THE VESSELS OF THE HEART

Transcription

1 1 THE VESSELS OF THE HEART The vessels of the heart include the coronary arteries, which supply the heart and the veins and lymph vessels, which drain the heart. THE CORONARY ARTERIES These are the blood vessels responsible for taking blood to the all the tissues of the heart with the exception of the fibrous and the parietal serous layers of the pericardium. The coronary arteries are modified muscular arteries with poorly developed internal elastic lamina. SOURCES (Figure 1) The coronary arteries originate from the ascending aorta. They are commonly two in number (Right and left) but could be up to four in number. The left artery usually has a larger diameter than the right one.

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3 3 THE RIGHT CORONARY ARTERY: This artery arises from the Right (Anterior) aortic sinus and passes between the right auricle and the root of the pulmonary trunk to enter the anterior part of the coronary sulcus (Groove). It runs towards the inferior border within the sulcus and curves over that border to enter the posterior part of the coronary sulcus, where it terminates just before the crux of the heart, at the crux or to the left of the crux. Its terminal twigs anastomose with terminal twigs of the Left coronary artery. Branches of the Right Coronary artery: 1. Right Conus artery (3 rd Coronary artery): This is usually the first branch of the right coronary artery but could arise directly from the right aortic sinus (36%). It supplies the infundibular part of the right ventricle and the proximal part of the pulmonary trunk. It terminates around the pulmonary trunk by anastomosing with a similar branch (Left Conus artery) of the left coronary artery. 2. The artery to the sinuatrial node: This artery is a branch of the right coronary artery in 60% of the population. This branch also supplies the right atrium, which accommodates the node. 3. Right anterior (atrial and ventricular) rami (Branches): These branches supply the sternocostal surface of the right atrium and right ventricle. 4. Right marginal artery: This artery runs towards the apex of the heart along the inferior border of the heart. 5. Right posterior (atrial and ventricular) rami: These arteries supply the diaphragmatic surface of the right ventricle and the right atrium. 6. Posterior interventricular artery: This artery runs in the posterior interventricular groove, sending short perforating septal branches to the interventricular septum. 7. Atrioventricular rami: These vessels supply adjacent areas of the atria and ventricle in the vicinity of the posterior aspect of the atrioventricular groove (Coronary sulcus). 8. The artery to the atrioventricular node. This artery arises in the region of the crux from the right coronary artery in 80% of the population. Summary of the distribution of the Right Coronary artery: In general, the right coronary artery supplies both right atrium and ventricle, parts of the left atrium and ventricle, part of the interventricular septum, SA and AV nodes. THE LEFT CORONARY ARTERY This artery has a short trunk and arises from the Left (Left posterior) aortic sinus. It emerges between the left auricle and the root of the pulmonary trunk and immediately bifurcates to form its circumflex and anterior interventricular branches. Anterior interventricular artery: This is the larger of the two main branches of the left coronary artery. It runs within the anterior interventricular groove up to the inferior margin of the heart around which it curves to reach the apical part of the posterior interventricular groove. Its terminal twigs anastomose within the groove with the terminal twigs of the posterior interventricular artery. Its branches include: a. Left conus artery: This branch anastomoses with a similar branch of the right coronary artery. b. Lateral diagonal branch. This is a large Left anterior ventricular branch.

4 4 c. Right and left anterior ventricular rami, which supply the sternocostal surface of the two ventricles. d. Anterior septal rami, which supply the anterior 2/3 of the interventricular septum. e. Posterior septal rami, which supply the apical part of the posterior 1/3 of the septum. Circumflex branch of Left Coronary artery This artery runs in the posterior part of the Coronary Groove (Sulcus) and terminates at or just before the crux of the heart by anastomosing with twigs of the right coronary artery. Its branches include: a. Left marginal branch, which supplies the left ventricle. b. Anterior and posterior ventricular branches c. Atrial branches, which supply the left atrium. d. The artery to the sinuatrial node: This artery arises from the left coronary artery in 40% of the population. e. The artery to the atrioventricular node. This artery arises from the Left coronary artery in 20% of the population. Summary of the distribution of the Left Coronary artery: In general, the left coronary artery supplies most of the left ventricle, a narrow strip of the right ventricle, the anterior 2/3 of the intereventricular septum and most of the left atrium. It also supplies the SA and AV nodes CORONARY ARTERIAL DOMINANCE Coronary arterial dominance is based on the pattern of distribution of the two coronary arteries and is determined by the artery, which gives rise to the posterior interventricular artery. The posterior interventricular artery supplies: a. The posterior part (1/3) of the interventricular septum. b. The posterolateral wall of the left ventricle. There are conflicting reports on the pattern of domination between the right and the left coronary arteries in the population. However, the popular view is that: 1. In 67% of the population, the right coronary artery is the dominant artery. (A) and (D) 2. In 15% of the population, the left coronary artery is the dominant artery. (B and C) 3. In 18% of the population, the distribution is shared equally.

5 5 NB: C in the diagram is an unusual case of a single coronary artery arising from the left aortic sinus. CORONARY ARTERIAL ANASTOMOSES In general, branches of the coronary arteries are referred to as End arteries (An artery whose area of distribution receives no supply from a branch or branches of another large artery). Nevertheless, some degree of anastomosis occurs between branches of the coronary arteries at various levels. Anastomotic Levels: a. Sub-endocardial In all the cavities. b. Myocardial- In the tunica media and the interventricular septum. c. Subepicardial In the coronary grooves d. Extracardial- Involving the pericardiacophrenic, bronchial and mediasternal branches. These anastomoses occur between branches of individual coronary arteries (Intracoronary) and between branches of the left and the right coronary arteries (Intercoronary). Extracardial and sub-epicardial amastomoses are usually arterial in nature while myocardial and sub-endocardial anastomoses are arteriolar in nature. The existence of cardiac arteriovenous shunts has also been suggested but yet to be substantiated. In cardiac anoxia and other obstructive coronary heart diseases, the anastomotic channels become pronounced but usually not enough to meet the need of the endangered heart. These situations usually result in Myocardial Infarction (MI).

6 VENOUS DRAINAGE OF THE HEART The heart is drained principally by the 2cm long Coronary sinus, which drains into the right atrium. It receives the following tributaries: 1. The great cardiac vein, which accompanies the anterior interventricular artery and enters the left end of the sinus. This vein usually has a valve at the point of entry into the coronary sinus 2. The left marginal vein also drains into the left end of the sinus. 3. The left posterior ventricular vein also drains into the left aspect of the sinus. 4. The middle cardiac vein, which accompanies the posterior interventricular artery drains into the right end of the sinus. 5. The small cardiac vein, which accompanies the right marginal artery drains into the right end of the sinus or drains directly into the right atrium. 6. The oblique vein of the left atrium drains the posterior wall of the left atrium into the left aspect of the sinus. The minor/accessory cardiac veins are: 6

7 7 1. Anterior cardiac veins, which cross the anterior part of the coronary groove and drain directly into the right atrium. Some of these veins drain into the small cardiac vein. 2. Venae cordis minimae: These are the smallest cardiac veins previously called Thebesian veins. They arise from the myocardium and drain directly into all four chambers of the heart but mainly into the right atrium. Blood could flow in the reverse direction in these veins thus; they could supply the myocardium with blood. LYMPHATIC DRAINAGE OF THE HEART The lymphatics of the heart consist of small lymph vessels in the connective tissues of the tunica intima and media, which drain into an extensive epicardial lymphatic plexus. Efferent vessels from the epicardial plexus converge in the cardiac sulci to form right and left cardiac collecting lymph trunks, which run along with branches of the coronary arteries towards the root of the ascending aorta and pulmonary trunk. Here they converge once again to form two lymph vessels, one draining the left trunks into the inferior tracheobronchial lymph nodes and the other draining the right trunks into the left brachiocephalic nodes.

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