An improved dobutamine protocol for myocardial perfusion imaging

The central role of the nurse in process improvement relating to pharmacologic stress testing

Pharmacologic stress myocardial perfusion imaging is a noninvasive method for evaluating coronary artery disease in patients unable to exercise sufficiently to achieve a heart rate high enough to facilitate satisfactory imaging. The nuclear cardiology nurse is an invaluable member of the laboratory team that performs these tests. In this specialist role, the nurse must have a thorough knowledge of the different pharmacologic stress agents (dipyridamole, adenosine, regadenoson, and dobutamine) that can be used. This should comprise an understanding of their mechanisms of action, contraindications, drug-drug interactions, adverse effects, and administration protocols. By drawing on this knowledge, the nurse is able to verify that the right agent has been selected for each patient based on his/her medical history. The nurse also can help patients follow pretest instructions (such as withholding caffeine and certain medications) by explaining that the measures are necessary for a safe and successful procedure and that violation may result in test cancellation or postponement. On the day of the stress test, the nurse has an important role in safeguarding the patient as well as providing support and reassurance throughout the different stages of the examination. Responsibilities include explaining the entire procedure to the patients, notably, what they will be asked to do, the effect of the stress agent, the timing of each step, the adverse effects that they may experience, how any adverse events will be managed, and the importance of remaining still during imaging. This central role of the nuclear cardiology nurse in overseeing the practical aspects of the pharmacologic stress test has important implications in terms of optimizing the productivity and efficiency of their noninvasive cardiology laboratory and nuclear medicine department.

Comparison between dobutamine stress and combination of handgrip exercise with dobutamine stress in myocardial perfusion SPECT

AIM

We compared the efficacy, side effects of combined handgrip exercise and dobutamine stress with dobutamine stress alone during myocardial perfusion imaging in patients unable to exercise, and in whom vasodilator stress was contraindicated.

METHODS

We studied 126 consecutive patients (89 male, 37 female; mean age 63+/-8 years) referred for dobutamine stress myocardial perfusion SPECT. Patients were divided into Group A (n=63), who underwent only dobutamine stress and group B (n=63) who were subjected to combined handgrip exercise and dobutamine infusion. In group A patients, dobutamine was administered at a starting dose of 5 microg x kg(-1) x min(-1) increased to 10, 20 and 30 microg x kg(-1) x min(-1) to a maximum dose of 40 microg x kg(-1) x min(-1) at 3 min intervals until the target heart rate (THR, 85% of age predicted maximum heart rate) or other standard end point criteria were achieved. Group B patients were made to perform handgrip exercise 3 min prior to dobutamine infusion and continued throughout the administration of dobutamine.

RESULTS

In group A, 11 (17.6%) patients failed to achieve target heart rate even with infusion of maximum dose of dobutamine compared to two (3.2%) in group B (P<0.01). The mean dose of dobutamine infused in group A was significantly higher than in group B (36.2 vs. 23.5 microg x kg(-1) x min(-1), P<0.01). Minor non-cardiac side effects like anxiety; flushing and nausea were observed in 25% of group A and in 11% of group B (P<0.05). Cardiac side effects and arrhythmias in group A and B were observed in 22% vs. 14.3% and 9.5% vs. 1.6% respectively (statistically insignificant).

CONCLUSION

Combination of handgrip exercise with dobutamine reduces the total dose of dobutamine required to achieve target heart rate and likely to minimize the side effects associated with dobutamine.

Lack of correlation between coronary artery calcium and myocardial perfusion imaging

BACKGROUND

Coronary artery calcium (CAC) provides evidence of coronary atherosclerosis and has significant prognostic power. Although prior studies have documented a relationship between CAC and hemodynamically significant coronary artery stenosis, the results have not been conclusive.

METHODS AND RESULTS

We evaluated 126 consecutive patients who underwent electron beam computed tomography CAC scoring by use of the Agatston method and stress myocardial perfusion imaging (MPI) within 3 months of each other. The analysis revealed no correlation between absolute CAC score and age- and gender-adjusted CAC scores with MPI. Overall, 18% of patients had abnormal MPI results irrespective of their CAC.

CONCLUSION

CAC scoring and stress MPI should be thus considered complementary approaches rather than exclusionary in the evaluation of the patient at risk for coronary artery disease.

Value of definitive diagnostic testing in the evaluation of patients presenting to the emergency department with chest pain

The optimal diagnostic evaluation of patients presenting to the emergency department (ED) with chest pain but without myocardial infarction or unstable angina is controversial. We performed a prospective, nonrandomized, observational study of 1,195 consecutive patients presenting to the ED with chest pain but who had normal or nondiagnostic electrocardiograms and negative cardiac biomarkers. Patients (mean +/- SD age 61 +/- 15 years; 55% women) were admitted to the hospital and a standard protocol for evaluation and treatment was suggested. The use of stress myocardial perfusion imaging (MPI) or cardiac catheterization during their index hospitalization, and the 3-month incidence of coronary angiography, percutaneous cardiac intervention, coronary artery bypass surgery, re-presentation to our institution's ED for chest pain, myocardial infarction, or death were followed. Five hundred nine of 1,195 patients (43%) underwent provocative stress MPI during their index hospitalization; 37% had perfusion defects (predominantly ischemia). Fifty-six of 1,195 patients (4%) underwent cardiac catheterization without stress MPI for their primary diagnostic evaluation. Six hundred thirty of 1,195 patients (53%) had neither MPI or cardiac catheterization during their index hospitalization. During the 3-month follow-up period, patients with a normal stress perfusion study during their index hospitalization had fewer return visits (4%) compared with patients with abnormal perfusion studies (19%), those who underwent catheterization directly (16%), or patients with no initial diagnostic evaluation (15%) (p <0.001). In addition, patients who had a diagnostic evaluation during their index hospitalization had a lower incidence of either acute myocardial infarction (0.9% vs 2.1%) or death (0.4% vs 3.0%, p <0.001) in the 3-month follow-up period. Accordingly, we strongly advocate provocative stress MPI early after presentation for chest pain in all patients with risk factors for coronary artery disease.