Assessment of coronary blood flow and the reactivity of the microcirculation non-invasively with transthoracic echocardiography

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.

Coronary microvascular dysfunction

Patients with coronary microvascular dysfunction (CMVD) represent a widespread population and despite the good prognosis, many of them have a poor quality of life with strong limitations in their daily activities because of the angina symptoms. This article summarizes the most frequent clinical presentation pictures like stable and unstable microvascular angina. Main risk factors are discussed, followed by the latest updates on the subject about different pathogenic hypotheses, diagnosis and treatment. Not very well understood microvascular alterations, like slow flow phenomenon and no reflow are discussed and both prognosis and the impact of the disease in the quality of life are analyzed.

Effect of interleukin-6 inhibition on coronary microvascular and endothelial function in myocardial infarction

OBJECTIVE

Interleukin-6 (IL-6) is a driver of inflammation and associated endothelial cell activation in acute coronary syndromes. We evaluated the effect of the IL-6 receptor antagonist tocilizumab on coronary microvascular function and endothelial dysfunction measured by coronary flow reserve (CFR) and markers of endothelial cell activation in patients with non-ST-elevation myocardial infarction (NSTEMI).

METHODS

This substudy was part of a two-centre, double-blind, randomised, placebo-controlled trial evaluating the effect of a single dose of tocilizumab in NSTEMI. Markers of endothelial cell activation (vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule-1 and von Willebrand factor) were assessed in 117 patients. In 42 of these patients, 20 assigned to placebo and 22 to tocilizumab, we measured CFR. Blood samples were obtained at seven consecutive time points between day 1 and 3. CFR was measured by transthoracic echocardiography during hospitalisation and after 6 months.

RESULTS

Tocilizumab did not affect CFR during hospitalisation (tocilizumab: 3.4±0.8 vs placebo: 3.3±1.2, p=0.80). CFR improved significantly in both groups at 6 months. Patients in the tocilizumab group had significantly higher area under the curve for VCAM-1 (median 622 vs 609 ng/mL/hour, tocilizumab and placebo respectively, p=0.003). There were inverse correlations between VCAM-1 and CFR in the placebo (hospitalisation: r=-0.74, p<0.01, 6 months: r=-0.59, p<0.01), but not in the tocilizumab group (hospitalisation: r=0.20, p=0.37, 6 months r=-0.28, p=0.20).

CONCLUSIONS

Tocilizumab did not affect CFR during hospitalisation or after 6 months. Tocilizumab increased VCAM-1 levels during hospitalisation, but this was not associated with reduced CFR in these patients.

Coronary microvascular function in patients with Cushing's syndrome

The aim of the study was to evaluate patients with Cushing's syndrome the coronary flow reserve (CFR), an index of coronary microvascular function. Fifteen newly diagnosed patients with Cushing's syndrome (1 male/14 females; mean age 45 ± 11 years), were selected for having no clinical evidence of ischemic heart disease. Twelve patients had pituitary-dependent Cushing's disease and three had an adrenal adenoma. Fifteen subjects matched for age, sex, and major cardiovascular risk factors were used as controls. Coronary flow velocity in the left anterior descending coronary artery was investigated by transthoracic Doppler echocardiography at rest and during adenosine infusion. CFR was obtained as the ratio hyperemic/resting diastolic flow velocity. A reduced coronary reserve (hyperemic/resting ratio ≤ 2.5) was found in 5/15 Cushing patients and 4/15 controls. In all patients with abnormal CFR, epicardial coronary stenosis was excluded by multi-slice computed tomographic coronary angiography. CFR was inversely related to urinary cortisol in patients with endogenous hypercortisolism (Spearman's rho = -0.57, P = 0.03), while no correlation was found in controls. Coronary microvascular function, as assessed by CFR, is pathologically reduced in a considerable number of patients with Cushing's syndrome without clinical symptoms of ischemic heart disease and in the absence of epicardial coronary artery lesions, as well as in controls matched for cardiovascular risk factors. The presence of comorbidities can explain this early coronary abnormality in both patients and controls. Whether urinary cortisol may be a predictor of coronary microvascular function in the setting of patients with Cushing's syndrome, needs further investigation.

Pravastatin-induced improvement in coronary reactivity and circulating ATP and ADP levels in young adults with type 1 diabetes

Aims: Extracellular ATP and ADP regulate diverse inflammatory, prothrombotic and vasoactive responses in the vasculature. Statins have been shown to modulate their signaling pathways in vitro. We hypothesized that altered intravascular nucleotide turnover modulates vasodilation in patients with type 1 diabetes (T1DM), and this can be partly restored with pravastatin therapy. Methods: In this randomized double blind study, plasma ATP and ADP levels and echocardiography-derived coronary flow velocity response to cold pressor test (CPT) were concurrently assessed in 42 normocholesterolemic patients with T1DM (age 30 ± 6 years, LDL cholesterol 2.5 ± 0.6 mmol/L) before and after four-month treatment with pravastatin 40 mg/day or placebo (n = 22 and n = 20, respectively), and in 41 healthy control subjects. Results: Compared to controls, T1DM patients had significantly higher concentrations of ATP (p < 0.01) and ADP (p < 0.01) and these levels were partly restored after treatment with pravastatin (p = 0.002 and p = 0.007, respectively), but not after placebo (p = 0.06 and p = 0.14, respectively). Coronary flow velocity acceleration was significantly lower in T1DM patients compared to control subjects, and it increased from pre- to post-intervention in the pravastatin (p = 0.02), but not in placebo group (p = 0.15). Conclusions: Pravastatin treatment significantly reduces circulating ATP and ADP levels of T1DM patients, and concurrently improves coronary flow response to CPT. This study provides a novel insight in purinergic mechanisms involved in pleiotropic effects of pravastatin.

Quantification of absolute coronary flow reserve and relative fractional flow reserve in a swine animal model using angiographic image data

Coronary flow reserve (CFR) and fractional flow reserve (FFR) are important physiological indexes for coronary disease. The purpose of this study was to validate the CFR and FFR measurement techniques using only angiographic image data. Fifteen swine were instrumented with an ultrasound flow probe on the left anterior descending artery (LAD). Microspheres were gradually injected into the LAD to create microvascular disruption. An occluder was used to produce stenosis. Contrast material injections were made into the left coronary artery during image acquisition. Volumetric blood flow from the flow probe (Q(q)) was continuously recorded. Angiography-based blood flow (Q(a)) was calculated by using a time-density curve based on the first-pass analysis technique. Flow probe-based CFR (CFR(q)) and angiography-based CFR (CFR(a)) were calculated as the ratio of hyperemic to baseline flow using Q(q) and Q(a), respectively. Relative angiographic FFR (relative FFR(a)) was calculated as the ratio of the normalized Q(a) in LAD to the left circumflex artery (LC(X)) during hyperemia. Flow probe-based FFR (FFR(q)) was measured from the ratio of hyperemic flow with and without disease. CFR(a) showed a strong correlation with the gold standard CFR(q) (CFR(a) = 0.91 CFR(q) + 0.30; r = 0.90; P < 0.0001). Relative FFR(a) correlated linearly with FFR(q) (relative FFR(a) = 0.86 FFR(q) + 0.05; r = 0.90; P < 0.0001). The quantification of CFR and relative FFR(a) using angiographic image data was validated in a swine model. This angiographic technique can potentially be used for coronary physiological assessment during routine cardiac catheterization.

Epicardial fat volume is associated with coronary microvascular response in healthy subjects: a pilot study

Epicardial fat (EF) is an active ectopic fat depot, which has been associated with coronary atherosclerosis, and which could early influence endothelial function. We thus investigated the relationship between EF and endothelium-dependent vasoreactivity of the coronary microcirculation, in highly selected healthy volunteers. Myocardial blood flow (MBF) was determined by measuring coronary sinus flow with velocity-encoded cine magnetic resonance imaging (MRI) at 3T. We measured MBF at baseline and in response to sympathetic stimulation by cold pressor testing (CPT) in 30 healthy volunteers with normal left ventricular (LV) function (age 22 ± 4 years, BMI = 21.3 ± 2.8 kg/m(2)). EF volume was volumetrically assessed by manual delineation on short-axis views. CPT was applied by immersing one foot in ice water for 4 min. Mean EF volume was 56 ± 26 ml and mean LV mass 100 ± 28 g. CPT significantly increased heart rate (HR) by 32 ± 19%, systolic blood pressure by 14 ± 10%, and rate-pressure product by 45 ± 25%, P < 0.0001. The increase in HR, reflecting sympathetic stimulation, was not influenced by sex, age or EF volume. CPT induced a decrease in coronary vascular resistance (135 ± 72 vs. 100 ± 42 mm Hg.ml(-1).min.g, P = 0.0006), and a significant increase in MBF (0.81 ± 0.37 vs. 1.24 ± 0.56 ml.min(-1).g(-1), P < 0.0001). Interestingly, we found a significant negative correlation between EF volume and ΔMBF (r= - 0.40, P = 0.03), which remained significant after adjusting for ΔHR. ΔMBF was also associated with adiponectin (r = 0.41, P = 0.046), but not with waist circumference, BMI, C-reactive protein, lipid or glycemic parameters. In multivariate analysis, adiponectin and EF volume remained both independently associated with ΔMBF. A high EF amount is associated with a lower coronary microvascular response, suggesting that EF could early influence endothelial function.

Impaired ATP-induced coronary blood flow and diminished aortic NTPDase activity precede lesion formation in apolipoprotein E-deficient mice

Intravascular ATP and ADP are important regulators of vascular tone, thrombosis, inflammation, and angiogenesis. This study was undertaken to evaluate the contribution of purinergic signaling to disturbed vasodilation and vascular remodeling during atherosclerosis progression. We used apolipoprotein E-deficient (Apoe(-/-)) mice as an appropriate experimental model for atherosclerosis. Noninvasive transthoracic Doppler echocardiography imaging with adenosine, ATP, and other nucleotides and nonhydrolyzable P2 receptor agonists and antagonists suggests that ATP regulates coronary blood flow in mice through activation of P2Y (most likely, endothelial ATP/UTP-selective P2Y(2)) receptors, rather than via its dephosphorylation to adenosine. Strikingly, compared to age-matched wild-type controls, young (10- to 15-week-old) Apoe(-/-) mice displayed diminished coronary reactivity in response to ATP but not adenosine. The impaired hyperemic response to ATP persisted in older (20- to 30-week-old) Apoe(-/-) mice, which were additionally characterized by mild atherosclerosis (as ascertained by aortic Oil Red O staining) and a systemic increase in plasma ATP and ADP levels. Concurrent thin-layer chromatographic analysis of nucleoside triphosphate diphosphohydrolase (NTPDase) and ecto-5'-nucleotidase/CD73 activities in thoracic aortas, lymph nodes, spleen, and serum revealed that aortic NTPDase was decreased by 40% to 50% in a tissue-specific manner both in young and mature Apoe(-/-) mice. Collectively, disordered purinergic signaling in Apoe(-/-) mice may serve as important prerequisite for impaired blood flow, local accumulation of ATP and ADP at sites of atherogenesis, and eventually, the exacerbation of atherosclerosis.

Gender differences in response to cold pressor test assessed with velocity-encoded cardiovascular magnetic resonance of the coronary sinus

BACKGROUND

Gender-specific differences in cardiovascular risk are well known, and current evidence supports an existing role of endothelium in these differences. The purpose of this study was to assess non invasively coronary endothelial function in male and female young volunteers by myocardial blood flow (MBF) measurement using coronary sinus (CS) flow quantification by velocity encoded cine cardiovascular magnetic resonance (CMR) at rest and during cold pressor test (CPT).

METHODS

Twenty-four healthy volunteers (12 men, 12 women) underwent CMR in a 3 Tesla MR imager. Coronary sinus flow was measured at rest and during CPT using non breath-hold velocity encoded phase contrast cine-CMR. Myocardial function and morphology were acquired using a cine steady-state free precession sequence.

RESULTS

At baseline, mean MBF was 0.63 ± 0.23 mL·g⁻¹·min⁻¹ in men and 0.79 ± 0.21 mL·g⁻¹·min⁻¹ in women. During CPT, the rate pressure product in men significantly increased by 49 ± 36% (p < 0.0001) and in women by 52 ± 22% (p < 0.0001). MBF increased significantly in both men and women by 0.22 ± 0.19 mL·g⁻¹·min⁻¹ (p = 0.0022) and by 0.73 ± 0.43 mL·g⁻¹·min⁻¹ (p = 0.0001), respectively. The increase in MBF was significantly higher in women than in men (p = 0.0012).

CONCLUSION

CMR coronary sinus flow quantification for measuring myocardial blood flow revealed a higher response of MBF to CPT in women than in men. This finding may reflect gender differences in endothelial-dependent vasodilatation in these young subjects. This non invasive rest/stress protocol may become helpful to study endothelial function in normal physiology and in physiopathology.

Coronary flow reserve is impaired in patients with nonalcoholic fatty liver disease: association with liver fibrosis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with an increased risk of cardiovascular disease. Coronary flow reserve (CFR) is widely used to examine the integrity of coronary microvascular circulation. We evaluated the prevalence of impaired CFR in patients with biopsy-proven NAFLD. We also investigated the independent clinical, biochemical, and liver histology predictors of CFR in the setting of NAFLD.

METHODS

Fifty-nine consecutive patients with NAFLD and 77 age- and gender-matched controls were evaluated. CFR recordings were performed by transthoracic Doppler harmonic echocardiography. CFR>or=2.0 was considered normal.

RESULTS

CFR was significantly lower in patients with NAFLD than in controls (2.11+/-0.45 vs. 2.52+/-0.62, P<0.001). An impaired CFR (i.e. <2) was found in 25 NAFLD patients (42.4%) whereas all controls had normal CFR values (P<0.001). A stepwise linear regression analysis in NAFLD patients identified liver fibrosis scores as the only independent predictor of CFR values (beta=-0.60; t=-2.44, P=0.021).

CONCLUSION

Our findings indicate that in patients with biopsy-proven NAFLD: (a) an abnormal CFR is found in approximately 42.4% of cases, and (b) liver fibrosis scores are an independent predictor of depressed CFR.

Dual frequency method for simultaneous translation and real-time imaging of ultrasound contrast agents within large blood vessels

A dual frequency excitation method for simultaneous translation and selective real-time imaging of microbubbles is presented. The method can distinguish signals originating from free flowing and static microbubbles. This method is implemented on a programmable scanner with a broadband linear array. The programmable interface allows for dynamic variations in the acoustic parameters and aperture attributes, enabling application of this method to large blood vessels located at varying depths. The performance of the method was evaluated in vitro (vessel diameter 2mm) by quantifying the sensitivity of the method to various acoustic, microbubble, and fluid flow parameters. It was observed that the static microbubble response maximized at the approximate resonance frequency of the microbubble population (estimated from a coulter counter measurement), thus, signifying the need for dual frequency excitation. The static microbubble signal declined from 25 to 12 dB with increasing centerline flow velocities (2.65-15.9cm/s); indicating the applicable range of flow velocities. The maximum intensity of the static microbubbles signal scaled with variations in the microbubble concentration. The rate of increment of static microbubble signal was independent of microbubble concentration. It was deduced that the rate of increment of the static microbubble signal is primarily a function of the pulse frequency, whereas the maximum static microbubble signal intensity is dependent on three parameters: (a) the pulse frequency, (b) the flow velocity and (c) the microbubble concentration. The proposed dual frequency sequence may enable the application of radiation force for optimizing the effect of targeted imaging and modulating drug delivery in large blood vessels with high flow velocities.

Effects of cognac on coronary flow reserve and plasma antioxidant status in healthy young men

Background

The cardioprotective effects of certain alcoholic beverages are partly related to their polyphenol content, which may improve the vasodilatory reactivity of arteries. Effect of cognac on coronary circulation, however, remains unknown. The purpose of this randomized controlled cross-over study was to determine whether moderate doses of cognac improve coronary reactivity as assessed with cold pressor testing (CPT) and coronary flow reserve (CFR) measument.

Methods

Study group consisted of 23 subjects. Coronary flow velocity and epicardial diameter was assessed using transthoracic echocardiography at rest, during CPT and adenosine infusion-derived CFR measurements before drinking, after a moderate (1.2 ± 0.1 dl) and an escalating high dose (total amount 2.4 ± 0.3 dl) of cognac. To explore the bioavailability of antioxidants, the antioxidant contents of cognac was measured and the absorption from the digestive tract was verified by plasma antioxidant capacity determination.

Results

Serum alcohol levels increased to 1.2 ± 0.2‰ and plasma antioxidant capacity from 301 ± 43.9 μmol/l to 320 ± 25.0 μmol/l by 7.6 ± 11.8%, (p = 0.01) after high doses of cognac. There was no significant change in flow velocity during CPT after cognac ingestion compared to control day. CFR was 4.4 ± 0.8, 4.1 ± 0.9 (p = NS), and 4.5 ± 1.2 (p = NS) before drinking and after moderate and high doses on cognac day, and 4.5 ± 1.4, and 4.0 ± 1.2 (p = NS) on control day.

Conclusion

Cognac increased plasma antioxidant capacity, but it had no effect on coronary circulation in healthy young men.

Trial Registration

NCT00330213