LEFT CORONARY ARTERY ANATOMY: The LMCA arises from the upper portion of the left sinus,just below the sinotubular ridge of the aorta. The diameter of the LMCA ranges from 3-6mm. The LMCA passes behind the right ventricular outflow tract and may extend for 0-10mm. It usually then bifurcates into LAD and LCx branches


LEFT ANTERIOR DESCENDING ARTERY(LAD): The LAD passes down the anterior interventricular groove towards the cardiac apex. Its major branches are Septal and Diagonal. The septal branches emanate from the LAD at 90 degree angle and pass into inter ventricular septum. These septal branches interconnect with similar branch passing upward from the posterior descending branch of the RCA to produce a collateral channels.The diagonal branch of the LAD pass over the antero lateral aspect of the heart.
In 37% of patients, the LMCA trifurcates into LAD, LCx and Ramus intermedianus. It usually supplies the free wall along the lateral aspect of the LV.

LEFT CIRCUMFLEX ARTERY (LCx): It originates at the bifurcation of the LMCA and passes down the left atrioventricular groove. The LCx gives one to three branches of large Obtuse marginal (OM) as it passes down the groove. It also gives rise to one or two left atrial circumflex branches. The branch supply the lateral and posterior aspects of left atrium.

RIGHT CORONARY ARTERY(RCA): The RCA originates from the right aortic sinus at a point lower than the origin of the LMCA from the left aortic sinus. It passes down the right AV groove toward the crux. The first branch of the RCA is Conus artery. The importance of this artery is to serve as collateral during LAD occlusion.
The second branch is Sino atrial node artery. It sends branches to the sinus node and usually to the RA or both atria.
The mid portion of the RCA usually gives rise to one or more medium sized Acute marginal branches. it supplies the anterior wall of the RV.
The other branch is Posterior descending artery (PDA). It passes forward in the posterior inter ventricular groove and gives rise to number of small inferior septal branch which pass upward to supply the lower portion of the IVS. After giving rise to the PDA, the RCA continue beyond the crux and begins to pass upward along the distal portion of the Posterior left ventricular branch(PLV) which supply the diaphragmatic surface of the LV.
At or near the Crux, the RCA gives rise to small AV nodal artery which passes upward to supply the node.

DOMINANCE: The dominant vessel is the one that supplies the Posterior Diaphragmatic portion of the IVs and the diaphragmatic portion of the LV.

RIGHT DOMINANCE: When the RCA gives rise to PDA. Seen in 85% of patients.

LEFT DOMINANCE: Where the LCx artery is large and continuous down to the diaphragmatic surface of the LV  where it gives rise to PLV and turn forward to become the PDA. Seen in 7.5% of patients.

CO-DOMINANCE:  Where the RCA gives rise to the PDA and the LCx gives rise to PLV branch. Seen in about 7.5%.

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