Transcript
Chapter 14: Alterations in Myocardial Tissue Perfusion
Chapter Summary
Atherosclerosis is the primary underlying cause of artery diseases (peripheral, coronary, and cerebral). It is an immune–inflammatory disease associated with injury to the intimal lining of blood vessels caused by chronic injury to the endothelium. Chronic injury causes endothelial cells to separate, allowing monocytes to enter the intimal lining of arteries. Macrophages engulf LDL and become foam cells that form a fatty streak. Fatty streaks may be the precursor to fibrous atheromatous plaque and atheromas that obstruct blood flow distal to the lesion.
Coronary artery disease (CAD) specifically refers to the narrowing of the coronary artery lumens through development and growth of complex plaque lesions that result in intimal thickening and increasing occlusion of the artery lumens. There are two types of plaque formations: stable and unstable. Stable plaque produces predictable impedance of blood flow that causes stable angina, an oxygen supply and demand problem. Unstable plaque is associated with acute-onset thrombus formation and is more threatening than stable plaque, resulting in acute coronary syndrome (ACS), which is clinically noted as either unstable angina or acute myocardial infarction.
There are modifiable and nonmodifiable risk factors in the development of atherosclerosis. Modifiable risk factors can be altered with lifestyle changes or medications. Aggressive reduction and management of risk factors are crucial to preventing/controlling the development of atherosclerosis.
There are four main arteries that supply the myocardium. Collateral channels provide an alternate route for myocardial tissue perfusion if one or more of these arteries become obstructed.
The classic presenting symptom of CAD is angina pectoris. It is important to remember that not all patients experience classic anginal chest pain. Use of the PQRST assessment tool and an anginal classifications scale may be helpful. Three types of angina include Prinzmetal’s angina, stable angina, and unstable angina. It is important to include a focused physical assessment for the patient who complains of chest pain. Subjective data should correlate with clinical signs.
ECG changes associated with myocardial ischemia and injury include ST segment and T wave changes. Serial serum CK-MB, troponin-I, and troponin-T are cardiac markers indicative of the extent of myocardial damage. Other diagnostic tests include the exercise stress test, echocardiography, and myocardial perfusion imaging.
ACS represents a continuum of atherosclerotic disease and includes unstable angina and MI that are associated with diagnostic criteria. Nursing care includes relieving chest pain, reducing myocardial oxygen demand while increasing myocardial oxygen supply, and providing psychosocial support to the patient and family. Medical management of ACS depends on initial 12-lead ECG findings, risk stratification, and evidence of serum cardiac markers.
Interventions to restore myocardial tissue perfusion include administration of thrombolytic therapy, PCI, and CABG surgery. Thrombolytic therapy uses drugs to break up blood clots. Nursing responsibilities for the patient receiving thrombolytics include monitoring evidence of bleeding, hemodynamic instability, reperfusion, and occlusion. PCI is the procedure of choice for STEMI. There are specific nursing interventions that must be implemented before, during, and after a patient receives PCI. CABG surgery is performed for patients who meet certain criteria. Postoperatively, the nurse must monitor CO and assess for complications, such as hypotension and cardiac tamponade.
