By the end of the chapter the student will be able to:
List and describe the factors regulating myocardial energy/oxygen supply and demand (coronary blood flow).
Describe the mechanisms of myocardial ischemia (reversible and irreversible).
Delineate the pathology and pathophysiology of myocardial infarction.
Discuss the clinical manifestations and diagnostic tests of cardiac ischemia.
Discuss the methods of prevention and treatment of myocardial ischemia.
Construct a list of complications of myocardial ischemia.
Ischemic heart disease is the leading cause of death in developed countries. It is the result of an imbalance between the myocardial energy/oxygen supply and demand, most frequently caused by atherosclerosis in the coronary arteries. The disease ranges from minor reversible ischemia with milder clinical manifestations, known as angina pectoris, to major irreversible ischemia with cell death and devastating consequences, called myocardial infarction (MI). Clinical manifestations of ischemic heart disease present with a variety of syndromes (eg, stable angina, unstable angina, variant angina, silent ischemia, and MI), more frequently with chest pain at rest or following exertion, in addition to changes in electrocardiogram (ECG) tracing and cardiac biomarkers. The high energy demands of the heart are met through the oxidative metabolism in the cardiac cells, which require a constant supply of oxygen from the coronary blood circulation. Although coronary atherosclerosis is the main cause of the reduction of oxygen and energy supply, other conditions can be implicated, such as a decrease in the oxygen-carrying capacity of the blood (eg, anemia) and an increase in the ventricular workload (eg, hypertension and aortic stenosis).
Selecting a treatment for ischemic heart patients is based on the severity of the ischemia, using a wide variety of medication(s) and/or surgical revascularization strategies. The severity of the ischemia is determined by patient history, ECG abnormalities, and by increasingly nuanced methods of lab tests such as biomarkers and imaging studies. Complications of ischemic heart disease depend upon the severity and the location of the ischemia as well as the onset and the availability of management intervention. In this chapter, we will discuss each parameter and objective in more detail.
Factors Regulating Myocardial Energy/Oxygen Supply and Demand
The Role of the Functional and Histological Features of the Heart
There are many functional and histological features of the heart that make it an organ that is highly dependent on aerobic metabolism and hence a competent and continual oxygen supply is required for its survival. For example, the clinical manifestations of angina pectoris often results if the myocardial oxygen supply does not meet the oxygen demand. Although the heart is less than 0.5% of the total body weight, it receives around 5% of the resting cardiac output with a capillary density and resting oxygen consumption ...