Quantitative comparison of thallium-201 scintigraphy after exercise and dipyridamole in coronary artery disease

Higher events rate in patients with a normal gated myocardial perfusion imaging with dipyridamole than exercise: "Run for reliability"

OBJECTIVE

The aim of this is to evaluate the negative predictive value (NPV) of a normal gated myocardial perfusion imaging (NGMPI) with exercise and dipyridamole in a propensity matched population.

MATERIALS AND METHODS

This is a prospective study conducted at Nuclear Cardiology Department of Karachi Institute of Heart Diseases, Karachi from December 2008 until June 2010. A total of 809 patients with a NGMPI with adequate exercise (558/809) or dipyridamole (251/809) stress were included and followed-up for 12-30 months (mean 24 ± 3 months) for fatal or non-fatal myocardial infarctions (MI).

RESULTS

Mean ejection fraction (%), end diastolic volume (ml), and end systolic volume (ml) in exercise and dipyridamole cohorts were (72 ± 08, 66 ± 11), (68 ± 13, 81 ± 17), and (19 ± 11, 26 ± 12) respectively. On follow-up, in dipyridamole cohort 2 fatal and 6 non-fatal MIs were reported. While in exercise cohort only 2 non-fatal MIs were reported. The NPV of a NGMPI with exercise was 99.7% (95% confidence interval [CI] 98.93-99.96%) with an event rate of 0.3% (95% CI; 0.03-0.6%) and annualized event rate of 0.15%. The NPV of NGMPI with dipyridamole was 96.80% (95% CI; 2.2-4.3%) with an event rate of 3.2% (95% CI; 1.39-3.83%) and annualized event rate of approximately 1.6%. Event free survival for dipyridamole group was significantly lower than exercise analyzed by Log-rank test (14.509, P < 0.001).

CONCLUSION

A NGMPI with dipyridamole stress has higher event rate (low-NPV) as compared with exercise and this raises concern over its credibility to label these patients into low-risk group.

Stress myocardial CT perfusion: an update and future perspective

Coronary computed tomography angiography (CTA) has been shown by several multicenter trials to have excellent diagnostic accuracy in the detection and exclusion of significant coronary stenosis. However, a major limitation of coronary CTA is that the physiological significance of stenotic lesions identified is often unknown. Stress myocardial computed tomography perfusion (CTP) is a novel examination that provides both anatomic and physiological information (i.e., myocardial perfusion). Multiple single-center studies have established the feasibility of stress myocardial CTP. Furthermore, it has been illustrated that a combined CTA/CTP protocol improves the diagnostic accuracy to detect hemodynamic significant stenosis as compared with CTA alone; this combined protocol can also be accomplished at a radiation dose comparable to nuclear myocardial perfusion imaging exams. Although initial results hold some promise, stress myocardial CTP is a modality in its infancy. Further research is required to define, validate, and optimize this new technique. However, it is a modality with significant potential, particularly in the evaluation of chest pain patients, given the advantages of short exam time and comprehensive data acquisition. This review highlights how to perform and interpret stress myocardial CTP, summarizes the current literature, and discusses some future directions.

Effect of caffeine on SPECT myocardial perfusion imaging during regadenoson pharmacologic stress: rationale and design of a prospective, randomized, multicenter study

BACKGROUND

Caffeine attenuates the coronary hyperemic response to adenosine by competitive A₂(A) receptor blockade. This study aims to determine whether oral caffeine administration compromises diagnostic accuracy in patients undergoing vasodilator stress myocardial perfusion imaging (MPI) with regadenoson, a selective adenosine A(2A) agonist.

METHODS

This multicenter, randomized, double-blind, placebo-controlled, parallel-group study includes patients with suspected coronary artery disease who regularly consume caffeine. Each participant undergoes three SPECT MPI studies: a rest study on day 1 (MPI-1); a regadenoson stress study on day 3 (MPI-2), and a regadenoson stress study on day 5 with double-blind administration of oral caffeine 200 or 400 mg or placebo capsules (MPI-3; n = 90 per arm). Only participants with ≥ 1 reversible defect on the second MPI study undergo the subsequent stress MPI test. The primary endpoint is the difference in the number of reversible defects on the two stress tests using a 17-segment model. Pharmacokinetic/pharmacodynamic analyses will evaluate the effect of caffeine on the regadenoson exposure-response relationship. Safety will also be assessed.

CONCLUSION

The results of this study will show whether the consumption of caffeine equivalent to 2-4 cups of coffee prior to an MPI study with regadenoson affects the diagnostic validity of stress testing (ClinicalTrials.gov number, NCT00826280).

Comparison of long-term mortality risk following normal exercise vs adenosine myocardial perfusion SPECT

BACKGROUND

A higher frequency of clinical events has been observed in patients undergoing pharmacological vs exercise myocardial perfusion single-photon emission computed tomography (SPECT). While this difference is attributed to greater age and co-morbidities, it is not known whether these tests also differ in prognostic ability among patients with similar clinical profiles.

METHODS AND RESULTS

We assessed all-cause mortality rates in 6,069 patients, followed for 10.2 ± 1.7 years after undergoing exercise or adenosine SPECT. We employed propensity analysis to match exercise and adenosine subgroups by age, gender, symptoms, and coronary risk factors. Within our propensity-matched cohorts, adenosine patients had an annualized mortality rate event rates that was more than twice that of exercise patients (3.9% vs 1.6%, P < .0001). Differences in mortality persisted among age groups, including those <55 years old. In the exercise cohort, mortality was inversely related to exercise duration, with comparable mortality noted for patients exercising <3 min and those undergoing adenosine testing.

CONCLUSIONS

Among patients with normal stress SPECT tests, those undergoing adenosine testing manifest a mortality rate that is substantially higher than that observed among adequately exercising patients, but comparable to that observed among very poorly exercising patients. This elevated risk underscores an important challenge for managing patients undergoing pharmacological stress testing.

Does beta blocker therapy affect the diagnostic accuracy of adenosine single-photon-emission computed tomographic myocardial perfusion imaging?

We retrospectively evaluated perfusion defect presence, extent, and severity in 158 consecutive patients receiving beta blockers, who underwent adenosine single-photon-emission computed tomography (SPECT) myocardial perfusion imaging (MPI) and coronary angiography. Seventy-six patients (group 1) had their beta blockers withdrawn 48 hours prior to testing, and 82 patients (group 2) remained on the beta blocker regimen. Groups 1 and 2 were similar in gender, age, pretest symptoms, and history of coronary artery disease (CAD). Group 1 patients had higher resting heart rates (79 +/- 19/min versus 68 +/- 13/min; P < 0.001), peak heart rates (91 +/- 21/min versus 80 +/- 15/min; P < 0.001), resting diastolic blood pressures (82 +/- 14 mm Hg versus 74 +/- 13 mm Hg; P < 0.001), peak systolic blood pressures (139 +/- 23 mm Hg versus 124 +/- 23 mm Hg; P < 0.001), and peak diastolic blood pressures (72 +/- 12 mm Hg versus 68 +/- 11 mm Hg; P = 0.04) than group 2 patients. Group 1 also had a higher incidence of angina during the 48 hours off beta blockers than group 2 (10% versus 2%; P < 0.001). There was no significant difference between the two groups in symptoms and side effects during adenosine infusion, quantitated lung/heart ratio, visually assessed lung uptake, transient ischemic dilation, post-stress ejection fraction, summed stress score, summed rest score, and summed difference score. In conclusion, in patients with CAD, beta blocker therapy does not affect the extent, severity, and reversibility of perfusion defects on adenosine SPECT MPI.

Impact of Body Mass Index on Cardiac Mortality in Patients With Known or Suspected Coronary Artery Disease Undergoing Myocardial Perfusion Single-Photon Emission Computed Tomography

OBJECTIVES

The purpose of this study was to assess the relationship between body mass index (BMI) and the prognostic value of myocardial perfusion single-photon emission computed tomography (MPS).

BACKGROUND

The prognostic value of MPS in the obese has not been evaluated.

METHODS

We studied 4,720 patients with and 10,019 patients without known coronary artery disease (CAD) who underwent rest Tl-201/stress Tc-99m sestamibi MPS, including 5,233 gated MPS studies and followed up (mean 2.7 to 3.2 years). Patients were categorized as normal weight (BMI 18.5 to 24.9 kg/m2), overweight (BMI 25.0 to 29.9 kg/m2), or obese (BMI > or =30.0 kg/m2).

RESULTS

Unadjusted annual rates of cardiac death (CD) rose versus stress MPS abnormalities in all weight groups (p < 0.001). Obese or overweight patients with or without known CAD who had normal MPS were at low CD risk (<1%/year), similar to normal weight patients. In CAD, obese and overweight patients with abnormal MPS had lower rates of CD compared with normal weight patients (p < 0.01). In patients with low ejection fraction (EF) by gated MPS, those with normal weight had highest CD rate (p = 0.001). Multivariable models revealed that BMI was not a predictor of CD in suspected CAD patients (hazard ratio [HR] 0.99; 95% confidence interval [CI] 0.95 to 1.02) but was an independent inverse predictor of CD in known CAD patients (HR 0.95; 95% CI 0.92 to 0.98), especially in women, adenosine stress, low EF, or abnormal perfusion.

CONCLUSIONS

Normal MPS was associated with low risk of CD in patients of all weight categories. In patients with known CAD undergoing MPS, obese and overweight patients were at lower risk of CD over three years than normal weight patients.

Relationship between stress-induced myocardial ischemia and atherosclerosis measured by coronary calcium tomography

OBJECTIVES

We assessed the relationship between stress-induced myocardial ischemia on myocardial perfusion single-photon emission computed tomography (MPS) and magnitude of coronary artery calcification (CAC) by X-ray tomography in patients undergoing both tests.

BACKGROUND

There has been little evaluation regarding the relationship between CAC and inducible ischemia or parameters that might modify this relationship.

METHODS

A total of 1,195 patients without known coronary disease, 51% asymptomatic, underwent stress MPS and CAC tomography within 7.2 +/- 44.8 days. The frequency of ischemia by MPS was compared to the magnitude of CAC abnormality.

RESULTS

Among 76 patients with ischemic MPS, the CAC scores were >0 in 95%, >or=100 in 88%, and >or=400 in 68%. Of 1,119 normal MPS patients, CAC scores were >0, >or=100, and >or=400 in 78%, 56%, and 31%, respectively. The frequency of ischemic MPS was <2% with CAC scores <100 and increased progressively with CAC >or=100 (p for trend <0.0001). Patients with symptoms with CAC scores >or=400 had increased likelihood of MPS ischemia versus those without symptoms (p = 0.025). Absolute rather than percentile CAC score was the most potent predictor of MPS ischemia by multivariable analysis. Importantly, 56% of patients with normal MPS had CAC scores >or=100.

CONCLUSIONS

Ischemic MPS is associated with a high likelihood of subclinical atherosclerosis by CAC, but is rarely seen for CAC scores <100. In most patients, low CAC scores appear to obviate the need for subsequent noninvasive testing. Normal MPS patients, however, frequently have extensive atherosclerosis by CAC criteria. These findings imply a potential role for applying CAC screening after MPS among patients manifesting normal MPS.

Improved coronary disease detection with quantitative attenuation-corrected Tl-201 images

BACKGROUND

The normal distribution of myocardial tracer activity is different in attenuation-corrected images compared with uncorrected images. We therefore postulated that quantitation of attenuation-corrected thallium 201 images with direct comparison to a database of healthy subjects could improve detection of coronary artery stenoses.

METHODS AND RESULTS

In 49 patients with angiographic evidence of coronary artery disease and 69 patients with a less than 5% likelihood of coronary artery disease, tomographic Tl-201 myocardial imaging was performed by means of a triple-headed camera with fan-beam collimators and the images were processed with attenuation correction, with attenuation and Compton scatter correction, and without correction. Images were subjectively interpreted in a blinded manner. From the group of 69 patients with a low likelihood of coronary disease, scintigraphic data from the first 20 men and the first 20 women were used to generate normal reference ranges for each of the 3 image-processing methods. Data from the 49 patients with angiographic coronary disease and from the remaining 29 patients with a low likelihood of coronary disease were then analyzed quantitatively in comparison to the gender-matched normal databases. With visual interpretation, attenuation-corrected images yielded an improved detection rate compared with uncorrected images (79% vs 46%, P =.008) for 70% or greater left anterior descending coronary artery stenoses. Attenuation-corrected images also provided an improved normalcy rate for the right coronary artery territory (91% vs 75%, P =.006) and an improved normalcy rate when the images were analyzed overall by patient (88% vs 74%, P =.009). With quantitative analysis, attenuation correction yielded an improved detection rate for patients with a significant coronary artery stenosis compared with uncorrected images (90% vs 71%, P =.016). Defect extent was also increased by attenuation correction. Compared with attenuation correction alone, the addition of scatter correction yielded no incremental improvement in detection rate or normalcy rate. Attenuation-scatter correction did produce a nonsignificant trend toward detection of more of the total number of stenotic arteries compared with uncorrected images (60 vs 48 of 79 arteries).

CONCLUSIONS

With the use of a triple-headed camera with fan-beam collimation, visual analysis of attenuation-corrected Tl-201 images improved detection of left anterior descending coronary artery disease without loss of detection in other coronary territories. Furthermore, quantitative analysis of attenuation-corrected Tl-201 images improved the overall detection rate for coronary artery disease in patients without compromise of the normalcy rate.

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.

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

Prediction of human transplantation arteriopathy and coronary events with lung/heart count ratios during intravenous dipyridamole thallium-201 imaging

BACKGROUND

Cardiac allograft arteriopathy often limits long-term survival in transplantation recipients but has been difficult to detect by standard diagnostic methods. Because of the diffuse nature of transplantation coronary disease, we postulated that a lung/heart ratio during dipyridamole thallium imaging might better predict arteriopathy-related complications than diagnostic methods that detect discrete luminal stenoses.

METHODS AND RESULTS

Sixty-six unselected heart transplantation recipients were evaluated with annual coronary arteriograms, endomyocardial biopsy, and intravenous dipyridamole thallium testing (initial study group). The mean lung/heart ratio on an anterior planar image was 0.40 for all patients; therefore <0.40 was arbitrarily defined as normal. After October 1992, 98 patients were tested (validation study group) and a lung/heart ratio cutoff of 0.40 was evaluated prospectively. Coronary end points were defined as (1) at least 1 coronary artery stenosis >/=50% of the luminal diameter, (2) sudden cardiac death, and (3) acute myocardial infarction. Stepwise logistic regression analysis was performed to identify independent predictors of future coronary end points. For the initial study group, the lung/heart ratio on the first annual thallium study was the only independent predictor of subsequent cardiac end points (0.47 +/- 0.13 [SD] with end points vs 0.38 +/- 0.11 without end points, P <.05). For the validation study group, independent predictors of subsequent coronary events included the lung/heart ratio and the radionuclide left ventricular ejection fraction. No patient with a lung/heart ratio <0.40 and a left ventricular ejection fraction >/=0.50 developed a cardiac event during 21 +/- 11 months of follow-up.

CONCLUSIONS

A lung/heart ratio >/=0.40 on dipyridamole thallium testing is a sensitive predictor of coronary events after heart transplantation. Patients with heart transplantion who have a lung/heart ratio <0.40 and normal systolic left ventricular function are at low risk for subsequent coronary events and may not require annual surveillance by coronary arteriography.

Tl-201 myocardial SPECT in patients with systemic arterial diseases

We compared the results of Tl-201 myocardial SPECT of patients with arteriosclerosis obliterans (ASO), abdominal aortic aneurysm (AAA), and Takayasu arteritis (TA), so that coronary artery disease could be evaluated in them. Twenty-three patients (ASO, 9; AAA, 8; TA, 6) had Tl-201 myocardial SPECT with stress testing, and SPECT data was assessed qualitatively and quantitatively. Qualitative analysis showed that myocardial perfusion was decreased most in patients with ASO, followed by patients with AAA, and was minimally decreased in patients with TA. Quantitative analysis indicated that segmental uptake was significantly less in four segments in ASO compared with TA, less in two segments in AAA compared with TA, and less in two segments in ASO compared with AAA. Thus patients with ASO and AAA were found to have a marked abnormality in Tl-201 myocardial SPECT, indicating that this procedure should be performed in these patients. In patients with TA, however, because of minimal abnormality in myocardial perfusion, the role of SPECT is limited.

Do we still need dipyridamole?

There is limited evidence that dipyridamole is generally an effective antithrombotic agent when used alone, nor is there convincing evidence that the combination of aspirin and dipyridamole is more effective than aspirin alone, except perhaps in cerebrovascular disease. There is no consistent evidence to support the routine use of dipyridamole after coronary artery bypass grafting and in patients with occlusive peripheral vascular disease, although these remain common reasons for its use. Dipyridamole is a useful agent in 'pharmacological stress' testing in nuclear cardiology imaging and may be valuable when combined with warfarin in certain patient groups, such as those with prosthetic heart valves. When combined with aspirin, dipyridamole may be of value in the secondary prophylaxis of cerebrovascular disease, although further studies are clearly needed. In a significant proportion of cases, evidence-based medicine cannot support the current widespread continued prescription of dipyridamole in cardiological practice, but the jury is still out on cerebrovascular disease.

Myocardial perfusion imaging: clinical experience and recent progress in radionuclide scintigraphy and magnetic resonance imaging

In the past 20 years, radionuclide scintigraphy has proven to be a sensitive clinical tool in the assessment of myocardial perfusion abnormalities. Magnetic resonance imaging may also be used to study myocardial perfusion, but its potential value still has to emerge in the clinical setting. This review addresses the potential and achievements of both methods in clinical cardiology.

Comparing a high-dose dipyridamole SPECT imaging protocol with dobutamine and exercise stress testing protocols

OBJECTIVE

To determine the safety, sensitivity, specificity, and accuracy of high-dose dipyridamole compared with treadmill and dobutamine stress imaging protocols.

BACKGROUND

Nuclear imaging studies using standard dose dipyridamole provide similar results to those obtained when treadmill stress is used. Recently dobutamine tomography and planar imaging with high-dose dipyridamole have been shown no improve nuclear imaging results.

METHODS

One hundred fifty-nine patients were imaged with thallium, teboroxime, or sestamibi per standard single photon emission computed tomography (SPECT) protocols. Pharmacologic stress was performed in 85 people with the remainder undergoing exercise testing by Bruce protocol. In this study, 0.852 mg dipyridamole was used per kilogram body weight and was infused over a four-minute period. Results from nuclear imaging were compared with those from coronary arteriograms.

RESULTS

The sensitivity and specificity of high-dose dipyridamole was 100% and 88.9%, respectively, which is statistically greater (P < 0.005) than that achieved when patients were stressed by treadmill. Side effects with the higher dose of dipyridamole were easily reversed with aminophylline. The sensitivity and specificity of intravenous dobutamine was 100%, but it was used in a limited number of subjects. When patients were stressed by Bruce protocol the sensitivity was 92.5% and specificity was 42.8%. The differences were not attributable to inadequate exercise duration.

CONCLUSIONS

High-dose dipyridamole is safe and easily reversed with intravenous aminophylline. The sensitivity and specificity of dipyridamole and dobutamine stress testing were statistically more accurate than results obtained with treadmill protocols when SPECT is used to image the heart. High-dose dipyridamole resulted in greater changes in heart rate and blood pressure response than seen with standard-dose dipyridamole. Associated side effects can be easily reversed with the administration of intravenous aminophylline without significant complications. The sensitivity, specificity, and accuracy of single photon emission computed tomography using high-dose dipyridamole are 100%, 88.9%, and 97.9%, respectively, for the overall presence or absence of disease when compared with coronary arteriography. This is significantly (P < 0.005) greater than that obtained by treadmill nuclear imaging protocols, independent imaging agent.

Intracoronary Doppler guide wire versus stress single-photon emission computed tomographic thallium-201 imaging in assessment of intermediate coronary stenoses

OBJECTIVES

The purpose of this study was to compare measures of coronary flow reserve by an intracoronary Doppler guide wire with results of stress single-photon emission computed tomographic (SPECT) thallium-201 imaging in patients with intermediate coronary artery disease (40% to 70% stenosis).

BACKGROUND

Visual assessment of the coronary arteriogram as a means of predicting the physiologic significance of intermediate coronary stenoses is inaccurate. Coronary flow reserve is a reliable marker of the functional importance of a coronary lesion. The recent development of an intracoronary Doppler guide wire permits routine assessment of coronary flow reserve distal to coronary artery stenoses.

METHODS

We prospectively evaluated coronary flow reserve in 30 subjects with intermediate stenoses using an intracoronary Doppler guide wire during elective coronary angiography. Patients subsequently underwent stress SPECT thallium-201 testing, and the blinded interpretations were correlated. Coronary flow reserve in a control group with normal coronary arteries classified our sample into group 1 (abnormal flow reserve, < 2.0) and group 2 (normal flow reserve, > or = 2.0).

RESULTS

As defined, the coronary flow reserve of 16 vessels in group 1 was diminished in comparison to that of 19 vessels in group 2 (p = 0.0001). Qualitative and quantitative analysis of stress SPECT thallium-201 images confirmed perfusion defects in 15 of 16 vascular territories in group 1 in contrast to 1 of 19 regions in group 2. The sensitivity, specificity and overall predictive accuracy of Doppler-determined coronary flow reserve for stress SPECT thallium-201 results were 94%, 95% and 94%, respectively.

CONCLUSIONS

In appropriately selected patients with intermediate coronary artery stenoses, Doppler guide wire determination of lesion significance provides equivalent data to those acquired by stress SPECT thallium-201 imaging.

Comparison of dobutamine and exercise using technetium-99m sestamibi imaging for the evaluation of coronary artery disease

Studies using dobutamine thallium-201 myocardial perfusion imaging have suggested a high sensitivity and specificity for the detection of coronary artery disease. However, few data are available comparing dobutamine with exercise stress for the detection and localization of perfusion defects. This study compared the effects of dobutamine and exercise stress using technetium-99m sestamibi single-photon emission computed tomographic imaging in the same patients in a prospective crossover trial. Twenty-four patients with a high likelihood of coronary artery disease underwent tomographic myocardial imaging at rest, after symptom-limited treadmill exercise, and after intravenous dobutamine (maximum 30 micrograms/kg/min). Tomograms of the left ventricle were divided into 20 segments and were interpreted without knowledge of patient identity or stress protocol. Dobutamine was well tolerated by all patients. Segment-by-segment concordance between exercise and dobutamine images was highly significant (kappa = 0.56, p < 0.0001). Global first-order agreement (normal vs abnormal) between exercise and dobutamine studies was 96% (kappa = 0.65, p = 0.02); global second-order agreement (normal vs fixed vs ischemic defect) was 88% (kappa = 0.45, p = 0.02). Regional first- and second-order agreement were 96 and 93%, respectively (p < 0.001 for both). Twenty patients underwent coronary angiography. Comparisons between exercise and angiography and between dobutamine and angiography were similar for both global agreement (95 vs 100%, p = NS) and regional agreement (77 vs 72%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison between reference values for 201thallium uptake and washout from the myocardium after exercise and after dipyridamole

A slow washout of 201Thallium has a high diagnostic and prognostic value for coronary artery disease. The aim of the present work was to contribute with reference data on 201Tl uptake and washout from the myocardium. With a quantitative method using circumferential profiles and interpolative background subtraction we performed 201Tl myocardial imaging in two groups of subjects with a low probability of coronary artery disease. Washout in per cent is defined as (1-D/I).100, where D is the delayed uptake rate and I the initial uptake rate. In group A (n = 16) myocardial hyperaemia was induced by maximal exercise, in group B (n = 15) by intravenous infusion of dipyridamole. In group A, the mean washout was 52%, and in group B it was 34% (P < 0.001). The delayed uptake rate D was significantly higher after dipyridamole, 58.4 cps, than after exercise, 44.5 cps (P < 0.05). There was no significant differences in I between the two groups. The findings regarding D and I explain that the washout is slower after dipyridamole than after exercise, as the mean D/I ratio was 0.48 in group A and 0.66 in group B (P < 0.001).

Safety of dobutamine stress for thallium-201 myocardial perfusion tomography in patients with asthma

Many patients undergoing investigation for coronary artery disease are unable to exercise adequately due to physical or psychological reasons. Thallium-201 imaging using dipyridamole or adenosine may then be a suitable method of assessing myocardial perfusion. In patients with asthma, these drugs are contraindicated because of the risk of provoking bronchospasm. This study assesses the safety of dobutamine for thallium-201 myocardial perfusion imaging in patients with asthma who were unable to perform adequate exercise. Dobutamine was infused at rates < or = 40 micrograms/kg/min in 30 asthmatic patients for thallium-201 emission tomography. The severity of the airway reactivity ranged from mild to severe (bronchodilator treatment ranging from inhaled beta 2 agonists alone to maximal therapy including oral steroids). Coronary angiography was performed in 20 patients. Minor side effects of dobutamine were frequent, but did not limit the infusion rate. There were no episodes of bronchospasm, but tolerable dyspnea occurred in 8 patients who had reversible ischemia; this rapidly resolved with termination of the infusion. There were no serious cardiac complications, but chest pain occurred in 67% of patients. Thallium-201 images were abnormal in 10 of 11 patients with coronary artery disease (sensitivity 91%) and normal in 7 of 9 with normal coronary arteries (specificity 79%). Dobutamine thallium-201 myocardial perfusion tomography is a safe procedure in patients with asthma.

Angiographic and hemodynamic determinants of myocardial ischemia during adenosine thallium-201 scintigraphy in coronary artery disease

BACKGROUND

Myocardial ischemia attributed to coronary steal may occur in some patients receiving pharmacological coronary vasodilation. ECG ST-segment depression is a marker of myocardial ischemia in these patients, but the factors determining the presence or absence of ischemia are not well known.

METHODS AND RESULTS

To examine the angiographic, hemodynamic, and scintigraphic determinants of adenosine-induced ischemic ST-segment depression in patients with coronary artery disease, we studied 65 consecutive patients (45 men and 20 women; mean age, 65 +/- 12 years) who showed reversible perfusion defects during adenosine (140 micrograms.kg-1.min-1 for 6 minutes) 201Tl single-photon emission computed tomography. Patients with prior myocardial infarction were excluded. Ischemic ST depression occurred in one third of the whole cohort (22 of 65 patients). The presence of coronary collateral vessels (p = 0.001), systolic blood pressure at baseline (p = 0.006), and adenosine-induced anginal chest pain (p = 0.011) were the only significant independent predictors of ischemic ST-segment depression by stepwise logistic regression analysis. Rate-pressure product at baseline, systolic blood pressure, heart rate, rate-pressure product, increase in heart rate, and rate-pressure product during adenosine infusion and maximal percent stenosis were variables also significantly related to ischemic ST depression by univariate analysis but were not predictive after the three primary variables were included in the regression model. Perfusion defect size, number of diseased vessels, and age did not correlate with ST-segment depression.

CONCLUSIONS

The presence of collaterals, which may predispose to coronary collateral steal, is the most significant correlate of ischemic ST-segment depression during adenosine infusion. Systolic blood pressure at baseline, which may affect the myocardial oxygen supply/demand ratio and anginal chest pain induced by adenosine, are additional variables related to ischemic ST-segment depression during adenosine infusion.

New directions in myocardial perfusion imaging

In recent years, substantial progress has been made in the field of nuclear cardiology. Pharmacologic stress perfusion imaging with intravenous administration of dipyridamole or adenosine provides comparable sensitivity and specificity values for detection of coronary artery disease (CAD) as exercise imaging and has been employed successfully for risk stratification prior to peripheral vascular or aortic surgery and after myocardial infarction. Detection of myocardial viability can be enhanced utilizing reinjection of a second dose of thallium-201 (Tl-201) at rest after acquisition of redistribution images with the single photon emission computerized tomography (SPECT) technique. Imaging solely in the resting state with Tl-201 can also provide information concerning presence of viable myocardium in asynergic regions that are stunned or hibernating. New technetium-99m (Tc-99m) perfusion agents have emerged in the clinical setting and have provided excellent predictive value for detection of CAD in patients with chest pain and permit simultaneous assessment of function and regional blood flow. Tc-99m Sestamibi, one of these agents, is also a valid marker of viability when assessing myocardial salvage after coronary reperfusion in acute myocardial infarction.

A comparison of tablets with oral suspension formulation of dipyridamole in thallium myocardial imaging

Dipyridamole stress thallium imaging has been widely employed to diagnose and assess the extent of coronary heart disease in patients who cannot exercise. When oral dipyridamole administration was used, a wide range of results for sensitivity, specificity, hemodynamic response and side effect profile has been reported. The authors hypothesized that the formulation used for oral administration of dipyridamole plays a major factor in this variability, and that the pulverized form of dipyridamole will achieve faster and more consistent response than the standard tablet form. The authors studied 13 consecutive patients who underwent thallium scintigraphy. Eight patients received dipyridamole pulverized and dissolved in a glycol/aqueous base diluent (group A), and five patients received the standard form of dipyridamole (group B). In group A, mean peak systolic blood pressure decreased from 142 +/- 31 (mean +/- standard deviation) to 109 +/- 30 (P = .05), and mean diastolic blood pressure decreased from 76 +/- 14 to 51 +/- 5. The mean heart rate changed from 78 +/- 26 to 80 +/- 10. In group B, baseline systolic blood pressure was 165 +/- 12 and decreased to 156 +/- 7 at 45 minutes and to 155 +/- 14 at 90 minutes. Heart rate increased from baseline of 69 +/- 9 to 75 +/- 8 at 45 minutes and to 76 +/- 11 at 90 minutes. At 45 minutes, the systolic blood pressure of the 8 group A patients dropped by 33 +/- 19 mm Hg, whereas group B's changed by 9 +/- 6 mm Hg (P less than .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Preoperative diagnosis of coronary artery disease in patients with valvular heart disease using technetium-99m isonitrile tomographic imaging together with high-dose dipyridamole and handgrip exercise

Forty-seven consecutive patients (mean age 61 +/- 8 years) referred for cardiac catheterization due to moderate to severe aortic (n = 30) or mitral (n = 17) valvular heart disease were examined by technetium-99m isonitrile tomography together with a high-dose dipyridamole infusion (0.7 mg/kg) and handgrip stress. Tomography did not identify coronary artery disease (CAD) in 3 of the 21 patients with angiographically proven disease (sensitivity 86%) and suggested false positive results in 5 of the 26 without the disease (specificity 81% and negative predictive accuracy 88%). No patient without angina pectoris and with negative scintigraphy (n = 14) had angiographically significant (greater than or equal to 50% diameter stenosis) CAD. Overall vessel sensitivity was 63%, and specificity was 92%. The frequency of side effects during the dipyridamole-handgrip test was only 7%. No serious complications occurred during stress tests. Thus, technetium-99m isonitrile tomographic imaging, together with high-dose dipyridamole and handgrip exercise, is a useful noninvasive method in excluding significant CAD in patients with valvular heart disease.

Excluding heart disease in the patient with chest pain

Angina pectoris is chest discomfort associated with myocardial ischemia. When coronary blood flow is inadequate to meet myocardial tissue demand, lactate accumulates, resulting in diastolic and systolic left ventricular dysfunction. This leads to ST-segment abnormalities and eventually to angina pectoris. Angina, most commonly a pressure-type sensation in the midanterior chest precipitated by exercise, stress, or cold, typically lasts 1-5 minutes and is alleviated by rest or nitroglycerin. Diagnostic studies to assess myocardial ischemia include treadmill exercise testing, Holter monitoring, and coronary angiography. Treadmill exercise testing has a relatively low accuracy for diagnosing coronary artery disease. This can be improved by combining exercise with thallium-201 imaging, two-dimensional echocardiography, or positron emission tomography (PET). Thallium-201 scintigraphy and exercise echocardiography have reported sensitivities of 70-85% and specificities of 50-60% when applied to low-risk, asymptomatic populations. PET scanning has a high predictive accuracy (sensitivity 90%, specificity 90-95%) and is more useful as a screening test; it can also assess the functional significance of coronary artery stenoses and differentiate viable myocardium from infarcted tissue. Holter monitoring is too insensitive and nonspecific to be used as a screening test for coronary artery disease; it can, however, assess the total ischemic burden in patients with known coronary artery disease and correlate symptoms and ST-segment abnormalities during episodes of pain at rest. Coronary angiography has been the gold standard for diagnosing coronary artery stenoses. Quantitative angiography has improved the assessment of coronary artery narrowing but is still limited in evaluating coronary blood flow. Doppler flow studies provide useful information regarding coronary flow reserve. Myocardial ischemia as a cause of chest pain is determined by evaluating the clinical characteristics consistent with angina, correlating electrocardiographic abnormalities with perfusion defects or wall motion abnormalities, and determining the extent and functional significance of coronary artery stenoses by coronary angiography.

ST-segment depression during dipyridamole infusion, and its clinical, scintigraphic and hemodynamic correlates

The goal of this study was to determine whether dipyridamole-induced ST-segment depression reflects more severe or extensive myocardial hypoperfusion than the absence of this electrocardiographic finding. The clinical, hemodynamic and scintigraphic correlates of ST-segment depression during intravenous dipyridamole infusion were studied in 204 consecutive patients undergoing dipyridamole stress thallium-201 (Tl-201) imaging for evaluation of coronary artery disease. Of 182 patients with a diagnostic baseline electrocardiogram, 28 (15%) developed ST depression after dipyridamole. Patients with ST depression, compared with those without, were older (64 +/- 1 vs 60 +/- 1 years; p less than 0.03) and had a higher frequency of chest pain (57 vs 23%; p less than 0.001) and a higher heart rate-blood pressure product (12.7 +/- 0.6 vs 11.2 +/- 0.2 x 10(3); p less than 0.008) after dipyridamole. Patients with ST depression were more likely to have Tl-201 redistribution (64 vs 38%; p less than 0.02) and a greater number of redistribution defects (2.3 +/- 0.04 vs 0.9 +/- 0.1, p less than 0.001) than were those without ST depression. By multivariate logistic regression analysis, the most powerful correlate of ST depression was the number of segments having Tl-201 redistribution (p less than 0.001). Other independent correlates were presence of chest pain, heart rate at Tl-201 injection, and age. Thus, the determinants of dipyridamole-induced ST-segment depression include the scintigraphic extent of reversible hypoperfusion, as well as indexes of myocardial oxygen demand.

Comparison of adenosine and exercise thallium-201 single-photon emission computed tomography (SPECT) myocardial perfusion imaging. The GE SPECT Multicenter Adenosine Study Group

Pharmacologic stress with dipyridamole has provided useful diagnostic, as well as prognostic, information in patients undergoing thallium-201 myocardial perfusion imaging. With its ultrashort half-life and a potent and consistent vasodilator effect, adenosine may be the coronary vasodilator of choice with myocardial perfusion imaging. Fifty-one healthy subjects and 93 patients with suspected coronary artery disease constituted the study group. In this multicenter study the comparative safety and diagnostic efficacy of single-photon emission computed tomography (SPECT) thallium imaging during adenosine-induced coronary hyperemia was compared with exercise treadmill stress. There was a mean increase in heart rate of 37% and a mean decrease in diastolic blood pressure of 5% during the adenosine infusion of 140 micrograms/kg per min for 6 min. Adenosine infusion was well tolerated in 95% of the subjects. Side effects requiring intervention occurred in seven subjects (5%). None of the subjects experienced a life-threatening complication. The sensitivity, specificity and predictive accuracy for detection of coronary artery disease with use of quantitative analysis was 83%, 87% and 84% for adenosine SPECT and 82%, 80% and 81% for exercise SPECT studies, respectively. Most false negative results with adenosine, as well as exercise SPECT studies, occurred in patients with single-vessel disease. The first-order concordance (no defect vs. defect) and second-order concordance (no defect vs. irreversible vs. reversible defect) was 89% and 78% between the two studies, respectively. Thus, the results of adenosine SPECT imaging are highly concordant with exercise SPECT thallium imaging. Adenosine SPECT thallium imaging provides a safe and highly accurate imaging mode for the detection of coronary artery disease.

Accuracy and safety of technetium-99m hexakis 2-methoxy-2-isobutyl isonitrile (Sestamibi) myocardial scintigraphy with high dose dipyridamole test in patients with effort angina pectoris: a multicenter study. Italian Group of Nuclear Cardiology

Clinical and physiologic evidence indicates that maximal coronary vasodilation is not achieved in a large number of patients with use of the standard dose of dipyridamole (0.56 mg/kg body weight over 4 min). The feasibility, safety and accuracy of technetium-99m hexakis 2-methoxy-2-isobutyl isonitrile (Sestamibi) scintigraphy associated with intravenous high dose dipyridamole (0.56 mg/kg over 4 min followed 4 min later by an additional 0.28 mg/kg over 2 min) were evaluated in a multicenter study. Planar myocardial perfusion images were obtained at rest and after dipyridamole in 101 patients with effort chest pain and no prior myocardial infarction. High dose dipyridamole (62 patients) was used when typical chest pain or electrocardiographic (ECG) signs of ischemia, or both, did not occur during or after the standard dose (39 patients). With high dose dipyridamole, 34 patients had pain (18 patients) or ECG signs of ischemia (ST depression greater than or equal to 2 mm) (8 patients), or both (8 patients), whereas the other 28 patients had Sestamibi injection in the absence of symptoms or ECG changes. All patients underwent coronary angiography: 81 had significant coronary artery disease (greater than or equal to 50% reduction of lumen diameter) (affecting one vessel in 38, two vessels in 19 and three vessels in 24 patients) and 20 patients had normal coronary arteries. The overall sensitivity, specificity and predictive accuracy of Sestamibi scintigraphy were 81%, 90% and 83%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous dipyridamole: use in thallous chloride TL 201 stress imaging

An intravenous form of dipyridamole has been approved for cardiac stress testing with thallous chloride Tl 201 (201Tl) imaging. The procedure provides an alternative method for stress testing of patients who cannot perform strenuous physical exercise because of physical limitations or those in the immediate postinfarction period. Dipyridamole simulates the physiologic effects of physical exercise by increasing adenosine concentrations, which in turn increases coronary blood flow. Dipyridamole maximizes the differences in uptake of radioactive thallium in myocardial regions supplied by normal coronary arteries and those distal to stenosed arteries where blood flow is reduced. The sensitivity and specificity of dipyridamole-201Tl stress imaging for the detection of coronary disease are comparable to those of traditional exercise-201Tl stress testing. The intravenous dipyridamole usually is well tolerated, and the majority of adverse effects can be reversed with the administration of aminophylline.

Usefulness of technetium-99m-MIBI and thallium-201 in tomographic imaging combined with high-dose dipyridamole and handgrip exercise for detecting coronary artery disease

Forty-two patients with known stable coronary artery disease, referred for coronary angiography, were examined with technetium-99m-hexakis-2-methoxy-2-methylpropyl-isonitrile (MIBI) tomography combined with a high-dose dipyridamole infusion (0.7 mg/kg) and handgrip stress. MIBI tomography was unable to show coronary artery disease only in 2 patients, thus yielding a sensitivity figure of 95%. MIBI tomography correctly identified 27 (82%) of 33 stenotic lesions (greater than or equal to 50% diameter stenosis) of the left anterior descending artery, 17 (61%) of 28 of those of the left circumflex artery, and 28 (90%) of 31 of those of the right coronary artery. The overall vessel sensitivity was 78%. The computed lumen diameter stenoses were more advanced in cases detected than in those not detected with MIBI tomography: 87 +/- 14 vs 76 +/- 14% (p less than 0.01). The 50 to 69% stenoses did not show any tendency to produce less positive findings than those with greater than or equal to 70% stenoses. In the subgroup of 21 patients who also presented for thallium scintigraphy, the overall diseased vessel identification rate was 76% for thallium tomography and 83% for MIBI tomography (p = not significant). Minor noncardiac side effects related to the dipyridamole-handgrip test occurred only in 5% of 63 study sessions. A high-dose dipyridamole combined with isometric exercise is a safe stress method, and when used during scintigraphy, MIBI tomography is at least as efficient a tool as thallium tomography in detecting diseased vessel territories in patients in coronary artery disease.

Dipyridamole perfusion scintigraphy

Dipyridamole is one of several agents that may be infused intravenously to nonivasively evaluate coronary perfusion without dynamic exercise. Among such agents it is the most investigated, and it is associated with the greatest clinical experience. Its mechanism of action utilizes intrinsic adenosine and does not require the induction of ischemia. Rather, the method tests the coronary flow reserve by dilating the precapillary and arteriolar capillary beds. Vessels with a limited coronary flow reserve demonstrate reduced responsiveness with relative flow reduction and a resultant defect on perfusion scintigraphy. Side effects are common and generally benign, but deaths have been reported and they generally relate to severe hypotension, prolonged dense ischemia and resultant infarction, or bronchospasm. Severe complications are rare and can be avoided by the prompt administration of aminophylline, the dipyridample antedote. Diagnostic accuracy for the identification of coronary disease appears similar to that for exercise perfusion scintigraphy. It should be applied to patients with known or suspected coronary disease who require coronary evaluation, but who cannot exercise adequately for diagnostic or prognostic purposes. In such patients, the method is useful for the preoperative assessment of risk at peripheral vascular and other major noncardiac surgery. It may be of value as well in the assessment of the otherwise uncomplicated patient postinfarction. Not yet established is its application to the patient with unstable angina or in the acute setting, after coronary reperfusion. Similarly, its comparison with direct adenosine infusion or with pharmacological agents whose mechanism rests entirely on ischemia induction, as does dobutamine, has until now been limited. Unlike its use with perfusion scintigraphy, the application of dipyridamole with echocardiography and other functional ischemic indicators is totally dependent on the induction of ischemia. This is likely less frequent than the induction of nonischemic perfusion heterogeneity. The agent is now commonly available and will make a significant beneficial impact on patient evaluation and management.

Dipyridamole thallium imaging

Dipyridamole cardiac imaging is a useful alternative to exercise stress testing in the evaluation of patients with ischemic heart disease. Intravenous dipyridamole has been approved recently for clinical use. Oral dipyridamole is widely available. The hemodynamic effects of dipyridamole include an increase in coronary blood flow in excess of the increase in myocardial oxygen consumption and cardiac output. The quality of the thallium images is better or similar to that of exercise thallium images. The optimal dose of intravenous dipyridamole is 0.56 mg/kg and the optimal oral dose is 300-375 mg, although higher doses may be necessary in some patients. The sensitivity and specificity of dipyridamole-thallium imaging, whether intravenous or oral, have been shown in a number of studies to be quite adequate and comparable to that achieved during exercise thallium imaging. Dipyridamole-thallium imaging has also been useful in identifying high-risk patients undergoing major elective vascular surgery. The relative merits of dipyridamole imaging versus exercise testing after acute myocardial infarction require further studies.

Pharmacological and other nonexercise alternatives to exercise testing to evaluate myocardial perfusion and left ventricular function with radionuclides

Pharmacological vasodilatation with either dipyridamole or adenosine is a safe and accurate alternative to exercise testing to diagnose coronary artery disease with thallium 201 myocardial perfusion imaging. The technique also provides important prognostic information with regard to future cardiac events in patients undergoing diagnostic testing, in those evaluated preoperatively, and in those with recent myocardial infarctions. Multigated equilibrium and first-pass radionuclide ventriculography also are well suited to evaluate the effects of interventional procedures. Success has been achieved using this methodology in a variety of interventions including conventional exercise testing, pharmacological stress testing, atrial pacing, assessment of myocardial viability with nitroglycerin, mental stress testing, and ambulatory monitoring of left ventricular ejection fraction.

Prevalence and correlates of increased lung/heart ratio of thallium-201 during dipyridamole stress imaging for suspected coronary artery disease

There is little information concerning the prevalence and clinical correlates of increased pulmonary thallium-201 uptake during dipyridamole thallium-201 stress imaging. Accordingly, the clinical characteristics and quantitative thallium-201 findings were correlated with quantitative lung/heart thallium-201 ratio in 87 patients undergoing dipyridamole thallium-201 stress testing. Nineteen patients (22%) had an elevated ratio (greater than 0.51). These patients were more likely to have had an infarction, to be taking beta blockers, and have a lower rate-pressure product after dipyridamole administration than those with a normal ratio (p less than 0.03). An elevated ratio was associated with a greater likelihood of initial, redistribution and persistent defects, as well as left ventricular cavity dilatation on thallium-201 imaging (p less than 0.05). In addition, the number of myocardial segments demonstrating initial, redistribution and persistent defects was also greater in patients with increased ratios (p less than 0.03). Multivariate analysis demonstrated that the presence of redistribution and left ventricular cavity dilatation were the most significant correlates of lung/heart thallium-201 ratio. It is concluded that the prevalence of increased lung/heart thallium-201 ratio with dipyridamole thallium-201 stress imaging is similar to that seen with exercise stress imaging. As with exercise thallium-201 imaging, increased pulmonary thallium-201 uptake may be a marker of functionally more significant coronary artery disease.

Effects of dipyridamole and aminophylline on hemodynamics, regional myocardial blood flow and thallium-201 washout in the setting of a critical coronary stenosis

Experiments were performed to characterize the interaction of intravenous dipyridamole and aminophylline on thallium-201 transport kinetics, regional myocardial blood flow and systemic hemodynamics in the presence of a critical coronary artery stenosis. In 12 dogs with a critical left anterior descending coronary artery stenosis, arterial pressure decreased from a mean value (+/- SEM) of 107 +/- 6 to 94 +/- 3 mm Hg (p less than 0.05) and distal left anterior descending artery pressure decreased from 70 +/- 7 to 55 +/- 4 mm Hg (p less than 0.05) after intravenous administration of dipyridamole (0.25 mg/kg body weight). In the left anterior descending perfusion zone, the endocardial/epicardial flow ratio decreased from 0.70 to 0.36 and the intrinsic thallium washout rate was significantly prolonged. Intravenous aminophylline (5 mg/kg) reversed the dipyridamole-induced systemic hypotension and transmural coronary steal and restored the thallium washout rate to baseline values. In six other dogs, aminophylline alone resulted in no alterations in systemic and coronary hemodynamics or regional myocardial blood flow. As expected, dipyridamole-induced vasodilation and coronary steal were prevented by aminophylline pretreatment. These data show that in a canine model of partial coronary stenosis, systemic hypotension, adverse regional flow effects (coronary steal) and prolonged thallium-201 washout consequent to intravenously administered dipyridamole are promptly reversed by intravenous aminophylline administration. Aminophylline alone had no significant hemodynamic and coronary flow effects. This study provides further insight into the altered thallium kinetics occurring as a consequence of dipyridamole-induced vasodilation and suggests that the prompt reversal of symptoms and signs of ischemia with aminophylline in patients receiving intravenous dipyridamole for clinical imaging studies probably reflects the reversal of transmural coronary steal.

Silent myocardial ischemia and infarction in diabetics with peripheral vascular disease: assessment by dipyridamole thallium-201 scintigraphy

We investigated the incidence of silent myocardial ischemia and infarction as assessed by dipyridamole thallium scintigraphy in 30 diabetic patients with peripheral vascular disease and without clinical suspicion of coronary artery disease. Seventeen patients (57%) had thallium abnormalities, with reversible thallium defects compatible with ischemia in 14 patients (47%) and evidence of prior, clinically silent myocardial infarction in 11 patients (37%). Thallium abnormalities were most frequent in patients with concomitant hypertension and cigarette smoking (p = 0.001). These results suggest that unsuspected coronary artery disease is common in this particular group of patients with diabetes mellitus.