Hemodynamic significance of the coronary vein valves

Mechanotransduction in Blood and Lymphatic Vascular Development and Disease

The blood and lymphatic vasculatures are hierarchical networks of vessels, which constantly transport fluids and, therefore, are exposed to a variety of mechanical forces. Considering the role of mechanotransduction is key for fully understanding how these vascular systems develop, function, and how vascular pathologies evolve. During embryonic development, for example, initiation of blood flow is essential for early vascular remodeling, and increased interstitial fluid pressure as well as initiation of lymph flow is needed for proper development and maturation of the lymphatic vasculature. In this review, we introduce specific mechanical forces that affect both the blood and lymphatic vasculatures, including longitudinal and circumferential stretch, as well as shear stress. In addition, we provide an overview of the role of mechanotransduction during atherosclerosis and secondary lymphedema, which both trigger tissue fibrosis.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Echocardiography of the coronary sinus in adults

The coronary sinus (CS) is a small tubular structure just above the posterior left atrioventricular junction. The CS can be imaged in several different echocardiographic views. Using zoom M-mode recordings of the CS in apical two-chamber view, CS caliber can be sharply imaged and easily measured during different phases of the cardiac cycle. We have recently shown that the CS narrows during atrial contraction in persons with sinus rhythm, but does not narrow at all if atrial fibrillation is present. Attenuation of CS narrowing occurs in patients with congestive heart failure and inferior vena cava plethora. Maximal CS caliber occurs during ventricular systole. Patients with poor left ventricular systolic function show mild CS dilatation. Greater CS dilatation is present in patients with persistent left superior vena cava, and huge dilatation when this anomaly is accompanied by absence of a right superior vena cava. Injection of sonicated saline into a left and then a right arm vein is diagnostically useful in confirming these two venous anomalies. Pulsed-wave Doppler of the CS can be recorded in the parasternal right heart inflow view. From this and from the CS cross-section area it may be possible to estimate coronary blood flow.

[Anatomy, special features and angiographic assessment of the coronary sinus]

The endovenous approach for left ventricular lead implantation can be used in most patients. A complete angiography of the coronary vein will increase the success rate of lead implantation. From a technical point of view, attention should be focused on anatomical variation, which leads to a higher number of complications like dissection or perforation of the vessel. However, in a number of cases a left verticular lead must be implanted epimyocardial due to anatomical reasons.

Optimal continuous retrograde coronary perfusion flow rate with beating heart in normal temperature

PURPOSE

We were led to the premise that with retrograde oxygenated blood perfusion, it would be possible to perform operations on the beating heart.

METHODS

The experiment consisted of two stages: procedure 1 and 2. In procedure 1, six pigs were used. Retrograde perfusion flow was controlled to be in the range of 5.0-10.0 mL/kg/min and was gradually increased. In procedure 2, six pigs were used. Retrograde perfusion was continued for 120 min at the optimal flow rate obtained from procedure 1.

RESULTS

The optimal flow rate was 7.0 mL/kg/min in procedure 1. In procedure 2, retrograde perfusions for 120 min were performed with perfusion flows set at optimal flow rate.

CONCLUSIONS

The procedure used in this study made it possible to maintain empty beating heart with normal sinus rhythm for 120 min, and the results suggest the possibility of clinical application to open heart surgery.

Endoscopic study of the morphology of Vieussens valve

Vieussens valve (Vv) is the ostial valve of the great cardiac vein located near the beginning of the coronary sinus. Knowledge of its anatomy is important for several trans-sinus cardiologic procedures. The frequency of its presence is reported to vary from 65-87%. We documented the post mortem morphology of Vieussens valve in 50 unfixed, intact human coronary sinuses using endoscopy. We believe this is the first study of the anatomy of the coronary sinus and the adjacent venous ostia to employ this technique. Vieussens valve was observed in 78% of specimens. Special attention was given to the shape of the valve leaflets. Five morphological types of Vv were distinguished: single leaflet, flat (16%); single leaflet, concave (20%); double leaflet, flat (8%); double leaflet, concave (32%); and triple leaflet, concave (2%). We found post mortem endoscopy of the coronary sinus to be a good and reliable method of visualizing Vieussens valve.

Update on echocardiography of coronary sinus anatomy and physiology

The coronary sinus (CS) can be imaged echocardiographically as a small tubular sonolucency in the posterior atrioventricular groove. To date, its importance to echocardiographers has been that CS dilatation usually signifies a persistent left superior vena cava. Recently, we developed a technique to image CS caliber over the duration of the cardiac cycle. CS contraction accompanies the P wave on the electrocardiogram, in sinus rhythm or in various arrhythmias. CS contraction is always absent in atrial fibrillation. In sinus rhythm, CS contraction may be attenuated or absent if congestive heart failure, with marked venous congestion, is present. Thus, this attenuation is a potentially valuable echocardiographic sign of elevated central venous pressure. We demonstrate the echo visualization of CS-related structures, such as tributary veins and the Thebesian valve. The potentially useful concept of the CS as a "miniventricle" is discussed. CS blood flow can be recorded by interrogation in the right heart inflow view. The pattern of CS antegrade flow and the exceptional situation of retrograde systolic CS flow from a posteriorly directed tricuspid regurgitant jet are demonstrated.

Anatomic and hemodynamic considerations influencing the efficiency of retrograde cardioplegia

One of the major issues raised by cardiac surgical procedures requiring cardiopulmonary bypass is the question of myocardial protection. The preferred route for the administration of cardioplegia is controversial. A number of studies show the beneficial effects of retrograde cardioplegia but some demonstrate only partial or poor myocardial protection. This paper reviews the anatomy and anatomic variations of the coronary sinus, the coronary sinus orifice and cardiac veins, and the major systemic venous drainage, all of which may affect the distribution of retrograde cardioplegia.

Assessment of retrograde cardioplegia with magnetic resonance imaging and localized 31P spectroscopy in isolated pig hearts

OBJECTIVE

This study was done to determine whether retrograde delivery of cardioplegic solution provides uniform blood flow to the myocardium supplied by an occluded coronary artery and whether it maintains myocardial energy levels beyond the coronary occlusion.

METHODS

Isolated pig hearts were used. A hydraulic occluder was placed at the origin of the left anterior descending coronary artery. The perfusion pressure for retrograde delivery of cardioplegic solution was controlled at 40 to 50 mm Hg. Magnetic resonance imaging and localized 31P magnetic resonance spectroscopy were used to assess myocardial perfusion and energy metabolism, respectively.

RESULTS

Magnetic resonance perfusion images (n = 7) showed that the perfusion defect that occurred during antegrade delivery of cardioplegic solution (as a result of the occlusion of the left anterior descending coronary artery) resolved during retrograde delivery of cardioplegic solution. Retrograde perfusion delivered similar amounts of flow to the jeopardized myocardium as it did to other areas of the myocardium. However, the distribution of cardioplegic solution by the retrograde route was heterogeneous (cloudlike) across both ventricular walls. 31P magnetic resonance spectra showed that the ischemic changes induced by occlusion of the left anterior descending artery during antegrade perfusion were greatly alleviated by retrograde perfusion; however, it took longer for retrograde cardioplegia (n = 7, 17.08 minutes) to restore the levels of inorganic phosphate/phosphocreatine relative to the effect of releasing the left anterior descending artery occluder during antegrade delivery of cardioplegic solution (n = 7, 5.3 minutes).

CONCLUSIONS

First, retrograde delivery of cardioplegic solution provides sufficient flow to the myocardium beyond a coronary occlusion to maintain near normal levels of energy metabolites, and second, the efficacy of the retrograde route of cardioplegic solution delivery (in terms of distribution of the solution and rate of myocardial energy recovery) is significantly lower than that of the antegrade route.

Coronary sinus pressure and arterial venting do not affect retrograde cardioplegia distribution

Retrograde techniques for the administration of cardioplegia solutions are of interest because of their relative practical convenience, and because of the possibility that they provide better delivery to myocardial regions jeopardized by coronary stenosis than can be achieved with traditional antegrade techniques. This study was designed to test the following three hypotheses about how the distribution of cardioplegia by retrograde techniques might be optimized: (1) venting an occluded coronary artery improves the distribution of cardioplegia to the myocardial region originally supplied by it; (2) increasing the coronary sinus perfusion pressure makes the distribution of cardioplegia through the myocardium more uniform; and (3) increasing the driving pressure, as achieved by increasing the coronary sinus perfusion pressure or occluding a left coronary artery, improves the distribution of flow to the right ventricular free wall and interventricular septum. Tracer microspheres infused retrogradely with cardioplegia solution into canine hearts in vitro showed that the distribution of flow through the coronary sinus is consistently and significantly nonuniform, and is not significantly altered by coronary arterial occlusion and venting, or by increases in coronary sinus perfusion pressure.