Cardiac anatomy and physiology

Cardiac anatomy and physiology Correct electrocardiogram (ECG) interpretation provides an important challenge to any practitioner. With a good understanding of ECGs, you'll be better able to provide expert care to your patients. For example, when you're caring for a patient with an arrhythmia or a myocardial infarction, an Cardiac anatomy and physiology waveform can help you quickly assess his condition and, if necessary, begin lifesaving interventions. To build Cardiac anatomy and physiology skills, begin with the basics covered in this chapter - an overview of the heart's anatomy and physiology and electrical conduction system. Cardiac anatomy The heart is a hollow, muscular organ that works like a mechanical pump. It delivers oxygenated blood to the body through the arteries. When blood returns through the veins, the heart pumps it to the lungs to be reoxygenated. Location and structure The heart lies obliquely in the chest, behind the sternum in the mediastinal cavity, or mediastinum. It's located between the lungs, in front of the spine. The top of the heart, called the base, lies just below the second rib. The bottom of the heart, called the apex, tilts forward and down toward the left side of the body and rests on the diaphragm. (See Where the heart lies.) The heart varies in size, depending on the person's body size, but is roughly 5″ (12 cm) long and 3½″ (9 cm) wide, or about the size of the person's fist. The heart's weight, typically 9 to 12 oz (255 to 340 g), varies depending on the individual's size, age, gender, and athletic conditioning. An athlete's heart usually weighs more than average, whereas an elderly person's heart weighs less. An infant's heart is positioned more horizontally in the chest cavity than an adult's. As a result, the apex is positioned at the fourth left intercostal space. Until age 4, a child's apical impulse is left of the midclavicular line. By age 7, his heart is located in the same position as an adult's heart is.