Myocardial Oxygen Extraction Research Articles

(683) - Benefits of an Intra-aortic Cardiorenal Support Pump in Chronic Heart Failure

PurposeThe Procyrion pump is an intra-aortic ambulatory support device for cardiorenal HF patients refractory to medical management and dependent on hospital care. Procyrion unloads the heart and perfuses the kidneys, improving HF symptoms caused by fluid overload.MethodsUsing an ovine model of chronic HF with decreased EF and an enlarged LV, the Procyrion pump was deployed into the proximal descending aorta. The animal was instrumented to observe ventricular volume and pressure, aortic pressure, renal function, myocardial oxygen extraction, and organ perfusion.ResultsThe Procyrion pump caused significant decreases in afterload and myocardial oxygen consumption as well as increases in cardiac output, ejection fraction, urine output, and glomerular filtration rate. Furthermore, the pump maintained aortic arch pressure and greatly improved myocardial oxygen supply/demand ratio.ConclusionCardiorenal HF patients are in need of treatment options to simultaneously unload the heart and perfuse the kidneys while minimizing coronary and carotid steal. Our data suggest that the Procyrion device meets these needs using an ambulatory, catheter-delivered pump. PurposeThe Procyrion pump is an intra-aortic ambulatory support device for cardiorenal HF patients refractory to medical management and dependent on hospital care. Procyrion unloads the heart and perfuses the kidneys, improving HF symptoms caused by fluid overload. The Procyrion pump is an intra-aortic ambulatory support device for cardiorenal HF patients refractory to medical management and dependent on hospital care. Procyrion unloads the heart and perfuses the kidneys, improving HF symptoms caused by fluid overload. MethodsUsing an ovine model of chronic HF with decreased EF and an enlarged LV, the Procyrion pump was deployed into the proximal descending aorta. The animal was instrumented to observe ventricular volume and pressure, aortic pressure, renal function, myocardial oxygen extraction, and organ perfusion. Using an ovine model of chronic HF with decreased EF and an enlarged LV, the Procyrion pump was deployed into the proximal descending aorta. The animal was instrumented to observe ventricular volume and pressure, aortic pressure, renal function, myocardial oxygen extraction, and organ perfusion. ResultsThe Procyrion pump caused significant decreases in afterload and myocardial oxygen consumption as well as increases in cardiac output, ejection fraction, urine output, and glomerular filtration rate. Furthermore, the pump maintained aortic arch pressure and greatly improved myocardial oxygen supply/demand ratio. The Procyrion pump caused significant decreases in afterload and myocardial oxygen consumption as well as increases in cardiac output, ejection fraction, urine output, and glomerular filtration rate. Furthermore, the pump maintained aortic arch pressure and greatly improved myocardial oxygen supply/demand ratio. ConclusionCardiorenal HF patients are in need of treatment options to simultaneously unload the heart and perfuse the kidneys while minimizing coronary and carotid steal. Our data suggest that the Procyrion device meets these needs using an ambulatory, catheter-delivered pump. Cardiorenal HF patients are in need of treatment options to simultaneously unload the heart and perfuse the kidneys while minimizing coronary and carotid steal. Our data suggest that the Procyrion device meets these needs using an ambulatory, catheter-delivered pump.

Mechanisms of increased right and left ventricular oxygen uptake during inotropic stimulation

AimsFew studies have investigated oxygen supply/demand relations in right ventricle (RV). The current study compared changes in myocardial oxygen uptake (MVO2) and its determinants, myocardial blood flow (MBF) and oxygen extraction (EO2), in RV and left ventricle (LV) during stimulation with inotropic drugs. Main methodsTwenty-one anesthetized dogs were studied. MBF was measured with radioactive microspheres. A-VO2 difference was determined separately for RV and LV, and used to calculate MVO2 (Fick equation) and EO2. Responses to iv. infusions of isoproterenol (0.1μg/kg/min), dobutamine (5μg/kg/min), and amrinone (1mg/kg+10μg/kg/min) were assessed. Key findingsBaseline MVO2 in RV was 50–60% of that in LV. The inotropes increased MVO2 in both RV and LV (range 32–63%; P<0.05). With isoproterenol, the increased MVO2 in the RV was due to increases in both MBF and EO2, whereas in LV it was due only to increases in MBF. With dobutamine and amrinone, the increased MVO2 in RV was due to increased MBF while EO2 was constant (dobutamine) or decreased (amrinone), and that in the LV was due to increased MBF while EO2 decreased. SignificanceRV possesses EO2 reserve that contributed to increased MVO2 during isoproterenol infusion, whereas LV depended on increased MBF alone. Because dobutamine and amrinone caused direct coronary vasodilation, i.e., “luxuriant perfusion,” it was not necessary to recruit the EO2 reserve. Thus, it remained available to meet further increases in MVO2 or to maintain MVO2 in the face of reductions in MBF.

Myocardial protection during elective coronary artery bypasses grafting by pretreatment with omega-3 polyunsaturated fatty acids

Despite recent advances in coronary artery bypass grafting (CABG), cardioplegic cardiac arrest and cardiopulmonary bypass (CPB) are still associated with myocardial injury. Accordingly, the efforts have been made lately to improve the outcome of CPB by glucose-insulin-potassium, adenosine, Ca(2+)-channel antagonists, L-arginine, N-acetylcysteine, coenzyme Q10, diazoxide, Na+/H+ exchange inhibitors, but with an unequal results. Since omega-3 polyunsatutated fatty acids (PUFAs) have shown remarkable cardioprotection in preclinical researches, the aim of our study was to check their effects in prevention of ischemia reperfusion injury in patients with CPB. This prospective, randomized, placebo-controlled study was performed with parallel groups. The patients undergoing elective CABG were randomized to receive preoperative intravenous omega-3 PUFAs infusion (n = 20) or the same volume of 0.9% saline solution infusion (n = 20). Blood samples were collected simultaneously from the radial artery and the coronary sinus before starting CPB and at 10, 20 and 30 min after the release of the aortic cross clamp. Lactate extraction/excretion and myocardial oxygen extraction were calculated and compared between the two groups. The levels of troponin I (TnT) and creatine kinase-myocardial band (CK-MB) were determined before starting CPB and 4 and 24 h postoperatively. Demographic and operative characteristics, including CPB and aortic cross-clamp time, were similar between the two groups of patients. The level of lactate extraction 10 and 20 min after aortic cross-clamp time has shown negative values in the control group, but positive values in the PUFAs group with statistically significant differences (-19.6% vs 7.9%; p < 0.0001 and -19.9% vs 8.2%; p < 0.0008, respectively). The level of lactate extraction 30 minutes after reperfusion was not statistically different between the two groups (6.9% vs 4.2%; p < 0.54). Oxygen extraction in the PUFAs group was statistically significantly higher compared to the control group after 10, 20 and 30 min of reperfusion (35.5% vs 50.4%, p < 0.0004; 25.8 % vs 48.7%, p < 0.0001 and 25.8% vs 45.6%, p < 0.0002, respectively). The level of TnT, 4 and 24 h after CPB, was significantly higher in the control group compared to PUFAs group, with statistically significant differences (11.4 vs 6.6, p < 0.009 and 12.7 vs 5.9, p < 0.008, respectively). The level of CK-MB, 4 h after CPB, was significantly higher in the control group compared to PUFAs group (61.9 vs 37.7, p < 0.008), but its level, 24 h after CPB, was not statistically different between the two groups (58.9 vs 40.6, p < 0.051). Treatment with omega-3 PUFAs administered preoperatively promoted early metabolic recovery of the heart after elective CABG and improved myocardial protection. This study showed that omega-3 emulsion should not be considered only as a nutritional supplement but also as a clinically safe and potent cardioprotective adjunct during CPB.

Beating heart repair of secondum atrial septal defect without aortic cross clamp—a safe alternative

Aim Determine the safety and efficacy of On pump beating heart repair of Atrial Septal Defect (ASD) with regard to postoperative neurocognitive function and to determine myocardial oxygen extraction during the procedure.

Quantifying Myocardial Oxygenation with Cardiac Magnetic Resonance Imaging

Myocardial ischemia, resulting from imbalance in myocardial oxygen supply and demand, can be quantitatively assessed by positron emission tomography (PET) with absolute measures of myocardial blood flow and oxygen consumption rate (MVO 2 ). Cardiac Magnetic Resonance (CMR) has notable advantages over PET, with no radiation, high spatial resolution, faster scan times, and excellent soft tissue contrast. We have developed and validated new quantitative CMR oximetry techniques, including measurements of hyperemic myocardial oxygen extraction fraction and MVO 2 through Fick's Law. These may lead to a new understanding of roles of myocardial microcirculation in myocardial ischemia. Other cardiac oximetry methods for directly quantifying MVO 2 with 17 O-labelled water are also under investigation. Quantitative CMR oximetry is a promising, non-invasive, non-radiation approach for exploring the myocardial metabolism's role in cardiac patients.

Management of Acute Cardiac Failure by Intracoronary Administration of Levosimendan

Acute cardiac failure caused by myocardial infarction or inadequate cardioprotection during heart surgery is associated with increased mortality and morbidity. Levosimendan is a new drug used in heart failure though it is limited by the systemic hypotension, which develops with intravenous administration. Intracoronary (IC) administration however should affect systemic circulation less while maintaining the beneficial cardiac effects of the drug. We herewith report the results from the first such clinical series. Levosimendan was administered IC in 33 consecutive patients who developed cardiogenic shock during heart surgery and were unable to wean off cardiopulmonary bypass despite maximal support. Preadministration/postadministration coronary graft flows, hemodynamic parameters, left ventricular function, and metabolic requirements were measured and compared. Levosimendan significantly increased graft flows and improved hemodynamic parameters. Systolic blood pressure (93 ± 26.4 vs. 106 ± 18.2 mm Hg, P < 0.05) and cardiac index (2.0 ± 0.5 vs. 3.1 ± 0.2, P < 0.001) were increased, whereas systemic vascular resistance (1470.7 ± 114 vs. 1195.8 ± 112, P < 0.01) was reduced. Better myocardial perfusion improved metabolic requirements, with myocardial oxygen extraction and glucose uptake increasing by 72% and 74%, respectively, whereas lactate production was reduced by 64%. Echocardiography demonstrated additional ventricular segment recruitment. Therefore, IC Levosimendan administration in acute heart failure is safe and efficacious producing improved cardiac function without significant detrimental hypotension.

Glutamine Restores Myocardial Cytochrome c Oxidase Activity and Improves Cardiac Function During Experimental Sepsis

Cardiac dysfunction occurs commonly in sepsis. Impaired mitochondrial function is a potential cause of sepsis-associated myocardial depression. Cytochrome oxidase (COX), the terminal oxidase of the electron transport chain, is inhibited in the septic heart. Glutamine (GLN) increases Krebs cycle intermediates and supports oxidative phosphorylation. Exogenous GLN has been shown to restore myocardial adenosine triphosphate levels and cardiac function following ischemia-reperfusion injury. The authors hypothesize that exogenous GLN will abrogate sepsis-induced myocardial COX inhibition and improve sepsis-associated myocardial depression. Under general anesthesia, male Sprague-Dawley rats underwent cecal ligation and double puncture (CLP) or sham operation. At the time of operation, rats underwent intraperitoneal injection of either GLN (0.75 g/kg) or an equal volume of saline. Twenty-four hours after the procedure, animals were killed, cardiac ventricles harvested, and mitochondria isolated. Steady-state COX kinetic activity was measured and normalized to citrate synthase activity. Steady-state levels of COX subunit I protein were determined with immunoblot analysis. Cardiac function was assessed using an isolated rat heart preparation. Five animals per group were evaluated. Significance was determined with analysis of variance and post hoc Tukey test. CLP significantly decreased myocardial COX activity, oxygen consumption, left ventricular pressure (LVP), and pressure developed during isovolumic contraction (+dP/dt) and relaxation (-dP/dt). GLN restored COX activity to sham levels, significantly increased myocardial oxygen extraction and consumption, increased LVP toward sham values, and increased ±dP/dt by >30% following CLP. The beneficial effects of GLN therapy during sepsis may be in part due to restoration of oxidative phosphorylation and abrogation of sepsis-associated myocardial depression.

Pathomechanisms of Myocardial Dysfunction in Sepsis

Sepsis remains one of the leading causes of death in intensive care units. Progressive cardiovascular failure is an important cause of the mortality. Septic patients with myocardial dysfunction have significantly higher mortality compared with patients without cardiovascular impairment. Myocardial dysfunction in sepsis is characterized by decreased contractility and impaired myocardial compliance. Experimental studies of sepsis showed heterogeneity of microvascular perfusion, as well as impaired myocardial oxygen extraction. The underlying cellular mechanisms include increased neutrophil adhesion to the endothelium, production of reactive free radicals and oxidants, and endothelial dysfunction. Superoxide, nitric oxide and peroxynitrite cardiac formation has been demonstrated in septic hearts, which has been implicated in the pathogenesis of the myocardial depression and cell death in sepsis. Nitric oxide, carbon monoxide and hydrogen sulfide are gaseotransmitters that may exert protective effects in the septic heart.

Improvement of hyperemic myocardial oxygen extraction fraction estimation by a diffusion‐prepared sequence

Myocardial oxygen extraction fraction (OEF) during hyperemia can be estimated using a double-inversion-recovery-prepared T(2)-weighted black-blood sequence. Severe irregular electrocardiogram (ECG) triggering due to elevated heart rate and/or arrhythmias may render it difficult to adequately suppress the flowing left ventricle blood signal and thus potentially cause errors in the estimates of myocardial OEF. Thus, the goal of this study was to evaluate another black-blood technique, a diffusion-weighted-prepared turbo spin echo sequence for its ability to determine regional myocardial OEF during hyperemia. Control dogs and dogs with acute coronary artery stenosis were imaged with both the double-inversion-recovery- and diffusion-weighted-prepared turbo spin echo sequences at rest and during either dipyridamole or dobutamine hyperemia. Validation of MRI OEF estimates was performed using blood sampling from the artery and coronary sinus in control dogs. The two methods showed comparable correlations with blood sampling results (R(2) = 0.9). Similar OEF estimations for all dogs were observed, except for the group of dogs with severe coronary stenosis during dobutamine stress. In these dogs, the diffusion-weighted method provided more physiologically reasonable OEF (hyperemic OEF = 0.75 +/- 0.08 versus resting OEF of 0.6) than the double-inversion-recovery method (hyperemic OEF = 0.56 +/- 0.10). Diffusion-weighted preparation may be a valuable alternative for more accurate oxygenation measurements during irregular ECG-triggering.

To BOLDly Go Where Positron Emission Tomography Has Been Before

Atherosclerotic disease remains concealed for many years and becomes clinically overt only when the growth of atherosclerotic plaques and the adverse remodeling of the arterial wall reach a critical stage that results in impairment of blood flow, ischemia, and angina. Large epicardial arteries have a diameter ranging from a few millimeters to ≈500 μm and are visible at coronary angiography. Prearterioles (diameter from ≈500 to ≈100 μm) and arterioles (diameter <100 μm) are beyond the resolution of current angiographic systems and hence are not visible at angiography. Each compartment is regulated by distinct mechanisms, and vascular resistance is distributed in series along the coronary vascular bed.1 The oxygen supply to the myocardium is determined by arterial oxygen saturation and myocardial extraction, which are relatively fixed in normal perfusion conditions. At constant distending pressure, variations of flow in epicardial coronary arteries can be achieved by means of intracoronary injection of arteriolar vasodilators.2 Near maximal hyperemia can be achieved using coronary vasodilators such as adenosine or dipyridamole, which induce vasodilatation, mainly in the coronary microcirculation. The functional severity of a stenosis cannot be estimated by anatomic imaging such as x-ray coronary angiography or multislice computed tomography, and, in addition, diffuse atherosclerosis and extensive arterial remodeling may contribute to the dissociation of anatomic and functional measurements of coronary stenosis severity. Therefore, the functional significance of coronary stenoses can only be evaluated by measures of coronary flow, and commonly the flow reserve, which is the ratio of nonregulated maximum (hyperemic) and autoregulated (resting) flow. This characterization requires accurate quantitative measurements of pressure and/or flow and can be estimated invasively as fractional flow reserve2 or measured noninvasively with positron emission tomography (PET).3 Articles see p 32 and 41 The relationship between resting and hyperemic myocardial blood flow and severity of coronary …

Quantification of Regional Myocardial Oxygenation by Magnetic Resonance Imaging

Background— A comprehensive evaluation of myocardial ischemia requires measures of both oxygen supply and demand. Positron emission tomography (PET) is currently the gold standard for such evaluations, but its use is limited because of its ionizing radiation, limited availability, and high cost. A cardiac MRI method was developed for assessing myocardial oxygenation. The purpose of this study was to evaluate and validate this technique compared with PET during pharmacological stress in a canine model of coronary artery stenosis. Methods and Results— Twenty-one beagles and small mongrel dogs without coronary artery stenosis (controls) or with moderate to severe acute coronary artery stenosis underwent MRI and PET imaging at rest and during dipyridamole vasodilation or dobutamine stress to induce a wide range of changes in cardiac perfusion and oxygenation. MRI first-pass perfusion imaging was performed to quantify myocardial blood flow and volume. The MRI blood oxygen level-dependent technique was used to determine the myocardial oxygen extraction fraction during pharmacological hyperemia. Myocardial oxygen consumption was determined by the Fick law. In the same dogs, 15 O-water and 11 C-acetate were used to measure myocardial blood flow and myocardial oxygen consumption, respectively, by PET. Regional assessments were performed for both MR and PET. MRI data correlated nicely with PET values for myocardial blood flow ( R 2 =0.79, P &lt;0.001), myocardial oxygen consumption ( R 2 =0.74, P &lt;0.001), and oxygen extraction fraction ( R 2 =0.66, P &lt;0.01). Conclusions— Cardiac MRI methods may provide an alternative to radionuclide imaging in settings of myocardial ischemia. Our newly developed quantitative MRI oxygenation imaging technique may be a valuable noninvasive tool to directly evaluate myocardial energetics and efficiency.

Comparison of active and passive coronary perfusion in off-pump coronary artery bypass grafting

The myocardial protective effects of active and passive coronary perfusion were compared during off-pump coronary artery bypass grafting (OPCAB) in coronary stenosis model. An internal shunt tube was placed in the proximal left anterior descending arteries of adult dogs to produce a 75% coronary stenosis model. In 10 animals passive coronary perfusion was performed using an internal shunt tube placed in a pseudo-anastomotic site, and active coronary perfusion was performed through an external shunt tube. Ischemia was examined at normal and low blood pressure, based on hemodynamics, regional myocardial blood flow, and oxygen and lactate extraction in the perfused area. With passive perfusion, regional myocardial blood flow decreased and oxygen extraction and regional lactate production increased at normal blood pressure, indicating myocardial ischemia. Regional myocardial blood flow further decreased at low blood pressure. In contrast, regional myocardial blood flow with active perfusion did not change at normal or low blood pressure, and oxygen and lactate extraction were unchanged, indicating prevention of myocardial ischemia. Myocardial ischemia can occur with passive perfusion even at normal blood pressure. Active coronary perfusion that provides sufficient regional perfusion prevents myocardial ischemia during coronary artery anastomosis in OPCAB.

Myocardial Protection During Elective Coronary Artery Bypass Grafting Using High-Dose Insulin Therapy

Coronary artery bypass grafting (CABG) with cardioplegic cardiac arrest and cardiopulmonary bypass (CPB) is associated with myocardial injury. The aim of this study was to investigate whether high-dose insulin therapy has a myocardial protective effect by enhancing early metabolic recovery of the arrested heart during revascularization. A total of 44 patients undergoing elective CABG were randomized to receive intraoperative titrated intravenous insulin infusion (n = 22) or a fixed high-dose systemic insulin infusion at 5 mU/kg/min (n = 22). Blood samples were collected simultaneously from the radial artery and the coronary sinus before starting CPB and at 5 and 10 minutes after the release of the aortic cross-clamp to determine lactate, oxygen saturation, and hemoglobin concentration. Lactate extraction/excretion and myocardial oxygen extraction were calculated and compared between the two groups. The change in cardiac indices was determined immediately postoperatively as a measure of functional recovery, and the troponin I level was measured 4 hours postoperatively as an indicator of myocardial protection. Operative characteristics, including CPB and aortic cross-clamp time, were similar between the two groups. Arterial oxygen content was similar in both groups. The high-dose insulin therapy group had early extraction of lactate and higher oxygen extraction immediately postoperatively compared with the standard group. In addition, the high-dose insulin group had a lower troponin I level 4 hours postoperatively, with greater improvement in cardiac indices. High-dose insulin therapy promotes early metabolic recovery of the heart during elective CABG, leading to better myocardial protection and functional recovery.

Effect of Altitude on the Heart and the Lungs

This review focuses on the effects of altitude exposure from 1 to several days or weeks as occurs in tourists, trekkers, and mountaineers who visit high altitude and normally reside near sea level. We briefly review the acute physiological adjustments and early acclimatization that occur in the cardiovascular system and the lungs of healthy individuals. These ensure life-sustaining oxygen delivery to the tissues despite a reduction in the partial pressure of inspired oxygen between 20% and 60% at 2500 and 8000 m, respectively. One of the acute adjustments, hypoxic pulmonary vasoconstriction (HPV), may be disadvantageous in those with a vigorous response and lead to 2 potentially lethal illnesses, high-altitude pulmonary edema (HAPE) and subacute mountain sickness (SAMS), which we present in more detail. Finally, on the basis of knowledge about the acute physiological adjustments and acclimatization and, when available, a review of the literature, we discuss the high-altitude tolerance of patients with coronary artery disease, congestive heart failure, arrhythmias, systemic hypertension, and pulmonary hypertension. ### Circulation The major effects of acute hypoxia on the heart and lung are shown in Figure 1. Hypoxia directly affects the vascular tone of the pulmonary and systemic resistance vessels and increases ventilation and sympathetic activity via stimulation of the peripheral chemoreceptors.1 Interactions occur between the direct effects of hypoxia on blood vessels and the chemoreceptor-mediated responses in the systemic and pulmonary circulation. Figure 1. Effects of hypoxia on systemic and pulmonary circulation. Unraveling the underlying mechanisms of the hypoxic vasodilatation of systemic arterioles is an active area of research. Several mechanisms appear to regulate local oxygen delivery according to the needs of the tissues2,3; for instance, the release of ATP from red blood cells and the generation of NO by various ways appear to regulate local oxygen delivery according to the needs …

Exercise hyperaemia in the heart: the search for the dilator mechanism

Coronary blood flow is tightly coupled to myocardial oxygen consumption to maintain a consistently high level of myocardial oxygen extraction over a wide range of physical activity. This tight coupling has been proposed to depend on periarteriolar oxygen tension, signals released from cardiomyocytes (adenosine acting on K(ATP) channels) and the endothelium (prostanoids(,) nitric oxide, endothelin) as well as neurohumoral influences (catecholamines, endothelin), but the contribution of each of these regulatory pathways, and their interactions, to exercise hyperaemia in the human heart are still incompletely understood. Thus, in the human heart, nitric oxide, prostanoids, adenosine and K(ATP) channels each contribute to resting tone, but evidence for a critical contribution to exercise hyperaemia is lacking. In dogs K(ATP) channel activation together with adenosine and nitric oxide contribute to exercise hyperaemia in a non-linear redundant fashion. In contrast, in swine nitric oxide, adenosine and K(ATP) channels contribute to resting coronary resistance vessel tone control in a linear additive manner, but are not mandatory for exercise hyperaemia in the heart. Rather, exercise hyperaemia in swine appears to involve K(Ca) channel opening that is mediated, at least in part, by exercise-induced beta-adrenergic activation, possibly in conjunction with exercise-induced blunting of an endothelin-mediated vasoconstrictor influence. In view of these remarkable species differences in coronary vasomotor control during exercise, future studies are required to determine whether exercise hyperaemia in humans follows a canine or porcine control design.

Impact of Different Pacing Modes on Left Ventricular Contractility Following Cardiopulmonary Bypass

Acute left ventricular (LV) dysfunction after cardiopulmonary bypass (CBP) is a serious complication in cardiac surgery. The aim of this study was to investigate the effect of different epicardial pacing modes on LV contractility and changes of myocardial oxygen extraction (MVO(2)) following CPB in an animal model. The utility of conductance catheter measurement versus left ventricular outflow tract mean systolic acceleration (LVOT(Acc)) for quantification of LV function was evaluated. Fourteen piglets underwent median sternotomy and CPB for 90 minutes, myocardial ischemia for 60 minutes, and reperfusion for 30 minutes. Different pacing modes were obtained before and after CPB to investigate changes in LV function. LV Function was quantified by end-systolic-pressure-volume relationships (ESPVR) as measured by the conductance catheter method and by LVOT(Acc) obtained from transepicardial echocardiographic studies. LV contractility improved significantly by biventricular and atrial pacing compared with natural sinus rhythm (SR). MVO(2) remained stable or even decreased with biventricular pacing after surgery compared with SR. Right ventricular pacing resulted in poor LV-function with a rise of MVO(2). LVOT(Acc) showed a strong correlation to invasively measured ESPVR. Postoperative biventricular pacing was associated with an improved LV contractility without rise of MVO(2) compared with SR and atrial pacing. At termination of CPB, this appears to facilitate the management of LV failure and potentially may reduce the need for inotropic support, additionally protecting myocardial metabolism. The echocardiographic assessment of LVOT(Acc) was a simple and reliable as well as effective method to quantify LV contractility and showed a good correlation with the more invasive conductance catheter.

Assessment of myocardial oxygen extraction fraction and perfusion reserve with BOLD imaging in a canine model with coronary artery stenosis

To determine the feasibility of T2-weighted BOLD imaging for estimating regional myocardial oxygen extraction fraction (OEF) and approximating perfusion reserve (MPR) simultaneously in a canine model with moderate coronary artery stenosis. Eight mongrel dogs with moderate coronary artery stenosis underwent BOLD imaging at rest and during dipyridamole-induced hyperemia, using a turbo spin echo (TSE) sequence. Based on a two-compartment model, myocardial OEF(hyperemia) was calculated with the corresponding T2. MPR could be approximated based on Fick's law. During responsive hyperemia, a regional hypointensity was observed in the abnormally perfused myocardium, reflecting a relatively smaller myocardial T2 increase (3.06% +/- 2.74%, in contrast to 10.19% +/- 4.12% in the normal region). The average OEFs in the normally and abnormally perfused myocardial territories were 0.21 +/- 0.11 and 0.43 +/- 0.12, respectively. For the MPR approximated from the BOLD imaging, a strong correlation (R = 0.9) in the normal myocardium and a good correlation (R = 0.6) distal to the stenosis were obtained compared to microsphere results. In a canine model with moderate coronary artery stenosis, TSE-based BOLD imaging can quantitatively estimate the regional OEF(hyperemia) and approximate the MPR, and can distinguish segments perfused by defected coronary artery.

Myocardial blood flow and oxygen consumption in patients with Friedreich's ataxia prior to the onset of cardiomyopathy

We tested the hypothesis, in patients with Friedreich's ataxia and no overt structural heart disease, that impairment of cardiac oxidative metabolism may be compensated for either by increased rest myocardial blood flow or more efficient oxygen consumption in performance of external work. Friedreich's ataxia is characterized by a mutant frataxin gene, which causes mitochondrial iron overload and impaired energy production. Further, it is frequently associated with cardiomyopathy. Studies using magnetic resonance spectroscopy, however, suggest impaired cardiac energetics even in the absence of structural heart disease. Positron emission tomography measured rest myocardial blood flow (N-13-ammonia method) and myocardial oxygen consumption (11-C-acetate, Kmono) in Friedreich's ataxia patients (n=8; 31+/-5 years, mean+/-SD, four women) and healthy controls (n=8; 30+/-7 years, five women) matched for stroke work index and age. Stroke work index and power were determined by electrocardiogram gated positron emission tomography N-13-ammonia using modified Simpson's rule to compute left ventricular volumes. Neither stroke work index nor rest myocardial blood flow differed significantly between the groups. Although myocardial oxygen consumption was lower in Friedreich's ataxia (P<0.001), Kmono/rest myocardial blood flow, an index of myocardial oxygen extraction, did not differ between the groups. Power/Kmono, an index of the efficiency of myocardial oxygen consumption, was greater in Friedreich's ataxia (P<0.04). Rest myocardial blood flow normalized to rate pressure product was lower in Friedreich's ataxia (P<0.05). Prior to the onset of cardiomyopathy, selected patients with Friedreich's ataxia may compensate for impaired cardiac energetics through more efficient oxygen consumption rather than increased rest myocardial blood flow. The data illustrate a more general mechanism pertaining to metabolic regulation of myocardial blood flow and myocardial oxygen consumption.

The Effect of Phenylephrine on Cardiac Performance and Myocardial Oxygen Balance in Resuscitation from Hemorrhagic Shock

Background: The issue of using phenylephrine in hemorrhagic shock treatment has been controversial because it is known that phenylephrine improves the tissue perfusion by increasing arterial blood pressure but deteriorates the myocardium by increasing afterload and decreasing myocardial oxygen delivery via coronary vasoconstriction. This study was aimed to assess the effects of phenylephrine on hemodynamic variables, cardiac performance, and myocardial oxygen balance in resuscitation from hemorrhagic shock. Methods: Twenty anesthetized dogs were randomly divided into phenylephrine group and control group. After inducing hemorrhagic shock, resuscitation was done with phenylephrine and 0.9% normal saline respectively. We measured hemodynamic indices, blood gas parameter and cardiac enzymes which indicate myocardial demage. Results: In both groups, cardiac output and hemodynamic indices improved. In phenylephrine group, the systemic oxygen delivery and consumption was much higher and the myocardial oxygen extraction ratio was maintained at the lower level than the control group. In addition, the CK-MB was higher at the early phase of resuscitation and the troponin T was also higher than the control group during the whole period of resuscitation. Creatine kinase-MB increased during early resuscitation in phenylephrine group but kept decreasing after that and there's no difference between two groups. Troponin T was higher in the phenylephrine group after resuscitation. Conclusions: We concluded that phenylephrine improves myocardial oxygen balance and contractility without serious myocardial demage during resuscitation from hemorrhagic shock.

Cardiac sequelae of haemorrhagic shock.

Abstract Using selective cardiac catheterization and a 133Xe wash-out technique, myocardial blood-flow and oxygen utilization were studied in greyhounds during and following brief and prolonged haemorrhagic hypotension. The progressive fall in myocardial oxygen extraction as the shock period was prolonged and the subsequent failure of myocardial oxygen consumption to rise during re-infusion suggested the presence of a metabolic defect in the myocardial cell. The use of a special ‘elemental’ diet was shown to eliminate the intestinal blood-loss typical of canine haemorrhagic shock models; despite this the apparent myocardial cellular metabolic defect persisted. In addition, a myocardial depressant factor which depressed myocardial function in vitro was isolated from ultrafiltrates of post-shock plasma.