Mechanisms of improved left ventricular function following intravenous MDL 17,043 in patients with severe chronic heart failure

Role of nonglycosidic inotropic agents: indications, ethics, and limitations

Nonglycosidic inotropic agents have been used for the short-term management of low output states and hypotension complicating acute myocardial infarction for several years. Without adequate reperfusion of the ischemic myocardium, inotropic agents are seldom effective in producing sustained hemodynamic responses. Furthermore, the potential exists for enhancement of ischemia and extension of myocardial necrosis. Thus, inotropic and vasopressors therapy should be regarded as temporary supportive treatment in patients with acute coronary syndrome and should be discontinued as soon as feasible. Parenteral sympathomimetic agents, usually dobutamine, and phosphodiesterase inhibitors, usually milrinone, are used for the management of exacerbations of chronic systolic heart failure. Although hemodynamics, and occasionally clinical status, improve, such therapy is associated with increased mortality and can potentially hasten a patient's demise. Nonparenteral sympathomimetics, such as ibopamine, phosphodiesterase-III inhibitors, such as milrinone and enoximone, calcium-sensitizing agents, such as pimobendan, and other novel inotropic agents, such as vesnarinone, all increase mortality of patients with chronic heart failure. Furthermore, newer noninotropic agents, such as B-natriuretic peptide, have been introduced for treatment of decompensated heart failure. New nonpharmacologic devices, such as biventricular pacing, are available for the treatment of advanced heart failure. Thus, indications for the use of presently available nonglycosidic inotropic agents are limited and should be considered only for short-term therapy or when no other treatment is available.

Refractory Heart Failure: A Therapeutic Approach

Optimal “triple therapy” for patients with chronic congestive heart failure (CHF) includes diuretics, digoxin, and either angiotensin-converting enzyme inhibitors or hydralazine plus nitrates. Refractory CHF is defined as symptoms of CHF at rest or repeated exacerbations of CHF despite “optimal” triple-drug therapy. Most patients with refractory CHF require hemodynamic monitoring and treatment in the intensive care unit. If easily reversible causes of refractory CHF cannot be identified, then more aggressive medical and surgical interventions are necessary. The primary goal of intervention is to improve hemodynamics to palliate CHF symptoms and signs (i.e., dyspnea, fatigue, edema). Secondary goals include improved vital organ and tissue perfusion, discharge from the intensive care unit, and, in appropriate patients, bridge to cardiac transplantation. Medical interventions include inotropic resuscitation (e.g., adrenergic agents, phosphodiesterase inhibitors, allied nonglycoside inodilators), load resuscitation (e.g., afterload and preload reduction with nitroprusside or nitroglycerin; preload reduction with diuretics and diuretic facilitators, such as dopaminergic agents or ultrafiltration), and electrical resuscitation (e.g., prevention of sudden death, correction of new or rapid atrial fibrillation, or dual chamber pacing in the setting of relative prolongation of the PR interval and diastolic mitral/tricuspid regurgitation). Surgical interventions are temporizing (e.g., intra-aortic balloon pump and other mechanical assist devices) or definitive (e.g., coronary artery revascularization, valvular surgery, and cardiac transplantation). Although these interventions may improve immediate survival in the short term, only coronary artery revascularization and cardiac transplantation have been shown to improve long-term survival.

Enoximone vs nicardipine during the early postoperative course of patients undergoing cardiac surgery. A prospective study of two therapeutic strategies

The hemodynamic effects of enoximone and nicardipine were compared during the early postcardiac surgery period in 40 patients with systemic hypertension and moderate cardiac dysfunction. Patients were prospectively randomized into two groups. Mean right atrial pressure was maintained above 7 mm Hg. The drug infusion rate was adjusted to maintain mean systemic artery pressure (SAP) within the 65 to 80 mm Hg range. Complete hemodynamic evaluations were performed before any drug infusion and during the following 24 h with special attention to O2-related variables. Oxygen consumption, cardiac index, and stroke index improved significantly and similarly in the two groups. The SAP and systemic vascular resistance decreased more rapidly in the enoximone group but whole body lactate level increased after the second hour of infusion. Furthermore, this was paralleled by an arteriovenous O2 contents difference deficit. In our study, nicardipine was found superior over enoximone in terms of recovery from intraoperative tissue hypoxia. Furthermore, enoximone's inotropic effects were not found to be clinically relevant.

Arterial hemodynamics and cardiac effects of enoximone, dobutamine, and their combination in severe heart failure

The acute systemic and regional hemodynamic effects of dobutamine (5, 10, and 15 micrograms/kg/min intravenously), of enoximone (1, 1.5, and 2 mg/kg intravenously), and of the dobutamine-enoximone combination were compared in eight patients with severe congestive heart failure. Dobutamine and enoximone similarly and dose-dependently increased cardiac index and decreased systemic vascular resistance, right atrial pressure, and mean capillary wedge pressure. Dobutamine, but not enoximone, increased heart rate after 10 and 15 micrograms/kg/min. The combination of the two drugs caused a greater increase in cardiac index and a greater decrease in total peripheral resistance than did each drug alone. In the forearm vascular bed, brachial blood flow and brachial artery diameter were increased by enoximone significantly and dose-dependently and by dobutamine only at 5 micrograms/kg/min. Finally, the combination of the two drugs increased brachial blood flow but not brachial artery diameter to a larger extent than enoximone alone. Hepatosplanchnic and renal blood flows were not altered by any of the treatments. These results indicate that (1) enoximone exerts a significantly greater muscular vasodilator action than dobutamine; (2) the dobutamine-enoximone combination potentiates the systemic and brachial vasodilator effects of each drug; and (3) high doses of dobutamine (10 and 15 micrograms/kg/min) improve hemodynamics through their positive inotropic and chronotropic effects, whereas at low doses (5 micrograms/kg/min) a peripheral vasodilation also contributes.

The role of phosphodiesterase inhibitors in heart failure

Myocardial contractility is dependent on available intracellular calcium and this can be enhanced by increasing intracellular cyclic adenosine monophosphate. One way of achieving this is by inhibiting the phosphodiesterase III enzyme. Over the last 15 years, a number of new drugs with this mechanism of action have been studied in man and have been found not only to have a positive inotropic action on the heart but also a vasodilating action on peripheral blood vessels. This combination of effects produces favourable haemodynamic improvement in patients with chronic heart failure. While some smaller studies showed that this did translate into an improvement in symptoms and functional capacity, a large well-designed and controlled clinical trial showed that survival was decreased when milrinone was used in target daily doses of 40 mg. For this reason, chronic long-term oral therapy with phosphodiesterase III inhibitors is not currently being actively pursued. They may still have a role as acute short-term therapy in severely ill patients who do not respond adequately to optimal standard drug therapy. Milrinone has been one of the most widely studied drugs in this regard. Even during short-term administration, its use should be closely monitored for any evidence of an increase in ventricular arrhythmias or decrease in ventricular function.

Inotropic therapy of the failing myocardium

The clinical syndrome of congestive heart failure remains a therapeutic dilemma and challenge for the physician in 1992. This is a disease process that appears to be increasing in frequency and continues to carry an unacceptably high mortality rate. For years it has been well recognized that the combination of digoxin, Lasix and vasodilator therapy improved symptoms in these patients and decreased hospitalization, but did not increase survival. It was not until 1986 that the combination of digoxin, Lasix, Isordil, and hydralazine was shown to increase survival. Further significant improvement in quality of life and survival has recently been established in three large clinical trials, and it is now safe to say that the standard of care for symptomatic congestive heart failure in 1992 is digoxin, furosemide, and an ACE inhibitor, with the survival trials favoring the ACE inhibitor enalapril. The IV inotropic drug dobutamine remains the mainstay of pharmacological therapy for the treatment of severely refractory heart failure. Unfortunately, the phosphodiesterase inhibitors--amrinone, milrinone, and enoximone--have demonstrated unacceptable clinical side effects and have been withdrawn from further clinical study. In spite of these promising developments, the mortality and morbidity of congestive heart failure remains unacceptably high, and continued investigation in the new fields of pharmacology and the pathophysiology of congestive heart failure still must be aggressively pursued.

Short-term effects of oral enoximone on hemodynamics, exercise capacity, anaerobic threshold, and arrhythmias in congestive heart failure

Enoximone, a phosphodiesterase-inhibitor, is a potent inotropic vasodilator agent that causes a marked improvement in hemodynamics in patients with congestive heart failure. The acute effects of oral enoximone on rest and exercise hemodynamics, ejection fraction, aerobic metabolism, exercise capacity, and arrhythmias were studied in 11 patients with moderate to moderately severe dilative cardiomyopathy after 8 days of enoximone (100 mg tid) in addition to baseline therapy (diuretics and digitalis). The cardiac index increased from 2.44 +/- 0.45 to 2.72 +/- 0.50 l/min/m2 (p less than 0.01) at rest and from 4.00 +/- 0.96 to 4.75 +/- 0.95 l/min/m2 (p less than 0.005) during exercise. Pulmonary wedge pressure decreased from 16.8 +/- 7.3 to 12.5 +/- 6.5 mmHg (p less than 0.005) at rest and from 28.2 +/- 8.0 to 24.5 +/- 10.3 mmHg (p less than 0.05) during exercise. Systemic vascular resistance decreased from 1608 +/- 243 to 1495 +/- 300 dynes*sec*cm-5 (p less than 0.05) at rest and from 1152 +/- 155 to 1027 +/- 236 dynes*sec*cm-5 (ns) during exercise. The anaerobic threshold, which was recorded simultaneously, increased from 13.2 +/- 2.7 to 15.5 +/- 2.5 ml/kg/min VO2 (p less than 0.02). The radionuclide ventriculography ejection fraction improved from 21.7 +/- 5.0 to 28.1 +/- 9.1% (p less than 0.01) during exercise; the changes at rest were not significant (20.8 +/- 6.2 vs 25.8 +/- 8.4%). Exercise tolerance showed an increase of 16% (492 +/- 133 to 573 +/- 135 sec, p less than 0.005). The resting heart rate remained unchanged (81.8 +/- 13.4 vs 81.8 +/- 11.9). Interestingly, 24-h Holter monitoring revealed more or new repetitive arrhythmias in 9/11 patients.

Oral enoximone therapy in chronic heart failure: a placebo-controlled randomized trial. The Western Enoximone Study Group

In a parallel study design, 164 patients with New York Heart Association Functional class II or III heart failure were randomized to receive either enoximone given as 50 mg three times a day, or 100 mg three times a day, or a matching placebo. All patients were receiving digitalis and/or diuretics and had left ventricular ejection fractions less than or equal to 45. Exercise tests were performed after 1, 4, 8, and 12 weeks of treatment. Enoximone produced significantly greater increases in exercise time than placebo treatment at weeks 4 and 8 (p = 0.012, p = 0.029, respectively) but not after 12 weeks. Left ventricular ejection fraction increased significantly after the first dose of enoximone but not after 12 weeks of long-term therapy. Heart failure symptoms and the physicians' evaluations of cardiac status were significantly improved in both enoximone therapy groups during the first 4 weeks of evaluation when compared with evaluations of cardiac status in the placebo group. Diuretic doses were increased more frequently for patients who were receiving a placebo. Adverse events were reported with similar frequency in the placebo and 50 mg enoximone treatment groups; 100 mg enoximone resulted in a significantly greater incidence of adverse events. Mean heart rate and ventricular ectopic activity were not significantly different among the three treatment limbs. Enoximone appears to improve exercise tolerance, ventricular function, and symptoms of heart failure for 4 to 8 weeks. Heart rate, ventricular ectopic activity, and mortality rate were not increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Management of low cardiac output syndrome after cardiac surgery using enoximone

This case report describes the use of enoximone, a potent phosphodiesterase F-IV inhibitor with inotropic and vasodilator actions, to treat low output syndrome after cardiac surgery. The reduced cardiac output was unresponsive to a combination of inotropic drugs and intra-aortic balloon counterpulsation was contraindicated. Cardiac output was increased dramatically by enoximone, but systemic vascular resistance and perfusion pressure remained low until the addition of metaraminol.

Phosphodiesterase inhibitors: alterations in systemic and coronary hemodynamics

This paper reviews the effect on myocardial contractility, left ventricular afterload and left ventricular distensibility induced by the following phosphodiesterase inhibitors: Enoximone, piroximone, RO 13-6438, amrinone and milrinone. For all these compounds, direct positive inotropic effects have been shown in experimental studies. For amrinone and milrinone, a direct stimulating effect on myocardial contractility has been demonstrated by an increase in dP/dtmax when intracoronary applications of the compounds were performed. A direct stimulating effect on the myocardium was also demonstrated for enoximone and piroximone by analyzing the systolic pressure versus end-systolic volume ratio. For all of the phosphodiesterase inhibitors, a marked decrease of systemic vascular resistance has been observed indicating direct peripheral vasodilation. Although it has been demonstrated that phosphodiesterase inhibition increases left ventricular distensibility, the nature of this effect is not clear. For most of the phosphodiesterase inhibitors an increase in myocardial oxygen requirements was demonstrated due to overall contractility increase. However, these phosphodiesterase inhibitors induce increased coronary blood flow in excess so that a direct effect of these compounds on the coronary vasculature has been postulated. The clinical significance of such changes, however, remains unclear.

Acute and long-term hemodynamic response to low-dose enoximone in refractory heart failure

Enoximone possesses both positive inotropic and vasodilatory properties. In heart failure, doses varying between 3 mg/kg and 6 mg/kg produce a beneficial acute hemodynamic response but have been associated with significant side effects. Little is known about the long-term hemodynamic efficacy of this agent. To assess whether a lower dose of enoximone could produce both acute and long-term hemodynamic benefits and be better tolerated, 15 patients with refractory heart failure were given enoximone 100 mg every 8 hours (mean dose, 1.7 mg/kg). The cardiac index, pulmonary capillary wedge pressure, pulmonary artery pressure, right atrial pressure, systemic vascular resistance, pulmonary vascular resistance, and stroke volume index all improved significantly during the first 24 hours. The systemic blood pressure and heart rate did not alter appreciably during this period. Five of six patients remaining on therapy at 6 months had a follow-up hemodynamic study. Sustained improvement was seen in the cardiac index, pulmonary capillary wedge pressure, and pulmonary artery pressure when compared to baseline (all p less than 0.05). A satisfactory trend, which did not reach statistical significance, was noted in the right atrial pressure (p = 0.09) and stroke volume index (p = 0.06). Diarrhea occurred in one patient. These findings indicate that enoximone has a beneficial acute and long-term hemodynamic effect at a low dose that is clinically well tolerated.

Controlled and uncontrolled studies of phosphodiesterase III inhibitors in contemporary cardiovascular medicine

The phosphodiesterase inhibitors are new inotrope vasodilators that have beneficial hemodynamic effects in patients with congestive heart failure (CHF). The most extensively studied agents are milrinone and enoximone. Both drugs have clearly been shown in numerous studies to improve hemodynamics in patients with CHF when given acutely by either the intravenous or oral route. In long-term studies, milrinone has been shown to have sustained beneficial hemodynamic effects during active treatment. Effects on exercise tolerance have been less clear-cut in several uncontrolled trials, but a recent large-scale randomized trial does show sustained improvement in exercise performance. When milrinone is withdrawn after long-term therapy, some studies show worsened cardiac performance; the exact cause remains ill-defined, but could be due to deterioration of baseline ventricular function or to "rebound." Both uncontrolled studies and a large recently reported randomized trial show that the hemodynamic response to readministration of milrinone after withdrawal is well-preserved, i.e., no tolerance is observed. Studies of enoximone show that its acute hemodynamic effects are similar to those of milrinone, but its long-term efficacy, using both hemodynamic and exercise end points, is less clear-cut, and no large-scale randomized trials of enoximone therapy have yet been reported. The studies of both these agents performed thus far indicate that the phosphodiesterase inhibitors have considerable promise for both acute and long-term treatment of patients with CHF.

Administration of enoximone in cardiogenic shock

Thirteen patients in severe cardiogenic shock, persisting despite the use of adrenergic agents, were treated with enoximone, a recently available phosphodiesterase inhibitor. Cardiogenic shock was characterized by low cardiac output (less than 2.5 liter.min-1.m-2), elevated pulmonary artery balloon-occluded pressure (greater than or equal to 15 mm Hg), decreased urine output (less than 20 ml.hour-1) and increased blood lactate (greater than or equal to 2.0 mEq.liter-1). Ten patients were mechanically ventilated. A short-term intravenous infusion of 0.5 mg.kg-1 in 20 minutes of enoximone resulted in significant increases in cardiac index (from 1.8 +/- 0.3 to 2.9 +/- 0.3 liter.min-1.m-2, p less than 0.001) and stroke index (from 17.8 +/- 3.3 to 21.9 +/- 5.1 ml.m-2, p less than 0.001) and significant decrease in pulmonary artery balloon-occluded pressure (from 21.7 +/- 5.8 to 19.8 +/- 6.0 mm Hg, p less than 0.01) without a consistent change in mean arterial pressure (from 79 +/- 8 to 76 +/- 9 mm Hg, difference not significant). Enoximone administration decreased arterial oxygen tension (from 108 +/- 42 to 94 +/- 36 mm Hg, p less than 0.01) and increased venous admixture (from 12.8 +/- 6.5 to 16.0 +/- 8.0%, p less than 0.01). In 8 patients, a second infusion of 0.5 mg.kg-1 immediately thereafter amplified these changes. All patients but one survived the episode of cardiogenic shock and 5 patients left the hospital alive. These results indicate that the addition of enoximone to adrenergic agents in the treatment of cardiogenic shock can markedly increase cardiac output and stroke volume without substantial effects on arterial pressure.

Central and regional hemodynamic effects of oral enoximone in congestive heart failure: a double-blind, placebo-controlled study

Twelve patients with congestive heart failure underwent a double-blind, placebo-controlled study for the purpose of examining the central and regional hemodynamic effects of first-dose (1 and 2 mg/kg) oral enoximone, a new phosphodiesterase III inhibitor. Enoximone augmented cardiac output, generally through a positive chronotropic response. Indices of left ventricular contractility, specifically stroke volume, delta P/delta t, fractional shortening rate, and the duration of the preejection period, were only modestly enhanced by enoximone. At 2 mg/kg, systemic vascular resistance fell below baseline values without affecting systemic blood pressure; these parameters were not altered by the 1 mg/kg dose. Both pulmonary artery pressure and pulmonary vascular resistance dropped below baseline and below placebo control for the 2 mg/kg dose. Enoximone at 2 mg/kg lowered right and left heart filling pressures below baseline. Examination of regional hemodynamic responses to both doses demonstrated a reduction in limb vascular resistance and an increase in limb blood flow proportional to the concomitant increase in cardiac output. Renal and hepatic-splanchnic blood flow and vascular resistances were not altered by enoximone. First-dose oral enoximone (1 and 2 mg/kg) alters hemodynamics in heart failure by predominant vasodilatation, particularly of limb-musculoskeletal and pulmonary vascular beds, some positive chronotropism, and modest positive inotropism.

The effects of enoximone (MDL-17043) on forearm venous circulation in healthy volunteers and patients with heart failure

The effect of intravenous enoximone on forearm venous circulation was studied in ten healthy volunteers (group A) and in ten patients with NYHA class III-IV congestive heart failure (group B). Distensibility of the forearm capacitance vessels was assessed from pressure-volume curves by venous occlusion plethysmography using a mercury-in-rubber strain gauge. Three recordings each at 3-min intervals were obtained before the infusion and again 20 min after completion of the infusion. Venous volume changes (VV) at congesting pressures of 10, 20, and 30 mmHg before and after enoximone were compared. Forearm muscle blood flow was also measured by venous occlusion plethysmography; electrocardiogram, heart rate, and cuff blood pressure were recorded throughout. Enoximone at a dose of 1 mg/kg body weight was infused over 10 min through a peripheral vein in group A and via a central line in group B. In group A, the effect of the injection vehicle was also assessed. VV10, VV20, and VV30 did not differ from baseline values after enoximone in both groups A and B. The vehicle caused a small but significant degree of venoconstriction in group A (VV20, 2.64 +/- 0.9 to 2.48 +/- 0.83 ml/100 ml, P less than 0.05; VV30, 3.47 +/- 1.27 to 3.33 +/- 1.20 ml/100 ml, P less than 0.05), which could be explained by an acute response to local pain from the infusion. This effect was not evident following enoximone, perhaps as a result of its counterbalancing vasodilating action to venoconstriction induced by acute pain.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential mechanisms of improved left ventricular function with enoximone in severe congestive heart failure

Enoximone, a phosphodiesterase inhibitor, is a potent inotropic vasodilator agent that causes a marked improvement in systemic hemodynamics in patients with severe chronic congestive heart failure. Cardiac index, stroke volume index and stroke work index increase, and there is a significant decrease in pulmonary capillary wedge pressure. Left ventricular dP/dt increases, despite a decrease in arterial pressure and systemic vascular resistance and without any significant change in heart rate, indicating a positive inotropic effect. A marked decrease in systemic vascular resistance indicates that decreased left ventricular outflow resistance resulting from peripheral vasodilation also contributes to improvement in left ventricular function. In some patients, left ventricular end-diastolic volume increases despite a marked decrease in pulmonary capillary wedge pressure, suggesting an improvement in apparent left ventricular compliance, which may also be contributory to improved left ventricular function.

Physiologic response to the inotropic and vasodilator properties of enoximone

In patients with chronic cardiac failure, improvement in ventricular function is observed after the administration of enoximone, a phosphodiesterase inhibitor with inotropic and vasodilator properties. The relative contributions of positive inotropy and vasodilation to the improvement in pump performance, however, remain uncertain. Therefore, findings from a series of dog experiments designed to resolve this issue are reviewed. Also, our current understanding of the physiologic response to enoximone in patients with cardiac failure, including the responses of myocardial oxygen consumption and efficiency, are considered. It is concluded that, enoximone produces a substantial (66 +/- 2% in dogs) increase in contractility, a relatively minor increase in heart rate (0 to 12%) and a decrease in systemic vascular resistance (-28 to -49%). These are the ranges of average responses based on review of published findings. These physiologic responses lead to an improvement in the pumping function of the failing heart; cardiac output (23 to 83%) and stroke work index (17 to 88%) are increased, and pulmonary capillary wedge pressure (-19 to -59%) and right atrial pressure (-29 to -60%) are decreased. The influence of enoximone on myocardial oxygen consumption is less consistent (-18 to +33%). Nevertheless, enoximone improves the efficiency of the failing heart.

Intravenous use of enoximone

To assess the efficacy and safety of acute therapy with intravenous enoximone in patients with severe congestive heart failure, 118 patients from 5 centers were treated with incremental doses following 2 schedules: to a maximum cumulative dose of 3.0 mg/kg (44 patients) and to a maximum cumulative dose of 10.5 mg/kg (74 patients). Both schedules produced significant increases in cardiac index (55% and 68%, p less than 0.01 for both) and decreases in pulmonary capillary wedge pressure (-29% and -42%, p less than 0.01 for both). Similar beneficial effects were observed in systemic vascular resistance (-33% and -44%) and right atrial pressure (-30% and -46%), which also were statistically significant (p less than 0.01). Heart rate increased modestly (6% and 13%) and mean systemic arterial pressure decreased (-5% and -14%). Some adverse effect occurred in 20% of the patients. Cardiovascular (10%) and central nervous system (6.7%) were the most frequent side effects. However, a direct relation to enoximone therapy could not be established in this uncontrolled open-label study of acutely ill patients. It is concluded that intravenous enoximone produces beneficial hemodynamic effects in patients with severe congestive heart failure with minimal changes in heart rate and blood pressure at cumulative doses less than 3 mg/kg.

A comparison of hemodynamic effects of one-month oral captopril and enoximone treatment for severe congestive heart failure

A double-blind, randomized, crossover trial was undertaken to compare the effect of enoximone (150 mg, 3 times daily) and captopril (25 mg, 3 times daily) added to conventional therapy with diuretics in the treatment of 13 patients with severe chronic heart failure. Each treatment was continued for 1 month. Heart failure was due to idiopathic dilated cardiomyopathy in 6 patients and coronary artery disease in 7. Hemodynamic measurements were made at rest and during exercise, on entry to the study and after each treatment period. The cardiac index at rest was 1.9 +/- 0.2 liters min-1 m2 (mean +/- 1 standard deviation) and did not change with either drug. Systemic vascular resistance at rest decreased with enoximone (p less than 0.05) and was unchanged with captopril. Systemic vascular resistance at peak exercise was not lowered by either drug. Both drugs caused an increase of cardiac index at peak exercise (p less than 0.04) and a prolongation of exercise time (p less than 0.05). No difference was detected between the hemodynamic response to the 2 drugs after 1 month treatment either at rest or during exercise.

Effects of low dose enoximone for chronic congestive heart failure

To examine the short-term hemodynamic and long-term clinical effects of oral enoximone at low doses, 12 patients with severe, chronic congestive heart failure (CHF) were given 1 mg/kg oral enoximone and followed with serial hemodynamic measurements for 24 hours. Control cardiac index was 1.9 +/- 0.5 liters/min/m2 and it increased significantly by 1 hour, with a peak effect at 2 hours to 2.4 +/- 0.4 liters/min/m2 (p less than 0.05). Similarly, wedge pressure, 22 +/- 8 mm Hg at control, decreased to 16 +/- 10 by 1 hour (p less than 0.05). Six of the 12 patients received 1 mg/kg of enoximone on day 1 and 2 mg/kg on day 2. The higher dose of enoximone caused no further improvement in cardiac performance but prolonged the salutary hemodynamic effect. Subsequently, 79 patients (18 in New York Heart Association class III and 61 in class IV) with CHF (ejection fraction 17 +/- 8%) were followed over a 3 year period; the average enoximone dose was 1.7 +/- 0.7 mg/kg 3 times daily. Improvement of at least 1 functional class occurred in 55 patients (70%) at 1 month, 27 patients (34%) at 6 months and 19 (24%) maintained their improvement for over 1 year. Enoximone was discontinued in 20 patients (25%); in 5 (6%) for adverse effects and in 13 patients because of no clinical benefit. Adverse effects occurred in 14 patients (18%); 6% of all patients required discontinuation of drug. Six month survival was 50%, 42% at 1 year and 30% at 2 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term treatment with oral enoximone for chronic congestive heart failure: the European experience

The long-term safety and efficacy of the inotropic/vasodilatory agent enoximone (50 to 100 mg 3 times daily) were evaluated in 30 patients with chronic congestive heart failure (New York Heart Association classes II to IV). Nineteen patients had idiopathic dilated cardiomyopathy and 11 had ischemic heart disease. Patients were receiving maintenance therapy of digitalis and diuretics. Cardiac function was assessed at 12 week intervals (physical examination, exercise testing, chest x ray, echocardiography, radionuclide angiography, 24-hour Holter monitoring and blood chemistry). During a mean follow-up of 40 weeks, 6 patients died, due to noncardiac (n = 1) and sudden death (n = 1) and to cardiac failure (n = 4) within 36 weeks of drug treatment. In the remaining patients New York Heart Association class improved in 18, was stationary in 5 and deteriorated in 1. Exercise capacity increased during the first 26 weeks and was maintained improved thereafter. Clinical improvement appeared not to wane with time. No change in heart rate, blood pressure and cardiothoracic ratio was observed. Echocardiographic left ventricular dimensions did not change significantly; however, the fractional shortening increased from baseline (14%) to 19% after 12 weeks, 17% after 26 weeks and 21% after 52 weeks (p less than 0.05). The preejection period/left ventricular ejection time ratio decreased from 0.74 to 0.35, 0.44 and 0.43 (p less than 0.05), respectively. There was an increase in radionuclide ejection fraction from 23% to 27% (difference not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Diastolic function in patients with severe heart failure: comparison of the effects of enoximone and nitroprusside

To assess whether the phosphodiesterase inhibitor enoximone has a specific, direct effect on left ventricular diastolic function distinct from its inotropic and vasodilator actions, we compared the effects of enoximone and the pure vasodilator nitroprusside in 11 patients with severe heart failure. Mean (+/- SEM) left ventricular ejection fraction was 0.20 +/- 0.03. Simultaneous left ventricular pressure and radionuclide angiographic volume were obtained at baseline, during infusion of nitroprusside, and after intravenous administration of enoximone. Left ventricular end-diastolic pressure (LVEDP) and volume (LVEDV) decreased with both agents (p less than .01 vs control); LVEDP was lower for nitroprusside than for enoximone (p less than .01) despite a similar LVEDV. Nitroprusside decreased the time constant of exponential left ventricular pressure decay, TL (measured by the logarithmic method), from 84 +/- 10 to 65 +/- 8 msec (p less than .01) but had no significant effect on TD (measured by the derivative method), maximum negative dP/dt, or the peak rate of early diastolic filling. Enoximone shortened TL from 86 +/- 12 to 61 +/- 9 msec (p less than .01) and increased maximum negative dP/dt from 897 +/- 101 to 1135 +/- 134 mm Hg/sec (p less than .01) but did not affect TD or the peak filling rate. The left ventricular diastolic pressure-volume relation was shifted downward in only three of 11 patients on nitroprusside and three of 11 patients on enoximone, and these shifts were attenuated by adjusting for simultaneous changes in right atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Inotropic effect of enoximone in patients with severe heart failure: demonstration by left ventricular end-systolic pressure-volume analysis

Left ventricular end-systolic pressure-volume analysis was employed to assess the inotropic effect of the phosphodiesterase inhibitor enoximone (formerly MDL-17,043) in nine patients with severe heart failure (New York Heart Association class IV symptoms, mean ejection fraction = 0.22). Left ventricular pressure-volume loops were constructed using high fidelity left ventricular pressure measured with micromanometer-tipped catheters and simultaneous left ventricular volume obtained by gated blood pool imaging. Afterload was reduced with the vasodilator nitroprusside to generate the baseline left ventricular end-systolic pressure-volume relation, a relatively load-independent measure of contractile function. The intravenous administration of enoximone (mean dose 75 mg) shifted the end-systolic pressure-volume point upward and leftward from the baseline pressure-volume relation in eight of the nine patients, demonstrating a positive inotropic effect of this agent. The maximal rate of left ventricular pressure development (peak positive dP/dt) increased from 1,030 +/- 142 to 1,381 +/- 219 mm Hg/s (p less than 0.01) on enoximone despite a significant decrease in preload (as assessed by left ventricular end-diastolic pressure and volume) and a small, insignificant decrease in mean arterial pressure. Two patients developed angina after enoximone administration; both patients had coronary artery disease and experienced a greater than 30% increase in heart rate-systolic blood pressure product. Thus, enoximone has a significant inotropic effect in patients with severe heart failure. Like other inotropic drugs, it has the potential to increase myocardial oxygen demand and thereby precipitate ischemia.

Hemodynamic and clinical evaluation of piroximone, a new inotrope-vasodilator agent, in severe congestive heart failure

To assess the potential utility of piroximone (MDL-19,205), an investigational inotrope-vasodilator agent, in severe heart failure, 15 patients with severe left ventricular failure refractory to conventional agents were enrolled in an acute hemodynamic study. After incremental intravenous dosing (mean total dose 1.8 +/- 0.4 mg/kg body weight), cardiac index increased (1.7 +/- 0.3 to 2.6 +/- 0.6 liters/min per m2; p less than 0.001) and left ventricular filling pressure decreased (25 +/- 7 to 19 +/- 7 mm Hg; p less than 0.001). Also decreasing significantly were right atrial pressure (13 +/- 6 to 7 +/- 5 mm Hg; p less than 0.005) and systemic vascular resistance (1,633 +/- 394 to 1,183 +/- 278 dynes.s.cm-5; p less than 0.001). Heart rate and mean arterial pressure did not change, whereas stroke work index increased significantly (13.3 +/- 4.3 to 21.6 +/- 7.3 g.m/m2; p less than 0.005). The increase in stroke work index with a concomitant decrease in left ventricular filling pressure indicates an improvement in systolic performance after treatment with piroximone. Similar responses were obtained after incremental doses of piroximone in oral solution. After oral doses of piroximone tablets, cardiac index also increased significantly (2.1 +/- 0.6 to 2.4 +/- 0.5 liters/min per m2; p less than 0.05), although this magnitude of increase was comparatively low. In a subgroup of 10 patients who underwent equilibrium gated radionuclide blood pool scintigraphy before and after intravenous piroximone, end-diastolic volume index tended to increase (106 +/- 42 to 132 +/- 60 ml/m2; p = 0.07), whereas left ventricular filling pressure decreased significantly (26 +/- 8 to 19 +/- 9 mm Hg; p less than 0.01).

Electrophysiological effects of intravenous MDL 17.043

MDL 17.043, a nonglycoside, noncatecholamine imidazolone derivative with phosphodiesterase inhibiting activity, has been shown to possess both positive inotropic and vasodilator properties. In the present study, the electrophysiological effects of intravenous MDL 17.043 were assessed in 10 patients undergoing programmed right atrial stimulation for diagnostic purposes. MDL 17.043 was administered as a single intravenous bolus injection of 1.5 mg/kg body weight over 4 min followed by an intravenous infusion of 0.75 mg/kg body weight over 20 min. With the dosage schedule used, the MDL 17.043 plasma levels achieved were similar to those previously reported to be associated with significant hemodynamic improvement of congestive heart failure. Electrophysiological measurements were performed before and during MDL 17.043 administration. MDL 17.043 consistently shortened basic sinus cycle length, sinus node recovery time and sinuatrial conduction time and decreased Wenckebach cycle length, atrioventricular and atrial refractoriness leading to positive chronotropic and dromotropic effects.

Milrinone in congestive heart failure: acute and chronic hemodynamic and clinical evaluation

Acute and chronic hemodynamic and clinical responses to milrinone, a new oral inotrope-vasodilator agent, were evaluated prospectively in 37 patients with severe congestive heart failure. The majority of patients (n = 31) had not responded to prior vasodilator therapy, with a substantial number (n = 8) requiring intravenous inotropic support at the time of initial study. All patients showed acute hemodynamic improvement with oral milrinone, and an optimal maintenance dose was chosen for each patient during dose-ranging studies (average dose 48 mg/day). Milrinone was discontinued before follow-up hemodynamic study in 12 patients (because of worsening congestive heart failure in 6 patients, sudden death in 3 patients, arrhythmia in 1 patient and refusal by 2 patients). Hemodynamic effects of milrinone both acutely and after chronic therapy (average 37 days) were compared in the remaining 25 patients. Acutely, mean cardiac index increased from 1.9 +/- 0.5 to 2.5 +/- 0.5 liters/min per m2 (p less than 0.001), and mean pulmonary capillary wedge pressure decreased from 28 +/- 9 to 18 +/- 8 mm Hg (p less than 0.001). When oral milrinone was readministered after chronic therapy, mean cardiac index increased from 1.9 +/- 0.5 to 2.5 +/- 1.7 liters/min per m2 (p less than 0.001), and pulmonary capillary wedge pressure decreased from 27 +/- 8 to 20 +/- 8 mm Hg (p less than 0.001) at 1 hour. New York Heart Association functional class improved in 18 of the 25 patients treated over a long-term period (mean 5.5 +/- 2.3 months).(ABSTRACT TRUNCATED AT 250 WORDS)