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Objective: To study the effect of intravenous (IV) terbutaline on potassium (K) and magnesium (Mg) distribution, ECG changes, and prevalence of ventricular ectopic beats in healthy subjects. Design: Randomized double-blind, [...]

There are conflicting data regarding the impact of serum potassium and magnesium levels on susceptibility to ventricular premature complexes (VPCs) in the clinical setting, The associations of serum potassium and magnesium levels with the prevalence of complex or frequent (>30/hour, multiform or repetitive) VPCs were examined after adjusting for age, sex, smoking, caffeinated coffee consumption, alcohol consumption, and left ventricular mass in Framingham Offspring Study subjects who were free of clinically apparent heart disease. There were 3,327 eligible subjects (mean age 44 years). Complex or frequent VPCs were present in 183 subjects (5.5%). When age-adjusted prevalences of complex or frequent VPCs were compared among quartiles of serum potassium and magnesium using a trend test, lower potassium (p = 0.002) and lower magnesium (p = 0.010) levels were associated with higher prevalence rates of arrhythmia. In logistic regression analyses that included potassium and magnesium simultaneously, potassium (p = 0.0021) and magnesium (p = 0.0311) levels were inversely associated with the occurrence of complex or frequent VPCs after adjustment for age, sex, smoking, coffee and alcohol consumption, diuretic use, and systolic blood pressure. These associations remained significant after accounting for left ventricular mass. A 1 SD decrement in potassium (0.48 mEq/liter) or magnesium (0.16 mEq/liter) level was associated with a 27% (95% confidence interval 6% to 51%) and a 20% (95% confidence interval 3% to 41%) greater odds of complex or frequent VPCs, respectively. Lower levels of serum potassium and magnesium were concurrently associated with higher prevalence rates of ventricular arrhythmias. (Am J Cardiol 1994;74-232-235)

Although the hypokalemic effect of inhaled [[unkeyable].sup.2]-adrenergic agonists has been well documented, little is known as to their effect on plasma magnesium. We therefore examined in ten healthy young volunteers [...]

Diuretics are still among the most frequently used antihypertensive drugs in the treatment of hypertension. Their pharmacologic and hemodynamic properties are based on the water and salt metabolism in the pathophysiology of high blood pressure. Initially, there is a reduction of plasma and extra-cellular fluid volume; cardiac output also decreases. After this early phase, cardiac output returns to normal with an accompanying decrease in peripheral resistance so as to correct the underlying hemodynamic fault of the hypertensive state. Diuretics have a high therapeutic efficacy either as monotherapy or in combination with [Beta] blockers, angiotensinconverting enzyme inhibitors or calcium antagonists. The main problem with the use of diuretics is related to their metabolic side effects, which are dose-related. Currently, there is a tendency to administer low-dose diuretics, which result in fewer clinical and metabolic side effects, but with a continued antihypertensive efficacy. Therefore, low doses of diuretics can be recommended as initial therapy in the stepped-care approach of hypertension. (Am J Cardiol 1990;65:72H-76H), Diuretic drugs are the most frequently prescribed treatment for hypertension and are recommended for initial therapy by the World Health Organization. Since their use is not without some adverse effects, however, the mechanisms of action and biochemical effects of diuretics should be reviewed. Initially, diuretics work by reducing the volume of extracellular fluid, which decreases the cardiac output. The cardiac output slowly returns to normal, with a compensatory decrease in the resistance of the blood vessels to blood flow. This resistance is the primary determinant of hypertension, and its reduction is the basis for long-term management of hypertension. Although the mechanism by which diuretics maintain the state of low vascular resistance is not certain, they may directly reduce the reactivity of the vessels to constricting influences. There may also be a contribution from the reduction of sodium and calcium in the smooth muscle cells of the arteries. The moderation of sodium, or salt, intake may contribute to this effect. In addition, diuretics may assist the action of other antihypertensive drugs such as minoxidil or hydralazine, which dilate blood vessels but also promote sodium retention. Although diuretics promote the loss of potassium as well as sodium, this loss may be countered by the use of prescribing more moderate diuretic doses, or the use of potassium supplements. Side effects of diuretics include nausea, dizziness, rash, cramps, and impotence. Many of these may be controlled by the use of low-dose treatments. Biochemical abnormalities include glucose intolerance, which may lead to diabetes in some individuals, particularly those with a family history of diabetes. Increases in uric acid in the blood are observed, but are generally not regarded as worth treating unless levels exceed 65 micromolar in women or 77 in men. Increases in serum triglycerides and low-density lipoproteins are observed, and may negate some of the beneficial effects of blood pressure reduction. Indapamide, a indoline diuretic with a mechanism similar to the thiazides, seems to effectively reduce blood pressure without the concomitant effects on serum lipids. (Consumer Summary produced by Reliance Medical Information, Inc.)

In view of the significant influence of potassium on the heart, a decision was made to study the effect of exercise on this important ion in two exercise groups of different intensity. The first group consisted of 44 individuals with known coronary artery disease participating in a supervised cardiac rehabilitation program while the other consisted of 30 healthy joggers. Postexercise mean potassium levels were higher in both groups than resting baseline values. In addition, 5 of 44 participants in the coronary artery disease group experienced major potassium increases of 0.9 mmol/L or more while 7 of 30 healthy joggers experienced this magnitude of increase. Remaining unanswered is the question of whether such abrupt rises in potassium levels in this subset of patients alter their vulnerability to cardiac rhythm and conduction disturbances. A question is also raised as to whether rapid return of potassium levels to baseline postexercise contributes to any risks. (Chest 1992; 101:398-400) CAD=coronary artery disease, Potassium is an important ion having a significant influence on cardiac rhythm and conduction.[1] While the serum concentration of potassium is known to increase in the face of anaerobic exercise, [...]

Its Correlates and Value as a Determinant of In-Hospital Outcome Study objectives: Although controversial, hypokalemia (LK) in patients with acute myocardial infarction (MI) is thought to predict increased in-hospital morbidity, [...]