Abnormalities in the cardiac cycle.

Essay by urfwendA-, June 2003

download word file, 7 pages 5.0

The heart is evolutionary masterpiece. Yet like everything else in nature, it is not perfect and problems may arise. However before its flaws can be mentioned and analysed. It would be prudent to understand how the heart functions in the first place before going in depth into the various problems that might arise within the cardiac cycle. Of which a large number are covered under the various Arrhythmias, which can be divided into two major groups, ventricular arrythythmias and supraventricular arrythythmias. I.e., arrythythmias that occur in the ventricles and arrythythmias that occur above them. Subdivision is possible, with arrhythmias further divided into Disorders of impulse conduction and disorders of impulse generation.

The various and detailed events that take place with every heart beat is referred to as the "cardiac cycle". The top chambers of the heart are called the atria and the bottom chambers, the ventricles. A normal heart beat begins when the Sino-Atrial Node, located on the posterior wall of the right atrium.

The Sino-Atrial Node initiates the "wave of contraction" which results in the contraction of the atria. The Atrio-Ventricular Node delays the signal initiates by the Sino-Atrial node for about 0.15 seconds, permitting full atrial systole before ventricular systole. This ensures that the ventricles are filled before the ventricles contract. When the "wave of contraction" reaches the apex of the ventricles, ventricular contraction begins. As the pressure in the ventricles increases, the AV valves close. This prevents the backward flow of blood. With continued contraction of the ventricles, blood leaves the heart via the aortic and pulmonary valves into the aorta and pulmonary artery respectively. At the end of the cardiac cycle, all the chambers relax, the aortic and pulmonary valves close, preventing the blood from flowing back into the heart. Atria begin to fill up...