STUDIES ON DIGITALIS. IV. OBSERVATIONS IN MAN ON THE EFFECTS OF DIGITALIS PREPARATIONS ON THE CONTRACTILITY OF THE NON-FAILING HEART AND ON TOTAL VASCULAR RESISTANCE

Qualitative and Quantitative Determination of Phytochemical Contents of Indigenous Nigerian Softwoods

The phytochemical contents of some milled Nigerian softwood chips were carried out in a quest to evaluate their potentials as sources of alternative medicine as well as uses in other industrial applications. The qualitative and quantitative analysis were ascertained. Tannin was found in all the Nigerian softwoods examined with the highest quantities obtained in Sterculia oblonga (1240 mg/100 g) and Barteria nigritiana (1230 mg/100 g). Highest quantities of alkaloid were obtained in Cordia millenii (11.2%) and Sterculia oblonga (10.4%). Barteria nigritiana (14.2%) and Moringa oleifera (12.2%) recorded more flavonoid content than other individual softwoods. Saponin was more in Anogeissus leiocarpus (12.5%) and Dichrostachys cinerea (9.8%). Oxalate was found to be higher in Combretodendron macrocarpum (5.84 g/100 g) and Glyphaea brevis (3.55 g/100 g). Pentaclethra macrophylla (890 mg/100 g) and Moringa oleifera (880 mg/100 g) contained more cyanogenic glycosides. Sacoglottis gabonensis (4.68 mg/g) and Pentaclethra macrophylla (4.04 mg/g) showed the highest contents of phenol, while more lipids (8% and 7.2%) were found in Anogeissus leiocarpus and Kaempferia galanga, respectively. The results showed that these Nigerian softwoods grains could be a source for the exploitation of these phytochemicals beneficial in the pharmaceutical and alternative medicine industries.

Effects of digoxin on muscle reflexes in normal humans

Blockade of the skeletal muscle Na(+)-K(+)-ATPase pump by digoxin could result in a more marked hyperkaliema during a forearm exercise, which in turn could stimulate the mechano- and metaboreceptors. In a randomized, double-blinded, placebo-controlled, and cross-over-design study, we measured mean blood pressure (MBP), heart rate (HR), ventilation (V(E)), oxygen saturation (SpO(2)), muscle sympathetic nerve activity (MSNA), venous plasma potassium and lactic acid during dynamic handgrip exercises, and local circulatory arrest in 11 healthy subjects. Digoxin enhanced MBP during exercise but not during the post-handgrip ischemia and had no effect on HR, V(E), SpO(2), and MSNA. Venous plasma potassium and lactic acid were also not affected by digoxin-induced skeletal muscle Na(+)-K(+)-ATPase blockade. We conclude that digoxin increased MBP during dynamic exercise in healthy humans, independently of changes in potassium and lactic acid. A modest direct sensitization of the muscle mechanoreceptors is unlikely and other mechanisms, independent of muscle reflexes and related to the inotropic effects of digoxin, might be implicated.

Hemodynamic and plasma atrial natriuretic peptide responses to acute digitalis therapy in patients with normal and impaired left ventricular function

BACKGROUND

Digitalis has a long history in the treatment of heart failure but its effects on cardiac hemodynamics and neurohormonal modulation are not well characterized.

AIMS

The purpose of this study was to evaluate the relationship between atrial natriuretic peptide (ANP) and the hemodynamic responses to acute digitalis administration in patients with normal and impaired left ventricular function (LVD).

METHODS AND RESULTS

Thirty patients were enrolled in the study, 20 with LVD (LVEF=22+/-8%) and 10 control subjects (LVEF=77+/-10%). Hemodynamics and plasma ANP concentrations were measured supine and with leg elevation before and after digitalis. In patients with normal ventricular function, the hemodynamic stress of leg elevation in the pre-digitalis state resulted in significant (P<0.05) increases in PAWP and MPAP. Digitalis administration in the supine position produced reductions in heart rate, PAWP, MPAP and CI; SVR was increased. In LVD patients leg elevation further increased PAWP, RAP and MPAP. Digitalis in the supine position, however, reduced RAP, MPAP and PAWP and increased CI. These improved hemodynamics were preserved during the stress of leg elevation. Leg elevation following digitalis resulted in increased ANP concentrations despite decreased cardiac filling pressures.

CONCLUSIONS

Acute digitalis administration results in hemodynamic improvement in LVD patients which may in part result from digitalis stimulated release of myocardial ANP under conditions of hemodynamic stress.

Pharmacological investigation on nigrescigenin-a cardenolide from Parquetina nigrescens (Afzel.) Bullock: comparative studies on cardiotonic effects of Parquetina nigrescens, g-strophanthin and noradrenaline in guinea-pig isolated atria

The cardiotonic and catecholamine-like effects of Parquetina nigrescens extract-induced contractile force of guinea-pig left and right atria were investigated in-vitro. Isometric contractions were recorded. P. nigrescens extract, 5-150 microg mL(-1), increased the force of contraction dose dependently in electrically driven left atria. The concentration of P. nigrescens extract producing 50% of the maximal effect (EC50 value) was 7.5 microg mL(-1). The positive inotropic response differed from that of g-strophanthin by its high rate of onset and its complete reversibility upon removal of the extract from the incubation medium. In spontaneously beating right atrial muscle, P. nigrescens extract increased the rate of contractions. Its positive chronotropic and inotropic effects were partly antagonized by propranolol and atenolol indicating the presence of an adrenergic acting principle in P. nigrescens extract. In contrast, the inotropic response to P. nigrescens extract could not be completely suppressed by beta-blocking agents, suggesting that the force of contraction is not only increased by a sympathomimetic ingredient of P. nigrescens extract but also by the cardenolides known to be present in P. nigrescens.

Studies on digitalis. VI. Reduction of the oxygen debt after exercise with digoxin in cardiac patients without heart failure

Three patients with acquired valvular heart disease and cardiac enlargement who were able to perform normal everyday activity without difficulty in the absence of digitalis therapy were exercised while receiving a placebo and again while receiving digoxin. Digoxin administration did not produce a significant change in body weight or in the subjective condition of the individuals. Varying degrees of exercise were performed on a treadmill in a Metabolic Chamber and oxygen consumption was measured cotinuously before, during, and after the period of exercise, utilizing a continuous gas flow paramagnetic oxygen analyzer. The oxygen debt that developed during digoxin administration was compared to that observed during placebo administration.

In all patients the oxygen debt was smaller during the period of digoxin administration, although the external work performed was identical. In the first patient, following a 7-minute walk, the oxygen debt was 53 per cent more and following a 10-minute walk it averaged 40 per cent more while not receiving digoxin than when receiving this drug. In the second subject the oxygen debt following a 7-minute walk was 34 per cent more and following 10-minute walk it averaged 74 per cent more when he was not receiving digoxin than when receiving this drug. In the third subject the oxygen debts were 46 per cent and 41 per cent greater following 10- and 15- minute walks respectively, when she was not receiving digoxin.

The accumulation of a smaller oxygen debt following exercise while these subjects were receiving digoxin indicates that the functional status of their circulatory system was improved by the drug. It would appear that digitalis administration is beneficial to at least some patients who have cardiac disease and enlarged hearts and some decrease in cardiac reserve without signs or symptoms of heart failure.

The short-term effects of digoxin in patients with right ventricular dysfunction from pulmonary hypertension

OBJECTIVE

Studies on the effects of digoxin in patients with right ventricular failure and normal left ventricular function have not been performed. We evaluated the short-term effects of digoxin administration in patients with primary pulmonary hypertension on hemodynamics, neurohormones, and baroreceptor responsiveness.

DESIGN

This was a prospective study with patients serving as their own controls.

SETTING

University Hospital Intensive Care Unit with central monitoring.

PATIENTS

Seventeen patients with primary pulmonary hypertension and symptomatic heart failure were enrolled.

INTERVENTIONS

Following baseline hemodynamics, neurohormonal samples were drawn and the heart rate response to change in blood pressure following a challenge of phenylephrine and nitroprusside were recorded. One mg of intravenous digoxin was given and the measurements repeated after 2 hours.

RESULTS

Following digoxin there was a significant increase in cardiac output (3.49+/-1.2 to 3.81+/-1.2 L/min., p=0.028), a significant fall in norepinephrine (680+/-89 to 580+/-85 pg/ml, p=.013), and a significant increase in atrial natriuretic peptide (311+/-44 to 421+/-9 pg/ml, p=0.01). All of the patients had changes in heart rate and blood pressure following phenylephrine and nitroprusside challenge, but there was no significant difference in the change in heart rate response to change in blood pressure when rechallenged after digoxin treatment.

CONCLUSION

Digoxin produces a modest increase in cardiac output in patients with pulmonary hypertension and right ventricular failure, as well as a significant reduction in circulating norepinephrine. No detectable effects of digoxin on baroreceptor responsiveness were apparent. The use of digoxin in pulmonary hypertension is warranted.

Morphological studies on experimental oleander poisoning in cattle

Oleander poisoning has been reported in man and animals. The present experiments address the gross and microscopic changes due to oleander poisoning in cattle. Minimum lethal doses (50 mg/kg) of oleander leaves were orally administered to three calves in a single dose each of the other three animals received the same lethal dose in three equal parts with 24-h intervals. The lesions in the three animals which received 50 mg/kg in a single dose resulted from the direct effect of the toxin on the vascular endothelial bed and demonstrated as petechial and diffused haemorrhages, congestion, oedema, cell degeneration and inflammatory cell infiltration in the lungs, heart, mesentry, kidneys, serosal and mucosal surfaces of omasum, abomasum and the intestine. The lungs also showed atelectasis, emphysema and disseminated intravascular coagulation. On the other hand, the animals which received divided doses showed lesions due to long-term exposure to the toxic agent and/or as the result of tissue ischaemia. The lungs also showed cell necrosis and mononuclear cell infiltration in the interstitial tissue, and some of the cardiac muscle fibres rather showed fibromyolysis and cell infiltration between muscle fibres, epicardium and endocardium. The intestinal villi showed haemorrhagic, degenerative and necrotic changes and the eosinophils were infiltrated in mucosal and submucosal layers of this organ. Multifocal degenerative and necrotic changes with inflammatory cell infiltration were also present in the liver parenchyma.

Altered sodium-calcium exchange in afferent arterioles of the spontaneously hypertensive rat

Studies were performed to determine if there is a derangement in Na-Ca exchange activity in afferent (AA) and efferent (EA) arterioles from 3- and 9-week-old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Cytosolic calcium concentration ([Ca2+]i) was assessed using microscope-based photometry in fura-2 loaded arterioles bathed in a Ringer's solution. Baseline [Ca2+]i was similar in the AA of 3- and 9-week-old WKY and SHR. In AA from 3-week-old rats, [Ca2+]i increased by 89 +/- 15 nM in WKY and by 73 +/- 13 nM in SHR during decreases in bath sodium concentration ([Na+]e) from 150 to 2 mM (Na+ replaced with n-methyl-D-glucamine). In 9-week-old hypertensive SHR (SBP = 150 mm Hg), increases in [Ca2+]i were attenuated (24 +/- 3 nM) relative to 3-week-old WKY and SHR, and 9-week-old WKY (90 +/- 9 nM; P < 0.05). Likewise, the rate of removal of Ca2+ in the continued presence of 2 mM Nae (Ca2+ sequestration and/or extrusion) was markedly reduced in AA of 9-week-old SHR (-0.15 +/- 0.03 nM/second) versus 3-week-old SHR (-0.72 +/- 0.12 nM/second) and 3- and 9-week-old WKY (-0.49 +/- 0.10 and -0.67 +/- 0.14 nM/second). In other experiments, AAs were preincubated in 1 mM ouabain to increase intracellular [Na+]. This maneuver augmented the increase in [Ca2+]i obtained with removal of Na+e; however, the responses obtained in 9-week-old SHR arterioles were still attenuated compared to those obtained in arterioles for 3- and 9-week-old WKY and 3-week-old SHR. These results suggest that exchanger number and/or sensitivity to the transmembrane Na gradient was reduced in the SHR AA. In EA, baseline [Ca2+]i was similar in 3- and 9-week-old WKY and SHR. In contrast to AA, the magnitude of Na-dependent and Na-independent changes in [Ca2+]i was not different in the EA of 3- and 9-week-old WKY and SHR. These results indicate that regulation of Na-Ca exchange activity may differ between AA and EA segments. Furthermore, diminished Na-Ca exchange and Na-independent Ca2+ sequestering/extrusion mechanisms could contribute to altered AA [Ca2+]i in the SHR.

Inotropic therapy for the failing myocardium

Congestive heart failure (CHF) is a common clinical entity with diverse causes. Patients may present with acute decompensation or have a more indolent course, with diminishing exercise tolerance and increasing dyspnea. The management of this clinical entity traditionally has focused on restricting fluid intake, decreasing dietary sodium, decreasing afterload with vasodilatory agents, and supporting the failing myocardium with agents which produce a positive inotropic response. In the acutely decompensated patient, short-term therapy with positive inotropics is clearly beneficial. The role of long-term inotropic therapy for chronic CHF remains less clear. A number of clinical trials have recently evaluated the effects of long-term therapy on morbidity and mortality, with disappointing results. For a number of the newer, nonglycocide oral positive inotropics, at doses of drug which produce measurable hemodynamic improvement, increased mortality in treatment groups has been unacceptably high. Ironically, patients with worse left ventricular dysfunction show the most clinical improvement, but have the highest increased mortality. However, as with digoxin, there is some evidence that employing lower doses of drug that do not produce measurable improvement in hemodynamic parameters may result in both improved clinical state and decreased mortality. This review discusses the role of both oral and intravenous inotropic agents, discusses the difficulty in translating short-term hemodynamic improvement into long-term clinical benefit, and presents a rationale for the use of lower-dose inotropic therapy to improve long-term clinical outcome.

Effects of intravenous digoxin on pulmonary venous and transmitral flows in patients with chronic heart failure of different degrees

Acute effects of digoxin on diastole were evaluated noninvasively by combining data simultaneously obtained by Doppler echocardiograms (echo-Doppler) of transmitral and pulmonary venous flow curves in 38 patients with dilated and failing hearts, who had been stable for at least 7 days before the study. According to the resting ejection fraction (EF), patients were subdivided into Group 1 (EF < 30%: n = 20, mean EF values 23 +/- 8%) and Group 2 (EF > or = 30%: n = 18, mean EF values 40 +/- 3%). Significant differences were observed at rest between the two groups in both transmitral (shorter deceleration time and isovolumic relaxation time and increased peak E and E/A ratio in Group 1 vs. Group 2) and transpulmonary (reduced systolic forward component and systolic fraction of the flow curves in Group 1 compared with Group 2 and control subjects) parameters. Digoxin (1 mg subdivided into two doses, each infused over a 15-min period with 2 h between the doses) significantly modified the diastolic profile in Group 1 patients in the absence of statistically relevant changes in EF: a significant decrease of transmitral peak E (from 76 +/- 17 to 60 +/- 15 cm/s, p < 0.05) and E/A ratio (from 2.5 +/- 1 to 1.6 +/- 0.6; p < 0.05) and a significant lengthening of deceleration time (from 115 +/- 20 to 160 +/- 18 ms; p < 0.05) were detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Digitalis and heart failure: does digitalis really produce beneficial effects through a positive inotropic action?

Although digitalis was introduced to medicine long ago, the drug is still extensively used in clinical practice today. Opinions on its mechanism of action have undergone much change in the course of time, and the way in which cardiovascular effects are produced is still not completely clear. Limitations and contraindications for the use of digitalis substances are reported, especially in the treatment of ischemic heart disease. Preliminary data regarding the effects of digitalis on the diastolic phase are unfavorable, although the relationship between digitalis and diastolic function ought to be studied in greater depth in various clinical conditions. In spite of many recent trials, the old question of the usefulness of digitalis in the chronic treatment of patients in sinus rhythm and heart failure is still debated. An important clinical benefit in the chronic use of digitalis appears restricted to a relatively small proportion of patients with severe congestive heart failure, while in the majority of chronically treated subjects the effects of the drug are scanty or insignificant. The beneficial effect of digitalis used chronically is essentially believed to be due to its positive inotropic action. Since the vagomimetic and the antiadrenergic effects of digitalis have been demonstrated to be independent from its inotropic action, they could be considered determinants of the clinical benefits of digitalis. These indirect effects may be useful in the control of the negative neuroendocrine response developing during congestive heart failure. Thus the statement that digitalis is essentially an inotropic agent seems restrictive; its definition should reflect the favorable effects obtained in some cases of congestive heart failure rather than its various and contrasting underlying mechanisms of action.

Review of randomized trials of digoxin therapy in patients with chronic heart failure

Although digitalis glycosides were introduced in the treatment of cardiac maladies greater than 200 years ago, controversy persists regarding the precise role of digoxin in any multidrug approach to the treatment of congestive heart failure (CHF). Despite its widespread use for more than 2 centuries, only recently have double-blind, randomized, placebo-controlled trials of digoxin therapy been conducted in patients with moderate CHF and sinus rhythm. These trials demonstrate that digoxin is superior to placebo in improving left ventricular (LV) ejection fraction, increasing exercise capacity, and preventing CHF worsening. Digoxin produces benefits similar to those seen with angiotensin converting enzyme (ACE) inhibitors with regard to clinical compensation and improvement in LV function. However, improved survival is demonstrated only in response to ACE inhibitors. The recently completed RADIANCE study addresses the value of combining digoxin with ACE inhibitor therapy in patients with mild-to-moderate CHF. Because increased mortality has been reported with the newer oral inotropic agents, it currently appears that digoxin is the only oral inotropic agent useful in clinical practice in the treatment of CHF. However, the effects of digoxin on mortality in patients with CHF remain unknown. In the large, double-blind, randomized trial conducted by the National Heart, Lung, and Blood Institute, the effects of digoxin on mortality in patients with CHF and already being treated with ACE inhibitors are currently being evaluated. Presently, based on the results of placebo-controlled studies, it appears that digoxin, alone or in combination with ACE inhibitors, is beneficial in patients with any signs or symptoms of CHF due to systolic LV dysfunction.

Acute hemodynamic effects of digoxin alone or in combination with other vasoactive agents in patients with congestive heart failure

Although digitalis preparations have been in use for greater than 200 years, it is only within the last 2 decades that the central hemodynamic and neurohumoral effects occurring over several hours following intravenous administration of digoxin have been investigated in patients with congestive heart failure (CHF). Although digoxin has been shown to stimulate myocardial contractility in tissue preparations, its positive inotropic activity does not consistently translate into improvements in hemodynamic measurements in humans. Digoxin given intravenously results in increased cardiac index and decreased heart rate, left ventricular filling pressure, and right atrial pressure, as well as in acute attenuation of neurohumoral abnormalities, in patients with chronic CHF who have abnormal baseline hemodynamic measurements. Unlike other drugs with positive inotropic activity, however, digoxin does not influence hemodynamics in normal volunteers or in CHF patients in whom hemodynamics have been normalized with other therapies. These differing effects may be related to the drug's diverse peripheral vascular effects in CHF patients in whom vasodilation may occur in comparison with those that occur in normal subjects in whom the peripheral vasoconstrictor effects may prevent the inotropic effects of the drug from being translated into an increase in cardiac output. The hemodynamic effects of digoxin in patients with chronic CHF due primarily to diastolic dysfunction have not been fully investigated. Intravenous digoxin produces hemodynamic effects in patients with CHF associated with acute myocardial infarction, but these changes are small compared with those resulting from the administration of dobutamine. Digoxin does not appear to influence hemodynamic measurements in patients with right ventricular dysfunction unless concomitant left ventricular failure is present. In patients with chronic left ventricular dysfunction, the hemodynamic effects of intravenous digoxin and vasodilators are enhanced when these agents are given in combination.

Control of arteriolar resistance in heart failure. Partial attenuation of specific phosphodiesterase inhibitor-mediated vasodilation by digitalis glycosides

BACKGROUND

The vasodilatory response to local specific type III phosphodiesterase inhibition with amrinone was evaluated before and immediately after local administration of digoxin in 14 patients with severe congestive heart failure (CHF).

METHODS AND RESULTS

A 3F polyethylene catheter was inserted into the common femoral artery for drug administration and pressure monitoring. Mean blood flow velocity (MBFV) was continuously determined in the superficial femoral artery by transcutaneous Doppler ultrasonography. After intra-arterial administration of 10 mg amrinone, group MBFV increased from 7.7 +/- 1.4 to 16.0 +/- 2.1 cm/sec (p less than 0.05, n = 10). Local administration of 20 micrograms digoxin, which was infused over 20 minutes, did not alter group MBFV (i.e., 8.2 +/- 1.6 versus 7.6 +/- 1.5 cm/sec; p = NS, n = 10). The second administration of 10 mg amrinone, which immediately followed completion of local digoxin infusion, increased group MBFV but to a lesser extent than that produced by the first amrinone administration (i.e., 11.9 +/- 1.9 versus 16.0 +/- 2.1 cm/sec; p less than 0.05, n = 10). When placebo was administered instead of digoxin, group MBFV was similar after the first and second administrations of amrinone (i.e., 15.3 +/- 3.3 versus 15.6 +/- 3.8 cm/sec; p = NS, n = 4).

CONCLUSIONS

Although local administration of digoxin did not significantly alter baseline vascular tone in patients with CHF, it substantially decreased the direct vasodilatory effect induced by specific type III phosphodiesterase with amrinone.

Acute myocardial uptake of digoxin in humans: correlation with hemodynamic and electrocardiographic effects

Acute myocardial uptake of digoxin was measured at a constant paced heart rate (75 beats/min) for 30 min after an intravenous bolus injection of 500 micrograms of digoxin in 14 patients with ischemic heart disease. Myocardial digoxin content, determined by serial measurement of aortocoronary sinus digoxin concentration gradients and coronary sinus blood flow, was expressed relative to coronary sinus blood flow at rest and correlated with simultaneous hemodynamic and electrocardiographic changes. Myocardial digoxin uptake was extensive (4.1 +/- 0.7% of total injected dose at 30 min) and prolonged, with rapid initial uptake (75.3 +/- 6.6% of maximum at 3 min), followed by a variable phase of slower accumulation. Peak left ventricular positive first derivative of left ventricular pressure (dP/dt) increased progressively (p less than 0.01), with a similar time course to that of myocardial digoxin accumulation; maximal change was 18.5 +/- 4.7% at 27 min. The ratio of inotropic effect to myocardial digoxin content did not vary significantly over the period of the experiment. However, peak inotropic effects in individual patients were not significantly related to peak myocardial digoxin content. The spontaneous PR interval increased transiently, with a peak increase of 5.9 +/- 1.8% (p less than 0.05) 12 min after digoxin administration. It is concluded that after intravenous bolus administration, 1) peak effects of digoxin on atrioventricular (AV) conduction occur early, whereas positive inotropic effects increase progressively for greater than or equal to 27 min; and 2) digoxin accumulation in the human myocardium is prolonged and is a determinant of inotropic effects, but not of prolongation of AV node conduction.

Diltiazem attenuates the inotropic and peripheral vascular effects of cardiac glycosides

The influence of diltiazem on the hemodynamic effects of ouabain in 10 preinstrumented awake dogs was studied. Mean aortic pressure increased from 102 to 119 mm Hg with ouabain (p less than 0.05), an effect that was attenuated by pretreatment with diltiazem. The increase in systemic vascular resistance of 30% with ouabain was ablated by prior diltiazem. Heart rate did not significantly change with ouabain or with diltiazem plus ouabain, but intravenous diltiazem alone produced a reflex increase in heart rate of 26%. Left ventricular (LV) end-diastolic dimension was significantly greater with ouabain alone, but not with ouabain after pretreatment with diltiazem. LV dP/dt max increased by 40% with ouabain alone, but by only 23% (p less than 0.001) after pretreatment with diltiazem plus ouabain. When observed at matched preload and heart rate, diltiazem markedly attenuates the positive inotropic and peripheral arterial constrictive effects of acute ouabain administration in the conscious animal with normal LV function.

The use of inotropic agents in acute and chronic congestive heart failure

This article reviews our current understanding of the physiology of myocardial contraction; recent research into its mechanical, macromolecular, and biochemical foundations; and its role in the clinical syndromes of congestive heart failure. This review serves as a background for discussing the mechanism of action and pharmacology of currently available and experimental inotropic agents. The clinical applications of these drugs are discussed and the successes and failures of the pharmacologic approach to patients with congestive heart failure analyzed.

Comparative hemodynamic and neurohormonal effects of intravenous captopril and digoxin and their combinations in patients with severe heart failure

The effects of intravenous captopril and intravenous digoxin given separately and in combination on rest and exercise hemodynamics were studied in 16 patients with severe heart failure and sinus rhythm. When given separately, both captopril and digoxin decreased the pulmonary capillary wedge pressure by, respectively, 24% (p = 0.003) and 34% (p = 0.004) and systemic vascular resistance by 23% (p = 0.09) and 20% (p = 0.03). Only digoxin increased cardiac index by 23% (p = 0.03) and stroke work index by 52% (p = 0.01). During maximal exercise, captopril alone decreased systemic vascular resistance by 28% (p = 0.0002) and increased cardiac index by 33% (p = 0.02). Digoxin alone decreased pulmonary capillary wedge pressure by 11% (p = 0.04) and increased stroke work index by 44% (p = 0.01). The combination of captopril and digoxin resulted in a decrease in pulmonary capillary wedge pressure and systemic vascular resistance and an increase in cardiac index and stroke work index both at rest and during exercise that was greater than values observed with either drug given alone. Cardiac index response to the combination of captopril and digoxin correlated with baseline serum aldosterone concentration (r = 0.81, p less than 0.001) and plasma renin activity (r = 0.74, p less than 0.0002). A significant decrease in norepinephrine concentration was noted after digoxin was administered alone or added to captopril. These findings demonstrate that in patients with severe heart failure, the acute administration of captopril and digoxin has an independent salutary hemodynamic effect. The combination of these agents, however, has an adjunctive effect on cardiac function at rest and during exercise.

Digoxin--a redundant drug in congestive cardiac failure

Controversy continues concerning the use of digoxin as a positive inotropic agent in the treatment of heart failure in patients in sinus rhythm. Digoxin is properly used to control the heart rate in patients in atrial fibrillation. The findings from 14 uncontrolled and 6 controlled clinical trials have been examined. Digoxin does exert a small chronic positive inotropic effect. Although some individual patients, particularly those with fluid overload, appear to benefit from digoxin, controlled clinical trials in patients, most of whom have been treated with diuretics, have failed to demonstrate an increase of exercise capacity. No mortality trial has been attempted. Digoxin has the potential to be harmful in patients with ischemic heart disease. Alternative and safer therapies have been shown to be equal or superior to digoxin.

Na+-Ca2+ exchange in cultured vascular smooth muscle cells

Vascular smooth muscle cells (VSMC) contract as intracellular free calcium ([Ca2+]i) rises. While Na+-Ca2+ exchange has been proposed to contribute to transmembrane Ca2+ flux, its role in cultured VSMC is unknown. Accordingly, we have investigated the role of Na+-Ca2+ exchange in unidirectional and net transmembrane Ca2+ fluxes in cultured rat aortic VSMC under basal conditions and following agonist-mediated stimulation. Transmembrane Ca2+ uptake was significantly increased in response to a low external Na+ concentration ([Na+]o) compared with 140 mM [Na+]o. Na+-dependent Ca2+ uptake in response to low [Na+]o was further increased by intracellular Na+ loading by preincubation of the VSMC with 1 mM ouabain. Under steady-state conditions, Ca2+ content varied inversely with [Na+]o, increasing from 1.0 nmol Ca2+/mg protein at 140 mM [Na+]o to 4.0 nmol Ca2+/mg protein at 20 mM [Na+]o. Increasing [K+]o to 55 mM also enhanced Na+-dependent Ca2+ influx. Augmentation of Ca2+ uptake with K+ depolarization was not significantly inhibited by the calcium channel antagonist verapamil. Transmembrane Ca2+ efflux was increased in response to 130 mM [Na+]o compared with zero [Na+]o (iso-osmotic substitution with choline+), and was further stimulated by the vasoconstrictor angiotensin II, which is known to elevate [Ca2+]i. These changes in [Ca2+]i were studied directly using fura-2 fluorescence measurements. Elevated [Ca2+]i levels returned to baseline more rapidly in the presence of normal (130 mM) [Na+]o compared with zero [Na+]o (iso-osmotic substitution with choline+). These findings suggest that a bidirectional Na+-Ca2+ exchange mechanism is present in cultured rat aortic VSMC.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of digoxin on the heart in normal subjects: influence of isometric exercise and autonomic blockade: a noninvasive study

1. Eight healthy subjects were studied before digoxin and after successive therapy periods of 1 week 0.125, 0.25 and 0.50 mg of digoxin. The mean serum concentrations (+/- s. d.) were 0.4 +/- 0.2, 0.6 +/- 0.3 and 1.4 +/- 0.5 nmol l-1, respectively. The effects of digitalis were studied by echocardiography and systolic time intervals at rest and after 3 min handgrip exercise. Effects of simultaneous autonomic blockade induced by atropine and propranolol were also examined. 2. Digoxin in increasing doses slowed the heart rate at rest; with the daily dose of 0.50 mg from 63 +/- 10 to 53 +/- 6 beats min-1, and fractional shortening rose from 28 +/- 6 to 33 +/- 3% (P less than 0.05 for both). Preload, afterload and cardiac output did not change. The electromechanic systolic time index (QS2I) decreased (P less than 0.001) and the observed alteration of QS2I was dose-related. 3. The influence of digoxin was similar during isometric exercise, except for unchanged fractional shortening. 4. During autonomic blockade digoxin slowed the intrinsic heart rate from 93 +/- 6 to 86 +/- 6 beats min-1 (0.25 mg) and to 83 +/- 6 beats min-1 (0.50 mg) (P less than 0.01 for both). QS2I was shortened (P less than 0.01). Echocardiographically determined ejection phase indices remained unchanged. 5. When handgrip stress was induced during autonomic blockade, digoxin evoked a clearcut increase in contractile function, resembling the effects of digoxin alone at rest. Thus, fractional shortening increased by 14% and QS2I decreased by 16 ms (P less than 0.01 for both). 6. We conclude that digoxin increases the contractility in normal heart without changes in loading conditions. The rise in inotropy at rest is obvious from both fractional shortening by echo and systolic time intervals. The same takes place during handgrip with autonomic blockade, when the heart lacks sympathetic support. The influence of long-term digoxin on heart rate is partly direct without autonomic mediation. The effect of digoxin is dose-dependent.

Hemodynamic effects of intravenous digoxin in patients with severe heart failure initially treated with diuretics and vasodilators

The purpose of this study was to assess the hemodynamic effects of intravenous digoxin in patients with New York Heart Association class IV heart failure, who had never previously been treated with digitalis drugs, and who were initially treated only with diuretics and systemic vasodilators to clinical end points of compensation. Eleven male patients, 5 with idiopathic and 6 with ischemic cardiomyopathy, had sinus rhythm and were hospitalized with congestive heart failure not precipitated by an acute ischemic event. All 11 patients were treated with intravenous furosemide and various vasodilators without invasive hemodynamic monitoring for a mean period of 4.3 +/- 2.1 days. This therapy resulted in subjective and objective improvement in all patients as reflected by a significant decrease in heart failure score from 9.5 +/- 2.2 to 2.7 +/- 2.3 (p less than 0.001). When compensation was achieved by clinical criteria, the patients were instrumented and hemodynamics obtained before and serially thereafter for 6 hours after the intravenous administration of digoxin given in two 0.5 mg doses 2 hours apart. In response to digoxin, cardiac index increased from 2.6 +/- 0.7 liters/min per m2 to a peak of 3.3 +/- 0.6 liters/min per m2 (p less than 0.005); left ventricular stroke work index (g X m/m2) increased from 27 +/- 16 to 43 +/- 23 (p less than 0.005) and the ejection fraction (eight patients) increased from 21 +/- 13% to 29 +/- 11% (p less than 0.04). Mean pulmonary capillary wedge pressure decreased from 24 +/- 7 to a minimum of 17 +/- 4 mm Hg (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylstrophanthidin does not enhance the reflex pressor response to static muscular contraction

Cardiac glycosides have been shown to enhance the sensitivity of the reflex cardiovascular responses to stimulation of mechanoreceptors in the heart, carotid sinus and aorta. Little is known, however, about the effect of glycosides on the reflex cardiovascular responses to the contraction-induced stimulation of afferent endings in hindlimb skeletal muscle. We therefore examined the reflex heart rate and arterial pressure responses to static contraction of the hindlimb muscles before and after femoral arterial injection of two doses of acetylstrophanthidin (20 and 80 micrograms/kg). Neither of the two doses enhanced the reflex cardiovascular responses to contraction, although the larger of the two significantly increased femoral venous potassium concentrations from 3.4 +/- 0.2 to 3.8 +/- 0.1 mM. Although injection of the two doses as well as injection of a very large dose of acetylstrophanthidin (400 micrograms/kg) increased baseline mean arterial pressure, these effects were probably caused by the vasoconstrictor action of this agent and not by a chemoreflex, because the increase was not attenuated by denervation of the hindlimb.

Acute effects of digoxin on total systemic vascular resistance in congestive heart failure due to dilated cardiomyopathy: a hemodynamic-hormonal study

The effects of the digitalis glycosides on systemic vascular resistance (SVR) in patients with congestive heart failure (CHF) are controversial. Most investigators report a reduction in total SVR, an action that has been attributed primarily to withdrawal of elevated sympathetic tone. Direct proof of this hypothesis is lacking, however, and the roles played by the renin-angiotensin-aldosterone and vasopressin systems have not been fully explored. Moreover, in several studies of patients with CHF, SVR did not decrease after the administration of digitalis. To clarify these issues, the hemodynamic and hormonal effects of digoxin were correlated in 11 normotensive men in sinus rhythm with CHF due to dilated cardiomyopathy. Patients were evaluated at rest and during submaximal exercise before and 6 hours after the intravenous infusion of 1.0 mg of digoxin (mean serum concentration 1.7 ng/ml). With digoxin therapy, heart rate, pulmonary wedge pressure and right atrial pressure declined and cardiac output increased. Although vasopressin was unchanged, both plasma norepinephrine concentrations and plasma renin activity decreased, the reduction in norepinephrine correlating with the increase in cardiac output. Despite these hemodynamic and hormonal effects, there was no change in total SVR at rest or during exercise. It is concluded that the improvement in cardiac function with digoxin in this patient group was a result of the inotropic properties of the drug, without an associated reduction in impedance. The failure of total SVR to decrease despite decreases in plasma norepinephrine levels and plasma renin activity might be explained by concomitant digitalis-induced vasoconstriction, impaired ability of arterioles to dilate in CHF, or offsetting alterations in other vasoactive hormone systems.

Extracardiac and coronary vascular effects of digitalis

The administration of digitalis glycosides causes a variety of extracardiac effects. In both normal human subjects and in other species, digitalis increases smooth muscle tone of resistance and capacitance vessels. The vasoconstriction is mediated, in part, by a direct action of these glycosides on smooth muscle and, in part, by an increase in alpha-adrenergic tone. Constriction of coronary and splanchnic vessels may lead to myocardial or mesenteric ischemia. In contrast to normal subjects, patients with congestive heart failure demonstrate arteriolar and venodilation in response to these glycosides, possibly because the myocardial effect, to increase cardiac output and peripheral blood flow, overcomes the vasoconstrictor properties of these drugs. Other important actions of digitalis glycosides occur in the central and peripheral nervous systems. Their effects on the area postrema of the medulla oblongata are largely responsible for the alpha-adrenergic-mediated peripheral vasoconstriction, as well as the nausea and vomiting that frequently accompany digitalis intoxication. Actions of glycosides on the cerebral cortex are responsible for the wide range of neurotoxic effects that range from visual disturbances and headaches to seizures and coma. Finally, peripheral neurologic effects of digitalis glycosides on baroreceptor and cardiac afferent fibers may: improve the depressed function of these receptors in the situation of heart failure, and reflexly lower peripheral vascular resistance, thereby partially preventing the vascular constrictor action of these glycosides.

Effects of digitalis on the normal and the failing heart

Although it has been known for more than a century that digitalis glycosides exert a powerful beneficial effect on patients with heart failure, atrial fibrillation and a rapid ventricular rate, it was believed for many years that the drug exerts this clinical effect primarily by slowing the heart rate. It was also thought that the extra-cardiac vascular actions of digitalis might be responsible for its therapeutic effect. It has now been established that cardiac glycosides cause arteriolar and venous constriction in a variety of mammalian species including human beings, and that this vasoconstriction involves the coronary vascular bed as well, but it is believed that these actions are not responsible for any beneficial clinical effect. A variety of investigations on cardiac muscle in vitro, anesthetized and conscious dogs and anesthetized and conscious human subjects have shown that cardiac glycosides improve the contractility of failing mammalian myocardium. It has become clear that digitalis also stimulates the contractility of the nonfailing heart. The degree of augmentation of contractility induced by cardiac glycosides is related inversely to the baseline contractile state. Myocardial oxygen consumption, which is increased in the normal heart by the positive inotropic action of glycosides, is actually reduced or remains constant in the failing heart. Cardiac glycosides increase the contractility of the globally ischemic heart, but their actions in chronic ischemic heart disease with regional impairment of function are complex. Deterioration of segmental performance occurs in ischemic and necrotic segments, while improvement of contractility occurs in adjacent normal segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the role of sodium- and potassium-activated adenosine triphosphatase inhibition in the pathogenesis of human hypertension. Changes in vascular and cardiac function following inhibition of the sodium pump in normotensive subjects and effects of calcium entry blockade

An endogenous humoral factor which inhibits the sodium- and potassium-activated adenosine triphosphatase (Na-K-ATPase) enzyme in vitro has been incriminated recently of playing a pathogenetic role in experimental and human hypertension. The present study was therefore performed in six healthy volunteers to investigate the hemodynamic consequences of an inhibition of this enzyme by ouabain, a potent and specific inhibitor of Na-K-ATPase. In addition, the role of intracellular calcium as a potential mediator was studied indirectly by the administration of nifedipine, a potent calcium entry blocker with predominant vasodilator properties. Intravenous administration of 8.5 micrograms ouabain/kg body weight inhibited red blood cell (RBC) - Na-K-ATPase by 49% which was accompanied by a significant increase in RBC - ATP and a decrease in intracellular potassium concentrations. This enzyme inhibition resulted in a 24% increase in peripheral vascular resistance. The parallel decrease in cardiac output and heart rate, however, prevented a rise in arterial pressure. This increase in vascular resistance was completely abolished by pretreatment with nifedipine (10 mg orally). In the absence of an effect of nifedipine on Na-K-ATPase, its attenuation of the vasoconstrictor effect of ouabain suggests that the effects of ouabain on the vascular smooth muscle cell are mediated by intracellular calcium. These results demonstrate that inhibition of the Na-K-ATPase enzyme in vivo causes a marked peripheral vasoconstriction. They are also compatible with the concept that an endogenous inhibitor of Na-K-ATPase - in the presence of decreased baroreceptor reflex sensitivity due to blood volume expansion - may play a role in the pathogenesis of human arterial hypertension.

Effect of intravenous digitoxin on inotropy, haemodynamics and P-Q interval in ischaemic heart disease

The haemodynamic and electrophysiologic responses to rapid intravenous injection of digitoxin (0.6 mg over 5 min) were measured in 6 patients with chronic coronary heart disease without clinical heart failure. Two minutes after end of injection peripheral resistance increased and stroke volume fell, while peak dP/dt in the right ventricle showed minimal increase. AV nodal conduction velocity decreased markedly. Thereafter, the peripheral resistance remained unchanged, stroke volume and peak dP/dt in the right ventricle increased slightly, while AV conduction remained stable. In 2 control patients stable values were found during 60 min. We conclude that digitoxin given intravenously as a single bolus injection induces an abrupt slight increase in peripheral resistance. Thereafter, a gradual increase in inotropy is found. The effect on the AV node appears rapidly and remains stable.

Effects of acetyl-strophanthidin on left ventricular function and ventricular arrhythmias

Digitalis drugs can suppress ventricular arrhythmias. It is uncertain whether this effect results from improved left ventricular (LV) function. We utilized radionuclide scanning techniques to evaluate changes in LV ejection fraction (EF) after an infusion of acetyl-strophanthidin in 43 patients with frequent ventricular premature beats (VPBs) (44 to 2400/hr). Acetyl-strophanthidin suppressed ventricular arrhythmia in 17 patients, but LVEF increased in only six of these patients (57% to 67%), while it was unaltered in 11 patients (28% to 30%). In 26 patients ventricular arrhythmia was not suppressed. Fifteen of these patients had an increase in LVEF (60% vs 71%), while this was unchanged in 11 patients (27% vs 29%). Thus no correlation was observed between the positive inotropic and antiarrhythmic action of acetyl-strophanthidin on ventricular arrhythmia and LVEF. We conclude that the suppression of VPBs by acetyl-strophanthidin is independent of the drug's effects on LV function. Evidence is reviewed suggesting that the antiarrhythmic effect of acetyl-strophanthidin on ventricular ectopic activity is due to its vagotonic action.

The role of digitalis in the future

Cardiac glycosides exert an acute positive inotropic effect on the normal and failing heart. Recent evidence establishes that the positive inotropic effect is maintained over several months in many patients. The effectiveness of long-term treatment with cardiac glycosides in relieving symptoms is less certain; only a small subset of patients benefits. An effect on mortality is not established. The use of digoxin in the treatment of mild heart failure is questionable since the drug has serious side-effects and the efficacy in patients already taking diuretics has not been established. The use of glycosides in the treatment of severe chronic heart failure is being challenged because of the availability of powerful diuretics, new vasodilators and alternative positive inotropes.

Effects of discontinuing maintenance digoxin therapy in patients with ischemic heart disease and congestive heart failure in sinus rhythm

To evaluate the importance of oral maintenance digoxin therapy in chronic congestive heart failure (CHF), 24 patients in sinus rhythm on maintenance digoxin for documented CHF were studied prospectively on and off the drug. The average duration of therapy was 39 months (range 2 to 180). All 24 patients had documented coronary artery disease (CAD): 22 were in New York Heart Association functional class III and 2 in class II. Twenty-one patients (88%) were receiving diuretic or vasodilator therapy, or both, before digoxin discontinuance. At 1 month off digoxin and with no increase in doses of other medications excepting minor increases in antianginal therapy in 2 patients, no difference was observed in the group as a whole in symptoms, resting heart rate, arterial blood pressure, physical findings, weight, cardiothoracic ratio, radiographic signs of pulmonary congestion, radionuclide left ventricular ejection fraction (LVEF), duration of symptom-limited treadmill exercise (14 patients), or CHF score, compared with evaluation during maintenance digoxin therapy. Similar results were obtained in a subgroup of 9 patients with a resting LVEF less than 0.35 (0.27 +/- 0.02; mean +/- standard error of the mean). Six patients had a decrease and 5 patients an increase in LVEF of greater than or equal to 0.05 units after cessation of digoxin. Off digoxin, the CHF score increased by only 1 point in 2 patients, but also decreased in 2 patients. Thus, in this study population comprised of patients with CAD with documented CHF, most of whom were receiving diuretics or vasodilators, or both, digoxin withdrawal had no adverse clinical or hemodynamic effects.

Haemodynamic effects of calcium chloride administered intravenously to patients with and without cardiac disease during neurolept anaesthesia

During neurolept anaesthesia, calcium chloride (15 mg/kg) was administered intravenously to two different groups of patients undergoing vascular surgery on the abdominal aorta. The patients in group I all suffered from cardiac disease and were treated with digoxin, while the patients in group II had no cardiac symptoms. Cardiovascular measurements were made during steady-state anaesthesia. In group I, CaCl2 increased cardiac index (CI) significantly while systemic vascular resistance index (SVRI) remained unchanged. Mean arterial pressure (MAP) increased. In group II, both MAP and SVRI increased while CI remained unchanged. No significant changes in heart rate were observed and no arrhythmias occurred. It is concluded that CaCl2 administered intravenously is an effective means of improving cardiac function when it is depressed by anaesthesia, underlying cardiac disease, or both.

Failure of dobutamine to increase exercise capacity despite hemodynamic improvement in severe chronic heart failure

The acute hemodynamic and metabolic effects of dobutamine administered during exercise were studied in 8 patients with severe chronic heart failure. Exercise was performed on an upright bicycle ergometer using a graded protocol. During exercise performed without administration of dobutamine, exhaustion occurred after 4.5 +/- 1.2 minutes of exercise. The cardiac index increased from 1.61 +/- 0.25 to 2.67 +/- 0.59 liters/min/m2 (p less than 0.001), the arteriovenous oxygen difference from 7.8 +/- 1.7 to 12.5 +/- 2.4 ml/100 ml (p less than 0.001), and oxygen uptake from 7.9 +/- 3.0 to 41.2 +/- 15.7 mg/100 ml (p less than 0.001). During exercise performed with the administration of dobutamine, the cardiac index was significantly greater than during the control state, 3.23 +/- 0.78 versus 2.67 +/- 0.59 liters/min/m2 (p less than 0.001), while the arteriovenous oxygen difference was significantly lower, 11.2 +/- 2.1 vs 12.5 +/- 2.4 ml/100 ml (p less than 0.01). The arterial lactate level was not significantly changed, 45.3 +/- 17.6 versus 41.2 +/- 15.7 mg/100 ml. Although the dobutamine level tended to increase maximal oxygen uptake compared with the control period of exercise, 9.1 +/- 1.2 versus 8.5 +/- 1.4 ml/kg/min (p less than 0.05), it did not significantly increase exercise capacity, 4.8 +/- 1.5 versus 4.5 +/- 1.2 min. Thus administration of dobutamine in patients with severe chronic heart failure increased the cardiac index during maximal exercise but failed to increase exercise capacity. Since arteriovenous oxygen difference is reduced, dobutamine probably increases blood flow to the nonexercising tissues and not to the actively metabolizing muscles.