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There are three methods that KMH uses to achieve the optimal stress for myocardial perfusion imaging: exercise, Persantine or Dobutamine. Patients who have poor exercise tolerance, physical disability that limits their exercise, or other contraindications for exercise should be considered for pharmacological stress using Persantine or Dobutamine. For patients with left bundle branch block, Persantine is the stress of choice.
The standard procedure for pharmacological stress involves the use of Persantine, which is a vasodilator. For those patients in whom Persantine cannot be used (due to allergy, use of theophylline-based drugs, lung disease, COPD, low blood pressure, in addition to not being able to exercise), there is the secondary option of performing the pharmacological stress portion using Dobutamine. Dobutamine is a synthetic catecholamine that simulates physical activity for patients unable to exercise by increasing heart rate, blood pressure and myocardial contractility. The diagnostic accuracy of Dobutamine Cardiolite scans is similar to that of exercise and Persantine Cardiolite scans. It has also been shown to have similar prognostic value and ability of stratifying patients into high or low risk categories for future cardiac death or myocardial infarction.
Regardless of the method employed for stress, the imaging protocol remains the same. A set of images following the injection of Cardiolite will be performed at rest and after the stress test for comparison. Beta blockers MUST be discontinued 48 – 72 hours (depending on the half-life of the beta blocker) prior to Dobutamine Cardiolite scans. For example, for Metoprolol, discontinue the medication for 72 hours prior to the test. If you feel that it is clinically not safe to discontinue the beta blocker, or you do not wish to discontinue beta blockers for other reasons, then Dobutamine stress cannot be performed. A Persantine or Exercise Cardiolite scan should be considered instead.
The Dobutamine protocol usually involves 4 stages of infusion, each 3 minutes in length. Termination occurs when the patient has either achieved 85% of the age-predicted maximum heart rate or prematurely due to serious side effects. IF 85% of the target heart rate has not been reached at maximum infusion rate, IV Atropine may be given to further enhance the heart rate response. Potential side effects of Dobutamine include chest pain, hypotension, headache, dyspnea, flushing, palpitations or nausea. Treatments for adverse reactions include terminating the infusion (due to very short half-life), injection of a beta-blocker, the use of nitrates, injection of Diltiazem and other appropriate supportive therapy.
A written report will be sent to you upon completion of the test within 48 hours. Urgent results will be provided to you the same day.
Write in “Dobutamine Cardiolite Scan” on the KMH Cardiology Requisition Form. Your office or your patient may call to book an appointment (905-855-1860 or 1-877-564-5227) at any of the eight KMH Cardiology & Diagnostic Centres in south-central Ontario. Patients can visit www.kmhlabs.com for the location most convenient for them