Myocardial imaging with dipyridamole: comparison of the sensitivity and specificity of 201Tl versus MUGA

Diagnostic and Prognostic Use of Stress Echocardiography and Radionuclide Scintigraphy

Stress echocardiography and radionuclide scintigraphy are effective diagnostic and prognostic techniques in patients with known or suspected coronary artery disease (CAD), myocardial infarction (MI), chronic left ventricular dysfunction (LVD), and those undergoing noncardiac surgery. Both are sensitive and specific for the detection and extent of CAD. Negative tests confer a high negative predictive value for cardiac events irrespective of clinical risk. Positive studies confer a high positive predictive value for ischemic events in patients with intermediate to high clinical risk. Both provide incremental diagnostic and prognostic information relative to clinical, resting echocardiographic, and angiographic data. Meta-analysis studies have shown that the diagnostic and prognostic information provided by stress echocardiography is comparable with radionuclide scintigraphic stress tests. Stress echocardiography may be more specific for the detection and extent of CAD, whereas radionuclide scintigraphy may be more sensitive for single-vessel disease. Sensitivities are similar for the detection and extent of disease in patients with multivessel CAD.

High dose dipyridamole as a pharmacological stress test during cardiac catheterisation in patients with coronary artery disease

AIM

To validate dipyridamole as a pharmacological stress test during cardiac catheterisation, allowing both functional and morphological estimation of stenosis severity.

METHODS

The study encompassed 74 patients: 62 patients with significant coronary artery disease (age 61 (SD 8) years; seven women, 55 men) and 12 controls. Regional wall motion, left ventricular ejection fraction and end diastolic pressure were analysed in the resting state and after high dose intravenous dipyridamole. Patients were subdivided into four groups: group I (n = 32, 43%) had stopped all anti-ischaemic treatment for > 24 h, group II (n = 14, 19%) was under treatment, group III (n = 16, 22%) had significant coronary artery disease only in regions with regional wall motion abnormalities at rest, and group IV consisted of 12 control patients (16%) with no significant coronary artery disease (age 62 (8) years, three women, nine men).

RESULTS

The sensitivity of dipyridamole testing in patients with coronary artery disease was poor. The best sensitivity was obtained with regional wall motion analysis (26/62 = 42%) and with global left ventricular ejection fraction (25/62 = 40%). Specificity was 100% for regional wall motion and 100% for ejection fraction. Calculated positive and negative predictive values for regional wall motion were 100% and 63%, respectively.

CONCLUSIONS

Although safe, handy, and inexpensive, dipyridamole is not an adequate pharmacological stress test during cardiac catheterisation because of its low sensitivity.

Dipyridamole first-pass radionuclide ventriculography: prediction of future cardiac events

Dipyridamole thallium myocardial perfusion imaging is a useful alternative to stress testing in the diagnostic and prognostic assessment of patients with coronary artery disease. The diagnostic use of dipyridamole radionuclide ventriculography is much more controversial, but no long-term prognostic studies have been reported. Imaging results of 159 consecutive patients who were referred for dipyridamole first-pass radionuclide ventriculography were correlated with subsequent cardiac events over a mean follow-up period of 11 months. An abnormal response to dipyridamole infusion (any reduction in wall motion or absolute decrease in global left ventricular ejection fraction of > or = 5 ejection fraction units) was associated with an increased incidence of nonfatal myocardial infarction (4.5% vs 0%, p < 0.05) and cardiac-related death (9% vs 1%, p < 0.001). The sensitivity, specificity, and negative predictive value of dipyridamole first-pass radionuclide ventriculography in predicting future cardiac events were 86%, 71%, and 98%, respectively, with a relative risk of 15 (confidence interval 12.06 to 18.1). In conclusion, dipyridamole first-pass radionuclide ventriculography demonstrated significant prognostic value in a large unselected patient population. This technique may provide a widely applicable and useful alternative to dipyridamole thallium perfusion imaging in the assessment of cardiac risk in patients with coronary artery disease.

Identification of hemodynamically significant coronary artery stenoses by dipyridamole-magnetic resonance imaging and 99mTc-methoxyisobutyl-isonitrile-SPECT

Magnetic resonance imaging (MRI) has been used in conjunction with dipyridamole induced wall motion abnormalities for the noninvasive detection of coronary artery disease (CAD). To assess the clinical usefulness of dipyridamole-MRI for the localization of CAD and to evaluate the relation between dipyridamole induced wall motion abnormalities and myocardial perfusion 33 patients with severe CAD (> 70% diameter reduction) underwent MRI at rest and after dipyridamole infusion (0.75 mg dipyridamole/kg over a period of 10 minutes). All patients performed exercise stress testing and 20 patients of the study group additionally had rest and exercise stress 99mTc-methoxyisobutyl-isonitrile-SPECT (MIBI-SPECT). Two patients (6%) could not be evaluated due to severe motion artifacts during dipyridamole MRI. Segmental wall motion and perfusion of corresponding short axis planes were related to the major coronary arteries using a standardized segmental coronary artery perfusion pattern. Detection of wall motion abnormalities or perfusion defects by 2 blinded observers in consensus was the criterion for grading a segment normal or pathologic. For localization of CAD, segmental gradings were related to the presumed coronary artery territories. Stress-ECG was pathologic in 19/31 patients yielding a sensitivity of 61% and dipyridamole induced angina was present in 68% (21/31) of patients. Dipyridamole-MRI detected coronary artery disease with a sensitivity of 84% (26/31 patients) and all patients with new wall motion abnormalities also had dipyridamole induced angina. For the subgroup of 20 patients with MIBI-SPECT images, CAD was detected by both MIBI-SPECT and Dipyridamole-MRI in 90% (18/20) of patients. Dipyridamole-MRI and MIBI-SPECT gradings agreed in 55/60 (92%) coronary artery perfusion territories. There were no significant differences with respect to the sensitivities of Dipyridamole-MRI/MIBI-SPECT for the localization of individual coronary artery stenoses yielding 81%/78% for left anterior descending, 80%/80% for left circumflex and 92%/89% for right coronary artery stenoses. However, specificity of Dipyridamole-MRI (89%) for the detection of RCA stenoses was slightly better than for MIBI-SPECT (80%).

Effects of the dipyridamole test on left ventricular function in coronary artery disease

The dipyridamole stress test is used with thallium-201 to detect areas of inhomogeneity of blood flow that point to coronary artery disease (CAD). It is unclear whether dipyridamole produces inhomogeneous perfusion only or whether it actually decreases net flow in the obstructed vessels and produces true ischemia. It is also unclear what effect dipyridamole has on global and segmental left ventricular function. Therefore, ejection fraction, segmental wall motion and ventricular volume equivalents were measured before and after dipyridamole in 113 patients and 32 normal subjects. Ejection fraction responded in an abnormal fashion in 98 patients (87%), decreasing from 49 +/- 11% to 43 +/- 13% (p less than 0.0001), whereas it increased in 29 normal subjects (90%) from 57 +/- 6% to 64 +/- 10% (p less than 0.0001). Wall motion worsened distinctly in 75 patients (66%), and pressure/volume ratio deteriorated in 72%. The effect of dipyridamole lasted between 10 and 25 minutes, but was promptly reversed by aminophylline. These findings indicate that dipyridamole generally induces true ischemia in CAD. Furthermore, the degree of dysfunction is related to the angiographically assessed severity of CAD. The shortness of breath (seen in 10% of patients) may be partially explained by the findings, and it seems advisable to give aminophylline to every patient in order to promptly correct left ventricular dysfunction.

Feasibility of high-dose dipyridamole-magnetic resonance imaging for detection of coronary artery disease and comparison with coronary angiography

To assess the feasibility, safety and usefulness of gradient-echo magnetic resonance imaging (MRI) combined with pharmacologic stress testing for the detection of coronary artery disease, 23 patients without previous myocardial infarction but with significant stenosis (greater than 70% diameter stenosis) of greater than or equal to 1 major coronary artery were selected for dipyridamole-MRI stress testing. Each patient underwent MRI at rest, and high-dose dipyridamole-MRI (0.75 mg/kg over 10 minutes) of corresponding basal and midventricular short-axis tomograms. Additionally, these patients performed symptom-limited exercise stress tests. All short-axis tomograms were evaluated on a standardized segmental basis by grading each segment as normal, hypokinetic, akinetic or dyskinetic. Dipyridamole-MRI was considered pathologic if segmental wall motion deteriorated by greater than or equal to 1 grade after dipyridamole. For comparison with coronary angiography, segmental wall motion gradings were related to the respective coronary artery territories in the short-axis plane. Pathologic dipyridamole-MRI was obtained in 18 of 23 (78%) patients. For 1- and 2-vessel diseases, sensitivity was 69 and 90%, respectively. Exercise stress tests were pathologic in 14 of 23 (66%) patients. For 1- and 2-vessel diseases, sensitivity of exercise stress test was 58% (7 of 12 patients) and 77% (7 of 9), respectively. Sensitivity/specificity of dipyridamole-MRI for the localization of the stenosed coronary artery was 78/100% for left anterior descending, 73/100% for left circumflex, and 88/87% for right coronary artery stenoses. It is concluded that dipyridamole-MRI is a feasible nonexercise-dependent test for detection and localization of functionally significant 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.

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.

Dipyridamole magnetic resonance imaging: a comparison with thallium-201 emission tomography

Limitation of space and motion artefact make magnetic resonance imaging during dynamic exercise difficult. Pharmacological stress with dipyridamole can be used as an alternative to exercise for thallium scanning. Forty patients with a history of angina and an abnormal exercise electrocardiogram were studied by dipyridamole thallium myocardial perfusion tomography and dipyridamole magnetic resonance wall motion imaging with a cine gradient refocused sequence. Images for both scans were obtained in the oblique horizontal and vertical long axis and short axis planes before and after pharmacological stress with dipyridamole. The myocardium was divided into nine segments for direct comparison of perfusion with wall motion. Segments were assessed visually into grades--normal, hypokinesis or reduced perfusion, and akinesis or very reduced perfusion. After dipyridamole there were reversible wall motion abnormalities in 24 (62%) of 39 patients with coronary artery disease and 24 (67%) of 36 patients with reversible thallium defects. The site of wall motion deterioration was always the site of a reversible thallium defect. Thallium defects affecting more than two segments were always associated with wall motion deterioration but most single segment thallium defects were undetected by magnetic resonance imaging. There was a significant correlation between detection of wall motion abnormality, the angiographic severity of coronary artery disease, and the induction of chest pain by dipyridamole. There were no significant differences in ventricular volume or ejection fraction changes after dipyridamole between the groups with and without detectable reversible wall motion changes but the normalised magnetic resonance signal intensity of the abnormally moving segments was significantly less than the signal intensity of the normal segments. In nine patients the change was apparent visually and it was maximal in the subendocardial region. Magnetic resonance imaging of reversible wall motion abnormalities in patients with coronary artery disease is feasible during pharmacological stress with dipyridamole and may be associated with a reduced magnetic resonance signal. The failure to show wall motion abnormalities in all cases of reversible thallium defects may be because the defect was small or because dipyridamole caused perfusion defects in the absence of myocardial ischaemia.

Use of digital subtraction fluorography in screening for coronary artery disease in patients with chronic renal failure

The diagnosis of coronary artery disease remains a major problem in patients with end-stage renal disease. Screening with conventional noninvasive techniques is limited by the poor exercise capacity of these patients. This study evaluated the accuracy of digital subtraction fluorography in detecting coronary calcification as a noninvasive, nonexercise screening test for coronary artery disease. Eighty-six patients under evaluation for renal transplantation and considered at increased risk of coronary artery disease were studied by coronary arteriography and digital subtraction fluorography for coronary calcification. Significant coronary disease (greater than or equal to 50% obstruction in at least one vessel) was present in 36 (42%) patients. The detection of coronary calcification by digital subtraction fluorography had a sensitivity of 78% and a specificity of 66%. The probability of disease being present in the absence of coronary calcification in this group was 18%. The detection of coronary calcification by digital subtraction fluorography appears to be a satisfactory and inexpensive screening test in this setting.

Dipyridamole radionuclide ventriculography: a test with high specificity for severe coronary artery disease

Ventricular dysfunction induced by dipyridamole would be evidence of myocardial ischemia in patients with limited ability to undergo standard exercise testing. Radionuclide ventriculography before and after intravenous dipyridamole infusion was compared with the results of exercise radionuclide ventriculography in a prospective study of 31 patients undergoing coronary angiography. Among these patients, 21 (68%) had significant coronary artery disease (greater than or equal to 50% stenosis), 19 (61%) had severe coronary disease (greater than or equal to 70% stenosis) and 10 (32%) were "normal" (less than 50% stenosis). The left ventricular ejection fraction was calculated, and regional wall motion was scored on a 6 unit scale. In the normal patients, the ejection fraction (+/- SEM) increased 5.6 +/- 2% (units) during exercise and 7.9 +/- 1 units after dipyridamole (both p less than or equal to 0.004 compared with that during rest). However, in patients with coronary artery disease, the ejection fraction failed to increase during exercise or after dipyridamole. In the patients with coronary artery disease, regional wall motion decreased by 4.1 +/- 0.5 units during exercise (p less than 0.003) and by 1.8 units after dipyridamole (p less than 0.02). Receiver operating characteristic analysis demonstrated general comparability between the sensitivity and specificity of exercise and dipyridamole ventriculography, with "optimal" operating points that favored choosing high sensitivity for the former and high specificity for the latter. Specific subsets of patients with severe coronary atherosclerosis were analyzed with use of these criteria. In patients with severe stenosis (greater than or equal to 70%), the sensitivity of dipyridamole ventriculography was 67% compared with 89% for exercise ventriculography. However, at these levels of sensitivity, the specificity of dipyridamole ventriculography was 92% compared with 67% for exercise ventriculography. In this and other subsets of patients, the specificity of dipyridamole ventriculography exceeded that of exercise ventriculography. Thus, it is concluded that dipyridamole radionuclide ventriculography is moderately sensitive and highly specific for detecting severe coronary atherosclerosis. This technique provides a widely applicable, useful alternative to exercise ventriculography in the diagnosis of coronary atherosclerosis in patients who have limited exercise tolerance.

Dipyridamole cardiac imaging

Dipyridamole cardiac imaging is a useful alternative technique to exercise stress testing in the evaluation of patients with ischemic heart disease. Intravenous dipyridamole is still in the investigational phase, while oral dipyridamole is widely available. The hemodynamic effects of dipyridamole include an increase in coronary blood flow (due to coronary vasodilation) which is in excess of the increase in myocardial oxygen consumption and cardiac output. The disparity in the increase in coronary blood flow relative to the cardiac output results in an increase in myocardial thallium activity and an increase in the myocardial/background activity ratio. 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 of the oral dose it is 300 to 400 mg, although higher doses may be necessary in some patients. Analysis of the thallium images has been to a large extent based on visual inspection of the planar images. Delayed images are helpful to establish the nature of the perfusion abnormalities (transient or fixed). The process of redistribution is based on disparate rates of washout from the normal and abnormal zones. 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 two-dimensional echocardiography has also been used in the detection of coronary artery disease; transient (new or worsening of preexisting) wall motion abnormalities have been found to be a specific marker of coronary artery disease. Transmural as well as regional coronary steal phenomena have been postulated as the mechanism for dipyridamole-induced regional wall motion abnormalities. Compared to exercise two-dimensional echocardiography, dipyridamole echocardiography provides high-quality studies and in higher proportions of patients. The results of dipyridamole thallium imaging have also been extremely important in identifying high-risk patients after acute myocardial infarction or patients with peripheral vascular disease undergoing elective vascular surgery; the presence of a dipyridamole-induced perfusion abnormality identifies patients at high risk for future cardiac events. Thus, dipyridamole cardiac imaging is helpful in the diagnosis of coronary artery disease and in risk stratification.