Exchangeable potassium in heart disease: long-term effects of potassium supplements and amiloride

Fiftieth anniversary of aldosterone: from discovery to cardiovascular therapy

Half a century after the elucidation of its molecular structure, aldosterone is generating the greatest interest, not in the fields of endocrinology or renal medicine but in cardiology-where aldosterone over-activation is now perceived as detrimental in heart failure (HF) and ischaemic heart disease. Clinically, excess aldosterone is associated with higher morbidity and mortality after myocardial infarction (MI) and HF. The Randomised Aldactone Evaluation Study (RALES) study in severe chronic heart failure and the Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival (EPHESUS) study in post-MI heart failure have shown that use of non-selective and selective aldosterone receptor antagonists, respectively, improves prognosis. The pathophysiological mechanisms underpinning these damaging aldosterone-mediated cardiovascular effects are still being elucidated, but prime candidates include cardiomyocyte necrosis and apoptosis, and myocardial fibrosis resulting in adverse cardiac remodelling, coronary vasculopathy, tachyarrhythmia and positive feedback activation of the renin-angiotensin-aldosterone system. Practical points for consideration when instigating therapy include preferential use of aldosterone receptor antagonists to maintain electrolyte balance whenever loop or thiazide diuretics are used (vulnerable HF patients require higher ranges of potassium and magnesium to minimise propensity for tachyarrthythmia), for renoprotection and for counteracting aldosterone breakthrough despite adequate ACE inhibition; use of the minimum doses of loop diuretics required to lessen activation of the renin-angiotensin-aldosterone system in HF; use of selective aldosterone receptor antagonists to avoid gynaecomastia/mastalgia and impotence; and prophylactic use of aldosterone receptor antagonists to improve prognosis.

Electrocardiographic changes associated with acute cerebrovascular disease: a clinical review

Patients with acute vascular disorders of the CNS demonstrate an abundance of both rhythm and morphologic changes in their ECG. Of these a few will demonstrate myocardial dysfunction and or damage. The value of the ECG in evaluating and predicting which patients will have myocardial dysfunction or damage is questionable. One would assume the echocardiogram would be of more help than the ECG in identifying patients with myocardial damage; however, little data are available. The reason for the poor correlation between ECG findings and clinical correlates has not been explained to date, but it is possible to postulate a theory. There are two mechanisms that might mediate ECG changes in these patients, ie, autonomic neural stimulation from the hypothalamus or elevated circulating catecholamines. Hypothalamic stimulation may cause ECG changes without associated myocardial damage whereas elevated catecholamines may result in myocardial damage. This might explain why so many patients have ECG changes and very few have demonstrable myocardial damage in general, or ischemic damage in particular. That cardiac antiischemic therapy does not change mortality may relate to the fact that treatment has been directed towards patients with ECG changes, which in turn do not correlate with myocardial damage. Better patient selection for such therapy might rest upon demonstration of wall motion abnormalities on echocardiogram. The weakness of this strategy is that many patients with stroke have preexisting coronary disease and wall motion abnormalities and thus echo findings may only document remote infarction rather than acute ischemia.

Mechanism of action, pharmacokinetics, adverse effects, and therapeutic uses of amiloride hydrochloride, a new potassium-sparing diuretic

Amiloride hydrochloride is a new, orally administered, potassium-sparing diuretic with mild natriuretic and diuretic properties. Its primary site of action is the distal tubule of the nephron where it selectively blocks sodium transport, thereby inhibiting sodium-potassium exchange. The mechanism of action of amiloride is independent of aldosterone. It is excreted unmetabolized in the urine and feces. Peak serum levels are seen at three hours, and the serum half-life is six hours. The drug can probably be safely administered to patients with hepatic dysfunction but should be used cautiously, if at all, in patients with renal insufficiency. Amiloride is well tolerated, and serious toxicity is rare. It should prove useful in edematous states and hypertension. When amiloride is used in fixed combination with a thiazide diuretic the risk of hypokalemia is minimal.

Relation of plasma aldosterone concentration to diuretic treatment in patients with severe heart disease

To assess the relation of hyperaldosteronism and potassium depletion to the intensity of diuretic therapy we have measured plasma aldosterone by radioimmunoassay and total exchangeable potassium by radioisotope dilution in 24 patients when they were stable at the end of their preparation for cardiac operation. Some patients required intensive frusemide therapy to reach an optimal state for operation and many showed hyperaldosteronism. Plasma aldosterone was significantly related to daily dose of frusemide (r=0.77). Depletion of total exchangeable potassium expressed in terms of predicted weight was significantly related to plasma aldosterone (r= -0.64). The reduction in total exchangeable potassium is interpreted as chiefly related to loss of lean tissue mass from the wasting that leads to cardiac cachexia, but evidence is presented on the basis of measurements of extracellular fluid volume as sulphate space (20 patients) of entry of sodium into the cells which may indicate a true cellular potassium loss. Although plasma potassium is usually easily maintained with oral potassium supplements or aldosterone antagonists, we postulate that intensive diuretic therapy in severe heart disease may provoke hyperaldosteronism which accentuates potassium loss and may contribute to wasting and to intracellular potassium depletion in critical tissue, such as myocardium.

Urinary electrolyte profiles after amiloride, hydrochlorthiazide and the combination

Acute effects of amiloride (5 mg) (A), hydrochlorthiazide (50 mg) (H) and the combination (50 + 5 mg) (HA) on urinary electrolyte excretion and pH of ten healthy volunteers--taking placebo five times and twice randomly A and HA and once H--were studied during one day. Amiloride showed a natriuretic effect, which in combination was additive to that of hydrochlorthiazide, but the excretion of water did not increase significantly after A. The urinary excretion of potassium decreased with amiloride below normal levels and was at the level of placebo after the combination (HA). There was a striking linear correlation between urinary sodium and potassium with all the drugs, although showing with A a higher potassium retention during high sodium excretion. Urinary pH rose after A and HA during the first 8 hours, but this effect was not seen, however, after H. No significant differences in the effect of the two brands of A (Medamor and Puritrid) on the urinary electrolyte excretion and pH, nor in those of the two brands of HA (Moduretic and Amitrid) were found. Similarly, the plasma concentrations of hydrochlorthiazide, determined gas chromatographically, were equal after Moduretic and Amitrid tablets. The systemic availability of H was faster in the combination of HA than alone. In the AUC value of H, however, there was no significant difference between HA and H tablets.

Effect of long-term diuretic treatment on body-potassium in heart-disease

Plasma and total body potassium have been measured in 151 patients with chronic heart-disease, 83 of whom were taking diuretics and potassium supplements. After allowance for age and body-size, the deficit in total body-potassium was only 3-5% (100-150 mmol) in the diuretic group. 13 of the 83 patients taking diuretic had hypokalaemia (less than 3-5 mmol/1) but the potassium deficit was no greater than in the patients with normal plasma-potassium. There was no relation between the dose of potassium supplements and either the plasma-potassium or the total body-potasium. It is suggested that potassium depletion is not a major problem in patients with heart-failure treated with diuretics. The dose of potassium supplements should therefore be determined entirely by the plasma-potassium.

Effect of potassium-sparing diuretics on the renin-angiotensin-aldosterone system and potassium retention in heart failure

The renin-angiotensin-aldosterone system and electrolyte levels in 11 patients with heart failure controlled on digoxin and frusemide were investigated after separate periods of Slow K, spironolactone, and amiloride therapy. When spironolactone or amiloride replaced Slow K, distinct parallel increments in the levels of renin, angiotensin II, and aldosterone resulted. Though plasma potassium was generally higher after spironolactone and amiloride than after Slow K, exchangeable potassium was similar with the three regimens. There was no significant relation between plasma potassium and concurrent exchangeable potassium.