Correlation between hemodynamic changes and tomographic sestamibi imaging during dipyridamole-induced coronary hyperemia

Comparison of two dipyridamole infusion protocols for myocardial perfusion imaging in subjects with low likelihood of significant obstructive coronary artery disease

BACKGROUND

Myocardial perfusion imaging (MPI) with positron emission tomography allows accurate measurements of myocardial blood flow (MBF). Stress MBF thresholds have been proposed to provide diagnostic and prognostic information in different pathology. Most studies relying on dipyridamole use a 5-minute infusion protocol, while current guidelines recommend a 4-minute infusion. The purpose of this study is to compare the effects of different dipyridamole infusion times on stress MBF.

METHODS

The charts of 2,207 patients who underwent rubidium-82 MPI were retrospectively reviewed and 147 subjects with low likelihood of significant coronary artery disease (CAD) defined as calcium score = 0, body mass index < 45 kg·m-2, and summed stress score ≤ 3 were included. Of those, 65 were imaged with a 4-minute dipyridamole infusion (0.56 mg·kg-1) protocol and 82 with a 5-minute protocol (0.70 mg·kg-1).

RESULTS

Stress MBF (3.23±0.76 vs 3.02±0.71 mL·min-1·g-1, P = 0.09), myocardial flow reserve (2.70±0.67 vs 2.85±0.74, P = 0.20), and coronary vascular resistance index (30±10 vs 31±9 mmHg × g × min·mL-1, P = 0.38) were not significantly different between the two protocols. The 5-minute protocol was associated with higher prevalence of symptoms (92.7% vs 81.5%, P = 0.04) and greater decrease in systolic blood pressure (- 9 vs - 6 mmHg, P = 0.03).

CONCLUSIONS

The 4-minute and 5-minute dipyridamole infusion protocols produce comparable myocardial flow response, hemodynamic changes, and symptoms, in subjects with low likelihood of significant obstructive CAD.

Electrocardiographic changes after dipyridamole infusion in patients undergoing myocardial perfusion imaging

OBJECTIVES

Although the diagnostic and prognostic importance of perfusion defects has been clearly established, the meaning of the development and characteristics of electrocardiographic (ECG) changes during dipyridamole infusion is less well defined. This study tries to evaluate the prevalence and significance of ECG changes after dipyridamole infusion and their relation to ischemia in myocardial perfusion single-photon emission computed tomography (SPECT).

METHODS

Two hundred patients underwent 2-day dipyridamole stress/rest Tc-99m-sestamibi myocardial perfusion SPECT. Basal and post dipyridamole ECGs were analyzed. Myocardial perfusion images were interpreted visually and semiquantitatively.

RESULTS

New ECG changes were noted in 20.2% of cases and consisted of 1.1% T-wave flattening, 1.1% T-wave inversion and 14.8% ST depression and 4.2% psuedonormalization. Abnormal ECG changes were noted after dipyridamole infusion in approximately 27.7% of patients with and 14.3% of patients without reversible defect in myocardial perfusion SPECT. A new ST depression was noted in lateral leads in 72.2% of new ST changes. The mean post-dipyridamole heart rate increment in patients with reversible or partially reversible defects was significantly lesser than in patients with normal myocardial perfusion SPECT. In addition, the corrected QT interval (QTc) increment in patients with reversible defects was significantly more than in patients with fixed defects; however, there was no difference when compared with patients with no defects. Using linear regression model, the severity of ST depression and QTc increment were significant predictors of summed difference score. Sensitivity, specificity, and negative and positive predictive values of ST-segment depression for the diagnosis of ischemia were 20.2, 89.5, 60.7, and 58.4%, respectively.

CONCLUSION

The most common ECG change seen after dipyridamole infusion is ST-segment depression. The new ST-segment depression after dipyridamole infusion is highly specific for ischemia. Reversible defects are associated with a lesser increment in heart rate, whereas QTc increment and severity of ST segment depression were significant predictors of summed difference score.

Diagnostic efficacy of a low-dose 32-projection SPECT 99mTc-sestamibi myocardial perfusion imaging protocol in routine practice

BACKGROUND

99mTc-labeled tracers can provide better imaging quality than does TI for myocardial perfusion imaging (MPI). Nevertheless, a large study showed no significant difference in diagnostic efficacy, implying that image quality, though not optimal, may be still adequate for reliable interpretation. We thus proposed a suboptimal low-dose 32-projection single-photon emission computed tomography (SPECT) 99mTc-sestamibi (99mTc-methoxyisobutylisonitrile) MPI protocol and evaluated its diagnostic efficacy.

METHODS

A total of 1007 patients undergoing the proposed rest-stress MPI protocol were included in the study for analysis. Among them, 218 had coronary angiography, which was used as the 'gold standard' for evaluating sensitivity and specificity. The normalcy rate was obtained from 47 patients with a low cardiovascular risk. The injected dosage for 99mTc-methoxyisobutylisonitrile resting and dipyridamole stress imaging is 185 and 555 MBq, respectively, with an interval of about 2 h between the two injections. Most of the patients completed the whole MPI within 3 h.

RESULTS

Using this protocol, the sensitivity and specificity of the 218 patients with subsequent coronary angiography for determining coronary artery disease were 95 and 63%, respectively. The normalcy rate was 87%. Both the rest and stress images were adequate for confident interpretation.

CONCLUSION

The proposed low-dose 32-projection SPECT protocol has a diagnostic efficacy comparable with that reported in the literature, most of which used a higher dose and 64-projection SPECT, with additional benefits of lower radiation exposure, lower cost, and shorter study time.

Myocardial perfusion scintigraphy: the evidence

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

Irbesartan has a masking effect on dipyridamole stress induced myocardial perfusion defects

BACKGROUND AND AIM

The angiotensin II type 1 (AT1) receptor antagonist irbesartan is used for the treatment of hypertension, but its anti-ischaemic effect is not yet known. Our aim was to assess the effect of irbesartan administration on the diagnostic yield of 99mTc sestamibi single photon emission computed tomography (SPECT) in patients with coronary artery disease (CAD) after dipyridamole stress.

METHODS

Our study group consisted of 13 patients (11 men and two women; mean age, 53.3 +/- 10.6 years; body mass index, 26.9 +/- 3.3 kg x m(-2)) with angiographically documented CAD. All patients underwent SmTc sestamibi SPECT studies at rest, before (STRESS-1) and 2 weeks after irbesartan (150 mg daily) administration (STRESS-2) at dipyridamole stress. The extent and severity of defects were analysed by using visual and quantitative 99mTc sestamibi SPECT.

RESULTS

The mean summed stress score was significantly higher during the STRESS-1 study than the STRESS-2 study (13.2 +/- 7.4 vs. 11 +/- 7.4, P=0.003). The mean size of perfusion defects at stress was significantly larger for the STRESS-1 group than the STRESS-2 group (17.8% +/- 2.85% vs. 15.3% +/- 2.95%, P=0.01).

CONCLUSION

Our study showed that the AT1 receptor blocker irbesartan reduces the extent and severity of 99mTc sestamibi perfusion defects after dipyridamole stress in patients with CAD. Irbesartan may alter coronary blood flow reserve. The continued use of irbesartan before stress myocardial perfusion SPECT has a masking effect on stress induced myocardial perfusion defects. For this reason AT1 receptor blockers must be stopped before stress myocardial perfusion scintigraphic examinations.

Pharmacologic stress testing for coronary disease diagnosis: A meta-analysis

BACKGROUND

Although noninvasive pharmacologic stress tests are widely used, their relative performance is not clear. We compared the performance of pharmacologic stress tests combined with echocardiography or nuclear imaging for the diagnosis of coronary disease.

METHODS

We performed a regression meta-analysis of published data. We included studies published between January 1975 and June 1999 in which subjects underwent echocardiographic or single-photon emission computed tomography (SPECT) stress testing with adenosine, dipyridamole, or dobutamine for diagnosis of coronary artery disease. All subjects also underwent coronary angiography. Two independent reviewers abstracted population characteristics, technical factors, methodologic factors, and results and calculated test sensitivity and specificity.

RESULTS

Eighty-two studies met the inclusion criteria. The sensitivity of dipyridamole SPECT imaging, 89% (95% CI, 84%-93%), was higher than that of dipyridamole echocardiography, but the specificity of dipyridamole SPECT imaging, 65% (95% CI, 54%-74%), was lower than that of dipyridamole echocardiography. Dipyridamole and adenosine tests had similar sensitivities and specificities. The sensitivity of dobutamine echocardiography, 80% (95% CI, 77%-83%) was similar to that of dobutamine SPECT imaging, but dobutamine echocardiography had a higher specificity, 84% (95% CI, 80%-86%) than dobutamine SPECT imaging did.

CONCLUSIONS

The findings of our study can be used to guide the selection of the optimal pharmacologic stress test for each patient. Maximum sensitivity can be attained by use of a vasodilator combined with SPECT imaging. Maximum specificity can be attained by use of a vasodilator with echocardiography. The highest combination of sensitivity and specificity can be attained with dobutamine echocardiography.

Simultaneous assessment of function and perfusion during dipyridamole-handgrip Tc-99m sestamibi imaging in chronic coronary artery disease

The main goal of this work was to know the value of ventricular function in addition to perfusion Tc-99m sestamibi images in the assessment of coronary artery disease (CAD) when using dipyridamole (DIP) associated to isometric exercise. We analyzed 52 patients with suspected CAD; 40 of them had coronary lesions > or = 50% and 12 patients without CAD, conforming study and control groups, respectively. Twenty-eight patients had prior myocardial infarction. A two-day sestamibi protocol was employed with i.v. DIP-handgrip and rest injections, acquiring ECG-gated first pass and planar perfusion images. Sensitivity for perfusion images was 85% and specificity was 91.7%. There was no change between rest and DIP ejection fraction (EF) in controls. CAD patients presented a significant EF decrease with DIP (p: 0.0015). Patients with ischemia in perfusion images had larger EF decrease (p: 0.0001). For the analysis, an EF drop > or = 5% and any wall motion abnormality (WMA) were considered as having an abnormal response to DIP. CAD sensitivity improved significantly to 92.5% when adding EF drop and to 90% when adding WMA parameters, but specificity decreased to 75% with EF drop, and to 58.3% with WMA. In conclusion, first pass parameters from DIP-isometric exercise in addition to perfusion images are not a significant help in the assessment of CAD.