B Coronary artery disease
Definition
Coronary artery disease (CAD) is a complex disease state that involves narrowing of the coronary arteries.
Incidence
Coronary heart disease caused about one of every six deaths in the United States in 2008. Coronary heart disease’s mortality in 2008 was 405,309. Each year, an estimated 785,000 Americans will have a new coronary attack, and about 470,000 will have a recurrent attack. It is estimated that an additional 195,000 silent first myocardial infarctions (MIs) occur each year. Approximately every 25 seconds, an American will have a coronary event, and approximately every minute, someone will die of one.
Pathophysiology
The pathogenesis of CAD is not definitively clear, but several theories have been proposed. Scientists believe the endothelium or innermost layer of the artery becomes injured. Over time, cholesterol agents such as low-density lipoproteins and macrophages adhere to the endothelium and form plaques. The plaques continue to build and decrease the vessels’ ability to distend. Because coronary oxygen extraction is maximal at rest, the only way to increase oxygen delivery to the tissues is to increase coronary flow. In normal coronaries, flow can increase three to five times over baseline when demand increases. However, this increase in flow, known as coronary reserve, is limited in patients with CAD. Thus, when patients with CAD increase demand by exercise or stress, they develop demand ischemia, which can then be symptomatically experienced as predictable stable angina.
Acute coronary syndromes (ACS) and perioperative ischemia are usually caused by supply ischemia. Ischemia occurs when a piece of the plaque ruptures causing a thrombus to form that significantly or totally occludes a segment of a coronary artery, leading to ischemia, dysrhythmias, or MI. The problem can be exacerbated by spasm, which can develop even in normal adjacent vessels.
Treatment
Great strides have been made in the nonsurgical treatment of patients with CAD and ACS in the past 2 decades. The development and evolution of coronary stents have revolutionized care. Most patients presenting for coronary artery bypass graft (CABG) surgery with CAD or ACS will have been referred for some type of percutaneous coronary intervention (PCI). Surgeons and anesthesia providers must take this into consideration when planning care. Much research has been done comparing the risk-to-benefit ratio of surgical intervention to optimal medical management. The American College of Cardiology/American Heart Association (ACC/AHA) guidelines state that surgical intervention is indicated for patients with stenosis of greater than 50% in the left main trunk or triple vessel disease. Additionally, patients who have failed PCI or who have coronary lesions not amenable to PCI benefit from surgery. In these situations, CABG has been found to have a lower mortality risk of major cardiovascular complications or cerebral events than optimal medical management.
