Last updated: December 27, 2020
The heart is a muscular organ that circulates blood throughout the body. The series of pressure changes that take place within the heart collectively form a cardiac cycle. The heart has four chambers; right and left atria and ventricles. The atrioventricular valves are present on the floor of atria which empty into ventricles. However, semilunar valves separate ventricles from the aorta and pulmonary trunk (i.e, great arteries). These pressure changes are caused by the movement of blood in the heart itself and the whole body. There are two main events in the cardiac cycle systole and diastole. Systole represents the ventricular ejection or contraction while diastole is characterized by ventricular filling1. These both occur in the heart but with very different pressures. When systole begins mitral and tricuspid valves are closed2. In this stage of the cardiac cycle, the ventricles contract and force the blood into the arteries. Systole ends with the closure of the aortic valve when the blood has been passed to the aorta from where it is sent to the rest of the body.
A cardiac conduction system is mainly a group of specialized muscle cells of the cardiac walls that send electrical signals or impulses to the cardiac muscles and as a result of these signals heart contracts. Cardiac muscles are tiny cells that form the cardiac electrical system which controls the timing of a person’s heartbeat by sending electrical impulses through these cells3. SA node and AV node are the main components of the heart’s conduction system. SA node (sinoatrial node) is a group of cells at the upper wall of the right atrium. The electrical signals start from the sinoatrial node then travel down through the heart triggering both atria (upper chambers of the heart) to contract. This signal consequently passes to the atrioventricular (AV) node through the bundle branches and Purkinje fibers which causes ventricles (lower chambers of the heart) to contract4. The sinoatrial node is considered as the pacemaker of the heart while the AV node is considered as a pacesetter. These signals produce an electrical that can be seen in a graphical form known as Electrocardiogram (EKG or ECG). In a healthy heart, the signals travel quickly allowing smooth contractions in an orderly fashion. Any disturbance in this electrical pathway causes arrhythmia (i.e irregular heartbeats).
Inferior position refers to a structure situated in, or towards the hind part. Referring to the body’s vertical axis, the parts located above the others are superior and conversely, the ones located below the others are said to be inferior5. The foot is located on the lower extremity. The foot is located inferior to the hip, conversely hip is superior to the foot. The foot is inferior to the knee. Distal position refers to the parts of the body farthest away from the point of origin or the trunk of the body. These are the parts of the body that are located away from the torso6. The foot is distal to the hip, such as the hand is located at the distal end of the forearm.
The blood pressure in the right atrium of the heart is termed as right atrial pressure (abbreviated as RAP). RAP reflects the ability of the heart to pump the blood into the arterial system and refers to the amount of blood returning to the heart. The stretch of the right ventricle depends upon the right atrial pressure, which determines the output of the right heart, consequently affecting the left heart output. Thus, RAP sets the cardiac output (i.e, the output of the left heart) which sets the RAP through interaction with the vasculature. Elevated RAP refers to the increased amount of blood returning to the heart than normal. Normal right atrial pressure ranges from 2–5mmHg. The increased pulmonary vascular resistance to the flow of blood leads to right heart failure and increased RAP. Cardiac catheterization is a procedure to measure right atrial pressure, independent of the risk for mortality. Right atrial pressure more than the normal range is considered to be elevated and needs to be treated by a medical professional7.
An exercise stress test is a cardiovascular stress test that uses exercise with blood pressure monitoring and electrocardiography (ECG). The exercise stress test is usually performed using a bicycle or treadmill with exercise protocol8. This test is performed under the supervision of a trained medical professional in a designated lab. Emergency resuscitation drugs and equipment are readily available. It is used to detect a decreased blood flow to the heart due to constriction and narrowing in the coronary arteries. A normal stress test results only show that there is no blockage in a significant coronary artery. The development of chest pain during an exercise has a great diagnostic impact. Discomfort and chest pain is usually caused by decreased blood flow to the heart9.