Figure 3. Flow-chart outlining the criteria for the selection of treadmill, dipyridamole/ adenosine or dobutamine stress.

Contraindications to the use of dobutamine include acute coronary syndromes (recent MI or unstable angina), significant LV outflow obstruction (hypertrophic cardiomyopathy, severe aortic stenosis), arrhythmia (atrial tachyarrhythmia with uncontrolled ventricular response, complex ventricular ectopy), Wolff-Parkinson-White (WPW) syndrome and severe hypertension.

A flow-chart outlining the approach to selecting a stress technique is shown in Figure 3. A comparison of the various stress modalities with regard to indications, contraindications, mechanisms of action, stopping conditions and treatment of side effects is presented in Table 1.


In MPI, the injected radiopharmaceutical will be delivered to the myocardium in proportion to flow. There will be reduced tracer uptake in regions with reduced blood flow and increased tracer uptake in regions with increased blood flow. The perfusion imaging agents most commonly used are 201Tl-thallium chloride (201Tl), 99mTc-sestamibi and 99mTc-tetrofosmin. Table 2 compares the properties of 201Tl and the 99mTc-perfusion agents.

201Tl-thallium Chloride

Thallium is a metal with properties similar to potassium. The uptake of thallium is primarily an active process involving the Na-K ATPase pump. The extraction efficiency of thallium (i.e., the percentage of thallium extracted by the heart in one circulation through the coronary vessels) is 85%. In the physiologic flow range, uptake is proportional to flow. At higher flow rates the extraction efficiency decreases modestly (Fig. 4). While the initial distribution of thallium is proportional to flow, over the next few hours there is a net washout of activity from the heart so that the late distribution of thallium reflects the potassium pool (i.e., viable myocytes).

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