The effect of elevated arterial free fatty acid concentrations on hemodynamics and myocardial metabolism and blood flow during ischemia

The relationships between acetylcholine-induced chest pain, objective measures of coronary vascular function and symptom status

Background

Acetylcholine-induced chest pain is routinely measured during the assessment of microvascular function.

Aims

The aim was to determine the relationships between acetylcholine-induced chest pain and both symptom burden and objective measures of vascular function.

Methods

In patients with angina but no obstructive coronary artery disease, invasive studies determined the presence or absence of chest pain during both acetylcholine and adenosine infusion. Thermodilution-derived coronary blood flow (CBF) and index of microvascular resistance (IMR) was determined at rest and during both acetylcholine and adenosine infusion. Patients with epicardial spasm (>90%) were excluded; vasoconstriction between 20% and 90% was considered endothelial dysfunction.

Results

Eighty-seven patients met the inclusion criteria. Of these 52 patients (60%) experienced chest pain during acetylcholine while 35 (40%) did not. Those with acetylcholine-induced chest pain demonstrated: (1) Increased CBF at rest (1.6 ± 0.7 vs. 1.2 ± 0.4, p = 0.004) (2) Decreased IMR with acetylcholine (acetylcholine-IMR = 29.7 ± 16.3 vs. 40.4 ± 17.1, p = 0.004), (3) Equivalent IMR following adenosine (Adenosine-IMR: 21.1 ± 10.7 vs. 21.8 ± 8.2, p = 0.76), (4) Increased adenosine-induced chest pain (40/52 = 77% vs. 7/35 = 20%, p < 0.0001), (5) Increased chest pain during exercise testing (30/46 = 63% vs. 4/29 = 12%, p < 0.00001) with no differences in exercise duration or electrocardiographic changes, and (6) Increased prevalence of epicardial endothelial dysfunction (33/52 = 63% vs. 14/35 = 40%, p = 0.03).

Conclusions

After excluding epicardial spasm, acetylcholine-induced chest pain is associated with increased pain during exercise and adenosine infusion, increased coronary blood flow at rest, decreased microvascular resistance in response to acetylcholine and increased prevalence of epicardial endothelial dysfunction. These findings raise questions about the mechanisms underlying acetylcholine-induced chest pain.

Lipid emulsion rapidly restores contractility in stunned mouse cardiomyocytes: a comparison with therapeutic hypothermia

OBJECTIVES

Cooling following cardiac arrest can improve survival significantly. However, delays in achieving target temperature may decrease the overall benefits of cooling. Here, we test whether lipid emulsion, a clinically approved drug reported to exert cardioprotection, can rescue heart contractility in the setting of delayed cooling in stunned mouse cardiomyocytes.

DESIGN

Cell culture study.

SETTING

Academic research laboratory.

SUBJECTS

Cardiomyocytes isolated from 1- to 2-day-old C57BL6 mice.

INTERVENTIONS

Cardiomyocytes were exposed to 30 minutes of ischemia followed by 90 minutes of reperfusion and 10 minutes of isoproterenol with nine interventions: 1) no additional treatment; 2) intraischemic cooling at 32 °C initiated 10 minutes prior to reperfusion; 3) delayed cooling started 20 minutes after reperfusion; 4) lipid emulsion + delayed cooling; 5) lipid emulsion (0.25%) administered at reperfusion; 6) lipid emulsion + intraischemic cooling; 7) delayed lipid emulsion; 8) lipid emulsion + delayed cooling + Akt inhibitor (API-2, 10 µM); and 9) lipid emulsion + delayed cooling + Erk inhibitor (U0126, 10 µM). Inhibitors were given to cells 1 hour prior to ischemia.

MEASUREMENTS AND MAIN RESULTS

Contractility was recorded by real-time phase-contrast imaging and analyzed with pulse image velocimetry in MATLAB (Mathworks, Natick, MA). Ischemia diminished cell contraction. The cardioprotective effect of cooling was diminished when delayed but was rescued by lipid emulsion. Further, lipid emulsion on its own improved recovery of the contractility to a greater extent as intraischemic cooling. However, cotreatment of lipid emulsion and intraischemic cooling did not further improve the recovery compared to either treatment alone. Furthermore, Akt and Erk inhibitors blocked lipid emulsion-induced protection.

CONCLUSIONS

Lipid emulsion improved contractility and rescued contractility in the context of delayed cooling. This protective effect required Akt and Erk signaling. Lipid emulsion might serve as a treatment or adjunct to cooling in ameliorating myocardial ischemia/reperfusion injury.

The effect of fat emulsion on hemodynamics following treatment with propranolol and clonidine in anesthetized rats

OBJECTIVES

There is evidence indicating that intravenous fatty emulsion (IFE) is beneficial in restoring circulatory function in certain types of drug overdose. The authors investigated the hemodynamic effects of IFE compared to epinephrine in rats treated with propranolol and clonidine.

METHODS

Anesthetized male Sprague-Dawley rats were instrumented for measurement of hemodynamics. Rats were randomly assigned to one of six groups (n = 6-8), and each received a clonidine infusion (150 μg/kg) or an equivalent volume of normal saline (0.9% NaCl) over 1 hour. Each rat then received normal saline (1.0 mL/kg) or propranolol (15 to 20 mg/kg). Thereafter, each rat received a dose of IFE (20% solution; 1.0 mL/kg) or epinephrine (2.0 μg/kg) or an equivalent volume of normal saline (1.0 mL/kg).

RESULTS

Propranolol alone or with clonidine significantly (p < 0.05) reduced a number of hemodynamic parameters (mean arterial pressure, 37% to 70%; heart rate, 30% to 51%; cardiac contractility [dP/dtmax], 50% to 67%; and abdominal aortic blood flow, 50% to 83%), while increasing PR intervals (65% to 85%) and QTc intervals (26% to 64%). Saline and epinephrine treatment after propranolol and clonidine combined resulted in no survivors in saline and two out of six in epinephrine group. IFE resulted in significant survival (seven out of eight) for 30 minutes in rats treated with propranolol alone, and propranolol combined with clonidine (seven out of eight).

CONCLUSIONS

These data demonstrate that IFE is effective for resuscitating rats overdosed on propranolol combined with clonidine. The effect of IFF is unlikely due to a direct positive inotropic or chronotropic action on the myocardium. IFE is also more effective than epinephrine treatment in this paradigm.

Intralipid infusion diminishes return of spontaneous circulation after hypoxic cardiac arrest in rabbits

BACKGROUND

Infusion of lipid emulsion has been shown to reverse lipophilic drug-induced cardiovascular collapse in laboratory models and humans. The effect of high dose lipid in nondrug-induced cardiac arrest is, however, uncertain. In a rabbit model of asphyxial pulseless electrical activity (PEA) we compared lipid augmented with standard advanced cardiac life support (ACLS) resuscitation.

METHOD

Adult New Zealand White rabbits underwent hypoxic PEA via tracheal clamping. After 2 min of cardiac arrest, basic life support cardiopulmonary resuscitation was commenced and 3 mL/kg 20% Intralipid or 3 mL/kg 0.9% saline solution infused. Adrenaline (100 microg/kg) was administered at 4 and 5 min. Return of spontaneous circulation (ROSC), hemodynamic metrics, and survival to 50 min were recorded.

RESULTS

Seven of 11 saline-treated rabbits developed ROSC versus 1 of 12 Intralipid-treated animals; P = 0.009. No significant difference in survival to 50 min was observed (3/11 saline vs 0/12 Intralipid; P = 0.211).

CONCLUSION

In this model of hypoxia-induced PEA, standard ACLS resulted in greater coronary perfusion pressure and increased ROSC compared with ACLS plus lipid infusion. Lipid emulsion may be contraindicated in cardiac arrest complicated by significant hypoxia.

Mechanism of reduced myocardial glucose utilization during acute hypertriglyceridemia in rats

PURPOSE

The purpose of the research is to study the effect of acute inhibition of intravascular lipolysis on myocardial substrate selection during hypertriglyceridemia using in vivo radiotracer analysis and positron emission tomography.

PROCEDURES

We induced acute hypertriglyceridemia in vivo using an intravenous infusion of Intralipid 20% (IL) without and with acute inhibition of fatty acid delivery from circulating triglycerides with injection of Triton WR-1339 (TRI) during a euglycemic-hyperinsulinemic clamp in Wistar rats. We determined the effect of TRI on myocardial uptake of circulating triglycerides and free fatty acids using intravenous injection of [(3)H]-triolein and [(14)C]-bromopalmitate, respectively. Myocardial blood flow, oxidative metabolism, and metabolic rate of glucose (MMRG) were determined using micro-positron emission tomography (microPET) with [(13)N]-ammonia, [(11)C]-acetate, and 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG).

RESULTS

TRI reduced myocardial incorporation of [(3)H]-triolein but not [(14)C]-bromopalmitate showing that it selectively reduces myocardial fatty acid delivery from circulating triglycerides but not from free fatty acids. IL reduced myocardial blood flow and MMRG by 37% and 56%, respectively, but did not affect myocardial oxidative metabolism. TRI did not abolish the effect of IL on myocardial blood flow and MMRG.

CONCLUSIONS

Hypertriglyceridemia acutely reduces myocardial blood flow and MMRG in rats, but this effect is not explained by increased myocardial fatty acid delivery through intravascular triglyceride lipolysis.

Metabolic effects of glucose-insulin infusions: myocardium and whole body

In target organs, insulin switches substrate utilization from free fatty acids to glucose, a change that: (i) is oxygen-efficient; (ii) repletes glycogen stores; (iii) removes potentially toxic fatty acids; and (iv) restores intracellular potassium. During or after an ischaemic challenge, the insulin metabolic mode should protect cellular functions provided that insulin can reach the ischaemic tissue. Insulin, however, also exerts non-metabolic effects, such as membrane hyperpolarization, the stimulation of adrenergic activity, and inhibition of parasympathetic tone, which may counter its beneficial metabolic actions. The net balance between the favourable and unfavourable effects of insulin on ischaemic tissues depends on: (i) the dose-response of the various effects; (ii) the presence of insulin resistance; (iii) the coexistence of hyperglycaemia; and (iv) the stage of ischaemic tissue damage. At present, a role for glucose-insulin-potassium infusions in clinical practice seems to be clearly established in the case of diabetic patients with acute coronary syndromes, and in patients undergoing urgent or elective cardiac surgery. Its role as an adjunctive therapy in the management of myocardial infarction in non-diabetic individuals has been tested in several clinical trials; however, the evidence emerging from them is inconclusive.

Coronary artery stenosis controlled by distal perfusion pressure: description of the servo-system and time-dependent changes in regional myocardial blood flow

An animal model for the induction of coronary artery stenosis is described. In this model the degree of stenosis, as induced with commercially available hydraulic occluders, can be easily controlled by keeping constant the mean perfusion pressure (pcor) distal to the site of stenosis. This pcor is the input signal for a servo-system feeding a motor-pump, which determines the degree of inflation of the cuff around the left anterior interventricular coronary artery (LAICA). In each experiment pcor did not vary more than 2 mm Hg from the preset value of about 25 mm Hg. In 60 anesthetized open-chest dogs the time course of standard hemodynamic variables and regional myocardial blood flow in the center of the underperfused area, using the radioactive microsphere technique, were determined. Within 1 min after induction of stenosis heart rate and end-diastolic left ventricular pressure (plved) increased (by 20 and 60%, respectively) and mean aortic pressure and dplv/dtmax decreased (by 10 and 25%, respectively). After the initial decrease median myocardial blood flow further decreased between 1 and 5 min of stenosis from 0.63 to 0.32 ml.min-1.g-1 in the outer layers (P less than 0.05) and from 0.26 to 0.15 ml.min-1.g-1 in the inner layers (P less than 0.05), despite constant hemodynamic conditions and pcor. Between 5 and 120 min of stenosis these values remained unchanged in the outer layers, but decreased further in the inner layers to 0.08 ml.min-1.g-1 (P less than 0.05). The accurate control of pcor, the reproducibility of the levels of residual blood flow and the ease of handling the stenosis system indicate that coronary artery stenosis controlled by perfusion pressure distal to the stenosis is a useful animal model to study events during regional myocardial ischemia. With the use of this model of low flow ischemia a biphasic increase of myocardial vascular resistance was observed, which is initiated during the first minutes of coronary artery stenosis.

Haemodynamic and metabolic consequences of elevated plasma free fatty acids during acute ischaemic left ventricular failure in dogs

Haemodynamic and metabolic effects of elevated plasma concentrations of free fatty acids (FFA) were studied during acute ischaemic left ventricular failure in closed-chest anaesthetized dogs. Embolization of the left main coronary artery with 50 micron plastic microspheres induced severe depression of left ventricular performance as indicated by a marked increase in left ventricular end-diastolic pressure (LVEDP), and marked reductions in LVdP/dtmax, cardiac output and myocardial oxygen consumption (MVO2). When stable conditions were reached, eight dogs received a triglyceride emulsion and heparin to raise plasma FFA. This was associated with increased MVO2 and further elevation of LVEDP. In two dogs receiving the triglyceride emulsion but no heparin, plasma FFA was not elevated, and MVO2 and LVEDP were unchanged. In conclusion, elevation of plasma FFA was associated with increased myocardial oxygen requirement and further depression of LV function in dogs with acute ischaemic LV failure.