الفهرس 
Arterial Supply of the Heart
Branches of the left coronary arteryOnly 14 pages are availabe for public view
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Abstract
The myocardium receives its blood supply through the right and left coronary arteries. Although the coronary arteries have numerous anastomoses at the arteriolar level, they are essentially functional end arteries.
The right coronary artery supplies all of the right ventricle (except for the small area to the right of the anterior interventricular groove).The left coronary artery supplies most of the left ventricle, a small area of the right ventricle to the right of the interventricular groove, the anterior two thirds of the ventricular septum, most of the left atrium.
A sudden block of one of the large branches of either coronary artery will usually lead to necrosis of the cardiac muscle (myocardial infarction) in that vascular area, and often the patient dies. Most cases of coronary artery blockage are caused by an acute thrombosis on top of a chronic atherosclerotic narrowing of the lumen.
Coronary Bypass Surgery, Coronary Angioplasty, and Coronary Artery Stenting are now commonly accepted methods of treating coronary artery disease.The coronary stent is a relatively new tool used to keep stenotic coronary arteries open. The number of patients with coronary artery stents presenting for surgery is on the rise. After stent implantation, it is recommended that patients receive 6 weeks to 12 months of dual antiplatelet therapy.
There are two major types of coronary artery stent: Bare Metal Stents (BMS) and Drug-Eluting Stents (DES).
After stent implantation, it is recommended that
patients receive 6 weeks to 12 months of dual antiplatelet
therapy.
In metallic coronary stent despite intensive anticoagulation with heparin and warfarin, was complicated by stent thrombosis in 5 to 10 percent of patients, and bleeding was a common complication.
DES were introduced in the late 1990s in response to the high observed incidence of late stent re-stenosis with BMS.
The components of a drug-eluting stent can be divided into a platform (the stent), a carrier (usually a polymer), and an agent (a drug) to prevent restenosis. Currently, there are two major types of DES being inserted,releasing either sirolimus (‘Cypher’ stent) or paclitaxel (‘Taxus’ stent).
The presence of exposed metal stents in the coronary arteries is highly thrombogenic, and the early use of stents. Coronary artery stents and non-cardiac surgery was associated with a high risk of stent thrombosis. This potentially devastating complication is associated with a 50% incidence of acute myocardial infarction (MI) and a 20% mortality rate, andconsequently, the prevention of stent thrombosis is of paramount importance.
Antiplatelet agents (platelet inhibitors) are drugs capable of inhibiting platelet function, in particular platelet activation and aggregation, so used for prevention of stent thrombosis.
The perioperative period for a patient having a coronary artery stent undergoing urgent surgery is especially problematic as surgery induces a hypercoagulable state, while surgeons often prefer to stop anti-platelet drugs pre-operatively to minimize the risk of surgical bleeding in some procedures, thus putting the patient at high risk of stent thrombosis. So, the perioperative management of antiplatelet
therapy in patients with coronary artery stenting undergoing urgent surgery to minimize the risk of stent thrombosis is becoming an increasingly frequent challenge for anaesthetists. These can achieved by adequate peri-operative monitoring and The anesthesiologist should also select the drugs with the objective of minimizing risk of stent stenosis through bridging therapy of dual antiplatelet.
It would be beneficial in perioperative management to have a routine and simple test of platelet function in patients exposed to antiplatelet therapy presenting for surgery in order to exclude lack of clinical effect and consequently a reduced risk of bleeding, The standard tests of coagulation, the prothrombin time (PT) and activated partial thromboplastin time (APTT), do not allow assessment of platelet function. The ‘bleeding time’ is the most accurate test of platelet function and the effect of antiplatelet agents, but in reality is not the most practical of tests and has not been shown to correlate well with perioperative bleeding.
A variety of tests are currently being assessed for measurement of platelet function. Optical light transmission platelet aggregometry is the most widely accepted technique of assessing platelet function being considered the ‘gold standard’.
Exercise Capacity and Functional Capacity Functional status is a reliable predictor of perioperative and long-term cardiac events. Patients with reduced functional status preoperatively are at increased risk of complications. Conversely, those with good functionl status preoperatively are at lower risk.
An emergency procedure is one in which life or limb is threatened if not in the operating room, typically within <6 hours. An urgent procedure is one in which there may be time for a limited clinical evaluation, typically between 6 and 24 hours. An elective procedure is one in which the procedure could be delayed for up to 1 year.
If the noncardiac surgery is urgent or an emergency, then the risks of ischemia and bleeding, and the long-term benefit of coronary revascularization must be weighed. If coronary revascularization is absolutely necessary, there are two options ; medical in form of bridging therapy, surgical in form of CABG combined with the noncardiac surgery may be considered a bridging strategy seems appealing in order to minimize bleeding risk without a trade-off in ischemic protection in patients at high thrombotic risk who require dual antiplatelet (DAPT) discontinuation. If bridging is needed, antiplatelet agents should be preferred over anticoagulants, as arterial thrombosis is primarily driven by platelet adhesion and aggregation at the site of vascular injury.
The ideal bridging agent should be able to achieve levels of platelet inhibition similar to that of the oral P2Y12 receptor inhibitors, but with a rapid onset and offset of antiplatelet effect. To date, the only intravenous approved agents with prompt and potent platelet inhibitory effect and a relatively short offset of action are the small-molecule glycoprotein IIb/IIIa inhibitors (GPIs) Tirofiban and Eptifibatide. Another drug has yet to be tested in this setting which called Cangrelor is a potent intravenous antiplatelet analog that directly and reversibly binds to the P2Y12 receptor without being metabolized. It has a very fast onset and offset of action, with platelet reactivity returning to baseline levels within 30-60 min from infusion discontinuation.