The relationship between plasma dobutamine concentrations and cardiovascular responses in cardiac failure

The Effects of Dobutamine in Septic Shock: An Updated Narrative Review of Clinical and Experimental Studies

The key objective in the hemodynamic treatment of septic shock is the optimization of tissue perfusion and oxygenation. This is usually achieved by the utilization of fluids, vasopressors, and inotropes. Dobutamine is the inotrope most commonly recommended and used for this purpose. Despite the fact that dobutamine was introduced almost half a century ago in the treatment of septic shock, and there is widespread use of the drug, several aspects of its pharmacodynamics remain poorly understood. In normal subjects, dobutamine increases contractility and lacks a direct effect on vascular tone. This results in augmented cardiac output and blood pressure, with reflex reduction in systemic vascular resistance. In septic shock, some experimental and clinical research suggest beneficial effects on systemic and regional perfusion. Nevertheless, other studies found heterogeneous and unpredictable effects with frequent side effects. In this narrative review, we discuss the pharmacodynamic characteristics of dobutamine and its physiologic actions in different settings, with special reference to septic shock. We discuss studies showing that dobutamine frequently induces tachycardia and vasodilation, without positive actions on contractility. Since untoward effects are often found and therapeutic benefits are occasional, its profile of efficacy and safety seems low. Therefore, we recommend that the use of dobutamine in septic shock should be cautious. Before a final decision about its prescription, efficacy, and tolerance should be evaluated throughout a short period with narrow monitoring of its wanted and side effects.

A Review of Inotropes and Inopressors for Effective Utilization in Patients With Acute Decompensated Heart Failure

ABSTRACT

Inotropes and inopressors are often first-line treatment in patients with cardiogenic shock. We summarize the pharmacology, indications, and contraindications of dobutamine, milrinone, dopamine, norepinephrine, epinephrine, and levosimendan. We also review the data on the use of these medications for acute decompensated heart failure and cardiogenic shock in this article.

Ranolazine may exert its beneficial effects by increasing myocardial adenosine levels

We hypothesized that ranolazine-induced adenosine release is responsible for its beneficial effects in ischemic heart disease. Sixteen open-chest anesthetized dogs with noncritical coronary stenosis were studied at rest, during dobutamine stress, and during dobutamine stress with ranolazine. Six additional dogs without stenosis were studied only at rest. Regional myocardial function and perfusion were assessed. Coronary venous blood was drawn. Murine endothelial cells and cardiomyocytes were incubated with ranolazine and adenosine metabolic enzyme inhibitors, and adenosine levels were measured. Cardiomyocytes were also exposed to dobutamine and dobutamine with ranolazine. Modeling was employed to determine whether ranolazine can bind to an enzyme that alters adenosine stores. Ranolazine was associated with increased adenosine levels in the absence (21.7 ± 3.0 vs. 9.4 ± 2.1 ng/mL, P < 0.05) and presence of ischemia (43.1 ± 13.2 vs. 23.4 ± 5.3 ng/mL, P < 0.05). Left ventricular end-systolic wall stress decreased (49.85 ± 4.68 vs. 57.42 ± 3.73 dyn/cm², P < 0.05) and endocardial-to-epicardial myocardial blood flow ratio tended to normalize (0.89 ± 0.08 vs. 0.76 ± 0.10, P = nonsignificant). Adenosine levels increased in cardiac endothelial cells and cardiomyocytes when incubated with ranolazine that was reversed when cytosolic-5'-nucleotidase (cN-II) was inhibited. Point mutation of cN-II aborted an increase in its specific activity by ranolazine. Similarly, adenosine levels did not increase when cardiomyocytes were incubated with dobutamine. Modeling demonstrated plausible binding of ranolazine to cN-II with a docking energy of -11.7 kcal/mol. We conclude that the anti-adrenergic and cardioprotective effects of ranolazine-induced increase in tissue adenosine levels, likely mediated by increasing cN-II activity, may contribute to its beneficial effects in ischemic heart disease.NEW & NOTEWORTHY Ranolazine is a drug used for treatment of angina pectoris in patients with ischemic heart disease. We discovered a novel mechanism by which this drug may exhibit its beneficial effects. It increases coronary venous levels of adenosine both at rest and during dobutamine-induced myocardial ischemia. Ranolazine also increases adenosine levels in endothelial cells and cardiomyocytes in vitro, by principally increasing activity of the enzyme cytosolic-5'-nucleotidase. Adenosine has well-known myocardial protective and anti-adrenergic properties that may explain, in part, ranolazine's beneficial effect in ischemic heart disease.

Engineered Cardiac Tissues Generated in the Biowire™ II: A Platform for Human-Based Drug Discovery

Recent advances in techniques to differentiate human induced pluripotent stem cells (hiPSCs) hold the promise of an unlimited supply of human derived cardiac cells from both healthy and disease populations. That promise has been tempered by the observation that hiPSC-derived cardiomyocytes (hiPSC-CMs) typically retain a fetal-like phenotype, raising concern about the translatability of the in vitro data obtained to drug safety, discovery and development studies. The Biowire™ II platform was used to generate 3D engineered cardiac tissues (ECTs) from hiPSC-CMs and cardiac fibroblasts. Long term electrical stimulation was employed to obtain ECTs that possess a phenotype like that of adult human myocardium including a lack of spontaneous beating, the presence of a positive force-frequency response from 1-4Hz and prominent post-rest potentiation. Pharmacology studies were performed in the ECTs to confirm the presence and functionality of pathways that modulate cardiac contractility in humans. Canonical responses were observed for compounds that act via the β-adrenergic/cAMP-mediated pathway, e.g. isoproterenol and milrinone; the L-type calcium channel, e.g. FPL64176 and nifedipine; and indirectly effect intracellular Ca2+ concentrations, e.g. digoxin. Expected positive inotropic responses were observed for compounds that modulate proteins of the cardiac sarcomere, e.g. omecamtiv mecarbil and levosimendan. ECTs generated in the BiowireTM II platform display adult-like properties and have canonical responses to cardiotherapeutic and cardiotoxic agents that affect contractility in humans via a variety of mechanisms. These data demonstrate that this human-based model can be used to assess the effects of novel compounds on contractility early in the drug discovery and development process.

Prognostic significance of sinus deceleration during dobutamine stress echocardiography test following acute myocardial infarction

Background/Aim. Chronotropic incompetence during exercise stress testing after acute myocardial infarction is an indicator of ischemia or impaired left ventricular function. On the other side, infusion of dobutamine leads to a typical dose-dependent increase in heart rate. The aim of this study was to evaluate of paradoxical sinus deceleration during dobutamine stress echocardiography (DSE), as the sign of ischemia and impaired left ventricular function, or the consequence of infarction localization, and the estimation of prognostic significance after acute myocardial infarction. Methods. Our investigation comprised 81 patients hospitalized because of the acute myocardial infarction, and all of them had uncomplicated infarction. Fifty five patients were treated with thrombolytic therapy (67.9%); 53 patients (65.4%) had anterior myocardial infarction, and 28 patients (34.6%) had inferoposterior localization of myocardial infarction. After 10-12 days all of them underwent dobutamine stress echocardiography examination. During the next 3-6 months, the patients underwent coronary angiography. The average follow-up period was 36?22 months. Results. A decrease in heart rate occurred at the dobutamine doses increasing from 15-40mcg/kg/min in 9 (11.1%) of the patients, in 1 patient with an anterior localization and in 8 patients with an inferoposterior localization. The decrease was sudden in 4 (44.4%), and gradual in 5 (55.6%) of the patients. In 3 patients (33.3%) junction rhythm was developed, and in 2 patients (22.2%) AV block II-III. Only in 2 of them, there was a worsening of regional function during a high dose dobutamine infusion, but 7 of them showed an improvement during a low dose. In 7 (77.8%) of the patients there was a simultaneous decrease in blood pressure. Coronary angiographic examination showed that in 4 (44.4%) of the patients there was a significant coronary artery disease and they underwent the revascularization procedure. During the follow up period, there was not any significant arrhythmic disorder in that group of the patients or repeated hospitalization because of postinfarction angina, re-infarction, or heart failure. Conclusion. We could conclude that paradoxical sinus deceleration is not only an indicator of a significant coronary artery disease and ?bad left ventricle?. It also may occur as a consequence of vasodepressor reflex (Bezold-Jarisch), even after acute myocardial infarction, without influencing a long-term prognosis.

Assessment of Myocardial Viability with Dobutamine Stress Echocardiography in Patients with Ischemic Left Ventricular Dysfunction

The noninvasive assessment of myocardial viability has proved clinically useful for distinguishing hibernating and/or stunned myocardium from irreversibly injured myocardium in patients with chronic ischemic heart disease or recent myocardial infarction, with marked regional and/or global left ventricular (LV) dysfunction. Noninvasive techniques utilized for the detection of viability in asynergic myocardial regions include positron emission tomographic imaging of residual metabolic activity, single photon emission tomography (SPECT) of radioisotope uptake with thallium-201, low-dose dobutamine echocardiography assessment of inotropic reserve and myocardial contrast echocardiography for evaluation of microvascular integrity. Of these techniques, dobutamine stress echocardiography is a safe, widely available and relatively inexpensive modality for the identification of myocardial viability for risk stratification and prognosis. Low-dose dobutamine response can accurately predict improvement of dysfunctional yet viable myocardial regions, and thus identify a subset of patients whose LV function will improve following successful coronary revascularization.

Low-dose dobutamine stress 99mTc tetrofosmin quantitative gated SPECT performed during the acute phase of myocardial infarction predicts subsequent myocardial viability and detects stunned myocardium

This study evaluated the ability of low-dose dobutamine stress 99mTc tetrofosmin (DSTF) quantitative gated single photon emission computed tomography (QGS) performed during the acute phase of myocardial infarction to predict subsequent myocardial viability and detect stunned myocardium. Twenty-four patients suffering their first acute myocardial infarction (AMI) underwent coronary angioplasty after coronary angiography (CAG) immediately following admission. Follow-up CAG and left ventriculography (LVG) were performed 10 days and 6 months later. All patients underwent DSTF QGS to measure left ventricular ejection fraction (LVEF) at rest and during dobutamine infusion (10 microg.kg(-1).min(-1)) 14 days after angioplasty. No patient suffered coronary restenosis. After 6 months, the LVEF measured by LVG improved >5% in 12 patients (group A), and did not improve in the remaining 12 patients (group B). The culprit coronary artery, the peak serum creatine phosphokinase concentration, the recanalization time, and the LVEF during the acute phase were similar in the two groups. However, the increase in the LVEF was greater in group A than in group B during dobutamine infusion (deltaLVEF) as measured by DSTF QGS (11.2+/-3.8% vs 2.9+/-4.7%, P <0.001). If a cut-off value of 6.5% for the deltaLVEF was used to predict the improvement in LVEF during the chronic phase, then the sensitivity of this test was 83.3% and its specificity was 83.3%. It is concluded that DSTF QGS during AMI can be used to predict myocardial viability and detect stunned myocardium.

Dobutamine gated blood pool scintigraphy predicts the improvement of cardiac sympathetic nerve activity, cardiac function, and symptoms after treatment in patients with dilated cardiomyopathy

BACKGROUND

We evaluated whether dobutamine gated blood pool scintigraphy (DOB-GBP) can predict improvement in cardiac sympathetic nerve activity and cardiac function after beta-blocker therapy in patients with dilated cardiomyopathy (DCM).

METHODS AND RESULTS

Twenty-two patients with DCM underwent DOB-GBP to measure left ventricular ejection fraction (LVEF) at rest, and during 5, 10, and 15 microg/kg/min of dobutamine infusion before therapy. Examinations were performed before and after 1 year of therapy. The heart/mediastinum count (H/M) ratio and total defect score (TDS) were determined for 123I-meta-iodobenzylguanidine images from anterior planar image and single-photon emission CT images. LVEF and left ventricular end-diastolic dimension (LVDd) were determined by echocardiography. After 1 year of treatment, the echocardiographic LVEF improved > 5% in 11 patients (group A), but did not improve in the remaining 11 patients (group B). Before treatment, TDS, H/M, LVEF, and LVDd were similar in both groups. However, there was a greater increase in the LVEF during dobutamine infusion in group A than in group B (21 +/- 8% vs 9 +/- 3%, p < 0.001). If a critical value of 15% for the DeltaLVEF was used to predict the improvement in LVEF after treatment, the sensitivity was 91% and specificity was 82%. The TDS, H/M ratio, LVDd, and New York Heart Association functional class improved in group A to a greater extent than in group B.

CONCLUSIONS

DOB-GBP can be used to predict improved cardiac sympathetic nerve activity, cardiac function, and symptoms after treatment in patients with DCM.

Myocardial contractile reserve under low doses of dobutamine and improvement of left ventricular ejection fraction with treatment by carvedilol

To examine the ability of myocardial contractile reserve (MCR) assessment to predict the improvement of left ventricular ejection fraction with treatment by carvedilol, a prospective study was undertaken in 85 patients with chronic heart failure and left ventricular ejection fraction < 45%. Low dose dobutamine echocardiography (DSE), a 6-min walk test and measured brain natriuretic peptide (BNP) were assessed in all the patients. Patients were separated into two groups. Group A were patients without any myocardial reserve and group B patients with a myocardial contractile reserve defined as an increment of more than 20% of the resting left ventricular ejection fraction during dobutamine infusion. The two groups differed for percentage of ischemic cardiomyopathy (67.8 in group A vs. 29.7% in group B P = 0.028), 6-min walk test performance (respectively, 343 vs. 415 meters P < 0.05) and BNP plasma levels (respectively, 184.5 vs. 70.1 P < 0.02) but not for left ventricular ejection fraction or NYHA class. During DSE, MCR and heart rate variation was higher in group B than in group A. At the end of the follow up, LVEF increased and NYHA class decreased in group B but not in group A. In multivariate analysis the existence of MCR could predict the improvement of LVEF with treatment by carvedilol. In our study, studying MCR could help to predict patients who will improve their LVEF with carvedilol prior to the administration of the treatment.

Low potential of dobutamine and dopexamine to block intestinal peristalsis as compared with other catecholamines

OBJECTIVE

Catecholamines are frequently used in critically ill patients to restore stable hemodynamics and to improve organ perfusion. One effect of short-term or long-term administration of catecholamines may be inhibition of propulsive motility in the intestine. We therefore analyzed the effect of dopexamine, dobutamine, and dopamine on ileal peristalsis and compared their action with that of epinephrine and norepinephrine, which have long been known to suppress intestinal peristalsis.

DESIGN

In vitro study on excised guinea pig ileum segments.

SETTING

Laboratory for experimental studies at the University.

SUBJECTS

Isolated guinea pig ileum.

INTERVENTIONS

Segments of ileum excised from guinea pigs were mounted in a tissue bath in Krebs-Henseleit solution and bubbled with 95% oxygen/5% CO2. Luminal perfusion with the same solution was performed at a rate of 0.35 mL/min. The bath temperature was kept at 36.5 degrees C. Peristalsis was recorded via changes in the intraluminal pressure. The drugs under investigation (dopamine, epinephrine, norepinephrine, dobutamine, and dopexamine) were added to the tissue bath.

MEASUREMENTS AND MAIN RESULTS

Low concentrations of each catecholamine, except epinephrine, caused a decrease in the pressure threshold, which reflects a stimulatory effect on peristalsis. Higher catecholamine concentrations caused a concentration-related increase in the threshold, cumulating in a complete block of peristalsis. The rank order of inhibitory potency was epinephrine > norepinephrine > dopamine > dobutamine approximately dopexamine. Dobutamine and dopexamine were about 500-fold less active than epinephrine in suppressing peristalsis.

CONCLUSIONS

This study shows that dobutamine and dopexamine have the least potential to block propulsive motility in the intestine, whereas epinephrine demonstrates the most adverse inhibitory effect. Because at low concentrations dobutamine and dopexamine even stimulate peristalsis, these drugs appear to be superior compared with other catecholamines with regard to their direct effects on intestinal motility.

Vasorelaxant actions of enoximone, dobutamine, and the combination on human arterial coronary bypass grafts

Enoximone (a type III-selective phosphodiesterase inhibitor) and dobutamine (a beta-receptor agonist) are positive inotropic drugs frequently used in the postoperative management of coronary bypass surgery. The purpose of this study was to characterize their relaxant effects on the human internal mammary artery (IMA) and the gastroepiploic artery (GEA) and to test the hypothesis that their combination may have greater than additive relaxant effects. In organ baths, the relaxant effects of enoximone and dobutamine were tested on rings of IMA (n = 86) precontracted with U46619 (a thromboxane A2 mimetic), norepinephrine (NE), or KCl. The relaxant effects of dobutamine and enoximone also were tested on rings of GEA (n = 42) precontracted with U46619 and NE. The effect of the combination of enoximone and dobutamine were tested on rings of IMA (n = 24) precontracted with U46619 or NE. With respect to maximal relaxations induced by papaverine (10(-4) M), enoximone (< or =10(-3) M) caused full relaxations of IMA precontracted with NE, U46619, or KCI. Dobutamine (< or =10(-3) M) caused full relaxations of IMA precontracted with NE or KCI but only 46% (95% CI, 27-65) relaxation in the rings precontracted with U46619. Similar patterns of relaxation were observed in GEA rings, with dobutamine inducing partial relaxation in GEA precontracted with U46619. The pD2 values of enoximone and dobutamine were both significantly lower in segments precontracted with U46619. The in vitro threshold relaxant concentrations were in the upper limits or over the range of therapeutic plasma concentrations. The relaxant effect of the combination was significantly more important than the theoretic additive effect in IMA contracted with U46619 or NE. Enoximone and dobutamine are potent in vitro vasodilators but exert weak relaxant effects in IMA and GEA at concentrations in the therapeutic range. There is, however, a greater than additive vasorelaxant effect of the combination, suggesting that the vasorelaxant effect of the combination, in addition to the additive inotropic effect, may be beneficial to patients undergoing coronary bypass grafting.

Parenteral inotropic support for advanced congestive heart failure

Parenterally administered positive inotropic agents remain an important component of the therapeutics of cardiac dysfunction and failure. Dobutamine, a catechol, remains the prototype of this drug group, but recently has been joined by the phosphodiesterase III inhibitor, milrinone. Compared with dobutamine, milrinone has greater vasodilating-unloading properties. The catecholamine, dopamine, is often used as a parenteral positive inotrope; but at moderate to high dose, it evokes considerable systemic vasoconstriction. At lower doses, dopamine appears to augment renal function. Levosimendan and toborinone, new compounds with several mechanisms of action, are under active clinical investigation and review for approval. Parenteral positive inotropic therapy is indicated for short-term (hours to days) treatment of cardiovascular decompensation secondary to ventricular systolic dysfunction, low-output heart failure. More prolonged or continuous infusion of one of these agents may be necessary as a "pharmacologic bridge" to cardiac transplantation, another definitive intervention, or more advanced, intense medical therapy. An occasional patient will require a continuous infusion via indwelling venous catheter and portable pump, simply to be able to be discharged from the hospital setting and function in the home environment. Intermittent parenteral inotropic therapy for chronic heart failure has provoked considerable controversy and passion among cardiologists and heart failure specialists; an attempt is made to present this topic in an objective manner.

Low-dose dobutamine stress echocardiography in children and young adults

Dobutamine stress echocardiography has become widely accepted in the evaluation of adult patients with coronary heart disease. We wanted to assess the feasibility and the physiologic responses of stress echocardiography at low doses of dobutamine in a population of normal children and adults. Once achieved, we submitted a group of post-anthracycline patients to the test to assess the sensitivity of low-dose dobutamine stress echocardiography in the detection of cardiac dysfunction. Thirty-two healthy children and young adults (19 male and 13 female subjects, median age 15 years [range 6 to 26]) were studied. After the initial study of normal subjects, we submitted a cohort of 39 patients (18 female and 21 male, aged 6 to 25 years), who completed anthracycline chemotherapy, to the same protocol. Dobutamine was infused at rates of 0.5 to 2.5 and 5 microg/kg/min and echocardiographic measurements were obtained at rest and at the end of each stage. The test could be completed in 100% of the subjects without major complications. Statistically significant differences between resting echocardiographic values of systolic and diastolic function and values at 2.5 and 5 microg/kg/min of dobutamine were found. Moreover, dobutamine revealed or enhanced differences between normal subjects and the post-anthracycline patients. Thus, low-dose dobutamine stress echocardiography is feasible and safe in older children. The test is very sensitive for the detection of subclinical cardiac dysfunction in post-anthracycline patients and could possibly assess functional myocardial reserve.

Is dobutamine-induced sinus node deceleration a marker of significant stenosis of the right coronary artery?

STUDY OBJECTIVES

Sinus node deceleration during exercise is a highly specific marker for significant stenosis of the right coronary artery. Prior studies of dobutamine-induced sinus node deceleration have contained relatively few patients, and the purpose of this study was to determine if sinus node deceleration is an accurate marker of right coronary artery disease in a much larger study population.

DESIGN

Dobutamine stress echocardiography was performed in a cohort of patients, and submaximal exercise testing and coronary angiography were performed in most of the patients.

SETTING

A university hospital.

PATIENTS AND INTERVENTIONS

Dobutamine stress echocardiography was performed in 757 patients, and symptom-limited submaximal treadmill ECG was also performed in 571 of those patients. Sinus node deceleration was defined as a decrease in the heart rate at peak stress compared with that at the previous stage. Coronary angiography was performed in 631 patients, 184 of whom were found to have significant right coronary artery stenosis.

MEASUREMENTS AND RESULTS

The prevalence of dobutamine-induced sinus node deceleration (54 [7%] of 757 patients) was significantly higher than that induced during treadmill ECG (3 [0.5%] of 571 patients; p<0.001). The prevalence of inferior ischemia by echocardiography did not differ between patients with dobutamine-induced sinus node deceleration (26%) and those without (30%). There was also no significant difference in the prevalence of right coronary artery stenosis between the two groups (27% vs 29%). The specificity of dobutamine-induced sinus node deceleration for detecting significant stenosis of the right coronary artery (92%) was higher than that of echocardiography (84%; p<0.00), but the positive predictive value was lower (28% vs 64%; p<0.001).

CONCLUSIONS

Although sinus node deceleration during dobutamine stress echocardiography is a relatively more common finding, it does not always accompany significant stenosis in the right coronary artery. The mechanism for its induction is postulated to be vagal activation caused by multiple factors.

A model for the design and evaluation of algorithms for closed-loop cardiovascular therapy

Developing a clinically useful closed-loop drug delivery system can be extremely time consuming and costly. One approach to reducing the time and cost associated with developing closed-loop systems is to reduce the number of animal experiments and perform an extensive set of simulation studies. Through simulations, a closed-loop controller's performance can be evaluated over a complete spectrum of the patient population, including boundary conditions. Simulation studies are repeatable, offering significant advantages in comparing modifications in control algorithms. Finally, simulation studies can be performed in a fraction of the time required for animal studies, at a fraction of the cost. We have developed a simulator, that included a nonlinear pulsatile-flow cardiovascular model, a physiological regulatory mechanism, and the pharmacology of four frequently titrated cardiovascular drugs. This simulator has already been used in the design and evaluation of two closed-loop algorithms-a self-tuning regulator (STR) and a multiple model adaptive controller (MMAC)-for blood pressure control during and after cardiac surgery.

Paradoxical sinus deceleration during dobutamine stress echocardiography: description and angiographic correlation

OBJECTIVES

This report characterizes the paradoxical sinus deceleration occasionally observed during dobutamine stress testing and determines its relation to myocardial ischemia.

BACKGROUND

Dobutamine stress echocardiography is widely accepted as a noninvasive tool for evaluating coronary artery disease. With infusion of dobutamine, there is typically a dose-dependent increase in heart rate. However, in some patients, a paradoxical decrease in heart rate has been observed during high dose dobutamine infusion.

METHODS

In 181 consecutive patients undergoing both dobutamine stress echocardiography and coronary angiography, electrocardiographic (ECG) data collected during dobutamine infusion were reviewed to identify patients with a decrease in heart rate. The clinical, stress echocardiographic, hemodynamic and angiographic correlates of patients with a decrease in heart rate were reviewed.

RESULTS

A decrease in heart rate ranging from 7 to 64 beats/min occurred during high dose dobutamine infusion in 14 patients (8%, 95% confidence interval [CI] 6% to 10%), including 3 in whom a junctional rhythm developed. The decrease was sudden in five patients (36%, 95% CI 13% to 65%) and gradual in nine (64%, 95% CI 35% to 87%). A decrease in blood pressure (12 patients [86%], 95% CI 57% to 98%) with simultaneous chest pain (7 patients [50%], 95% CI 23% to 77%) and nausea (5 patients [36%], 95% CI 13% to 65%) was common. Significant coronary artery disease (> or = 50% diameter stenosis) was present in 8 (57%) of 14 patients (95% CI 29% to 82%). Two patients (14%, 95% CI 2% to 43%) had no clinical, ECG or echocardiographic evidence of ischemia and no significant coronary artery disease by angiography. There was no increased incidence of right coronary artery stenosis in patients with paradoxical sinus deceleration.

CONCLUSIONS

Paradoxical sinus deceleration occurs in 8% of patients during dobutamine stress testing. Although most often observed in patients with coronary artery disease, it can occur in the absence of ischemia and coronary artery disease, and in some patients may be due to a vasodepressor reflex.

Pharmacology of pediatric resuscitation

The resuscitation of children from cardiac arrest and shock remains a challenging goal. The pharmacologic principles underlying current recommendations for intervention in pediatric cardiac arrest have been reviewed. Current research efforts, points of controversy, and accepted practices that may not be most efficacious have been described. Epinephrine remains the most effective resuscitation adjunct. High-dose epinephrine is tolerated better in children than in adults, but its efficacy has not received full analysis. The preponderance of data continues to point toward the ineffectiveness and possible deleterious effects of overzealous sodium bicarbonate use. Calcium chloride is useful in the treatment of ionized hypocalcemia but may harm cells that have experienced asphyxial damage. Atropine is an effective agent for alleviating bradycardia induced by increased vagal tone, but because most bradycardia in children is caused by hypoxia, improved oxygenation is the intervention of choice. Adenosine is an effective and generally well-tolerated agent for the treatment of supraventricular tachycardia. Lidocaine is the drug of choice for ventricular dysrhythmias, and bretylium, still relatively unexplored, is in reserve. Many pediatricians use dopamine for shock in the postresuscitative period, but epinephrine is superior. Most animal research on cardiac arrest is based on models with ventricular fibrillation that probably are not reflective of cardiac arrest situations most often seen in pediatrics.

Dobutamine stress echocardiography in the evaluation of late anthracycline cardiotoxicity in childhood cancer survivors

Late anthracycline cardiotoxicity has been of increasing concern to pediatric oncologists. An increasing number of patients with cardiac dysfunction has been reported without a good correlation between cardiac function or symptoms and routine echocardiographic follow-up. We studied dobutamine stress echocardiography in patients who had received moderate doses of anthracyclines years before. Twenty-three patients (14 male, 9 female; 7-25 y) who completed chemotherapy with moderate doses of anthracyclines (180-380 mg/m2) more than 2 y previously underwent dobutamine stress echocardiography and were compared with a control group of 26 healthy young people (15 male, 11 female; 6-26 y) matched for age and weight. Dobutamine was administered in three periods up to a rate of 5 micro g/kg/min. Eighty-five percent of the patients showed an abnormal response to dobutamine. Both systolic and diastolic functions were affected. The systolic dysfunction was not related to diminished contractility but to an elevated systolic wall stress due to inadequate cardiac muscle thickening. The diminished wall thickening was related to the length of follow-up. Dobutamine proved to be a very sensitive method to detect clinical and subclinical cardiac dysfunction in patients post anthracycline chemotherapy and questions the concept of a safe dose.

Vascular smooth muscle relaxation by alpha-adrenoceptor blocking action of dobutamine in isolated rabbit aorta

We investigated the mechanism of vascular relaxation produced by dobutamine, a positive inotropic agent with beta 1-adrenergic action. Dobutamine concentration-dependently (10 nM-10 microM) relaxed ring segments of rabbit aorta partially precontracted with 1 microM phenylephrine (PE) but did not relax those precontracted with 40 mM K+ or 5 microM prostaglandin F2 alpha (PGF2 alpha). The relaxation was not completely inhibited by pretreatment with 10 microM propranolol. Dobutamine did not significantly increase tissue cyclic AMP levels concomitantly with relaxation as does isoproterenol (ISO) in rabbit aorta. Dobutamine produced a parallel rightward shift in concentration-response curves to PE. The Schild plot analysis resulted in a linear regression of a slope of 1.077 +/- 0.077, which was not significantly different from unity. The pA2 value of dobutamine as compared with PE in rabbit aorta was 6.81 +/- 0.03. Dobutamine causes arterial dilatation mediated not only through a beta-adrenergic action but also through an alpha-adrenergic blocking action in rabbit aorta.

Difference between the measured and ordered dose of catecholamine infusions

OBJECTIVE

To measure the actual concentrations of dopamine, dobutamine, and epinephrine in infusates prepared for patients, and to compare these concentrations with those of the dopamine HCl, dobutamine, and epinephrine HCl infusates that had been prescribed to evaluate drug preparation accuracy.

DESIGN

Prospective, unblind study.

SETTING

Pediatric intensive care unit in a tertiary-care teaching hospital.

PARTICIPANTS

All dopamine, dobutamine, and epinephrine infusions ordered for patients during the 2-month study period were eligible for inclusion in the study.

MEASUREMENTS

Daily samples of dopamine, dobutamine, and epinephrine infusates that were prepared for 41 pediatric patients were obtained; the infusate catecholamine concentration was measured by HPLC and compared with the ordered concentration. The concentration than was multiplied by the rate of infusion to determine the catecholamine dose.

MAIN RESULTS

There were significant differences between the measured doses of dopamine, dobutamine, and epinephrine and the dopamine HCl, dobutamine, and epinephrine HCl doses (p = 0.0001, p = 0.039, and p = 0.0009, respectively) that had been ordered because of preparation inaccuracies. Failure to account for the HCl salt in the stock drug accounted for some, but not all, of the inaccuracy of the dopamine HCl and epinephrine HCl infusates. There was a wide interday variability in the measured catecholamine dosage in patients receiving the same dose for 3 days or more.

CONCLUSIONS

There are daily fluctuations in the preparation of dopamine, dobutamine, and epinephrine infusates that could alter the amount of drug actually delivered to critically ill patients and potentially contribute to their hemodynamic instability.

Cardiovascular response in patients with and without myocardial ischaemia during dobutamine echocardiography stress test for coronary artery disease

Dobutamine is widely used in cardiac stress testing for coronary artery disease and myocardial viability. To assess the systemic cardiovascular response during dobutamine echocardiography stress testing, we investigated nine patients without myocardial ischaemia (group 1, aged 48 to 72 years) and nine patients with myocardial ischaemia during the test (group 2, aged 53 to 73 years), by use of Doppler/echocardiography and subclavian artery pulse trace calibrated with brachial artery pressures. Peripheral resistance, total arterial compliance, and aortic characteristic impedance were estimated using a 3-element windkessel model of the systemic circulation. During infusion of dobutamine up to 40 micrograms kg-1 min-1, arterial pressure was maintained near baseline levels, whereas heart rate and cardiac index increased, more so in group 1 (mean: 89 and 79%) than in group 2 (58 and 52%; P < 0.05 vs. group 1). Peripheral resistance was decreased by > or = 32% at peak stress, whereas characteristic impedance was maintained at or above baseline in both groups, and total arterial compliance was not significantly altered. The cardiovascular response in group 2 was not influenced by the wall motion abnormalities. Thus, in these patients the inotropic, chronotropic, and vasodilatory effects of dobutamine balanced the ischaemic impairment of left ventricular function during the stress test.

Stress echocardiography. Part II. Dobutamine stress echocardiography: techniques, implementation, clinical applications, and correlations

OBJECTIVE

To describe the rationale, methods, and clinical applications for dobutamine stress echocardiography.

DESIGN

We review our experience with the first 1,000 Mayo Clinic patients who underwent this procedure and discuss studies from the literature that have assessed the accuracy of dobutamine stress echocardiography in determining the presence and extent of coronary artery disease.

MATERIAL AND METHODS

The Mayo protocol for dobutamine stress echocardiography is presented, and the indications for use of this test and comparisons of sensitivity and specificity with other tests are summarized.

RESULTS

Although exercise stress testing is the usual noninvasive method for the detection and assessment of coronary artery disease, a substantial number of patients are unable to perform adequate exercise because of physical limitations. In these patients, dobutamine stress echocardiography has emerged as a feasible, safe, and accurate method for the evaluation of coronary artery disease. The test has been proved to be valuable in the noninvasive diagnosis of coronary artery disease and to have an accuracy comparable to that of tomographic perfusion imaging. Other indications for dobutamine stress echocardiography include risk stratification before noncardiac surgical procedures, risk stratification after myocardial infarction, and identification of viable myocardium in patients with left ventricular dysfunction.

CONCLUSION

Dobutamine stress echocardiography is an accurate, safe, cost-effective, and portable procedure for the noninvasive diagnosis of coronary artery disease and for the preoperative assessment of patients with such disease, especially those who are unable to perform adequate exercise tests.

Pharmacokinetics of cardiovascular drugs in children. Inotropes and vasopressors

Infants and children with congenital or acquired heart disease and children with systemic disease often require pharmacological support of their failing circulation. Catecholamines may serve as inotropic (enhance myocardial contractility) or vasopressor (elevate systemic vascular resistance) agents. Noncatecholamine inotropic agents, such as the cardiac glycosides or the bipyridines, may be used in place of, or in addition to, catecholamines. Developmental changes in neonates, infants and children will affect the response to inotropic or pressor therapy. Maturation of the gastrointestinal tract, liver and kidneys alters absorption, metabolism and elimination of drugs, although there are few clear examples of this among the vasoactive drugs considered in this review. Changes in body composition affect the volume of distribution (Vd) and clearance (CL) of drugs. Developmentally based pharmacodynamic differences also affect the responses to both therapeutic and toxic effects of inotropes. These pharmacodynamic differences are based in part upon developmental changes in myocardial structure, cardiac innervation and adrenergic receptor function. For example, the immature myocardium has fewer contractile elements and therefore a decreased ability to increase contractility; it also responds poorly to standard techniques of manipulating preload. Available data suggest that dopamine and dobutamine pharmacokinetics are similar to those in adults. Wide interindividual variability has been noted. A consistent relationship between CL and age has not been demonstrated, although one investigator demonstrated an almost 2-fold increase in the CL of dopamine in children under the age of 2 years. The CL of dopamine appears to be reduced in children with renal and hepatic failure. Fewer data are available regarding the pharmacokinetics of epinephrine (adrenaline), norepinephrine (noradrenaline) and isoprenaline (isoproterenol). Digoxin pharmacokinetics have been extensively evaluated in infants and children. The Vd for digoxin is increased in infants and children. Children beyond the neonatal period display increased CL of digoxin, approaching adult values during puberty. Although it was previously thought that children both needed and tolerated higher serum concentrations of digoxin than adults, more recent studies indicate that adequate clinical response can be achieved with serum concentrations similar to those aimed for in adults, with decreased toxicity. Evaluation of studies of digoxin pharmacokinetics is complicated by the presence of an endogenous substance with digoxin-like activity on radioimmunoassay. Limited studies of amrinone pharmacokinetics in infants and children indicate a dramatically larger Vd, and a decreased elimination half-life in older infants and children, compared with values observed in adults.

Inotropic support of the critically ill patient. A review of the agents

Intensive care patients often require inotropic support to stabilise circulation and to optimise oxygen supply. In this context, the catecholamines norepinephrine (noradrenaline), epinephrine (adrenaline), dopamine and dobutamine are still the mainstay of therapy. They provide, to different extents, a variety of adrenoceptor-mediated actions comprising vasoconstriction (via alpha-receptors) as well as vasodilatation (via beta 1-receptors), and an increase in cardiac output by enhancing inotropy and heart rate (again via beta 1-receptors). Because of their favourable pharmacokinetic profile (plasma half-lives of about 2 minutes) their actions can easily be controlled. Combinations of different catecholamines with each other or with other drugs such as phosphodiesterase inhibitors or nitrates lead to a broad spectrum of possible haemodynamic actions. However, the use of catecholamines is limited by side effects like tachycardia, hypertension and disturbances of organ perfusion caused by vasoconstriction. Furthermore, as a result of receptor downregulation during long term therapy, the efficacy of catecholamine treatment decreases. These shortfalls stimulated the search for alternatives to catecholamine treatment. Among these, phosphodiesterase inhibitors (e.g. enoximone and amrinone) appear to be the most promising drugs which have been introduced into acute clinical practice up to now. They act via inhibition of the phosphodiesterase isoenzyme III, leading to higher intracellular calcium levels by increasing cyclic adenosine monophosphate (cAMP) levels. These agents improve cardiac performance by enhancing contractility, reducing left ventricular afterload and improve diastolic relaxation. In cases of failing catecholamine therapy due to receptor downregulation, treatment with phosphodiesterase inhibitors may still be effective since their action is not receptor-mediated. Inhibition of the phosphodiesterase enzyme in vascular smooth muscle leads to vasodilatation. Therefore, in low cardiac output states combined with increased total peripheral or pulmonary vascular resistance, phosphodiesterase inhibitor therapy is particularly effective. Depending on the dosage and the speed of intravenous administration, the use of phosphodiesterase inhibitors sometimes results in pronounced decrease of blood pressure which may require vasopressor therapy. Other drugs including histamine H2-agonists are currently under investigation. Their value in the treatment of intensive care patients has still to be evaluated.

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.

Catecholamines in critical care. The commonly used catecholamines: receptor and clinical profile, indications and dosages

The pharmacology, pattern of receptor activation and resulting clinical impact of the currently most widely used intravenous catecholamines are reviewed. A brief physiological description of the alpha, beta and dopaminergic receptors is used in order to explain the clinical effects of norepinephrine, epinephrine, isoproterenol, dopamine, dobutamine and dopexamine. Each drug is discussed separately according to receptor profile, indications, dosages and current application in critical care. Tables are provided for comparison of relative strengths of these drugs regarding receptor activation, haemodynamic effects, organ perfusion and recommended dosages. The use of combinations of catecholamines to meet a variety of circulatory demands is commented upon.

New developments in pharmacologic stress imaging

The clinical usefulness of cardiac imaging modalities that rely upon the detection of perfusion defects and wall motion disturbances requires conditions that provoke a heterogeneity of coronary flow and a myocardial oxygen imbalance, respectively. Traditionally, this has been achieved by exercise stress testing. Many patients cannot perform dynamic exercise sufficiently for various reasons. Pharmacologic stress has been proven to be an attractive alternative for physical exercise. Currently, several stressing agents are used in conjunction with thallium-201 scintigraphy, 2-D echocardiography and, recently, MRI. The most employed agents include vasodilators, such as dipyridamole and adenosine, and catecholamines, such as dobutamine (Table VI). The predominant rationale of thallium-201 perfusion scintigraphy is based on the creation of a flow maldistribution between territories supplied by normal arteries and those supplied by stenotic arteries that does not necessarily require ischemia. Dipyridamole and adenosine, as rather selective coronary vasodilators, are well suited to provoke such a condition and may be classified as the ideal markers of myocardial perfusion. 2-D echocardiography and MRI have the potential to provide noninvasively derived information of cardiac dynamics and regional myocardial function. To assess the functional significance of coronary artery disease, detection of wall motion abnormalities and alterations in ejection fraction require the presence of myocardial ischemia. Dobutamine, as a widely applied inotropic agent in the management of severely depressed left ventricular contractile function, seems to be an appropriate pharmacologic stressor when heart failure is absent. By increasing contractility, heart rate, and systolic arterial pressure, it is capable of inducing an imbalance between myocardial oxygen demand and supply, leading to ischemia in patients with coronary artery disease.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of dobutamine infusion and exercise during radionuclide ventriculography in the evaluation of coronary arterial disease

Twenty-six patients with "chest pain" syndrome were subjected to radionuclide ventriculography during exercise and dobutamine infusion. All 10 patients with normal coronaries were identified correctly by normal ventriculographic responses to both tests. Of 16 patients with significant coronary arterial disease, dobutamine stress identified 15 patients correctly, whereas only 12 of these had an abnormal exercise response. Three patients with one-vessel disease with a normal exercise response had an abnormal dobutamine stress response. Dobutamine radionuclide stress testing is an acceptable alternative to exercise testing in patients who cannot exercise and its incremental diagnostic yield in patients with one-vessel disease requires further evaluation.

Acute positive inotropic intervention: the catecholamines

The catecholamines remain a major therapeutic group in intensive cardiac care; this group of compounds evokes a positive inotropic response and vascular effects ranging from vasoconstriction to little net effect to vasodilatation. Hemodynamics and clinical guidelines now allow a proper selection of the optimal catecholamine. Additional mechanisms of action and a better understanding of the clinical application of this important drug group are continuing to unfold.

Influence of positive inotropic therapy on pulsatile hydraulic load and ventricular-vascular coupling in congestive heart failure

The aortic input impedance spectrum provides a description of the total hydraulic load imposed on the left ventricle and may be used to assess the coupling of the ventricle to the vasculature. The adaptation of the vasculature to positive inotropic intervention was examined in 10 patients with idiopathic dilated cardiomyopathy to test the hypothesis that increased myocardial contractility is matched by complementary changes in aortic impedance that optimize ventricular-vascular coupling and maximize power transfer to the circulation. High fidelity intravascular recordings of aortic pressure and flow were obtained at baseline study and during infusion of dobutamine to derive the aortic input impedance spectrum. In eight patients in whom increased staged infusion of dobutamine resulted in a significant increase in stroke volume (22.3 +/- 14.5 ml/beat increase over baseline), the significant (p less than 0.05) increase in the maximum of the first derivative left ventricular pressure pulse (dP/dt) was accompanied by significant decreases in characteristic impedance of the aorta (138 +/- 88 to 92 +/- 44 dyne.s.cm-5) wave reflection index (238 +/- 144 to 109 +/- 59 dyne.s.cm-5), and low frequency moduli of impedance. Effective positive inotropic therapy with dobutamine in the setting of congestive heart failure is accompanied by complementary changes in the aortic impedance spectrum, which represent a matching of impedance to the increased contractile state of the ventricle and facilitation of ventricular-vascular coupling.

Dobutamine: ten years later

Dobutamine is a commonly used positive inotrope for the short-term management of heart failure. It is commercially available as a 50:50 mixture of two isomers with unique effects on alpha- and beta adrenergic receptors. In dosages of 2-15 micrograms/kg/minute, dobutamine has been shown to increase cardiac output (mainly through stroke volume), reduce systemic vascular resistance, lower central venous and pulmonary artery wedge pressures, improve renal blood flow, and relieve signs and symptoms of congestive heart failure. At higher dosages it can increase heart rate and induce arrhythmias. Recent evidence indicates that effects of dobutamine last long after the drug has been eliminated from the plasma, and some work has been done on ambulatory use of this agent. Dobutamine has been used successfully in several circumstances, such as after cardiac surgery, in patients with myocardial infarction, and in various shock states. An understanding of the pathophysiology of the underlying disorder is important in deciding which catecholamine to use. With this in mind, monotherapy or combination therapy with inodilators such as dobutamine, or inopressors like dopamine will follow logically.

Intracoronary infusion of dobutamine to patients with and without severe congestive heart failure. Dose-response relationships, correlation with circulating catecholamines, and effect of phosphodiesterase inhibition

We infused dobutamine into the left main coronary artery of 24 patients with severe congestive heart failure (CHF) and 8 normal subjects without hemodynamic dysfunction. The maximal +dP/dt response to intracoronary (IC) dobutamine in CHF patients was only 37% of that in normals. This decrease in maximal response was not associated with a rightshift in the EC50 for dobutamine's effect on +dP/dt, or a decrease in the affinity of myocardial beta adrenergic receptors for dobutamine determined in vitro. In nine of the CHF patients, IC dobutamine infusion was followed by IC infusion of the phosphodiesterase inhibitor milrinone, and subsequently, by a second IC infusion of dobutamine. After IC milrinone, the increase in +dP/dt caused by IC dobutamine (74 +/- 10%) was significantly greater than that caused by the first infusion of dobutamine (52 +/- 11%; P less than 0.003) or milrinone (42 +/- 6%; P less than 0.001). Resting plasma norepinephrine was markedly elevated in CHF patients (837 +/- 208 ng/liter), but not in normal subjects (142 +/- 32 ng/liter); and the increase in +dP/dt caused by IC dobutamine was inversely related to resting plasma norepinephrine levels (r = -0.653; P less than 0.001). IC dobutamine caused a dose-related decrease in plasma norepinephrine (maximal effect, -160 +/- 31 ng/liter; P less than 0.001). Thus, (a) the maximal inotropic response to dobutamine is markedly depressed in patients with severe CHF, and is significantly greater after pretreatment with the phosphodiesterase inhibitor milrinone; (b) the impairment in inotropic response to dobutamine is inversely related to circulating norepinephrine levels; and (c) myocardial stimulation by dobutamine results in withdrawal of sympathetic tone.

The pharmacokinetics and pharmacodynamics of newer inotropic agents

In the past few years an intense effort has been directed toward the development of new inotropic agents for the treatment of chronic cardiac failure. Traditionally, therapy of this disease has included treatment with digitalis glycosides, diuretics, sodium restriction and vasodilators. While digitalis has proven to be an effective inotropic agent, it possesses a low therapeutic index and many patients remain symptomatic or 'refractory' despite its inotropic effects. This review focuses on the pharmacokinetics and pharmacodynamics of newer inotropic agents that have been developed or which are currently undergoing investigation. Amrinone and milrinone are two bipyridine derivatives which have been shown to be effective in the short term treatment of cardiac failure. Milrinone is currently being evaluated for its long term efficacy. The mechanism of action of amrinone and milrinone appears to be unrelated to the cardiac glycosides and sympathomimetic agents, and they are rapidly and well absorbed following oral administration. The bioavailability of milrinone appears to be somewhat reduced in patients with chronic cardiac failure. The distribution of these drugs to extravascular tissues is very rapid; the volume of distribution suggests that they are not extensively bound to tissues. While the volume of distribution of amrinone appears to be unaffected by the presence of heart failure, that of milrinone appears to be somewhat enhanced. The major route of elimination of both drugs appears to be excretion into urine as unchanged drug. A substantial fraction of the amrinone dose, however, undergoes hepatic metabolism to many metabolites, including an N-acetyl derivative. Clearance of amrinone and milrinone is dramatically reduced in patients with chronic cardiac failure compared with normal volunteers, resulting in proportionate increases in the serum half-lives of these drugs. Studies examining the acute and chronic disposition of these agents in cardiac failure patients have not demonstrated changes in their pharmacokinetics secondary to improvements in cardiocirculatory function. Both drugs show strong correlations between mean improvements in haemodynamics and drug serum concentrations, although considerable intrapatient variability may exist. It is currently unclear as to whether the site for the pharmacological action of amrinone is pharmacokinetically distinguishable from plasma. Enoximone and its sulphoxide metabolite, piroximone, are two compounds currently undergoing investigation for the treatment of chronic cardiac failure.(ABSTRACT TRUNCATED AT 400 WORDS)

Dobutamine in elderly septic shock patients refractory to dopamine

The hemodynamic effects of dobutamine (2.5-20 micrograms/kg per min) were studied in six elderly patients with septic shock which was refractory to dopamine (15 micrograms/kg per min). Dobutamine infusion resulted in significant increases in cardiac index (CI), stroke index (SI) and left ventricular stroke work index (LVSWI) and similar declines in heart rate (HR), mean pulmonary artery pressure (MPAP), pulmonary capillary wedge pressure (PCWP), systemic vascular resistance (SVR) and total pulmonary resistance (TPR). Dose response curves demonstrated a linear rise in CI with increasing doses of dobutamine and parallel decreases in HR and PCWP. MAP was unchanged. These data indicate that dobutamine may be a useful adjunct to dopamine therapy in the management of elderly patients with septic shock.

Use of intermittent dobutamine infusion in congestive heart failure

Dobutamine is a cardiac inotrope useful in the acute treatment of congestive heart failure. Dobutamine improves cardiac output, decreases pulmonary wedge pressure, and decreases total systemic vascular resistance with little effect on heart rate or systemic arterial pressure. Clinical benefit has been observed to continue for weeks to months following the discontinuation of dobutamine. In addition, tolerance to dobutamine has been observed when infusions last 72 hours or longer. This has led investigators to study the effectiveness of chronic intermittent infusions of dobutamine. Studies utilizing dobutamine doses ranging from 1.5 to 15 micrograms/kg/min for 4-48 h/wk have shown sustained clinical and hemodynamic improvement in patients suffering from congestive heart failure. The mechanism by which dobutamine creates this effect is not entirely known; however, studies suggest dobutamine exerts a physical conditioning effect similar to exercise. Dobutamine infusions have also been associated with morphological and metabolic changes in myocardial tissue consistent with improved myocardial structure and function. The intermittent use of dobutamine may be beneficial in the chronic treatment of congestive heart failure in patients who fail to respond to conventional therapy.

Intermittent, ambulatory dobutamine infusions in patients with severe congestive heart failure

Thirteen ambulatory patients with severe congestive heart failure were treated with weekly, outpatient 48-hour infusions of dobutamine. All 13 patients had at least a 25% increase in cardiac output during initial dobutamine titration, with a corresponding improvement in systemic vascular resistance. Improvement in functional class was achieved in only seven patients. Additionally, only three patients survived the 26-week study period. Although no change in ventricular ectopy was noted during the initial dobutamine infusions, six patients experienced sudden death; three other patients died of progressive heart failure and one died from pulmonary embolism. These data suggest that chronic intermittent ambulatory dobutamine infusions are only partly successful in improving symptoms and probably do not prolong survival in patients with severe congestive heart failure. Administration of this form of therapy on a clinical basis should be undertaken cautiously until safety and efficacy are demonstrated in prospective, controlled trials.