Cardiac Stress Test

A cardiac stress test aids in assessing how the heart can cope during exercise, especially when the body need for oxygen puts extra demands on the heart. A cardiac stress test is called a graded test or exercise tolerance test, exercise stress test or exercise electrocardiography. It helps to primarily evaluate the heart and vascular systems during the exercise. In fact, the American Heart Association has recommended the Cardiac stress test (EKG treadmill in particular) as the first choice to be tried on patients with medium risk of coronary heart disease and who exhibit certain risk factors of smoking, family history of coronary stenosis, high blood pressure, and high cholesterol.

• It helps to determine whether coronary arteries are clogged or blocked.
  
• To find the cause of chest pain.
  
• To assess the heart's capability after a heart attack or heart surgery.
  
• To discover the presence of any heart disease.
  
• To set limits on a person's exercise.
  
• To detect arrhythmia, that is extra heart beats, during the exercise.
  
• To assess the capacity of medicine used to control chest pain or extra beats during exercise.

The cardiac stress test can be done in a clinic or a hospital. The patient may be asked to exercise using a bicycle, treadmill or arm ergometer. The patient is attached to an ECG machine. The blood pressure cuff is placed on any one arm. The patient's heart is usually monitored using a 12 - lead EKG or ECG machine. A heart monitor may be used during and after exercise. After a baseline ECG is obtained, the patient begins to perform a low level of exercise, either by walking on a treadmill or pedaling on a stationary bicycle.

At each stage of the exercise, the pulse, the blood pressure and ECG are recorded along with any symptoms that the patient may be experiencing.

The level of exercise is gradually increased until the patient cannot keep up any longer because of fatigue or until symptoms like chest pain, shortness of breath or lightheadedness prevent further exercise. The goal of this stress test is to diagnose the presence or absence of coronary artery disease. In a sub maximal stress test, the patient exercises only until a pre-determined level of exercise is attained. These tests are used in patients with known coronary artery disease, to measure whether the patient can perform a specific level of exercise with relative safety.

The side effects of a cardiac stress test also include palpitation, chest pain, and shortness of breath, headache, nausea and fatigue. The hypertension caused by stress testing is always considered abnormal and it may lead to severe coronary disease. In stress tests, false positive results are not uncommon. There can be occasions when the patient's ECG changes could suggest ischemia, even in the absence of coronary artery disease. Similarly, in stress test, false negatives are also not uncommon. In some patients, no significant ECG changes will be seen even in the presence of coronary artery disease. Presently, a new concept called nuclear perfusion study is added to the stress test. This factor has helped to minimize the limitations and improve the diagnostic capability of stress tests.

Stress echocardiography

Cardiac stress determination or stress echo is done to investigate underlying coronary artery disease. It helps determine blood flow and the pumping rate of the heart. The preliminary tests performed before stress echocardiography include the assessment of ventricular function, wall motion thickness and aortic root. These tests indicate cardiac conditions along with ischemic heart disease and other cardiac conditions. Stress echocardiography is recommended over pharmacological assessment, because of its advantage in describing the cardiac performance during the test through images. Pictures are taken of your heart before and after exercise to check the efficiency of the heart.

Stress echocardiography is carried out on a treadmill or by a bicycle in a supine position. A work load of 25W is given initially with subsequent rise in intensity. Stress echocardiography also determines the aerobic capacity. The use of bicycle exercise has an advantage as it gives the Doppler information of the test. This provides information about the blood flood through the heart's pumping chambers and valves. Stress echocardiography has been extensively used in the risk evaluation for coronary artery disease even in patients who are asymptomatic. The usual protocol followed for the test is fasting for at least three hours before the test is performed.

Before commencing the stress test, your blood pressure and electrocardiogram (EKG) is also done. The stress echo is taken during the rest phase, stress phase and a repeat when the heart is still beating fast. Pregnant women are not advised to undergo this test. You will be connected to an ECG monitor to record the heart activity through small electrodes. Stress echocardiography is beneficial for physicians to determine the treatment options for asymptomatic conditions pertaining to coronary artery disease. It also aids the detection of angina or chest pain in the patients and also conditions like cardiomegaly and myocardial infarction.

Adenosine Stress Test

Coronary artery disease is diagnosed by many stress tests such as echocardiography and treadmill. They determine cardiac activity with details of blood circulation and blood pressure. The stress tests are measured based on activity of the heart when subjected to exertion. The coronary arteries are examined for accumulation of plaque through triglyceride estimation and various other tests. In many scenarios the results of stress test are correlated with the laboratory analysis to identify the underlying conditions such as atherosclerosis.

Stress examinations of the heart also help in the detection of ischemia and arrhythmia. The adenosine stress test is done to identify underlying coronary artery disease. Adenosine helps in inducing the vasodilation of the coronary artery directly through the activation of the A2A receptor. The myocardial blood volume increases to a greater extent through this activity. The stenotic coronary arteries display an attenuated hyperemic response in the myocardial region of the heart. The radio tracer for the identification of coronary artery disease undergoes heterogeneous distribution. Adenosine is an endogenous nucleoside predominantly produced in the arterial vascular region. Its action is mediated through the G protein coupled adenosine receptors.

Methodology of adenosine infusion

The adenosine infusion is administered at a rate of 140 mcg/kg/min. The echocardiogram is taken by attaching twelve leads. The values of ECG are taken every minute. Along with these procedures, the blood pressure is consistently monitored for stability during the entire procedure of adenosine stress testing.

A2A receptor protein plays a significant role in the regulation of inflammatory response and immune response. A2A agonists act as effective catalysts in the identification of various diseases such as myocardial infarction and infectious diseases. These receptors help in the reduction of tissue damage.

Patient information and risk factors

The patient is advised not to consume any solid food. Water and juices are allowed prior to the procedure. The nuclear technologist injects the cardiolite and adenosine into the blood stream through an intravenous line. The cardiolite is administered to capture the cardiac images.

Water is given to patients before the start of the imaging procedure through the induced cardiolite. Adenosine is introduced through the IV line after acquiring the resting images. Anticipated side effects of adenosine are generally nausea, angina, shortness of breath and flushing. Most of these side effects are monitored by the technicians. The side effects are usually short lived. A second round of cardiolite is administered after the adenosine to acquire the second set of images. In order to reduce the side effects, patients are advised to walk on the treadmill. The entire procedure lasts for a period of two and a half hours. A comparative account is made of both sets of images at resting stage and also during stress (exercise induced). Patients are advised to take fluids preferably juices after the procedure.

The adverse effects of adenosine stress test include wheezing, hypotension with a systemic hypotension of less than 80 mm of hg, second degree heart block and cyanosis. Pregnant and lactating women are not advised to undergo adenosine stress test because of radio tracers. Incidences of hypersensitivity to adenosine have also been reported. Although adenosine stress is pharmacologically recommended for myocardial stress, one of the predominant side effects during the procedure is myocardial infarction.