Digitalis Investigation Group (DIG) trial: a stimulus for further research

Whither digitalis? What we can still learn from cardiotonic steroids about heart failure and hypertension

Cloning of the "Na⁺ pump" (Na⁺,K⁺-ATPase or NKA) and identification of a circulating ligand, endogenous ouabain (EO), a cardiotonic steroid (CTS), triggered seminal discoveries regarding EO and its NKA receptor in cardiovascular function and the pathophysiology of heart failure (HF) and hypertension. Cardiotonic digitalis preparations were a preferred treatment for HF for two centuries, but digoxin was only marginally effective in a large clinical trial (1997). This led to diminished digoxin use. Missing from the trial, however, was any consideration that endogenous CTS might influence digitalis' efficacy. Digoxin, at therapeutic concentrations, acutely inhibits NKA but, remarkably, antagonizes ouabain's action. Prolonged treatment with ouabain, but not digoxin, causes hypertension in rodents; in this model, digoxin lowers blood pressure (BP). Furthermore, NKA-bound ouabain and digoxin modulate different protein kinase signaling pathways and have disparate long-term cardiovascular effects. Reports of "brain ouabain" led to the elucidation of a new, slow neuromodulatory pathway in the brain; locally generated EO and the α2 NKA isoform help regulate sympathetic drive to the heart and vasculature. The roles of EO and α2 NKA have been studied by EO assay, ouabain-resistant mutation of α2 NKA, and immunoneutralization of EO with ouabain-binding Fab fragments. The NKA α2 CTS binding site and its endogenous ligand are required for BP elevation in many common hypertension models and full expression of cardiac remodeling and dysfunction following pressure overload or myocardial infarction. Understanding how endogenous CTS impact hypertension and HF pathophysiology and therapy should foster reconsideration of digoxin's therapeutic utility.

The sodium pump and digitalis drugs: Dogmas and fallacies

The sodium pump (Na/K-ATPase) is a plasma membrane enzyme that transports Na+ and K+ against their physiological gradients in most eukaryotic cells. Besides pumping ions, the enzyme may also interact with neighboring proteins to activate cell signaling pathways that regulate cell growth. Digitalis drugs, useful for the treatment of heart failure and atrial arrhythmias, inhibit the pumping function of Na/K-ATPase and stimulate its signaling function. In the current field of research on the sodium pump and digitalis drugs, some issues that are commonly accepted to be well established are not so, and this may impede progress. Here, several such issues are identified, their histories are discussed, and their open discussions are urged. The covered unsettled questions consist of (a) the suggested hormonal role of endogenous digitalis compounds; (b) the specificity of Na/K-ATPase as the receptor for digitalis compounds; (c) the relevance of the positive inotropic action of digitalis to its use for the treatment of heart failure; (d) the conflicting findings on digitalis-induced signaling function of Na/K-ATPase; and (e) the uncertainties about the structure of Na/K-ATPase in the native cell membrane.

The pump, the exchanger, and the holy spirit: origins and 40-year evolution of ideas about the ouabain-Na+ pump endocrine system

Two prescient 1953 publications set the stage for the elucidation of a novel endocrine system: Schatzmann's report that cardiotonic steroids (CTSs) are all Na⁺ pump inhibitors, and Szent-Gyorgi's suggestion that there is an endogenous "missing screw" in heart failure that CTSs like digoxin may replace. In 1977 I postulated that an endogenous Na⁺ pump inhibitor acts as a natriuretic hormone and simultaneously elevates blood pressure (BP) in salt-dependent hypertension. This hypothesis was based on the idea that excess renal salt retention promoted the secretion of a CTS-like hormone that inhibits renal Na⁺ pumps and salt reabsorption. The hormone also inhibits arterial Na⁺ pumps, elevates myocyte Na⁺ and promotes Na/Ca exchanger-mediated Ca²⁺ gain. This enhances vasoconstriction and arterial tone-the hallmark of hypertension. Here I describe how those ideas led to the discovery that the CTS-like hormone is endogenous ouabain (EO), a key factor in the pathogenesis of hypertension and heart failure. Seminal observations that underlie the still-emerging picture of the EO-Na⁺ pump endocrine system in the physiology and pathophysiology of multiple organ systems are summarized. Milestones include: 1) cloning the Na⁺ pump isoforms and physiological studies of mutated pumps in mice; 2) discovery that Na⁺ pumps are also EO-triggered signaling molecules; 3) demonstration that ouabain, but not digoxin, is hypertensinogenic; 4) elucidation of EO's roles in kidney development and cardiovascular and renal physiology and pathophysiology; 5) discovery of "brain ouabain", a component of a novel hypothalamic neuromodulatory pathway; and 6) finding that EO and its brain receptors modulate behavior and learning.

Regenerative principles enrich cardiac rehabilitation practice

Cardiovascular morbidity imposes a high degree of disability and mortality, with limited therapeutic options available in end-stage disease. Integral to standard of care, cardiac rehabilitation aims on improving quality-of-life and prolonging survival. The recent advent of regenerative technologies paves the way for a transformative era in rehabilitation medicine whereby, beyond controlling risk factors and disease progression, the prospect of curative solutions is increasingly tangible. To date, the spectrum of clinical experience in cardiac regenerative medicine relies on stem cell-based therapies delivered to the diseased myocardium either acutely/subacutely, after a coronary event, or in the setting of chronic heart failure. Application of autologous/allogeneic stem cell platforms has established safety and feasibility, with encouraging signals of efficacy. Newer protocols aim to purify cell populations in an attempt to eliminate nonregenerative and enrich for regenerative cell types before use. Most advanced technologies have been developed to isolate resident cell populations directly from the heart or, alternatively, condition cells from noncardiac sources to attain a disease-targeted lineage-specified phenotype for optimized outcome. Because a multiplicity of cell-based technologies has undergone phase I/II evaluation, pivotal trials are currently underway in larger patient populations. Translation of regenerative principles into clinical practice will increasingly involve rehabilitation providers across the continuum of patient care. Regenerative rehabilitation is thus an emerging multidisciplinary field, full of opportunities and ready to be explored.

Interaction of digitalis-like compounds with liver uptake transporters NTCP, OATP1B1, and OATP1B3

Digitalis-like compounds (DLCs) such as digoxin, digitoxin, and ouabain, also known as cardiac glycosides, are among the oldest pharmacological treatments for heart failure. The compounds have a narrow therapeutic window, while at the same time, DLC pharmacokinetics is prone to drug-drug interactions at the transport level. Hepatic transporters organic anion transporting polypeptide (OATP) 1B1, OATP1B3, and Na(+)-dependent taurocholate co-transporting polypeptide (NTCP) influence the disposition of a variety of drugs by mediating their uptake from blood into hepatocytes. The interaction of digoxin, digitoxin, and ouabain with hepatic uptake transporters has been studied before. However, here, we systematically investigated a much wider range of structurally related DLCs for their capability to inhibit or to be transported by these transporters in order to better understand the relation between the activity and chemical structure of this compound type. We studied the uptake and inhibitory potency of a series of 14 structurally related DLCs in Chinese hamster ovary cells expressing NTCP (CHO-NTCP) and human embryonic kidney cells expressing OATP1B1 and OATP1B3 (HEK-OATP1B1 and HEK-OATP1B3). The inhibitory effect of the DLCs was measured against taurocholic acid (TCA) uptake in CHO-NTCP cells and against uptake of β-estradiol 17-β-d-glucuronide (E217βG) in HEK-OATP1B1 and HEK-OATP1B3 cells. Proscillaridin A was the most effective inhibitor of NTCP-mediated TCA transport (IC50 = 22 μM), whereas digitoxin and digitoxigenin were the most potent inhibitors of OATP1B1 and OAPTP1B3, with IC50 values of 14.2 and 36 μM, respectively. Additionally, we found that the sugar moiety and hydroxyl groups of the DLCs play different roles in their interaction with NTCP, OATP1B1, and OATP1B3. The sugar moiety decreases the inhibition of NTCP and OATP1B3 transport activity, whereas it enhances the inhibitory potency against OATP1B1. Moreover, the hydroxyl group at position 12 reinforces the inhibition of NTCP but decreases the inhibition of OATP1B1 and OATP1B3. To investigate whether DLCs can be translocated, we quantified their uptake in transporter-expressing cells by LC-MS. We demonstrated that convallatoxin, ouabain, dihydroouabain, and ouabagenin are substrates of OATP1B3. No transport was observed for the other compounds in any of the studied transporters. In summary, this work provides a step toward an improved understanding of the interaction of DLCs with three major hepatic uptake transporters. Ultimately, this can be of use in the development of DLCs that are less prone to transporter-mediated drug-drug interactions.

Cell therapy for cardiac repair--lessons from clinical trials

The global impetus to identify curative therapies has been fuelled by the unmet needs of patients in the context of a growing heart failure pandemic. To date, regeneration trials in patients with cardiovascular disease have used stem-cell-based therapy in the period immediately after myocardial injury, in an attempt to halt progression towards ischaemic cardiomyopathy, or in the setting of congestive heart failure, to target the disease process and prevent organ decompensation. Worldwide, several thousand patients have now been treated using autologous cell-based therapy; the safety and feasibility of this approach has been established, pitfalls have been identified, and optimization procedures envisioned. Furthermore, the initiation of phase III trials to further validate the therapeutic value of cell-based regenerative medicine and address the barriers to successful clinical implementation has led to resurgence in the enthusiasm for such treatments among patients and health-care providers. In particular, poor definition of cell types used, diversity in cell-handling procedures, and functional variability intrinsic to autologously-derived cells have been identified as the main factors limiting adoption of cell-based therapies. In this Review, we summarize the experience obtained from trials of 'first-generation' cell-based therapy, and emphasize the advances in the purification and lineage specification of stem cells that have enabled the development of 'next-generation' stem-cell-based therapies targeting cardiovascular disease.

Digoxin intoxication: An old enemy in modern era

Objectives

Although development of new treatment modalities limited digoxin usage, digoxin intoxication is still an important issue which could be easily overlooked. In this report, we analyzed a case series definitively diagnosed as digoxin intoxication in the modern era.

Methods

We analyzed 71 patients hospitalized with digoxin intoxication confirmed by history, complaints, clinical and electrocardiograph (ECG) findings, and serum digoxin levels > 2.0 ng/mL, during a five year period. The demographic and clinical data, indications for digoxin use, digoxin dosage, concurrent medications, laboratory data, hospital monitoring, and ECG findings were obtained from all patients.

Results

Thirty-eight of 71 patients (53.5%) had symptoms of heart failure during admission or later. Sixty-four percent of patients were older than 75 years. The percentage of females was 67%. Atrial fibrillation, hypertension and gastrointestinal complaints were more frequent in the females (64% in females, 30% in males, P = 0.007; 81% in female, 52% in males, P = 0.01; 50% in female, 17.3% in males, P = 0.008, respectively). The mortality rate during the hospital course was 7%.

Conclusions

This report demonstrated the reduced mortality rates in patients with digoxin intoxication over the study period. Gastrointestinal complaints are the most common symptoms in this population.

Mice expressing ouabain-sensitive α1-Na,K-ATPase have increased susceptibility to pressure overload-induced cardiac hypertrophy

The Na,K-ATPase is a ubiquitous transmembrane pump and a specific receptor for cardiac glycosides such as ouabain and digoxin, which are used in the management of congestive heart failure (CHF). A potential role for these so-called endogenous cardiotonic steroids (CS) has been explored, and it has become apparent that such compounds are elevated and may play an important role in a variety of physiological and pathophysiological conditions such as hypertension and CHF. Recent evidence suggests that the Na,K-ATPase may act as a signal transducer upon CS binding and induce nonproliferative cardiac growth, implicating a role for endogenous CS in the development of cardiac hypertrophy and progressive failure of the heart. In the present study, we tested whether hypertrophic responses to pressure overload would be altered in mutant mice that specifically express ouabain-sensitive or ouabain-resistant α1- and α2-Na,K-ATPase subunits, as follows: α1-resistant, α2-resistant (α1(R/R)α2(R/R)); α1-sensitive, α2-resistant (α1(S/S)α2(R/R)); and α1-resistant, α2-sensitive (α1(R/R)α2(S/S), wild-type). In α1(S/S)α2(R/R) mice, pressure overload by transverse aortic coarctation induced severe left ventricular (LV) hypertrophy with extensive perivascular and replacement fibrosis at only 4 wk. Responses in α1(R/R)α2(S/S) and α1(R/R)α2(R/R) mice were comparatively mild. Mutant α1(S/S)α2(R/R) mice also had LV dilatation and depressed LV systolic contractile function by 4 wk of pressure overload. In separate experiments, chronic Digibind treatment prevented the rapid progression of cardiac hypertrophy and fibrosis in α1(S/S)α2(R/R) mice. These data demonstrate that mice with a ouabain-sensitive α1-Na,K-ATPase subunit have a dramatic susceptibility to the development of cardiac hypertrophy, and failure from LV pressure overload and provide evidence for the involvement of endogenous CS in this process.

Pharmacological profile of the new inotropic agent AT-11

Although there are many classes of drugs, including cardiac glycosides, sympathomimetic inotropes, beta-adrenergic antagonists, angiotensin-converting enzyme inhibitors (ACE inhibitors) and spironolactone etc. used for the treatment of heart failure, the morbidity and mortality rates of patients after these treatments are not ameliorated. Chronic administration of Sympathomimetic inotropes also increased the arrhythmogenic effects. Consequently, improvement of treatment for heart failure remains a major medical challenge for the coming years. In this present experiment, the novel Na(+)-K(+) ATPase inhibitor AT-11 was characterized for its inotropic and toxic properties. Comparing AT-11 with ouabain, we found that AT-11 concentration-dependently increased contractility in guinea pig heart preparations, and the safety index of AT-11 was better than ouabain in vitro. In the in vivo study, AT-11 was also safer than ouabain at the equieffective dose. Moreover, AT-11 slowed heart rate more than ouabain did. This may be due to a larger AT-11-induced increase in vagal reflex than with ouabain and an indirect decrease in sympathetic tone to prevent Ca(2+) overload.

[Cognitive impairment induced by digoxin intake in patients older than 65 years]

Cognitive impairment or clinical signs of dementia in an old patient who receives digoxin, should suggest a digitalis intoxication. Symptoms can be present although a normal digoxin serum concentration. It is recommended to stop the treatment to obtain a regression of dementia symptoms.

Pharmacological treatment of chronic heart failure

Heart failure (HF) is associated with a high morbidity and mortality in the Western World. Our knowledge of the epidemiology, pathophysiology, and therapy has improved dramatically during the last 20 years. Pharmacological treatment, as it stands today, is a combination of preventive and symptomatic strategies. The mainstay life-saving drugs are angiotensin-converting enzyme inhibitors and beta-blockers. Additional benefits are obtained when angiotensin-receptor blockers or aldosterone antagonists are added. Digitalis and/or diuretics are useful for symptom reduction. In addition, combination therapy with hydralazine and isosorbide dinitrate is recommended in African Americans.

Influence of carvedilol on serum digoxin levels in heart failure: is there any gender difference?

OBJECTIVE

The activity of the human cytochrome P450 and P-glycoprotein (P-gp) changes according to gender. The present study evaluated the effect of gender on the influence of carvedilol on serum digoxin levels in patients with heart failure.

METHODS

Twenty-four patients (12 female and 12 male) with New York Heart Association class II-III heart failure were included in the study. Patients were taking oral digoxin (0.0625-0.25 mg, once a day) and were administered oral carvedilol (6.25 mg, two times daily) for 7 days.

RESULTS

In the male group, carvedilol led to statistically significant increases in the area under the concentration time curve to 16 h (AUC(0-16h)) and the peak concentration (C(max)) for digoxin, with no change in time to peak (t(max))(AUC(0-16h)= 24.1+/-9.2 ng.h/ml vs. 15.4+/-5.8 ng.h/ml, p<0.001, C(max)=2.2+/-1.0 ng/ml vs. 1.6+/-0.6 ng/ml, p<0.01, t(max)=2.4+/-2.2 h vs. 2.1+/-1.0 h, p>0.05). In the female group, carvedilol administration did not cause statistically significant change in the AUC(0-16h), C(max), or t(max) for digoxin (p>0.05). In the male group, carvedilol resulted in a significant increase in the AUC(0-16h) and C(max) for digoxin compared with the female group (AUC(0-16h)=24.1+/- 9.2ng.h/ml vs. 17.0+/-6.8 ng.h/ml, C(max)=2.2+/-1.0 ng/ml vs. 1.5+/-0.6 ng/ml, p<0.05, respectively).

CONCLUSION

Men seem to have a higher activity relative to women for the drug efflux transporter P-gp. Our results suggest that carvedilol will cause drug interaction with digoxin following the inhibition of P-gp-mediated transcellular transport of digoxin in males.

The emerging role of echocardiography in the screening of patients at risk of heart failure

A large number of patients without symptoms of heart failure (HF) have asymptomatic left ventricular (LV) dysfunction owing to the compensatory mechanisms acting through the autonomic nervous system and neurohormones. In the setting of screening for prevention, one must identify the subgroup of these patients at high risk for symptomatic HF to establish appropriate therapy. As a first step to identify the subgroup of patients at high risk, clinical screening scores and natriuretic peptide measurements are used. Second, the definite diagnosis of asymptomatic LV dysfunction must be confirmed with echocardiography, occasionally with the help of new technologic developments to establish prompt, appropriate treatment to prevent disease progression. Therefore, the screening role of echocardiography is the early identification of patients with structural cardiopathy who are at risk of developing symptomatic HF and detection of those without LV dysfunction (diabetic and hypertensive) whose condition is prone to advance rapidly to structural cardiopathy or to symptomatic HF.

Digoxin in heart failure

Digoxin is an agent with a long history of use in the management of heart failure; its benefits have just been quantified in recent years. It has long been known that digoxin provides a small amount of inotropic augmentation; however, it is now realized that digoxin also modulates the neurohormonal activation that occurs in heart failure. Although long-term therapy with digoxin does not decrease mortality, it does provide clinical benefit in terms of improved exercise tolerance and decreased hospitalizations across all severities of heart failure. Serum concentrations of digoxin associated with clinical benefits are lower than previously recognized (0.8-1.0 ng/mL). Digoxin toxicity can be easily avoided by maintaining these relatively low serum concentrations, avoiding and aggressively treating hypokalemia, and being mindful of poor renal function and drug interactions that may result in digoxin accumulation.

Pharmacologic therapy for patients with chronic heart failure and reduced systolic function: review of trials and practical considerations

Heart failure (HF) is a complex clinical syndrome resulting from any structural or functional cardiac disorder impairing the ability of the ventricles to fill with or eject blood. The approach to pharmacologic treatment has become a combined preventive and symptomatic management strategy. Ideally, treatment should be initiated in patients at risk, preventing disease progression. In patients who have progressed to symptomatic left ventricular dysfunction, certain therapies have been demonstrated to improve survival, decrease hospitalizations, and reduce symptoms. The mainstay therapies are angiotensin-converting enzyme (ACE) inhibitors and beta-blockers (bisoprolol, carvedilol, and metoprolol XL/CR), with diuretics to control fluid balance. In patients who cannot tolerate ACE inhibitors because of angioedema or severe cough, valsartan can be substituted. Valsartan should not be added in patients already taking an ACE inhibitor and a beta-blocker. Spironolactone is recommended in patients who have New York Heart Association (NYHA) class III to IV symptoms despite maximal therapies with ACE inhibitors, beta-blockers, diuretics, and digoxin. Low-dose digoxin, yielding a serum concentration <1 ng/mL can be added to improve symptoms and, possibly, mortality. The combination of hydralazine and isosorbide dinitrate might be useful in patients (especially in African Americans) who cannot tolerate ACE inhibitors or valsartan because of hypotension or renal dysfunction. Calcium antagonists, with the exception of amlodipine, oral or intravenous inotropes, and vasodilators, should be avoided in HF with reduced systolic function. Amiodarone should be used only if patients have a history of sudden death, or a history of ventricular fibrillation or sustained ventricular tachycardia, and should be used in conjunction with an implantable defibrillator [corrected]. Finally, anticoagulation is recommended only in patients who have concomitant atrial fibrillation or a previous history of cerebral or systemic emboli.

Phospholemman (FXYD1) associates with Na,K-ATPase and regulates its transport properties

A family of small, single-span membrane proteins (the FXYD family) has recently been defined based on their sequence and structural homology. Some members of this family have already been identified as tissue-specific regulators of Na,K-ATPase (NKA). In the present study, we demonstrate that phospholemman (PLM) (FXYD1), so far considered to be a heart- and muscle-specific channel or channel-regulating protein, associates specifically and stably with six different alpha-beta isozymes of NKA after coexpression in Xenopus oocytes, and with alpha1-beta, and less efficiently with alpha2-beta isozymes, in native cardiac and skeletal muscles. Stoichiometric association of PLM with NKA occurs posttranslationally either in the Golgi or the plasma membrane. Interaction of PLM with NKA induces a small decrease in the external K+ affinity of alpha1-beta1 and alpha2-beta1 isozymes and a nearly 2-fold decrease in the internal Na+ affinity. In conclusion, this study demonstrates that PLM is a tissue-specific regulator of NKA that may play an essential role in muscle contractility.

Lower serum digoxin concentrations in heart failure and reassessment of laboratory report forms

Serum digoxin concentrations (SDC) have been used clinically since the early 1970s. Whereas the therapeutic range for SDC is frequently cited as either 0.8 to 2.0 ng/mL or 0.5 to 2.0 ng/mL, studies over the past decade suggest an upper limit of 1.0 ng/mL for treating heart failure. The same upper limit for SDC is suggested for patients with heart failure and atrial fibrillation with rapid ventricular response. Reducing the upper limit of the therapeutic range to 1.0 ng/mL on computerized and paper laboratory report forms may guide clinicians to avoid unnecessarily high SDC, thus minimizing risk of digoxin toxicity without sacrificing therapeutic benefit for heart failure.

Clinical benefits of low serum digoxin concentrations in heart failure

OBJECTIVES

We sought to determine whether there was a relationship between serum digoxin concentration (SDC), including SDCs typically regarded as low, and clinical efficacy related to digoxin in patients with symptomatic left ventricular dysfunction.

BACKGROUND

Digitalis glycosides have been used for 200 years in the treatment of heart failure (HF), but the SDC required for optimal clinical efficacy and acceptable toxicity remains controversial.

METHODS

This relationship was investigated by utilizing data from two randomized, double-blinded, placebo-controlled, digoxin-withdrawal trials: the Prospective Randomized study Of Ventricular failure and Efficacy of Digoxin (PROVED) and the Randomized Assessment of Digoxin on Inhibitors of Angiotensin-Converting Enzyme (RADIANCE). Major end points were worsening HF, change in left ventricular ejection fraction and treadmill time after randomization. The primary analysis investigated the relationship between SDC at randomization and these end points. A secondary categorical analysis compared these end points in patients who discontinued digoxin versus patients who continued digoxin and had low (0.5 to 0.9 ng/ml), moderate (0.9 to 1.2 ng/ml) or high (>1.2 ng/ml) SDCs at randomization.

RESULTS

Multiple regression analysis failed to find a relationship between randomization SDC, considered as a continuous variable, and any study end point (all p > 0.236). Multivariable Cox analysis found that the risk of worsening HF was significantly less (all p < 0.02) for patients in any category of SDC who continued digoxin, as compared with patients withdrawn from digoxin. Specifically, patients in the low SDC category were significantly less likely than placebo patients to experience worsening HF during follow-up (p = 0.018).

CONCLUSIONS

The beneficial effects of digoxin on common clinical end points in patients with HF were similar, regardless of SDC.

Inappropriate use of digoxin in older hospitalized heart failure patients

BACKGROUND

Older adults are more likely to suffer from the adverse effects of digoxin. Studies have described the inappropriate use of digoxin in various populations. The objective of this study was to determine the correlates of inappropriate digoxin use in older heart failure patients.

METHODS

We studied older hospitalized heart failure patients with documented left ventricular (LV) function evaluation and electrocardiography. Digoxin use was considered inappropriate if patients had preserved LV systolic function (ejection fraction greater > or =40%) or if they had no atrial fibrillation (AF). We compared baseline patient characteristics by indication for digoxin and tested statistical significance using Pearson's chi-square analysis and Student's t tests. Using logistic regression, we determined the correlates of inappropriate use and initiation of digoxin.

RESULTS

Subjects (N = 603) had a mean age of 79 (+/-7) years; 59% were women, and 18% were African American. A total of 376 patients (62%) were discharged on digoxin, and 223 (37%) had no indication for its use. Half of the patients without an indication for digoxin received the drug. Of 132 patients without an indication and not already on digoxin, 38 (29%) were initiated on it. After adjustment for various patient and care characteristics, prior digoxin use (adjusted odds ratio [OR] 11.47, 95% confidence interval [CI] 5.72-23.02) and pulse > or =100/min (adjusted OR 2.33, 95% CI 1.10-4.94) were associated with inappropriate digoxin use. Pulse > or =100/min was also associated with inappropriate initiation of the drug (adjusted OR 2.95, 95% CI 1.28-6.78).

CONCLUSIONS

Inappropriate use of digoxin was common and was associated with prior use. Tachycardia was associated with inappropriate use and initiation. Electrocardiography and echocardiography should be performed in all older heart failure patients. Digoxin therapy should not be initiated or continued in patients without any evidence of LV systolic dysfunction or chronic AF.

Digoxin

After 200 years of use, digitalis still appears to have a place in our armamentarium for heart failure and atrial fibrillation despite the proven survival benefits with ACE inhibitors and beta-blockers. Digoxin therapy is inexpensive and well tolerated and may result in considerable savings. Digoxin is the only oral inotrope that does not increase mortality in heart failure patients, particularly if low doses are being used. Digoxin therapy should be used in patients with systolic heart failure who continue to have signs and symptoms despite therapeutic doses of ACE inhibitors or diuretics or in patients with atrial fibrillation with or without heart failure for rate control.

Effect of concomitant digoxin and carvedilol therapy on mortality and morbidity in patients with chronic heart failure

We retrospectively performed stepwise logistic regression analysis on 1,509 patients with chronic heart failure in 4 multicenter United States studies and 1 Australia-New Zealand study to examine the effect of digoxin in patients randomized to carvedilol or placebo. Patients receiving digoxin had more advanced heart failure, the incidence of hospitalization for any cause and the combination of all-cause death and all-cause hospitalization were the same in the digoxin versus no-digoxin groups.

The treatment of diastolic heart failure

Recommendations for the treatment of diastolic heart failure must be based on theoretical issues. Evidence-based outcomes from clinical trials are not available at this time, but there is an increasing mandate for more focused studies for this clinical disorder. Meaningful outcomes require delineation of patient populations, including identification of underlying disease and comorbid cardiovascular disorders. Until such information is available, we must rely on an understanding of the natural history of associated disorders, extrapolation of treatment strategies that are successful for systolic heart failure management, and use of pharmacologic agents that empirically target the observed hemodynamic abnormalities of diastolic heart failure.

Heart failure with preserved LV function: pathophysiology, clinical presentation, treatment, and nursing implications

The syndrome of congestive heart failure occurring secondary to diastolic dysfunction accounts for the major pathophysiologic mechanism in up to one-third of patients who present with dyspnea on exertion and pulmonary congestion. Diastolic dysfunction is characterized by an alteration in the normal diastolic pressure-volume relationship while systolic function may be normal. It is manifested by impairment in the left ventricle's ability to relax and fill completely during diastole at normal low ventricular pressures. This subset of heart failure is most commonly associated with concentric left ventricular hypertrophy and ischemic states. Symptom presentation is similar to that associated with systolic dysfunction as are rates of rehospitalization. Diagnosis is made based on data obtained from invasive and noninvasive procedures. Unlike in the setting of systolic dysfunction, however, there are no large-scale randomized clinical trials evaluating drug efficacy that could be used to guide treatment for the management of diastolic dysfunction. Treatment recommendations, therefore, are empiric. Identifying and aggressively treating potentially reversible causes is a priority. Many of the same drugs used in the management of heart failure associated with systolic dysfunction are also used in the setting of diastolic impairment; however, dosages and rationale for administration may differ. Nursing interventions too are similar. Monitoring response to medications, especially in the acute setting, and comprehensive patient education are paramount. Much is yet to be learned about the management of diastolic dysfunction.

Surviving heart failure: Robert L. Frye lecture

Heart failure is increasing in both incidence and prevalence and is associated with a high mortality. In patients with heart failure, coronary artery disease is the cause for about two thirds. Pathophysiologic changes have been linked to altered muscle function and hemodynamics, elevated neurohormones, and, more recently, cellular mechanisms, including apoptosis. Standard triple therapy for symptomatic heart failure consists of an angiotensin-converting enzyme (ACE) inhibitor, digoxin, and a diuretic. In patients with severe heart failure, spironolactone should be added. In large clinical trials, ACE inhibitors, spironolactone, and beta-blockers have reduced mortality. Other drugs may be helpful in the treatment of heart failure. Amiodarone is the antiarrhythmic drug of choice in patients with symptomatic arrhythmias and also has a role in the treatment of dilated cardiomyopathy. Angiotensin II receptor blockers are being compared with ACE inhibitors and appear promising. Newer agents being tested include antagonists to endothelin and tumor necrosis factor. Overall, it is clear that polypharmacy is the standard of care for patients with heart failure. A future challenge will be to prevent heart failure from occurring.

Myocardial region (right or left ventricle) and aetiology of heart failure can influence the inotropic effect of ouabain in failing human myocardium

AIMS

To investigate whether the inotropic effect of ouabain in failing human myocardium varies according to the heart chamber tested (right or left ventricle) or the aetiology of the heart disease, i.e. ischaemic or idiopathic.

METHODS

The inotropic effect of ouabain was measured, as the percentage change in baseline tension, in myocardial strips isolated from right (RV; n=21) and left ventricles (LV; n=21) of hearts explanted from patients with idiopathic (IDC; n=11) and ischaemic cardiomyopathy (CAD; n=10). Concentration-effect curves obtained with ouabain (0.05-1.6 micromol l-1 ) were analysed using the Emax sigmoidal model, and the following parameters were calculated: Emax, EC50, n and EC10 (threshold concentration). The influence of ventricular chamber and heart failure aetiology on these parameters was evaluated by means of a two-way anova.

RESULTS

Age and baseline haemodynamic parameters did not differ between IDC and CAD patients. Baseline strip contractility was highly variable (range: 0.48-10.0 mN), but neither ventricular chamber nor aetiology could explain such variability. A two-way anova showed that EC10 was greater in CAD than in IDC preparations (0.097+/-0.013 micromol l-1 vs 0.059+/-0. 009 micromol l-1; 95% C.I. for difference 0.043, 0.071) and Emax was lower in RV than in LV (121+/-21% vs 250+/-38%; 95% C.I. -221, -36), while EC50 and n were not significantly different between groups.

CONCLUSIONS

The inotropic effect of ouabain in human myocardium may vary according to aetiology of heart failure and the ventricle being tested. Although our results do not support the hypothesis of increased sensitivity to cardiac glycosides in CAD patients, they may explain the diminished effect observed in patients with RV failure.

Therapeutic range of digoxin's efficacy in heart failure: what is the evidence?

Clinical studies have solidified the utility of digoxin in patients with left ventricular dysfunction and normal sinus rhythm. No definitive data have been published to clarify the range of serum digoxin concentrations associated with clinical benefit. The traditional therapeutic range of 0.8-2.0 ng/ml was developed originally to classify digoxin toxicity, not efficacy. In addition, this reference range was used before publication of the Digitalis Investigators Group trial. Clinical and neurohormonal studies have attempted to characterize serum concentrations that are associated with clinical efficacy.

A case series of hospitalized patients with elevated digoxin levels

PURPOSE

Although there is renewed enthusiasm for the use of digoxin in patients with heart failure, current dosing guidelines are based on a nomogram published in 1974. We studied the incidence of and risk factors for elevated digoxin levels in patients admitted to a community hospital, and compared their dosage regimens to published guidelines.

SUBJECTS AND METHODS

We reviewed the charts of all patients who had serum digoxin levels greater than 2.4 ng/mL during a 6-month period. We collected demographic and clinical data, indications for digoxin use, digoxin dosage, concurrent medications, laboratory data, and clinical and electrocardiographic features of digoxin toxicity.

RESULTS

Of the 1,433 patients with digoxin assays, 115 (8%) patients had elevated levels. Of the 82 patients with complete records and correctly timed digoxin levels, 59 (72%) had electrocardiographic or clinical features of digoxin toxicity. Patients with serum digoxin levels >2.4 ng/mL were slightly older (78 +/- 8 versus 73 +/- 9 years of age; P = 0.12) and had greater serum creatinine levels (3.1 +/- 7.3 versus 1.4 +/- 0.3 mg/dL; P = 0.01) than those with levels < or =2.4 ng/mL. Forty-seven patients had elevated digoxin levels on admission, including 21 patients admitted for digoxin toxicity. Impaired or worsening renal function contributed to high levels in 37 patients, and a drug interaction was a contributory factor in 10 cases. Twenty (43%) of these patients were taking the recommended maintenance dose based on the scheme employed in the Digitalis Investigation Group study. Thirty-five patients developed high digoxin levels while in hospital. In 26 patients, this followed a loading dose of digoxin for the control of rapid atrial fibrillation. Impaired renal function was implicated in all of these patients. Despite the elevated digoxin level, rate control was achieved in only 11 patients of these patients.

CONCLUSIONS

Elevated digoxin levels and clinical toxicity remains a common adverse drug reaction. Elderly patients, particularly those with impaired renal function and low body weights, are at the greatest risk. As published digoxin nomograms often result in toxicity, clinical variables need to be monitored. In patients with congestive heart failure and normal sinus rhythm the potential benefit of digoxin is small; thus, patients should receive a dose that minimizes the risk of toxicity. For patients with new onset atrial fibrillation, other agents may be preferable for rate control.

Prospective investigations of concentration–clinical response for immunosuppressive drugs provide the scientific basis for therapeutic drug monitoring

The performance of prospective concentration–clinical response investigations during the early stages of the development of new therapeutic agents can provide a more rigorous basis for therapeutic drug monitoring than the traditional retrospective review of drug concentrations vs clinical outcome. Here we discuss the application of the multicenter randomized concentration-controlled clinical trial study design, and related study designs, as applied to older commonly used and monitored drugs and to two new immunosuppressant drugs, mycophenolate mofetil and tacrolimus. Such studies can provide a more rigorous basis for assessing the risk/benefit associated with a target drug concentration in the individual patient and for designing future prospective pharmacokinetic and therapeutic drug monitoring investigations.