Pharmacological stress test: Pharmacological stress test is a stress test using medications instead of the usual exercise stress test. This is done by giving medications to stress the heart rather than by exercise which is more often used to stress the heart for a test. Pharmacological stress test is considered for those who cannot exercise due to disability of the limbs or due to any other reason. Any stress test can be done only if the individual has reasonable medical fitness to undergo the test, as decided by the treating physician or supervising physician.

What medications can be used for pharmacological stress test?

Adenosine, dipyridamole and dobutamine are some of the medications which can be used for pharmacological stress test. Newer derivative of adenosine known as regadenoson have also been used. Adenosine, dipyridamole and regadenoson produces stress by dilating (increase the diameter) the non diseased blood vessels of the heart and diverting blood supply away from the diseased region (coronary steal!). Dobutamine increases the workload of the heart by increasing the contractile force of the heart and increasing the heart rate.

How is the response to stress assessed?

Response to stress is noted initially as an increase in heart rate when dobutamine is given, which progressively increases as the dosage is increased. Changes in the ECG in response to stress is continuously monitored. Changes in the contraction pattern of heart muscle can be noted by ultrasound imaging (dobutamine stress echocardiography). Normally the heart muscle contracts more vigorously in response to dobutamine. But a region of the heart muscle to which blood supply is reduced, contracts less vigorously as dobutamine dose is increased.

Nuclear scan can also be used to assess the contractile response to dobutamine, but is more expensive and not available in many centers.

What are the precautions for a pharmacological stress test?

General precautions for exercise stress test also applies to pharmacological stress test. Patient should be stable and unlikely to deteriorate much with the stress. All measures to counter any worsening should be available in the room where the stress test is being done. ECG and all vital parameters like blood pressure, heart rate and oxygen saturation should be continuously monitored. Emergency team back up may be needed in those who have borderline stability. In general those considered for pharmacological stress test are more likely to have other diseases than who undergo regular exercise stress test. Dobutamine stress echocardiography is becoming part of regular preoperative evaluation for older patients planned for liver transplantation. Such patients are likely to be much sicker than those coming for a treadmill test.