Pharmacologic stress perfusion imaging with adenosine: role of simultaneous low-level treadmill exercise

The Effect of Monitored Walking on Extracardiac Intestinal Activity in Myocardial Perfusion Imaging

Various techniques have been used in attempts to reduce interfering gastrointestinal activity in myocardial perfusion imaging (MPI); however, these approaches have yielded inconsistent results. The goal of this study was to investigate the efficacy of monitored walking, a previously unexplored technique, in reducing subdiaphragmatic activity-related artifacts during pharmacologic stress 99mTc-tetrofosmin MPI with SPECT to improve the overall image quality. Methods: The study included patients who underwent MPI with pharmacologic stress. They were given a step counter immediately after the radiotracer injection and were randomized into a group A, with a request to walk at least 1,000 steps before imaging, and a group B, with no specific instructions about walking. The reconstructed SPECT images were assessed visually. Moderate and severe levels of subdiaphragmatic tracer activity were considered relevant for the interpretation of the scans. Additionally, myocardial and abdominal activity was semiquantitatively assessed on raw planar images, and the mean myocardium-to-abdomen count ratios were calculated. Results: We enrolled 199 patients (95 patients in group A and 104 patients in group B). Clinical characteristics did not differ significantly between the 2 groups. Patients in group A walked more steps than patients in group B (P < 0.001), but there were no differences in the proportion of accepted scans between the 2 groups (P = 0.41). Additionally, there were no differences in the proportion of relevant subdiaphragmatic activity between the groups (P = 0.91). The number of steps did not impact the acceptance rate (P = 0.29). Conclusion: A higher number of steps walked during the waiting period between pharmacologic stress and acquisition does not affect subdiaphragmatic activity-related artifacts or the proportion of accepted scans after pharmacologic stress. However, pedometer use and clear instructions motivate patients to walk while awaiting imaging. Larger studies are required to compare a higher-step-count group with a sedentary control group to assess the influence of walking on gastrointestinal artifacts in MPI.

Clinical experience with regadenoson SPECT myocardial perfusion imaging: insights into patient characteristics, safety, and impact of results on clinical management

The Henry Ford Hospital (HFH) regadenoson (REG) registry includes patients with a variety of comorbidities allowing for the evaluation of outcomes in a large, unselected population. Using a database of electronic medical records and nuclear cardiology reports, patients aged > 18 years who underwent REG-facilitated single-photon emission computed tomography (SPECT) testing at HFH between January 2009 and August 2012 were identified. The primary objective was to describe the clinical and demographic characteristics of patients who had undergone REG only vs REG WALK (REG + low-level exercise) SPECT. A total of 2104 patients were included in the analysis (mean age 65.3 years; 50% women; 51% African American, 43% Caucasian). For the REG only (n = 1318) and REG WALK (n = 786) cohorts, SPECT was abnormal in 37% of patients (REG only, 39%; REG WALK, 34%; P < 0.01). No differences in diagnostic modalities or interventions in 90 days after SPECT were observed. Immediate safety analysis showed no deaths 48 h after REG SPECT testing. Although they guide invasive therapy, abnormal scans do not automatically lead to invasive testing. This demonstrates the focus on initial medical management, which reflects the existing evidence of initial goal-directed medical management of stable coronary disease.

Short-duration, submaximal intensity exercise stress combined with adenosine triphosphate decreases artifacts in myocardial perfusion single-photon emission computed tomography

BACKGROUND

Myocardial perfusion single-photon emission computed tomography (SPECT) imaging with stress is a useful examination for detecting coronary artery disease. Since the presence of artifacts is remaining challenges, we aimed to define the minimum intensity of low-grade exercise stress levels combined with drug stress to reduce undesired artifacts and their related factors.

METHODS

We divided patients with suspicious coronary artery disease into 4 groups as follows: group A, adenosine triphosphate (ATP) for 6 min; group A + 25 W, ATP + 25 W exercise for 6 min; group A + 35 W, ATP + 35 W exercise for 6 min; group A + 45 W, ATP + 45 W exercise for 6 min) and enrolled only those whose summed stress scores were < 3. Undesired artifacts were evaluated on the basis of heart-to-liver activity (H/L) ratio and heart-to-10 pixels below the heart (H/below the H) ratio.

RESULTS

The logarithmic values of H/L and H/below the H ratios were significantly higher in groups A + 35 W and A + 45 W than in group A (p < 0.05, each). In all the patients, the logarithmic values of H/L and H/below the H ratios positively correlated with the increment of rate pressure product (RPP, p = 0.002 and p = 0.005, respectively) after stress in the univariate analysis. The left ventricular end-diastolic volume (LVEDV) after stress (p = 0.002) negatively correlated with the logarithmic value of H/below the H ratio, but not H/L ratio. Although the increment of RPP was independently associated with the logarithmic values of both H/L (p = 0.001) and H/below the H ratios (p = 0.005), LVEDV was also independently associated with the logarithmic value of H/below the H ratio (p < 0.001) in multivariate regression analysis under adjusting with age and sex.

CONCLUSION

ATP plus ≥35 W exercise stress for 6 min was useful for reducing undesired artifacts after stress in myocardial perfusion SPECT. LVEDV after stress in addition to the increment of RPP was independently associated with the H/below the H ratio, but not the H/L ratio.

Trials and Tribulations of Assessing New Imaging Protocols: Combining Vasodilator Stress With Exercise

Among all patients referred for stress myocardial perfusion imaging (MPI), a substantial proportion in contemporary practice cannot exercise. Another group of patients are those who are thought to be able to achieve an adequate workload with treadmill (or bicycle) exercise but do not achieve at least 85% of maximum predicted heart rate without developing symptoms. There has been substantial interest and literature on the adjunctive use of vasodilator stress during the same visit to generate best-quality results for patients who do not exercise adequately. Current American Society of Nuclear Cardiology Guidelines recommend the possible use of vasodilator stress agents to supplement exercise in those patients who do not achieve target heart rate. However, optimal timing of administration is not clear. Herein, we summarize literature to date on the combination of vasodilator and exercise stress testing in light of the recently published Exercise to Regadenoson in Recovery Trial (EXERRT).

A Comparison of Iterative Reconstruction and Prone Imaging in Reducing the Inferior Wall Attenuation in Tc-99m Sestamibi Myocardial Perfusion SPECT

Objective:

Prone positioning, iterative reconstruction (IR-OSEM) and electrocardiography (ECG) gating have been demonstrated to improve the specificity of myocardial perfusion SPECT (MPS) in the diagnosis of coronary artery disease.

Methods:

The gated supine and prone MPS images of 45 patients were reconstructed with both IR-OSEM [supine (SIR) and prone (PIR)] FBPs [supine (SFBP), prone (PFBP)] for comparison. Perfusion, wall motion (WM) and wall thickening were also interpreted semi-quantitatively. Two groups were generated as those with normal or abnormal findings. Segmental myocardial tracer uptake values were noted from four of the reconstructed images from 17 segment model of bullseye.

Results:

The difference between mean values and the standard deviations of the % tracer uptakes of inferior wall segments were statistically significant in all images. The normalcy rates were highest in PIR images, followed by PFBP and SIR images. The number of patients with any perfusion abnormality were 42, 12, 32, and 6, in SFBP, PFBP, SIR and PIR images, respectively. The six patients with perfusion abnormality in PIR images were re-evaluated with rest images and were diagnosed with a fixed perfusion defect. There was positive correlation between WM and either PFBP or PIR images. Sixteen patients’ WM were evaluated as abnormal while only 6 patients’ perfusions were abnormal in PIR.

Conclusion:

Prone imaging in addition to a supine perfusion SPECT improves imaging quality of the inferior wall, especially when reconstructed with iterative methods. If prone imaging can not be performed, ECG-gating can also be used as a beneficial method.

The EXERRT trial: "EXErcise to Regadenoson in Recovery Trial": A phase 3b, open-label, parallel group, randomized, multicenter study to assess regadenoson administration following an inadequate exercise stress test as compared to regadenoson without exercise for myocardial perfusion imaging using a SPECT protocol

BACKGROUND

This study assessed the non-inferiority and safety of regadenoson administration during recovery from inadequate exercise compared with administration without exercise.

METHODS

Patients unable to achieve adequate exercise stress were randomized to regadenoson 0.4 mg either during recovery (Ex-Reg) or 1 hour after inadequate exercise (Regadenoson) (MPI1). All patients also underwent non-exercise regadenoson MPI 1-14 days later (MPI2). The number of segments with reversible perfusion defects (RPDs) detected using single photon emission computerized tomography imaging was categorized. The primary analysis evaluated the majority agreement rate between Ex-Reg and Regadenoson groups.

RESULTS

1,147 patients were randomized. The lower bound of the 95% confidence interval of the difference in agreement rates (-6%) was above the -7.5% non-inferiority margin, demonstrating non-inferiority of Ex-Reg to Regadenoson. Adverse events were numerically less with Ex-Reg (MPI1). In the Ex-Reg group, one patient developed an acute coronary syndrome and another had a myocardial infarction following regadenoson after exercise. Upon review, both had electrocardiographic changes consistent with ischemia prior to regadenoson.

CONCLUSIONS

Administering regadenoson during recovery from inadequate exercise results in comparable categorization of segments with RPDs and with careful monitoring appears to be well tolerated in patients without signs/symptoms of ischemia during exercise and recovery.

Chronotropic response to vasodilator-stress in patients submitted to myocardial perfusion imaging: impact on the accuracy in detecting coronary stenosis

AIMS

A lower heart rate response (HRR) during vasodilator MPI has been shown to have a relevant adverse prognostic impact. We sought to evaluate the interaction among individual HRR to vasodilator stress and myocardial perfusion imaging (MPI) accuracy in patients with suspected ischemic heart disease (IHD).

METHODS AND RESULTS

One hundred and sixty-five consecutive patients were submitted to vasodilator-stress MPI on a cardiac camera equipped with cadmium-zinc-thelluride detectors and coronary angiography. A coronary stenosis >70 % was considered significant. In every patient, the summed difference score (SDS) was computed from MPI images. Patients were categorized according to the tertiles of the distribution of individual HRR during dipyridamole: "Group 1" (HRR < 8 bpm; lowest tertile); "Group 2" (8 ≤ HRR ≤ 12 bpm; middle tertile); "Group 3" (HRR >12 bpm; highest tertile). Significant coronary artery disease (CAD) was present in 102 (62 %) patients. In the overall population, MPI showed a significant accuracy (AUC: 0.81, 95 % CI 0.74-0.86; p < 0.001) in unmasking the presence of significant coronary stenosis. Interestingly, in patients with a blunted HRR during dipyridamole ("Group 1") MPI showed a significantly lower sensitivity (68 %) in detecting CAD than in those with a higher HRR ("Group 3") (91 %, p = 0.007), despite a preserved specificity (76 % vs 77 %, P=NS). Similarly, the correlation among CAD extent and post-stress LV functional stunning was limited to "Group 3" patients, while it disappeared in those with blunted HRR.

CONCLUSIONS

In patients with suspected IHD, MPI sensitivity is strongly influenced by the magnitude of patient heart rate increase to the pharmacologic stressor, suggesting an interaction among blunted HRR and lower accuracy in unmasking CAD.

Comparison of Tc-99m tetrofosmin myocardial perfusion scintigraphy and exercise F18-FDG imaging in detection of myocardial ischemia in patients with coronary artery disease

BACKGROUND

Direct ischemia imaging with F18-FDG can potentially overcome many limitations of SPECT-MPS inherent to "cold imaging". We compared SPECT-MPS with exercise F18-FDG PET in detection of ischemia in patients with suspected CAD.

METHODS

45 patients with clinical suspicion of CAD without the history of myocardial infarction were prospectively included. All patients underwent Tc-99m tetrofosmin SPECT-MPS and exercise F18-FDG PET imaging within 7 days of SPECT-MPS, and both modalities were compared with coronary angiography for detecting ischemia.

RESULTS

27 patients had an abnormal coronary angiography (at least one coronary artery with stenosis >50%). Exercise F18-FDG performed better than SPECT-MPS in LAD and LCX territory with comparably good performance in RCA territory. Exercise F18-FDG performed better in single-vessel disease and equally good in multi-vessel disease compared to SPECT-MPS. Performance of exercise 18F-FDG study was significantly better than SPECT-MPS (P = .0014) in the analysis of the 81 vascular territories in the 27 patients with abnormal coronary angiography. Performance of exercise F18-FDG was significantly better than SPECT-MPS in detecting ischemia in suspected CAD patients.

CONCLUSION

Exercise F18-FDG imaging is a potentially useful ischemia imaging modality which offers the advantages of direct ischemia imaging in CAD patients.

Is regadenoson an appropriate stressor for MPI in patients with left bundle branch block or pacemakers?

BACKGROUND

Patients with LBBB or ventricular pacemaker undergoing MPI are at risk for false positive MPI results in the setting of an elevated heart rate (HR) with exercise or dobutamine stress. The areas of increased apparent ischemia are typically the LAD and septal territories.

METHODS

In a subanalysis of the ADVANCE MPI 1 and 2 studies, perfusion on an initial adenosine and a second MPI study with regadenoson or adenosine was compared by visual and quantitative analysis. Among 2,015 patients, 64 had LBBB and 93 had pacemakers. The hemodynamic response during the second scan was compared in those with and without LBBB and PM.

RESULTS

Following regadenoson, peak HR in the LBBB group increased by a mean of 25.4 compared to 15.3 bpm following adenosine (P = .0083). In the pacemaker group HR was blunted, 11.8 and 8.1 following regadenoson and adenosine, respectively (P = .1262). However, the visually assessed summed difference score and the quantitatively assessed extent of ischemia for the LAD and septal territories and the entire LV did not differ between the initial adenosine and subsequent regadenoson scans.

CONCLUSIONS

The significant increase in HR observed with regadenoson compared to adenosine did not translate into greater perfusion defects in the LAD or septal territories in patients undergoing regadenoson stress.

Diagnosing CAD: additional markers from myocardial perfusion SPECT

Over the past decades, stress/rest myocardial perfusion SPECT (MPS) has been utilized as a standard modality for the diagnosis, risk stratification and prognostic assessment of coronary artery disease (CAD). In addition to the perfusion information, MPS can also provide functional information of the left ventricle, including volume, ejection fraction, wall motion and dyssynchrony. This article introduces the incremental value of these non-perfusion parameters as markers and prognosticators of CAD.

Left ventricular functional changes after adenosine vasodilator stress evaluated by gated single-photon emission computed tomography

OBJECTIVES

Gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging is useful in assessing left ventricular (LV) myocardial perfusion and function. This study evaluated the LV functional changes after adenosine vasodilator stress, using gated SPECT.

METHODS

The study population consisted of 70 patients who underwent adenosine-mediated stress and rest SPECT. All patients underwent coronary angiography. Semi-quantitative assessment of perfusion was analyzed and produced the summed rest score (SRS), the summed stress score (SSS) and the summed difference score (SDS). The global LV function parameters [ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV)] and regional LV function [the summed motion score (SMS) and the summed thickening score (STS)] were quantified by gated SPECT.

RESULTS

Patients were divided into 2 groups: group 1 comprised 16 patients with worsening of LVEF (LVEFrest-LVEFado ≥5%), and group 2 comprised the other 54 patients. Compared with group 2, patients in group 1 had a significantly higher SSS and SDS (9.1 ± 6.8 vs. 5.6 ± 4.5 and 6.6 ± 3.8 vs. 3.6 ± 4.0, respectively; p < 0.05) and the severity of coronary artery stenosis was more serious (p < 0.05).

CONCLUSION

Worsening of LVEF after adenosine-induced vasodilator stress, as shown by (99m)Tc-MIBI gated SPECT, is a valuable nonperfusion marker of significant CAD.

A strategy of symptom-limited exercise with regadenoson-as-needed for stress myocardial perfusion imaging: a randomized controlled trial

BACKGROUND

Ambulatory patients with uncertain functional capacity may benefit from combined exercise and vasodilator stress protocols for myocardial perfusion imaging (MPI). The safety and MPI image quality with regadenoson administered during symptom-limited exercise have not been prospectively evaluated.

METHODS AND RESULTS

A total of 140 patients (mean age 61 years, 48% female) referred for exercise with vasodilator stress MPI were randomized 2:1 to a strategy of exercise with regadenoson-as-necessary (Ex-Reg, n = 96) or dipyridamole with exercise (Dip-Ex, n = 44) after Duke Activity Status Index (DASI) scoring (median score 28 vs 24, P = .09). Ex-Reg subjects commenced treadmill exercise and regadenoson was administered only if the subject was unable to reach standard endpoints. Dip-Ex subjects received dipyridamole prior to symptom-limited exercise. Hemodynamics were recorded throughout. Subjects completed symptom questionnaires and MPI image quality was assessed by blinded read. Ex-Reg subjects were more likely to achieve ≥85% age-predicted maximum heart rate than Dip-Ex subjects (57% vs 32%, P < .01). Only 50% of subjects meeting inclusion criteria and randomized to Ex-Reg required regadenoson and none had symptomatic hemodynamic changes. Severe side effects or adverse events occurred in 16% of Ex-Reg and 24% of Dip-Ex subjects (P = .12). MPI image quality was "good" or "excellent" in 88% of Ex-Reg subjects and 86% of Dip-Ex subjects (P = .33).

CONCLUSION

A strategy of exercise with regadenoson-as-needed for MPI offers similar safety and side effect profile with similar image quality compared to dipyridamole with exercise, with reduced pharmaceutical use.

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.

The impact of adenosine pharmacologic stress combined with low-level exercise in patients undergoing myocardial perfusion imaging (BIWAKO adenosine-Ex trial)

BACKGROUND

The combination of adenosine infusion with low-level exercise has become a common approach for inducing stress during stress myocardial perfusion imaging (MPI). We investigated stress MPI performed by combined low-level exercise and adenosine infusion. This combined protocol can decrease adverse reactions and reduce the effect of scattered rays from the liver.

METHODS AND RESULTS

Subjects were clinically referred for a 53-min rest-stress Tc-99m Sestamibi MPI procedure using BIWAKO PROTOCOL. Ninety-eight patients (44.5%) underwent adenosine infusion with ergometer exercise testing and 122 patients (55.5%) underwent adenosine infusion without exercise testing. We evaluated the liver/heart (L/H) uptake ratio, background activity in the upper mediastinum, and adverse reactions.

RESULTS

The L/H ratio and background activity were lower in the adenosine-exercise group than in the adenosine-non-exercise group (1.8 ± 0.54 vs. 2.1 ± 0.62, P < 0.0056; 43.1 ± 12.2 vs. 61.5 ± 15.4, P < 0.0001). The adenosine-exercise group had fewer adverse reactions than the adenosine-non-exercise group (11.2 vs. 19.7%). All of the adverse reactions were minor, with the exception of severe back pain in one case. The incidence of adverse reactions in our study was lower than that in previous studies for unknown reason.

CONCLUSION

Adenosine infusion in combination with low-level exercise seems to result in higher-quality images and fewer adverse reactions than adenosine infusion without exercise. The combined protocol decreases adverse reactions and improves the quality of myocardial perfusion images by decreasing background activity.

[Study of efficacy and safety of pharmacological stress tests in nuclear cardiology]

BACKGROUND/AIM

Treadmill test combined with myocardial perfusion scintigraphy (MPS) is a commonly used technique in the assessment of coronary artery disease. Many patients who cannot adequately perform exercise stress testing may nevertheless undergo pharmacological tests, most commonly with the vasodilator agents (adenosine and dipyridamole), as well as the positive inotropic agent dobutamine. Patients undergoing vasodilators stress testing with either dipyridamole or adenosine also perform simultaneous low-intensity exercise. The aim of this study was to compare various pharmacological stress tests alone or in combination with low intensity exercise as preparation for MPS in regard to incidence of adverse effects, quality of diagnostic image and the acquisition initial time.

METHODS

A total of 2 205 patients underwent pharmacological stress tests. Pharmacological stress test with adenosine was applied in 493 patients. In 405 of them we performed concomitant low level exercise (50 W) by bicycle ergometar (AdenoEX). In 88 of them we performed adenosine abbreviated protocol (AdenoSCAN). In 1 526 patients we performed pharmacological stress test with dipyridamole. In 871 of them we performed concomitant low level exercise (50 W) by bicycle ergometar (DipyEX), and in 775 we used only dipyridamole protocol (DipySCAN). In 186 patients we used pharmacological stress test with dobutamine. We followed side effects of adenosine, dipyiridamole and dobutamine, compared results between protocols with concomitant low level exercise and vasodilatators only. We also compared image quality, and suggested time of acquisition after stress test.

RESULTS

We found numerous side effects especially with adenosine, but these effects were short-lived and not required active interventions. Benefit with concomitant exercise in booth AdenoEX and DipyEX included decreased side effects (AdenoEX vs AdenoSCAN 620% vs 87%, respectively, and DipyEX vs DipySCAN 37% vs 59%, respectively) improved safety and patients tolerance, improved target-to-background ratios because of less subdiaphragmal activity, and earlier acquisition time. Because of producing a lot of arrhythmias (in 49% of patients) dobutamin was considered a last choice for pharmacological stress testing.

CONCLUSION

Safety and efficacy of vasodilatators (adenosine, dipyridamole) pharmacological stress tests are good, but with concomitant exercise even better. The safety and efficacy of adenosin are better than those of dipyridamole. AdenoEX protocol provides good safety and patients tolerancy. In light of these benefits we recommend AdenoEX whenever possible. Dobutamine is the last pharmacological toll for MPS.

Evaluation of 99mTcN-15C5 as a new myocardial perfusion imaging agent in normal dogs and canines with coronary stenosis

OBJECTIVES

This study was designed to evaluate the biodistribution and blood clearance characteristics of 99mTcN-15C5 and its potential as a myocardial perfusion radiotracer.

METHODS

Five normal mongrel dogs were injected with 99mTcN-15C5 intravenously. Blood samples were collected at 0.5, 1, 2, 3, 4, 5, 10, 15, and 30 min postinjection (p.i.). Anterior planar images were acquired at 5, 15, 30, 60, 90, and 120 min p.i. Regions of interest (ROIs) were drawn around heart, liver, and lungs. The raw activity in each ROI was expressed as counts/pixel/min. Heart/liver and heart/lung ratios were calculated by dividing the mean counts in heart ROI by the mean counts in liver and lung ROI, respectively. For comparison, 99mTc-sestamibi was also evaluated in the same five dogs. In dogs with coronary stenoses, single photon emission computed tomography images were acquired at 30, 60, and 120 min after administration of 99mTcN-15C5 with/without adenosine.

RESULTS

99mTcN-15C5 and 99mTc-sestamibi had very similar blood clearance characteristics during the first 30 min p.i. The heart/liver ratio of 99mTcN-15C5 increased from 0.48+/-0.05 at 5 min p.i. to 1.85+/-0.11 at 120 min p.i., whereas the heart/liver ratio of 99mTc-sestamibi was improved only slightly from 0.45+/-0.04 at 5 min p.i. to 0.74+/-0.15 at 120 min p.i. SPECT imaging studies in canines with coronary stenoses indicated that good visualization of the perfusion defect could be achieved at 30 min after administration of 99mTcN-15C5 with the adenosine stress.

CONCLUSION

The combination of high heart uptake and rapid liver clearance makes 99mTcN-15C5 a promising new radiotracer for myocardial perfusion imaging.

[Adenosine stress protocols for myocardial perfusion imaging]

BACKGROUND/AIM

Treadmill test combined with myocardial perfusion scintigraphy (MPS) is a commonly used technique in the assessment of coronary artery disease. There are many patients, however, who may not be able to undergo treadmill test. Such patients would benefit from pharmacological stress procedures combined with MPS. The most commonly used pharmacological agents for cardiac stress are coronary vasodilatators (adenosine, dipyridamol) and catecholamines. Concomitant low-level treadmill exercise with adenosine pharma cologic stress (AdenoEX) during MPS has become commonly used in recent years. A number of studies have demonstrated a beneficial impact of AdenoEX protocol. The aim of the study was, besides introducing into practice the two types of protocols of pharmatological stress test with adenosine, as a preparation for MPS, to compare and monitor the frequency of their side effects to quality, acquisition, as well as to standardize the onset time of acquisition (diagnostic imaging) for both protocols.

METHODS

A total of 130 patients underwent pharmacological stress test with adenosine (vasodilatator). In 108 of the patients we performed concomitant exercise (AdenoEX) of low level (50W) by a bicycle ergometar. In 28 of the patients we performed Adenosine ab breviated protocol (AdenoSCAN). Side effects of adenosine were followed and compared between the two kinds of protocols AdenoEX and AdenoSCAN. Also compared were image quality and suggested time of acquisition after the stress test.

RESULTS

Numerous side effects were found, but being short lived they did not require any active interventions. The benefit of AdenoEX versus AdenoSCAN included decreased side effects (62% vs 87%), improved safety and patients tolerance, improved target-to-background ratios because of less subdiaphragmatic activity, earlier acquisition, and improved sensitivity.

CONCLUSION

The safety and efficacy of adenosine pharmacological stress is even better with concomitant exercise. In the light of these benefits we recommend AdenoEX whenever possible.

Symptom-limited exercise combined with dipyridamole stress: prognostic value in assessment of known or suspected coronary artery disease by use of gated SPECT imaging

BACKGROUND

Combining vasodilator and exercise stress reduces noncardiac side effects, improves image quality, and enhances the detection of ischemia, compared with suboptimal exercise or vasodilator stress alone. However, prognostic data with combined protocols are limited.

METHODS AND RESULTS

Consecutive patients (n = 2064) who underwent symptom-limited exercise and dipyridamole stress with gated single-photon emission computed tomography (SPECT) imaging, without early revascularization, were studied. Subsequent cardiac death or nonfatal myocardial infarction was related to exercise and gated SPECT variables. Cox proportional hazards regression modeling was performed to identify predictors of adverse outcome. Annualized event rates in patients with normal and abnormal images were 0.96% and 2.71%, respectively (P < .001). With abnormal imaging, annualized event rates were 0.86% and 3.13% in patients with average to high and fair or poor functional capacity, respectively (P = .019). Abnormal imaging, a severely reduced post-stress ejection fraction, transient ischemic dilation, and fair or poor functional capacity emerged as predictors of adverse outcome. Accordingly, patients were stratified into low-risk, intermediate-risk, and high-risk cohorts with annualized event rates of 0.94%, 2.24%, and 8.19%, respectively (P < .001 in any two-way comparison).

CONCLUSIONS

A protocol that combines symptom-limited exercise and dipyridamole stress with gated SPECT imaging provides highly effective risk stratification for adverse outcomes.

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.

Nuclear Cardiology: Present and Future

Nuclear cardiology has made significant advances since the first reports of planar scintigraphy for the evaluation of left ventricular perfusion and function. While the current "state of the art" of gated myocardial perfusion single-photon emission computed tomographic (SPECT) imaging offers invaluable diagnostic and prognostic information for the evaluation of patients with suspected or known coronary artery disease (CAD), advances in the cellular and molecular biology of the cardiovascular system have helped to usher in a new modality in nuclear cardiology, namely, molecular imaging. In this review, we will discuss the current state of the art in nuclear cardiology, which includes SPECT and positron emission tomographic evaluation of myocardial perfusion, evaluation of left ventricular function by gated myocardial perfusion SPECT and gated blood pool SPECT, and the evaluation of myocardial viability with PET and SPECT methods. In addition, we will discuss the future of nuclear cardiology and the role that molecular imaging will play in the early detection of CAD at the level of the vulnerable plaque, the evaluation of cardiac remodeling, and monitoring of important new therapies including gene therapy and stem cell therapy.

Comparison of post-exercise and post-vasodilator stress myocardial stunning as assessed by electrocardiogram-gated single-photon emission computed tomography

BACKGROUND

Exercise gated single-photon emission computed tomography (SPECT) using technetium-99m (99mTc)-sestamibi evaluates both myocardial perfusion during stress and wall motion >30 min after the stress, which has the potential to assess not only exercise-induced myocardial ischemia but also the development of myocardial stunning.

METHODS AND RESULTS

To evaluate the incidence of post-stress myocardial stunning, as well as comparing the effects of different stress methods on the development of stunning, 179 consecutive patients with known or suspected coronary artery disease (CAD) underwent (99m)Tc-sestamibi SPECT with either exercise (n=135) or adenosine triphosphate disodium (ATP) (n=44). Electrocardiogram-gated SPECT images were acquired >30 min after the stress and again 4 h later, and perfusion and wall motion were evaluated. Post-stress myocardial stunning occurred in 24 patients (13%): 22 after exercise and 2 after ATP stress. The magnitude of the transient wall motion abnormality after exercise was greater in patients with severe ischemia, compared with those with mild-to-moderate ischemia (p<0.0001). By contrast, with ATP stress, the magnitude of the transient wall motion abnormality was similar, regardless of the severity of perfusion abnormality. Furthermore, a significant correlation between summed difference score and transient wall motion abnormality was found after exercise (r=0.68, p<0.0001). With ATP, however, no such correlation was observed (r=0.28, p=NS).

CONCLUSIONS

Using 99mTc-sestamibi gated SPECT, myocardial stunning is frequently observed after exercise and correlates with the severity of myocardial ischemia, but this does not occur with ATP, which is regarded as a specific marker for severe CAD.

Worsening of left ventricular ejection fraction induced by dipyridamole on Tl-201 gated myocardial perfusion imaging predicts significant coronary artery disease

BACKGROUND

Vasodilator stress on myocardial perfusion imaging has been found to induce ischemic stunning, which may present as transient worsening of left ventricular ejection fraction (LVEF) or regional wall motion abnormality. This study aimed to evaluate the significance of stress-induced worsening of LVEF in the diagnosis of coronary artery disease (CAD) on dipyridamole thallium 201 gated single photon emission computed tomography (SPECT).

METHODS AND RESULTS

The study included 126 patients who underwent dipyridamole Tl-201 gated SPECT and coronary angiography within 3 months. Poststress and 4-hour rest images were obtained, and LVEF was calculated by use of automated software (QGS 3.0). A decrease in LVEF of 6% or greater from rest to poststress was considered significant, and this threshold was determined by the serial reproducibility assessment of Tl-201 gated SPECT. If worsening of LVEF was used as the criterion for detecting significant CAD (> or = 70% coronary stenoses in > or = 1 vessel), the sensitivity, specificity, positive predictive value, and negative predictive value were 35%, 93%, 90%, and 44%, respectively.

CONCLUSION

Dipyridamole-induced worsening of LVEF, as shown by Tl-201 gated SPECT, is a valuable nonperfusion marker of significant CAD. Although the sensitivity of LVEF worsening in detecting significant CAD is only 35%, the specificity is as high as 93%.

Significance of ST depression during exercise treadmill stress and adenosine infusion myocardial perfusion imaging

BACKGROUND

ST segment depression on the electrocardiogram during the exercise treadmill test (ETT) is used as a predictor of coronary artery disease (CAD), although it is recognised that both false-positive and false-negative results limit the value of this procedure. Although adenosine does not produce an inotropic or chronotropic effect upon the myocardium it may cause ST depression during infusion.

METHODS

The 12-lead ECG recordings obtained during 825 adenosine stress and 425 ETT procedures, performed as part of a 2-day Tc-MIBI protocol, were retained for examination and comparison with the appearances at subsequent myocardial perfusion imaging (MPI).

RESULTS

ST depression was associated with 44 (4.9%) of the adenosine stress and 44 (10.4%) of the ETT procedures. Both 1 and 2 mm ST depression during adenosine stress were significant predictors of reversible ischaemia (p < 0.01; p < 0.01). However, even though 2 mm ST depression on ETT was significant as a predictor of reversible ischaemia (p < 0.01), 1 mm ST depression on ETT was not (p = 0.4). There were more female cases with false positive ECG changes in both the adenosine stress (63.6%) group and the ETT (66.7%) group. There was no significant correlation between the territory of the ischaemic changes seen on the ECG with the location of defects developing on MPI in both the adenosine stress and ETT groups.

CONCLUSIONS

ST depression of 1 mm occurring with adenosine stress, unlike with the ETT, is a significant predictor of ischaemia.

EANM/ESC procedural guidelines for myocardial perfusion imaging in nuclear cardiology

The European procedural guidelines for radionuclide imaging of myocardial perfusion and viability are presented in 13 sections covering patient information, radiopharmaceuticals, injected activities and dosimetry, stress tests, imaging protocols and acquisition, quality control and reconstruction methods, gated studies and attenuation-scatter compensation, data analysis, reports and image display, and positron emission tomography. If the specific recommendations given could not be based on evidence from original, scientific studies, we tried to express this state-of-art. The guidelines are designed to assist in the practice of performing, interpreting and reporting myocardial perfusion SPET. The guidelines do not discuss clinical indications, benefits or drawbacks of radionuclide myocardial imaging compared to non-nuclear techniques, nor do they cover cost benefit or cost effectiveness.

Myocardial perfusion scintigraphy: patients' perception of benefit and risk

BACKGROUND AND AIM

Myocardial perfusion scintigraphy is a useful and safe investigation, which has now received approval by the National Institute of Clinical Excellence (NICE). However, there are common unpleasant side-effects to the drugs used and there is a risk from radiation. This study was performed to assess patients' perceptions of the benefits and risks of myocardial perfusion scintigraphy, and to determine whether the cardiac stress component influenced these perceptions.

METHODS

Ninety patients attending our institution for thallium-201 myocardial perfusion study over a period of 2 months were interviewed with regard to their perception of the benefits of the study. Patients were interviewed prior to and following the stress study.

RESULTS

On average, patients thought they had a good (three in four) chance of benefiting from myocardial perfusion imaging. Sixty per cent of patients were unaware that they were going to be exposed to ionizing radiation and over 80% were unaware of the side-effects. Two-thirds of the patients said they would undergo the test even if there was only a one in ten chance of benefiting. The majority of patients were uninfluenced by the stress component of the study.

CONCLUSIONS

Many patients lack a knowledge of the risks of myocardial perfusion scintigraphy. Most patients would undergo myocardial perfusion studies even if they had a poor chance of benefit.

Postischemic stunning after adenosine vasodilator stress

BACKGROUND

Ischemic left ventricular (LV) dysfunction may occur after exercise but is regarded as uncommon after vasodilator stress. We evaluated the prevalence of LV dysfunction after adenosine stress in relation to reversible perfusion defects and angiographic coronary artery disease (CAD).

METHODS AND RESULTS

We studied 86 patients referred for clinically indicated adenosine dual-isotope gated single photon emission computed tomography: 43 with 1 or more reversible perfusion defects (reversible defect group) and 43 age- and sex-matched patients with no known CAD and normal LV perfusion and function (control group). Coronary angiography was performed in 36 of 43 patients (84%) in the reversible defect group. Perfusion was interpreted based on 20-segment/5-point summed rest and stress scores. The extent of reversibility was defined by the summed difference score. LV ejection fraction and volumes at rest and 60 minutes after adenosine and segmental wall thickening were quantified by QGS (Cedars-Sinai Medical Center, Los Angeles, Calif). In patients with extensive reversible perfusion defects (summed difference score > or =8), 8 of 25 (32%) demonstrated depressed post-adenosine LV ejection fraction, abnormal segmental wall thickening, end-systolic dilation, and extensive CAD.

CONCLUSION

Adenosine is believed to be less likely than exercise to induce ischemia. However, myocardial stunning occurred in one third of the patients with severe reversible defects, consistent with ischemia.

Should simultaneous exercise become the standard for adenosine myocardial perfusion imaging?

Concomitant low-level treadmill exercise with adenosine pharmacologic stress (AdenoEx) during radionuclide myocardial perfusion imaging has become commonly used in recent years, particularly in large-volume laboratories. A number of studies have demonstrated a beneficial impact of AdenoEx protocols. These benefits include decreased side effects, improved safety and patient tolerance, improved target-to-background ratios because of less subdiaphragmatic activity, and improved sensitivity and defect reversibility. In light of these benefits, recent reviews and guidelines call for the addition of low-level exercise to adenosine stress whenever possible.

First annual Mario S. Verani, MD, Memorial lecture: clinical value of myocardial perfusion imaging in coronary artery disease

I am honored to give this lecture in memory of Dr Mario S. Verani, a friend and a respected colleague in the field of nuclear cardiology. Dr Verani made many immense contributions to the field of nuclear cardiology during his lifetime. He was a pioneer in the field of pharmacologic stress imaging and played a leading role in validating the utility of intravenous adenosine infusion for stress imaging in detecting significant coronary stenoses and assessing prognosis. He and his colleagues at Baylor reported that pharmacologic stress imaging could separate high- and low-risk patient subsets after acute myocardial infarction, particularly among patients who underwent thrombolytic therapy. He informed us that certain drugs that patients took could influence perfusion defect severity. This work led to a clinical study showing that ischemic defect size could be substantially reduced with medical therapy in patients who had recently had an acute infarction. An outcome of this observation was the launching of the INSPIRE (adenosINe technetium-99m Sestamibi single-photon emission computed tomography Post-InfaRction Evaluation) trial in which postinfarction patients are randomized to medical therapy or revascularization. Dr Verani was an able debater when assigned the position for advocating for stress radionuclide perfusion imaging against stress echocardiography. He engaged in these debates with substantial knowledge but always with a touch of humor. Dr Verani's courage was an inspiration to all of us during his illness. His legacy as a pioneer will endure as the field of nuclear cardiology continues to mature and expand.

Technetium 99m sestamibi myocardial perfusion imaging predicts clinical outcome in the community outpatient setting. The Nuclear Utility in the Community (NUC) Study

OBJECTIVES

The purpose of this study was to evaluate the prognostic value of community-based myocardial perfusion imaging (MPI) and to assess the incremental value of individual components of (99m)Tc-sestamibi single photon emission computed tomography (SPECT).

BACKGROUND

Although the most rapid growth of MPI has been in community outpatient laboratories, its prognostic value has not been validated in this setting.

METHOD

We prospectively followed 1,612 consecutive patients undergoing stress (99m)Tc-sestamibi SPECT in an outpatient community laboratory who experienced 71 hard events over 24 +/- 7 months (0.2% lost to follow-up).

RESULTS

Patients whose scans were normal incurred an annualized event rate of 0.4%, compared with 2.3% for those with abnormal scans (p < 0.0001). Subset analysis demonstrated comparable risk stratification for women and men, diabetics, patients with normal resting ECGs, and those referred for pharmacologic and exercise stress. After adjusting for pre-test variables, multivariable Cox regression analysis found the most potent independent components of MPI to be, in order of importance, transient ischemic dilation, extent of reversibility, post-stress ejection fraction, extent and severity of the stress perfusion defect, and the overall test result (normal or abnormal). Each 1% decrement of ejection fraction predicted a 3% increase in risk (p = 0.0009). Post-MPI angiography and revascularization increased commensurate with the extent and severity of MPI result.

CONCLUSIONS

The prognostic value of perfusion imaging is portable and transferable to the outpatient community setting, with multiple components of MPI providing incremental prognostic information.

The impact of adjunctive adenosine infusion during exercise myocardial perfusion imaging: Results of the Both Exercise and Adenosine Stress Test (BEAST) trial

BACKGROUND

Failure to achieve an adequate heart rate limits the sensitivity of exercise myocardial perfusion imaging (MPI) for the detection of coronary artery disease. In addition, it is often not possible to discontinue medications that may blunt the heart rate response to exercise, because of conditions such as hypertension or angina. However, if pharmacologic stress testing is performed, the ability to assess functional capacity is lost. Accordingly, we developed a protocol that incorporates adenosine stress with symptom-limited exercise.

METHODS AND RESULTS

As part of a multicenter study, 35 patients were enrolled prospectively and underwent both exercise MPI and exercise MPI with a 4-minute adenosine infusion on a separate day. Technetium 99m sestamibi was injected at or near peak exercise (exercise only) and at 2 minutes into the adenosine infusion (combined exercise and adenosine). The perfusion images were interpreted in a blinded fashion. The combined adenosine and exercise protocol was well tolerated. The summed stress scores and summed difference scores were greater in the exercise-plus-adenosine group than in the exercise-only group (10.0 vs 8.5, P =.02, and 4.9 vs 3.3, P =.002, respectively). Exercise time was slightly but significantly less with the exercise-plus-adenosine protocol (8 minutes 46 seconds vs 8 minutes 11 seconds, P =.027).

CONCLUSION

A protocol combining 4 minutes of adenosine infusion with symptom-limited exercise was safe and well tolerated. Furthermore, this protocol resulted in a greater amount of myocardial ischemia detected on MPI while allowing for the assessment of functional capacity. A combined exercise and adenosine protocol may be a useful test for patients undergoing MPI who are unlikely to achieve an adequate chronotropic response.