Dobutamine infusion in conscious dogs with and without acute myocardial infarction. Effects on systemic hemodynamics, myocardial blood flow, and infarct size

Predicting the Time Course of Ventricular Dilation and Thickening Using a Rapid Compartmental Model

The ability to predict long-term growth and remodeling of the heart in individual patients could have important clinical implications, but the time to customize and run current models makes them impractical for routine clinical use. Therefore, we adapted a published growth relation for use in a compartmental model of the left ventricle (LV). The model was coupled to a circuit model of the circulation to simulate hemodynamic overload in dogs. We automatically tuned control and acute model parameters based on experimentally reported hemodynamic data and fit growth parameters to changes in LV dimensions from two experimental overload studies (one pressure, one volume). The fitted model successfully predicted the reported time course of LV dilation and thickening not only in independent studies of pressure and volume overload but also following myocardial infarction. Implemented in MATLAB on a desktop PC, the model required just 6 min to simulate 3 months of growth.

Effect of dobutamine combined with intra-aortic balloon counterpulsation on left ventricular function early after acute myocardial infarction: experimental study

Acute myocardial infarction (AMI) causes left ventricular (LV) remodeling, which forms the substrate for its early and late complications. The purpose of this study was to compare the acute effect of dobutamine or intra-aortic balloon pumping (IABP), alone or in combination, on LV function in the early phase of an experimental AMI. In 18 pigs, AMI was induced by ligation of the left anterior descending artery (LAD). IABP or dobutamine infusion at a rate of 5 µg/kg/min, or a combination of the two, was applied immediately after ligation of the LAD. Echocardiographic measurements of the long and short LV axes were obtained before (baseline) and post LAD ligation and at the end of each intervention for 5, 15, and 30 min. The fractional shortening (FS) of both axes, as well as the ejection fraction (EF), was calculated. The combination of dobutamine with IABP increased the EF significantly after the AMI in comparison to dobutamine or IABP alone, and improved the stroke volume, cardiac output, and long axis FS in comparison to IABP alone. Dobutamine alone produced a significantly higher increase of EF in comparison to IABP alone. These results indicate that the combination of dobutamine with IABP may be useful during AMI.

Captopril and its time of administration in myocardial ischaemic-reperfusion injury

The present study was designed to investigate the role of captopril in an in vivo model of myocardial ischaemic-reperfusion injury with respect to its time of administration. In open-chest pentobarbitone anaesthetized cats, the left anterior descending coronary artery was occluded for 15 min followed by 60 min of reperfusion. Vehicle (saline) or captopril (4 mg kg(-1)) was administered 10 min before instituting ischaemia (pre-treatment) or 5 min before reperfusion (post-treatment). In the vehicle-treated group, ischaemic-reperfusion injury (IRI) was evidenced by enhanced plasma renin activity, depression of global haemodynamic function (mean arterial pressure, left ventricular-end-diastolic-pressure, peak positive and negative dP/dt) along with depletion of myocardial high energy phosphate (HEP) compounds. Oxidant stress in IRI was evidenced by raised levels of myocardial thiobarbituric acid reactive substances (TBARS) and depletion of endogenous myocardial antioxidants (glutathione, superoxide dismutase and catalase). Pre-treatment with captopril prevented (i) loss of myocardial haemodynamic function, (ii) rise in TBARS and (iii) depletion of myocardial HEP compounds. However, in the post-treatment group, only partial recovery of myocardial haemodynamic function, with no significant reduction in TBARS, was observed. Glutathione, superoxide dismutase and catalase were unaffected by either treatment schedules. The results of the present study suggest that captopril is more effective in attenuating ischaemic-reperfusion injury when administered before ischaemia rather than before reperfusion.

Comparison of 2 myocardial velocity gradient assessment methods during dobutamine infusion with Doppler myocardial imaging

Myocardial velocity gradient (MVG) has been shown to be the best quantitative parameter for the detection of ischemic myocardium during dobutamine infusion with the use of Doppler myocardial imaging. MVG has been previously assessed by velocity measurements across the thickness of the myocardium at the time of visually selected maximal color brightness (thickness-velocity plot method). We hypothesized that MVG could be assessed by velocity measurements throughout the cardiac cycle in the subendocardium parallel to the endocardial boundary to the left ventricular cavity and in the subepicardium parallel to the epicardial boundary (time-velocity plot method). This study was designed to compare MVG obtained from the thickness-velocity plot method and from the time-velocity plot method in quantifying dobutamine-induced changes in myocardial wall motion in 8 phases of the cardiac cycle on color M-mode Doppler myocardial imaging recordings of the left ventricular posterior wall performed in 8 conscious dogs at baseline and at steady state during dobutamine infusion (10 microg/kg per minute). For both methods, MVG was considered present if its mean value was significantly different from zero and if endocardial and epicardial velocities were significantly different. There was close agreement between the 2 methods. MVG was present during the preejection period, systole, rapid ventricular filling, and atrial contraction. Dobutamine induced a significant increase in MVG during the preejection period (from 2.64 +/- 0.83 to 4.05 +/- 0.81 seconds-1 ), systole (from 2.14 +/- 0.59 to 6.08 +/- 2.20 seconds-1 in early systole, from 1.90 +/- 1.06 to 5.31 +/- 2.95 seconds-1 in mid systole, from 1.37 +/- 0.57 to 2.44 +/- 0.53 seconds-1 in end systole), and rapid ventricular filling (from 3.06 +/- 1.12 to 7.82 +/- 2.58 seconds-1 ), related to a greater rise in endocardial than in epicardial velocities. The time-velocity plot method showed that ejection and diastole were 11% and 28% decreased during dobutamine infusion, respectively, as heart rate was 31% increased. Thus according to our quantitative criteria, both MVG assessment procedures enabled objective interpretation of dobutamine effects on left ventricular wall motion. In addition, the time-velocity plot method provided automatic detection of peak velocity, timing, and duration of wall velocity changes over time.

Effects of dobutamine on isovolumic and ejection phase indices of cardiac contractility in conscious healthy dogs

The aim of this study was to determine cardiac contractility using indices derived from cardiac catheterisation in conscious healthy dogs during dobutamine infusion. Eight dogs were studied. An ECG was recorded together with left ventricular pressure and volume which were measured using a conductance catheter with an integrated microtip pressure sensor. Eight indices of left ventricular systolic performance were derived from these records. Measurements were realised under basal conditions and during an incremental dobutamine challenge. The maximal rate of rise in ventricular pressure (max dP/dt), max dP/dt divided by the developed pressure and the mean systolic ejection rate were the most sensitive indices to detect dobutamine induced changes in contractility with maximal percentage changes of 122+/-11 per cent, 130+/-7 per cent and 102+/-24 per cent respectively. Ejection fraction increased significantly during dobutamine infusion (maximal percentage change of 43+/-9 per cent) whereas the pre-ejection period (PEP) and the left ventricular ejection time (LVET) decreased significantly (maximal percentage change of -41+/-2 per cent and -28+/-3 per cent respectively). All these six indices were significantly correlated with each other. Conversely, the ratio PEP/LVET and the LVET corrected for heart rate dependency showed a maximal percentage change of only -10+/-1 per cent and -16+/-7 per cent, respectively, during the dobutamine infusion and were not significantly correlated with the other contractility indices. This study demonstrated the feasibility of the conductance method to determine cardiac contractility in conscious healthy dogs submitted to a pharmacological stress testing and provides control values for eight indices of left ventricular contractility during dobutamine infusion at increasing dosages.

Hemodynamic responses to dobutamine during acute normovolemic hemodilution

The effects of dobutamine (DOB) on myocardial performance, systemic hemodynamics, and oxygen delivery during acute normovolemic hemodilution in anesthetized rats were studied. Forty-two Sprague Dawley rats (body weight 375 to 425 g) were divided into six equal groups. Hemodynamic and cardiac indices were measured or calculated at baseline, 30 minutes after the initiation of hemodilution (HD), and 15 minutes after DOB or saline infusion. Myocardial performance in response to acute pressure or volume loads was studied in all groups of animals. HD to a hematocrit (Hct) value of 20% resulted in no change in heart rate (HR), increased CI, SVI, and LV dP/dt, and decreased MAP, SVRI, and oxygen delivery index (O2DI). HD increased peak SV and CI after preload stress while the left ventricular developed pressure (LVDP) was unchanged. Infusion of DOB as 7.5 or 15 micrograms/kg/min increased HR, CI, and LV dP/dt as well as LVDP. At the same time, DOB decreased MAP and SVR, whereas the SVI remained unchanged. In non-HD animals both doses of DOB increased LVDP, but only the larger dose increased CI, whereas peak SV decreased with the smaller dose. Arterial carbon dioxide tension (PaCO2) increased, whereas pH and arterial oxygen tension (PaO2) decreased; however, O2DI remained unchanged. Concomitant hemodilution and DOB infusion resulted in attenuation of HR response to DOB, exaggerated the drop in MAP and SVR, and increased LV dP/dt. Only the larger dose of DOB increased the CI, whereas neither dose could alter the SVI in HD animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Prehospital Treatment with Dobutamine

Purpose:

To assess the effectiveness of the use of dobutamine hydrochloride in out-of hospital emergency situations.

Population:

Patients with severe circulatory insufficiency caused by acute illness or injury encountered by the Mobile Intensive Care Unit of Copenhagen (population 467,000) during a 15-month study period.

Methods:

A newly developed dobutamine solution was administered by infusion pump to patients in whom normal emergency treatment failed to restore an acceptable circulatory state.

Results:

A total of 40 patients were treated with 4–48 μg dobutamine/kg/minute. The treatment was judged to be primary life-saving in 15 patients, the condition was improved in 16 patients, and nine patients died. Systolic blood pressures (in those who survived) rose from a mean value of 45 mmHg (range 0–80 mmHg) to 105 mmHg (range 65–180 mmHg). No tachycardia or arrhythmias were noted.

Conclusion:

This newly developed dobutamine solution is very useful in prehospital treatment of patients with circulatory failure and is recommend for use by mobile intensive care unit teams.

Compared peripheral vascular responses to intravenous and intra-arterial administrations of positive inotropic agents in conscious dogs

In addition to their direct effects on cardiac contractility, a number of positive inotropic agents also induce, through direct peripheral vasodilation, a reduction in afterload which is of major importance in their beneficial effects in the treatment of congestive heart failure. However, the induced increase in cardiac output can indirectly improve perfusion of peripheral vessels through a flow-mediated mechanism. Thus, the goal of the present study was to compare the direct peripheral vasomotor effects assessed in the iliac vascular bed of four positive inotropic agents: DPI 201-106, ouabain, milrinone and dobutamine, in the presence and absence of simultaneous changes in cardiac function. These drugs were administered either through intravenous or intra-arterial (aorto-iliac catheter) routes in 6 conscious dogs, chronically instrumented for the measurement of heart rate, arterial pressure, left ventricular dP/dt, iliac artery blood flow and iliac artery diameter (sonomicrometry). Intravenous doses were selected as those inducing equipotent positive inotropic responses whereas intra-arterial doses were below those required to induce any significant change in systemic hemodynamics. Ouabain decreased and milrinone increased both iliac blood flow and diameter after either intravenous or intra-arterial administrations. In contrast, iliac blood flow did not change after intra-arterial administration of DPI 201-106 and dobutamine whereas iliac diameter was not modified by DPI 201-106 and even decreased with dobutamine. After intravenous administration, DPI 201-106 but not dobutamine, increased both iliac blood flow and diameter. Thus, this experimental preparation can differentiate inotropic agents with direct vasodilating (milrinone) or constricting (ouabain) properties and those (DPI 201-106 and dobutamine) with indirect vasodilating effects most likely mediated by the improvement in cardiac function.

Comparison of hemodynamic and oxygen transport effects of dopamine and dobutamine in critically ill surgical patients

Hemodynamic and oxygen transport effects of dopamine and dobutamine were studied in a series of 25 critically ill postoperative general surgical patients by a prospective, randomized crossover design after maximal response to fluids had been obtained. Dopamine increased MAP, HR, CI, PvO2, DO2, and Qsp while decreasing PaO2. Dobutamine increased HR, CI, SI, stroke work, DO2, VO2, and Qsp while decreasing PAWP and SVRI and PVRI. In general, the effects of the two drugs were greater in patients in the first 72 hours after surgery. The effects of dobutamine on flow and oxygen transport were greater than those of dopamine, especially in the early postoperative period. The effects were smaller and not significant in patients more than three days after surgery, as well as in those with sepsis, respiratory failure, renal failure, age over 65 years, and hyperdynamic states, in part because of the small number of patients in each group. These data are consistent with the hypothesis that the beta 2-adrenergic action of dobutamine vasodilates the previously constricted peripheral circulation, enhances tissue perfusion by improving micro-circulatory flow distribution, and improves DO2 and VO2.

Can new inodilators displace digitalis in the therapy of congestive heart failure?

New inodilators that possess both positive inotropic and vasodilator actions have many favorable effects in patients with congestive heart failure, even in those with refractory heart failure. These effects are expected to prevent myocardial injury, improve peripheral circulation, depress the excessive endogenous neurohumoral activation, and, finally, improve the quality of life, and increase lifespan. However, experience with new inodilators has only begun. Several questions remain to be answered before these drugs can be widely used with safety, including whether life-threatening adverse effects appear, mortality rate is lessened, and drug tolerance occurs. The therapeutic level of the dose and the relation between the effectiveness of the drug and the degree of the severity of heart failure should also be established. Therefore, long-term, randomized, double-blind, placebo-controlled clinical trials will be necessary before the new inodilators can take the place of digitalis and thus become the mainstay of the therapy of congestive heart failure.

The rational selection of inotropic drugs in cardiac surgery

Despite improvements in surgical technique and intraoperative myocardial protection, certain patients have need for inotropic drug support after cardiac surgery. This review examines drugs that are currently in use for inotropic support of the heart, including calcium, epinephrine, dopamine, dobutamine, isoproterenol, and amrinone. Patient factors that may have an impact on the selection of appropriate drugs are also examined. Application of these data to specific patients must be guided by the particular hemodynamic derangements present. Careful analysis of the specific hemodynamic disorder and tailoring of inotropic therapy to these abnormalities are crucial. Such a rational approach to the selection of inotropic agents requires continuous hemodynamic assessment and recognition that the patient's condition and needs may change rapidly early after heart surgery dictating adjustment of subsequent therapy.

Cardiac pumping capability and prognosis in heart failure

In 63 patients with severe acute or chronic heart failure maximum cardiac performance was determined by calculation of the maximum hydraulic power output achieved by the heart during dobutamine challenge. After one year, all but 3 of the 23 patients with maximum cardiac power output (Wmax) less than the normal resting value of 1 W had died of progressive heart failure. Of the 40 with Wmax more than 1 W, all but 4 (who died suddenly) survived longer than one year. Hydraulic power output is a clinically important measure of cardiac pumping performance and a maximum power output value below the normal resting value indicates that long-term survival is unlikely.

Hemodynamic abnormalities in acute myocardial infarction

Great strides have been made in the management of patients with acute myocardial infarction since the advent of coronary care units. However, congestive heart failure continues to be the major cause of in-hospital mortality. The accurate diagnosis and classification of hemodynamic abnormalities allow the application of specific therapies for each patient. Because clinicians can now routinely measure left and right ventricular preload, systemic and pulmonary vascular resistance, cardiac output, and arteriovenous oxygen difference, pharmacologic and surgical interventions can be applied in a scientific manner. In addition, mechanical complications can be promptly recognized and aggressively treated. Although the mortality rate for patients with severe left ventricular dysfunction after myocardial infarction remains high, expert management offers an improved prognosis for many patients.

Is inotropic therapy appropriate for patients with chronic congestive heart failure? Or is the digitalis leaf withering?

The appropriateness of inotropic therapy in chronic heart failure was examined by critically reviewing five assumptions upon which this form of therapy has been justified. Only the first, that cardiac performance can be acutely improved by inotropic therapy, has been empirically proven. That such acute improvement is sustained appears to be true with non-catecholamine agents whereas the chronic haemodynamic efficacy of oral catecholamines remains in doubt. That any inotropic agent can improve exercise tolerance, make the patient feel better, or effect a change without deleteriously affecting the myocyte is very much in doubt. Thus, although the prospect of using powerful inotropic therapy in the patient with heart failure is theoretically appealing, its utility remains to be proven.

Influence of heart rate on the effects of prenalterol on regional myocardial blood flow and function during coronary stenosis in dogs

The effects of prenalterol, a selective beta 1-adrenoceptor agonist with potent cardiac positive inotropic properties have been investigated on regional myocardial blood flow (RMBF) (microspheres) and contractile function (ultrasonic crystals) during partial circumflex coronary artery stenosis in 8 open-chest anaesthetized dogs. Prenalterol was investigated at two intravenous doses: 5 micrograms kg-1, which increased myocardial contractility (dP/dt max: +29%) more than heart rate (+12%, up to 150 beats min-1) and 20 micrograms kg-1 which induced almost similar increases in contractility (+35%) and heart rate (+31% up to 175 beats min-1). The induced modifications of regional flow and function were then compared to those produced in another series of 6 dogs by atrial pacing at 150 and 175 beats min-1 respectively. Prenalterol significantly increased RMBF and segment length (SL)-shortening in a dose-dependent manner in the nonischaemic zone. In the ischaemic zone, RMBF was maintained and SL-shortening increased with prenalterol, 5 micrograms kg-1 whereas both RMBF and contractile function were severely decreased with prenalterol, 20 micrograms kg-1. Atrial pacing had almost no effect on RMBF and SL-shortening in the nonischaemic zone. In the ischaemic zone, atrial pacing rate-dependently decreased both RMBF and SL-shortening. Thus, a significant increase in contractility, associated with little tachycardia (prenalterol, 5 micrograms kg-1), induces beneficial effects on RMBF and function in both the nonischaemic and ischaemic myocardium. In contrast, a strong tachycardia, whether accompanied by positive inotropic effects (prenalterol, 20 gig kg-') or not (atrial pacing at 175 beats min-1) induces deleterious effects on RMBF and cardiac function in the ischaemic myocardium.

The effect of dobutamine on exercise performance in patients with symptomatic ischemic heart disease

The effect of dobutamine on exercise performance was assessed in 20 patients with ischemic heart disease (CAD) and a positive stress test. These patients had a wide range of resting left ventricular ejection fraction (range 22% to 69%, mean 42%). Each patient entered a double-blind crossover study in which two identical exercise radionuclide ventriculograms were performed in patients on dobutamine, 5 micrograms/kg/min intravenously, or placebo. Dobutamine increased resting left ventricular ejection fraction. Although ejection fraction fell with dobutamine during submaximal exercise, it remained higher than with placebo. At peak exercise, ejection fraction fell to the same level on dobutamine as with placebo. Dobutamine diminished exercise time and time to ischemia while peak pressure-rate product was unchanged. Four of 20 patients developed complex ventricular premature beats, all while on dobutamine. Although useful when administered to resting patients with acute left ventricular failure, dobutamine's effects may be deleterious in exercising patients with chronic ischemic heart disease.