The heart is one of the most important organs in the human body because of its role as the pump that drives blood through the circulatory system. While cardiac function may seem fairly straightforward, it actually requires the coordination of both electrical conduct and cellular contracting in order to pump blood efficiently through the body. Individuals who suffer from heart disease often experience signs and symptoms associated with the heart's ability to function properly. Damage to the cardiac conduct pathways or the contractile cells can lead to severe pulmonary congestion, oxygen deprivation throughout the body, and fluid accumulation in the arms and legs. Because heart disease has become one of the largest morbidity and mortality risks in developed countries, it is now increasingly important for EKG technicians and other medical personnel to educate the public about cardiac function so that steps can be taken to reverse the trend towards widespread heart disease .
The human heart is constructed of four chambers that each have a separate role in the pumping of blood to the lungs and the vessels that deliver oxygen and other nutrients to the body. The two smaller chambers that are located at the top of the heart serve to force blood into the ventricles before it is pumped to the body. These chambers are called atria and they are smaller because they do not encounter as much resistance as the ventricles. Once the blood has filled the ventricles, the valves between each atrium and ventricle snaps shut in order to prevent the blood from flowing back into the atria. Damage to the valves can result in backward flow that creates audible murmurs when listening to the heart with a stethoscope. Once the valves have closed, an electrical signal travels along ventricular nerve pathways causing all of the cardiac cells in each chamber to contract together.
In order for blood to flow in the proper direction, the electrical impulse that signals contraction must start at the top of the atria and travel down through the ventricles. This ensures that the atria are able to force blood into the ventricles before the ventricles attempt to circulate blood to the rest of the body. The electrical pathway in the heart consists of two areas of tissue that are responsible for generating the pacemaker that determines when the atria and ventricles contract. The sinoatrial (SA) node is located near the top of the right atrium and it is responsible for creating the electrical impulse that depolarizes the atria as it travels along nerve branches that lead to the atrioventricular (AV) node. This initial wave of electrical conduct causes the atria to contract before the ventricles.
While the AV node is capable of setting the pace of ventricular contracting independent of the SA node, it typically complies with the pace that has already been established. As the electrical impulse passages through the AV node it encounters an anatomical structure known as the Bundle of His. This tissue is the point where the right and left bundle branches that travel through the ventricles originate from. These branches travel along their respective ventricles and conduct electrical impulses to smaller nerves that are called Purkinje fibers. These fibers conduct electrical signals directly to individual cardiac cells. Once the electrical impulse has traveled through the entire heart and the cells have contracted, the heart returns to its resting state and waits for the next signal to come along. During this period of rest, blood flows into the chambers in preparation for the next contracting.
In order to ensure that the appropriate amount of blood is circulated through the body, it is important for all of the cardiac cells in a specific chamber to contract together. The uniform contraction of cardiac cells is accomplished through the rapid propagation of electrical impulses through a unique system of cellular connections. When cardiac cells become damaged and die, they are no longer able to assist with the contractile process. These results in decrees in circulatory capacity and may lead to fluid buildup in the lungs. Patients who have suffered from a heart attack often have a difficult time breathing because of the fluid accumulation.