery, suggesting a causal relation to this type of arrest.

Evaluation of dilated cardiomyopathy by pulsed Doppler echocardiography

The ability of pulsed Doppler echocardiography to identify patients with left ventricular systolic dysfunction was evaluated in 12 patients with dilated (congestive) cardiomyopathy. A range-gated, spectrum analyzer-based Doppler velocimeter was used to record blood flow velocity in the ascending aorta and main pulmonary artery. The following blood flow velocity parameters were measured or derived: peak flow velocity, acceleration time, average acceleration, deceleration time, average deceleration, ejection time, and aortic flow velocity integral. Doppler blood flow velocity data in the cardiomyopathy patients were compared to data from 20 normal subjects. Measurements from the ascending aorta revealed that peak aortic flow velocity discriminated between cardiomyopathy patients (mean 47 cm/sec, range 35 to 62) and normal subjects (mean 92 cm/sec, range 72 to 120) with no overlap in data (p less than 0.001). Aortic flow velocity integral was also able to separate the patients with dilated cardiomyopathy (mean 6.7 cm, range 3.5 to 9.1) from normal subjects (mean 15.7 cm, range 12.6 to 22.5) with no overlap in data (p less than 0.001). Although mean values for average aortic acceleration and aortic ejection time were also significantly different (both p less than 0.005), there was some overlap between the two groups. Pulmonary artery blood flow studies demonstrated significantly increased average acceleration, as well as decreased ejection time (both p less than 0.05), but no difference in average deceleration or peak flow velocity in cardiomyopathy patients compared to normals. Compared to pulmonary flow measurements, aortic Doppler flow velocity measurements allowed better separation of cardiomyopathy and normal groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of concentrated contrast media during angiography on plasma volume and plasma osmolality

Abstract The effect of injection of hypertonic radiopaque solutions on the plasma volume, hematocrit, osmolality, and chloride levels was studied in 8 patients undergoing retrograde aortography and venography. A sudden increase in plasma volume, with a concomitant rise in plasma osmolality and fall in blood hematocrit and plasma chloride concentration, were observed. The changes were ascribed to the passage of cellular water into the plasma in response to a sudden elevation of plasma osmolality, and the passage of interstitial fluid into the plasma in response to changes in acid-base balance. The subsequent decrease in plasma volume, which tended to fall below the control volume, was thought to be due primarily to osmotic diuresis produced by the hyperosmotic radiopaque solution. The relationship of these changes to certain complications of retrograde aortography and angiocardiography are discussed.

Magnesium therapy in new-onset atrial fibrillation

Abstract In new-onset atrial fibrillation (AF), digoxin has a limited ability to control ventricular response, is no better than placebo for facilitating conversion to sinus rhythm, and has a slow onset of action with a narrow toxic-therapeutic ratio.1,2 Magnesium (Mg) has been shown to slow and sometimes normalize the heart rhythm in supraventricular tachyarrhythmias.3,4 A randomized trial found Mg prevents AF in patients after cardiac surgery.5 Because of these factors, we conducted a prospective, randomized, double-blind, placebo-controlled study addressing whether Mg and digoxin were superior to digoxin alone in controlling the ventricular response of AE.

Magnesium sulfate therapy for sustained monomorphic ventricular tachycardia

Abstract A variety of supraventricular and ventricular arrhythmias have responded favorably to therapy with intravenous magnesium sulfate (MgSO 4 ) regardless of the patients initial serum magnesium level. 1–9 The ventricular arrhythmia most commonly reported to be responsive to MgS 4 is torsades de pointes. 3,5–7,9 We report the responses of 11 patients with sustained monomorphic ventricular tachycardia (VT) to a bolus injection of MgSO 4 .

Ionic biology and ionic medicine in cardiac arrhythmias with particular reference to magnesium.

In this day and age, when so much advancement is being made in molecular biology, we tend to lose sight of the importance of basic ions in clinical medicine. This report deals with the concept of ionic biology involving Na+, K+, Ca++, and Mg++ ions with respect to the membrane and action potential of cardiac cells in the genesis of tachyarrhythmias. Various clinical disorders leading to arrhythmias will be examined as examples of ionic medicine, and treatment protocols will be recommended according to these concepts. Basic concepts. The cell membrane separates the various ions, and the concentrations of these ions vary considerably outside and inside the cell. Naf and K+ are fully ionized so that their concentrations represent their total ionic concentrations. Ca++ and Mg++, on the other hand, form complexes with proteins, organic acids, and phosphates so that their total extracellular and intracellular concentrations do not represent their ionic concentrations. The extracellular concentration of Na+ is as high as 140 mmol/L, whereas the intracellular concentration is only about 10 to 20 mmol/L. The reverse is true of K+. Extracellular K+ is approximately 4 mmol/L, whereas intracellular K+ is approximately 140 mmol/L. More than half of serum Ca++ is complexed so that its ionic strength is only about 1.3 mmol/L (5.2 mg/ dl). This extracellular Ca++ concentration, however, is still much greater than the micromolar (0.1 pmol/L) ionic concentration inside the cell. It is interesting to note that an ionic Mg++ concentration of 0.5 mmol/L (1.2 mg/dl) is approximately the same outside and

Role of magnesium in cardiac tachyarrhythmias

The efficacy of magnesium therapy in patients with ventricular tachycardia has previously been reported. Recently completed and ongoing studies validate earlier observations that potassium and magnesium supplementation may control other cardiac arrhythmias, particularly in hypomagnesemic patients. Magnesium treatment is a viable therapeutic option when other antiarrhythmic agents fail to suppress ventricular tachycardia, ventricular fibrillation, multifocal atrial tachycardia, atrial fibrillation and supraventricular tachycardia.

Detection and quantitation of coronary artery stenoses from digital subtraction angiograms compared with 35-millimeter film cineangiograms

To assess the ability to detect coronary artery narrowings from computer-acquired angiograms, a panel of 4 observers independently identified and measured focal coronary narrowings from digital subtraction angiograms and compared the results to those obtained from standard 35-mm cine film angiograms. Both cine and digital angiograms were obtained sequentially using selective intracoronary artery injection of standard amounts of iodinated contrast media. Digital images were obtained at 8 frames/s with a 512 X 512 X 8-bit pixel matrix. Modifications in the imaging chain for computer acquisition included a slower pulsed radiographic mode, a progressive scan camera, and initial storage of the images on an 80-megabyte digital hard disk. Postprocessing computer algorithms were used to enhance the unsubtracted digital images; these included single-frame, mask-mode subtraction, vessel boundary edge enhancement, and 4-fold pixel magnification. In 19 patient studies, 32 arteries were reduced more than 25% in diameter according to at least 1 of 4 observers on either the digital or cine film angiograms. There was no significant difference in the mean percent diameter narrowing for all the narrowings between the digital angiograms (53 +/- 31%) and the cineangiograms (52 +/- 31%). In addition, a 2-way analysis of variance yielded no significant difference between the amount of variability in the measurements between the cine film and the digital technique. This similar variability persisted when subsets of patients based on the degrees of stenosis were considered (e.g., only narrowings from 50 to 90% diameter reduction).(ABSTRACT TRUNCATED AT 250 WORDS)