Exercise tolerance testing (ETT)
There is usually no problem at rest in early stages of vascular occlusion in patients with stable angina and the symptoms of obstructive coronary arteries disease often appear when patient is in state of an activity; so for a better evaluation of the heart, it is better to measure the effect of exercise on the heart so that if one segment is subject to the restriction of blood flow (ischemia) due to arterial stenosis (atherosclerosis) is better indicated. Sometimes stable angina is not discerned by ECGs at rest. ETT has largely resolved this ambiguity; in the other words ETT reveals the potential ECG changes through causing heart stress by exercise and physical activity.
Patient preparation before exercise test
The patient is required not to eat, drink or smoke 3 hours before the test. It is better to wear comfortable clothes and shoes. Do warm up but avoid doing intense physical activities. If you have diabetes, 1 hour fasting after eating a snack is enough and there is no need to change the amount of Insulin and be sure to inform your doctor. Note that some intervening medicines that prevent heart rate increase during exercise (such as digoxin, propranolol, metoprolol, atenolol, diltiazem, etc.) should be cut out under the supervision of your doctor at a given time interval before exercise test.
To do the test, first heart rate and blood pressure should be measured and recorded. ECG electrodes are placed on the patient's body and an initial ECG is recorded, then the patient goes on the treadmill to exercise (run). This device contains a moving and rolling rubber like a conveyor belt. The belt moves to the rear, requiring the patient to run at a speed matching that of the belt. Every 3 minute the slope and the speed of movement increases, based on predefined schedules. The patient's vital signs and ECG are controlled and evaluated in different levels so that ECG changes and waves are detected during exercise. According to patient's age and gender a certain exercise level and a maximum heart rate that the patient is to achieve is predefined and running continues to that level. If during the test heart rate reaches 85% of the desired heart rate proportionate to age and gender, the rest result would be interpretable. The desired testing end point usually reaches within 10-12 minutes of testing. By the way, if the patient feels discomfort or symptoms such as chest pain, shortness of breath, dizziness and severe headache appears or when ECG changes or abnormal blood pressure responses are seen, the exercise should end. People who, for whatever reason, are unable to do the exercise test, can choose radio-isotope scan (thallium stress test) or stress echocardiography instead. Scan and stress echocardiography are easier and more precise compared with exercise test but cost more.
The use of exercise testing
In general exercise test displays coronary arteries stenosis (narrowing of up to 60%) and helps the physician to decide whether or not to perform invasive procedures (such as angiography). This test is also used to evaluate functional strength (endurance exercise) of the people with heart failure or those who have suffered a stroke, in order to specify the amount and type of activities they are allowed to be involved in. Some exercise testing limitations are as follows: up to 25% of the cases may be falsely reported as negative (negative report despite coronary obstruction) and vice versa sometimes it may be falsely reported as positive. In addition, mild atherosclerotic narrowing is not diagnosed by exercise testing. Although atherosclerotic plaques are of less significance, sometimes they lead to heart attack.
Cases of exercise testing prohibition
Active ischemia, recent stroke or cases of ECG changes that are not interpretable are among the cases for which an exercise testing is prohibited. Also in case of patients, who for whatever reason, are unable to do the exercise test or exercise cause them harm. In these cases some inject able drugs are used to create stress, then heart imaging methods (stress echocardiography or nuclear medicine scans) are used.