Quantitative relationship between coronary calcium content and coronary flow reserve as assessed by integrated PET/CT imaging

The power of zero calcium in 82-Rubidium PET irrespective of sex and age

BACKGROUND

Despite clinical suspicion, many non-invasive tests for coronary artery disease (CAD) are normal. Coronary artery calcification score (CACS) is a well-validated method to detect and risk stratify CAD. Patients with zero calcium score (ZCS) rarely have abnormal tests. Therefore, aims were to evaluate CACS as a gatekeeper to further functional downstream testing for CAD and estimate potential radiation and cost savings.

METHODS

Consecutive patients with suspected CAD referred for PET were included (n = 2640). Prevalence and test characteristics of ZCS were calculated in different groups. Summed stress score ≥ 4 was considered abnormal and summed difference score ≥ 7 equivalent to ≥ 10% ischemia. To estimate potential radiation/cost reduction, PET scans were hypothetically omitted in ZCS patients.

RESULTS

Mean age was 65 ± 11 years, 46% were female. 21% scans were abnormal and 26% of patients had ZCS. CACS was higher in abnormal PET (median 561 vs 27, P < 0.001). Abnormal PET was significantly less frequent in ZCS patients (2.6% vs 27.6%, P < 0.001). Sensitivity/negative predictive value (NPV) of ZCS to detect/exclude abnormal PET and ≥ 10% ischemia were 96.8% (95%-CI 95.0%-97.9%)/97.4% (95.9%-98.3%) and 98.9% (96.7%-99.6%)/99.6% (98.7%-99.9%), respectively. Radiation and cost reduction were estimated to be 23% and 22%, respectively.

CONCLUSIONS

ZCS is frequent, and most often consistent with normal PET scans. ZCS offers an excellent NPV to exclude an abnormal PET and ≥ 10% ischemia across different gender and age groups. CACS is a suitable gatekeeper before advanced cardiac imaging, and potential radiation/cost savings are substantial. However, further studies including safety endpoints are needed.

Advances in positron emission tomography tracers related to vascular calcification

Microcalcification, a type of vascular calcification, increases the instability of plaque and easily leads to acute clinical events. Positron emission tomography (PET) is a new examination technology with significant advantages in identifying vascular calcification, especially microcalcification. The use of the ¹⁸F-NaF is undoubtedly the benchmark, and other PET tracers related to vascular calcification are also currently in development. Despite all this, a large number of studies are still needed to further clarify the specific mechanisms and characteristics. This review aimed at providing a summary of the application and progress of different PET tracers and also the future development direction.

The diagnosis and prognosis of coronary microvascular disease using PET/CT

OBJECTIVE

This study aimed to evaluate the diagnostic and prognostic value of 13N-NH3·H2O positron emission tomography combined with computed tomography (PET/CT) for non-obstructive coronary microvascular disease (CMVD).

METHODS

A retrospective analysis was conducted on 70 patients with clinically suspected non-obstructive CMVD (35 males, 35 females) between March 2017 and August 2019. The average age of the patients was 53.32±7.82 years. The patients underwent 13N-NH3·H2O PET/CT and were divided into two groups based on diagnostic criteria: a CMVD group and a non-CMVD group. They were then followed up for 180-1,095 days. Data were analyzed using an χ 2 test, the logistic regression model, the multiple linear regression model, the Kaplan-Meier method, the Cox proportional hazards regression model, and a receiver operating characteristic (ROC) curve.

RESULTS

(1) The incidence of cardiovascular family history and a high calcification score (11-400) was higher in the CMVD group than in the non-CMVD group (58.8% vs. 20.8% and 29.4% vs. 5.7%, respectively; P <  0.05 for all), stress myocardial blood flow (MBF) and coronary flow reserve (CFR) values were lower in the CMVD group than in the non-CMVD group (2.280±0.693 vs. 3.641±1.365 and 2.142±0.339 vs. 3.700±1.123, respectively), and calcification score was higher in the CMVD group than in the non-CMVD group (110.18±165.07 vs. 13.21±41.68, respectively; P <  0.05 for all). Gender and diabetes were risk factors for stress MBF reduction (β= 1.287 and β= -0.636, respectively), calcification score and hypertension were risk factors for CFR reduction (β= -0.004 and β= -0.654, respectively), and hypertension, family history, and calcification score were risk factors in the CMVD group (OR = 7.323, OR = 5.108, OR = 1.012, respectively; P <  0.05 for all). (2) The prognosis of patients with CFR <  2.5 was worse than that of patients with CFR≥2.5 (x2 value: 27.404, P <  0.001). The risk of adverse cardiovascular events in diabetic patients was also increased (β= 0.328, P <  0.001). When CFR was set to 2.595, the prognostic sensitivity was 94% and the specificity was 80%.

CONCLUSION

The technology of 13N-NH3·H2O PET/CT can be used for the diagnosis and prognosis of non-obstructive CMVD. Cardiovascular risk factors are related to the occurrence and prognosis of CMVD.

Relation between myocardial blood flow and cardiac events in diabetic patients with suspected coronary artery disease and normal myocardial perfusion imaging

BACKGROUND

We assessed the prognostic value of structural abnormalities and coronary vasodilator function in diabetic patients referred to a PET/CT for suspected coronary artery disease (CAD).

METHODS

We studied 451 diabetics and 451 nondiabetics without overt CAD and normal myocardial perfusion. Myocardial blood flow (MBF) was computed from the dynamic rest and stress imaging. Myocardial flow reserve (MFR) was defined as ratio of hyperemic to baseline MBF and was considered reduced when < 2.

RESULTS

During a mean follow-up of 44 months 33 events occurred. Annualized event rate (AER) was higher in diabetic than nondiabetic patients (1.4% vs 0.3%, P < .001). Diabetic patients with reduced MFR had higher AER compared to those with preserved MFR (3.3% vs 0.4%, P  < .001). At Cox analysis, age, BMI and reduced MFR were independent predictors of events in diabetic patients. Patients with diabetes and reduced MFR had lower event-free survival compared to nondiabetic patients and MFR < 2 (P < .001). Event-free survival was similar in patients with diabetes and normal MFR and those without diabetes and reduced MFR.

CONCLUSIONS

Diabetic patients with reduced MFR had higher AER and lower event-free survival compared to those with preserved MFR and to nondiabetic patients.

Evolution of coronary artery calcium and absolute myocardial perfusion after percutaneous revascularization: A 3-year serial hybrid [15O]H2O PET/CT imaging study

BACKGROUND AND AIMS

The value of serial coronary artery calcium (CAC) scores to predict changes in absolute myocardial perfusion and epicardial vasomotor function is poorly documented. This study explored the association between progression of CAC score and changes in absolute myocardial perfusion.

METHODS

Fifty-three patients (26% female) with de novo single-vessel coronary artery disease underwent [¹⁵O]H₂O positron emission tomography/computed tomography at 1 month (baseline), 1 year, and 3 years after complete revascularization with percutaneous coronary intervention (PCI) to assess CAC scores, hyperemic myocardial blood flow (hMBF), coronary flow reserve (CFR) and cold pressor test MBF (CPT-MBF), within the context of the VANISH trial.

RESULTS

Baseline CAC score was 0 in 9%, 0.1-99.9 in 40%, 100-399.9 in 36% and ≥400 in 15% of patients, respectively. Mixed model-analysis allowed for averaging perfusion indices over all time points: hMBF (3.74 ± 0.83; 3.33 ± 0.79; 3.08 ± 0.78 and 2.44 ± 0.74 mL min^-1·g^-1) and CFR (3.82 ± 1.12; 3.17 ± 0.80; 3.19 ± 0.81; 2.63 ± 0.92) were lower among higher baseline CAC groups (p < 0.01; p = 0.03). However, no significant interaction was found between baseline CAC groups and time after PCI for all perfusion indices, denoting that evolution of perfusion indices over time was not significantly different between CAC groups. Furthermore, CAC progression was not correlated with evolution of hMBF (r = 0.08, p = 0.57), CFR (r = 0.09, p = 0.53) or CPT-MBF (r = 0.03, p = 0.82) during 3 years of follow-up.

CONCLUSIONS

Higher baseline CAC was associated with lower hMBF and CFR. However, both baseline CAC and its progression were not associated with evolution of absolute hMBF, CFR and CPT-MBF over time, suggesting that CAC score and progression of CAC are poor indicators of change in absolute myocardial perfusion.

Quantitative relationship between coronary artery calcium and myocardial blood flow by hybrid rubidium-82 PET/CT imaging in patients with suspected coronary artery disease

BACKGROUND

We assessed the relationship between coronary artery calcium (CAC) score, myocardial blood flow (MBF) and coronary flow reserve (CFR) in patients undergoing hybrid 82Rb positron emission tomography (PET)/computed tomography (CT) imaging for suspected CAD. We also evaluated if CAC score is able to predict a reduced CFR independently from conventional coronary risk factors.

METHODS

A total of 637 (mean age 58 ± 13 years) consecutive patients were studied. CAC score was measured according to the Agatston method and patients were categorized into 4 groups (0, 0.01-99.9, 100-399.9, and ≥400). Baseline and hyperemic MBF were automatically quantified. CFR was calculated as the ratio of hyperemic to baseline MBF and it was considered reduced when <2.

RESULTS

Global CAC score showed a significant inverse correlation with hyperemic MBF and CFR (both P < .001), while no correlation between CAC score and baseline MBF was found. At multivariable logistic regression analysis age, diabetes and CAC score were independently associated with reduced CFR (all P < .001). The addition of CAC score to clinical data increased the global chi-square value for predicting reduced CFR from 81.01 to 91.13 (P < .01). Continuous net reclassification improvement, obtained by adding CAC score to clinical data, was 0.36.

CONCLUSIONS

CAC score provides incremental information about coronary vascular function over established CAD risk factors in patients with suspected CAD and it might be helpful for identifying those with a reduced CFR.

Coronary atherosclerotic burden vs. coronary vascular function in diabetic and nondiabetic patients with normal myocardial perfusion: a propensity score analysis

PURPOSE

To assess the relationship between coronary atherosclerotic burden and vascular function in diabetic and nondiabetic patients after balancing for coronary risk factors.

METHODS

We studied 672 patients without overt coronary artery disease and normal myocardial perfusion on stress ⁸²Rb PET/CT imaging. To account for differences in baseline characteristics between diabetic patients and nondiabetic patients, we created a propensity score-matched cohort considering clinical variables and coronary risk factors.

RESULTS

Before matching, diabetic patients had higher coronary artery calcium (CAC) scores (p < 0.001) and lower coronary flow reserve (CFR; p < 0.001) than nondiabetic patients. After matching, CAC scores were comparable between diabetic and nondiabetic patients, but diabetic patients still had lower hyperaemic myocardial blood flow (p < 0.001) and CFR (p < 0.05). Patients were categorized by ln(CAC score) quartiles. There was a decrease in CFR with increasing CAC score quartile in both diabetic patients (p for trend < 0.01) and nondiabetic patients (p for trend < 0.005). Diabetes was associated with lower CFR across quartile categories (p < 0.002). In a multivariable linear regression analysis, CAC score was inversely related to CFR in both diabetic patients (p < 0.05) and nondiabetic patients (p < 0.001).

CONCLUSION

Diabetic patients had higher CAC scores than nondiabetic patients, but the difference disappeared when clinical characteristics were taken into account. Of note, diabetic patients also had lower CFR regardless of CAC score than nondiabetic patients after matching. Thus, coronary atherosclerotic burden and vascular function have to be seen as two different entities.

Comparison of rubidium-82 myocardial blood flow quantification with coronary calcium score for evaluation of coronary artery stenosis

INTRODUCTION

PET myocardial perfusion imaging (MPI) is the standard technique for assessing myocardial function, but provides limited information on the anatomy of cardiac structures whereas the coronary artery calcium (CAC) score provides information on calcified plaque burden and the anatomical structure of the coronary arteries. The aim of this study was to determine the relationship between quantitative myocardial blood flow (MBF), CAC, and coronary artery disease (CAD). This work also aims to determine whether MBF quantification and/or CAC add value to relative MPI, and aid in the reclassification of patients with CAD. This way, a 'gatekeeper' study could be identified to predict coronary artery stenosis and improve our clinical service.

MATERIALS AND METHODS

Rubidium-82 PET/CT MPI, calcium score, and computed tomographic coronary angiography imaging were performed in 128 patients with known or suspected CAD. The presence of ischemia was assessed from qualitative reporting of rubidium-82 MPI, and using the same data, quantitative values of MBF and coronary flow reserve (CFR) were derived. Calcium score images were quantitatively analyzed and categorized into three groups defined by CAC values of 0, 1-400, and >400. Significant stenosis was classified as stenosis of 50% or more on computed tomographic angiography.

RESULTS

A total of 120 patients were included in the final analysis (77 men, 43 women). Our results showed an inverse correlation between stress MBF, CFR, and the percentage stenosis as well as an inverse correlation compared with CAC. A direct correlation between CAC and the percentage stenosis was observed, indicating that an increase in coronary calcification in individual coronary arteries is related to the severity of the coronary stenosis. These results proved that the addition of stress MBF to relative MPI (32%) resulted in a significantly higher sensitivity (48%, P=0.002), which increased significantly more with the addition of CFR (58%, P≤0.001). The further addition of CAC resulted in a significantly higher sensitivity (80%, P=0.001), with an even higher sensitivity with the addition of both CFR and CAC (95%, P≤0.001) to relative MPI.

CONCLUSION

The addition of quantitative MBF conferred a substantial added diagnostic value to relative MPI for the diagnosis of CAD by highlighting compromised flow with the addition of CAC, increasing this added value even more. We recommend that this approach should be used to predict the presence of coronary artery stenosis at its earliest stage and guide physicians when making decisions on the management pathway of CAD without exposing patients to a high radiation dose during cardiac angiography.

Cardiac (82)Rb PET/CT for fast and non-invasive assessment of microvascular function and structure in asymptomatic patients with type 2 diabetes

AIMS/HYPOTHESIS

Coronary flow reserve (CFR) and coronary artery calcium (CAC) represent functional and structural aspects of atherosclerosis. We examined the prevalence of reduced CFR and high CAC scores in three predefined groups of participants without known cardiovascular disease: (1) patients with type 2 diabetes and albuminuria; (2) patients with type 2 diabetes and normoalbuminuria; and (3) non-diabetic controls.

METHODS

In a cross-sectional design, cardiac (82)Rb positron emission tomography/computed tomography was conducted in 60 patients with type 2 diabetes who were free of overt cardiovascular disease and who were stratified by normoalbuminuria (<30 mg/24 h) (n = 30; age [mean ± SD] 60.9 ± 10.1 years) and albuminuria (≥ 30 mg/24 h) (n = 30; age 65.6 ± 4.8 years), and in 30 healthy, non-diabetic controls (age 59.8 ± 9.9 years).

RESULTS

In controls, normoalbuminuric and albuminuric patients, CFR was 3.0 ± 0.8, 2.6 ± 0.8 and 2.0 ± 0.5, respectively. Reduced CFR (<2.5) was observed in 16.7%, 40.0% and 83.3% of participants, respectively, and median (interquartile range) CAC scores were 0 (0-81), 36 (1-325) and 370 (152-1,025), respectively (p for trend <0.01). After adjustment, the difference in CFR and CAC between albuminuric patients and controls remained significant (p ≤ 0.001). There were trends towards lower CFR and higher CAC scores in normoalbuminuric patients vs controls (p ≤ 0.023) and towards higher CAC scores in albuminuric vs normoalbuminuric patients (p = 0.026). In multivariate regression analysis, a higher urinary albumin excretion rate (UAER) tended to predict reduced CFR in the total population (p = 0.045). When the CAC score was added, there was also a trend (p = 0.032) towards an inverse association with reduced CFR.

CONCLUSIONS/INTERPRETATION

Type 2 diabetic patients who were free of overt cardiovascular disease had a high prevalence of coronary microvascular dysfunction, especially with concomitant albuminuria, suggesting a common microvascular impairment occurring in multiple microvascular beds. Prospective studies are needed to show the prognostic significance of this finding.

Characteristics of anginal patients with high resting myocardial blood flow measured with N-13 ammonia PET/CT

OBJECTIVES

We hypothesized that anginal patients with low coronary flow reserve (CFR) could have variable clinical features according to resting myocardial blood flow (MBF). Therefore, we analyzed the clinical and imaging characteristics according to resting MBF in anginal patients.

METHODS

We enrolled 70 patients who underwent N-13 ammonia PET-computed tomography (CT) for evaluation of angina. Resting and stress MBF values were obtained and resting MBF was corrected with rate-pressure product to exclude the effect of heart rate and blood pressure on resting MBF. Clinical and imaging characteristics were compared on the basis of MBF and CFR.

RESULTS

Among patients with CFR less than 2.0, those with high resting MBF (≥1.0 ml/min/g) had significantly fewer number of smokers, were younger, had lower Agatston calcium scores, and had less coronary stenosis compared with those with low resting MBF (<1.0 ml/min/g). In contrast, there was no significant difference in clinical or imaging findings according to resting MBF when compared among all patients or within those with CFR greater than or equal to 2.0. The subgroup analysis of patients with CFR less than 2.0 revealed lower Agatston calcium score and less coronary stenosis in patients with high resting MBF regardless of stress MBF.

CONCLUSION

High resting MBF is associated with a lower rate of smoking, younger age, less coronary calcium burden, and less coronary stenosis compared with low resting MBF in anginal patients with low CFR. Moreover, in these patients, favorable angiographic features were mainly associated with high resting MBF, irrespective of stress MBF. Therefore, resting MBF should be reviewed to validate the clinical significance of low CFR measured by N-13 ammonia PET/CT especially in anginal patients showing low CFR.

Role of Coronary Calcium Scoring in the Assessment of Physiological Ischemia in Patients with Intermediate Stenosis

Although coronary artery calcium (CAC) is an established marker of coronary atherosclerosis, whether it also reflects the physiological significance is unknown. This study aims to evaluate if CAC could indicate physiological ischemia in intermediate stenosis defined by an invasive fractional flow reserve (FFR). CAC score (CACS) derived from either whole coronary arteries or individual arteries was measured by computed tomography among patients with intermediate de novo lesions (percent diameter stenosis from 30% to less than 70%). All stenoses were evaluated by invasive FFR; lesions with an FFR ≤ 0.80 were considered significant. We enrolled 119 patients with 143 lesions. Of these, 42 lesions (29.4%) demonstrated significant ischemia by FFR measurement. FFR values had modest but significant correlations with CACS in individual arteries with intermediate stenosis (r = - 0.290; p < 0.001). A receiver operating characteristic curve analysis showed that CACS of individual arteries with intermediate stenosis had 71.4% sensitivity and 67.3% specificity as a predictor of significant ischemia at a cut off value of 145.9. Multivariable analysis showed that percent diameter stenosis and CACS in individual arteries with intermediate stenosis were independent predictors for significant ischemia. By net reclassification improvement analysis, CACS in individual arteries with intermediate stenosis provided incremental prediction for significant ischemia over minimum lumen diameter, percent diameter stenosis, and lesion length. CACS measured in each artery, but not the total CACS, provides additional information as to whether an angiographically intermediate stenosis within the artery is significant enough to cause myocardial ischemia.

Coronary flow reserve estimated by positron emission tomography to diagnose significant coronary artery disease and predict cardiac events

Coronary artery disease (CAD) is a major cause of death in Japan. Coronary angiography is useful to assess the atherosclerotic burden in CAD patients, but its ability to predict whether patients will respond favorably to optimal medical therapy and revascularization is limited. The measurement of the fractional flow reserve with angiography is a well-validated method for identifying ischemic vessels. However, neither an anatomical assessment nor a functional assessment can delineate microvasculature or estimate its function. The quantitative coronary flow reserve (CFR) estimated from sequential myocardial perfusion images obtained by positron emission tomography (PET) during stress provides an accurate index of hyperemic reactivity to vasodilatory agents in the myocardium. In fact, there is growing evidence that the CFR reflects disease activity in the entire coronary circulation, including epicardial coronary artery stenosis, diffuse atherosclerosis, and microvascular dilatory function. Importantly, reduced CFR is observed even in patients without flow-limiting coronary stenosis, and its evaluation can improve the risk stratification of patients at any stage of CAD. This review focuses on the application of CFR estimated by cardiac PET for the diagnosis and risk stratification of patients with CAD.

Performance evaluation of the Ingenuity TF PET/CT scanner with a focus on high count-rate conditions

This study evaluated the positron emission tomography (PET) imaging performance of the Ingenuity TF 128 PET/computed tomography (CT) scanner which has a PET component that was designed to support a wider radioactivity range than is possible with those of Gemini TF PET/CT and Ingenuity TF PET/MR. Spatial resolution, sensitivity, count rate characteristics and image quality were evaluated according to the NEMA NU 2-2007 standard and ACR phantom accreditation procedures; these were supplemented by additional measurements intended to characterize the system under conditions that would be encountered during quantitative cardiac imaging with (82)Rb. Image quality was evaluated using a hot spheres phantom, and various contrast recovery and noise measurements were made from replicated images. Timing and energy resolution, dead time, and the linearity of the image activity concentration, were all measured over a wide range of count rates. Spatial resolution (4.8-5.1 mm FWHM), sensitivity (7.3 cps kBq(-1)), peak noise-equivalent count rate (124 kcps), and peak trues rate (365 kcps) were similar to those of the Gemini TF PET/CT. Contrast recovery was higher with a 2 mm, body-detail reconstruction than with a 4 mm, body reconstruction, although the precision was reduced. The noise equivalent count rate peak was broad (within 10% of peak from 241-609 MBq). The activity measured in phantom images was within 10% of the true activity for count rates up to those observed in (82)Rb cardiac PET studies.

Detection of coronary artery disease using coronary flow velocity reserve by transthoracic Doppler echocardiography versus multidetector computed tomography coronary angiography: influence of calcium score

BACKGROUND

There have been no clinical data specifying the degree of calcium deposition at which coronary flow velocity reserve (CFVR) measurement using transthoracic Doppler echocardiography surpasses 320-row multidetector computed tomographic coronary angiography (CTCA) in detecting obstructive coronary artery disease.

METHODS

One hundred seventy patients who underwent invasive coronary angiography, transthoracic Doppler echocardiography, and CTCA were prospectively enrolled. Coronary artery stenosis was defined as percentage diameter stenosis ≥ 50% on invasive coronary angiography. CFVR < 2.0 and narrowing ≥ 50% measured with CTCA were the thresholds indicating the presence of coronary artery stenosis. The degree of coronary artery calcification was also assessed using the Agatston calcium score method by computed tomography.

RESULTS

The majority of patients (89%) were classified as having either high or intermediate pretest probability of coronary artery disease. Significant coronary artery stenoses by invasive coronary angiography were found in 71 patients and 104 vessels. Although the overall diagnostic performance of CTCA was comparable with that of CFVR measurement for detecting coronary artery stenosis, only the diagnostic performance of CTCA was negatively affected by the extent of a patient's coronary artery calcification. Receiver operating characteristic curve analysis indicated that only CFVR measurement is diagnostically accurate when calcium scores are >319 in the patient-based assessment, 189 for the left anterior descending coronary artery, 98 for the left circumflex coronary artery and 282 for the right coronary artery.

CONCLUSIONS

Transthoracic Doppler echocardiography and 320-row multidetector CTCA successfully diagnosed significant coronary artery stenosis with high feasibility and accuracy. However, only the diagnostic performance of CTCA was negatively affected by the extent of a patient's coronary artery calcification, and therefore the diagnostic performance of CFVR measurement for detecting coronary artery stenosis surpassed that of CTCA when the calcium score exceeded specified cutoff values.

Epicardial adipose tissue thickness as a predictor of impaired microvascular function in patients with non-obstructive coronary artery disease

OBJECTIVE

To determine if increased epicardial adipose tissue (EAT) measured by cardiac CT could be associated with impaired myocardial flow reserve (MFR) in patients with non-obstructive coronary artery disease (CAD).

BACKGROUND

Studies have shown that EAT volume is related to epicardial obstructive CAD, myocardial ischemia and major adverse cardiac events. However, the association between EAT with coronary microvascular dysfunction and impaired MFR has not been well clarified.

METHODS

Consecutive patients who underwent Rb-82 positron emission tomography (PET), coronary artery calcium (CAC) scoring and non-invasive coronary computed tomography angiography (CCTA) were screened. PET scans were analysed for standard myocardial perfusion (MPI) and MFR. CCTA results were analysed and only patients with non-obstructive CAD (<50% luminal diameter stenosis) were included. EAT thickness and volumes were measured from CT scans.

RESULTS

Of 137 patients without obstructive CAD by CCTA and with normal Rb-82 PET relative MPI, 26 (19.0%) patients had impaired MFR < 2 and 87 (64%) patients had CAC. EAT(thickness), EAT(volume) and CAC values were higher in patients with impaired MFR < 2 than those with normal MFR ≥ 2 (6.7 ± 1.6 mm vs 4.4 ± 1.0 mm, P < .0001; 119.0 ± 25.3 cm(3) vs 105.8 ± 30.5 cm(3), P < .04 and 508.9 ± 554.3 vs 167.8 ± 253.9, P < .0001, respectively). However, EAT(thickness) had a stronger negative correlation with MFR than EAT(volume) and CAC (r = -0.78 vs r = -0.25 and ρ = -0.32, P < .0001). With multivariable logistic regression analysis, only EAT(thickness) was independently associated with impaired MFR (OR 20.7, 95% CI 4.9-87.9, P < .0001). Importantly, the receiver-operator characteristic (ROC) curves demonstrated a superior performance of EAT(thickness) vs EAT(volume) and EAT(thickness) vs CAC in detecting impaired MFR (AUC: 0.945 vs 0.625, difference between AUC: 0.319, P < .0001; AUC: 0.945 vs 0.710, difference between AUC: 0.235, P < .0006, respectively). On ROC curve analysis, an EAT(thickness) cut-off value > 5.6 mm was optimal in detecting impaired MFR with a sensitivity and specificity of 81% and 92%, respectively.

CONCLUSIONS

Increased EAT appears to be associated with impaired MFR. This parameter may help improve detection of patients at risk of microvascular dysfunction.

Coronary artery and thoracic aorta calcification is inversely related to coronary flow reserve as measured by ⁸²Rb PET/CT in intermediate risk patients

BACKGROUND

The strength and nature of the relationship between myocardial perfusion imaging (MPI), coronary flow reserve (CFR), and coronary artery calcium (CAC) and thoracic aorta calcium (TAC) remain to be clarified.

METHODS

Dynamic rest-pharmacological stress (82)Rb positron emission tomography/computed tomography MPI with CFR, CAC, and TAC was performed in 75 patients (59 ± 13 years; F/M = 38/37) with intermediate risk of coronary artery disease.

RESULTS

A total of 29 (39%) patients had ischemic and 46 (61%) had normal MPI. CAC was correlated with TAC (ρ = 0.7; P < .001), and CFR was inversely related with CAC and TAC (ρ = -0.6 and -0.5; P < .001, respectively). By gender-specific univariate analysis, age (P = .001), CAC (P = .004), and CFR (P = .008) in males, but CFR (P = .0001), age (P = .002), and TAC (P = .01) in females were significant predictors of ischemic MPI. By multiple regression, the most potent predictor was CFR [odds ratio (OR) = 0.17, P = .01), followed by age (OR = 1.07, P = .02), gender (OR = 4.01, P = .03), and CAC (OR = 1.002, P = .9).

CONCLUSIONS

Combination of MPI, CFR, CAC, and TAC has complementary roles in intermediate risk patients.

Prognostic interplay of coronary artery calcification and underlying vascular dysfunction in patients with suspected coronary artery disease

OBJECTIVES

This study sought to evaluate the interrelation of atherosclerotic burden, as assessed by coronary artery calcium (CAC) score and coronary vascular function, as assessed by quantitative estimates of coronary flow reserve (CFR), with respect to prediction of clinical outcomes.

BACKGROUND

The contribution of coronary vascular dysfunction, atherosclerotic burden, and the 2 combined to cardiac events is unknown.

METHOD

A total of 901 consecutive patients underwent (82)Rubidium myocardial perfusion imaging (MPI) positron emission tomography (PET) and CAC scan. All patients had normal MPI. The primary endpoint was a composite of major adverse cardiac events (MACE) including cardiac death, nonfatal myocardial infarction, late revascularization, and admission for heart failure.

RESULTS

At baseline, CFR decreased (2.15 ± 0.72, 2.02 ± 0.65, and 1.88 ± 0.64, p < 0.0001) with increasing levels of CAC (0, 1 to 399, and ≥400). Over a median of 1.53 years (interquartile range: 0.77 to 2.44), there were 57 MACE. Annual risk-adjusted MACE rates were higher for patients with CFR <2.0 compared with ≥2.0 (1.9 vs. 5.5%/year, p = 0.0007) but were only borderline associated with CAC (3.1%, 3.4%, and 6.2%/year for CAC of 0, 1 to 399, and ≥400, respectively; p = 0.09). Annualized adjusted MACE was increased in the presence of impaired CFR even among patients with CAC = 0 (1.4% vs. 5.2%, p = 0.03). Cox proportional hazards analysis revealed that CFR improved model fit, risk discrimination, and risk reclassification over clinical risk, whereas CAC only modestly improved model fit without improving risk discrimination or reclassification.

CONCLUSIONS

In symptomatic patients with normal MPI, global CFR but not CAC provides significant incremental risk stratification over clinical risk score for prediction of major adverse cardiac events.

The association between coronary flow reserve and development of coronary calcifications: a follow-up study for 11 years in healthy young men

AIMS

We studied whether a reduced coronary flow reserve (CFR) in healthy young men independently predicts the presence of coronary artery disease as assessed by coronary artery calcification after 11 years of follow-up.

METHODS AND RESULTS

Coronary microvascular dysfunction in early stages of coronary artery disease can be detected as a reduced CFR by positron emission tomography (PET). Seventy-seven healthy, lean, normotensive, non-smoking and non-diabetic men underwent 15-Oxygen ((15)O) water myocardial perfusion PET at rest and during vasodilator stress at the age of 35 ± 4 years at baseline. The subjects were followed-up for 11 ± 1 years and the coronary artery calcium score (CCS) was measured with computed tomography at the end of the follow-up. At the end of the follow-up, 30 (39%) individuals had CCS >0 (average 65 ± 93), but none had clinical symptoms or evidence of ischaemia in stress echocardiography. At baseline, the average CFR was comparable in individuals with CCS >0 and CCS = 0 (4.2 ± 1.4 vs. 4.0 ± 1.2, P = 0.4). Logistic regression analysis showed no associations between CFR, serum glucose, cholesterol levels, systolic blood pressure or body mass index at baseline and CCS at the end of the follow-up (P always >0.05). The presence of CCS (CCS >0) was associated with higher systolic and diastolic blood pressures at the end of the follow-up (137 ± 18 vs. 128 ± 11 mmHg, P = 0.04 and 86 ± 12 vs. 78 ± 11 mmHg, P = 0.01).

CONCLUSIONS

Coronary reactivity to vasodilator-induced hyperaemia as assessed by perfusion PET was not predictive of the presence of coronary calcification after 11 years of follow-up in asymptomatic men with very low likelihood of coronary artery disease.

Does quantification of myocardial flow reserve using rubidium-82 positron emission tomography facilitate detection of multivessel coronary artery disease?

BACKGROUND

Relative myocardial perfusion imaging (MPI) is the standard imaging approach for the diagnosis and prognostic work-up of coronary artery disease (CAD). However, this technique may underestimate the extent of disease in patients with 3-vessel CAD. Positron emission tomography (PET) is also able to quantify myocardial blood flow. Rubidium-82 ((82)Rb) is a valid PET tracer alternative in centers that lack a cyclotron. The aim of this study was to assess whether assessment of myocardial flow reserve (MFR) measured with (82)Rb PET is an independent predictor of severe obstructive 3-vessel CAD.

METHODS

We enrolled a cohort of 120 consecutive patients referred to a dipyridamole (82)Rb PET MPI for evaluation of ischemia neither with prior coronary artery bypass graft nor with recent percutaneous coronary intervention that also underwent coronary angiogram within 6 months of the PET study. Patients with and without 3-vessel CAD were compared.

RESULTS

Among patients with severe 3-vessel CAD, MFR was globally reduced (<2) in 88% (22/25). On the adjusted logistic Cox model, MFR was an independent predictor of 3-vessel CAD [.5 unit decrease, HR: 2.1, 95% CI (1.2-3.8); P = .015]. The incremental value of (82)Rb MFR over the SSS was also shown by comparing the adjusted SSS models with and without (82)Rb MFR (P = .005).

CONCLUSION

(82)Rb MFR is an independent predictor of 3-vessel CAD and provided added value to relative MPI. Clinical integration of this approach should be considered to enhance detection and risk assessment of patients with known or suspected CAD.

Quantitative relationship between coronary artery calcium score and hyperemic myocardial blood flow as assessed by hybrid 15O-water PET/CT imaging in patients evaluated for coronary artery disease

BACKGROUND

The incremental value of CAC over traditional risk factors to predict coronary vasodilator dysfunction and inherent myocardial blood flow (MBF) impairment is only scarcely documented (MBF). The aim of this study was therefore to evaluate the relationship between CAC content, hyperemic MBF, and coronary flow reserve (CFR) in patients undergoing hybrid (15)O-water PET/CT imaging.

METHODS

We evaluated 173 (mean age 56 ± 10, 78 men) patients with a low to intermediate likelihood for coronary artery disease (CAD), without a documented history of CAD, undergoing vasodilator stress (15)O-water PET/CT and CAC scoring. Obstructive coronary artery disease was excluded by means of invasive (n = 44) or CT-based coronary angiography (n = 129).

RESULTS

91 of 173 patients (52%) had a CAC score of zero. Of those with CAC, the CAC score was 0.1-99.9, 100-399.9, and ≥400 in 31%, 12%, and 5% of patients, respectively. Global CAC score showed significant inverse correlation with hyperemic MBF (r = -0.32, P < .001). With increasing CAC score, there was a decline in hyperemic MBF on a per-patient basis [3.70, 3.30, 2.68, and 2.53 mL · min(-1) · g(-1), with total CAC score of 0, 0.1-99.9, 100-399.9, and ≥400, respectively (P < .001)]. CFR showed a stepwise decline with increasing levels of CAC (3.70, 3.32, 2.94, and 2.93, P < .05). Multivariate analysis, including age, BMI, and CAD risk factors, revealed that only age, male gender, BMI, and hypercholesterolemia were associated with reduced stress perfusion. Furthermore, only diabetes and age were independently associated with CFR.

CONCLUSION

In patients without significant obstructive CAD, a greater CAC burden is associated with a decreased hyperemic MBF and CFR. However, this association disappeared after adjustment for traditional CAD risk factors. These results suggest that CAC does not add incremental value regarding hyperemic MBF and CFR over established CAD risk factors in patients without obstructive CAD.

Structural abnormalities of the coronary arterial wall--in addition to luminal narrowing--affect myocardial blood flow reserve

Multislice CT provides information on coronary luminal narrowing and on the structural abnormalities of the coronary arterial wall using densitometric analysis. We sought to investigate the effects of coronary luminal narrowing, structural abnormalities of the coronary arterial wall, and cardiovascular risk factors on regional and global myocardial blood flow (MBF) reserve.

METHODS

We studied 68 patients (mean age ± SD, 61 ± 10 y; 41 men, 27 women) with an intermediate probability of coronary artery disease. We measured the severity of coronary stenoses and the fibroadipose, fibromuscular, and calcium components of the coronary arterial wall by 64-row multislice CT coronary angiography. We also measured regional and global MBF reserve by PET using (13)N-ammonia as a flow tracer at rest and after dipyridamole.

RESULTS

One or more significant coronary stenoses (≥50% luminal narrowing) was present in 32 patients (47%), and nonsignificant stenoses were present in 15 patients (22%). Regional MBF reserve was significantly different in the territories perfused by normal coronary arteries, nonsignificant coronary stenoses, and significant coronary stenoses (P < 0.001). Calcium content was higher in the coronary arteries with significant or nonsignificant stenoses (0.95% ± 1.08% and 0.73% ± 0.93%, respectively) than in those without stenoses (0.11% ± 0.38%, P < 0.001). Significant coronary stenosis (P = 0.047) and calcium content (P = 0.017) were the only independent determinants of impaired regional MBF reserve using multivariate analysis. At multiple logistic regression analysis, the Framingham risk score, an index of global cardiovascular risk burden, was the only significant determinant of global MBF reserve (P = 0.028).

CONCLUSION

Coronary stenoses and coronary calcium content independently affect regional MBF reserve. Framingham risk score is the only significant determinant of global MBF reserve.