Effects of acetylcholine on the coronary artery

Acetylcholine acts on the different components of the coronary arterial wall by 1) initiating endothelium-dependent relaxation of the smooth muscle cells; 2) inhibiting the exocytotic release of norepinephrine (NE), which could result in either vasodilator or vasoconstrictor effects depending on whether the main action of NE is alpha- or beta-adrenergic, respectively; and 3) activating the contractile process of the smooth muscle cells. These different effects of the cholinergic transmitter are muscarinic in nature. Their relative importance varies among species, or when acetylcholine is given exogenously rather than released from cholinergic nerves.     

Simulation of coronary artery revascularization

Simulation of the commonly constructed geometries of aorto-coronary bypass anastomoses was carried out using especially fabricated distensible tubes and a pulsatile pump. The system pressure was maintained between 80 and 120 mmHg. The total mean flow was set at 250 ml min-1 (Reynolds number of 200) and the pulsatile frequency was varied from 0 to 2 Hz. A water-glycerine mixture having a density and viscosity similar to that of blood was used throughout. A 16 mm film of the front of black dye injected proximal to the anastomosis was made as the dye approached and passed through the anastomosis. Anastomotic geometries consisted of: end to side, parallel, 45 degree angle, and 90 degree angle. Stenoses, located in the tube representing the coronary artery, were simulated using a bevelled insert which represented an 80-85% area reduction. Flow visualization revealed that distensible tubes gave more realistic flow patterns than rigid tubes, a result particularly evident when a stenosis was present. Pulsatile flow demonstrated considerably more mixing than steady flow. The use of pulsatile flow in distensible tubing with a partial stenosis showed retrograde flow through the stenosis which was not evident for either steady flow or for flow in rigid tubing. The flow at the anastomatic site of the graft having an angle of 0 degrees showed a jetting action with a zone of recirculating fluid being present whereas for a 90 degree graft a distinct helical flow was formed distal to the anastomosis.     

Endothelin-induced Ca-independent contraction of the porcine coronary artery

Front surface fluorometry and porcine coronary arterial strips loaded with fura-2 were used to investigate the effect of endothelin on cytosolic Ca concentrations, [Ca]i, and on contractile force, the objective being to elucidate the mechanism of action. Both in the presence and absence of extracellular Ca, endothelin induced rapid and dose-dependent increases in [Ca]i and in contraction. When caffeine-sensitive and histamine-sensitive intracellular Ca stores were depleted, in Ca-free medium, a transient contraction but no increase in [Ca]i followed the subsequent application of endothelin. This Ca-independent component was largely inhibited by the relative protein kinase C inhibitor, H-7, but not inhibited by W-7, calmodulin antagonist. This component is probably linked to activation of protein kinase C.     

Patterns of flow in the left coronary artery

The purpose of this investigation is to describe our preliminary observations of the overall pattern of flow in a mold of the left coronary artery of a pig. Flow in the coronary mold was visualized by the injection of dye into the sinus of Valsalva. Studies were performed during steady flow at rates of 100, 200, 300, 400, and 500 mL/min. Studies were also performed during pulsatile flow, using a pulse duplicator that simulated the magnitude and phasic pattern of coronary flow at rest and during reactive hyperemia. At conditions that simulated rest, mean coronary flow was adjusted to 121 mL/min of which 24 mL/min (20 percent) was systolic. During simulated reactive hyperemia, mean flow was 440 mL/min. Visualization of flow revealed the absence of disturbances of turbulence during both steady and pulsatile flow in the left anterior descending (LAD) and left circumflex (CIRC) coronary arteries throughout the entire range of flow studied. Prominent spiraling of flow occurred during steady and pulsatile flow. Spiraling of flow was not observed in the LAD at rest during pulsatile flow, but developed during simulated reactive hyperemia. Helical flows were observed in the CIRC both during simulated rest and reactive hyperemia. These observations suggest that helical flows may be characteristic features of flow in the left coronary artery; whereas turbulence may not be a feature of this flow field. Whether the spiraling of flow that we observed related to the spiral distribution of early atheroma reported by others, is undetermined.     

Plasma tissue factor in coronary artery disease: further step to the understanding of the basic mechanisms of coronary artery thrombosis

Tissue factor is a cell surface protein that is expressed constitutively by monocytes, macrophages and fibroblasts, but also by some other cells in response to a variety of stimuli. The main function of the tissue factor is to form a complex with factor VII/VIIa that converts factors IX and X to their active forms. Tissue factor is also involved in the pathophysiology of systemic inflammatory disorders, coagulopathies, atherosclerotic disease, tumor angiogenesis and metastasis. Increased tissue factor expression either locally in the coronary plaques or systematically on circulating blood elements of patients with acute coronary syndromes may be responsible for increased thrombin generation, thus leading to platelet activation and fibrin formation. Tissue factor therefore plays a pivotal role in the initiation of thrombotic complications in patients with coronary artery disease.     

Surgical revascularization for 'atherosclerotic' coronary artery aneurysms associated with multiple obstructive coronary artery disease

Coronary artery aneurysms (CAA) were originally described in a series of post-mortem studies but are now more commonly observed during the widely used coronary angiography.This article reports on four adult patients with CAA associated with obstructive coronary atherosclerosis. Arterial and venous conduits were successfully performed in all four. The aetiology and treatment are discussed.     

Extensive right coronary artery thrombosis

A 65-year-old man presented with a non-ST-elevation acute coronary syndrome. His medical history was unremarkable. Apart from a brother, who sustained a myocardial infarction at the age of 40, no cardiovascular risk factors were present. Coronary angiography revealed normal left anterior descending and circumflex arteries. The right coronary artery was subtotally occluded with an extensive thrombus running into the posterolateral branch (figures 1A and B). Despite appropriate medical treatment, intermittent chest pain persisted. The patient underwent a percutaneous coronary intervention with mechanical removal of the thrombus by aspiration followed by balloon dilatation.     

Biaxial vasoactivity of porcine coronary artery

The passive mechanical properties of blood vessel mainly stem from the interaction of collagen and elastin fibers, but vessel constriction is attributed to smooth muscle cell (SMC) contraction. Although the passive properties of coronary arteries have been well characterized, the active biaxial stress-strain relationship is not known. Here, we carry out biaxial (inflation and axial extension) mechanical tests in right coronary arteries that provide the active coronary stress-strain relationship in circumferential and axial directions. Based on the measurements, a biaxial active strain energy function is proposed to quantify the constitutive stress-strain relationship in the physiological range of loading. The strain energy is expressed as a Gauss error function in the physiological pressure range. In K(+)-induced vasoconstriction, the mean ± SE values of outer diameters at transmural pressure of 80 mmHg were 3.41 ± 0.17 and 3.28 ± 0.24 mm at axial stretch ratios of 1.3 and 1.5, respectively, which were significantly smaller than those in Ca(2+)-free-induced vasodilated state (i.e., 4.01 ± 0.16 and 3.75 ± 0.20 mm, respectively). The mean ± SE values of the inner and outer diameters in no-load state and the opening angles in zero-stress state were 1.69 ± 0.04 mm and 2.25 ± 0.08 mm and 126 ± 22°, respectively. The active stresses have a maximal value at the passive pressure of 80-100 mmHg and at the active pressure of 140-160 mmHg. Moreover, a mechanical analysis shows a significant reduction of mean stress and strain (averaged through the vessel wall). These findings have important implications for understanding SMC mechanics.     

Different aspects of coronary artery disease

In the Netherlands, coronary-vascular disease is still the main cause of death with around 48,000 deaths each year. This means that one out of three deaths is due to coronary-vascular disease. Therefore knowledge of epidemiology, diagnosis and treatment (by medication, PCI or CABG) of vascular disease is of utmost importance. This issue of the Netherlands Heart Journal is dedicated to coronary artery disease and deals with several of its aspects, by means of interesting case reports and reports on imaging modalities.