Coronary arteries

The cardiac muscle needs nutrients and oxygen, which are delivered by the cardiac vessels, also known as the coronary arteries. The left side of the heart has coronary arteries in front and behind it; the right side relies on just one artery.

Human heart valves are tissue-paper thin membranes attached to the heart wall that constantly open and close to regulate blood flow (causing the sound of a heartbeat). This flexing of the tissue occurs continually, withstanding about 80 million beats a year or five to six billion beats in an average lifetime. The heart has four valves, the mitral valve and tricuspid valve, which control blood flow from the atria to the ventricles, and the aortic valve and pulmonary valve, which control blood flow out of the ventricles.

The heart beats because the atria and ventricles contract rhythmically using low natural electrical signals that originate in the SA node , a network of nerves. From there, the signals spread through conductive tissue in the myocardium (the electrical conduction system) until they reach the heart’s most remote cells. The SA node, which triggers the heartbeat and controls the regular sequence of the individual phases, is often called “the body’s natural pacemaker” [2].

Ejection fraction (EF)

A measurement of the percentage of blood leaving the heart with each contraction. During each heartbeat cycle, the heart contracts and relaxes. When the heart contracts, it ejects blood from the two pumping ventricles. When relaxed, the ventricles refill with blood. No matter how forceful the contraction, the heart does not empty all the blood from a ventricle. The term “ejection fraction” refers to the percentage of blood that’s pumped out of a filled ventricle with each heartbeat.

The ejection fraction is usually measured only in the left ventricle (LV), the heart’s principal pumping chamber. An LV ejection fraction of 55 % or higher is considered normal. An LV ejection fraction of 50 % or lower is considered reduced.

The oxygen consumption of the whole body, representing the peripheral skeletal muscles rather than the myocardial muscles.

Aerobic capacity (VO2 max)

Measures the work capacity of an individual. As the exercise workload is increased, the VO2 increases in a linear fashion until it plateaus even with increased workloads.

Myocardial consumption (MVO2)

The actual oxygen consumption of the heart. It can be measured via the rate pressure product (RPP) since the heart rate and systolic blood pressure correlate well with the MVO2.

Metabolic equivalent (MET)

A resting metabolic unit where one MET = 3.5 mL O2 consumed per kilogram of body weight per minute.

EKG

An electrocardiogram, also called an EKG, or ECG, records the heart’s electrical activity. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the signal causes the heart to contract and pump blood. The process repeats with each new heartbeat. The heart’s electrical signals set the rhythm of the heartbeat. The EKG shows how fast the heart is beating, whether the heart rhythm is steady or irregular, and the strength and timing of electrical signals as they pass through each part of the heart [3]

Cardiac echocardiogram

An echocardiogram is a test that uses sound waves to create a moving picture of the heart. The picture is much more detailed than a plain x-ray image and involves no radiation exposure [4].

Exercise cardiac stress testing (ECST) is the most commonly used cardiac stress test. The patient exercises on a treadmill according to a standardized protocol, with progressive increases in the speed and elevation of the treadmill, usually at 3 min intervals. During the ECST, the patient’s electrocardiogram, heart rate, heart rhythm, and blood pressure are continuously monitored. If a coronary arterial blockage results in decreased blood flow to a part of the heart during exercise, certain changes may be seen in the EKG in addition to the response of the heart rate and blood pressure [5].

A thallium stress test is a nuclear imaging method that shows how well blood flows into the heart muscle, both at rest and during activity. An IV (intravenous line) is started, and a radiopharmaceutical, such as thallium, is injected into a vein. The patient reclines and waits for between 15 and 45 min. A special camera scans the heart and pictures how the radiopharmaceutical has traveled through the blood and into the heart. Patients then walk on a treadmill or pedal on an exercise machine. Blood pressure and heart rhythm via EKG are monitored, and with increased effort, when the heart is at maximal exertion, a radiopharmaceutical is again injected into the vein. After a waiting period, the camera again scans the heart and produces pictures. Comparing the initial and follow-up images allows an evaluation of potential heart disease onset or worsening [6].