Myocardial response to acetyl strophanthidin in congestive heart failure; a study of electrolytes and carbohydrate substrates

Effect of digoxin upon intracellular potassium in man

The effect of digoxin upon intramuscular potassium was studied by use of whole body counting and biopsy technique. Twelve healthy subjects and twelve outpatients with mild cardiac insufficiency or atrial arrhythmia were digitalised. Before and after digitalization total body potassium (TBK) was measured. Potassium concentration in muscle specimens (MK) was analysed by the neutron activation technique. Digoxin was measured in serum and in skeletal muscle tissue by radioimmunoassay, and QS2-index as a measure of the electromechanical systole. In both groups a significant decrease in TBK (P less than 0.05) and MK (P less than 0.01) was demonstrated in connection to digitalization. There was no correlation between the decrease in TBK and MK, or between the concentrations of digoxin in serum or muscle and the decrease in potassium concentration. The digoxin in serum in healthy subjects was 0.9 +/- 0.33 nmol/l and in patients 1.2 +/- 0.41 nmol/l. The digoxin in muscle was 39 +/- 10.9 nmol/kg dry weight in seven of the healthy individuals and 37 +/- 9.5 nmol/kg dry weight in nine patients. After digitalization a decrease of QS2-index was found in both groups (P less than 0.01).

[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.

Effects of ouabain on myocardial potassium and sodium balance in man

Myocardial electrolyte balance and hemodynamics were studied in 14 patients before and after the administration of ouabain. The drug caused a significant loss of potassium from the myocardium. This was accompanied by a significant positive inotropic response, indicated by an increase in the rate of rise of left ventricular pressure and systolic ejection-rate index. Heart rate, cardiac output, left ventricular end-diastolic pressure, brachial artery pressure, and left ventricular stroke-work index remained unchanged. These observations in man are compatible with those theories of digitalis action which associate inotropic effect with the inhibition of membrane sodium- and potassium-activated adenosine triphosphatase.

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.

Effects of Digitalis Upon Body Electrolytes

Studies of the electrolyte alterations in 54 dogs during 165 discrete digitalizations with acetyl strophantbidin to an endpoint of ventricular tachycardia are reported. In 94 per cent of digitalizatious, increase in arterial potassium concentration occurred. This was noted as early as five niinutes after drug administration. At the time of ventricular tachycardia, the increase was 0.67 mEq./L. When digitalization was carried to ventricular fibrillation, the increase was 3.1 mEq./L. In 75.5 per cent of the digitalizations, arterial sodium concentration decreased; average de crease was 2.6 mEq./L. At ventricular fibril lation, the decrease amounted to 11.0 mEq./L. Arterial calcium concentration and oxygen saturation were not altered. There was a modest decrease in CO 2 content and an increase in arterial pH and hcmatoerit. Peaking of the late portion of the T wave was common during acute digitalization and correlated with the increase in extracellular potassium concentration. The relationship of the electrolyte changes to the process of digitalization is discussed.