Quantitative relationship between coronary vasodilator reserve assessed by 82Rb PET imaging and coronary artery stenosis severity

Abstract

The relationship between myocardial blood flow (MBF) and stenosis severity has been determined previously using cyclotron-produced radiotracers such as 15 O-H 2 O and 13 N-ammonia. An attractive alternative to overcome the limitations related to the use of cyclotron might be to use the generator-produced Rubidium-82 as a flow tracer. The current study was undertaken to investigate the relationship between MBF and coronary vasodilator reserve (CVR) as measured by Rubidium-82 positron emission tomography (PET) and the percent diameter stenosis as defined by quantitative coronary arteriography.Methods-We prospectively evaluated 22 individuals: 15 patients (60±11 years of age) with angiographically documented coronary artery disease (CAD) and seven age-matched (56±9 years) asymptomatic individuals without risk factors for CAD. Dynamic Rubidium-82 PET was performed at rest and after dipyridamole vasodilation. MBF, CVR and an index of "minimal coronary resistance" (MCR) were assessed in each of the three main coronary territories.Results-Rest and stress MBF in regions subtended by vessels with <50% diameter stenosis was similar to that of the individuals with no risk factors for CAD. As a result, CVR was also similar in the two groups (1.9, interquartile [IQ] range from 1.7 to 2.7 vs. 2.2, IQ range from 2 to 3.4 respectively, p=0.09)). CVR successfully differentiated coronary lesions with stenosis severity 70% to 89% from those with 50% to 69% stenosis (1, IQ range from 1 to 1.3 vs. 1.7, IQ range from 1.4 to 2), respectively, p=0.001. In addition, hyperaemic MBF (r 2 =.74, p<0.001), CVR (r 2 =. 69, p<0.001), and MCR (r 2 =.78, p<0.001) measurements were inversely and non-linearly correlated to the percent diameter stenosis on angiography.

Clinical Quantification of Myocardial Blood Flow Using PET: Joint Position Paper of the SNMMI Cardiovascular Council and the ASNC

“…[85][86][87] • In general, hyperemic MBF and MFR are relatively preserved for coronary lesions with less than 70% angiographic stenosis or with preserved fractional flow reserve (FFR) ([ 0.8). 45,47,51,52,[85][86][87][88][89]91,141,142 However, both Figure 7. Receiver-operator characteristic curves for detection of severe CAD using MFR.…”

“…85 Though initially established using 15 O-water, this finding was quickly replicated using 13 N-ammonia [86][87][88] and more recently using 82 Rb. 89,90 The application of stress MBF and MFR for improving the diagnostic accuracy of PET MPI with clinical protocols has been investigated by many groups with both 13 N-ammonia 47,48,88 and 82 Rb. 52, 91 Although these studies have consistently demonstrated improved diagnostic sensitivity (case example in Figure 6), at least 2 large studies have raised concerns about potential for decreased specificity (Figure 7), 52,91 possibly due to the contributions of diffuse atherosclerosis and microvascular disease to stress MBF and MFR measurements.…”

Quantification of myocardial blood flow will reform the detection of CAD

“…In the study by Anagnostopoulos et al 22 linearity with the However, in all tracers except 15O-water, the tracer extraction is reduced when perfusion is increased leading to underestimation of perfusion if only tracer uptake is used.…”

“…5 As regard to absolute perfusion in mL/g/minute, a little clinical evidence is available and it also appears that different traces may provide different cutoffs. 15,[21][22][23] In the study by Muzik et al 5 using 13 N-ammonia as tracer, the optimal cutoff value was found to be quite low (1.52 mL/g/minute) to separate ischemic from noninschemic regions. In our recent analysis using 15 O-water the ideal cutoff for absolute stress perfusion was 2.5 mL/g/minute, the range from 2.0 to 2.5 being mildly reduced.…”

Risk Assessment and Predictive Value of Coronary Artery Disease Testing

“…In a recent study with 82 Rb PET/ CT, the diagnostic sensitivity and specificity were 93% and 83%, respectively (35); in particular, the accuracy for detecting multivessel CAD was exceedingly high. Major advantages of the use of myocardial perfusion PET are the abilities to quantify measures of absolute blood flow and to define areas of dampened coronary flow reserve (36). The addition of nonperfusion findings, such as changes in the left ventricular ejection fraction, and the addition of a CAC scan can further improve the detection of CAD by PET (13).…”