The coronary circulation Flashcards
Describe the arterial supply to the heart
- The left and right coronary arteries arise in the aortic sinuses
- The three aortic sinuses are bulges in the wall of the ascending aorta that lie just above the orifice of the aortic valve
- Right coronary artery arises in the anterior sinus, left coronary artery in the left posterior sinus
Describe the anatomy of the left coronary artery (course, supplies, branches)
Course:
* Arises in the left posterior sinus, near the left auricular appendage
* Passes posteriorly to the atrioventricular groove
Supplies
* blood to the left atrium, left ventricle and interventricular septum, and the SA node
Two main branches
* left anterior descending artery
* left circim
Describe the left anterior descending artery (origin, course, branches)
- arises from the left coronary artery
- follows the anterior interventricular sulcus around the pulmonary trunk, descends in the interventricular groove towards the apex of the heart).
- two main branches: the diagonal arteries
Describe the left circumflex artery (course, supplies, branches)
- Arises from the left coronary artery
- Descends in the coronary sulcus on the posterior surface of the heart
- Supplies the posterior aspect of the left ventricle, and in 40% cases, the SAN
- Two main branches: the obtuse marginal arteries
Describe the right coronary artery (origin, course, supplies, branches)
- Arises in the anterior sinus
- Passes beween the right atrial appendage and the right ventricle, descends vertically on the front of the heart in the atrioventricular groove
- Supplies both ventricles, the interventricular septum and the conducting system of the heart
- Three main branches:
1. Right marginal artery
2. Posterior interventricular artery (aka posterior descending)
3. Aterioventricular nodal artery - supplies conducting system of the heart
What is coronary dominance? Which side is most commonly dominant
- Coronary dominance = ‘that major branch which supplies the AV node by the posterior descending artery’.
- In 70% of cases it is the right coronary artery and is termed ‘right dominant’.
- However, it may be supplied by the left circumflex artery in 10% of cases or a mixed supply in 20% of cases, i.e. co-dominant.
Do anastamoses occur between the coronary arteries? Are these clinically relevant?
- Anastomoses occur between the coronary arteries, but only at an arteriolar level.
- These anastomoses do not constitute a collateral circulation and an ischaemic event caused by sudden blockage of a coronary artery leads to cellular death within the distribution of the heart supplied.
Describe the overall venous drainage of the heart
- 60% is drained via the coronary sinus: opens in the right atrium just above the septal cusp of the tricuspid valve, and has a rudimentary valve
- Smaller venous networks are responsible for the drainage of the residual 40% - there are many small veins that empty into all four chambers of the heart, called the venae cordis minimae
Describe the venous drainage of the left ventricle
- Lateral or marginal veins lie on the posterior surface of the heart and drain blood from the left ventricle. These give tributaries to the great cardiac vein
- The anterior interventricular vein accompanies the LAD in the interventricular groove and then continues as the great cardiac vein
- The great cardiac vein drains into the coronary sinus
Describe the venous drainage of the right ventricle
- Middle cardiac vein: follows the inferior interventricular branch of the RCA and drains into either the coronary sinus or the right atrium
- Small cardiac vein drains the inferior and lateral wall of the right ventricle, directly into the right atrium. One of the anterior cardiac veins, that runs across the surface of the RV.
Describe the lymphatic drainage of the heart
- Accompanies the coronary arteries
- Emerge through the pericardium at the site of the major vessels
- Drain into the tracheo-bronchial and mediastinal nodes
What is the rate of blood supply to the heart?
1ml/min/g, i.e. about 300mls/minute for the average heart
How does blood flow to the heart change during the cardiac cycle, and as stress increases, and what are the clinical implications
- There is cyclical compression of the coronary arteries during contraction, and most blood flow occurs during diastole
- Heart rate is a major determinant of cardiac work
- Subendocardial perfusion is particularly vulnerable to cyclical compression
- The heart demonstrates autoregulation, which ensures consistent blood flow over a broad range of mean pressures, and can increase it’s blood flow consistent with metabolic demands when the myocardium is under stress: the small blood vessels vasodilate
