Cardiac energetics after intravenous enoximone in idiopathic dilated cardiomyopathy

Na(+)-channel modulation, a new principle of inotropic intervention: effects on hemodynamic and myocardial energetics in the immature rabbit heart

Na+-channel modulators exert their positive inotropic action without affecting the adenylate-cyclase pathway by an increase in the open probability of the sarcolemmal Na+ channels. Although inotropic effects in neonatal hearts are less pronounced compared with adult hearts, the Na+-channel modulator BDF 9148 increases contractility and relaxation velocity in immature myocardium. Effects on hemodynamics and myocardial energetics are not known. Therefore, we studied the Na+-channel modulator BDF 9148 in isolated antegrade perfused rabbit hearts of different ages (2-28 d) and compared the effects with isoproterenol, enoximone, and ouabain. ANOVA showed significant effects in the concentration response curves for heart rate, stroke volume, cardiac output, and oxygen consumption but not for myocardial efficiency (p = 0.06). Age-dependent differences were observed for heart rate and stroke volume. Administration of BDF 9148 resulted in a maximal increase in stroke volume and cardiac output up to 25% in neonatal and 40% to 60% in adult preparations. Heart rate decreased by 15% in adult hearts only. Myocardial oxygen consumption was increased in a concentration-dependent manner between 25% in neonatal and 50% in adult hearts. Myocardial efficiency was increased by 35% in adult and by 10% in neonatal preparations. Although positive hemodynamic and energetic effects were less pronounced in immature compared with adult hearts, neonatal hearts also profited from the administration of the Na+-channel modulator BDF 9148. Further studies are necessary to clarify the risk of arrhythmia during application of Na+-channel modulators such as BDF 9148.

Low-level inotropic stimulation with type III phosphodiesterase inhibitors in patients with advanced symptomatic chronic heart failure receiving beta-blocking agents

beta-blocking agents are now well established as a cornerstone therapy in mild to moderate heart failure. Patients with more advanced heart failure depend on adrenergic activation to maintain adequate myocardial function. This leads to significant difficulties in using beta-blockers in advanced or severe heart failure. In addition, recent data indicate that adrenergic withdrawal might be detrimental in some of these patients. In higher doses, positive inotropic agents have been shown to increase mortality when used alone in subsets with advanced heart failure. Preliminary data suggest that the combination of low-dose phosphodiesterase inhibitors and a beta-blocker may be better tolerated and does not appear to be associated with the adverse effects of either therapy used alone. We discuss the theoretic underpinning of this approach and the supportive clinical data.

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.

Effect of enoximone alone and in combination with metoprolol on myocardial function and energetics in severe congestive heart failure: improvement in hemodynamic and metabolic profile

The hemodynamic and myocardial metabolic effects of enoximone (phosphodiesterase III inhibitor), alone or in combination with metoprolol (beta-adrenergic blocker), were studied in patients with congestive heart failure. Ten patients (New York Heart Association Class III-IV) underwent right heart and coronary sinus catheterization, and parameters were assessed at basal condition, at peak enoximone response (mean intravenous loading dose = 2.2 mg/kg), and after the combination with metoprolol (mean intravenous dose = 8.5 mg). Heart rate tended to increase during enoximone administration (from 102 +/- 16 to 107 +/- 16 min-1, ns) and was reduced during enoximone plus metoprolol (to 88 +/- 15 min-1, p < 0.05 vs. basal). Cardiac index was increased during enoximone (from 2.2 +/- 0.2 to 3.8 +/- 0.5 1/min/m2, p < 0.05) and decreased during enoximone plus metoprolol (to 2.8 +/- 0.5 1/min/m2, p < 0.05 vs. enoximone). Mean pulmonary wedge pressure fell during enoximone and remained reduced during enoximone plus metoprolol (from 27 +/- 9 to 9 +/- 3 and to 13 +/- 4 mmHg, respectively, both p < 0.05). Myocardial oxygen consumption did not change during enoximone (from 27 +/- 8 to 25 +/- 13 ml/min, ns) and was reduced during enoximone plus metoprolol (to 19 +/- 8 ml/min, p < 0.05 vs. basal). Myocardial lactate extraction tended to be lower during enoximone and during enoximone plus metoprolol conditions (from 38 +/- 17% to 26 +/- 20% and to 29 +/- 24%, respectively), but no statistical significance was found. Myocardial efficiency was increased during enoximone and during enoximone plus metoprolol (from 9 +/- 3% to 15 +/- 6% and to 14 +/- 6%, respectively, both p < 0.05). Thus in patients with congestive heart failure enoximone improves hemodynamics and, in most cases, it does not influence energetics. The addition of metoprolol to enoximone reduces heart rate, cardiac index, and myocardial oxygen consumption without any other major changes, producing a more physiologic hemodynamic and metabolic profile.

The use of intravenous milrinone in chronic symptomatic ischemic heart disease

To evaluate the antiischemic effects of intravenous milrinone, 20 patients with angiographically proved coronary artery disease and stable angina were studied at rest and during exercise under control conditions and after an intravenous loading injection of milrinone (50 micrograms/kg/10 min) followed by an infusion with 0.5 micrograms/kg/min. Hemodynamic parameters, epinephrine, norepinephrine, and atrial natriuretic factor were assessed. Control ergometry revealed ischemia; however, during exercise with intravenous milrinone, ischemia was eliminated. Because of unloading effects, there was also a significant decrease in ST segment depression (p less than 0.001). Heart rate increased significantly (p less than 0.001) at rest but increased significantly less after exercise testing (p less than 0.001). The changes in mean arterial pressure, cardiac output, and myocardial oxygen consumption during exercise were not significantly different between the milrinone and control phase. Intravenous milrinone delayed the onset of angina (p less than 0.001) and significantly shortened the duration of anginal attacks (p less than 0.05); exercise duration in the milrinone phase was longer than in the control phase (p = 0.051). Because of vasodilatation, a mild secondary increase in norepinephrine was observed during the milrinone phase, and there was a significantly smaller increase in atrial natriuretic factor during exercise while receiving milrinone as a result of preload reduction (p less than 0.05). Intravenous milrinone produced beneficial hemodynamic and antiischemic effects in patients with coronary artery disease, stable angina, and reproducible ST segment depression probably by enhancing myocardial contractility and reducing preload and afterload.

Myocardial energetics in dilated cardiomyopathy

To assess hemodynamic and energetic effects of different drug interventions on idiopathic dilated cardiomyopathy (IDCM), we determined hemodynamic variables of myocardial oxygen consumption (MVO2) in 37 patients with IDCM. Hemodynamics were measured during routine left and right heart catheterization. MVO2 was analyzed from myocardial blood flow (measured by the argon method) and aortocoronary sinus blood oxygen difference. The hemodynamic variable which correlated best with MVO2 was shown to be the systolic stress time integral (STI). Four different representative compounds were tested with respect to their acute effects on myocardial energetics (MVO2/STI) in patients with IDCM who were in compensated heart failure (NYHA class II-III). The drug interventions were performed at rest. Intravenous injection of the vasodilator nitroprusside yielded a 35% reduction in STI and a 30% reduction in MVO2; in other words, the ratio MVO2/STI was not altered. Injection of the calcium sensitizer and phosphodiesterase inhibitor pimobendan also did not alter this ratio, as both STI (36%) and MVO2 (33%) were lowered. The profound reduction in STI (60%) seen with the phosphodiesterase inhibitor enoximone was accompanied by a much smaller decrease in MVO2 (19%); therefore, the ratio of MVO2/STI increased significantly. An increase of this ratio was also seen with the partial beta-1 receptor agonist xamoterol. However, in this case STI did not change, whereas MVO2 increased by 26%. In summary, vasodilation has energy-saving effects, whereas positive inotropism is an energy-consuming process. We conclude that the overall effect on myocardial energetics of a drug which possesses both positive inotropic and vasodilating properties depends on the balance of the two properties.

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.

Effect of phosphodiesterase inhibition on myocardial oxygen consumption and coronary blood flow

The phosphodiesterase inhibitors (amrinone, milrinone and enoximone) can cause major improvement in the performance of the failing heart without increasing myocardial oxygen consumption. This appears to be the result of a reduction in left ventricular systolic wall stress due to peripheral arteriolar vasodilatation, which offsets the increase in myocardial oxygen consumption that would otherwise result from an enhanced inotropic state. In comparison, catecholamine agents such as dobutamine, given at doses that achieve the same level of inotropic enhancement or improved left ventricular performance, produce less associated arteriolar vasodilatation and a significant (approximately 30%) increase in myocardial oxygen consumption. This difference between the phosphodiesterase inhibitors and the conventional catecholamine agents may be of clinical importance in patients with limited coronary flow reserve due to severe congestive heart failure.

Influence of enoximone and UDCG-115 on coronary hemodynamics in idiopathic dilated cardiomyopathy

Coronary hemodynamics were studied in 24 patients with idiopathic dilated cardiomyopathy and in 17 patients without any significant heart disease under resting conditions using the argon method. Neither myocardial blood flow normalized for 100 g muscle tissue nor myocardial oxygen consumption per minute (MVO2) or oxygen supply-demand ratio were different between these 2 groups of patients. When enoximone (1 to 2 mg/kg body weight) was given intravenously in patients with idiopathic dilated cardiomyopathy, myocardial oxygen consumption decreased by only 8% (difference not significant), whereas a significant (p less than 0.05) 26% decrease of myocardial oxygen consumption was observed after UDCG-115 (1.25 mg/hour intravenously). However, with both substances the oxygen supply-demand ratio significantly increased from 1.46 +/- 0.10 to 1.57 +/- 0.20 (p less than 0.025; enoximone) and from 1.40 +/- 0.08 to 1.56 +/- 0.19 (p less than 0.05; UDCG-115), respectively. It is concluded from these data that (1) resting coronary hemodynamics related to a unit of myocardium are not different between normal and idiopathic dilated cardiomyopathy, and (2) phosphodiesterase inhibitors exert beneficial effects on coronary hemodynamics by improving the oxygen supply-demand ratio.