Inhibition of red cell aggregation prevents spontaneous echocardiographic contrast formation in human blood

Prediction of spontaneous echocardiographic contrast within the left atrial appendage in cardiac computed tomography of patients with atrial fibrillation

This study aimed to assess the predictors of spontaneous echocardiographic contrast (SEC) using left atrial appendage (LAA) findings in cardiac computed tomography (CT) of patients with atrial fibrillation (AF). We retrospectively analyzed cardiac CT findings of the LAA, including morphology, volume, and filling defects, of 641 patients who underwent transesophageal echocardiography (TEE) prior to pulmonary vein isolation (PVI) from January 6, 2013 through December 16, 2019 at our institution. We investigated potential associated factors that might be predictors of SEC using cardiac CT findings and computed a receiver operator characteristic, choosing a threshold value at which the likelihood of SEC could be predicted based on the LAA volume indexed for body size. SEC correlated significantly with indexed LAA volume (P < 0.001; odds ratio [OR], 1.31; 95% confidence interval [CI], 1.17-1.48) of 7.75 cm3/m2 or greater (sensitivity, 76.0%; specificity, 57.7%), LAA early filling defect (P = 0.005; OR, 2.72; 95% CI, 1.35-5.48), a history of persistent AF (P < 0.001; OR, 3.81; 95% CI, 1.86-7.80), and LAA flow velocity (P < 0.001; OR, 0.97; 95% CI, 0.96-0.99). Findings of LAA in cardiac CT can allow for the noninvasive estimation of SEC to determine the need for additional TEE investigation and the need to obtain additional information for risk stratification and management of thromboembolic events in patients with AF.

Quantification of the Phenomena Affecting Reflective Arterial Photoplethysmography

Photoplethysmography (PPG) is a widely emerging method to assess vascular health in humans. The origins of the signal of reflective PPG on peripheral arteries have not been thoroughly investigated. We aimed to identify and quantify the optical and biomechanical processes that influence the reflective PPG signal. We developed a theoretical model to describe the dependence of reflected light on the pressure, flow rate, and the hemorheological properties of erythrocytes. To verify the theory, we designed a silicone model of a human radial artery, inserted it in a mock circulatory circuit filled with porcine blood, and imposed static and pulsatile flow conditions. We found a positive, linear relationship between the pressure and the PPG and a negative, non-linear relationship, of comparable magnitude, between the flow and the PPG. Additionally, we quantified the effects of the erythrocyte disorientation and aggregation. The theoretical model based on pressure and flow rate yielded more accurate predictions, compared to the model using pressure alone. Our results indicate that the PPG waveform is not a suitable surrogate for intraluminal pressure and that flow rate significantly affects PPG. Further validation of the proposed methodology in vivo could enable the non-invasive estimation of arterial pressure from PPG and increase the accuracy of health-monitoring devices.

[A case of cerebral embolism treated with early surgical intervention for aneurysm of sinus of Valsalva as embolic source]

The patient was a 78-year-old man. He was transferred to the emergency room presenting with aphasia and right hemiplegia. Head CT and CT angiography demonstrated a narrow territory of early ischemic signs and occlusion of the horizontal segment of the left middle cerebral artery (MCA), respectively. Endovascular thrombectomy was performed and complete recanalization of MCA was achieved. After admission, transthoracic echocardiography revealed a cystic mass near the left coronary apex of the aortic valve, which was diagnosed as an aneurysm of the sinus of Valsalva (ASV) by contrast-enhanced chest computed tomography. Transesophageal echocardiography showed a severe smoke-like echo within ASV, despite being in sinus rhythm. Intravenous anticoagulant therapy was started, and patch closure was performed by cardiovascular surgeons on the 13th day despite of early period after stroke onset. During the operation, no thrombus was seen around the inlet of ASV. On the two days after the operation, paroxysmal atrial fibrillation was detected and anticoagulant therapy was continued. In this patient, ASV was regarded as the embolic source of cerebral embolism, and anticoagulant therapy and surgical intervention were selected in the early period after stroke onset to prevent embolism recurrence, resulting in a favorable clinical course.

Left atrial spontaneous echo contrast: relationship with clinical and echocardiographic parameters

Spontaneous echo contrast (SEC) indicates blood stasis in cardiac chambers and major vessels, and is a known precursor of thrombus formation. Transesophageal echocardiography plays a pivotal role in detecting and grading SEC in the left atrial (LA) cavity. Assessing LA SEC can identify patients at increased risk for thromboembolic events. LA SEC also develops in patients who have sinus rhythm, especially in those with heart failure. Detection of LA SEC is not uncommon in subjects who have multiple cardiovascular comorbidities, although mechanisms behind this association are not fully understood. In patients with atrial fibrillation, the role of mitral regurgitation in counteracting LA SEC and subsequent thromboembolism is controversial. Moreover, alterations of blood coagulability and elevated levels of certain biological markers in the blood contribute to occurrence of LA SEC. This review describes the pathogenesis and assessment of SEC, in addition to the relationship between LA SEC and clinical, biological and echocardiographic parameters.

Quantitative Measurement of Erythrocyte Aggregation as a Systemic Inflammatory Marker by Ultrasound Imaging: A Systematic Review

This systematic review is aimed at answering two questions: (i) Is erythrocyte aggregation a useful biomarker in assessing systemic inflammation? (ii) Does quantitative ultrasound imaging provide the non-invasive option to measure erythrocyte aggregation in real time? The search was executed through bibliographic electronic databases CINAHL, EMB Review, EMBASE, MEDLINE, PubMed and the grey literature. The majority of studies correlated elevated erythrocyte aggregation with inflammatory blood markers for several pathologic states. Some studies used "erythrocyte aggregation" as an established marker of systemic inflammation. There were limited but promising articles regarding the use of quantitative ultrasound spectroscopy to monitor erythrocyte aggregation. Similarly, there were limited studies that used other ultrasound techniques to measure systemic inflammation. The quantitative measurement of erythrocyte aggregation has the potential to be a routine clinical marker of inflammation as it can reflect the cumulative inflammatory dynamics in vivo, is relatively simple to measure, is cost-effective and has a rapid turnaround time. Technologies like quantitative ultrasound spectroscopy that can measure erythrocyte aggregation non-invasively and in real time may offer the advantage of continuous monitoring of the inflammation state and, thus, may help in rapid decision making in a critical care setup.

High Cardiac Troponin I Is Associated With Transesophageal Echocardiographic Risk of Thromboembolism and Ischemic Stroke Events in Non-Valvular Atrial Fibrillation Patients

BACKGROUND

Abnormalities in the left atrium (LA) detected on transesophageal echocardiography (TEE) are reliable predictors of thromboembolism in patients with atrial fibrillation (AF). Cardiac troponin I, a marker of subclinical myocardial damage, may also be a predictor of thromboembolic events in patients with AF. The relationship between cardiac troponin I and thromboembolic risk on TEE, however, remains unclear.Methods and Results:TEE and laboratory data, including high sensitivity cardiac troponin I (hs-cTnI) and CHA₂DS₂-VASc score, were analyzed in 199 patients with non-valvular AF (NVAF). Patients were stratified into those with or without LA abnormality, defined as LA appendage flow velocity <20 cm/s or dense spontaneous echo contrast. On multiple logistic analysis of the clinical variables, hs-cTnI was associated with LA abnormality (95% CI: 1.0003-1.020, P=0.034). The area under the curve for LA abnormality increased on addition of hs-cTnI to CHA₂DS₂-VASc score. The incidence rate of ischemic stroke was higher in the high hs-cTnI group than in the low-hs-cTnI group (log-rank test, P<0.05).

CONCLUSIONS

Elevated hs-cTnI was independently associated with LA abnormality in NVAF patients. hs-cTnI level may be a useful biomarker for risk stratification of thromboembolism in NVAF patients.

Severity of spontaneous echo contrast in the jugular vein associated with ischemic stroke

This study evaluated the relationship between spontaneous echo contrast (SEC) in the internal jugular vein (JV), atherosclerotic markers and ischemic stroke. One hundred twenty patients with acute ischemic stroke and 120 controls were recruited. SEC score correlated with plasma level of fibrinogen (coefficient: 0.105, p = 0.022), hemoglobin (coefficient: 0.122, p = 0.008) and presence of JV reflux (coefficient: 0.314, p < 0.001) and peak flow velocity (coefficient: -0.244, p < 0.001) in the corresponding JV, but did not correlate with carotid plaque score (coefficient: 0.042, p = 0.358) or intima-media thickness (coefficient: 0.067, p = 0.303). Multivariate regression analysis revealed that fibrinogen level, SEC score, intima-media thickness, plaque score and history of coronary artery disease were associated with acute ischemic stroke. In conclusion, the severity of SEC in the JV might represent the tendency toward thrombogenesis in diseased cerebral circulation possibly through mechanisms other than arterial atherosclerosis.

Feasibility of TEE-guided stroke risk assessment in atrial fibrillation-background, aims, design and baseline data of the TIARA pilot study

Background

Antithrombotic management in atrial fibrillation (AF) is currently based on clinical characteristics, despite evidence of potential fine-tuning with transoesophageal echocardiography (TEE). This open, randomised, multicentre study addresses the hypothesis that a comprehensive strategy of TEE-based aspirin treatment in AF patients is feasible and safe.

Methods

Between 2005 and 2009, ten large hospitals in the Netherlands enrolled AF patients with a moderate risk of stroke. Patients without thrombogenic TEE characteristics were randomised to aspirin or vitamin K antagonists (VKA). The primary objective is to show that TEE-based aspirin treatment is safe compared with VKA therapy. The secondary objective tests feasibility of TEE as a tool to detect echocardiographic features of high stroke risk. This report compares randomised to non-randomised patients and describes the feasibility of a TEE-based approach.

Results

In total, 310 patients were included. Sixty-nine patients were not randomised because of non-visualisation (n = 6) or TEE risk factors (n = 63). Compared with non-randomised patients, randomised patients (n = 241) were younger (65 ± 11 vs. 69 ± 9 years, p = 0.004), had less coronary artery disease (9 vs. 20%, p = 0.018), previous TIA (1.7 vs. 7.2%, p = 0.029), AF during TEE (25 vs. 54%, p < 0.001), mitral incompetence (55 vs. 70%, p = 0.038), VKA use (69 vs. 82%, p = 0.032), had a lower mean CHADS₂ score (1.2 ± 0.6 vs. 1.6 ± 1.0, p = 0.004), and left ventricular ejection fraction (59 ± 8 vs. 56 ± 8%, p = 0.016).

Conclusions

This study shows that a TEE-based approach for fine-tuning stroke risk in AF patients with a moderate risk for stroke is feasible. Follow-up data will address the safety of this TEE-based approach.

Sonographic diagnosis of pulmonary embolism with cardiac arrest without major dilation of the right ventricle or direct sign of lower limb venous thrombosis

Bedside focused echocardiography diagnosis of massive pulmonary embolism during cardiac arrest is mainly based on the detection of a dilated right ventricle, while the lack of compressibility of a deep vein of the lower limbs confirms diagnosis in doubtful cases. We describe a case of unusual sonographic signs in a young woman with cardiac arrest due to massive pulmonary embolism showing spontaneous blood echogenicity in the inferior vena cava ("sludge sign") and nonmodulated ("flat") Doppler waveform in the left lower limb veins, suggesting isolated iliac vein thrombosis.

Spontaneous echo contrast in internal jugular veins: a probable indicator for systemic inflammation and a prothrombotic state

The hypothesis that spontaneous echo contrast (SEC) in the internal jugular vein (IJV) is a clinical indicator for systemic inflammation and thrombogenesis is investigated in this study. Fifty-two patients with cardiovascular diseases and 25 nondiseased subjects were evaluated. SEC was observed in 96 of 154 IJVs. The visual grading of SEC showed good interobserver agreement on SEC grades (κ value: 0.846, p < 0.001). Generalized estimating equations analysis was used for univariate and multivariate analysis. Univariate analysis showed that peak flow velocity in corresponding IJV (coefficient -0.001 [95% CI -0.019, -0.001], p = 0.031), jugular venous reflux (JVR, -0.010 [-0.019, -0.001], p = 0.002), plasma levels of fibrinogen (0.464 [0.208, 0.719], p < 0.001) and hs-C-reactive protein (hs-CRP) (0.479 [0.184, 0.774], p = 0.001) and previous history of ischemic stroke (0.779 [0.139, 1.417]; p = 0.017) correlated with the grades of SEC in IJV. Increased plasma levels of fibrinogen and hs-CRP, previous ischemic stroke, lower peak velocity in corresponding IJV and JVR were also independent predictors for the higher grades of SEC in IJV in multivariate regression analysis. SEC in IJV could be evaluated easily and semiquantitatively. SEC in IJVs could be a putative marker of cerebral circulation disturbance and an indicator of systemic inflammatory or prothrombotic state.

Integrin-associated protein (CD47) is a putative mediator for soluble fibrinogen interaction with human red blood cells membrane

Fibrinogen is a multifunctional plasma protein that plays a crucial role in several biological processes. Elevated fibrinogen induces erythrocyte hyperaggregation, suggesting an interaction between this protein and red blood cells (RBCs). Several studies support the concept that fibrinogen interacts with RBC membrane and this binding, due to specific and non-specific mechanisms, may be a trigger to RBC hyperaggregation in inflammation. The main goals of our work were to prove that human RBCs are able to specifically bind soluble fibrinogen, and identify membrane molecular targets that could be involved in this process. RBCs were first isolated from blood of healthy individuals and then separated in different age fractions by discontinuous Percoll gradients. After isolation RBC samples were incubated with human soluble fibrinogen and/or with a blocking antibody against CD47 followed by fluorescence confocal microscopy, flow cytometry acquisitions and zeta potential measurements. Our data show that soluble fibrinogen interacts with the human RBC membrane in an age-dependent manner, with younger RBCs interacting more with soluble fibrinogen than the older cells. Importantly, this interaction is abrogated in the presence of a specific antibody against CD47. Our results support a specific and age-dependent interaction of soluble fibrinogen with human RBC membrane; additionally we present CD47 as a putative mediator in this process. This interaction may contribute to RBC hyperaggregation in inflammation.

Measurement of red blood cell aggregation using X-ray phase contrast imaging

When a coherent beam illuminates spatially disordered particles, speckle patterns are formed due to interference of the scattered light waves. Speckle patterns from biological tissues using synchrotron phase contrast X-ray imaging can provide functional information about micro-scale morphological structures of the tissues. In this study, we investigated the size and contrast variations of the speckles of aggregated red blood cells (RBCs) suspensions with varying the degree of RBC aggregation. Results show that the degree of RBC aggregation is a governing parameter on the change of speckle characteristics. This blood speckle analysis method can be used as a novel modality for monitoring RBC aggregation.

Left atrial appendage thrombus detected by intraoperative transesophageal echocardiography in a patient with acute small bowel infarction -A case report-

Acute mesenteric ischemia and infarction is an emergent situation associated with high mortality, commonly due to emboli or thrombosis of the mesenteric arteries. Embolism to the mesenteric arteries is most frequently due to a dislodged thrombus from the left atrium, left ventricle, or cardiac valves. We report a case of 70-year-old female patient with an acute small bowel infarction due to a mesenteric artery embolism dislodged from a left atrial appendage detected by intraoperative transesophageal echocardiography and followed by anticoagulation therapy.

Fibrinogen-dependent signaling in microvascular erythrocyte function: implications on nitric oxide efflux

Experimental evidence has shown that plasma fibrinogen plays a key role as a major cardiovascular risk factor, acting directly to trigger erythrocyte aggregation in occlusive vascular disease. However, due to the complex and hitherto unclear interaction between fibrinogen and the erythrocyte membrane, no study has yet evaluated the effects of fibrinogen, under physiological range values, on the erythrocyte nitric oxide (NO) mobilization. Taking into consideration the potential NO-derived molecules, we have raised the hypothesis that fibrinogen, under physiological conditions, may act to influence blood flow via erythrocyte NO modulation. In this in vitro study whole-blood samples were harvested from healthy subjects, erythrocyte suspensions were incubated in the absence (control aliquots) and presence of different fibrinogen concentrations and levels of NO, nitrite, nitrate and S-nitroglutathione (GSNO) were determined. Our results showed, when compared with control aliquots, that the presence of fibrinogen modulates the NO mobilization in erythrocytes by (1) decreasing erythrocyte NO efflux levels (P < 0.001); (2) increasing levels of intraerythrocytic NO oxidative metabolites, namely, nitrite (P < 0.0001) and nitrate (P < 0.0001); and (3) enhancing the formation of GSNO (P < 0.001). In conclusion, this study provides new insights into an unknown mechanism by which fibrinogen modulates the erythrocyte capacity to supply NO, the effects of which on inflammation profiles (generally associated with blood hyperviscosity and hyperaggregation) still need to be elucidated. Also, increased erythrocyte GSNO levels may be associated with platelet NO metabolism, its activation status and hypotension, which may be extremely relevant in the clinical setting as biomarkers.

Three-dimensional reconstruction of the "bright ring" echogenicity from porcine blood upstream in a stenosed tube

To investigate the echogenicity variation due to blood flow disturbance near a stenosis under pulsatile flow, a series of in vitro experiments were performed in a rigid tube with an eccentric stenosis of 70% area reduction in a mock flow loop. An ultrasonic B-mode with a Doppler spectrogram was used to correlate echogenicity with flow speed and stroke rate. This paper reports echogenicity variation upstream of a stenosis under pulsatile flow. The experimental results showed that blood flow disturbed by the stenosis affects echogenicity and red blood cell rouleaux upstream. A hypoechoic "black hole" was shown at the center of the stream at systole. During diastole, the "bright ring" in cross-sectional images was observed as eddy-like or parabolic profiles in longitudinal images. These images could be reconstructed into a 3-dimensional animation, providing a better understanding of dynamic changes of the rouleaux distribution upstream of a stenosis under pulsatile flow.

The effect of transient balloon occlusion of the mitral valve on left atrial appendage blood flow velocity and spontaneous echo contrast

BACKGROUND

Spontaneous echo contrast (SEC) is a phenomenon that is commonly seen in areas of blood stasis. It is a slowly moving, cloud-like swirling pattern of "smoke" or increased echogenicity recorded on echocardiography. SEC is commonly seen in the left atrium of patients with mitral stenosis or atrial fibrillation. The presence of SEC has been shown to be a marker of increased thromboembolic risk.

HYPOTHESIS

By using transesophageal echocardiography during percutaneous balloon mitral valvotomy (PBMV), the study investigated the relationship between SEC and varying left atrial appendage (LAA) blood flow velocity in the human heart.

METHODS

Thirty-five patients with rheumatic mitral stenosis underwent percutaneous balloon mitral valvotomy with intraoperative transesophageal echocardiography monitoring. We alternatively measured LAA velocities and observed the left atrium for various grades of SEC (0 = none to 4 = severe) before and after each balloon inflation.

RESULTS

Left atrial appendage maximal ejection velocity was reduced from 35 +/- 14 to 6 +/- 2 mm/s at peak balloon inflation and increased to 40 +/- 16 mm/s after balloon deflation. In comparison with the values before balloon inflation and after balloon deflation, LAA velocities were significantly lower (p < 0.001). New or increased SEC grade was observed during 54 of 61 (88%) inflations and unchanged in 7 (12%) inflations at peak balloon inflation. Spontaneous echo contrast became lower in grade after 55 balloon deflations (90%), completely disappeared after 18 deflations (30%), and remained unchanged after 6 deflations (10%). The mean time to achieve maximal SEC grade (2.5 +/- 1.2 s) coincided with the mean time to trough LAA velocities (2.3 +/- 1.1 s) after balloon inflation. Upon deflation, the mean time to lowest SEC grade (2.9 +/- 1.8 s) coincided with mean time to achieve maximal LAA velocities (2.7 +/- 1.6 s).

CONCLUSION

During balloon inflation, the severity of SEC was enhanced with corresponding reduction in LAA flow velocity. Upon balloon deflation, SEC lightens or disappears with increase in LAA flow velocity.

Ultrasonic backscatter from rat blood in aggregating media under in vitro rotational flow

Ultrasonic backscatter from flowing and static rat red blood cells (RBCs) in autologous plasma and in 360 kDa polyvinylpyrrolidone (PVP 360) solution was measured as a function of hematocrit. The flow speed was varied by a stirring magnet in a cylindrical chamber. The radio-frequency (RF) signals backscattered by RBC samples were measured over 5 min in a pulse-echo setup with a 5 MHz focused transducer. Although the intact rat blood has poor RBC aggregability, RBC aggregation of rat blood was enhanced by replacing its plasma with a higher molecular weight polymer solution. The experimental results showed that the nonlinear relationship between hematocrit and ultrasonic backscatter from rat RBCs in plasma and aggregating media is affected by flow speed, which may provide a unified insight into hematocrit dependence of RBC aggregation under flowing and static conditions.

Acoustic determination of early stages of intravascular blood coagulation

The blood coagulation system (BCS) is a complex biological system playing a principal role in the maintenance of haemostasis. Insufficient activity of the BCS may lead to bleeding and blood loss (e.g. in the case of haemophilia). On the other hand, excessive activity may cause intravascular blood coagulation, thromboses and embolization. Most of the methods currently used for BCS monitoring suffer from the major disadvantage of being invasive. The purpose of the present work is to demonstrate the feasibility of using ultrasonic methods for non-invasive registration of the early stages of blood coagulation processes in intensive flows. With this purpose, a special experimental set-up was designed, facilitating the simultaneous detection of optical and acoustic signals during the clotting process. It was shown that (i) as microemboli appear in the flow during the early stage of blood coagulation, the intensity of the Doppler signal increases twofold, and (ii) microemboli formation in the early stages of blood clotting always reveals itself through an acoustic contrast. Both of these effects are well defined, so we hope that they may be used for non-invasive BCS monitoring in clinical practice.

The relationship between spontaneous echocontrast, transesophageal echocardiographic parameters, and blood hemoglobin levels

BACKGROUND

Spontaneous echocontrast (SEC) or "smoke" is an intracavitary echocardiographic finding seen in situations of stasis or low blood flow. Increased hematocrit and fibrinogen levels have been associated with SEC in prior studies. Whether low hemoglobin (Hb) levels are an independent predictor of lower prevalence of SEC is a question that remains unanswered.

METHODS

A total of 266 transesophageal echocardiographic (TEE) studies were reviewed. Hb levels within 1 month from the TEE study were used as the baseline Hb before the study (75% had Hb on the same day of the TEE study). Clinical characteristics and demographics, and all relevant TEE variables including left atrial (LA) size, LA appendage emptying velocity (LAAEV), and presence or absence of SEC, were obtained using electronic patient information system search of TEE reports. Multivariate regression analysis was performed to identify the independent predictors of SEC.

RESULTS

Two groups were analyzed SEC (n = 45) or no SEC (n = 221). Only 7 patients had both LA and right atrial SEC. On univariate analysis, male sex, greater age, prior coronary artery bypass grafting, low ejection fraction (<50%), atrial fibrillation, renal failure, aortic atheroma, dilated LA, and decreased LAAEV (<40 cm/s) predicted SEC whereas low Hb levels were significantly associated with a lower prevalence of SEC (P = .01). However, after adjusting for clinical and echocardiographic variables, low Hb levels did not independently predict absence of SEC. Low LAAEV (P < .001), dilated LA (P = .001), and prior statin therapy (P = .001) were the most powerful independent predictors of SEC.

CONCLUSION

A low Hb level is not associated with a lower prevalence of SEC when controlled for clinical and echocardiographic variables. Our study confirms the importance of LAAEV and dilated LA in determining presence of SEC, but also raises interesting questions of the relationship between statins and SEC that warrant further study.

High frequency ultrasound device to investigate the acoustic properties of whole blood during coagulation

This study was designed to investigate the changes in acoustic properties of whole blood during the coagulation process. High frequency (from 20 to 40 MHz) ultrasound parameters were measured both in double transmission (DT) and backscattering (BS) mode to assess sound velocity and backscatter coefficient, respectively. The integrated backscatter coefficient (IBC) and the effective scatterer size (ESS) were deducted from the backscatter coefficient. Measurements were performed on whole blood samples collected from 12 healthy volunteers. During the blood clotting process (2 h observation), acoustic parameters were measured with 15 s time resolution for the transmission parameter and 5 s (for the 5 first min) and 30 s (for the end of the observation time) for the backscattering parameters. The results obtained clearly showed that simultaneous measurements of parameters in DT and BS modes are able to identify several stages during the in vitro blood clotting process. In particular, red blood cell (RBC) aggregation can be described from the backscattering parameters and liquid-gel transition phase of blood from the sound velocity. Intra- and inter-individual dispersion of these parameters were also measured and discussed.

Dextran 40 reduces in vitro platelet aggregation in peripheral arterial disease

Dextran 40 has been used to prevent post-operative thrombosis. However, its antithrombotic and antiplatelet effects in peripheral arterial disease (PAD) are poorly understood. We studied the in vitro effects of Dextran 40 on platelet function in control subjects and PAD patients using whole blood methods. Platelet function was assessed in 20 control subjects and 20 PAD patients. Spontaneous platelet aggregation (SPA) and agonist-induced platelet aggregation in response to increasing concentrations of Dextran 40 in vitro were measured by whole blood aggregometry. Flow cytometric measurements of platelet P-selectin, GpIIb/IIIa, GpIb and PAC-1 binding were also performed. There was no difference in SPA or ADP-induced aggregation in control patients with Dextran 40 in vitro. However, Dextran 40 inhibited collagen-induced aggregation in control patients (P < 0.05, Friedman test). In PAD patients, SPA and ADP (1 microM)-induced aggregation were significantly reduced by Dextran 40 in vitro (P < 0.001, Friedman test). In PAD patients, collagen-induced platelet aggregation (1 and 5 microg/ml) was significantly reduced by Dextran 40 in vitro (P < 0.01, Friedman test). GpIIb/IIIa, PAC-1 and P-selectin expression were significantly reduced in whole blood samples from PAD patients following incubation with Dextran 40 (P < 0.05, Wilcoxon rank test) but not in samples from control patients. Dextran 40 reduces spontaneous and agonist-induced platelet aggregation as well as the surface expression of markers of platelet activation in PAD patients. This antiplatelet effect may be of benefit to patients undergoing vascular surgical procedures where thrombosis is a significant risk.

Left Atrial Appendage Function and Abnormal Hypercoagulability in Patients With Atrial Flutter *

STUDY OBJECTIVES

The prevalence of thromboembolism might be higher than previously recognized in patients with atrial flutter (AFL) based on findings of transesophageal echocardiography (TEE). To evaluate the potential prothrombotic state in patients with AFL, TEE findings and hemostatic markers were compared among patient groups with AFL, normal sinus rhythm (NSR) and chronic nonvalvular atrial fibrillation (AF).

DESIGN AND SETTINGS

Cross-sectional study at a university hospital.

METHODS

In 28 patients (mean age, 63 years) with AFL, 58 patients (mean age, 66 years) with AF, and 27 patients (mean age, 61 years) with NSR who underwent TEE, plasma levels of markers for platelet activity (platelet factor 4 and beta-thromboglobulin [beta-TG]), thrombotic status (thrombin-antithrombin III complex and prothrombin fragments 1 and 2) and fibrinolytic status (d-dimer and plasmin-alpha(2)-plasmin inhibitor complex) were determined.

RESULTS

Left atrial appendage (LAA) blood flow velocity in patients with AFL was higher (p < 0.05) than that in patients with AF, but was lower (p < 0.05) than that in patients with NSR (AF, 25 +/- 2; AFL, 44 +/- 4; NSR, 60 +/- 4 cm/s). Dense left atrial spontaneous echo contrast (SEC) was found in 4 patients (14%) with AFL and 16 patients (28%) with AF. There was no significant difference in plasma levels of hemostatic markers between the AFL group and the NSR group. AFL patients with impaired LAA function (LAA flow < 30cm/s, dense SEC, or both), however, showed higher level of d-dimer and beta-TG than those without impaired LAA function (d-dimer, 1.9 +/- 0.6 microg/mL vs 0.4 +/- 0.1 microg/mL; beta-TG, 73 +/- 17 ng/mL vs 33 +/- 5 ng/mL, p < 0.05).

CONCLUSIONS

Patients with AFL as a whole are not in the prothrombotic state as compared with those with AF. However, patients with AFL and impaired LAA function are at potentially high risk for thromboembolism and might require anticoagulation.

Spontaneous echo contrast videodensity is flow-related and is dependent on the relative concentrations of fibrinogen and red blood cells

OBJECTIVES

The purposes of the present study were to: 1) determine whether fibrinogen (Fg) is the plasma protein responsible for spontaneous echo contrast (SEC), and 2) investigate modulators of SEC.

BACKGROUND

Spontaneous echo contrast has been linked to the development of thromboemboli. The blood products and their interaction responsible for SEC formation have not been fully elucidated.

METHODS

Blood echogenicity was examined with the use of quantitative videodensitometry over a controlled range of flow velocities in an in vitro model. Human blood samples were analyzed in a manner to methodically eliminate individual blood components from whole blood to determine which components are responsible for the formation of SEC.

RESULTS

The videodensity (VD) of whole blood was found to be flow-dependent, with higher VD at lower flow rates, and correlated with visually dense SEC. The following blood products produced faint VD values: washed red blood cells (wRBCs), platelet-depleted plasma, Fg, defibrinated plasma, wRBCs plus defibrinated plasma, and physiologic saline. The VD of wRBCs increased incrementally as increasing concentrations of Fg were added. At each hematocrit (Hct) range, as Fg concentration increased, the SEC became denser, and the VD level also increased until a plateau level was reached that was distinct for each Hct. The addition of sialic acid, which inhibits RBC-RBC aggregation, decreased the amount of SEC, even in the presence of Fg.

CONCLUSION

These results demonstrated that Fg-mediated RBC aggregation may be responsible for SEC generation. Furthermore, a unique stoichiometric relationship exists between Fg and RBC concentrations that is necessary for blood echogenicity.

Haematologic determinants of left atrial spontaneous echo contrast in mitral stenosis

OBJECTIVES

To determine if a relationship exists in mitral stenosis, in patients with either sinus rhythm or atrial fibrillation, between left atrial spontaneous echo contrast and the haematologic indices haematocrit, red cell concentration, mean corpuscular volume, platelet count and volume.

METHODS

Left atrial spontaneous echo contrast severity was graded on a scale of 0-4 in 163 patients with symptomatic mitral stenosis (84 patients in sinus rhythm, 79 patients in atrial fibrillation) undergoing transesophageal echocardiography, cardiac catheterization and full blood examination as part of assessment prior to balloon mitral valvuloplasty.

RESULTS

In sinus rhythm, spontaneous echo contrast grade was negatively correlated with cardiac index (r=-0.33), mitral valve area (r=-0.25) and mitral regurgitation grade (r=-0.22) and positively correlated with haematocrit (r=0.24) and red cell concentration (r=0.25). Spontaneous echo contrast grade was not correlated with left atrial diameter or mean corpuscular volume. In atrial fibrillation, spontaneous echo contrast grade was also negatively correlated with mitral valve area (r=-0.25) and mitral regurgitation (r=-0.36) but was positively correlated with left atrial diameter (r=0.34) and was not correlated with cardiac index, haematocrit or red cell concentration. There was no correlation between spontaneous echo contrast grade and platelet variables in either group.

CONCLUSIONS

Natural variation in red cell concentration in patients with symptomatic mitral stenosis was an independent predictor of the severity of left atrial spontaneous echo contrast in sinus rhythm, but no relationship between red cell concentration and spontaneous echo contrast grade was evident in atrial fibrillation.

Spontaneous echo contrast in descending aorta correlates with low blood-flow velocity in carotid arteries and hemostatic abnormalities

Spontaneous echo contrast in the descending aorta (DA-SEC) was examined as a possible risk factor for cerebral thromboembolism. In 19 patients (10 males, 9 females) in the chronic stage of cerebral infarction, abnormal findings by transesophageal echocardiography, flow dynamics of the common carotid artery (CCA), and hemostatic factors including blood coagulation and fibrinolysis were investigated. In nine patients, DA-SEC was detected, and SEC in left atrium (LA-SEC) was detected in nine patients. The DA-SEC positive group showed decreased blood-flow velocity (BFV) in bilateral CCA, high levels of thrombin-antithrombin III complex (TAT) and prothrombin fragment 1.2 (F1+2), a decrease in platelet count and a slight increase in D-dimer, which means an activated state of thrombin generation and resulting fibrinolysis, compared to the DA-SEC negative group. On the other hand, the LA-SEC positive group showed normal BFV in CCA and only a slight increase in D-dimer. We conclude that the condition producing DA-SEC is a stronger risk factor for cerebral infarction than that producing LA-SEC.

Coexpression of CD4 and CD8alpha on rat T-cells in whole blood: a sensitive marker for monitoring T-cell immunosuppressive drugs

The aim of this study was to develop a new quantitative method for measuring in vitro the effects of T-cell immunosuppressive drugs by flow cytometry. Rat whole blood samples were stimulated with the T-cell mitogen succinylated concanavalin A in the presence or absence of different drugs. After 3 days, the expression of CD25 and CD8alpha in mitogen-stimulated CD4(+) cells increased 10- to 20-fold as measured by flow cytometry. Drug efficacy and potency was calculated based on dose-response curves of the drug-mediated decrease in CD4(+)/CD8alpha(+)/CD25(+) cells. The expression of CD8alpha in mitogen-stimulated CD4(+) cells was blocked completely by calcineurin inhibitors (cyclosporine A and FK-506), and partially by rapamycin and SDZ-RAD. The IC(50) (50% inhibitory concentration) values obtained were (mean+/-S.E.): 99.5+/-16.6 nM for cyclosporine A, 10.4+/-1.3 nM for FK-506, 1.8+/-0.7 nM for rapamycin, and 6.4+/-1.1 nM for SDZ-RAD. Our results show, for the first time, that CD8alpha, used as an activation antigen, is a sensitive marker for monitoring T-cell immunosuppression.

Correlation between quantitative left atrial spontaneous echocardiographic contrast and intact fibrinogen levels in mitral stenosis

An association between left atrial spontaneous echocardiographic contrast (LASEC) and thromboembolic events has been recognized. However, the appearance of LASEC and the assessment of its intensity are gain dependent. To evaluate the relation between LASEC intensity and coagulation activity, 11 patients with mitral stenosis underwent transesophageal echocardiography with quantitative integrated backscatter assessment of LASEC. Right and left atrial blood samples were evaluated for concentrations of coagulation markers, including intact fibrinogen, fibrinopeptide A, D-dimer, prothrombin fragment 1+2, and thrombin-antithrombin III complex. The patients were found to have significantly higher mean left atrial concentrations compared with right atrial concentrations of thrombin-antithrombin III (28.46 +/- 21.05 versus 3.21 +/- 7.16 ng/mL, respectively; P =.001) and fibrinopeptide A (32.78 +/- 17.54 versus 7.42 +/- 8.27 nmol/L, respectively; P <.001). Intact fibrinogen levels were similar in both atria, and a strong, direct correlation existed between left and right atrial intact fibrinogen levels (r = 0.78, P =.005). Quantitative integrated backscatter of LASEC correlated directly with left atrial fibrinogen level (r = 0.78, P =.013) but not with markers of thrombin generation (thrombin-antithrombin III) or activity (fibrinopeptide A). Our results confirm that patients with mitral stenosis have evidence of a regional hypercoagulable state in the left atrium. However, the intensity of LASEC assessed by quantitative integrated backscatter correlates with both right and left atrial intact fibrinogen level, a systemic marker of coagulation.

Clinical and echocardiographic characteristics of left atrial spontaneous echo contrast in sinus rhythm

OBJECTIVES

In this study we attempt to define the clinical and echocardiographic characteristics of patients with left atrial spontaneous echo contrast (LASEC) in sinus rhythm (NSR).

BACKGROUND

Left atrial spontaneous echo contrast in atrial fibrillation (AF) is associated with increased risk of thromboembolism. Little is known about its significance in NSR.

METHODS

We reviewed reports of 1,288 transesophageal echocardiogram (TEE) studies done with a 5 MHz probe. Patients with swirling LASEC who were in NSR during TEE were analyzed. We compared them with a control group of 45 age matched patients selected to have NSR, left atrium (LA) > 4.0 cm but no SEC.

RESULTS

Spontaneous echo contrast in NSR was noted in 24 patients (2%) and formed our study group. All patients with SEC had enlarged LA, mean 5.6 cm +/- 0.6 cm. There was a higher prevalence of cerebrovascular accident (CVA) in patients with SEC when compared with controls with no SEC, 83% versus 56%, p = 0.02. Patients with SEC had larger LA, 5.6 versus 4.9 cm, p < 0.0001 and lower mean peak left atrial appendage emptying velocity (LAAEV), 38 versus 56 cm/s, p = 0.001. Thirteen percent of patients with SEC had LA thrombus as compared with none in the control group, p = 0.02. By multivariate analysis, SEC in NSR was found to be associated with CVA, larger LA size and decreased mean LAAEV. Even after adjusting for LA size, patients with SEC had a higher prevalence of CVA than controls, p = 0.03.

CONCLUSIONS

Spontaneous echo contrast in NSR occurs in patients with significantly dilated LA and depressed atrial function. Left atrial thrombus is noted in 13% of such patients despite NSR. Spontaneous echo contrast in NSR is associated with a higher prevalence of CVA. Further, SEC is found to be an independent and more powerful correlate of CVA than reduced LAAEV or atrial size. These data indicate that LASEC in NSR is a prothombotic condition.

Spontaneous echo contrast: where there's smoke there's fire

Left atrial (LA) spontaneous echo contrast (SEC), or "smoke," is a frequent finding on transesophageal echocardiography (TEE), but it is rarely detected with transthoracic echocardiography. LA SEC is characterized by dynamic smoke-like echoes within the LA cavity or appendage. Most patients with LA SEC have atrial arrhythmias, mitral stenosis, or a mitral valve prosthesis, and they have an enlarged LA, conditions that are associated with LA stasis. Conversely, mitral regurgitation is protective against LA SEC. LA SEC is present in almost all patients with LA thrombus and is associated with previous embolic events in many patient populations. In patients with nonvalvular atrial fibrillation, LA SEC predicts future embolism and death. LA SEC may therefore assist in selecting patients with atrial fibrillation or with mitral stenosis and sinus rhythm who benefit the most from anticoagulation. Hematological studies have shown that LA SEC is a marker of an hypercoagulable state. LA SEC is a manifestation of red cell aggregation, arising from an interaction between red cells and plasma proteins such as fibrinogen, at low shear rates. LA SEC does not require platelets. The detection of LA SEC on ultrasound arises from the increased amplitude of backscatter from red cell aggregates rather than single cells. Patients with LA SEC should be considered for anticoagulant therapy and may require correction of underlying cardiovascular abnormalities. Future directions in LA SEC include further assessment of integrated backscatter for quantification, assessment of its prognostic role in clinically low-risk patients with nonvalvular AF, and novel pharmacological treatment.

Pharmacological concentrations of arginine influence human whole blood viscosity independent of nitric oxide synthase activity in vitro

l-Arginine, the natural precursor of NO, is infused in patients to restore endothelial function. Concentrations up to 7.5 mM l-arginine have been measured after parenteral administration. We investigated whether such high concentrations of amino acids influence blood viscosity in vitro. Incubation of whole blood from healthy volunteers with l-arginine, d-arginine, which has no effect on stereospecific NO synthases (NOS), the NOS substrate L-AME, the NOS inhibitor L-NNA, the amino acids l-lysine and l-glutamic acid, and finally NaCl dose-dependently decreased (up to 30% at 10(-2) M) low shear viscosity, which is primarily determined by erythrocyte aggregation. In contrast, the lipophilic NOS inhibitor L-NAME had no effect on low shear viscosity. All molecules failed to influence high shear viscosity, which is primarily determined by red cell deformability, and the erythrocyte shape remained unaltered. We conclude that high concentrations amino acids may decrease blood viscosity at low shear rate independent of NOS activity. This effect may contribute to the improved blood flow after intravascular administration of l-arginine.

Rapid onset and dissipation of left atrial spontaneous echo contrast during percutaneous balloon mitral valvotomy

BACKGROUND

Thromboembolism after percutaneous balloon mitral valvotomy (PBMV) has been attributed to dislodement of preexisting thrombus during transseptal puncture and instrumentation of the left atrium. The occurrence of thromboembolic events after PBMV in the absence of demonstrable left atrial thrombus before PBMV suggests that thrombus might form during the procedure. Spontaneous echo contrast (SEC) is a swirling pattern of blood echogenicity that is a marker of blood stasis in the left atrium. Exacerbation of left atrial SEC during PBMV may be indicative of an increased thromboembolic risk.

METHODS

Transesophageal echocardiography was performed during PBMV in 20 patients with mitral stenosis. Grades of severity of left atrial SEC [0 (nil) to 4+ (severe)] were allocated before and after each balloon inflation.

RESULTS

Before PBMV, SEC was present in 17 patients. New SEC or increased severity of SEC was observed during 49 of 56 balloon inflations. SEC was unchanged after six deflations, decreased after 14 deflations, and disappeared after 36 deflations. The mean times to onset and dissipation of SEC after balloon inflation and deflation were 3.1+/-1.5 and 3.9+/-1.6 seconds, respectively. After successful PBMV, SEC was unchanged in three patients, decreased in one, and resolved in 13.

CONCLUSIONS

SEC is a dynamic and acutely reversible phenomenon that is highly sensitive to changes in left atrial hemodynamic conditions. Left atrial blood stasis induced by balloon inflation may promote thrombogenesis during PBMV.