Relation of coronary vasoreactivity and coronary calcification in asymptomatic subjects with a family history of premature coronary artery disease

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.

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.

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.

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.

Long-term prognostic value of 13N-ammonia myocardial perfusion positron emission tomography added value of coronary flow reserve

OBJECTIVES

The goal of this study was to assess the predictive value of myocardial perfusion imaging with (13)N-ammonia positron emission tomography (PET) and coronary flow reserve (CFR) on long-term prognosis in patients with suspected myocardial ischemia.

BACKGROUND

No prognostic data exist on the predictive value of CFR and (13)N-ammonia PET.

METHODS

Perfusion and CFR were assessed in 256 patients using (13)N-ammonia PET, and follow-up was obtained in 245 (96%) patients. Sixteen early revascularized patients were excluded and 229 were assigned to normal versus abnormal perfusion or normal versus abnormal CFR (<2.0). Major adverse cardiac events (MACE) (cardiac death, nonfatal myocardial infarction, late revascularization, or hospitalization for cardiac reasons) were assessed using the Kaplan-Meier method. Cox proportional hazard regression was used to identify independent predictors for cardiac events.

RESULTS

During follow-up (5.4 +/- 2.2 years), 78 patients had at least 1 cardiac event, including 29 cardiac deaths. Abnormal perfusion (n = 126) was associated with a higher incidence of MACE (p < 0.001) and cardiac death (p < 0.05). In patients with normal perfusion, abnormal CFR was independently associated with a higher annual event rate over 3 years compared with normal CFR for MACE (1.4% vs. 6.3%; p < 0.05) and cardiac death (0.5% vs. 3.1%; p < 0.05). In abnormal perfusion, CFR remained predictive throughout the 10-year follow-up (p < 0.001).

CONCLUSIONS

Perfusion findings in (13)N-ammonia PET and CFR are strong outcome predictors. CFR allows further risk stratification, suggesting a "warranty" period of 3 years if normal CFR is associated with normal perfusion. Conversely, in patients with abnormal perfusion, an impaired CFR has added value for predicting adverse outcomes.

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

PURPOSE

To evaluate the relationship between coronary artery calcium (CAC) and coronary vasodilator function.

METHODS

We evaluated 136 patients without known coronary artery disease (CAD) undergoing vasodilator stress (82)Rb PET/CT and CAC scoring who showed normal myocardial perfusion. The CAC score, resting and hyperemic myocardial blood flow (MBF), coronary flow reserve (CFR) and coronary vascular resistance were analyzed.

RESULTS

Global and regional CAC scores showed significant but weak inverse correlations with hyperemic MBF (r=-0.31 and r=-0.26, p< or =0.0002 respectively) and CFR (r=-0.28 and r=-0.2, p< or =0.001 respectively). With increasing CAC score, there was a modest stepwise decline in CFR on a per-patient basis (1.8+/-0.5 vs 1.7+/-0.5 vs 1.5+/-0.4, p=0.048, with total CAC=0, 1-400 and >400, respectively) and on a per-vessel basis. In multivariable modeling only body mass index and CAC score were predictive of CFR.

CONCLUSION

In patients with an intermediate likelihood of, but without overt, CAD, there is a statistically significant but weak inverse correlation between CAC content and coronary vasodilator function. The strength of this association weakens after adjusting CAC scores for age, gender and coronary risk factors. This suggests that CAC and coronary vasodilator function provide biologically different information regarding atherosclerosis.

Usage of the T1 effect of an iron oxide contrast agent in an animal model to quantify myocardial blood flow by MRI

BACKGROUND

To present a new method for fully quantitative analysis of myocardial blood flow (MBF) using magnetic resonance imaging. The first pass of an intravascular iron oxide contrast medium can be used to quantify myocardial perfusion. The technique was validated in an animal model using colored microspheres.

MATERIALS AND METHODS

In six pigs, a tracking catheter was positioned in the left anterior descending artery (LAD). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed on a 1.5-T scanner using a hybrid gradient-echo/echoplanar imaging (GRE-EPI) sequence. Regional myocardial blood flow (rMBF) was altered by either inducing vasodilatation with adenosine or creating coronary artery obstruction. The T(1) effect of a superparamagnetic iron oxide-based contrast medium (Resovist) administered at a dose of 8 micromol/kg was used. Upslope, time-to-peak and peak intensity were calculated from the signal intensity-time curves and absolute rMBF using the Kety-Schmidt equation; results were compared to those obtained using colored microspheres.

RESULTS

The mean rMBF calculated by MRI was 1.49 (+/-6.91, quartile width) ml/min/g versus 3.21 (+/-1.61) ml/min/g measured by means of microspheres under resting conditions. rMBF increased to a mean of 6.21 (+/-2.83) ml/min/g versus 4.22 (+/-1.70) ml/min/g under adenosine and was reduced to zero flow in total occlusion. Linear regression showed the best correlation for upslope (R=0.714), time-to-peak (R=0.626) and the Kety-Schmidt equation (R=0.584).

CONCLUSIONS

The T(1) effect of an iron oxide-based contrast medium allows determination of rMBF when using the Kety-Schmidt equation. The results are similar to those obtained with the standard of reference, colored micropheres, but not better than the results of the semiquantitative approach.

Assessment of intra- and interobserver reproducibility of rest and cold pressor test-stimulated myocardial blood flow with 13N-ammonia and PET

PURPOSE

We investigated the intraobserver reproducibility of myocardial blood flow (MBF) measurements with PET at rest and during cold pressor test (CPT), and the interobserver agreement.

METHODS

Twenty normal volunteers were studied. Using (13)N-ammonia, MBF was measured at rest and during CPT and measurement was repeated in a 1-day session (short-term reproducibility; SR). After a follow-up of 2 weeks, MBF was measured again at rest and during CPT and compared with the initial baseline measurement (long-term reproducibility; LR). In addition, adenosine-induced hyperemic MBF increases were assessed.

RESULTS

Assessment of the SR did not show a significant absolute difference in MBF at rest, MBF during CPT or the endothelium-related change in MBF from rest to CPT (DeltaMBF) (0.09 +/- 0.10, 0.11 +/- 0.09, and 0.08 +/- 0.05 ml/g/min; p = NS), and they were linearly correlated (r = 0.72, r = 0.76 and r = 0.84; p < 0.0001). Corresponding values for standard error of the estimate (SEE), as indicative for the range of MBF measurement error, were 0.14, 0.14, and 0.09 ml/g/min. The LR yielded relatively higher but non-significant absolute differences in the MBF at rest, MBF during CPT and DeltaMBF (0.10 +/- 0.10, 0.14 +/- 0.10, and 0.19 +/- 0.10 ml/g/min; p = NS), and paired MBFs significantly correlated (r = 0.75, r = 0.71, and r = 0.60; p < 0.001). Corresponding SEEs were 0.13, 0.15, and 0.16 ml/g/min. The interobserver analysis yielded a high correlation for MBF at rest, MBF during CPT, and hyperemic MBF (r = 0.96, SEE=0.04; r = 0.78, SEE=0.11; and r = 0.87, SEE=0.28; p < 0.0001, respectively), and also a good interobserver correlation for DeltaMBF (r = 0.62, SEE=0.09; p < 0.003).

CONCLUSION

Short- and long-term MBF responses to CPT, as an index for endothelium-related coronary vasomotion, can be measured reproducibly with (13)N-ammonia PET. In addition, the high interobserver reproducibility for repeat analysis of MBF values suggests the measurements to be largely operator independent.

Positive family history of coronary artery disease is associated with reduced myocardial vasoreactivity in healthy men

OBJECTIVE

Positive family history as a risk factor for coronary artery disease seems to be most important in subjects who otherwise are at low risk. We examined the association between family history of coronary artery disease and myocardial vasoreactivity in healthy men.

METHODS

35 non-smoking healthy men (age 35+/-7 years) were studied: 16 had positive family history of coronary artery disease and 19 had negative family history. The myocardial blood flow measurements were performed basally and during adenosine infusion (140 mug/kg/min) with and without simultaneous physiological hyperinsulinemia (insulin infusion at a rate of 1 mU/kg/min) using positron emission tomography and O-15-water.

RESULTS

Basal myocardial blood flow was similar between the subjects with positive and negative family history of coronary artery disease (0.79+/-0.19 and 0.79+/-0.21 mL g(-1) min(-1), NS). Adenosine stimulated flow was significantly reduced in subjects with positive family history (3.0+/-0.5 vs 4.0+/-1.2 mL g(-1) min(-1), respectively, p=0.003). During physiological hyperinsulinemia adenosine stimulated flow was further enhanced in both groups but significantly blunted in subjects with positive family history (3.7+/-0.9 vs 5.2+/-1.5 mL g(-1) min(-1), respectively, p=0.001). These differences remained significant after simultaneous controlling for age, BMI, HbA1c, LDL-cholesterol, HDL-cholesterol and blood pressure (p=0.002).

CONCLUSIONS

Healthy non-smoking men with positive family history of coronary artery disease are characterized by impaired myocardial vasoreactivity.

Coronary artery calcification and myocardial perfusion in asymptomatic adults: the MESA (Multi-Ethnic Study of Atherosclerosis)

OBJECTIVES

This study assessed the cross-sectional association between coronary artery calcification (CAC) and myocardial perfusion in an asymptomatic population.

BACKGROUND

Clinical studies showed that the prevalence of stress-induced ischemia increased with CAC burden among patients with coronary heart disease (CHD). Whether an association between CAC and myocardial perfusion exists in subjects without a history of CHD remains largely unknown.

METHODS

A total of 222 men and women, ages 45 to 84 years old and free of CHD diagnosis, in the Minnesota field center of the MESA (Multi-Ethnic Study of Atherosclerosis) were studied. Myocardial blood flow (MBF) was measured using magnetic resonance imaging during rest and adenosine-induced hyperemia. Perfusion reserve was calculated as the ratio of hyperemic to resting MBF. Agatston CAC score was determined from chest multidetector computed tomography.

RESULTS

Mean values of hyperemic MBF and perfusion reserve, but not resting MBF, were monotonically lower across increasing CAC levels. After adjusting for age and gender, odds ratios (95% confidence intervals) of reduced perfusion reserve (<2.5) for subjects with CAC scores of 0, 0.1 to 99.9, 100 to 399, and > or =400 were 1.00 (reference), 2.16 (0.96 to 4.84), 2.81 (1.04 to 7.58), and 4.99 (1.73 to 14.4), respectively. Further adjustment for other coronary risk factors did not substantially modify the association. However, the inverse association between perfusion reserve and CAC attenuated with advancing age (p for interaction < 0.05).

CONCLUSIONS

Coronary vasodilatory response was associated inversely with the presence and severity of CAC in asymptomatic adults. Myocardial perfusion could be impaired by or manifest the progression to subclinical coronary atherosclerosis in the absence of clinical CHD.

Quantification of Calcification in Atherosclerotic Lesions

Calcification can be deposited throughout the vasculature in several forms of calcium phosphate, including calcium hydroxyapatite (CHA). Calcium accumulation in arteries by mineralization and calcium loss from bone by osteoporosis often coexist, and vascular calcification may share common mechanisms with bone remodeling. Deposition of calcification in valves and arteries diminishes the valvular or arterial wall elasticity, a major cause of aneurysm and stenosis. Obstruction of arteries by calcification and other components can lead to heart attack and stroke. Mineralization in the femoral arteries can cause intermittent claudication in the legs, causing decreased mobility. Accurate measurement of calcification is essential for identifying other factors associated with this process and ultimately for elucidating the mechanism(s) of calcification. A wide range of methods for visualizing and measuring calcification for diagnosis and treatment in vivo and for studying the calcification process ex vivo are available. This review provides a critical comparison of older established methods and newer evolving technologies for quantifying calcification.