Our heart beats continuously through out life. It modifies it rate and force of contraction according to needs. At rest heart beats slowly, but during exercise it beets faster to meet the increasing demand from contracting muscles for supplying more oxygen and nutrition to them.
Our heart gets it share of blood from coronary circulation. In normal heat, this coronary circulation is capable of supplying the heart both during rest and exercise i.e. if they are fully patent or and normal. During partial obstruction, blood supply to heart at rest may be OK, but during exercise may fall short and patient may develop heart attack during this period.
Patients who present to with chest pain, resting ECG/EKG is first taken, but in some patients, this ECG may be normal, because of above mentioned reasons, i.e resting coronary circulation may adequate and at exercise may be falling short. During such time doctors advise stress testing. To know about possibility of exercise induced angina.
During stress two things are of concern to get proper result one how to apply stress to patient and how monitor its response to know whether ischemia manifest during stress test
Limitation of stress testing from patient side
|Treadmill with ECG monitoring|
• Inability to walk
• Joint pain
• Old age
• Uncontrolled hypertension
Because of above problems, different methods of applying stress are in use, most common is treadmill. Patient who have lower limb problems can go arm bicycle ergometry, if patient is, unfit for any physical form stress then pharmacological stress is applied. Final goal of applying stress is to increase heart rate at least 80% maximum predicated heart for that age i.e. 220-age
ECG monitoring: This is the most common form of stress test , where ECG/EKG is monitored throughout the stress test and compared with rest. There are some limitation with test, as some resting ECG can cause problem in interpreting stress test .in such case other modalities are preferred.
Nuclear perfusion scan Radioactive dye is injected to blood and picture are taken of the heart for distrubution of dye. Depending on the amount of blood supply dye distrubution throughout the heart is noted. In areas of decreased perfusion, dye is less compared to well per-fused areas.
|Nuclear perfusion scan|
Stress Echocardiography: this modality is ultrasonic imaging of the heart. Area of the heart which suffer decreased perfusion will have decreased contraction so this can be imaged during exercise and signs of heart attack can be diagnosed.
Other uses of stress test are to know exact time some valvular heart surgeries. As these surgeries are to be done at exact point of time. Because they are high-risk surgeries and timing of surgery is very important to give maximum benefit to patient. About these issues we discuss in next post