Dobutamine thallium myocardial perfusion tomography

Prognostic value of treadmill exercise and dobutamine stress positron emission tomography

BACKGROUND

Although positron emission tomography (PET) is routinely performed using vasodilator stress, exercise and dobutamine stress are available alternatives. Evidence suggests that vasodilator PET myocardial perfusion imaging (MPI) has prognostic value, but the prognostic value of treadmill exercise and dobutamine PET MPI is unknown.

OBJECTIVE

To determine the potential prognostic value of nonvasodilator stress PET MPI.

METHODS

Patients underwent treadmill exercise or dobutamine PET MPI. Images were assessed qualitatively and semiquantitatively. PET results were categorized as normal (summed stress score [SSS] of less than 4), abnormal (SSS of 4 or greater) or inconclusive (SSS of less than 4 and submaximal peak stress heart rate). Patient follow-up (cardiac death, nonfatal myocardial infarction [MI] and/or late revascularization) was performed.

RESULTS

Of the 124 patients (mean follow-up period of 2.3+/-1.6 years), 46 patients (37%) had a normal study, 15 patients (12%) had an inconclusive study and 63 (51%) had an abnormal PET. Patients with a normal PET had no deaths or nonfatal MI. One patient with a normal PET underwent late revascularization (annual event rate of 1.7%). Patients with an abnormal PET had 15 cardiac events (one cardiac death, four nonfatal MIs and 10 late revascularizations), with an annual event rate of 13.0% (P=0.002).

CONCLUSIONS

Although small, the present study suggests that defects seen on PET myocardial perfusion, resulting from stressors (treadmill exercise and dobutamine) that increase myocardial oxygen demand, may have prognostic value.

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.

Diagnostic and prognostic value of dobutamine thallium-201 single-photon emission computed tomography after heart transplantation

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a major cause of mortality in heart transplant recipients. We investigated the diagnostic and prognostic value of dobutamine thallium-201 ((201)Tl) single-photon emission computed tomography (SPECT) in heart transplant recipients.

METHODS

We studied 47 patients (age 51.6 +/- 11.7 years, 37 men), at a mean of 34.0 +/- 21.4 months after heart transplant, who received dobutamine (201)Tl SPECT, echocardiography and coronary angiography within 1 month of each other. SPECT was considered abnormal in the presence of reversible or fixed defects in >/=2 segments. Significant CAV was defined as >/=50% luminal stenosis.

RESULTS

Coronary angiograms were normal in 37 patients. Non-significant CAV was detected in 1 patient and significant CAV in 9 patients. The sensitivity, specificity, positive predictive value and negative predictive value of SPECT for the detection of significant angiographic CAV were 89%, 71%, 42% and 96%, respectively. Large reversible perfusion defects (>/=6 segments) always indicated significant CAV. In patients with normal left ventricular function, a lung/heart ratio (LHR) of >/=0.37 during stress was also an independent predictor of significant CAV (odds ratio 15.5, p = 0.04). A higher stress LHR was associated with greater vessel involvement (r = 0.516, p = 0.0002). Patients with impaired left ventricular function also had higher stress and resting LHR. Over 40.3 +/- 21.9 months after the first SPECT, 1 patient developed significant angiographic CAV and another 4 had cardiac death. Large reversible perfusion defect was a significant predictor of cardiac death (p = 0.002).

CONCLUSIONS

Dobutamine (201)Tl SPECT is a useful method for detecting patients with significant CAV and assessing prognosis. It is reasonable and safe to design individualized surveillance intensity of coronary angiography for post-transplant patients on the basis of non-invasive monitoring of dobutamine (201)Tl testing.

Dobutamine stress-induced ischemic right ventricular dysfunction and its relation to cardiac output in patients with three-vessel coronary artery disease with angina-like symptoms

We investigated markers of ischemic dysfunction and their relation to overall right ventricular (RV) performance during dobutamine stress echocardiography in patients who had coronary artery disease. Thirty-three patients (58 +/- 10 years old) who had 3-vessel coronary artery disease were compared with 17 age-matched controls (58 +/- 11 years old). RV long-axis amplitude (M mode), systolic and diastolic myocardial tissue Doppler velocities, and filling and ejection velocities were measured, and cardiac output (CO) was calculated at rest and during peak stress. There was no difference in RV size (inlet dimension <3.5 cm), RV systolic long-axis amplitude, systolic and diastolic velocities, peak early/late diastolic velocity ratio, and RV CO between patients and controls at rest. During stress, RV systolic long-axis amplitude increased in controls (from 24 +/- 6 to 30 +/- 5 mm) and CO increased significantly (from 4.9 +/- 1.2 to 12.5 +/- 2.1 L/min, p <0.001 for the 2 items). In contrast, RV amplitude did not change with stress in patients (from 24 +/- 5 to 22 +/- 6 mm, p = NS), and the stress-increment in CO was augmented (from 4.2 +/- 1.2 to 8.3 +/- 2.0 L/min, p <0.001 vs control stress increment). Failure to increase RV systolic amplitude >2 mm was 79% sensitive and 88% specific for detecting ischemic RV dysfunction, and there was a close correlation between stress-induced change in RV systolic amplitude and change in CO in patients (r = 0.56, p <0.001). Early diastolic velocity increased in controls (from 10.8 +/- 3.2 to 13.1 +/- 3.6 cm/s, p <0.01) but did not change in patients (from 11.5 +/- 3.7 to 11.3 +/- 4.8 cm/s, p = NS). RV shortening after ejection did not appear in any control subject but did develop in 8 of 33 patients, thus contributing to the decrease in RV peak early/late diastolic velocity ratio in patients (from 1.1 +/- 0.3 to 0.76 +/- 0.4, p <0.001) compared with that in controls (1.3 +/- 0.3 to 1.0 +/- 0.2, p <0.001). In conclusion, markers of RV dysfunction are not related to left ventricular wall motion score index or long-axis changes with stress.

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.

Pharmacologic interventions in nuclear radiology: indications, imaging protocols, and clinical results

Nuclear radiology is valuable in assessing pathophysiology of a variety of organ systems. Pharmacologic interventions are often employed in radionuclide imaging to monitor the physiologic changes, which in turn facilitate the diagnosis. Metoclopramide, erythromycin, and cisapride have been used for gastric emptying studies. To overcome false-negative results, cimetidine, pentagastrin, and glucagon have been used in imaging of Meckel diverticula. Pharmacologic intervention with either cholecystokinin-8 or morphine is used primarily for the assessment of diseases of the gallbladder, common bile duct, and sphincter of Oddi. Pharmacologic interventions performed during renography include diuretic administration, angiotensin-converting enzyme inhibition, and aspirin renography. Recombinant thyrotropin can be used in patients with previously treated thyroid carcinoma who require lifelong follow-up for recurrent disease. Cardiac pharmacologic stress agents fall into two categories: coronary vasodilating agents, such as dipyridamole and adenosine, and cardiac positive inotropic agents, such as dobutamine and arbutamine. Measurement of hemodynamic responses to pharmacologic flow augmentation with carbon dioxide or acetazolamide is valuable in cerebrovascular perfusion studies.

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.

Exercise-induced myocardial perfusion abnormalities in sickle beta-thalassemia: Tc-99m tetrofosmin gated SPECT imaging study

PURPOSE

To determine the mechanism of myocardial ischemia in patients with sickle beta-thalassemia, we performed a scintigraphic evaluation of myocardial perfusion during exercise.

SUBJECTS AND METHODS

We studied 30 patients with sickle beta-thalassemia, (mean [+/-SD] age, 37 +/- 10 years) who had no electrocardiographic (ECG), radiographic, or echo-Doppler signs of pulmonary hypertension, left ventricular hypertrophy, or impaired contractility. All patients had a hemoglobin level greater than 7 g/dL. Treadmill exercise test was performed according to the Bruce protocol. Myocardial perfusion was assessed by single-photon emission computed tomography, using Tetrofosmin Tc-99 m Myoview as radiotracer, at peak exercise and again 4 hours later.

RESULTS

Eight patients (27%) developed stress-induced scintigraphic perfusion abnormalities that were reversible in all but 1 patient. Subsequent coronary angiograms were normal in all 8 patients. ST segment depression was seen during exercise in 5 of the 7 patients who had reversible perfusion defects. Except for a significantly greater white blood cell count, these 5 patients did not differ from the rest of patients by sex, age, hemoglobin level, percentage hemoglobin F, beta-thalassemia genotype, or risk factors for coronary artery disease. Three of the 5 patients with perfusion and ECG abnormalities (and another with only perfusion defects) developed a stress-induced sickling crisis.

CONCLUSION

Physical stress may induce myocardial ischemia in sickle beta-thalassemia patients with normal coronary arteries and elicit painful crises. The sickling process, activated by exercise, could be the common underlying mechanism.

Inhomogeneity of myocardial perfusion in heart transplant recipients: evaluation with dobutamine thallium-201 SPECT

Progressive heterogeneity of thallium-201 single photon emission computed tomography (Tl-201 SPECT) in heart transplant recipients has been documented in Caucasians. However, in Chinese heart transplant recipients, a lower incidence of transplant coronary artery disease (CAD) has been noted than in Western transplant recipients. In this study, we examine whether heterogeneity of Tl-201 SPECT exists in Chinese transplant recipients. Dobutamine Tl-201 SPECT was performed in 40 heart transplant recipients and the inhomogeneity scores were calculated. The difference between the scores of transplant recipients surviving less than 12 months and those of control subjects were not statistically significant. One year after transplantation, the inhomogeneity score increased progressively. The scores of transplant patients in the second and third years after transplant were similar to those of single-vessel CAD patients. Three years after transplant the scores were greatly increased. Thus, our data suggest that the progressive nature of graft vasculopathy also exists in Chinese heart transplant recipients. The progressive Tl-201 abnormalities may be one of the early signs of graft vasculopathy.

Dobutamine stress surface mapping of myocardial ischemia in Kawasaki disease

BACKGROUND

To detect and localize myocardial ischemia, a method that does not require physical exertion is sometimes needed in children with Kawasaki disease.

METHODS

Dobutamine stress body surface mapping was performed in 115 children with a history of Kawasaki disease (58 without coronary artery lesions, 40 who had coronary lesions without myocardial ischemia and 17 with myocardial ischemia). The maximum infusion rate of dobutamine was 30 microg/kg per min. Myocardial ischemia was diagnosed by the presence of an area of hypoperfusion on scintigraphy at rest and/or an increase in hypoperfusion during a dobutamine stress test compared with resting scintigraphy. We studied the number of leads that showed significant ST depression on the isopotential map (nST), the number of the row containing the lead with the smallest negative value on the isointegral map (I(min)), and the localization of myocardial ischemia on the isointegral map. Based on findings in patients without coronary artery lesions, we defined the criteria for detecting myocardial ischemia as nST > or = 1 and I(min) < or = 4.

RESULTS

The sensitivity of detecting myocardial ischemia was 94.1% using nST and 41.7% using I(min), while the specificity of these methods was 98.9 and 96.9%, respectively. The localization of myocardial ischemia on stress body surface mapping was 100% concordant with that determined by stress myocardial scintigraphy.

CONCLUSIONS

Dobutamine stress body surface mapping for the detection of myocardial ischemia is a non-invasive, more convenient and repeatable test compared with exercise myocardial scintigraphy and it is a more objective test compared with exercise echocardiography. Dobutamine stress body surface mapping is useful for the identification and localization of silent myocardial ischemia in pediatric patients with Kawasaki disease, especially those who cannot perform tests involving physical exercise.

Does inadequate exercise lower the accuracy of myocardial perfusion scintigraphy?

The predictive accuracy of exercise myocardial perfusion scintigraphy (EMPS) in detecting coronary artery disease (CAD) in patients who fail to achieve an adequate level of exercise is not clear. This investigation was carried out in order to compare the sensitivity, specificity and accuracy of EMPS in adequate exercise patients with those in inadequate exercise patients. We have retrospectively compared the results of EMPS with coronary angiography (CAG). One hundred and forty-eight patients with both tests within 6 weeks were included. Adequate exercise was defined as > or = 85% maximally predicted heart rate for age. The overall sensitivity and specificity of EMPS to detect CAD were 92.5% (74/80) and 75%, (51/68), respectively. The sensitivity and specificity in adequate exercise patients were 94.1% (32/34) and 67.6% (23/34), whereas those in inadequate exercise patients were 91.3% (42/46) and 82.4% (28/34). The accuracy was 80.9% (55/68) and 87.5% (70/80), respectively. Patients with inadequate exercise had lower sensitivity but higher specificity of EMPS for detecting CAD, and achieved a higher accuracy than those with adequate exercise.

Technetium-99m-labeled myocardial perfusion agents: Are they better than thallium-201?

Currently, thallium-201 (201Tl)- and technetium-99m (99mTc)-labeled tracers are used interchangeably for the detection of coronary artery disease, the assessment of myocardial viability, and risk stratification. This article reviews some of the potential advantages and disadvantages of the 99mTc-labeled tracers relative to 201Tl. The basic myocardial kinetic properties and biodistribution of the commonly used 99mTc-labeled perfusion tracers are compared with those of 201Tl. The clinical value of the 99mTc-labeled perfusion tracers is then compared with that of 201Tl imaging. With regard to imaging physics and radiation safety, the 99mTc-labeled tracers are superior to 201Tl. Cost and tracer availability also may favor 99mTc-labeled perfusion tracers rather than 201Tl imaging. However, the most widely used 99mTc-labeled perfusion tracers currently approved for clinical use-99mTc-sestamibi and 99mTc-tetrofosmin-do not track myocardial flow as well as 201Tl does. This shortcoming of 99mTc-labeled perfusion tracers may reduce the sensitivity of these agents in detecting subcritical coronary artery disease. The most notable new perfusion agent is 99mTc-labeled bis(N-ethoxy, N-ethyl dithiocarbamato) nitrido technetium(v), which is considered to be the 99mTc-labeled equivalent of 201Tl. However, 99mTc-labeled bis(N-ethoxy, N-ethyl dithiocarbamato) nitrido technetium(v) is a neutral compound with kinetic properties that are very different from those of 201Tl. Myocardial perfusion imaging is often conducted in conjunction with exercise or with different pharmacologic stressors, both of which augment regional flow heterogeneity. Each of these stressors has unique effects on the coronary vasculature and influences the behavior of the radiolabeled perfusion agents. The substantial differences in myocardial uptake, clearance kinetics, and biodistribution between each of the 99mTc-labeled perfusion tracers and 201Tl should be considered in the clinical application of perfusion imaging. The myocardial retention of all of the agents is affected by myocardial viability. However, 201Tl demonstrates greater differential clearance from normal and ischemic regions (redistribution), making 201Tl a better agent for assessment of viability, particularly in patients with extremely low flow. In contrast, agents that do not redistribute, such as 99mTc-tetrofosmin, might be better for acute assessment of "risk areas" or of chest pain. Each of the available perfusion tracers has unique advantages and disadvantages that must be considered to ensure its optimal application.

[Prognostic value of cardiac perfusion scintigraphy associated with the dobutamine test in acute coronary syndromes]

OBJECTIVES

This study aimed to establish the value of myocardial ischemia induced by the dobutamine infusion test associated to 99m technetium isonitrile single photon emission computed tomography in patients with unstable angina or non Q-wave infarction during the first days in the Coronary Care Unit.

METHODS

Fifty three patients with unstable coronary syndromes and common medical treatment were studied with a moderate-dose dobutamine test (5 to 20 microgram/Kg/min) using a 99mTc-MIBI SPECT. The results were correlated with the incidence of recurrent angina, infarction, death or revascularization.

RESULTS

The dobutamine test induced a reversible perfusion defect in 36 patients (68%) and angina in 12 of them (12/36, 33%). However, the patients who had a positive test had a similar incidence of events as those with a negative test (58% vs 59%). Thus, while the sensitivity of the dobutamine test to identify patients at risk was relatively high (68%), its specificity (32%) and its negative predictive value (41%) were low. The patients with dobutamine-induced angina, however, had a higher scintigraphy score (3.0 +/- 1,7 vs 1.6 +/- 1.8, p < 0.02) and a higher incidence of recurrent angina (8/12, 67% vs 13/41, 31%, p < 0.04) than those without, at a comparable double product.

CONCLUSIONS

In conventionally treated patients with unstable coronary syndromes, the specificity of the inducible scintigraphic ischemia with moderate dose of dobutamine performed during the first days is too low to be used as a marker for in-hospital events. However, inducible angina with dobutamine suggests an extensive jeopardized area and/or a particularly reduced ischemic threshold.

The clinical use of imaging techniques with exercise testing

The addition of nuclear imaging techniques to basic exercise electrocardiography (ECG) has provided significant diagnostic and prognostic information in the evaluation of patients with suspected coronary artery disease. During the last decade, new classes of isotopes (technetium-and rubidium-based perfusion agents) and refinements in single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have become better accepted. These new studies have added to the diagnostic armamentarium available to physicians, but at considerable costs with an estimated 4.8 million procedures performed this year. Nuclear imaging techniques can assess myocardial blood flow (perfusion imaging) or function (ventriculography). Another imaging modality, stress echocardiography, has also achieved widespread acceptance with clinical guidelines for its use published in 1997. This review addresses these imaging techniques in diagnostic evaluation of the patient with suspected coronary artery disease.

Principal uses of myocardial perfusion scintigraphy in the management of patients with known or suspected coronary artery disease

The use of myocardial perfusion single photon emission computed tomography (SPECT) has undergone considerable expansion and evolution over the past 2 decades. Although myocardial perfusion imaging was first conceived as a noninvasive diagnostic tool for determining the presence or absence of coronary artery disease, its prognostic value is now well established. Thus, identification of patients at risk for future cardiac events has become a primary objective in the noninvasive evaluation of patients with chest pain syndromes and among patients with known coronary artery disease. In particular, the ability of myocardial perfusion SPECT to identify patients at low (< 1%), intermediate (1% to 5%) or high (> 5%) risk for future cardiac events is essential to patient management decisions. Moreover, previous studies have conclusively shown the incremental prognostic value of myocardial perfusion SPECT over clinical and treadmill exercise data in predicting future cardiac events. This report addresses the current role and new developments, with respect to the use of myocardial perfusion imaging, in determining patient risk for cardiac events and the cost-effective integration of such information into patient management decisions.

Dobutamine stress myocardial perfusion imaging

In patients with limited exercise capacity and (relative) contraindications to direct vasodilators such as dipyridamole or adenosine, dobutamine stress nuclear myocardial perfusion imaging (DSMPI) represents an alternative, exercise-independent stress modality for the detection of coronary artery disease (CAD). Nondiagnostic test results (absence of reversible perfusion defects with submaximal stress) do occur in approximately 10% of patients. Serious side effects during DSMPI are rare, with no death, myocardial infarction or ventricular fibrillation reported in three DSMPI safety reports for a total of 2,574 patients. On the basis of a total number of 1,014 patients reported in 20 studies, the sensitivity, specificity and accuracy of the test for the detection of CAD were 88%, 74% and 84%, respectively. Mean sensitivities for one-, two- and three-vessel disease were 84%, 95% and 100%, respectively. The sensitivity for detection of left circumflex CAD (50%) was lower, compared with that for left anterior descending CAD (68%) and right CAD (88%). The sensitivity of predicting multivessel disease by multiregion perfusion abnormalities varied widely, from 44% to 89%, although specificity was excellent in all studies (89% to 94%). In direct diagnostic comparisons, DSMPI was more sensitive, but less specific, than dobutamine stress echocardiography and comparable with direct vasodilator myocardial perfusion imaging. In the largest prognostic study, patients with a normal DSMPI study had an annual hard event rate less than 1%. An ischemic scan pattern provided independent prognostic value, with a direct relationship between the extent and severity of the perfusion defects and prognosis. In conclusion, DSMPI seems a safe and useful nonexercise-dependent stress modality to detect CAD and assess prognosis.

Accuracy of dobutamine tetrofosmin myocardial perfusion imaging for the noninvasive diagnosis of transplant coronary artery stenosis

BACKGROUND

Exercise stress myocardial perfusion scintigraphy has been used for the diagnosis of transplant coronary artery stenosis (TCAS) in cardiac allograft recipients. However, the role of pharmacologic stress myocardial perfusion imaging has not been evaluated. Aim of the study is to assess the accuracy of dobutamine stress 99m technetium tetrofosmin myocardial perfusion imaging for the diagnosis of TCAS in heart transplant recipients.

PATIENTS AND METHODS

We studied 50 patients (age 56 +/- 8 year, 45 men) at a mean of 6.4 +/- 2.8 years after cardiac transplant with dobutamine (up to 40 ìg/kg/min) stress 99m technetium tetrofosmin SPECT. Resting images were acquired 24 hours after the stress study. Significant TCAS was defined as > or =50% luminal diameter stenosis by coronary angiography.

RESULTS

Significant TCAS was detected in 30 patients (60%). Myocardial perfusion abnormalities (reversible and/or fixed defects) were detected in 27 of the 30 patients with and in 9 of the 20 patients without significant TCAS (sensitivity = 90%, CI 82-98, specificity = 55% CI 41-69, positive predictive value = 75%, CI 63-87, negative predictive value = 79%, CI 67-90 and accuracy = 76%, CI 64-88). Patients with multivessel TCAS had a larger stress perfusion defect score (5.6 +/- 3.1 vs 3.2 +/- 2.4, p < 0.05) compared to patients with single vessel TCAS. Among patients with abnormal perfusion who had no significant TCAS, 2 had lesions <50%, 2 had luminal irregularities and 5 had no abnormalities at angiography. Therefore specificity was 62% (8/13) in patients without any detectable angiographic abnormalities.

CONCLUSIONS

Dobutamine stress tetrofosmin myocardial perfusion imaging is a highly sensitive method for the detection of TCAS in recipients of cardiac allografts. The high negative predictive value of the test indicates that patients who demonstrate normal perfusion by this method may be excluded from further invasive studies.

Safety, hemodynamic profile, and feasibility of dobutamine stress technetium myocardial perfusion single-photon emission CT imaging for evaluation of coronary artery disease in the elderly

OBJECTIVES

Cardiovascular disease is the leading cause of morbidity and mortality in the elderly. The evaluation of coronary artery disease by exercise stress testing is frequently limited by the patient's inability to exercise. Although pharmacologic stress testing with dobutamine is an alternative, the safety of dobutamine myocardial perfusion scintigraphy in the elderly has not been previously studied.

PATIENTS AND METHODS

We studied the safety and feasibility of dobutamine (up to 40 microg/kg/min)-atropine (up to 1 mg) stress myocardial perfusion scintigraphy using technetium single-photon emission CT imaging in 227 patients > or = 70 years old (mean +/- SD age, 75 +/- 4 years). A control group of 227 patients < 70 years old (mean age, 55 +/- 11 years; matched for gender, prevalence of previous infarction, beta-blocker therapy, and severity of resting perfusion abnormalities) was studied to assess age-related differences in the safety and the hemodynamic response. A feasible test was defined as the achievement of the target heart rate and/or an ischemic end point (angina, ST-segment depression, or reversible perfusion abnormalities).

RESULTS

No myocardial infarction or death occurred during the test. The target heart rate was achieved more frequently in the elderly patients (87% vs 79%; p < 0.05). The elderly patients had a higher prevalence of supraventricular tachycardia (7% vs 1%; p < 0.005) and premature ventricular contraction (74% vs 32%; p < 0.005) during the test, as compared to the younger patients. There was a trend to a higher prevalence of ventricular tachycardia (5% vs 2%) and atrial fibrillation (3% vs 0.4%) in the elderly patients. Arrhythmias were terminated spontaneously by termination of dobutamine infusion or by administration of metoprolol. Independent predictors of supraventricular tachyarrhythmias and ventricular tachycardia were older age (p < 0.001; chi(2), 9.8) and myocardial perfusion defect score at rest (p < 0.01; chi(2), 6.8) respectively, by using a multivariate analysis of clinical and stress test variables. Elderly patients had a higher prevalence of systolic BP drop > 20 mm Hg during the test (37% vs 12%; p < 0.05). The test was terminated due to hypotension in 2% of the elderly patients and in 1% of the control group. Age was the most powerful predictor of hypotension (p < 0.005; chi(2), 10.3). The test was considered feasible in 216 elderly patients (95%) and in 209 patients of the control group (92%).

CONCLUSION

Dobutamine-atropine stress myocardial perfusion scintigraphy is a highly feasible method for the evaluation of coronary artery disease in the elderly. Elderly patients have a higher risk for developing hypotension and supraventricular tachyarrhythmias during a dobutamine stress test. However, dobutamine-induced hypotension is often asymptomatic and rarely necessitates the termination of the test.

The carvedilol hibernation reversible ischaemia trial, marker of success (CHRISTMAS) study. Methodology of a randomised, placebo controlled, multicentre study of carvedilol in hibernation and heart failure

BACKGROUND

Carvedilol reduces mortality and improves symptoms and ejection fraction in ischemic heart failure, but its mode of action is not well defined and not all patients respond to treatment. The aim of the CHRISTMAS (Carvedilol Hibernation Reversible Ischaemia Trial, Marker of Success) study is to examine whether hibernation may be a significant factor determining this response. This paper describes the methodology and the rationale for the choice of the nuclear cardiology and echocardiography imaging techniques used in the study.

METHODS AND RESULTS

The CHRISTMAS study is a double-blind, randomised, parallel group, multinational study of oral carvedilol versus placebo in patients with chronic stable heart failure due to left ventricular systolic dysfunction from coronary artery disease. The study aims to randomise 400 patients who are on optimal treatment. Two parallel groups will be randomised to carvedilol or placebo, namely 200 with hibernating myocardium at baseline and 200 matched patients without. The presence of hibernation is defined from a mismatch between regional contractile function and regional viability, measured by echocardiography (severe segmental asynergy) and nitrate prepared resting Tc99m-MIBI myocardial perfusion imaging (segmental activity >60%). The primary treatment-related end-point of the study is the comparison of the mean change, from baseline to the final visit, in radionuclide-determined left ventricular ejection fraction in patients on placebo with those on carvedilol, between the groups designated as hibernating and non-hibernating. Other end-points being examined include the prevalence of hibernation in heart failure, the relationship between the volume of hibernating myocardium and the ejection fraction response, the prevalence of reversible ischemia in heart failure, and the comparison of echo with gated SPECT. To date, 303 patients have been screened and 251 patients randomised in the study. The study aims to report in 2000.

CONCLUSIONS

The CHRISTMAS study addresses the issue of whether the presence of hibernation is a predictor of the ejection fraction response to carvedilol in heart failure. It also examines the potential role of medical therapy in hibernation as well as a number of other end-points. The study may potentially lead to an important new role for nuclear cardiology in heart failure, and demonstrates important synergy between cardiac imaging and the pharmaceutical industry.

[Nuclear cardiology: technical bases and clinical applications]

Although the role of nuclear cardiology is currently well consolidated, the addition of new radiotracers and modern techniques makes it necessary to continuously update the requirements, equipment and clinical applications of these isotopic tests. The characteristics of the radioisotopic drugs and examinations presently used are explained in the first part of this text. In the second, the indications of them in diagnostic and prognostic evaluation of the different coronary diseases are presented.

Comparison of exercise stress testing with dobutamine stress echocardiography and radionuclide ventriculography for diagnosis of coronary artery disease

Dobutamine stress echocardiography, Tc-99m radionuclide ventriculography (RNVG), and exercise stress testing were performed prospectively in 63 patients with suspected coronary artery disease to compare the values of exercise testing, dobutamine stress echocardiography and RNVG in the non-invasive diagnosis of coronary artery disease. The sensitivities of dobutamine stress echocardiography and RNVG were found to be higher than that of exercise testing (93-62%, p < 0.001; 83-62%, p < 0.05). The sensitivities of dobutamine stress echocardiography and RNVG were similar (p > 0.05). There were no differences between the sensitivities of the three techniques in multiple vessel disease (p > 0.05). The specificities of dobutamine stress echocardiography and RNVG were higher than that of exercise testing (for both of the tests 86-62%, p < 0.05). The diagnostic accuracy of dobutamine stress echocardiography and RNVG were similar (p > 0.05). The results of dobutamine stress echocardiography RNVG were concordant with each other in 46 patients (76%, kappa = 65%) in sectional analysis. Dobutamine stress echocardiography and RNVG tests were comparable with each other in 85% of the 189 segments (kappa = 64%). The expected 5% decrease at peak doses of dobutamine was not detected in stress echocardiography in 25 patients and in RNVG in 26 of the patients. Dobutamine stress echocardiography and RNVG are superior to exercise testing in the diagnosis of single vessel disease and there is no significant difference between the two techniques. When the ejection fraction is considered in dobutamine stress echocardiography and RNVG, it does not make an additional contribution to the diagnosis of coronary artery disease.

Myocardial perfusion abnormalities in treated hypertensive patients without known coronary artery disease

OBJECTIVE

Myocardial perfusion abnormalities may occur in hypertensive patients in absence of significant coronary artery disease. However, it is not well established whether hypertensive patients without known coronary artery disease have a higher prevalence or extent of myocardial perfusion abnormalities compared with normotensive patients with similar clinical features.

DESIGN

This study compares the prevalence and extent of rest and stress-induced myocardial perfusion abnormalities in patients with and without hypertension.

METHODS

Dobutamine (up to 40 microg/kg per min) stress technetium-99m myocardial perfusion SPECT imaging was performed for evaluation of myocardial ischaemia in 350 patients (mean age = 60+/-13 years, 146 men) without known coronary artery disease. One hundred and forty-eight patients were hypertensive. Rest SPECT images were acquired 24 h after the test Abnormal perfusion was defined as the presence of reversible or fixed perfusion defects.

RESULTS

No significant difference was detected between patients with and without hypertension regarding gender, prevalence of symptoms, risk factors, pretest probability of coronary artery disease (52+/-28 versus 53+/-29%), peak rate pressure product (21040+/-4755 versus 20774+/-4865) or number of patients achieving the target heart rate during stress (85 versus 86%). Hypertensive patients were significantly older (62+/-11 versus 58+/-13 years, P = 0.005) and were receiving beta-blockers more frequently (34 versus 18%, P = 0.0001). The prevalence of myocardial perfusion abnormalities was similar in patients with and without hypertension (28 versus 31% in patients with low, 38 versus 33% in patients with intermediate and 60 versus 58% in patients with high pretest probability of coronary artery disease, respectively). No significant difference was detected between the two groups regarding stress perfusion defect score (1.45+/-2.5 versus 1.50+/-2.6) or rest score (0.72+/-1.8 versus 0.68+/-1.6).

CONCLUSION

Treated hypertensive patients without known coronary artery disease have a similar prevalence and severity of myocardial perfusion abnormalities at rest and at dobutamine stress compared with normotensive patients with similar clinical characteristics.

Myocardial uptake of (99m)Tc-N-NOET and (201)Tl during dobutamine infusion. Comparison with adenosine stress

BACKGROUND

The myocardial uptake of (99m)Tc-sestamibi is attenuated by dobutamine stress, resulting in underestimation of ischemia. N-Ethyl-N-ethoxy-dithiocarbamato-N-(99m)Tc ((99m)Tc-N-NOET) is a new (99m)Tc-labeled perfusion agent that is highly extracted by the myocardium by a mechanism different from that defined for (99m)Tc-sestamibi. We therefore hypothesized that (99m)Tc-N-NOET uptake would not be attenuated by dobutamine and that (99m)Tc-N-NOET uptake would be comparable to (201)Tl uptake during dobutamine stress.

METHODS AND RESULTS

In 28 open-chest dogs, after placement of a stenosis in the left anterior descending coronary artery that reduced flow reserve by >50%, adenosine (300 microgram. kg(-1). min(-1); n=15) or dobutamine (2.5 to 30 microgram. kg(-1). min(-1); n=13) was infused. During adenosine stress, the stenotic-to-normal activity ratio for (99m)Tc-N-NOET was 0.55+/-0.05. The stenotic-to-normal flow ratio was 0.33+/-0.04 at the time of (99m)Tc-N-NOET injection. During dobutamine stress, the stenotic-to-normal (99m)Tc-N-NOET activity ratio was 0.63+/-0.04, comparable to the (201)Tl activity ratio of 0.59+/-0.04. The stenotic-to-normal flow ratio was 0.47+/-0.04 at the time of (99m)Tc-N-NOET and (201)Tl injection. The relationship between (99m)Tc-N-NOET uptake and blood flow was comparable for adenosine and dobutamine stress, with no evidence of attenuation of (99m)Tc-N-NOET extraction by dobutamine. Conclusions-In the presence of coronary stenoses that reduced regional flow reserve, the myocardial uptake of (99m)Tc-N-NOET and (201)Tl are closely proportional to blood flow during both adenosine and dobutamine stress, suggesting that the adverse effect of dobutamine on (99m)Tc-sestamibi uptake is a tracer-specific phenomenon rather than a generalized effect. The clinical implication of this finding is that (99m)Tc-N-NOET might be preferable to (99m)Tc-sestamibi when used with dobutamine stress for detection of coronary stenoses.

Pharmacological stress testing

Pharmacological stress in conjunction with radionuclide myocardial perfusion imaging has become a widely used noninvasive method of assessing patients with known or suspected coronary artery disease. In the United States, over one third of perfusion imaging studies are performed with pharmacological stress. Pharmacological stress agents fall into two categories: coronary vasodilating agents such as dipyridamole and adenosine, and cardiac positive inotropic agents such as dobutamine and arbutamine. For both, in the presence of coronary artery disease (CAD), perfusion image abnormalities result from heterogeneity of coronary blood flow reserve. Vasodilating agents work directly on the coronary vessels to increase blood flow, whereas inotropic agents work indirectly by increasing myocardial work load, which then leads to an increase in coronary blood flow. Both classes of agents have high accuracies for diagnosing coronary artery disease, and they have excellent safety records with acceptably low occurrences of side effects. For dipyridamole planar thallium imaging, pooled analysis yields a sensitivity of 85% and a specificity of 87% for diagnosis of coronary disease, but there is a large variation in reported values depending on various factors, such as the extent of postcatheterization referral bias, the type of imaging (planar versus single photon emission computed tomography [SPECT]), the types of patients being studied (single versus multivessel disease, men versus women), and the imaging agent used (thallium versus one of the technetium-based agents). Diagnostic accuracies for adenosine are similar to those of dipyridamole, with reported overall sensitivities ranging from 83% to 97%, and specificities ranging from 38% to 94%. For dobutamine, pooled analyses yield a sensitivity of 82% and a specificity of 75%. There is some concern that dobutamine may interfere with uptake of technetium-99m sestamibi, lowering the sensitivity for detection of disease, and thus the vasdodilating agents are generally preferred. Pharmacological stress testing has high clinical use for risk stratifying patients with known or suspected CAD, in patients after myocardial infarction, and in patients needing noncardiac surgery. Vasodilating agents are particularly advantageous in assessing post-myocardial infarction patients, allowing testing as soon as 2 days after the event. Like patients undergoing exercise stress testing, patients with normal perfusion images by pharmacological stress have a <1% annual incidence of cardiac events. The likelihood of an event increases with the extent and severity of perfusion abnormalities. However, it is important to consider clinical variables when using perfusion imaging for risk stratification, particularly in the presurgery patients. As with exercise testing, adjunct markers such as ST segment depression during testing, lung uptake of radiotracer (if thallium is used), and ventricular cavity dilatation add additional prognostic information to that available from the perfusion images alone. The aim of current research is to find better agents that are easier to use and that have fewer side effects. MRE-0470 is an experimental vasodilating agent that is more receptor selective than adenosine and promises a lower incidence of hypotension. Arbutamine more closely simulates exercise than dobutamine, and it can be administered by a closed-loop computerized delivery device. Work is also underway to look at novel uses of pharmacological stress agents, such as acquiring gated SPECT images during dobutamine infusion to enhance detection of myocardial viability. With increasing use of noninvasive testing in elderly patients and in patients with comorbidities that preclude adequate exercise, pharmacological stress testing has become an indispensable tool for radionuclide myocardial perfusion imaging studies. A good understanding of pharmacological stress testing is essential for performing high-quality nuclear cardiology

Coronary artery disease in potential lung transplant recipients > 50 years old: the role of coronary intervention

STUDY OBJECTIVES

To review the experience of the Alfred Hospital in the systematic assessment of coronary artery disease (CAD) using coronary angiography (CA), and the subsequent management of CAD, in potential lung transplant recipients.

DESIGN

Retrospective study.

SETTING

The Alfred Hospital Lung and Heart Transplant Service.

PATIENTS

CAD risk factors were sought in potential recipients of lung transplantation (LTx) who were > 50 years old, including a history of smoking, male gender, hypertension, diabetes, hypercholesterolemia, angina, and a family history of CAD. When feasible, and in the presence of more than one cardiac risk factor, CA was performed.

RESULTS

From 243 referral patients who were > 50 years old, 97 were listed for LTx, and 77 underwent LTx. Four patients were refused LTx on the basis of CAD. Of 101 patients undergoing a detailed cardiac assessment for LTx, 83 had smoked, 56 were male, 48 had hypercholesterolemia, 22 had hypertension, 4 had diabetes, and 3 had a history consistent with angina. Eighty-five patients underwent CA. In 32 cases, CA revealed CAD, and half of these cases were significant stenoses. Eight patients who were assessed required intervention. Five patients of this group have been transplanted; of these, three patients underwent coronary artery grafting at the time of LTx, and two patients underwent preoperative angioplasty or stenting. Only one of these five patients died < 90 days postoperatively.

CONCLUSION

Significant CAD is a common finding in older patients who are presenting for LTx. Coronary revascularization for severe large vessel stenoses can allow safe LTx. CAD risk factors may predict who should undergo CA, but further studies of clinical and noninvasive assessments of CAD are needed if CA is to be safely avoided in patients at low risk of CAD.

Changes in endothelium-derived vascular regulatory factors during dobutamine-stress-induced silent myocardial ischemia in patients with Kawasaki disease

The changes in endothelium-derived vascular regulatory factors during dobutamine (DOB)-induced myocardial ischemia (MI) were investigated in 21 patients with Kawasaki disease aged from 11 months to 18 years. They were classified into an ischemia group (8 patients) and a non-ischemia group (13 patients) based on the results of 99mTc myocardial scintigraphy and DOB stress 99mTc myocardial scintigraphy. In the ischemia group, MI was relatively mild, because there were ischemic changes on the electrocardiogram and no significant symptoms during DOB stress. Catheters were positioned near the orifice of the coronary artery (Ao) and at the coronary sinus (CS). Hemodynamics and the blood concentrations of lactic acid and endothelin-1, as well as NO3-, 6-keto-prostaglandin F1alpha, and thromboxane B2, (which are inactive metabolites of nitric oxide, prostaglandin I2 and thromboxane A2, respectively), were measured at rest and after DOB stress (maximum dose: 30 microg x kg(-1) x min(-1)). The CS/Ao ratio was determined for all parameters. The rate-pressure product, an index of work load, and the cardiac index were significantly increased by DOB stress in both groups. Coronary angiography showed no vasospasm of the epicardial coronary arteries before or after DOB stress in either group. The plasma concentrations of endothelin-1 and 6-keto-prostaglandin F1alpha were significantly increased after DOB stress in the ischemia group, but the serum concentration of NO did not increase. The lack of an increase in NO production during DOB stress may have contributed to the worsening of MI in patients with Kawasaki disease.

The significance of stress-induced ST segment depression in patients with inferior Q wave myocardial infarction

OBJECTIVES

This study was conducted to evaluate the relationship between ST segment depression (STD) during dobutamine stress tests in different electrocardiogram (ECG) leads and myocardial ischemia assessed by simultaneous single photon emission computed tomography (SPECT) imaging in patients with inferior Q wave myocardial infarction.

BACKGROUND

STD is a standard electrocardiographic sign of myocardial ischemia. Although STD may represent reciprocal changes in patients with previous myocardial infarction, studies of reciprocal changes during stress tests are scarce.

METHODS

Dobutamine (up to 40 microg/kg/min) stress and rest myocardial perfusion scintigraphy using technetium SPECT imaging was performed in 125 patients >3 months after Q wave inferior myocardial infarction. The location of STD at the ECG was defined as anterior (V1-4), high lateral (I, aVL) and lateral (V5,6). Ischemia was defined as reversible perfusion abnormalities.

RESULTS

STD occurred in the high lateral leads in 20 patients, in the anterior leads in 12 patients and in the lateral leads in 2 patients. ST segment elevation occurred in 25 patients in the inferior leads. High lateral STD was associated with inferior ST elevation in 16 patients (80%). There was a significant inverse linear correlation between the magnitude of ST segment shift from rest to peak stress in the inferior and the high lateral leads (r = -0.8, p < 0.0005), whereas no significant correlation was found between ST segment shift in the inferior and the anterior leads (r = -0.1, p = NS) or between the inferior and the lateral leads (r = 0.15, p = NS). Ischemia was detected in 45% of patients with and in 42% of patients without high lateral STD (p = NS). Patients with high lateral STD had a higher prevalence of fixed perfusion defects in the inferior wall (100% vs. 70%) and in the posterolateral wall (55% vs. 29%) compared with other patients (both p < 0.05). Ischemia was more prevalent in patients with anterior STD than without (75% vs. 39%, p < 0.05).

CONCLUSIONS

In patients with inferior Q wave myocardial infarction, stress-induced STD in high lateral leads should be recognized as a reciprocal change for ST elevation in the inferior leads, and therefore, should be interpreted with the consideration of the significance of ST elevation if present, rather than being indicative of myocardial ischemia on its own. The STD found in the anterior leads appears to be a sign of myocardial ischemia. These findings should be considered in the definition of a positive ECG stress test and in establishing the criteria for the termination of stress test.

Noninvasive diagnosis of coronary artery stenosis in women with limited exercise capacity: comparison of dobutamine stress echocardiography and 99mTc sestamibi single-photon emission CT

OBJECTIVES

To compare the accuracy of dobutamine stress echocardiography (DSE) and simultaneous 99mTc sestamibi (MIBI) single-photon emission CT (SPECT) imaging for the diagnosis of coronary artery stenosis in women.

PATIENTS

Seventy women with limited exercise capacity referred for evaluation of myocardial ischemia.

METHODS

DSE (up to 40 microg/kg/min) was performed in conjunction with stress MIBI SPECT. Resting MIBI images were acquired 24 h after the stress test. Ischemia was defined as new or worsened wall motion abnormalities confirmed by DSE and as reversible perfusion defects confirmed by MIBI. Significant coronary artery disease was defined as > or = 50% luminal diameter stenosis.

RESULTS

DSE was positive for ischemia in 35 of 45 patients with coronary artery stenosis and in 2 of 25 patients without coronary artery stenosis (sensitivity = 78% CI, 68 to 88; specificity = 92% CI, 85 to 99; and accuracy = 83% CI, 74 to 92). A positive MIBI study for ischemia occurred in 29 patients with coronary artery stenosis and in 7 patients without coronary artery stenosis (sensitivity = 64% CI, 53 to 76; specificity = 72% CI, 61 to 83; and accuracy = 67% CI, 56 to 78 [p < 0.05 vs DSE]). In the 59 vascular regions with coronary artery stenosis, the regional sensitivity of DSE was higher than MIBI (69% CI, 62 to 77 vs 51% CI, 42 to 59, p < 0.05), whereas specificity in the 81 vascular regions without significant stenosis was similar (89% CI, 84 to 94 vs 88% CI, 82 to 93, respectively).

CONCLUSION

DSE is a useful noninvasive method for the diagnosis of coronary artery stenosis in women and provides a higher overall and regional diagnostic accuracy than dobutamine MIBI SPECT in this particular population.

Hemodynamic effects of arbutamine

This study examined the hemodynamic effects of arbutamine, a synthetic catecholamine, in 12 patients with and 7 patients without coronary artery disease. Arbutamine produced a balanced positive inotropic (increase in left ventricular dp/dt) and chronotropic effect (increase in heart rate).

Dobutamine-atropine stress myocardial perfusion SPECT imaging in the diagnosis of graft stenosis after coronary artery bypass grafting

OBJECTIVE

To assess the accuracy of dobutamine stress myocardial perfusion single photon emission computed tomographic imaging (SPECT) for the diagnosis of vascular stenosis after coronary artery bypass grafting (CABG).

BACKGROUND

Exercise thallium scintigraphy is a clinically useful method for the diagnosis of graft stenosis after CABG. Although dobutamine perfusion scintigraphy is an alternative method for the evaluation of patients with limited exercise capacity, its value in the diagnosis of vascular stenosis after CABG has not been studied.

METHODS

Dobutamine (up to 40 lg/kg/min)-atropine (up to 1 mg) stress test in conjunction with myocardial perfusion SPECT imaging (201T1 or 99m technetium sestamibi [MIBII) was performed in 71 patients (mean age 58 9 years, 57 men) with limited exercise capacity referred for evaluation of myocardial ischemia 3.7 3.5 years after CABG. Significant vascular stenosis was defined as >50% luminal diameter stenosis of a graft or a native nongrafted coronary artery and was predicted on the basis of reversible perfusion abnormalities.

RESULTS

Significant vascular stenosis was detected in 52 patients. Sensitivity, specificity, and accuracy of reversible perfusion defects at dobutamine SPECT for the overall diagnosis of vascular stenosis were 81%, confidence interval (CI) 72 to 90, 79%, CI 69 to 88, and 80%, CI 71 to 90, respectively. Significant vascular stenosis was detected in 73 arterial regions. Sensitivity, specificity, and accuracy of dobutamine SPECT for the diagnosis of regional vascular stenosis were 66%, CI 58 to 74, 83%, CI 76 to 89, and 74%, CI 67 to 81, respectively. Patients with multivessel stenosis had a higher number of ischemic segments (1.6 + 1.3 vs 1 + 1, P < .05) and ischemic perfusion score (3.2 2.7 vs 2.2 + 2.3, P < .05) than patients with single-vessel stenosis, respectively. Significant graft stenosis was detected in 67 graft regions. Sensitivity, specificity, and accuracy of dobutamine SPECT for the diagnosis of regional graft stenosis were 64%, CI 56 to 73, 85%, CI 78 to 91, and 74%, CI 66 to 82, respectively.

CONCLUSION

Dobutamine stress myocardial perfusion SPECT imaging is a useful method for the diagnosis of significant vascular stenosis after CABG in patients with limited exercise capacity.

Assessment of myocardial perfusion and contractile function by inotropic stress Tc-99m sestamibi SPECT imaging and echocardiography for optimal detection of multivessel coronary artery disease

OBJECTIVE

To assess whether inotropic stress myocardial perfusion imaging, echocardiography, or a combination of the two could enhance the detection of multivessel disease, over and above clinical and exercise electrocardiographic data.

DESIGN

100 consecutive patients investigated by exercise electrocardiography and diagnostic coronary arteriography underwent simultaneous inotropic stress Tc-99m sestamibi SPECT (MIBI) imaging and echocardiography. MIBI imaging and echocardiographic data were analysed using a 12 segment left ventricular model, and each segment was ascribed to a particular coronary artery territory. The presence of perfusion defects with MIBI imaging or of wall thickening abnormality with echocardiography in at least two coronary artery territories at peak stress was taken as diagnostic of multivessel disease. Arteriographic evidence of > or = 50% stenosis was considered significant.

RESULTS

56 patients had multivessel disease. The sensitivity of the combination of MIBI imaging and echocardiography for detecting this was greater than either MIBI imaging or echocardiography alone (82%, 68%, and 68%, respectively; p = 0.005). Clinical and exercise electrocardiographic variables gave an R2 value of 18.2% for predicting multivessel disease. The addition of either MIBI imaging (R2 = 29.2%; p = 0.002) or echocardiography (R2 = 28.8%; p < 0.001) enhanced the detection of multivessel disease, and the inclusion of both had further incremental value (R2 = 34.8%; p = 0.003). Age (p = 0.03), MIBI imaging (p = 0.007), and echocardiography (p = 0.001) were independent predictors of multivessel disease.

CONCLUSIONS

The assessment of both myocardial perfusion and contractile function by simultaneous inotropic stress MIBI imaging and echocardiography optimises the non-invasive detection of multivessel disease.

Measurement of aortic and pulmonary flow with MRI at rest and during physical exercise

PURPOSE

Our aim was to assess the feasibility of measuring great vessel flow during submaximal exercise using MR flow mapping.

METHOD

In 16 healthy volunteers, MR measurements of great vessel flow were obtained at rest and during two levels of submaximal physical exercise using an MR-compatible bicycle ergometer.

RESULTS

Great vessel flow showed good correlation at rest and during exercise (r = 0.9, p < 0.0005). Significant increase in heart rate was observed during exercise. Aortic flow volume increased from 64 +/- 13 ml/beat at rest to 71 +/- 11 ml/beat at 50 W (p < 0.0005) to 79 +/- 13 ml/beat at 100 W (p < 0.0005). Pulmonary flow volume increased from 63 +/- 14 ml/beat at rest to 70 +/- 13 ml/beat at 50 W (p < 0.005) to 76 +/- 12 ml/beat at 100 W (p = NS).

CONCLUSION

Quantification of great vessel flow can be performed safely in healthy volunteers using MR flow measurements during submaximal physical exercise. These measurements may be used to study hemodynamic abnormalities in patients with cardiac disease.

Evaluation of myocardial ischemia in Kawasaki disease by dobutamine stress signal-averaged ventricular late potentials

OBJECTIVE

To determine the possibility of diagnosing myocardial ischemia from signal-averaged electrocardiographic late potentials (LPs) in patients with Kawasaki disease.

METHODS

Dobutamine stress LPs were obtained in 85 children with a history of Kawasaki disease (48 without coronary artery lesions, 19 with coronary artery lesions without myocardial ischemia, and 18 with myocardial ischemia). The infusion of dobutamine was started at 5 micrograms/kg/min, increased to 30 micrograms/kg/min. The presence of LPs was determined by the filtered QRS duration, the root mean square voltage during the last 40 ms, and the duration of the signal under 40 microV.

RESULTS

Among the children without coronary lesions, LPs were detected in 4.2% at rest and in 2.1% with dobutamine stress. Among the group with coronary lesions but without ischemia, LPs were found in 5.3% at rest and in 5.3% with stress. In the group with ischemia, LPs were present in 44.4% at rest and in 77.8% with stress. The sensitivity for myocardial ischemia was 72.7% at rest and 87.5% with stress (p < 0.05), and the specificity was 86.5% at rest and 94.2% with stress.

CONCLUSION

LPs associated with dobutamine stress testing are useful for identifying myocardial ischemia in children with Kawasaki disease, especially in those who cannot tolerate testing involving physical exercise.

Direct comparison of arbutamine and dobutamine stress testing with myocardial perfusion imaging and echocardiography in patients with coronary artery disease

Arbutamine, a new sympathomimetic compound, appears to elicit a more balanced inotropic and chronotropic response than dobutamine, currently used as a pharmacologic stress agent. The present study was performed to compare standard dobutamine stress testing with arbutamine for the detection of myocardial ischemia with technetium (Tc)-99m sestamibi tomographic imaging and 2-dimensional echocardiography in patients with coronary artery disease. Twenty-six patients with evidence of coronary artery disease underwent dobutamine infusion of 5 to 40 microg/kg/min in 3-minute stages. On a separate day, arbutamine was administered by an automated, computerized, closed-loop device monitoring both heart rate and blood pressure. Both infusions were terminated upon achievement of target heart rate, completion of maximal infusion dose (dobutamine), heart rate saturation (arbutamine), or standard clinical end points. Tc-99m sestamibi was injected before termination of both infusions followed by tomographic myocardial perfusion imaging, whereas echocardiography was performed at baseline and throughout the infusions. There were no significant differences in maximal heart rate, blood pressure, and rate-pressure product as well as in the development of anginal symptoms or electrocardiographic changes during both infusions. The location and severity of myocardial perfusion defects and echocardiographic wall motion abnormalities were similar between both agents. It is concluded that arbutamine produces similar imaging results compared with standard dobutamine stress with both Tc-99m sestamibi single-photon emission computed tomographic myocardial perfusion imaging and 2-dimensional echocardiography.

Inotropic stress with arbutamine is superior to vasodilator stress with dipyridamole for the detection of reversible ischemia with Tc-99m sestamibi single-photon emission computed tomography

BACKGROUND

There is a paucity of data comparing the relative merits of inotropic and vasodilator stress Tc-99m sestamibi single-photon emission computed tomography (SPECT) for the detection of coronary artery disease and reversible ischemia.

METHODS AND RESULTS

Twenty-seven patients referred for diagnostic coronary arteriography underwent separate day dipyridamole and arbutamine Tc-99m sestamibi SPECT imaging with simultaneous two-dimensional echocardiography. The sensitivity of arbutamine and dipyridamole Tc-99m sestamibi for the detection of coronary artery disease was 100% (21 of 21) and 90% (19 of 21), respectively, with a specificity of 66% (4 of 6) for both. Coronary artery disease was detected in all six patients with single vessel disease by both stress modalities. The sensitivity for prediction of multivessel disease was 66% (10 of 15) for arbutamine and 46% (7 of 15) for dipyridamole stress. Arbutamine stress induced a greater extent and severity of perfusion abnormality at peak stress (peak perfusion score 25 +/- 6.2 and 21 +/- 5.9 for arbutamine and dipyridamole, respectively, p = 0.001) and reversible perfusion defects (difference between peak stress and rest scores 8.8 +/- 5.5 and 5.2 +/- 4.4 for arbutamine and dipyridamole, respectively, p = 0.001). Furthermore a significantly higher percentage of reversible defects induced by arbutamine stress was associated with wall thickening abnormality on simultaneous echocardiography, which is a more specific marker of myocardial ischemia (88% and 24% for arbutamine and dipyridamole, respectively, p = 0.002).

CONCLUSION

Inotropic stress may be superior to vasodilators for the determination of the extent and severity of myocardial involvement and reversible ischemia by Tc-99m sestamibi SPECT.

Comparison of Tc-99m sestamibi perfusion imaging and echocardiography using an arbutamine infusion for the detection of coronary artery disease

Arbutamine, a synthetic catecholamine, coupled with a closed-loop, computerized delivery system was evaluated in conjunction with technetium-99m sestamibi scintigraphy and echocardiography for the detection of coronary artery disease. Concordance between the imaging methods was 68%, with a similar sensitivity for coronary disease using echocardiography (78%) and technetium-99m sestamibi (76%), although more arbutamine-induced ischemia was noted with perfusion imaging.

Comparison of arbutamine stress 99mTc-labeled sestamibi single-photon emission computed tomographic imaging and echocardiography for detection of the extent and severity of coronary artery disease and inducible ischemia

BACKGROUND

Arbutamine is a new synthetic catecholamine developed specifically for pharmacologic stress testing.

METHODS AND RESULTS

We investigated 39 patients undergoing coronary arteriography to compare arbutamine stress (99m)Tc-labeled sestamibi single-photon emission computed tomographic imaging and echocardiography for detection of the extent and severity of coronary artery disease and inducible ischemia. Rest and stress studies were analyzed blindly according to a 12-segment left ventricular model for both techniques. Each segment was graded according to severity of wall thickening abnormality and perfusion defect (1 = normal to 4 = severe). Total perfusion defect and wall thickening scores were calculated at peak stress and the difference in scores between stress and rest (delta perfusion defect; delta wall thickening) were used as indexes of inducible ischemia. Twenty-one patients had multivessel disease, nine had single-vessel disease, and nine had normal coronary arteries. Diagnostic accuracies for the detection of coronary artery disease for single-photon emission computed tomographic imaging and echocardiography were 95% and 92%, respectively. Extent and severity of coronary artery disease indicated by a peak stress perfusion defect score of 26 +/- 6.4 and wall thickening score of 25.1 +/- 8.4 were similar, and there was no significant difference in the delta perfusion defect and delta wall thickening scores of 8.7 +/- 5.5 and 10.4 +/- 7.1, respectively. Segmental concordance rates for the detection of coronary artery disease and inducible ischemia were 74% (K = 0.47; confidence interval 0.39 to 0.55) and 74% (kappa = 0.42; confidence interval 0.34 to 0.51), respectively. Regional concordance for coronary artery disease was 84% (kappa = 0.68; confidence interval 0.51 to 0.84). Where discordance was present, there was a greater prevalence of perfusion abnormality compared with wall thickening abnormality.

CONCLUSION

Arbutamine stress single-photon emission computed tomographic imaging and echocardiography provide largely equivalent and accurate pathophysiologic information for the evaluation of coronary artery disease and inducible ischemia.

Relation between ambulatory electrocardiographic monitoring and myocardial perfusion imaging to detect coronary artery disease and myocardial ischemia: an ACIP ancillary study. The Asymptomatic Cardiac Ischemia Pilot (ACIP) Investigators

OBJECTIVES

This study sought to explore the relation between markers of ischemia detected by ambulatory electrocardiographic (AECG) monitoring and stress myocardial perfusion single-photon emission computed tomography (SPECT).

BACKGROUND

Stress myocardial SPECT and AECG monitoring are both utilized in evaluating patients with coronary artery disease. However, information is limited regarding the relation between the presence and extent of ischemia as detected by these two modalities.

METHODS

This was an ancillary study of the Asymptomatic Cardiac Ischemia Pilot (ACIP) trial. One hundred six patients with previous coronary angiography underwent AECG monitoring and stress SPECT within a close temporal time period. The frequency and duration of ischemia as assessed by AECG monitoring and the total and ischemic stress-induced myocardial perfusion defect sizes as assessed by SPECT were quantified in separate core laboratories. Multivariate logistic regression and linear regression analysis were used to determine associations between AECG and SPECT abnormalities with regard to angiographic, demographic and treadmill exercise variables.

RESULTS

Seventy-four percent of patients with significant (> or = 50%) coronary artery stenosis had SPECT abnormalities, whereas 61% had ischemia by AECG monitoring. The most important predictors of SPECT abnormalities were severity (p < 0.001) of coronary artery stenosis, followed by total exercise duration (p = 0.016) and patient age (p = 0.04). The only predictor of AECG abnormalities was the presence of ST segment depression on the initial exercise treadmill test (p = 0.021). Only a 50% concordance for normalcy or abnormalcy was observed between the SPECT and AECG results, and no relation was observed between the frequency or duration of AECG ischemia and the quantified total or ischemic myocardial perfusion defect size as assessed by SPECT.

CONCLUSIONS

Ischemia as detected by AECG monitoring does not correlate with the presence and extent of ischemia as quantified by stress SPECT. Because these techniques appear to detect different pathophysiologic manifestations of ischemia, they may be complementary in more fully defining the functional significance of coronary artery disease and, in particular, which patients are at highest risk for adverse cardiac events.

Comparison of dobutamine stress echocardiography and 99m-technetium sestamibi SPECT myocardial perfusion scintigraphy for predicting extent of coronary artery disease in patients with healed myocardial infarction

This study compares the value of dobutamine stress echocardiography and 99m-technetium methoxyisobutyl-isonitrile (MIBI) single-photon emission computed tomography (SPECT) in the assessment of extent and location of coronary narrowing in patients with healed myocardial infarction. Dobutamine (up to 40 microg/kg/ min)-atropine (up to 1 mg) stress echocardiography (DSE) in conjunction with MIBI SPECT was performed in 72 patients (52 men, mean age 57 +/- 11 years) with healed myocardial infarction referred for evaluation of myocardial ischemia. Ischemia was defined as new or worsened wall motion abnormalities at DSE and reversible perfusion defects at MIBI SPECT. Significant stenosis (> or = 50% luminal diameter stenosis) of the infarct-related artery was detected in 45 patients and of other coronary arteries in 22 patients. Sensitivity and specificity of remote ischemia for diagnosis of remote coronary stenosis were 68% (95% confidence interval [CI] 57 to 80) and 93% (CI 86 to 99) for DSE, and 64% (CI 52 to 76), and 90% (CI 83 to 98) for MIBI SPECT, respectively. The positive predictive value and specificity of peri-infarction ischemia for the diagnosis of infarct-related artery stenosis were 89% (CI 81 to 97) and 82% (CI 73 to 92) for DSE, and 87% (CI 79 to 95) and 82% (CI 73 to 92) for SPECT, respectively. The agreement between both techniques was higher for the diagnosis of remote than peri-infarction ischemia (84% vs 66%, p = 0.02). It is concluded that in patients with myocardial infarction undergoing dobutamine stress testing, both echocardiography and MIBI SPECT are clinically useful methods for the diagnosis of remote and infarct-related coronary artery stenosis.