Pharmacology, Part 4: Nuclear Cardiology

Which Test Should I Order for an Inpatient Evaluation of Cardiac Ischemia?

AbstractTesting for cardiac ischemia, or for the obstructive coronary artery disease (CAD) that causes cardiac ischemia, is common among hospitalized patients. Many testing options exist. Choosing an appropriate test can be challenging and requires accurate risk stratification. Two major categories of testing are available: stress testing (also known as functional testing) and anatomical testing. Stress testing evaluates specifically for ischemia and can be conducted with or without imaging. Anatomical testing visualizes the obstructive CAD that causes ischemia. This article reviews how to choose an appropriate test for the evaluation of cardiac ischemia in the inpatient setting, using case examples to illustrate the considerations involved.

How to assess nonresponsiveness to vasodilator stress

Myocardial perfusion imaging (MPI) is a powerful tool for the functional assessment of ischemia in patients with suspected or known coronary artery disease (CAD). Given that the diagnostic accuracy and prognostic value of MPI and post-test management are highly dependent on achieving an adequate stress vasodilatory response, it is critical to identify those who may not have adequately responded to vasodilator pharmacological stress agents such as adenosine, dipyridamole, and regadenoson. Caffeine, a potent inhibitor of the adenosine receptor, is a compound that can affect vasodilatory hemodynamics, result in false negative studies, and potentially alter management in cases of inaccurate test results. Vasodilator non-responsiveness can be suspected by examining hemodynamics, quantitative positron emission tomography (PET) metrics such as myocardial flow reserve (MFR), and splenic response to stress. Quantitative MFR values of 1-1.2 should raise suspicion for nonresponsiveness in the setting of normal perfusion, along with the absence of a splenic switch off. Newer metrics, such as splenic response ratio, can be used to aid in the identification of potential nonresponders to pharmacologic vasodilators.

Highly Sensitive Real-Time Monitoring of Adenosine Receptor Activities in Nonsmall Cell Lung Cancer Cells Using Carbon Nanotube Field-Effect Transistors

Adenosine metabolism through adenosine receptors plays a critical role in lung cancer biology. Although recent studies showed the potential of targeting adenosine receptors as drug targets for lung cancer treatment, conventional methods for investigating receptor activities often suffer from various drawbacks, including low sensitivity and slow analysis speed. In this study, adenosine receptor activities in nonsmall cell lung cancer (NSCLC) cells were monitored in real time with high sensitivity through a carbon nanotube field-effect transistor (CNT-FET). In this method, we hybridized a CNT-FET with NSCLC cells expressing A2A and A2B adenosine receptors to construct a hybrid platform. This platform could detect adenosine, an endogenous ligand of adenosine receptors, down to 1 fM in real time and sensitively discriminate adenosine among other nucleosides. Furthermore, we could also utilize the platform to detect adenosine in complicated environments, such as human serum. Notably, our hybrid platform allowed us to monitor pharmacological effects between adenosine and other drugs, including dipyridamole and theophylline, even in human serum samples. These results indicate that the NSCLC cell-hybridized CNT-FET can be a practical tool for biomedical applications, such as the evaluation and screening of drug-candidate substances.

A preliminary study of dobutamine myocardial flow reserve on 99mTc-Sestamibi CZT-SPECT

BACKGROUND

With improved resolution and sensitivity, the cadmium zinc telluride (CZT) detector measures myocardial blood flow (MBF) and myocardial flow reserve (MFR) via single photon emission computed tomography (SPECT). Recently, many studies have used vasodilator stress to obtain quantitative indexes. However, dobutamine used as a pharmaceutical stress has been rarely used to quantify myocardial perfusion using CZT-SPECT. Our study retrospectively analyzed the blood flow performance of ^99mTc-Sestamibi (^99mTc -MIBI) CZT-SPECT comparing dobutamine to adenosine.

PURPOSE

The study aims to explore whether dobutamine stress can be used for the myocardial perfusion quantitative analysis via CZT-SPECT as well as compare dobutamine MBF and MFR to adenosine.

METHODS

It was a retrospective study. A total of 68 patients with suspected or known coronary artery disease (CAD) were consecutively enrolled in this study. Thirty-four patients underwent dobutamine stress ^99mTc-MIBI CZT-SPECT. Another thirty-four patients underwent adenosine stress ^99mTc-MIBI CZT-SPECT. Patient characteristics, myocardial perfusion imaging (MPI) results, gated-myocardial perfusion imaging (G-MPI) results and quantitative analysis of MBF and MFR were collected.

RESULTS

In dobutamine stress group, stress MBF was significantly higher than rest MBF (median [interquartile range], 1.63 [1.46-1.94] vs. 0.89 [0.73-1.06], P < 0.001). In adenosine stress group, similar results were observed (median [interquartile range], 2.01 [1.34-2.20] vs. 0.88 [0.75-1.01], P < 0.001). When comparing the dobutamine and adenosine stress group, global MFR showed significant differences (median [interquartile range], the dobutamine group: 1.88 [1.67-2.38] vs. the adenosine group: 2.19 [1.87-2.64], P = 0.037).

CONCLUSION

MBF and MFR can be measured using dobutamine ^99mTc -MIBI CZT-SPECT. In small sample single-center study, there was a difference in MFR produced by adenosine and dobutamine within the suspected or the known CAD population.

Emergency pharmacology for the CT technologist

The scope of practice of the medical radiation practitioner demands knowledge and understanding of the indications, contraindications, warnings, precautions, proper use, drug interactions and adverse reactions of a variety of medications. The risk of patient deterioration or acute emergent event, particularly following contrast administration, makes the command of crash cart medications particularly important. This article explores the pharmacological principles of medications most likely to be required in a medical emergency in the medical radiation department and in particular by the computed tomography (CT) technologist. The article also outlines early warning signs to assist in identifying the emergent or deteriorating patient. The learning outlined is designed to equip medical radiation practitioners with the capacity to identify and respond to a medical emergency typical of the medical radiation department, and to respond to that situation with the appropriate use of emergency medications where appropriate. The ability of medical radiation practitioners to recognise and respond to (including the use of medicines) the deteriorating patient or circumstances of a medically urgent nature are key capabilities required to meet minimum standards for Medical Radiation Practice Board of Australia registration and National Safety and Quality Health Service standards.

Nicotine and Nicotine Replacement Therapy Use During Myocardial Perfusion Imaging

Background

Myocardial perfusion imaging (MPI) is commonly used to assess the presence and severity of coronary artery disease (CAD). A radiopharmaceutical is used before and after patients undergo either exercise-induced stress via a treadmill or medication-induced stress. While certain therapies that are known to influence the accuracy of results are avoided prior to conducting MPI, it is currently unknown whether nicotine and nicotine replacement therapy (NRT) should be avoided, even though they may have significant effects on coronary circulation.

Observations

Nicotine has been demonstrated to have both vasoconstrictive and vasodilatory properties. However, in patients with underlying CAD, vasoconstrictive properties appear to predominate and can allow the disease to appear more severe than it is during MPI. Similarly, NRT products may cause vasoconstriction but to a lesser degree given the lower concentration of nicotine present. Due to the lack of robust studies, the clinical impact of these findings on clinician diagnosis and patient management remains unclear.

Conclusions

Based on the available data, nicotine and NRT should ideally be avoided prior to MPI. The specific time frame in which they would be stopped before conducting MPI differs based on the pharmacokinetics of each product. More studies are needed to analyze the impact of nicotine and NRT on the accuracy of MPI using medication.

Pharmacology, Part 5: CT and MRI Contrast Media

Pharmacology principles provide key understanding that underpins the clinical and research roles of nuclear medicine practitioners. The scope of practice of the nuclear medicine technologist demands knowledge and understanding of indications, contraindications, warnings, precautions, proper use, drug interactions, and adverse reactions for each medication to be used. This article is part of a series that aims to enhance understanding of pharmacologic principles relevant to nuclear medicine. This article will build on the introductory concepts, terminology, and principles of pharmacology explored in the first 2 articles in the series. Specifically, this article will focus on the pharmacologic principles and adverse reactions associated with iodinated and gadolinium contrast media used in CT and MRI, respectively.