STUDIES IN CONGESTIVE HEART FAILURE: IV. The Potassium Content of Skeletal and Cardiac Muscle

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration-historical developments

This historical review traces key discoveries regarding K+ and Na+ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na+,K+-ATPase (NKA) and exercise effects on plasma [K+] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K+ loss and gains in Na+, Cl- and H20, then subsequently bidirectional muscle K+ and Na+ fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na+/K+ radioisotope fluxes, [3H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na+/K+ homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K+] falls by 21 mM (range - 13 to - 39 mM), interstitial [K+] increases to 12-13 mM, and plasma [K+] rises to 6-8 mM, whilst post-exercise plasma [K+] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [3H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α2 isoforms in rats. Acute or chronic exercise affects human muscle K+, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K+] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.

Studies on curative efficacy of monoterpene eugenol on anti- leukemic drug arsenic trioxide induced cardiotoxicity

BACKGROUND

Arsenic trioxide (As₂O₃) is emerging as a frontline agent for the treatment of acute promyelocytic leukemia (APL) but the therapeutic application is limited by its toxicity. QT prolongation, torsades de pointes and sudden cardiac death have been implicated in the As₂O₃ therapy. So eugenol is a monoterpene compound is well known for its antioxidant properties and protective effect on the cardiovascular system.

OBJECTIVE

In this study, the cardioprotective effect of eugenol on cardiac electrical conductivity, tissue electrolytes, myocardial markers, antioxidant system, lipid peroxidation and nitric oxide production was investigated in male Wistar rats treated with arsenic trioxide.

RESULTS

The Inductively coupled plasma emission spectroscopic (ICP-OES) analysis pointed out the accumulation of arsenic in heart tissue. The rats administered with arsenic trioxide (4mg/kg body wt) exhibited myocardial damage that was manifested by the elevation of cardiac markers (LDH, CK-MB) enzymes and deterioration in the antioxidant enzymes (GSH, GST, GPx). Combination treatment with eugenol (5mg/kg of body wt) upholds the tissue antioxidant level, Na⁺/K⁺ - ATPase and Ca^2+- ATPase activity and brings the cytosolic Ca^2+, K⁺ and Na ⁺ levels near to normal value. Conjoined therapy with eugenol ameliorated the membrane peroxidation, restored the normal heart rate and rectified the prolongation of QT interval in the electrocardiogram. Histological examination of cardiac segments also supported the beneficial role of eugenol against arsenic-induced oxidative damages.

CONCLUSION

Our in vivo experimental findings suggest that monoterpenoid eugenol could be a potent and novel cytoprotective agent of clinical application against As₂O₃ induced cardiotoxicity.

Current Perspectives of Electrical Remodeling and Its Therapeutic Implications

Electrical remodeling involves alterations in the electrophysiologic milieu of myocardium in various disease states, such as ventricular hypertrophy, heart failure, atrial tachyarrhythmias, myocardial ischemia, and infarction that are associated with cardiac arrhythmias. Although research in this area dates back to early part of the 19th century, we still lack the exact knowledge of ionic remodeling, the role of various genes and channel proteins, and their relevance for the newer antiarrhythmic therapies. Structural remodeling may also have an impact on the electrical remodeling process, although differences in both structural and electrical remodeling are associated with different disease states. Various electrophysiologic, cellular, and structural alterations, including anisotropic conduction, increased intracellular calcium levels, and gap junction remodeling predispose to increased dispersion of action potential duration and refractoriness. This constitutes a favorable substrate for early and late afterdepolarizations and reentrant arrhythmias. Studying the role of ionic remodeling in the initiation and propagation of cardiac arrhythmias has significant relevance for developing newer antiarrhythmic therapies, for identifying patients at risk of developing fatal arrhythmias, and for implementing effective preventive measures. Further research is required to understand the specific effects of individual ion channel remodeling, to understand the signal transduction mechanisms, and to address whether detrimental effects of electrical remodeling can be altered.

Sailing between Scylla and Charybdis: the high serum K-low dialysate K quandary

In HD patients, the optimal choice of dialysate K concentration is of paramount importance. Recent large observational studies have documented an association between low dialysate K concentration (< 2 or even <3 mEq/L) and a higher risk of sudden death. In this review, we first briefly discuss the available data concerning the link between hypokalemia and negative outcomes in non-CKD populations, especially after an acute myocardial infarction or in congestive heart failure. We next review the pathophysiology of the arrhythmogenic effect related to K fluxes during HD and discuss the dialytic strategies aiming at making potassium fall more gradual and thus at reducing the electrical disturbances triggered by the HD session. We conclude with practical recommendations regarding the optimal choice of K bath and the importance of more frequent monitoring of serum K in some clinical scenarios.

Serum potassium levels and its variability in incident peritoneal dialysis patients: associations with mortality

Background

Abnormal serum potassium is associated with an increased risk of mortality in dialysis patients. However, the impacts of serum potassium levels on short- and long-term mortality and association of potassium variability with death in peritoneal dialysis (PD) patients are uncertain.

Methods

We examined mortality-predictability of serum potassium at baseline and its variability in PD patients treated in our center January 2006 through December 2010 with follow-up through December 2012. The hazard ratios (HRs) were used to assess the relationship between baseline potassium levels and short-term (≤1 year) as well as long-term (>1 year) survival. Variability of serum potassium was defined as the coefficient of variation of serum potassium (CVSP) during the first year of PD.

Results

A total of 886 incident PD patients were enrolled, with 248 patients (27.9%) presented hypokalemia (serum potassium <3.5 mEq/L). During a median follow-up of 31 months (range: 0.5–81.0 months), adjusted all-cause mortality hazard ratio (HR) and 95% confidence interval (CI) for baseline serum potassium of <3.0, 3.0 to <3.5, 3.5 to <4.0, 4.5 to <5.0, and ≥5.0 mEq/L, compared with 4.0 to <4.5 (reference), were 1.79 (1.02–3.14), 1.15 (0.72–1.86), 1.31 (0.82–2.08), 1.33 (0.71–2.48), 1.28 (0.53–3.10), respectively. The increased risk of lower potassium with mortality was evident during the first year of follow-up, but vanished thereafter. Adjusted all-cause mortality HR for CVSP increments of 7.5% to <12.0%; 12.0% to <16.7% and ≥16.7%, compared with <7.5% (reference), were 1.35 (0.67–2.71), 2.00 (1.05–3.83) and 2.18 (1.18–4.05), respectively. Similar association was found between serum potassium levels and its variability and cardiovascular mortality.

Conclusions

A lower serum potassium level was associated with all-cause and cardiovascular mortality during the first year of follow-up in incident PD patients. In addition, higher variability of serum potassium levels conferred an increased risk of death in this population.

Hypokalemia and sudden cardiac death

Worldwide, approximately three million people suffer sudden cardiac death annually. These deaths often emerge from a complex interplay of substrates and triggers. Disturbed potassium homeostasis among heart cells is an example of such a trigger. Thus, hypokalemia and, also, more transient reductions in plasma potassium concentration are of importance. Hypokalemia is present in 7% to 17% of patients with cardiovascular disease. Furthermore, up to 20% of hospitalized patients and up to 40% of patients on diuretics suffer from hypokalemia. Importantly, inadequate management of hypokalemia was found in 24% of hospitalized patients. Hypokalemia is associated with increased risk of arrhythmia in patients with cardiovascular disease, as well as increased all-cause mortality, cardiovascular mortality and heart failure mortality by up to 10-fold. Long-term potassium homeostasis depends on renal potassium excretion. However, skeletal muscles play an important role in short-term potassium homeostasis, primarily because skeletal muscles contain the largest single pool of potassium in the body. Moreover, due to the large number of Na(+)/K(+) pumps and K(+) channels, the skeletal muscles possess a huge capacity for potassium exchange. In cardiovascular patients, hypokalemia is often caused by nonpotassium-sparing diuretics, insufficient potassium intake and a shift of potassium into stores by increased potassium uptake stimulated by catecholamines, beta-adrenoceptor agonists and insulin. Interestingly, drugs with a proven significant positive effect on mortality and morbidity rates in heart failure patients all increase plasma potassium concentration. Thus, it may prove beneficial to pay more attention to hypokalemia and to maintain plasma potassium levels in the upper normal range. The more at risk of fatal arrhythmia and sudden cardiac death a patient is, the more attention should be given to the potassium homeostasis.

What is the optimal serum potassium level in cardiovascular patients?

Humans are prone to sodium overload and potassium depletion. This electrolyte imbalance is important in the pathogenesis of cardiovascular disease and sudden cardiac death. Avoiding hypokalemia is beneficial in several cardiovascular disease states including acute myocardial infarction, heart failure, and hypertension. The evidence highlighting the importance of potassium homeostasis in cardiovascular disease and possible mechanisms explaining potassium's benefits are reviewed. Targets for serum potassium concentration are suggested.

Ionic remodeling in the heart: pathophysiological significance and new therapeutic opportunities for atrial fibrillation

Heart disease has long been recognized to alter cardiac electrical function. Detailed studies of disease-induced remodeling of ionic transport processes that underlie ventricular electrophysiological alterations have been performed over the past 10 years, but our knowledge of atrial ionic remodeling is more limited and has emerged much more recently. The present review focuses on recent findings regarding ionic remodeling at the atrial level, particularly with respect to two conditions that promote atrial fibrillation (AF) in well-developed clinically relevant animal models: (1) sustained atrial tachycardia and (2) ventricular tachypacing-induced congestive heart failure. Complementary data from experimental models and from observations in atrial tissue samples from patients are examined critically and integrated. Consideration is also given to potential molecular mechanisms underlying remodeling, the relationship between atrial and ventricular ionic remodeling in response to similar stimuli, and the potential relevance of insights into ionic remodeling for understanding the pathophysiology of AF and developing improved therapeutic approaches.

Clinical relevance and management of the major electrolyte abnormalities in congestive heart failure: hyponatremia, hypokalemia, and hypomagnesemia

Electrolyte disturbances are a common complication of CHF. CHF provides a perfect milieu for the development of these disturbances; renal dysfunction, elevation of neurohormonal substances, activation of the renin-angiotensin-aldosterone axis, and diuretic therapy represent the major contributory factors. Hyponatremia is closely aligned with an unfavorable clinical course. Hypokalemia is associated with increased ventricular dysrhythmias. Hypomagnesemia noted in advanced CHF can be accompanied by arrhythmias and refractory hypokalemia. CHF also offers the ideal milieu (diseased, ischemic, and arrhythmogenic myocardium; elevated catecholamines; and arrhythmogenic drugs) for the threatening clinical consequences (clinical deterioration, dysrhythmias, or death) of these disturbances. These consequences underscore the importance of the recognition, appreciation, and management of these electrolyte abnormalities.

Potential role of potassium as a determinant of morbidity and mortality in patients with systemic hypertension and congestive heart failure

Prehistoric animals and humans consumed a diet low in sodium but high in potassium, and thus, evolutionary forces fostered the development of physiologic systems that conserved sodium and excreted potassium. With the advent of civilized societies, food cooking and processing have greatly increased the sodium but decreased the potassium content of the diet. However, there has been little time for physiologic systems to adapt. The resulting excess of sodium has been implicated as an important factor in the development of hypertension and congestive heart failure. This traditional focus on sodium has ignored the potential role that an inadequate dietary intake of potassium might play in the degenerative diseases of the heart, brain and kidney. Yet dietary potassium may be as powerful a determinant of cardiovascular morbidity and mortality as dietary sodium. In experimental and clinical hypertension, an increased intake of potassium (without a change in dietary sodium) can reduce blood pressure, may suppress the activity of the sympathetic nervous and renin-angiotensin systems, and can prevent the development of vascular injury; conversely, potassium depletion has been associated with an increase in stroke and sudden death. In patients with chronic heart failure, potassium can modify both the mechanical and electrical properties of the heart, it can exert diuretic effects, and it can reduce the frequency and complexity of potentially lethal ventricular tachyarrhythmias. Given this central role, the effects of many pharmacologic interventions on the morbidity and mortality of patients with hypertension or chronic heart failure can be enhanced or diminished by the effect that these treatments might have on potassium homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic digoxin treatment on cardiac function, electrolytes, and sarcolemmal ATPase in the canine failing heart due to chronic mitral regurgitation

This study was designed to determine whether digoxin therapy in the canine heart failing because of mitral regurgitation (MR) provides only hemodynamic benefit and accompanying subjective improvement or if it also reverses the changes in intracellular Ca++ and sarcolemmal Na+-K+-ATPase. The dogs were divided into four groups: control, MR of 3 months' duration, MR of 6 months', and digoxin treatment for 3 months after 3 months of MR. Six months of MR produced a marked decrease in the index of myocardial contractility and function associated with a decrease in intracellular Ca++ and Na+, and an increase in intracellular K+, extracellular space, sarcolemmal Na+-K+-ATPase, and Mg++-ATPase. Digoxin treatment tended to return the changes in the index of myocardial contractility and cardiac function, intracellular Ca++, Na+, K+, extracellular space, and sarcolemmal Na+-K+-ATPase of the failing heart toward control levels. Digoxin treatment did not affect Mg++-ATPase. The right ventricle, which did not fail, also did not show any significant changes in the parameters measured. The results showed that digoxin treatment not only improved the index of myocardial contractility and cardiac function of the failing heart but also tended to return the electrolytes and sarcolemmal Na+-K+-ATPase toward control levels.

[Influence of spirolactone on the myocardial potassium balance following strophanthin in man (author's transl)]

In order to examine the question, whether improved digitalis tolerance by Spirolactone may be partially a result of antagonism on myocardial potassium balance, 6 patients without clinical signs of heart failure were given 400 mg, 3 were given 200 or 300 mg Spirolactone orally daily and 6 patients received placebo during a 5 to 7 days period. During cardiac catheterization hemodynamics and serum potassium concentrations were determined repeatedly prior to and following intravenous administration of 0,375 to 0,625 mg Strophanthin. Injection of Strophanthin resulted in a significant drop in left ventricular enddiastolic pressure and a rise in dp/dt max. In the control group a significant increase in arterial and coronary sinus potassium concentration was observed. Myocardial potassium balance was definitely negative from the third to the eighth minute. Values in the group receiving Spirolactone did not differ significantly from the placebo group. It is suggested that therapeutic doses of Strophanthin resllt in a loss of potassium from the myocardium by inhibition of the Na+, K+ membrane ATPase not influenced by pretreatment with Spirolactone.

[Mineral content and morphology of heart muscle in different causes of death (author's transl)]

Mineral and water content of the right and left heart muscle were analyzed by atomic absorption spectrophotometry in 93 autopsy cases. Sodium, potassium, magnesium, and calcium concentrations were measured after acid digestion of tissues. Marked differences of the element distribution of both ventricles are seen constantly, although a significant correlation between water content and sodium as well as potassium and magnesium concentrations in both ventricles in seen. Comparing multiple causes of death (cardiac and non-cardiac) there are no differences in the postmortem mineral contents of heart muscle. Age-dependent correlations of mineral concentrations (as seen by Burger, 1960) were not detectable in this investigation. Postmortem mineral analyses of human heart muscles are excessively influenced by modern intensive care. Most of our cases had several causes of death, one of which was to be declared as the main cause of death in the necropsy record. Postmortem chemical mineral analysis of heart muscle can give an exact description of local variations and-in special cases-signs of general disorders of mineral metabolism, which are not detected by exclusively histologic investigations.

Depressed transmembrane potentials during experimentally induced ventricular failure in cats

Transmembrane potentials and isometric force were recorded in right ventricular muscles from cats with right ventricular failure 3-127 days after chronic partial pulmonary artery obstruction. For the majority of failed muscles (at 36°C, 30 stimuli/min), resting potential, action potential overshoot, action potential maximum rate of rise, isometric active force at optimal length (P o ), and dP/dt were decreased compared with the same parameters in normal muscles. Time to peak force and duration of contraction were unaltered. Action potential configuration was changed and action potential duration was lengthened in failed muscles. Epinephrine (10 -6 M) markedly increased P o and resting potential in severely depolarized failed muscles. These data suggest that electrical depression might exacerbate the contractile deficit in experimental chronic right ventricular failure.

Mechanism of norepinephrine depletion in experimental heart failure produced by aortic constriction in the guinea pig

The present study was undertaken to evaluate the influence of heart failure on the cardiac stores of norepinephrine, and to elucidate the mechanisms responsible for the changes observed. Congestive heart failure was produced in the guinea pig by supravalvular aortic constriction. Significant reductions in both the concentration and content of norepinephrine in the ventricles were observed, the magnitude of changes being related to the severity of the constriction. The renal concentration of norepinephrine was not usually affected. Infusions of large quantities of norepinephrine produced elevations of ventricular norepinephrine concentrations which were significantly less in guinea pigs with heart failure than in normal animals. Injections of lesser quantities of radioactive norepinephrine also resulted in smaller amounts of this material in the hearts of animals with failure. Measurement of the decay of specific activity indicated that heart failure did not alter the net turnover of norepinephrine in the left ventricle. From these findings it has been concluded that a defect in the uptake and/or retention of norepinephrine exists in these hearts and that this defect may be responsible for the depletion of norepinephrine.

Effect of Experimental Congestive Heart Failure and Acetyl Strophanthidin on Myocardial Electrolyte and Water Content

The syndrome of chronic congestive heart failure was produced in female dogs by progressive pulmonary artery constriction. A factorial experimental design, containing seven experiments of four dogs each, was employed. Each experiment was completed in one day and consisted of two groups of two dogs each, one group containing dogs with heart failure and the other, normal dogs. One animal from each group received intravenous acetyl strophanthidin, 0.015 mg/kg ascites-free weight, while the other was given an injection of inert material. The heart was quickly removed from the chest nine minutes after the injection and the right ventricle was taken for analysis. Previous work indicated that this dose of the drug produced and inotropic effect both in normal animals and in dogs with heart failure without producing digitalis toxicity.

The myocardium from animals with congestive heart failure contained significantly less potassium but more sodium, chloride, and water per kilogram of dry fat-free blood-free myocardium than the myocardium from normal dogs. The concentration of sodium plus potassium in tissue water was subnormal in failing hearts. The sodium and chloride composition of the fluid gained by failing hearts differed significantly from that of interstitial fluid.

Acetyl strophanthidin increased myocardial chloride and water. Although potassium in the myocardium was unchanged in treated control dogs, it increased significantly after acetyl strophanthidin in animals with heart failure.

The findings are consistent with myocardial cellular swelling in congestive heart failure. The quantity of blood in each kilogram of failing myocardial tissue was severely reduced, probably because of muscle fiber hypertrophy. The possibility is considered that this alteration, together with the increased tissue water, may lead to lowered oxygen tension in failing heart muscle.

It is suggested that digitalis exerts two opposing effects on ion transport through the myocardial cell membrane and that neither of these is fundamental to its inotropic action.

Exchangeable potassium content of the body in congestive failure; changes during treatment

The increase in body weight in congestive heart failure is generally attributed to the retention of sodium and water in the extracellular compartment. Important changes also occur in the intracellular space, particularly in the metabolism of potassium. The isotope-dilution technic permits more precise determination of the exchangeable potassium content of the body in congestive failure before and during diuresis. The results of 27 such determinations in 11 patients with congestive heart failure are correlated with the clinical status of the patient and the serum concentration.