Acute myocardial dysfunction and recovery: a common occurrence after coronary bypass surgery

8-epi PGF2 alpha generation during coronary reperfusion. A potential quantitative marker of oxidant stress in vivo

BACKGROUND

Myocardial reperfusion is believed to be associated with free radical injury. However, indexes of oxidative stress in vivo have been limited by their poor specificity and sensitivity. Isoprostanes are stable products of arachidonic acid formed in a nonenzymatic, free radical-catalyzed manner. We have developed a sensitive and specific assay for one of these compounds, 8-epi prostaglandin (PG) F2 alpha.

METHODS AND RESULTS

To address its utility as an index of oxidative stress during coronary reperfusion, we measured urinary levels by gas chromatography/mass spectrometry in a canine model of coronary thrombolysis, in patients with acute myocardial infarction treated with thrombolytic therapy, and in patients after elective coronary artery bypass surgery. Urinary 8-epi PGF2 alpha was unchanged after circumflex artery occlusion in a canine model of coronary thrombolysis (n = 13; 437.2 +/- 56.4 versus 432.7 +/- 55.2 pmol/mmol creatinine) but increased significantly (P < .05) immediately after reperfusion (553.8 +/- 64.7 pmol/mmol). Urinary levels were increased (P < .001) in patients (n = 12) with acute myocardial infarction given lytic therapy (265.8 +/- 40.8 pmol/mmol) compared with age-matched control subjects (n = 20; 91.5 +/- 11.8 pmol/mmol) and patients with stable coronary disease (n = 20; 95.7 +/- 6.3 pmol/mmol). Preoperative levels rose from 113.2 +/- 11.8 to 248.2 +/- 86.3 pmol/mmol at 30 minutes into revascularization to 332.2 +/- 82.6 pmol/mmol by 15 minutes after global myocardial reperfusion (P < .05) and dropped to 181.2 +/- 50.4 pmol/mmol at 30 minutes and 120.2 +/- 9.9 pmol/mmol at 24 hours after bypass surgery (n = 5). Corresponding changes in spin adduct formation, found with electron paramagnetic resonance, were noted in 2 patients.

CONCLUSIONS

These data support the hypothesis that free radical generation occurs during myocardial reperfusion. Measurement of isoprostane production may serve as a noninvasive index of oxidative stress.

Acetylcholine reactivity in the pulmonary artery during cardiac surgery in patients with ischemic or valvular heart disease

OBJECTIVE

During cardiopulmonary bypass, there is almost no blood flow through the pulmonary artery. Ischemia and reperfusion are known to attenuate the reaction to acetylcholine. An attenuated reactivity to acetylcholine in the pulmonary circulation after cardiopulmonary bypass was previously shown in children. The current study in adult patients was designed to analyze the change over time of acetylcholine reactivity after cardiac surgery.

DESIGN

A prospective study.

SETTING

The operating room and intensive care unit of a university hospital.

PARTICIPANTS

Eighteen patients with ischemic or valvular heart disease.

INTERVENTIONS

Pulmonary vascular resistance was measured with a pulmonary artery catheter before and during an infusion of acetylcholine. This procedure was done after induction of anesthesia before surgery and 1, 4, 8, and 20 to 24 hours after cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

Pulmonary vascular resistance index decreased during infusion of acetylcholine before surgery by 27% from 286 +/- 27 dyne/sec/cm-5/m2 (mean and standard error of mean) to 209 +/- 28 and at 8 and 20 to 24 hours by 23% and 34%, respectively, 288 +/- 27 to 221 +/- 29 and 229 +/- 22 to 150 +/- 17 (p < 0.001, paired t-test). One and 4 hours after cardiopulmonary bypass, no significant decrease was observed.

CONCLUSIONS

These results confirm the finding of altered reactivity to acetylcholine in the pulmonary circulation after cardiopulmonary bypass. In view of the often prolonged tendency toward pulmonary hypertension observed in children, the recovery at 8 hours after surgery was unexpectedly rapid. The attenuated response to acetylcholine is most likely explained by relative ischemia in the pulmonary circulation during cardiopulmonary bypass.

Reduction of oxidative stress does not affect recovery of myocardial function: warm continuous versus cold intermittent blood cardioplegia

OBJECTIVE

To compare oxidative stress after cardiac surgery in patients treated with two different methods of myocardial protection: warm continuous versus cold intermittent blood cardioplegia. To correlate oxidative stress with postoperative myocardial dysfunction.

DESIGN

Prospective, randomised, double blind, trial.

SETTING

Institutional centre of cardiovascular surgery.

PATIENTS

20 patients were selected for coronary artery bypass surgery (CABG) on the following basis: stable angina, ejection fraction > 50%, double or triple vessel disease, no previous CABG or associated disease. Patients were randomised to two groups of 10 patients each.

INTERVENTIONS

Patients underwent CABG with one of two different methods of myocardial protection and cardiopulmonary bypass. CBC group: intermittent cold blood antegrade-retrograde cardioplegia with moderate hypothermic cardiopulmonary bypass; WBC group: continuous warm blood antegrade-retrograde cardioplegia with mild hypothermic cardiopulmonary bypass.

MAIN OUTCOME MEASURE

The index of oxidative stress used was the alteration of whole blood and plasma glutathione redox status. Samples were collected from the coronary sinus and peripheral vein before anaesthesia (T1), before aortic unclamping (T2), 15 minutes (T3), and 30 minutes (T4) after unclamping. Haemodynamic parameters were measured with thermodilution techniques.

RESULTS

Oxidised glutathione and glutathione-cysteine mixed disulphide significantly increased in the coronary sinus plasma in the CBC group, and the overall redox balance of glutathione was decreased (P < 0.01) at T2-T4 versus T1, and compared with the WBC group. Comparable results were obtained for coronary sinus blood. There was no correlation between postoperative haemodynamic measurements and oxidative stress markers.

CONCLUSIONS

Oxidative stress was significant in patients undergoing CABG using cold blood cardioplegia, while the warm technique minimised the effects of ischaemia. However, oxidative stress was not correlated with myocardial dysfunction following CABG.

Platelet activating factor and thromboxane B2 production after cardiopulmonary bypass

Platelet-activating factor (PAF) is believed to have a central role in the pathogenesis of ischemia-reperfusion injury. The purpose of this study was to investigate the relationships among production of PAF, thromboxane B2 (T alpha B2), and cardiopulmonary sequelae in patients undergoing coronary artery bypass graft surgery (CABGS). Venous blood from nine patients (eight men, one woman) undergoing scheduled CABGS, was sampled from central venous catheters before anesthetic induction, pre-cardiopulmonary bypass (CPB), 10 and 30 minutes post-CPB, 10 and 30 minutes post-aortic declamping, and 120 minutes and 24 hours after the conclusion of CPB. Plasma levels of PAF and T alpha B2 were determined by radioimmunoassay kits (Amersham Canada Ltd.). PAF and T alpha B2 were significantly different between high-risk patients (group I; Canadian Cardiovascular Society class 3-4; n = 4) and low-risk patients (group II; Canadian Cardiovascular Society class 2; n = 5): group I PAF = 960 pg/mL, group II PAF = 159 pg/mL (P = 0.0029); group I T alpha B2 = 320 pg/mL, group II T alpha B2 = 229 pg/mL (P = 0.0262). Group I PAF was significantly greater than group II PAF: before CPB = 825 pg/mL (group I), 138 pg/mL (group II); during initiation of CPB = 1600-2015 pg/mL (group I), 158-200 pg/mL (group II) (P = 0.0143). Correlations between duration of CPB and peak PAF (r = 0.7049, P = 0.0339), peak PAF level, and time to extubation (r = 0.8863, P = 0.0079) were significant. PAF levels were different in patients requiring postoperative epinephrine (2124 +/- 700 pg/mL) or dopamine (667 +/- 266 pg/mL) (P = 0.0042). The production of PAF is determined by preoperative patient characteristics and duration of CPB. Increased levels of PAF in patients with unstable angina, left main coronary artery disease, or recent myocardial infarction are associated with the need for increased inotropy and prolonged ventilatory support following CABGS. The degree of PAF production during CPB may be a factor in postoperative instability in high-risk patients.

Minimal operative mortality in patients undergoing coronary artery bypass with significant left ventricular dysfunction by maximization of metabolic and mechanical support

Between January 1, 1992, and January 23, 1996, 111 consecutive patients with severe left ventricular dysfunction underwent isolated coronary artery bypass grafting. The ejection fraction in these patients ranged from 10% to 34% (mean 27.9% +/- 5.4%); in 18 patients the value was less than 20%. The high operative mortality rate (7.6% in Society of Thoracic Surgeons database) in this group of patients at high risk was targeted for reduction by provision of, in addition to the usual inotropic support, progressively more intensive metabolic and mechanical support. The metabolic support consisted of triiodothyronine; glucose, insulin, and potassium; aspartate/glutamate in the cardioplegic solution; and warm-cold-warm/antegrade-retrograde-antegrade cardioplegia. Mechanical support included liberal use of the intraaortic balloon pump, use of a new occlusive retrograde cardioplegia catheter, ultrafiltration to remove myocardial depressant factors, and, finally, delayed sternal closure. The operative mortality rate was 1.8% (2/111). Complications included reoperation because of bleeding (3.6%, 4/111), mediastinitis (1.8%, 2/111), and stroke (0.9%, 1/111) and there were no occurrences of new postoperative acute renal failure (0.0%, 0/111). The intensive care unit stay was 2.2 +/- 0.9 days with a length of stay in the hospital of 13.7 +/- 22.1 days. These techniques done before operation, intraoperatively, and postoperatively optimize the milieu of the depressed left ventricle by maximizing perioperative high-energy phosphate bonds; increasing the effectiveness of inotropic agents; unloading the left ventricle by chemical, metabolic, and mechanical support; and removing known myocardial depressant factors, which reduced the operative mortality rate to 1.8% compared with 7.6% as reported in the Society of Thoracic Surgeons' database.

Monitoring of left ventricular ejection fraction with a miniature, nonimaging nuclear detector: accuracy and reliability over time with special reference to blood labeling

BACKGROUND

The purpose of this study was to determine the accuracy of determinations of left ventricular ejection fraction (LVEF) by a nonimaging miniature nuclear detector system (Cardioscint) and to evaluate the feasibility of long-term LVEF monitoring in patients admitted to the coronary care unit, with special reference to the blood-labeling technique.

METHODS AND RESULTS

Cardioscint LVEF values were compared with measurements of LVEF by conventional gamma camera radionuclide ventriculography in 33 patients with a wide range of LVEF values. In 21 of the 33 patients, long-term monitoring was carried out for 1 to 4 hours (mean 186 minutes), with three different kits: one for in vivo and two for in vitro red blood cell labeling. The stability of the labeling was assessed by determination of the activity of blood samples taken during the first 24 hours after blood labeling. The agreement between Cardioscint LVEF and gamma camera LVEF was good with automatic background correction (r = 0.82; regression equation y = 1.04x + 3.88) but poor with manual background correction (r = 0.50; y = 0.88x - 0.55). The agreement was highest in patients without wall motion abnormalities. The long-term monitoring showed no difference between morning and afternoon Cardioscint LVEF values. Short-lasting fluctuations in LVEFs greater than 10 EF units were observed in the majority of the patients. After 24 hours, the mean reduction in the physical decay-corrected count rate of the blood samples was most pronounced for the two in vitro blood-labeling kits (57% +/- 9% and 41% +/- 3%) and less for the in vivo blood-labeling kit (32% +/- 26%). This "biologic decay" had a marked influence on the Cardioscint monitoring results, demanding frequent background correction.

CONCLUSION

A fairly accurate estimate of LVEF can be obtained with the nonimaging Cardioscint system, and continuous bedside LVEF monitoring can proceed for hours with little inconvenience to the patients. Instability of the red blood cell labeling during long-term monitoring necessitates frequent background correction.

Evaluation of oxygen availability with oxygen status algorithm in patients undergoing open heart surgery treated with epoetin beta

We evaluated in a double-blind randomized study the effect of epoetin beta (recombinant human erythropoietin) therapy on oxygen status in patients undergoing cardiac surgery who were contraindicated for autologous blood donation. All 76 patients enrolled in this study were randomized to the two treatment groups (5 x 500 U epoetin beta or placebo/kg body weight intravenously over a 14-day period before surgery) and received 300 mg Fe2+ per day orally before surgery. Before and after surgery the lactate level and the following parameters according to the oxygen status algorithm by Siggaard-Andersen were evaluated: arterial oxygen tension (PaO2), effective hemoglobin concentration (ceHb), arterial oxygen saturation (SaO2), oxygen half saturation tension (p50), red cell 2.3 diphosphoglycerate (2.3 DPG), arterial total oxygen concentration (ctO2), concentration of extractable oxygen (cx), and oxygen compensation factor (Qx). Therapy with epoetin beta led to increases in ceHb, PaO2, ctO2, and cx and to a decrease in Qx before surgery (p < 0.05 for PaO2, p < 0.0001 for the other parameters vs placebo). The cx in patients who received epoetin beta rose by approximately 20%, thus indicating a considerable improvement in O2 delivery. In patients receiving placebo the hemoximetric parameters remained outside the normal limits at all times after surgery, but in the epoetin beta group PaO2, ctO2, cx, and Qx returned almost to their baseline values by the second or fifth postoperative day, even though the frequency of transfusions was significantly higher in the placebo group. Whereas p50 and 2.3 DPG fell in the placebo group after surgery, these two parameters were significantly higher in the epoetin beta group and led to a further increase in cx (from 24% to 38%) versus the placebo group as a result of the right shift in the hemoglobin O2-binding curve. The postoperative incidence and severity of lactic acidosis were higher in the placebo group. Preoperative epoetin beta therapy is a safe way of providing increased extractable O2 (by 24% to 38%) and decreasing the risk of lactic acidosis after surgery. This therapy has a more favorable effect on the O2 binding curve than the transfusion of erythrocyte concentrate and enhances the effect of epoetin beta therapy on the postoperative oxygen status.

Propofol-alfentanil versus fentanyl-midazolam in coronary artery surgery

OBJECTIVE

To compare intraoperative hemodynamics profiles and recovery characteristics of propofol-alfentanil with fentanyl-midazolam anesthesia in elective coronary artery surgery.

DESIGN

Prospective, randomized study.

SETTING

University hospital.

PARTICIPANTS

Fifty patients with impaired or good left ventricular function.

INTERVENTIONS

In group 1, (n = 25) anesthesia was induced with an infusion of propofol, 3 to 4 mg/kg/h, alfentanil, 500 micrograms, and pancuronium 0.1 mg/kg, and maintained with propofol, 3 to 6 mg/kg/h (variable rate), and alfentanil infusions, 30 micrograms/kg/h (fixed rate). Additional boluses of alfentanil, 1 mg, were administered before noxious stimuli; group 2 (n = 25) received a loading dose of fentanyl, 25 micrograms/kg, midazolam, 1.5 to 3 mg, and pancuronium, 0.1 mg/kg for induction, followed by an infusion of fentanyl, 7 micrograms/kg/h, for maintenance. Additional boluses of midazolam (1.5 to 3 mg) and fentanyl (250 micrograms) were administered before noxious stimuli. MEASUREMENTS AND MAIN RESULTS. Cardiovascular parameters at eight intraoperative time points as well as time to extubation, morphine consumption, and pain scores were recorded. Induction of anesthesia was associated in both groups with a small but significant decrease in mean arterial pressure (1: 15 mmHg (15%); 2: 8 mmHg (8%) with significant decreases in cardiac index (1: 8%; 2: 8%) and left ventricular stroke work index (1: 24%; 2: 21%). Throughout surgery, hemodynamic profiles were comparable between groups except after intubation when the MAP was significantly lower in group 1 (75 +/- 12 mmHg) than in group 2 (89 +/- 17 mmHg). Group 1 required less inotropic support. Extubation was performed faster in group 1 (7.6 h) than in group 2 (18.0 h). Morphine requirements and pain scores were comparable between groups.

CONCLUSIONS

Propofol-alfentanil anesthesia provides good intraoperative hemodynamics and allows early extubation after coronary artery surgery.

Anti-CD18 antibodies improve cardiac function following cardiopulmonary bypass in dogs

PURPOSE

Cardiopulmonary bypass is associated with activation of neutrophils, which may adhere to vascular endothelium causing lung, heart, and brain injury. We tested whether blocking neutrophil adherence would improve organ function following cardiopulmonary bypass in dogs.

MATERIALS AND METHODS

All dogs received a standard anesthetic, and then one group (n = 6) received 2 hours of cardiopulmonary bypass followed by 4 hours of observation. A second group (n = 6) received a monoclonal antibody (6 mg/kg) to CD18, a neutrophil adherence factor, immediately before cardiopulmonary bypass. A third group (n = 6) did not receive cardiopulmonary bypass or antibody.

RESULTS

Using flow cytometry we found that the antibody bound essentially all neutrophil CD18 sites. All three groups had similar gas exchange and hemodynamics. Lung and heart histology results were similar between groups. By echocardiography, five animals receiving cardiopulmonary bypass alone showed regional wall abnormalities, whereas only one receiving antibody showed wall motion abnormality (P < .05). Following cardiopulmonary bypass, intracellular myocardial pH was higher (P < .05) in the antibody-treated group compared with the group that had cardiopulmonary bypass alone (7.23 +/- 0.05 v 7.07 +/- 0.07 respectively).

CONCLUSION

Monoclonal antibodies to CD18 can prevent the deterioration in cardiac function routinely observed following cardiopulmonary bypass.

Effects of dobutamine and enoximone on transmitral and pulmonary venous flow characteristics in patients with left ventricular dysfunction after coronary artery bypass grafting

OBJECTIVES

To assess the effects of dobutamine and enoximone on transmitral (TMF) and pulmonary venous flow (PVF) characteristics.

DESIGN

Prospective and randomized.

SETTING

A university hospital intensive care unit.

PARTICIPANTS

Thirty patients with moderate left ventricular dysfunction after coronary artery bypass grafting (CABG).

INTERVENTIONS

Patients received either dobutamine, 10 micrograms/kg/min, or enoximone, 20 micrograms/kg/min, for the treatment of a low cardiac index (CI) (< 2.2 L/min/m2).

MEASUREMENTS AND MAIN RESULTS

Both drugs significantly (p < 0.05) increased CI from 1.91 +/- 0.17 (dobutamine) and 1.97 +/- 0.17 (enoximone) at baseline to 2.86 +/- 0.70 and 2.84 +/- 0.39 L/min/m2, respectively. Compared with the enoximone (enox)-treated group, the administration of dobutamine (dob) resulted in significantly (p < 0.05) greater increases in mean arterial pressure (dob: 18 +/- 9% v enox: -2 +/- 7%), heart rate (dob: 24 +/- 13% v enox: 3 +/- 5%) and pulmonary artery pressure (dob: 5 +/- 10% v enox: -4 +/- 9%). In contrast, the increase in stroke volume index was significantly less in the dobutamine-treated group (dob: 22 +/- 27% v enox: 41 +/- 21%). The TMF indices, peak E, and peak A wave increased significantly (p < 0.05) after both dobutamine (baseline: 37.3 +/- 6.7 and 41.1 +/- 9.3; max dose: 42.4 +/- 4.3 and 49.0 +/- 10.2 cm/s) and enoximone (baseline: 36.2 +/- 7.5 and 44.2 +/- 10.9; max dose: 40.5 +/- 5.0 and 49.4 +/- 12.1 cm/s) without significantly altering the E/A ratio. Only dobutamine significantly (p < 0.05) decreased isovolumic relaxation time from 109 +/- 24 to 94 +/- 21 ms. There was no significant change in isovolumic relaxation time between the dobutamine (-12% +/- 17%)- and the enoximone (-4% +/- 21%)- treated group. PVF recordings demonstrated a significant increase in time velocity integrals of the S wave with both dobutamine (12.2 +/- 3.1 v 13.7 +/- 3.2 cm) and enoximone (11.0 +/- 3.0 v 12.2 +/- 3.2 cm). No changes in the systolic fraction of the PVF were noted.

CONCLUSIONS

There were no major differences in parameters reflecting diastolic function between the dobutamine- and the enoximone-treated groups.

Myocardial stunning, hibernation, and ischemic preconditioning

From the present review, it may be concluded that myocardial ischemia results in far more complicated syndromes than previously realized. Although not all aspects of the issues discussed in this review are currently a clinical reality in the daily practice of cardiovascular anesthesiologists, the understanding and application of these concepts are growing rapidly. Indications for revascularization procedures will be adjusted in patients with evidence of hibernating myocardium. In the future, postoperative myocardial dysfunction may be diminished by the prevention of myocardial stunning, for instance by altering the composition of the cardioplegic solution and other interventions. Finally, additional advances may involve reduction of the extent of perioperative myocardial infarctions by application of ischemic preconditioning.

Early effects of coronary artery bypass surgery and cold cardioplegic ischemia on left ventricular diastolic function: evaluation by computer-assisted transesophageal echocardiography

OBJECTIVE

Although left ventricular (LV) systolic function undergoes a temporary decrease after cardiopulmonary bypass (CPB) in patients undergoing coronary artery bypass grafting (CABG), data on the effects of CABG and cardioplegic arrest on LV diastolic function are contradictory. The objective of the present study was to further evaluate the effects of CABG and CPB on LV diastolic function.

DESIGN

A prospective study.

SETTING

A multi-institutional investigation at a university hospital.

PARTICIPANTS

20 patients on beta-receptor antagonists, scheduled for CABG and with a preoperative ejection fraction over 0.5.

INTERVENTIONS

Central hemodynamic measurements, transesophageal LV short-axis images, and mitral Doppler flow profiles were obtained before and after volume loading that in turn was performed both before surgical incision and after weaning from CPB.

MEASUREMENTS AND MAIN RESULTS

Heart rate, cardiac output, and peak atrial filling velocity increased; systemic vascular resistance decreased; whereas stroke volume, LV area ejection fraction, deceleration rate and slope of early diastolic filling, time-velocity integral of early diastolic filling, and the ratio between early and atrial peak filling velocity were unchanged post-CPB compared with pre-CPB. LV end-diastolic stiffness that was calculated for each patient pre-CPB and post-CPB using the formula: P = B*eS*A), where P is the LV filling pressure and A is the end-diastolic short-axis area, was unchanged post-CPB compared with pre-CPB.

CONCLUSIONS

Both the active and passive components of LV diastolic function are well maintained shortly after CABG and cardioplegic arrest in patients with a good preoperative systolic LV function.

Immediate postoperative care of cardiac surgical patients

Anesthetic care of the cardiac surgery patient is a continuum, beginning with the preoperative visit and ending when the patient is ambulatory and breathing well on the postoperative floor. Anesthesiologists are well-suited to provide postoperative care because the respiratory and cardiovascular management techniques are an extension of OR management. Attention to details is as important in the ICU as in the OR and offers the opportunity to forestall or reduce morbidity.

Effects of gradual volume loading on left ventricular diastolic function in dogs: implications for the optimisation of cardiac output

BACKGROUND

Volume loading is commonly used to adjust preload and optimise cardiac output. It is difficult to monitor preload at the bedside because filling affects ventricular diastolic function and consequently end diastolic pressure, which is the variable used to monitor preload.

OBJECTIVE

To assess the effects of gradual volume loading on the different components of left ventricular diastolic function---filling velocities, relaxation, and chamber compliance---to identify how excessive loading produces diastolic dysfunction.

METHODS AND RESULTS

Eight mongrel dogs, anaesthetised and mechanically ventilated with both the chest and the pericardium closed, were studied during basal conditions (B), during gradual volume loading with physiological saline---5 ml/kg (VL5), 10 ml/kg (VL10), and 15 ml/kg (VL15)---and during infusion of isosorbide dinitrate (10 g/kg/min) started after the VL15 load was achieved. Dogs were monitored haemodynamically and by transthoracic Doppler echocardiography to assess peak modal velocities of the E and A waves, E/A ratios, and the deceleration time of the E wave. M mode recordings of aligned mitral and aortic valve motion were also obtained to calculate the isovolumic relaxation time. Effects of volume loading on ventricular diastolic function seemed to occur in two phases. Small and moderate volume loads (VL5 and VL10) promoted early ventricular filling, increasing E wave velocities, improving the mean (SD) E/A ratio from 1.95 (0.3) (B) to 2.0 (0.27) (VL5) and 2.6 (0.3) (VL10) (P < 0.00005), prolonging the E wave deceleration time, and only slightly increasing ventricular diastolic pressures. These changes suggest an improvement in ventricular compliance. Extreme volume loads (VL15) produced an abrupt reduction in early ventricular filling, which was transfered to late in diastole, by decreasing E wave velocity, by increasing A wave velocity, and by decreasing E/A ratio from 2.6 (0.3) (VL10) to 0.8 (0.05) (VL15) (P < 0.00005). The E wave deceleration time was shortened and left ventricular diastolic pressures were much increased, all suggesting a deterioration in chamber compliance. All these restrictive changes were promptly reversed by the perfusion of isosorbide dinitrate. The isovolumic relaxation time steadily increased with volume loading.

CONCLUSIONS

Small and moderate volume loads improved ventricular diastolic function by promoting early ventricular filling and increasing ventricular compliance. Extreme volume loads promptly induced a diastolic restrictive pattern, transferring filling to the second part of diastole (increasing dependence on atrial contraction) and reducing ventricular compliance. These changes in ventricular diastolic function were independent of simultaneously measured haemodynamic systolic performance and were promptly reversed by isosorbide dinitrate, which after extreme loading promoted early filling, myocardial relaxation, and improved chamber compliance.

Ischemic event characteristics determine the extent of myocardial stunning in conscious dogs

Both the severity and duration of postischemic myocardial dysfunction ("stunned" myocardium) are unpredictable and may vary considerably between subjects that underwent apparently similar ischemic insults. To explain this heterogeneous response of the heart to ischemia and reperfusion, we investigated the determinants of stunning in conscious dogs. Twenty-five dogs were chronically instrumented for measurement of global and regional myocardial performance (wall thickening) and myocardial perfusion (coloured microspheres). A hydraulic occluder was positioned around the LAD coronary artery. Conscious dogs were subjected to acute coronary artery occlusions of predetermined duration (2, 5 and 10 min), followed by complete reperfusion. Multiple regression analysis identified the following variables as determinants of postischemic contractile recovery: 1) the duration of ischemia (p < 0.01),2) the amount of collateral perfusion (p = 0.01) and 3) left ventricular end-diastolic pressure during ischemia (p < 0.01). Neither the severity of regional dyskinesia during ischemia nor indices of global systolic hemodynamic performance correlated with the rate of recovery. Our data confirm that myocardial stunning relates primarily to the intensity of preceding ischemia. Variations in the preexisting level of collateral perfusion may result in markedly different recovery profiles. Except for LV end-diastolic pressure during ischemia, indices of global and regional cardiac performance fail to predict the severity of postischemic contractile failure.

St. Thomas' Hospital cardioplegia: enhanced protection with exogenous creatine phosphate

BACKGROUND

Experimentally, creatine phosphate (CP) improves postischemic recovery of function and reduces postischemic arrhythmias.

METHODS

We studied 50 patients undergoing valve replacement. They were randomized into either a control group, who received St. Thomas' Hospital cardioplegic solution No. 1, or a CP-treated group, receiving the same cardioplegic solution plus CP (10 mmol/L). There were no preoperative clinical differences between groups. Assessment was by electrocardiographic analysis, inotropic drug requirement, quantitative birefringence, myocardial high-energy phosphate content, function, and semiquantitative ultrastructural assessment.

RESULTS

Direct-current shocks were reduced in the CP-treated group (0.88 +/- 0.15) compared with the control group (1.40 +/- 0.14; p < 0.02), as was the total number of joules (22.0 +/- 3.5 versus 34.4 +/- 3.7, respectively; p <0.02). The incidence of spontaneous sinus rhythm was higher in the CP-treated group (40% versus 8%; p < 0.05) and the incidence of postoperative arrhythmias, lower (8% versus 32%; p < 0.05). Prolonged inotropic administration (12 hours or longer) occurred in fewer patients in the CP-treated group (4% versus 28%; p < 0.05). Response to inotropic support (in the subset of patients requiring this treatment) was significantly greater in the CP-treated group than in the control group. There were no differences in recovery of function, birefringence changes, myocardial high-energy phosphate content, or ultrastructure between groups.

CONCLUSIONS

St. Thomas' Hospital cardioplegic solution No. 1 plus CP enhanced myocardial protection and conferred a direct benefit to the patient by reducing postoperative arrhythmias and need of prolonged inotropic support.

A pharmacokinetic and pharmacodynamic evaluation of milrinone in adults undergoing cardiac surgery

Milrinone can reverse acute postischemic myocardial dysfunction after cardiopulmonary bypass, although neither the appropriate bolus dose nor its pharmacokinetics has been established for cardiac surgical patients. Consenting patients undergoing cardiac surgery received milrinone (25, 50, or 75 micrograms/kg) in an open-label, dose-escalating study if their cardiac index was < 3 L.min-1.m-2 after separation from bypass. Heart rate, mean arterial blood pressure, pulmonary capillary wedge pressure, and cardiac index were determined before and after the administration of milrinone. Timed blood samples were obtained for measurement of milrinone plasma concentrations and pharmacokinetic analysis. Twenty-nine of 60 consenting patients had cardiac indices < 3 L.min-1.m-2 after separation from bypass, received milrinone, and completed the protocol. All three bolus doses of milrinone significantly increased cardiac index. The 50- and 75-micrograms/kg doses produced significantly larger increases in cardiac index than the 25-micrograms/kg dose; however, the 75-micrograms/kg dose did not produce a significantly larger increase in cardiac index than did the 50-micrograms/kg dose. Two of 10 patients receiving milrinone 25 micrograms/kg, but no patient receiving either 50 or 75 micrograms/kg, required early epinephrine rescue when the cardiac index failed to increase by > 15%. The 75-micrograms/kg dose was associated with a case of ventricular tachycardia. The three-compartment model better described milrinone drug disposition than the two-compartment model by both visual inspection and Schwartz-Bayesian criterion. There was only limited evidence of dose-dependence, so data from all three doses are reported together (and normalized to the 50-micrograms/kg dose). Data from one patient was discarded (samples mislabeled). Using mixed-effects nonlinear regression (for n = 28), the following volumes were determined for the three compartments: V1 = 11.1 L, V2 = 16.9 L, and V3 = 363 L. Similarly, the following clearances were estimated for the three compartments: Cl1 = 0.067 L/min, Cl2 = 1.05 L/min, and Cl3 = 0.31 L/min. The 50-micrograms/kg loading dose appeared more potent than the 25-micrograms/kg dose, and, as potent, but with possibly fewer side-effects than the 75-micrograms/kg dose. The short context-sensitive half-times of 6.7 or 10.2 min after 1- or 10-min bolus infusions underscore the need for prompt institution of a maintenance infusion when milrinone concentrations must be maintained.(ABSTRACT TRUNCATED AT 400 WORDS)

Right ventricular dysfunction in low output syndrome after cardiac operations: assessment by transesophageal echocardiography

BACKGROUND

Low output syndrome after cardiac operations is associated with high morbidity and mortality rates. The contribution of right ventricular dysfunction to this syndrome has not been fully characterized. The purpose of this study was to evaluate the utility of transesophageal echocardiography to identify the frequency and the in-hospital mortality from right ventricular dysfunction in patients with this syndrome.

METHODS

Seventy-five consecutive patients undergoing transesophageal echocardiography for low output syndrome early after cardiac operations were evaluated. The findings from transesophageal echocardiography were correlated with the type of surgical procedure, cross-clamp time, right heart hemodynamics, and coronary angiography.

RESULTS

Right ventricular systolic dysfunction occurred in 36 patients (42%); in 17 patients it was isolated and in 19 patients it occurred in combination with left ventricular dysfunction. Postoperative right ventricular dysfunction was not uniformly associated with important right coronary artery disease or with prolonged ischemic time during cardiopulmonary bypass. Hemodynamic data were not useful to distinguish the group with postoperative right ventricular dysfunction. Patients with right ventricular dysfunction had a high (44%) in-hospital mortality rate.

CONCLUSIONS

Right ventricular dysfunction occurs frequently in patients with low output syndrome after cardiac operations and is associated with a high in-hospital mortality rate. Better understanding of the mechanisms causing postoperative right ventricular dysfunction may provide insight for preventing this complication.

Sternal traction after open heart operation: an effective alternative to delayed sternal closure

BACKGROUND

Routine closure of the sternum after cardiovascular surgical procedures sometimes causes severe cardiac depression because of a tamponade-like reduction in ventricular filling, leading to cardiogenic shock. Leaving the sternal halves apart, sealing the mediastinum by simply approximating the skin or using a prosthetic patch, and then performing delayed sternal closure in several days is a widely practiced life-saving maneuver.

METHODS

Described herein is an experience with 5 patients with severe cardiac output depression of the type usually treated by delayed sternal closure. Instead, upward (outward) traction was applied to the anterior chest while the sternum was primarily closed. Traction was maintained with full-thickness chest wall sutures.

RESULTS

The traction sutures were removed successfully in the intensive care unit between 1 and 4 days postoperatively, after appropriate vigorous treatment of postbypass myocardial enlargement and pulmonary distention and edema.

CONCLUSIONS

This method of sternal traction allows physiologic improvement equivalent to delayed sternal closure in some patients and obviates the need for returning to the operating room to close the sternum in the early postoperative period.

Myocardial ischemia after cardiopulmonary bypass

Intraoperatively, myocardial ischemia is more common after cardiopulmonary bypass (CPB) than before CPB. Ischemia associated with coronary vasospasm and thrombosis may be much more common toward the end of surgery and early in the postoperative period than previously appreciated. This may be because the coagulation system is altered during CPB, and the coronary endothelium is damaged significantly as a result of cardioplegic arrest followed by reperfusion. In this milieu, vasospasm and thrombosis may be caused by the administration of protamine. Some of the ischemia observed in this period actually is not reversible and is associated with myocardial injury and infarction. It may be ameliorated by the administration of calcium channel blockers, aspirin, and anticoagulants. Electrocardiography may be the most suitable modality for the detection of ischemia after CPB and postoperatively. During this period, many episodes of ST deviation are of a nonischemic etiology, and the ECG needs careful interpretation. Transesophageal echocardiography is suitable for use intraoperatively and early on in the intensive care unit.

Treatment of perioperative low cardiac output syndrome

New approaches to the treatment of perioperative low cardiac output are considered. In particular, use of the phosphodiesterase III inhibitors and their cardiovascular actions are reviewed and contrasted with those of conventional inotropic agents. The increasing recognition of right-sided dysfunction is highlighted, and appropriate therapeutic strategies are considered. The increasing role of pulmonary-specific vasodilators such as inhaled nitric oxide is emphasized. Strategies to preserve right heart perfusion while producing pulmonary vasodilatation are discussed.

Effects of phenylephrine or volume loading on right ventricular function in patients undergoing myocardial revascularization

The acute effects of phenylephrine (PHE) administration or intravascular volume loading on right ventricular (RV) function were examined in 34 patients undergoing elective coronary artery surgery. After anesthetic induction with sufentanil and midazolam, 20 patients received PHE to treat hypotension and increase systemic arterial pressure 20% above baseline values. PHE effectively restored arterial pressure without changing stroke index (SI), although RV ejection fraction (RVEF) declined (41.3% to 37.6%) with concomitant increases in RV end-diastolic volume index (RVEDVI) (86.3 to 97.5 mL/m2) and RV end-systolic volume index (51.8 to 63.4 mL/m2). In the first 6 to 8 hours after surgery, 18 patients received intravascular volume expansion with 5% albumin when the clinical perfusion state was inadequate and accompanied by pulmonary artery occlusion pressure (PAOP) less than 15 mmHg and a hemoglobin level greater than 8 g/dL. Volume loading with 500 mL of albumin increased SI(27.0 to 31.8mL/m2), PAOP (12.2 to 15.4 mmHg) and RVEDVI (69.0 to 86.5 mL/m2), although RVEF declined (39.3% to 37.6%). Baseline values of RVEF and SI (but not PAOP or right atrial pressure [RAP]) were lower in 9 of 18 patients who exhibited declines in RVEF after volume loading, and RAP was a poor indicator of RVEDVI (r = 0.17). RVEDVI (but not RAP or PAOP) had significant correlation with SI during volume loading. There was no relationship between the presence of hemodynamically significant right coronary artery stenoses requiring revascularization or other perioperative factors with the response to PHE before revascularization or to volume loading after revascularization.(ABSTRACT TRUNCATED AT 250 WORDS)

One-stage surgery of coronary arteries and abdominal aorta in patients with impaired left ventricular function

BACKGROUND

Coronary artery disease (CAD) is common in patients with abdominal aortic aneurysms (AAA). Some patients will present with the combination of unstable angina, impaired left ventricular function, and a large symptomatic (ie, leaking, expanding) AAA. In this subgroup of high-risk patients, aortic cross-clamping may have a deleterious effect on cardiac function, whereas coronary artery bypass graft surgery before aneurysmectomy (staged operation) carries the risk of perioperative aneurysm rupture. One-stage surgery, ie, myocardial revascularization and simultaneous aortic aneurysm repair, has been proposed in this situation. This article summarizes our results with the combined one-stage approach in patients with symptomatic CAD, impaired left ventricular function, and large symptomatic aortic aneurysms or severe aortic occlusive disease. As yet, this cohort is the largest reported in the English literature.

METHODS AND RESULTS

In 25 patients (24 men) with a mean age of 69.4 years (range, 55 to 80 years), we performed combined open heart and intra-abdominal aortic surgery. Eighteen patients had severe three-vessel disease and impaired left ventricular function (ejection fraction, < 35%). In addition, 3 of these patients had severe aortic valvular stenosis and/or insufficiency. Seven patients had one- or two-vessel disease with a low left ventricular ejection fraction in the range of 15% to 30%. All patients were in New York Heart Association functional class III or IV. Twenty-one of 25 patients had symptomatic infrarenal AAA (perianeurysm hematoma was present in 9 patients, and 12 patients had signs of beginning perforation). Four patients with aortoiliac occlusive disease and limb ischemia were simultaneously operated on. The surgical procedure started with the performance of coronary artery bypass graft surgery. After completion of myocardial revascularization, aortic aneurysm repair was performed while extracorporeal circulation was continued for mechanical cardiac assist until aortic surgery was fully accomplished. An average of 3.3 (3 to 5) coronary bypass grafts were placed, including 17 internal thoracic artery grafts. In addition, three aortic valves were replaced. In the abdominal aortic position, 12 straight tube grafts and 13 bifurcation grafts were implanted, and three renal and two carotid arteries were simultaneously repaired. The total time of surgery varied from 2.3 to 8.5 hours, with a mean time of 3.9 +/- 1.4 hours. One intraoperative myocardial infarction occurred despite open grafts. Intensive care unit treatment lasted 1 to 13 days, with a mean of 3.6 +/- 2.5 days. Three patients (12%) died after surgery--1 because of acute renal failure induced by an adverse reaction to heparin, 1 because of myocardial infarction, and 1 because of multiorgan failure. One-year actuarial survival rate was 88%, which compares favorably with survival after isolated AAA surgery in this high-risk patient subgroup and equals survival in patients with severe CAD and severely depressed myocardial function.

CONCLUSIONS

One-stage surgery is a possible approach to highly symptomatic patients with severe multivascular disease and has acceptable early morbidity and mortality. Patients with severely impaired left ventricular function and unstable CAD carry a high risk of left heart failure and/or myocardial infarction during abdominal aortic surgery. Extracorporeal circulation protects the heart from the hemodynamic changes after aortic clamping or declamping during abdominal aortic surgery. The present study demonstrates that one-stage procedure is a reasonable option for this patient subgroup.

Reversible diastolic dysfunction after successful coronary artery bypass surgery. Assessment by transesophageal Doppler echocardiography

To assess the potential effects of coronary artery bypass surgery on left ventricular diastolic filling, 12 patients, aged 65 +/- 11 years, were studied by serial transesophageal Doppler echocardiograms. Doppler measures of mitral inflow velocity were made before, immediately after, 4 h after, and 20 h after cardiopulmonary bypass (CPB). Left atrial pressure was directly measured and controlled at 10 +/- 2 mm Hg for each study period. Mitral maximal early inflow velocity (E)/maximal atrial velocity (A) ratios and atrial filling fractions were calculated as indexes of diastolic function from maximal E and A velocities and their time velocity integrals, respectively. Data sets were available for serial comparison in 11 patients and were also compared with an age-matched control group of normal values. The results of E/A ratios were as follows: control group--1.4 +/- 0.2; before CPB--1.7 +/- 0.6; immediately after CPB--1.0 +/- 0.2 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); 4 h after CPB--0.8 +/- 0.2 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); and 20 h after CPB--1.3 +/- 0.4. Atrial filling fractions were as follows: control group--0.29 +/- 0.05; before CPB--0.25 +/- 0.06; immediately after CPB--0.43 +/- 0.07 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); 4 h after CPB, 0.46 +/- 0.07 (p < 0.05 vs control group, before CPB, and 20 h after CPB values); and 20 h after CPB--0.35 +/- 0.06. Alterations in Doppler indexes of left ventricular filling occurred immediately after CPB and persisted 4 h after CPB. These indexes returned to baseline values by 20 h after CPB. This suggests reversible diastolic dysfunction in patients after coronary artery bypass surgery.

Emergency and long-term extracorporeal life support following acute myocardial infarction: rescue from severe cardiogenic shock related to stunned myocardium

There has been no report regarding therapy of extracorporeal life support (ECLS) that showed stunned myocardium echocardiographically and electrocardiographically in patients with acute myocardial infarction. ECLS was performed in eight patients with cardiogenic shock or arrest unresponsive to catecholamines and intra-aortic balloon pumping following myocardial infarction; these patients required prolonged external cardiac massage. After the initiation of ECLS, both blood pressure and metabolic acidosis improved in all patients. Four of eight patients were weaned from ECLS after a mean of 69.3 h, which was far longer than previously reported in patients with ischemic heart disease. Three of these patients survived, and cardiac function recovered to NYHA class II in two of the survivors and class III in the other. The other five patients did not recover from coma during ECLS and died. A marked improvement of ventricular wall motion was seen in two survivors with the disappearance of pathologic Q waves after the initiation of ECLS. No occlusion of the coronary arteries or bypass grafts was observed in any of the survivors. These findings suggested the existence of stunned myocardium with myocardial reperfusion. The recovery of stunned myocardium may be delayed for days or even weeks, hence the extended period of ECLS therapy was theoretically justifiable. We conclude that long-term ECLS is a useful therapeutic method for patients with severe cardiogenic shock that is related to stunned myocardium.

Early extubation after cardiac surgery using combined intrathecal sufentanil and morphine

The records of 10 patients who had well-preserved respiratory and ventricular function and had received 50 micrograms of sufentanil and 0.5 mg of morphine intrathecally before induction of anesthesia for cardiopulmonary bypass surgery were reviewed. Anesthesia was maintained with isoflurane and no patient received intravenous narcotics intraoperatively. Postoperative analgesic requirements were low, with 7 of 10 patients requiring no supplemental analgesic during the first 12 hours. Early extubation (within 8 hours of arrival in the intensive care unit) was possible in 8 patients; two patients remained intubated for reasons unrelated to the anesthetic technique. No patient required naloxone, reintubation, or treatment for respiratory depression. Combined intrathecal sufentanil and morphine provided conditions that allowed successful early extubation in 8 of 10 of these selected cardiac surgery patients.

Hemodynamic and renal effects of dopexamine and dobutamine in patients with reduced cardiac output following coronary artery bypass grafting

OBJECTIVE

Dopexamine hydrochloride is a novel synthetic adrenergic agonist that combines the renal effects of dopamine with the hemodynamic effects of dobutatmine. Our study is designed to compare the hemodynamic, diuretic, and natriuretic effects of dopexamine and dobutamine in patients with reduced cardiac index following heart surgery.

DESIGN

Prospectively randomized, blinded study.

SETTING

Operating room and intensive care unit of a large, urban, academic medical center.

PATIENTS

Twenty-eight patients undergoing elective coronary artery bypass grafting (CABG) with preoperative ejection fraction of at least 40 percent gave informed consent. The study group consisted of the ten patients who had a cardiac index < or = 2.5 L/min/m2 (while receiving no inotropic medication) immediately after separation from cardiopulmonary bypass.

INTERVENTIONS AND MEASUREMENTS

Study patients were randomly given a starting dose of either 5 micrograms/kg/min of dobutamine (n = 5) or 2 micrograms/kg/min of dopexamine (n = 5). During the initial 30 min following separation from bypass, dosages were titrated incrementally to maintain cardiac index > or = 3.0/L/min/m2. Further titrations of the drug were done only if cardiac index fell below 3.0 L/min/m2 or if sustained tachycardia occurred during the 24-h study period. Data were collected at 5- and 10-min intervals for the first 30 min after separation from bypass, hourly for the next 8 h, then every 2 h for the remainder of the study period.

RESULTS

Both drugs increased cardiac index by more than 50 percent over baseline (dobutamine 2.2 +/- 0.1 to 3.5 +/- 0.2 [p < 0.05]; dopexamine, 2.3 +/- 0.1 to 3.5 +/- 0.1 [p < 0.05] L/min/m2). The mean dose required to maintain cardiac index > or = 3.0L/min/m2 was 1.5 micrograms/kg/min for dopexamine and 3.5 micrograms/kg/min for dobutamine. There were no significant differences in either urinary output or net sodium excretion in the dopexamine group compared with the dobutamine group, and tachycardia (heart rate > 120 beats/min) was more common in the dopexamine group.

CONCLUSIONS

Our study demonstrates that dopexamine produces hemodynamic, diuretic, and natriuretic effects similar to dobutamine in patients with reduced cardiac index following CABG.

Bedside assessment of myocardial performance in the critically ill

No measurement of myocardial performance currently available in the ICU can be regarded is ideal. Table 2 summarises the main features of the major monitoring techniques. As many of the indices of myocardial performance are interdependent, quantifying the contribution of each component to overall cardiac function is not possible currently, and the clinical utility of monitoring each individually is not therefore established. Bedside measurements of LV dimensions, volumes and ejection fraction, and the other indices of systolic and diastolic function can now be made, but the case for their routine use in influencing clinical practice remains unproven. Transoesophageal echocardiography has an important and established diagnostic role and has been used successfully for continuous monitoring during surgery, but practical considerations seriously limit its potential for routine use. Radionuclide techniques allow the measurement of many of the same parameters and have the potential for continuous use, but practical problems and the additional risk of radiation exposure may limit this application in the critical care environment. Doppler techniques are non-invasive, provide continuous data and are simple to operate, but the data provided has important limitations. Although the pulmonary artery catheter has been in use for over twenty years, questions regarding the information is provides concerning myocardial function remain and the extent to which it should influence therapeutic decisions is still controversial. However with the development of additional facilities, particularly the continuous measurement of cardiac output the pulmonary artery catheter seems likely to remain the mainstay of bedside monitoring of myocardial performance in the critically ill in the immediate future.

Clinical evidence for stunned myocardium after coronary artery bypass surgery

Stunned myocardium is defined as postischemic dysfunction of viable myocardium. This phenomenon was initially described in animal models of brief ischemia followed by reperfusion, but is becoming increasingly recognized in clinical situations. One of these situations is ventricular dysfunction following coronary artery bypass surgery. Several clinical reports have demonstrated depressed ventricular function in the initial hours after coronary artery bypass surgery: this dysfunction is usually resolved within 24 to 48 hours, and does not appear to be dependent upon alterations in preload, afterload, or temperature. New therapies for improving postischemic myocardial function following cardiopulmonary bypass are under investigation.

Stunned myocardium following prolonged cardiopulmonary bypass: effect of warm versus cold cardioplegia in the canine model

"Stunned myocardium" is defined as the prolonged but transient postischemic contractile dysfunction of viable myocardium that has been salvaged by reperfusion. This phenomenon, although first characterized in the experimental canine model of coronary artery occlusion/reperfusion, also occurs following transient global ischemia. Moreover, despite the superb cardioprotection conferred by administration of cold cardioplegia during aortic cross-clamping, stunned myocardium is a well-recognized sequela of prolonged cardiopulmonary bypass. Using the anesthetized open chest dog, we tested the concept that continuous retrograde infusion of warm blood cardioplegia would effectively prevent ischemia during prolonged aortic cross-clamping and thereby preclude the development of stunned myocardium following bypass. Thirteen dogs were placed on cardiopulmonary bypass and randomized to receive: (1) continuous retrograde administration of warm blood cardioplegia (n = 8); or (2) intermittent retrograde cold blood cardioplegia (n = 5) during a 3-hour cross-clamp period. Left ventricular (LV) systolic function (i.e., area LV ejection fraction and posterior LV free wall thickening assessed by two-dimensional echocardiography) and hemodynamic parameters were monitored at baseline and at 1 and 2 hours postbypass and, at the end of the protocol, transmural myocardial biopsies were obtained for electron microscopic analysis. All dogs in both treatment groups showed electron microscopic evidence of mild and reversible morphological injury indicative of stunned myocardium, with no difference between dogs that received warm versus cold cardioplegia. Direct comparison of LV function between the two groups was confounded by a profound decrease in afterload in dogs that received cold cardioplegia. However, incorporation of systemic vascular resistance as a covariate revealed that LV function following bypass was modestly depressed at approximately 85% of baseline values, and that continuous administration of warm cardioplegia did not prevent this hypokinesis. Thus, in our canine model: (1) morphological injury and LV dysfunction induced by 3 hours of aortic cross-clamping is subtle; and (2) continuous retrograde infusion of warm blood cardioplegia during the cross-clamp period failed to preclude myocardial stunning following prolonged cardiopulmonary bypass.

The role of amrinone in treating heart failure during and after coronary artery surgery supported by cardiopulmonary bypass

Amrinone and dobutamine compare favorably in the treatment of chronic congestive heart failure. There is increasing evidence that amrinone alone or in combination with a catecholamine may be used with considerable success in treating patients who are difficult to wean from cardiopulmonary bypass or who have a low cardiac output syndrome after coronary artery bypass grafting surgery. Amrinone increases intramyocardial cyclic adenosine monophosphate and exerts positive inotropic activity in addition to being a potent vasodilator. It may also improve diastolic function by increasing sarcoplasmic reticulum reuptake of calcium during diastole. It has been administered to patients prior to weaning from cardiopulmonary bypass and has improved hemodynamics and oxygen transport. When compared with dobutamine as primary treatment for depressed myocardial function in patients being weaned from cardiopulmonary bypass after coronary artery bypass grafting surgery, it was more effective in achieving primary treatment objectives. Patients given dobutamine had a higher incidence of myocardial infarction, ventricular fibrillation, supraventricular tachyarrhythmias, sinus tachycardia, and hypertension compared to those given amrinone. It is concluded that amrinone compares favorably with dobutamine and may even be superior when used as primary treatment for treating myocardial depression in patients having coronary artery surgery supported by cardiopulmonary bypass.

Open heart surgery increases the levels of histamine in arterial and coronary sinus blood

The possible release of histamine into the coronary circulation during reperfusion of the cold, cardioplegic heart was investigated during open heart surgery in 13 patients (cardioplegic arrest 54 (35-120 min) (median (range)), cardiopulmonary bypass (CPB) 96 (65-360) min. Samples were drawn concomitantly from coronary sinus and arterial blood before cardioplegia and during myocardial reperfusion for measurement of histamine (radioenzymatic method). Additional arterial samples were drawn pre-, per- and postoperatively. CPB induced a sustained increase in arterial histamine (from 4.02 +/- 2.71 nmol/l preoperatively (mean +/- SD) to maximum 16.31 +/- 7.12 nmol/l, p < 0.009). Immediately before cardioplegia histamine levels were higher in arterial than coronary sinus blood (9.24 +/- 4.85 versus 4.04 +/- 2.07 nmol/l, p < 0.002). During myocardial reperfusion coronary sinus histamine increased to levels similar to that of arterial blood. In conclusion, histamine is released during CPB. Before cardioplegic arrest, there is a net uptake of histamine by the heart, which is abolished during reperfusion, possibly due to increased cardiac release of histamine.

Assessment of the immediate effects of cardiopulmonary bypass on left ventricular performance by on-line pressure-area relations

BACKGROUND

Pressure-volume relations have been established as useful measures of left ventricular (LV) performance. Application of these methods to the intraoperative setting have been limited because of difficulties acquiring LV volume data. Transesophageal echocardiographic automated border detection can measure LV cross-sectional area as an index of volume, which can be coupled with pressure data to construct pressure-area loops on-line. The purpose of this study was to evaluate intraoperative LV performance in patients undergoing coronary bypass surgery before and immediately after cardiopulmonary bypass using on-line pressure-area relations.

METHODS AND RESULTS

Studies were attempted in 13 consecutive patients. Simultaneous measures of LV cross-sectional area, LV pressure, and electromagnetic flow probe-derived aortic flow recorded on a computer work station interfaced with the ultrasound system. Pressure-area loops were compared with simultaneous pressure-volume loops constructed from pressure and flow data during inferior vena caval occlusions before and after bypass. Pressure-volume calculations (end-systolic elastance, maximal elastance, and preload-recruitable stroke work) were then applied to pressure-area loops with area substituted for volume data. Changes in stroke force from pressure-area loops were closely correlated with changes in estimates of stroke work from pressure-volume loops for individual patients before bypass (r = .99 +/- .03, SEE = 5 +/- 2%, n = 10) and after bypass (r = .96 +/- .05, SEE = 5 +/- 2%, n = 9). Pressure-area estimates of end-systolic elastance, maximal elastance, and preload-recruitable stroke force decreased significantly from before to after cardiopulmonary bypass in the 7 patients with paired data sets. Load-dependent measures of LV function (stroke volume, cardiac output, and fractional area change) were unchanged after surgery in these same patients.

CONCLUSIONS

Intraoperative pressure-area loops may be acquired and displayed on-line using transesophageal echocardiographic automated border detection and readily analyzed in a manner similar to pressure-volume loops. LV performance was depressed immediately after cardiopulmonary bypass compared with before. On-line pressure-area relations may be clinically useful to assess LV performance in patients undergoing cardiac surgery in whom load and contractility may be expected to vary rapidly.

Anaesthesia for coronary artery surgery--a plea for a goal-directed approach

The purpose of the current literature review was to examine whether changes in current anaesthetic techniques are warranted for patients undergoing coronary artery surgery in light of recent information presented in the literature. The objectives of a cardiac anaesthetic technique are to maintain haemodynamic stability and myocardial oxygen balance, minimize the incidence and severity of ischaemic episodes, be aware of cardiopulmonary bypass-induced pharmacokinetic changes, and facilitate early tracheal extubation if appropriate. Many techniques have been utilized. Provided attention is paid to the details of managing myocardial oxygen supply and demand, none has emerged as superior in preventing intraoperative myocardial ischaemia. Silent myocardial ischaemia (i.e., ischaemia occurring in the absence of haemodynamic aberrations) is common throughout the perioperative period and may occur even in the presence of an appropriately used anaesthetic technique. The incidence and severity appear to be greatest in the postoperative period when the effects of anaesthesia are dissipating. The use of high-dose opioid anaesthesia may no longer be the most appropriate technique to facilitate the anaesthetic objectives. The role of pain management in altering the incidence of ischaemia requires further study. Increased waiting lists for cardiac surgery and ever-diminishing resources should prompt a re-evaluation of early extubation (i.e., within eight hours) as a method of improving utilization of scarce ICU resources. It is suggested that this should be possible with currently available agents to achieve the anaesthetic objectives. Future suggestions for research in this area are made.

Amrinone in cardiac surgical patients with left-ventricular dysfunction. A prospective, randomized placebo-controlled trial

STUDY OBJECTIVE

To evaluate the efficacy of amrinone for facilitating weaning from cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, double-blind, placebo-controlled trial with epinephrine as "rescue" therapy.

SETTING

Operating room of a large, metropolitan tertiary-care center.

PATIENTS

Thirty-nine patients with preoperative left ventricular dysfunction undergoing cardiac surgery. Thirty-three patients underwent aortocoronary bypass grafting; six patients underwent valve replacement for severe mitral or aortic regurgitation.

INTERVENTIONS

Patients received either amrinone (1.5 mg/kg loading dose plus 10 micrograms/kg/min maintenance infusion; n = 20) or placebo (n = 19) in a randomized double-blind fashion shortly (median, 10.5 min; range, 2 to 24 min) before separation from CPB. Inotropic drugs (other than the study drug) were withheld prior to separation from CPB unless safety considerations demanded that the protocol be broken. Patients who could not be weaned from CPB, as well as those with a cardiac index of 2.2 L/min/m2 or less after weaning from CPB, received epinephrine (60 to 120 ng/kg/min) by infusion.

MEASUREMENTS AND RESULTS

Fourteen of 19 patients receiving placebo but only 1 of the 20 patients receiving amrinone (p = 0.00001) required epinephrine infusion to separate from bypass. The cardiac index of 4 patients receiving placebo (but no patients with amrinone) failed to exceed 2.2 L/min/m2 despite epinephrine infusion, requiring the protocol to be broken (p < 0.08). Blood concentrations of amrinone determined (only in the amrinone group) after separation from CPB confirmed that the dosage of amrinone produced an effective blood concentration. Fourteen of 19 patients receiving placebo and 17 of 20 patients receiving amrinone required an infusion of phenylephrine titrated to maintain systolic blood pressure less than 90 mm Hg. Seven patients (four with amrinone and three with placebo) required antiarrhythmic drug therapy. The outcome at 3 months was similar in the 2 groups.

CONCLUSIONS

Amrinone by itself is an effective agent to facilitate weaning from CPB, and therapy with amrinone reduced the need for individualized titration of epinephrine. Amrinone is as effective as individualized titration of epinephrine (after CPB) to improve cardiac function. Patients in the group receiving amrinone had no greater need for vasoconstricting agents than did patients in the group receiving placebo; however, proactive administration of amrinone before separation from CPB appears to offer no greater benefit to high-risk patients than selective administration of drugs (epinephrine) only to those patients who demonstrate the need for drug support at the time of weaning.

Support of the perioperative failing heart with preexisting ventricular dysfunction: currently available options

Perioperative support of the patient with preexisting biventricular failure requires simultaneous optimal manipulation of heart rate and rhythm, loading conditions, and contractility. Patients with preexisting ventricular dysfunction will have alterations in beta-adrenergic receptors, resulting in decreased responsiveness to catecholamines. Even patients with previously normal ventricular function can develop ventricular dysfunction caused by reperfusion injury and other potentially damaging effects of extracorporeal circulation. The mainstay of therapeutic agents used to allow separation from cardiopulmonary bypass are catecholamines, which stimulate alpha- and beta-adrenergic receptors. Submaximal responses to beta 1-adrenergic stimulation can occur in the down-regulated heart. The phosphodiesterase inhibitors provide both inotropic support and vasodilatation, which improves both systolic and diastolic function and bypasses beta-adrenergic receptors. When administered in combination, catecholamine and cyclic-AMP-specific phosphodiesterase inhibitors can have additive effects to restore beta 1-adrenergic responsiveness. Combination therapy provides an important therapeutic option to facilitate separation from cardiopulmonary bypass. Pharmacologic intervention for right ventricular dysfunction focuses on reversal of pulmonary vasoconstriction with nitrates, beta 2-adrenergic agents, phosphodiesterase inhibitors and prostaglandin E1.

Myocardial dysfunction following cardiopulmonary bypass: recovery patterns, predictors of inotropic need, theoretical concepts of inotropic administration

Clinical myocardial dysfunction following cardiopulmonary bypass commonly occurs in patients with good preoperative ventricular function. Following separation from cardiopulmonary bypass, ventricular function improves initially, but then begins to worsen and reaches a nadir between 4 and 6 hours after surgery with full recovery occurring around 24 hours postoperatively. However, in patients with preoperative ventricular dysfunction, the depression of ventricular function is more severe and recovery is longer. Despite this high frequency of myocardial dysfunction, many patients do well without requiring pharmacologic intervention after cardiopulmonary bypass to augment contractility and peripheral perfusion. Factors that may predict the need for inotropic support in patients following cardiopulmonary bypass include low ejection fraction, older age, cardiac enlargement, female sex, the length of cardiopulmonary bypass and the duration of aortic cross-clamping. The patient with preoperative ventricular dysfunction has many of these preoperative and intraoperative predictors for inotropic support. The pharmacologic regimen to support the myocardium during the recovery period following cardiopulmonary bypass must take into consideration the pathophysiologic processes of chronic congestive heart failure and reperfusion injury. Reduction of cyclic adenosine monophosphate (cAMP) levels is a fundamental problem in congestive heart failure and results from either down-regulation of beta-receptors or a defect in the G-regulatory proteins controlling adenylyl cyclase production. This diminishes the effectiveness of agents dependent on cAMP to produce an inotropic response. However, amplification of the reduced cAMP produced by beta-agonists may occur in association with the inhibition of cAMP breakdown resulting from phosphodiesterase inhibitors. All inotropic agents are usually effective in reversing the reperfusion-induced stunned myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Selecting an inotrope for the cardiac surgery patient

Although a wide variety of positive inotropic agents have been administered to cardiac surgery patients, few of them have been carefully studied in controlled clinical trials, in surgical patient populations. The limited data available suggest that one of the more widely used agents, calcium, may lack efficacy and possibly inhibit the actions of catecholamines. Dopamine, dobutamine, and dopexamine are highly effective agents, but more prone to produce tachycardia than epinephrine. Amrinone is an effective agent by itself, but is especially useful in combination with a beta-adrenergic agonist for patients with severe left-ventricular dysfunction.

Postcardioplegia acute cardiac dysfunction and reperfusion injury

In cardiac surgery, an obligatory period of ischemia is imposed in order to provide a convenient operative field. Brief periods of ischemia produce systolic and diastolic abnormalities related to pathology occurring during ischemia per se (ischemic injury) or expressed after the onset of reperfusion (reperfusion injury). In the surgical setting, ischemia may be encountered preoperatively with preexisting coronary disease, hypotension, or ventricular fibrillation, between intermittent infusions of cardioplegia solutions, or as a result of maldistribution of cardioplegia solution. The potential for reperfusion injury exists not only at the time of cross-clamp removal, but also with each infusion of cardioplegia solution. Infusion of cardioplegic solution is, in fact, a form of reperfusion to previously ischemic myocardium. Ischemic injury and reperfusion injury are intimately linked in that the severity of ischemia sets the stage for and determines, in part, the extent of reperfusion injury. Mild-to-moderate systolic dysfunction, which may be called "postcardioplegia stunning," remains a significant complication after cardiac surgery. More significant postoperative functional depression may occur in hearts with severe preoperative dysfunction, and in operations requiring long cross-clamp times. In addition, the failure to adequately distribute cardioplegic solution to all areas of the myocardium because of coronary stenoses, high coronary resistance or inadequate delivery pressure-flow relations, contributes to postcardioplegia dysfunction. However, the cardioplegic solution itself may also contribute to postcardioplegic dysfunction by creating temporary ionic and metabolic abnormalities. In addition, systemic hypocalcemia or hyperkalemia resulting from using large doses of cardioplegic solution may temporarily aggravate postcardioplegic mechanical dysfunction. Current formulations and strategies for delivery of cardioplegia solutions are designed to address the various contributors to both ischemic and reperfusion injury that may impact on postoperative mechanical performance. Ischemic injury is avoided by reducing myocardial oxygen demand by engaging immediate arrest and cooling the heart to approximately 10 degrees centigrade, and intermittently infusing solution to reoxygenate the myocardium, maintain hypothermia, and wash out accumulated metabolites. Reperfusion injury may be avoided by infusing hyperosmotic solutions at moderate pressures, and by incorporating oxygen radical scavengers or inhibitors to reduce membrane lipid peroxidation, myocellular and microcirculatory (endothelium) damage.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanisms of chronic regional postischemic dysfunction in humans. New insights from the study of noninfarcted collateral-dependent myocardium

BACKGROUND

Even in the absence of a previous myocardial infarction, patients with coronary artery disease often present with chronic regional wall motion abnormalities that are reversible spontaneously or after coronary revascularization. In these patients, regional dysfunction has been proposed to result either from prolonged postischemic dysfunction (myocardial "stunning") or from adaptation to chronic hypoperfusion (myocardial "hibernation"). This study examines which of these two mechanisms is responsible for the chronic regional dysfunction often detected in patients with angina and noninfarcted collateral-dependent myocardium.

METHODS AND RESULTS

Twenty-six anginal patients (19 men; mean age, 60 +/- 9 years old) with chronic occlusion of a major coronary artery but without previous infarction were studied. Positron emission tomography was performed to measure absolute regional myocardial blood flow with 13N-ammonia at rest (n = 26) and after intravenous dipyridamole (n = 11). The kinetics of 18F-deoxyglucose and 11C-acetate were measured to calculate the rate of exogenous glucose uptake and the regional oxidative metabolism (n = 15). Global and regional left ventricular function was evaluated by contrast ventriculography at baseline (n = 26) and after revascularization (n = 12). Transmural myocardial biopsies from the collateral-dependent area were obtained in seven patients during bypass surgery and analyzed by optical and electron microscopy. According to resting regional wall motion, patients were separated into groups with and without dysfunction of the collateral-dependent segments. In patients with normal wall motion (n = 9), regional myocardial blood flow, oxidative metabolism, and glucose uptake were similar among collateral-dependent and remote segments. By contrast, in patients with regional dysfunction (n = 17), collateral-dependent segments had lower myocardial blood flow (77 +/- 25 versus 95 +/- 27 mL.min-1.100 g-1, p < 0.001), smaller k values (slope of 11C clearance reflecting oxidative metabolism, 0.049 +/- 0.015 versus 0.068 +/- 0.020 min-1, p < 0.001) and higher glucose uptake (relative 18F-deoxyglucose-to-flow ratio of 1.9 +/- 1.6 versus 1.2 +/- 0.2, p < 0.05) compared with remote segments. However, myocardial blood flow and k values were similar among collateral-dependent segments of patients with and without segmental dysfunction. After intravenous dipyridamole, collateral-dependent myocardial blood flow increased from 78 +/- 5 to 238 +/- 54 mL.min-1.100 g-1 in three patients with normal wall motion and from 88 +/- 17 to only 112 +/- 44 mL.min-1.100 g-1 in eight patients with regional dysfunction. There was a significant (r = -0.85, p < 0.001) inverse correlation between wall motion abnormality and collateral flow reserve. Analysis of the tissue samples obtained at the time of bypass surgery showed profound structural changes in dysfunctioning collateral-dependent areas, including cellular swelling, loss of myofibrillar content, and accumulation of glycogen. Despite these alterations, the regional wall motion score improved significantly in the patients studied before and after revascularization (from 3.8 +/- 1.3 to 0.8 +/- 0.9, p < 0.005).

CONCLUSIONS

In a subgroup of patients with noninfarcted collateral-dependent myocardium, immature or insufficiently developed collaterals do not provide adequate flow reserve. Despite nearly normal resting flow and oxygen consumption, these collateral-dependent segments exhibit chronically depressed wall motion and demonstrate marked ultrastructural alterations on morphological analysis. We propose that these alterations result from repeated episodes of ischemia as opposed to chronic hypoperfusion and represent the flow, metabolic, and morphological correlates of myocardial "hibernation."

Pharmacologic and mechanical methods of discontinuing extracorporeal circulation in patients with heart failure

Separation from EC requires simultaneous optimal manipulation of heart rate and rhythm, loading conditions, afterload, and contractility. Patients with preexisting ventricular dysfunction will have alterations in beta-adrenergic receptors and responsiveness to catecholamines, but patients with previously normal ventricular function can also develop ventricular dysfunction. Catecholamines, by stimulating beta-adrenergic receptors, decrease systolic function to allow separation from EC. The phosphodiesterase inhibitors provide both inotropic support and vasodilation, to improve both systolic and diastolic function. When administered in combination, catecholamines and cyclic-AMP-specific phosphodiesterase inhibitors can have additive effects to restore beta 1-adrenergic responsiveness. Combination therapy provides an important support during biventricular dysfunction and facilitates separation from EC. Finally, mechanical support provides a therapeutic option when pharmacologic therapy is ineffective.

Clinical evidence of myocardial stunning in patients undergoing CABG surgery

Although patients who have undergone coronary artery bypass graft (CABG) surgery frequently present with symptoms suggesting that myocardial stunning has occurred, measurements of regional myocardial function and perfusion are difficult in clinical settings. Several studies have used left ventricular function indices (i.e., cardiac index, left ventricular stroke work index, ejection fraction) to assess myocardial stunning immediately following CABG surgery. These changes in ventricular function have been found to be reversible and the clinical data are consistent with the occurrence of myocardial stunning. Myocardial metabolism is also reportedly depressed following CABG surgery. Decreases in myocardial oxygen extraction, consumption, and lactate utilization all point to the presence of myocardial stunning, as do abnormalities in regional wall-motion and electrocardiographic changes (i.e., transient Q waves) described in patients who have undergone CABG surgery. New approaches to differentiating viable from nonviable myocardial tissue will likely include stress echocardiography using new stress agents, ultrasound contrast agents, and high frequency ultrasound.

Pathophysiology and mediators of ischemia-reperfusion injury with special reference to cardiac surgery. A review

Although necessary for the ultimate tissue survival, reperfusion may paradoxically exacerbate the ischemic injury. Ischemia and reperfusion injury is intimately woven together. The relative role of reperfusion injury is not clarified and probably varies with the ischemic insult: Reperfusion is always preceded by ischemia, and some of the reperfusion-related events may represent a process continuing from the ischemic period; thus the proper designation should be ischemia-reperfusion injury. The reperfusion-related events are: arrhythmias, myocardial stunning with both systolic and diastolic dysfunction, and low reflow and microvascular stunning. Of pathogenetic importance are the mode and speed of reperfusion as well as the initiation of an intracoronary inflammatory reaction during reperfusion, including endothelium-leukocyte interaction, platelets, generation of oxygen free radical, generation and release of arachidonic acid metabolites, platelet activating factor, endothelium derived relaxing factor, endothelins, kinins, and histamine, complement activation, disturbances in calcium homeostasis, and disturbances in lipid and fatty acid metabolism.

Intravenous nifedipine for prevention of myocardial ischaemia after coronary revascularization

We sought to determine the pharmacokinetic and pharmacodynamic behaviour of a continuous infusion of nifedipine given for prevention of myocardial ischaemia following coronary artery bypass graft (CABG) surgery. Patients scheduled for elective CABG, who had good left ventricular function, were included. Only normotensive patients who did not require treatment with vasoactive drugs and were bleeding less than 100 ml.hr-1 following surgery were included. The patients were randomly distributed into two groups: a control group not receiving any treatment and a treated group receiving a bolus (3 micrograms.kg-1.min-1 for 5 min) and maintenance (0.2 micrograms.kg-1.min-1) infusion of nifedipine, starting upon arrival in the recovery room and continuing for four hours. Patients given nifedipine were compared with control patients in order to determine the effects of nifedipine on haemodynamic function and on the postoperative incidence of hypotension, hypertension, myocardial ischaemia and infarction. Continuous 2-lead Holter monitoring was used to detect myocardial ischaemia. Infarction was diagnosed by 12-lead ECGs and by assessment of the MB-isoenzyme creatine kinase. The infusion of nifedipine rapidly achieved and maintained plasma concentrations between 30 and 40 ng.ml-1. The pharmacokinetic studies revealed a systemic clearance of nifedipine of 0.371 +/- 0.101 L.hr-1.kg-1, an apparent volume of distribution of 0.764 +/- 0.288 L.kg-1 and an elimination half-life of 1.4 +/- 0.6 hr. No correlation was found between plasma concentration of nifedipine and mean arterial pressure (MAP). The incidence of postoperative hypotension (MAP < 70 mmHg) and hypertension (MAP > 100 mmHg) was comparable between the groups. All haemodynamic variables were similar in both groups during the study period. Of 23 patients who received nifedipine, none showed evidence of ischaemia within six hours of starting the infusion. During the same period, five of 24 patients in the control group had ST-segment deviation suggestive of myocardial ischaemia (P = 0.05, Fisher's exact test). Three patients in the control group and none in the nifedipine group suffered perioperative myocardial infarction (P = NS). In conclusion, the continuous infusion of nifedipine used in this study is safe and reduces the incidence of myocardial ischaemia in normotensive patients with good left ventricular function following CABG. Further studies of larger number of patients are required to determine the role of calcium entry blockers following coronary artery surgery.