T. Baudhuin

Coronary flow reserve calculated from pressure measurements in humans. Validation with positron emission tomography.

BACKGROUND Experimental studies have shown that fractional flow reserve (defined as the ratio of maximal achievable flow in a stenotic area to normal maximal achievable flow) can be calculated from coronary pressure measurements only. The objectives of this study were to validate fractional flow reserve calculation in humans and to compare this information with that derived from quantitative coronary angiography. METHODS AND RESULTS Twenty-two patients with an isolated, discrete proximal or mid left anterior descending coronary artery stenosis and normal left ventricular function were studied. Relative myocardial flow reserve, defined as the ratio of absolute myocardial perfusion during maximal vasodilation in the stenotic area to the absolute myocardial perfusion during maximal vasodilation (adenosine 140 micrograms.kg-1 x min-1 intravenously during 4 minutes) in the contralateral normally perfused area, was assessed by 15O-labeled water and positron emission tomography (PET). Myocardial and coronary fractional flow reserve were calculated from mean aortic, distal coronary, and right atrial pressures recorded during maximal vasodilation. Distal coronary pressures were measured by an ultrathin, pressure-monitoring guide wire with minimal influence on the trans-stenotic pressure gradient. Minimal obstruction area, percent area stenosis, and calculated stenosis flow reserve were assessed by quantitative coronary angiography. There was no difference in heart rate, mean aortic pressure, or rate-pressure product during maximal vasodilation during PET and during catheterization. Percent area stenosis ranged from 40% to 94% (mean, 77 +/- 13%), myocardial fractional flow reserve from 0.36 to 0.98 (mean, 0.61 +/- 0.17), and relative flow reserve from 0.27 to 1.23 (mean, 0.60 +/- 0.26). A close correlation was found between relative flow reserve obtained by PET and both myocardial fractional flow reserve (r = .87) and coronary fractional flow reserve obtained by pressure recordings (r = .86). The correlations between relative flow reserve obtained by PET and stenosis measurements derived from quantitative coronary angiography were markedly weaker (minimal obstruction area, r = .66; percent area stenosis, r = -.70; and stenosis flow reserve, r = .68). CONCLUSIONS Fractional flow reserve derived from pressure measurements correlates more closely to relative flow reserve derived from PET than angiographic parameters. This validates in humans the use of fractional flow reserve as an index of the physiological consequences of a given coronary artery stenosis.

Optimal use of dobutamine stress for the detection and evaluation of coronary artery disease: combination with echocardiography or scintigraphy, or both?

OBJECTIVES This study was conducted to examine the efficacy of dobutamine stress two-dimensional echocardiography and perfusion scintigraphy for the detection of coronary artery disease in routine practice, to establish the causes of erroneous results and to derive appropriate criteria for the selection of either or both tests. BACKGROUND Dobutamine stress combined with echocardiography or perfusion scintigraphy may be used to detect coronary artery disease. Although both imaging approaches have demonstrated similar levels of accuracy, it is not known whether there may be particular indications for the use of one or the other technique or a rationale for their combination. METHODS Two hundred seventeen patients without previous infarction were studied prospectively with dobutamine stress echocardiography and technetium-99m methoxy isobutyl nitrile (sestamibi) single-photon emission computed tomography at the time of diagnostic coronary angiography. The presence of coronary stenoses of > or = 50% diameter was compared with the presence of rest or stress-induced abnormalities of perfusion and regional function. The extent of these abnormalities was correlated with an equivalent score of extent of angiographic disease. RESULTS Significant coronary artery disease was found in 142 patients; 102 (72%) were identified by dobutamine echocardiography and 108 (76%, p = NS) by perfusion imaging. In 75 patients without significant disease, the specificity of dobutamine echocardiography was 83% compared with 67% for scintigraphy (p = 0.05). Echocardiographic sensitivity was lower in patients unable to complete the test because of side effects (n = 64) than in the remainder (59% vs. 77%, p = 0.02); this influence was less apparent with scintigraphy (71% vs. 78%, p = NS). Selective use of scintigraphy in the 31 patients with a negative submaximal stress echocardiogram led to a sensitivity of 80% for this combination. Patients with left ventricular hypertrophy accounted for most of the difference in specificity between echocardiography and scintigraphy (94% vs. 59%, p = 0.02). Their respective accuracies were 76% and 73%. CONCLUSIONS Dobutamine stress echocardiography and perfusion scintigraphy have equivalent accuracy. In patients with left ventricular hypertrophy, echocardiography appears to be the test of choice. Selective use of sestamibi scintigraphy in patients with a negative submaximal echocardiogram enhances the accuracy of stress echocardiography alone.

Selection of the optimal nonexercise stress for the evaluation of ischemic regional myocardial dysfunction and malperfusion. Comparison of dobutamine and adenosine using echocardiography and 99mTc-MIBI single photon emission computed tomography.

BackgroundThe mechanisms of action of exercise-simulating and vasodilator stressors support their combination with imaging techniques that evaluate left ventricular function and perfusion, respectively. However, reported accuracies of either pharmacological stress together with two-dimensional echocardiography (2DE) or single photon emission computed tomography (SPECT) of myocardial perfusion are similar. The purpose of this study was to establish the optimal stress for each imaging technique by comparing the results of digitized 2DE and 99mTc-methoxyisobutyl isonitrile (MIBI) SPECT using both dobutamine and adenosine stresses in the same patients and conditions. Methods and ResultsNinety-seven consecutive patients without evidence of previous infarction undergoing coronary angiography for clinical indications were studied prospectively. Dobutamine was infused during clinical, ECG, and echocardiographic monitoring in dose increments from 5 to 40 μg kg-1 min-1. Adenosine was infused under the same conditions in doses of 0.10, 0.14, and 0.18 mg

How accurate is dobutamine stress electrocardiography for detection of coronary artery disease? Comparison with two-dimensional echocardiography and technetium-99m methoxyl isobutyl isonitrile (mibi) perfusion scintigraphy.

kg-1min-1. For each protocol, the end points were achievement of peak dose, development of severe ischemia, or intolerable side effects. At peak stress, 20 mCi of MIBI was injected, and SPECT imaging was performed 2 hours later, abnormal poststress images were compared with resting SPECT. Digitized 2DE images were compared qualitatively before, during, and after stress in a cine-loop display. Significant coronary disease (n=59 patients) was defined by the quantification of >50% stenosis in a major epicardial vessel. The sensitivity of adenosine 2DE was 58%, less than those of adenosine MIBI (86%, p=0.001), dobutamine 2DE (85%, p=0.001), and dobutamine MIBI (80%, p=0.01). Their respective specificities were 87%, 71%, 82%, and 74% (p=NS). The accuracy of adenosine 2DE was 69%Y, compared with 80%Yo for adenosine MIBI (p<0.001), 84% for dobutamine 2DE (p=0.001), and 77% for dobutamine MIBI (p=0.005); the latter three did not differ significantly in either sensitivity or accuracy. ConclusionThis prospective, direct comparison of alternative pharmacological stresses in patients without myocardial infarction shows vasodilator stress scintigraphy and dobutamine stress echocardiography and scintigraphy to share equivalent levels of sensitivity. All three are significantly more sensitive than adenosine stress echocardiography. Dobutamine stress may be used for wall motion or perfusion imaging, but adenosine stress is best combined with perfusion scintigraphy.

Relation Between Myocardial Blood Flow and the Severity of Coronary-artery Stenosis

OBJECTIVES This study was designed to establish the appropriate diagnostic criteria for positive dobutamine electrocardiographic (ECG) stress test results and to compare their accuracy with those of dobutamine two-dimensional echocardiography and perfusion scintigraphy. BACKGROUND Conventional criteria for positive findings on ECG exercise testing may not be appropriate for use with dobutamine ECG stress testing. METHODS One hundred twenty-nine consecutive patients with an interpretable ECG and without previous myocardial infarction were prospectively studied at the time of coronary arteriography. All completed a standard dobutamine protocol (5 to 40 micrograms/kg body weight per min in 3-min dose increments) without side effects. Significant coronary artery disease, defined as > 50% lumen diameter stenosis of a major epicardial coronary artery on coronary angiography, was present in 83 patients. Empiric receiver operating curves were generated for various ECG criteria derived from computer-averaged signals. RESULTS The best ECG criterion, with a sensitivity of 42% and a specificity of 83%, was an ST segment shift, relative to baseline, of 0.5 mm 80 ms after the J point. The sensitivity of this criterion was greater than that of the conventional criterion of 1-mm ST segment depression 60 (23%) or 80 (18%) ms after the J point, was comparable to that of chest pain occurring during the test (44%, p = NS) but remained inferior to the sensitivities of technetium-99m methoxyl isobutyl isonitrile (mibi) perfusion (76%) or stress echocardiography (76%, p < 0.001, for both). The specificity of this criterion was not significantly different from that of technetium-99m mibi perfusion tomography (65%) or stress echocardiography (89%) but was superior to that of chest pain (59%, p < 0.025). CONCLUSIONS We conclude that this new criterion for dobutamine electrocardiography is specific but that an imaging technique is still required to accurately predict coronary artery disease.

Discrepancies in Perfusion Defect Estimates Between Tc-99m Mibi Spect and N-13 Ammonia Pet Are Not Explained By Differences in Tracer Behavior

Comment: At rest (the condition during this study) metabolic demands of the myocardium will be the major determinant of blood flow. Thus the finding that, up to the limits of the coronary artery disease in the patients studied, basal flow was independent of degree of coronary artery stenosis is not surprising. To anesthetists, the study indicates how, in a situation in which myocardial oxygen demand is raised–tachycardia for example, a degree of stenosis that was sufficient for basal oxygen supply needs may be unable to provide flow requirements under the new conditions of oxygen supply and demand, hence the need for careful evaluation of the limited clinical evidence that most of us have of myocardial function during management of our cases. Clearly, few of us have the sophisticated tools used in this study. Only in some parts of the world is intraoperative echocardiography available. Many of us must rely on the relatively insensitive electrocardiogram or else try to avoid situations in patients with known coronary artery disease that we know increase myocardial oxygen demands. Finally, note that this study had to be limited to patients with single-vessel coronary artery disease only. Where there is multiple vessel disease, the situation is likely to be even more critical. On the other side of the coin is the reassurance that a major degree of vessel stenosis is needed before all coronary vasodilator capacity is lost.