Erythrocyte aggregation as a cause of slow flow in patients of acute coronary syndromes

A mechanistic model of cross-bridge migration in RBC aggregation and disaggregation

Red blood cells (RBCs) clump together under low flow conditions in a process called RBC aggregation, which can alter RBC perfusion in a microvascular network. As elevated RBC aggregation is commonly associated with cardiovascular and inflammatory diseases, a better understanding of aggregation is essential. Unlike RBC aggregation in polymer solutions which can be well explained by polymer depletion theory, plasma-mediated RBC aggregation has features that best match explanations with cross-bridging mechanisms. Previous studies have demonstrated the dominant role of fibrinogen (Fg) in promoting aggregate formation and recent cell-force spectroscopy (CFS) experiments on interacting RBC doublets in plasma have reported an inverse relationship between disaggregation force and the adhesive contact area between RBCs. This has led investigators to revisit the hypothesis of inter-RBC cross-bridging which involves cross-bridge migration under interfacial tension during the forced disaggregation of RBC aggregates. In this study, we developed the cross-bridge migration model (CBMM) in plasma that mechanistically represents the migrating cross-bridge hypothesis. Transport of mobile Fg cross-bridges (mFg) was calculated using a convection-diffusion transport equation with our novel introduction of convective cross-bridge drift that arises due to intercellular friction. By parametrically transforming the diffusivity of mFg in the CBMM, we were able to match experimental observations of both RBC doublet formation kinematics and RBC doublet disaggregation forces under optical tweezers tension. We found that non-specific cross-bridging promotes spontaneous growth of adhesion area between RBC doublets whereas specific cross-bridging tends to prevent adhesion area growth. Our CBMM was also able to correlate Fg concentration shifts from healthy population blood plasma to SLE (lupus) condition blood plasma with the observed increase in doublet disaggregation forces for the RBC doublets in SLE plasma.

Multimodal Diagnostics of Microrheologic Alterations in Blood of Coronary Heart Disease and Diabetic Patients

Coronary heart disease (CHD) has serious implications for human health and needs to be diagnosed as early as possible. In this article in vivo and in vitro optical methods are used to study blood properties related to the aggregation of red blood cells in patients with CHD and comorbidities such as type 2 diabetes mellitus (T2DM). The results show not only a significant difference of the aggregation in patients compared to healthy people, but also a correspondence between in vivo and in vitro parameters. Red blood cells aggregate in CHD patients faster and more numerously; in particular the aggregation index increases by 20 ± 7%. The presence of T2DM also significantly elevates aggregation in CHD patients. This work demonstrates multimodal diagnostics and monitoring of patients with socially significant pathologies.

The effects of stenting on hemorheological parameters: An in vitro investigation under various blood flow conditions

 Despite their wide clinical usage, stent functionality may be compromised by complications at the site of implantation, including early/late stent thrombosis and occlusion. Although several studies have described the effect of fluid-structure interaction on local haemodynamics, there is yet limited information on the effect of the stent presence on specific hemorheological parameters. The current work investigates the red blood cell (RBC) mechanical behavior and physiological changes as a result of flow through stented vessels. Blood samples from healthy volunteers were prepared as RBC suspensions in plasma and in phosphate buffer saline at 45% haematocrit. Self-expanding nitinol stents were inserted in clear perfluoroalkoxy alkane tubing which was connected to a syringe, and integrated in a syringe pump. The samples were tested at flow rates of 17.5, 35 and 70 ml/min, and control tests were performed in non-stented vessels. For each flow rate, the sample viscosity, RBC aggregation and deformability, and RBC lysis were estimated. The results indicate that the presence of a stent in a vessel has an influence on the hemorheological characteristics of blood. The viscosity of all samples increases slightly with the increase of the flow rate and exposure. RBC aggregation and elongation index (EI) decrease as the flow rate and exposure increases. RBC lysis for the extreme cases is evident. The results indicate that the stresses developed in the stent area for the extreme conditions could be sufficiently high to influence the integrity of the RBC membrane.

Diagnostic Ultrasound and Microbubbles Treatment Improves Outcomes of Coronary No-Reflow in Canine Models by Sonothrombolysis

Supplemental Digital Content is available in the text.

Objectives:

Effective treatment for microvascular thrombosis-induced coronary no-reflow remains an unmet clinical need. This study sought to evaluate whether diagnostic ultrasound and microbubbles treatment could improve outcomes of coronary no-reflow by dissolving platelet- and erythrocyte-rich microthrombi.

Design:

Randomized controlled laboratory investigation.

Setting:

Research laboratory.

Subjects:

Mongrel dogs.

Interventions:

Coronary no-reflow models induced by platelet- or erythrocyte-rich microthrombi were established and randomly assigned to control, ultrasound, recombinant tissue-type plasminogen activator, ultrasound + microbubbles, or ultrasound + microbubbles + recombinant tissue-type plasminogen activator group. All treatments lasted for 30 minutes.

Measurements and Main Results:

Percentage of microemboli-obstructed coronary arterioles was lower in ultrasound + microbubbles group than that in control group for platelet- (> 50% obstruction: 10.20% ± 3.56% vs 31.80% ± 3.96%; < 50% obstruction: 14.80% ± 4.15% vs 28.20% ± 3.56%) and erythrocyte-rich microthrombi (> 50% obstruction: 8.20% ± 3.11% vs 30.60% ± 4.83%; < 50% obstruction: 12.80% ± 4.15% vs 25.80% ± 3.70%) (p < 0.001). Percentage change of myocardial blood flow in left anterior descending artery-dominated region, left ventricular ejection fraction, fractional shortening, and ST-segment resolution were higher, whereas infarcted area, troponin I, and creatine kinase MB isoenzyme were lower in ultrasound + microbubbles group than that in control group for both types of microthrombi (p < 0.001). Percentage change of myocardial blood flow, ejection fraction, fractional shortening, and ST-segment resolution were higher, whereas infarcted area, troponin I, and creatine kinase MB isoenzyme were lower in ultrasound + microbubbles and ultrasound + microbubbles + recombinant tissue-type plasminogen activator groups than that in recombinant tissue-type plasminogen activator group for platelet-rich microthrombi (p < 0.05).

Conclusions:

Ultrasound + microbubbles treatment could dissolve platelet- and erythrocyte-rich microthrombi, thereby improving outcomes of coronary no-reflow, making it a promising supplement to current reperfusion therapy for acute ST-segment elevation myocardial infarction.

Significantly increased low shear rate viscosity, blood elastic modulus, and RBC aggregation in adults following cardiac surgery

Open heart surgeries are common for treating ischemic and heart valve disease. During cardiac surgery, cardiopulmonary bypass (CPB) can temporarily take over the function of heart and lungs. However, elevated red blood cell (RBC) aggregation may lead to the common side-effects such as microinfarction. We investigated blood physical properties changes and the correlation between blood microstructure, viscoelastic response and biochemical changes following surgery with CPB. We examined shear-rate dependent blood viscosity, elasticity and RBC aggregate size in the pre-surgery disease state, post-surgery state and long-term recovery state of cardiac surgical patients. Within a week following surgery, the patient hematocrit was significantly lower due to CPB. Despite lower RBC concentration, the RBC aggregate shape became larger and more rounded, which is correlated to the elevated plasma fibrinogen related to systemic inflammatory response. During the same period, the hematocrit-adjusted low shear rate viscosity increased significantly, as did the yield stress, indicating more solid-like behavior for blood. Six months to one year later, all the physical and biochemical properties measured returned to baseline.

Influence of red blood cell aggregation on perfusion of an artificial microvascular network

OBJECTIVE

RBCs suspended in plasma form multicellular aggregates under low-flow conditions, increasing apparent blood viscosity at low shear rates. It has previously been unclear, however, if RBC aggregation affects microvascular perfusion. Here, we analyzed the impact of RBC aggregation on perfusion and 'capillary' hematocrit in an AMVN at driving pressures ranging from 5 to 60 cm H₂ O to determine if aggregation could improve tissue oxygenation.

METHODS

RBCs were suspended at 30% hematocrit in either 46.5 g/L dextran 40 (D40, non-aggregating medium) or 35 g/L dextran 70 (D70, aggregating medium) solutions with equal viscosity.

RESULTS

Aggregation was readily observed in the AMVN for RBCs suspended in D70 at driving pressures ≤40 cm H₂ O. The AMVN perfusion rate was the same for RBCs suspended in aggregating and non-aggregating medium, at both 'venular' and 'capillary' level. Estimated 'capillary' hematocrit was higher for D70 suspensions than for D40 suspensions at intermediate driving pressures (5-40 cm H₂ O).

CONCLUSIONS

We conclude that although RBC aggregation did not affect the AMVN perfusion rate independently of the driving pressure, a higher hematocrit in the 'capillaries' of the network for D70 suspensions suggested a better oxygen transport capacity in the presence of RBC aggregation.

High red blood cell distribution width is associated with the metabolic syndrome

OBJECTIVES

High values of Red Blood Cell Distribution Width (RDW) have been associated with adverse outcome in various clinical settings. The mechanism behind this association is not clear. The Metabolic Syndrome (MetS) is a chronic inflammatory disorder that increases the risk for cardiovascular disease and death. The aim of our study was to evaluate the association between high RDW and the MetS in a relatively large cohort of patients.

METHODS

A cohort of 3,529 consecutive patients undergoing coronary angiography was used to evaluate the association between RDW and the MetS. The association was assessed by using a logistic regression. Cox's regression analysis was used to evaluate the impact of RDW on long term mortality.

RESULTS

The mean age was 65 years (range 24-97), with 27% women. Overall, 30% were diagnosed with metabolic syndrome. The prevalence of MetS was 29% in patients with RDW <14% and 34% in patients with RDW ≥14% (P = 0.003).Using multivariate analysis, RDW values above 14% were independently associated with MetS (odds ratio 1.2 [95% CI 1.0-1.4], P = 0.043). Among all the criteria of the metabolic syndrome, hypertension, elevated glucose levels and abdominal obesity were associated with high RDW, with hypertension being the strongest criteria, with an increased risk of 1.8 fold ([95% CI 1.5-2.1]; P = 0.001). During follow up (1614 ± 709 days, 2-2763 days), long term mortality was 8% in the low RDW group and 28% in the high RDW group (p < 0.001).

CONCLUSION

RDW ≥14% is independently associated with higher rates of metabolic syndrome and long-term all-cause mortality.

Iron-induced fibrin in cardiovascular disease

Accumulating evidence within the last two decades indicates the association between cardiovascular disease (CVD) and chronic inflammatory state. Under normal conditions fibrin clots are gradually degraded by the fibrinolytic enzyme system, so no permanent insoluble deposits remain in the circulation. However, fibrinolytic therapy in coronary and cerebral thrombosis is ineffective unless it is installed within 3-5 hours of the onset. We have shown that trivalent iron (FeIII) initiates a hydroxyl radical-catalyzed conversion of fibrinogen into a fibrin-like polymer (parafibrin) that is remarkably resistant to the proteolytic dissolution and thus promotes its intravascular deposition. Here we suggest that the persistent presence of proteolysis-resistant fibrin clots causes chronic inflammation. We study the effects of certain amphiphilic substances on the iron- and thrombin-induced fibrinogen polymerization visualized using scanning electron microscopy. We argue that the culprit is an excessive accumulation of free iron in blood, known to be associated with CVD. The only way to prevent iron overload is by supplementation with iron chelating agents. However, administration of free radical scavengers as effective protection against persistent presence of fibrin-like deposits should also be investigated to contribute to the prevention of cardiovascular and other degenerative diseases.

Comparison of outcomes in patients ≤85 versus >85 years of age undergoing transcatheter aortic-valve implantation

The impact of age on baseline characteristics and outcomes in patients with severe aortic stenosis who undergo transcatheter aortic valve implantation (TAVI) has not been thoroughly investigated. To describe the baseline clinical profile of TAVI patients aged >85 and ≤85 years and to evaluate the influence of age differences on outcomes, we evaluated a consecutive cohort of 293 patients who underwent transfemoral TAVI at the Tel Aviv Medical Center. The cohort was divided into 2 groups: patients aged >85 years (n = 93) and patients aged ≤85 years (n = 200). Mean age was 83 ± 5.3 years (range 63 to 98) for the entire cohort. Women comprised 70% of the older group and 57.5% of the younger age group (p = 0.043). Baseline clinical profile, including EuroSCORE index and preprocedural aortic valve area were similar in both age groups. Thirty-day mortality, major vascular complications, need for permanent pacemaker implantation, length of hospital stay, and improvement in functional class after the procedure showed no differences between the 2 groups. Adjustment for baseline clinical differences between groups did not change the results. In conclusion, among patients who underwent transfemoral TAVI, older patients (>85 years) experience similar benefits and outcomes regarding functional status, complication rates, and 30-day mortality.

Impaired Erythrocyte Deformability in Patients with Coronary Risk Factors: Significance of Nonvalvular Atrial Fibrillation

Although coronary risk factors promote the formation of atherosclerotic plaque containing activated platelets and inflammatory leukocytes, and play a pivotal role in the development of coronary artery diseases (CAD), the hemorheological effects of these risk factors on circulating intact erythrocytes, a major component of whole blood cells, are poorly understood. Therefore, this study aimed to quantify erythrocyte deformability in patients with coronary risk factors, and enrolled 320 consecutive cardiac outpatients including 33 patients with nonvalvular atrial fibrillation (AF). Patients with acute coronary syndrome or valvular AF were excluded. Demographic variables obtained by medical records were correlated with erythrocyte deformability investigated by our highly sensitive and reproducible filtration technique. Among demographic variables, triglyceride (p = 0.004), HbA1c (p = 0.014) and body weight (p = 0.020) showed significant inverse correlation to the erythrocyte deformability. This deformability was not associated with types of CAD (old myocardial infarction vs. stable angina) or modality of treatment (percutaneous intervention vs. coronary artery bypass grafting). Unexpectedly, stepwise multiple regression analysis demonstrated that nonvalvular AF was the most significant contributor to the impaired erythrocyte deformability (p = 0.002). Hypertension and dyslipidemia are more prevalent in the AF patients (p < 0.001), and the erythrocyte deformability was found to be impaired synergistically and significantly (p < 0.001) during the stepwise accumulation of the coronary risk factors in addition to AF. In conclusion coronary risk factors synergistically impair the erythrocyte deformability, which may play an important role in critically stenotic coronary arteries. Since the impairment of intact erythrocyte deformability is mostly associated with nonvalvular AF, this common arrhythmia may reflect the coronary risk accumulation.