Porth's Essentials of Pathophysiology, 4e

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Disorders of Cardiac Function

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arrhythmias, limited infarct size, improved infarct heal- ing, and myocardial remodeling. 12 These agents interact with plasminogen to generate plasmin, which lyses fibrin clots and digests clotting factors V and VIII, prothrom- bin, and fibrinogen (see Chapter 12). The person must be at low risk for complications caused by bleeding, with no intracranial hemorrhage or significant trauma within the last 3 months. 14 Percutaneous coronary intervention (PCI) is indicated as an early invasive procedure for patients with unstable angina/NSTEMI. 19 Percutaneous coronary intervention includes percutaneous transluminal coronary angioplasty (PTCA) and stent implantation. Balloon PTCA involves dilating the coronary artery with an inflatable balloon positioned at the narrowing of stenotic atherosclerotic plaque within the vessel (Fig. 19-7). Similar to an angio- gram, the procedure is performed under local anesthesia in the cardiac catheterization laboratory. Balloon PTCA is almost exclusively used in conjunction with coronary stenting. The addition of coronary stenting significantly improved short- and long-term outcomes for patient with ACS compared with PTCA alone but patients remain at risk for restenosis and thrombosis following the procedure. Persons undergoing stent procedures must be treated with antiplatelet and anticoagulant drugs to prevent throm- bosis and restenosis. Drug-eluting stents that provide sustained delivery of an antiproliferative pharmacologic agent may be used to decrease the risk of thrombosis. 19 Coronary artery bypass grafting (CABG) may be the treatment of choice for people with significant CAD who do not respond to medical treatment and who are not suitable candidates for PCI. It may also be indi- cated as an emergent treatment for STEMI, in which case the surgery should be done within 4 to 6 hours

Vein graft

Left subclavian artery Internal mammary artery

Anterior descending

of symptom onset if possible. The procedure involves revascularization of the affected myocardium by attach- ing a saphenous vein graft between the aorta and the affected coronary artery distal to the site of occlusion, or by using the internal mammary artery to revascular- ize the left anterior descending artery or its branches (Fig. 19-8). This procedure often involves one to five distal anastomoses. Using emergent or urgent CABG as a reperfusion strategy is indicated in situations such as failed PCI with persistent pain or hemodynamic insta- bility, or for patients who are not candidates for PCI or fibrinolytic therapy. Myocardial Postinfarction Recovery Period. After a MI, there usually are three zones of tissue damage: a zone of myocardial tissue that becomes necrotic because of an absolute lack of blood flow; a surrounding zone of injured or hypoxic cells, some of which will recover; and an outer zone in which cells are ischemic and can be sal- vaged if blood flow can be reestablished. The boundaries of these zones may change with respect to the timeliness of treatment to successfully reestablish blood flow. If blood flow can be restored within 20 to 40 minutes, loss of cell viability is minimized. 6 The process of ischemic necrosis usually begins in the subendocardial area of the Saphenous vein bypass graft.The vein segment is sutured to the ascending aorta and the right coronary artery at a point distal to the occluding lesion. (Bottom) Mammary artery bypass graft.The mammary artery is anastomosed to the descending branch of the left coronary artery, bypassing the obstructing lesion. branch of the left coronary artery FIGURE 19-8. Coronary artery revascularization. (Top)

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B

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FIGURE 19-7. Balloon-expandable stent insertion. (A) Insertion of a guide catheter with a collapsed balloon-expandable stent mounted over a guide wire into a coronary artery. (B) Advancement of guide wire across the coronary lesion. (C) Positioning of the balloon-expandable stent across the lesion. (D) Balloon inflation with deployment of the stent. Once the stent is expanded, the balloon system is removed.