Ischemic stroke and systemic embolism among patients with non-valvular atrial fibrillation who abandon oral anticoagulant therapy

OBJECTIVES

To compare the risk of stroke and systemic embolism (SE) among patients with nonvalvular atrial fibrillation (NVAF) who abandoned their first direct oral anticoagulant (DOAC) fill ("abandoners") relative to patients who continued DOACs beyond the first fill ("continuers").

METHODS

In this retrospective longitudinal study, adults with NVAF prescribed DOACs were selected from Symphony Health, an ICON plc Company, PatientSource, 1 April 2017 to 31 October 2020. A 90-day landmark period following the first DOAC fill was used to classify patients as abandoners or continuers. Inverse probability of treatment weighting was used to balance baseline characteristics between cohorts. Time to ischemic stroke/SE was described and compared between cohorts using weighted Kaplan-Meier and Cox proportional hazard models from the end of the landmark period until end of clinical activity or data.

RESULTS

After weighting, 200,398 and 211,352 patients comprised the abandoner and continuer cohorts, respectively. The mean duration of follow-up was 14.9 and 15.7 months, respectively. At 12 months of follow-up, the probability of ischemic stroke/SE was 1.34% in the abandoner cohort and 1.00% in the continuer cohort; the risk of ischemic stroke/SE was 35% higher in the abandoner versus continuer cohort (hazard ratio [95% confidence interval] = 1.35 [1.20, 1.51]; p < 0.0001).

CONCLUSIONS

Patients with NVAF who abandoned the first DOAC fill had significantly higher risk of ischemic stroke/SE compared to patients who continued therapy beyond the first fill. There is an unmet need for better access to DOACs so that the long-term risk of poor outcomes may be minimized.

Preprocedural determination of an occlusion pathomechanism in endovascular treatment of acute stroke: a machine learning-based decision

OBJECTIVE

To evaluate whether an occlusion pathomechanism can be accurately determined by common preprocedural findings through a machine learning-based prediction model (ML-PM).

METHODS

A total of 476 patients with acute stroke who underwent endovascular treatment were retrospectively included to derive an ML-PM. For external validation, 152 patients from another tertiary stroke center were additionally included. An ML algorithm was trained to classify an occlusion pathomechanism into embolic or intracranial atherosclerosis. Various common preprocedural findings were entered into the model. Model performance was evaluated based on accuracy and area under the receiver operating characteristic curve (AUC). For practical utility, a decision flowchart was devised from an ML-PM with a few key preprocedural findings. Accuracy of the decision flowchart was validated internally and externally.

RESULTS

An ML-PM could determine an occlusion pathomechanism with an accuracy of 96.9% (AUC=0.95). In the model, CT angiography-determined occlusion type, atrial fibrillation, hyperdense artery sign, and occlusion location were top-ranked contributors. With these four findings only, an ML-PM had an accuracy of 93.8% (AUC=0.92). With a decision flowchart, an occlusion pathomechanism could be determined with an accuracy of 91.2% for the study cohort and 94.7% for the external validation cohort. The decision flowchart was more accurate than single preprocedural findings for determining an occlusion pathomechanism.

CONCLUSIONS

An ML-PM could accurately determine an occlusion pathomechanism with common preprocedural findings. A decision flowchart consisting of the four most influential findings was clinically applicable and superior to single common preprocedural findings for determining an occlusion pathomechanism.

Drought-induced fiber water release and xylem embolism susceptibility of intact balsam poplar saplings

Balsam poplar (Populus balsamifera L.) is a widespread tree species in North America with significant ecological and economic value. However, little is known about the susceptibility of saplings to drought-induced embolism and its link to water release from surrounding xylem fibers. Questions remain regarding localized mechanisms that contribute to the survival of saplings in vivo of this species under drought. Using X-ray micro-computed tomography on intact saplings of genotypes Gillam-5 and Carnduff-9, we found that functional vessels are embedded in a matrix of water-filled fibers under well-watered conditions in both genotypes. However, water-depleted fibers started to appear under moderate drought stress while vessels remained water-filled in both genotypes. Drought-induced xylem embolism susceptibility was comparable between genotypes, and a greater frequency of smaller diameter vessels in GIL-5 did not increase embolism resistance in this genotype. Despite having smaller vessels and a total vessel number that was comparable to CAR-9, stomatal conductance was generally higher in GIL-5 compared to CAR-9. In conclusion, our in vivo data on intact saplings indicate that differences in embolism susceptibility are negligible between GIL-5 and CAR-9, and that fiber water release should be considered as a mechanism that contributes to the maintenance of vessel functional status in saplings of balsam poplar experiencing their first drought event.

Outcomes of patients with atrial fibrillation on oral anticoagulation with and without heart failure: the ETNA-AF-Europe registry

AIMS

Heart failure (HF) is a risk factor for major adverse events in atrial fibrillation (AF). Whether this risk persists on non-vitamin K antagonist oral anticoagulants (NOACs) and varies according to left ventricular ejection fraction (LVEF) is debated.

METHODS AND RESULTS

We investigated the relation of HF in the ETNA-AF-Europe registry, a prospective, multicentre, observational study with an overall 4-year follow-up of edoxaban-treated AF patients. We report 2-year follow-up for ischaemic stroke/transient ischaemic attack (TIA)/systemic embolic events (SEE), major bleeding, and mortality. Of the 13 133 patients, 1854 (14.1%) had HF. Left ventricular ejection fraction was available for 82.4% of HF patients and was <40% in 671 (43.9%) and ≥40% in 857 (56.1%). Patients with HF were older, more often men, and had more comorbidities. Annualized event rates (AnERs) of any stroke/SEE were 0.86%/year and 0.67%/year in patients with and without HF. Compared with patients without HF, those with HF also had higher AnERs for major bleeding (1.73%/year vs. 0.86%/year) and all-cause death (8.30%/year vs. 3.17%/year). Multivariate Cox proportional models confirmed HF as a significant predictor of major bleeding [hazard ratio (HR) 1.65, 95% confidence interval (CI): 1.20-2.26] and all-cause death [HF with LVEF <40% (HR 2.42, 95% CI: 1.95-3.00) and HF with LVEF ≥40% (HR 1.80, 95% CI: 1.45-2.23)] but not of ischaemic stroke/TIA/SEE.

CONCLUSION

Anticoagulated patients with HF at baseline featured higher rates of major bleeding and all-cause death, requiring optimized management and novel preventive strategies. NOAC treatment was similarly effective in reducing risk of ischaemic events in patients with or without concomitant HF.

In AF, the effects of DOACs vs. warfarin on death and stroke/systemic embolism vary by baseline CrCl level

SOURCE CITATION

Harrington J, Carnicelli AP, Hua K, et al. Direct oral anticoagulants versus warfarin across the spectrum of kidney function: patient-level network meta-analyses from COMBINE AF. Circulation. 2023;147:1748-1757. 37042255.

Non-vitamin K Antagonist Oral Anticoagulants (NOACs) Versus Warfarin in Patients with Atrial Fibrillation Using P-gp and/or CYP450-Interacting Drugs: a Systematic Review and Meta-analysis

PURPOSE

Non-vitamin K antagonist oral anticoagulants (NOACs) are excreted by P-glycoprotein (P-gp) and some are metabolized by CYP450 enzymes such as CYP3A4. Although fewer drug interactions are present with NOACs, it is unclear whether NOACs should also be preferred over vitamin K antagonists (VKAs) in patients with atrial fibrillation (AF) using pharmacokinetically interacting drugs. Therefore, the benefit-risk profile of NOACs versus VKAs was investigated in AF patients treated with P-gp and/or CYP450-interacting drugs.

METHODS

Using PubMed and Embase, randomized controlled trials and observational studies on the effectiveness and safety of NOACs versus VKAs in AF patients using P-gp and/or CYP450-interacting drugs were included. A meta-analysis was performed, calculating relative risks (RR) and 95% confidence intervals (CI) with the Mantel-Haenszel method.

RESULTS

Twelve studies were included, investigating 10,793 NOAC and 10,096 VKA users treated with P-gp/CYP3A4 inhibitors, whereas no studies on P-gp and/or CYP450-inducing drugs were identified. Compared to VKAs, NOACs were associated with a borderline non-significantly lower stroke or systemic embolism (stroke/SE) risk (RR 0.85, 95%CI (0.72-1.01)), significantly lower intracranial bleeding (RR 0.47, 95%CI (0.34-0.65)) and all-cause mortality risks (RR 0.87, 95%CI (0.79-0.95), but significantly higher gastrointestinal bleeding risk (RR 1.74, 95%CI (1.06-2.86)). Among AF patients using amiodarone, NOACs were associated with significantly lower stroke/SE (RR 0.71, 95%CI (0.54-0.93)) and intracranial bleeding risks (RR 0.51, 95%CI (0.29-0.88)), but significantly higher gastrointestinal bleeding risk (RR 2.15, 95%CI (1.24-3.72)) than VKAs.

CONCLUSION

The benefit-risk profile of NOACs compared to VKAs was preserved in AF patients using P-gp/CYP3A4 inhibitors, including amiodarone.

CYP metabolic pathway related gene polymorphism increases the risk of embolic and atherothrombotic stroke and vulnerable carotid plaque in southeast China

OBJECTIVE

To investigate the association of CYP metabolic pathway-related genetic polymorphisms with the susceptibility to ischemic stroke and stability of carotid plaque in southeast China.

METHODS

We consecutively enrolled 294 acute ischemic stroke patients with carotid plaque and 282 controls from Wenling First People's Hospital. The patients were divided into the carotid vulnerable plaque group and stable plaque group according to the results of carotid B-mode ultrasonography. Polymorphisms of CYP3A5 (G6986A, rs776746), CYP2C9*2 (C430T, rs1799853), CYP2C9*3 (A1075C, rs1057910), and EPHX2 (G860A, rs751141) were determined using polymerase chain reaction and mass spectrometry analysis.

RESULTS

EPHX2 GG may reduce the susceptibility to ischemic stroke (OR = 0.520, 95% CI: 0.288 ∼ 0.940, P = 0.030) and AA+AG may increase the risk for ischemic stroke (OR = 1.748, 95% CI: 1.001 ∼ 3.052, P = 0.050). The distribution of CYP3A5 genotypes showed significant differences between the vulnerable plaque and stable plaque groups (P = 0.026). Multivariate logistic regression analysis found that CYP3A5 GG could reduce the risk of vulnerable plaques (OR = 0.405, 95% CI: 0.178 ∼ 0.920, P = 0.031).

CONCLUSION

EPHX2 G860A polymorphism may reduce the stroke susceptibility, while other SNPs of CYP genes are not associated with ischemic stroke in southeast China. Furthermore CYP3A5 polymorphism was related with carotid plaque instability.

Surgical Transmitral Thrombectomy to Prevent Recurrent Stroke in Acute Myocardial Infarction

Left ventricular (LV)-thrombi occur in up to 14 % of patients with acute myocardial infarction (AMI) in the era of primary percutaneous coronary intervention. For these patients, anticoagulant therapy (AC) is recommended by AMI-guidelines. When, despite AC, LV-thrombi lead to embolism, surgical thrombectomy is an option, which is not mentioned or not recommended in AMI-guidelines. We report a 46-year old female patient with AMI. An 80 % stenosis of the proximal left anterior descending coronary artery was treated by a drug-eluting stent. Thrombi within the akinetic LV-apex became mobile despite AC and dual antiplatelet therapy, and a cerebellar stroke occurred. By a transmitral surgical approach with endoscopic assistance the thrombi were completely removed. Postoperative course and 12-months follow-up were uneventful. LV-thrombi should be observed carefully regarding changes in morphology. Surgical thrombectomy of LV-thrombi is a rare treatment option to prevent imminent embolism. Benefits versus risks of surgical removal of LV-thrombi need to be carefully weighted.

Diagnostic and therapeutic pathways for the malignant left atrial appendage: European Heart Rhythm Association physician survey

AIMS

Patients with atrial fibrillation who despite taking oral anti-coagulant therapy (OAT) suffer a stroke or systemic embolism (SSE) without vascular cause or who develop left atrial appendage (LAA) thrombus (LAAT) should be considered as having malignant LAA. The optimal treatment strategy to reduce SSE risk in such patients is unknown. The aim of the study is to investigate the diagnostic and therapeutic pathways for malignant LAA practiced in European cardiac centres.

METHODS AND RESULTS

An 18-item online questionnaire on malignant LAA was disseminated by the European Heart Rhythm Association (EHRA) Scientific Initiatives Committee. A total of 196 physicians participated in the survey. There seems to be high confidence in transoesophageal echocardiography (TEE) imaging, considering LAAT diagnosis. Switching to another direct oral anti-coagulant (DOAC) is the preferred initial step for the treatment of malignant LAA followed by a switch to vitamin K antagonist (VKA), low-molecular-weight heparin, or continued/optimized DOAC dosage, whereas LAA closure is the last option. Left atrial appendage closure is a viable option in patients with embolic stroke despite OAT and no evidence of thrombus at TEE (empty LAA) after comprehensive diagnostic measures to exclude other sources of embolism.

CONCLUSION

This EHRA survey provides a snapshot of the contemporary management of patients diagnosed with malignant LAA. Currently, the majority of patients are treated on an outpatient basis with either shifting from VKA to DOAC or from one DOAC to another. Left atrial appendage closure in this population seems to be reserved for patients with higher bleeding risk or complications of malignant LAA, such as stroke.

Effectiveness and safety of Dabigatran 110 mg versus 150 mg for Stroke Prevention in Patients with Atrial Fibrillation at High Bleeding Risk

PURPOSE

The effectiveness and tolerability of a reduced dose (110 mg) of dabigatran versus the standard dose (150 mg) were evaluated in subgroups of patients with atrial fibrillation (AF) at high bleeding risk.

METHODS

Eligible patients were adults with AF and a creatinine clearance rate ≥30 mL/min who were initiated on treatment with dabigatran (index) between 2016 and 2018. High-bleeding-risk subgroups were identified: (1) age ≥80 years; (2) moderate renal impairment (creatinine clearance rate 30-<50 mL/min); and (3) recent bleeding or a HAS-BLED score of ≥3. Fine-Gray subdistribution hazard regression models with inverse probability of treatment weights were used to investigate associations between dabigatran dose and three outcomes: stroke or systemic embolism, major bleeding requiring hospitalization, and all-cause mortality.

FINDINGS

Among 7858 patients with AF and a high bleeding risk (age ≥80 years, 3472; moderate renal impairment, 1574; recent bleeding or HAS-BLED score ≥3, 2812), 32.3% received reduced-dose dabigatran. Compared with the standard dose, use of the reduced dose of dabigatran was not associated with an increased risk for stroke or systemic embolism but was associated with a lower risk for major bleeding (HR = 0.65; 95% CI, 0.44-0.95) and all-cause mortality (HR = 0.78; 95% CI, 0.65-0.92) in patients aged ≥80 years. The use of reduced-dose dabigatran was associated with a lower risk for major bleeding (HR = 0.54; 95% CI, 0.30-0.95) and all-cause mortality among patients with moderate renal impairment (HR = 0.53; 95% CI, 0.40-0.71).

IMPLICATIONS

Lower risks for bleed and mortality associated with reduced- versus standard-dose dabigatran in patients with AF and a high bleeding risk suggest a better dosing strategy.

Surgical and percutaneous left atrial appendage intervention: silent cerebral embolism considerations

OBJECTIVES

Left atrial appendage intervention is an alternative to oral anticoagulation for thromboprophylaxis in atrial fibrillation. The aim of our study was to compare the incidence of silent cerebral embolisms after surgical and percutaneous intervention and to identify the risk factors for procedure-related silent cerebral embolisms after intervention.

METHODS

This prospective observational study included consecutive atrial fibrillation patients from 2 independent cohorts (left atrial appendage excision (LAAE) cohort and left atrial appendage occlusion cohort) between September 2018 and December 2020. All patients underwent cerebral magnetic resonance imaging before and after the procedure. Silent cerebral embolism was defined as new focal hyperintense lesions detected only on postprocedural sequence.

RESULTS

Thirty-two patients from the LAAE cohort and 42 patients from the occlusion cohort were enrolled. A significantly lower incidence of silent cerebral embolism was observed in the LAAE cohort as compared with occlusion (6.3% vs 54.8%, P < 0.001). In the left atrial appendage occlusion cohort, patients who developed silent cerebral embolism after the procedure had significantly higher CHA2DS2-VASc scores [odds ratio (OR) 2.172; 95% confidence interval (CI) 1.149-4.104; P = 0.017], longer occlusion placement time (OR 1.067; 95% CI 1.018-1.118; P = 0.006) and lower peak activated clotting time level after transseptal puncture (OR 0.976; 95% CI 0.954-0.998; P = 0.035).

CONCLUSIONS

The incidence of procedure-related silent cerebral embolism was strikingly lower in patients with LAAE than in patients with occlusion. More cardiovascular comorbidities, longer occlusion placement time and lower activated clotting time level were significantly associated with the development of procedure-related silent cerebral embolism.

ACR Appropriateness Criteria® Workup of Noncerebral Systemic Arterial Embolic Source

Noncerebral systemic arterial embolism, which can originate from cardiac and noncardiac sources, is an important cause of patient morbidity and mortality. When an embolic source dislodges, the resulting embolus can occlude a variety of peripheral and visceral arteries causing ischemia. Characteristic locations for noncerebral arterial occlusion include the upper extremities, abdominal viscera, and lower extremities. Ischemia in these regions can progress to tissue infarction resulting in limb amputation, bowel resection, or nephrectomy. Determining the source of arterial embolism is essential in order to direct treatment decisions. This document reviews the appropriateness category of various imaging procedures available to determine the source of the arterial embolism. The variants included in this document are known arterial occlusion in the upper extremity, lower extremity, mesentery, kidneys, and multiorgan distribution that are suspected to be of embolic etiology. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Does early detection of atrial fibrillation reduce the risk of thromboembolic events? Rationale and design of the Heartline study

BACKGROUND

The impact of using direct-to-consumer wearable devices as a means to timely detect atrial fibrillation (AF) and to improve clinical outcomes is unknown.

METHODS

Heartline is a pragmatic, randomized, and decentralized application-based trial of US participants aged ≥65 years. Two randomized cohorts include adults with possession of an iPhone and without a history of AF and those with a diagnosis of AF taking a direct oral anticoagulant (DOAC) for ≥30 days. Participants within each cohort are randomized (3:1) to either a core digital engagement program (CDEP) via iPhone application (Heartline application) and an Apple Watch (Apple Watch Group) or CDEP alone (iPhone-only Group). The Apple Watch Group has the watch irregular rhythm notification (IRN) feature enabled and access to the ECG application on the Apple Watch. If an IRN notification is issued for suspected AF then the study application instructs participants in the Apple Watch Group to seek medical care. All participants were "watch-naïve" at time of enrollment and have an option to either buy or loan an Apple Watch as part of this study. The primary end point is time from randomization to clinical diagnosis of AF, with confirmation by health care claims. Key secondary endpoint are claims-based incidence of a 6-component composite cardiovascular/systemic embolism/mortality event, DOAC medication use and adherence, costs/health resource utilization, and frequency of hospitalizations for bleeding. All study assessments, including patient-reported outcomes, are conducted through the study application. The target study enrollment is approximately 28,000 participants in total; at time of manuscript submission, a total of 26,485 participants have been enrolled into the study.

CONCLUSION

The Heartline Study will assess if an Apple Watch with the IRN and ECG application, along with application-facilitated digital health engagement modules, improves time to AF diagnosis and cardiovascular outcomes in a real-world environment.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04276441.

Addressing controversies in the xylem embolism resistance-vessel diameter relationship

Although xylem embolism is a key process during drought-induced tree mortality, its relationship to wood anatomy remains debated. While the functional link between bordered pits and embolism resistance is known, there is no direct, mechanistic explanation for the traditional assumption that wider vessels are more vulnerable than narrow ones. We used data from 20 temperate broad-leaved tree species to study the inter- and intraspecific relationship of water potential at 50% loss of conductivity (P₅₀ ) with hydraulically weighted vessel diameter (D_h ) and tested its link to pit membrane thickness (T_PM ) and specific conductivity (K_s ) on species level. Embolism-resistant species had thick pit membranes and narrow vessels. While D_h was weakly associated with T_PM , the P₅₀ -D_h relationship remained highly significant after accounting for T_PM . The interspecific pattern between P₅₀ and D_h was mirrored by a link between P₅₀ and K_s , but there was no evidence for an intraspecific relationship. Our results provide robust evidence for an interspecific P₅₀ -D_h relationship across our species. As a potential cause for the inconsistencies in published P₅₀ -D_h relationships, our analysis suggests differences in the range of trait values covered, and the level of data aggregation (species, tree or sample level) studied.

Study of the mechanism of embolism removal in xylem vessels by using microfluidic devices

Determining the mechanism that effects embolism repair in the xylem vessels of plants is of great significance in predicting plant distribution and the screening of drought-resistant plants. However, the mechanism of perforation plates of xylem vessels in the acceleration of embolism repair is still not clear by using conventional methods of anatomy and visualization technology. Microfluidic devices have shown their ability to simulate physiological environments and conduct quantitative experiments. This work proposes a biomimetic microfluidic device to study the mechanism of perforation plates of xylem vessels in the acceleration of embolism repair. The results proffered that the perforation plates increase the rate of embolism removal by increasing the pressure differential through the vessel, and the rate of embolism removal is related to the structural parameters of the perforation plate. A combination of the perforation size, the vessel diameter and the perforation plate angle can be optimised to generate higher pressure differentials, which can accelerate the process of embolism repair. This work provides a new method for studying the mechanism of microstructures of natural plants. Furthermore, the mechanism that perforation plates accelerate embolism repair was applied to an electrochemical flow sensor for online determination of heavy metal ions. Test results of this application indicate that the mechanism can be applied in the engineering field to solve the problems of reduced sensitivity of devices, inaccuracy of analysis results and poor reaction performance caused by bubbles that are generated or introduced easily in microdevices, which paves the way for applying the theory to engineering.

Stem hydraulic conductivity and embolism resistance of Quercus species are associated with their climatic niche

The hydraulic traits of a plant species may reflect its climate adaptations. Southwest China is considered as a biodiversity hotpot of the genus Quercus (oak). However, the hydraulic adaptations of Asian oaks to their climate niches remain unclear. Ten common garden-grown oak species with distinct natural distributions in eastern Asia were used to determine their stem xylem embolism resistance (water potential at 50% loss of hydraulic conductivity, P50), stem hydraulic efficiency (vessel anatomy and sapwood specific hydraulic conductivity (Ks)) and leaf anatomical traits. We also compiled four key functional traits: wood density, hydraulic-weighted vessel diameter, Ks and P50 data for 31 oak species from previous literature. We analyzed the relationship between hydraulic traits and climatic factors over the native ranges of 41 oak species. Our results revealed that the 10 Asian oak species, which are mainly distributed in humid subtropical habitats, possessed a stem xylem with low embolism resistance and moderate hydraulic efficiency. The deciduous and evergreen species of the 10 Asian oaks differed in the stem and leaf traits related to hydraulic efficiency. Ks differed significantly between the two phenological groups (deciduous and evergreens) in the 41-oak dataset. No significant difference in P50 between the two groups was found for the 10 Asian oaks or the 41-oak dataset. The oak species that can distribute in arid habitats possessed a stem xylem with high embolism resistance. Ks negatively related to the humidity of the native range of the 10 Asian oaks, but showed no trend when assessing the entire global oak dataset. Our study suggests that stem hydraulic conductivity and embolism resistance in Quercus species are shaped by their climate niche. Our findings assist predictions of oak drought resistance with future climate changes for oak forest management.

A Fluid-Structure Interaction Analysis of Blood Clot Motion in a Branch of Pulmonary Arteries

INTRODUCTION

Pulmonary embolism (PE) is one of the most prevalent diseases amid hospitalized patients taking many people's lives annually. This phenomenon, however, has not been investigated via numerical simulations.

METHODS

In this study, an image-based model of pulmonary arteries has been constructed from a 44-year-old man's computed tomography images. The fluid-structure interaction method was used to simulate the motion of the blood clot. In this regard, Navier-Stokes equations, as the governing equations, have been solved in an arbitrary Lagrangian-Eulerian (ALE) formulation.

RESULTS

According to our results, the velocity of visco-hyperelastic model of the emboli was relatively higher than the emboli with hyperelastic model, despite their similar behavioral pattern. The stresses on the clot were also investigated and showed that the blood clot continuously sustained stresses greater than 165 Pa over an about 0.01 s period, which can cause platelets to leak and make the clot grow or tear apart.

CONCLUSIONS

It could be concluded that in silico analysis of the cardiovascular diseases initiated from clot motion in blood flow is a valuable tool for a better understanding of these phenomena.

Foliar water uptake enables embolism removal in excised twigs of Avicennia marina

Embolism refilling is thought to require relaxation of xylem tension, and it is unclear whether and how tall trees or plants growing in arid or saline soils recover from embolism. We tested whether foliar water uptake could enable embolism refilling in dehydrated twigs of the grey mangrove (Avicennia marina). Four dehydrated twigs were imaged by laboratory-based micro-computed tomography before and after wetting leaves. Emboli were observed in dehydrated stems and leaves. Embolism decreased with increasing distance from the cut end of stems, suggesting that stem emboli were caused by cutting. A significant (P = 0.026) c. 80% reduction in the embolised area was observed in leaves between the start and the end of the experiment (29 ± 10 h after wetting). Embolus diameter was unaffected by wetting. Embolism refilling occurred slowly, in stems embolised by cutting and leaves embolised by cutting and/or dehydration. The lack of response of embolus diameter to wetting suggests that capillarity was not the main mechanism for refilling. Results show that excised twigs of A. marina are able to recover from embolism by absorption of atmospheric water and call for studies under natural conditions.

The relative area of vessels in xylem correlates with stem embolism resistance within and between genera

The resistance of xylem conduits to embolism is a major factor defining drought tolerance and can set the distributional limits of species across rainfall gradients. Recent work suggests that the proximity of vessels to neighbors increases the vulnerability of a conduit. We therefore investigated whether the relative vessel area of xylem correlates with intra- and inter-generic variation in xylem embolism resistance in species pairs or triplets from the genera Acer, Cinnamomum, Ilex, Quercus and Persea, adapted to environments differing in aridity. We used the optical vulnerability method to assess embolism resistance in stems and conducted anatomical measurements on the xylem in which embolism resistance was quantified. Vessel lumen fraction (VLF) correlated with xylem embolism resistance across and within genera. A low VLF likely increases the resistance to gas movement between conduits, by diffusion or advection, whereas a high VLF enhances gas transport thorough increased conduit-to-conduit connectivity and reduced distances between conduits and therefore the likelihood of embolism propagation. We suggest that the rate of gas movement due to local pressure differences and xylem network connectivity is a central driver of embolism propagation in angiosperm vessels.

A unit pipe pneumatic model to simulate gas kinetics during measurements of embolism in excised angiosperm xylem

The pneumatic method has been introduced to quantify embolism resistance in plant xylem of various organs by applying a partial vacuum to cut-open xylem. Despite the similarity in vulnerability curves between the pneumatic and other methods, a modeling approach is needed to investigate if changes in xylem embolism during dehydration can be accurately quantified based on gas diffusion kinetics. Therefore, a unit pipe pneumatic (UPPn) model was developed to estimate gas extraction from intact conduits, which were axially interconnected by inter-conduit pit membranes to cut-open conduits. The physical laws used included Fick's law for diffusion, Henry's law for gas concentration partitioning between liquid and gas phases at equilibrium and the ideal gas law. The UPPn model showed that 91% of the extracted gas came from the first five series of embolized, intact conduits and only 9% from the aqueous phase after 15 s of simulation. Considering alternative gas sources, embolism resistance measured with a pneumatron device was systematically overestimated by 2-17%, which corresponded to a typical measuring error of 0.11 MPa for P50 (the water potential equivalent to 50% of the maximum amount of gas extracted). It is concluded that pneumatic vulnerability curves directly measure embolism of intact conduits due to the fast movement of gas across interconduit pit membranes, while gas extraction from sap and diffusion across hydrated cell walls is about 100 times slower. We expect that the UPPn model will also contribute to the understanding of embolism propagation based on temporal gas dynamics.

VENOUS THROMBOEMBOLISM - PECULIARITIES OF COURSE IN EMERGENCY SURGERY DURING COVID-19 PANDEMIC

OBJECTIVE

The aim: To perform a comparative analysis of VTE in patients with acute surgical abdominal pathology before and during the COVID-19 pandemic.

PATIENTS AND METHODS

Materials and methods: Retrospective study covered 53062 patients operated in the surgical clinic (Lviv city emergency hospital) in 2000-2019. Prospective analysis was based on the results of treatment of 546 patients operated at the same surgical clinic from April 2020 (1st surgical patient with COVID-19) till December 2021. The study analyzed 48 (8.8%) patients operated for acute abdominal pathology and confirmed diagnosis of COVID-19.

RESULTS

Results: In the 1st group, heparin prophylaxis was used in 42.3% of patients, of which non-fractionated heparin were used in 58.6% and low molecular weight heparin - in the remaining patients. From 2020 to 2021, pharmacoprophylaxis was used in 84.5% of cases, of which 67.2% - low molecular weight heparins, 20.1% - non-fractionated heparins and 12.7% - modern oral anticoagulants. The results were unexpected: with a significant increase in the ve¬nous thromboembolism prevention in the 2nd group, a decrease in the number of episodes of thromboembolic complications was not observed. In contrast, pulmonary artery embolism was recorded in 10.6% of patients in the 1st group and 23.5% - in 2nd group, which is a 2.2-fold increase in fatal cases of venous thrombosis (p<0.05) in patients with COVID-19.

CONCLUSION

Conclusions: Increase of mortality due to pulmonary artery embolism more than twicefold in patients with COVID-19 operated for acute surgical abdominal pathology is an objective evidence of a potentiated, uncontrolled risk of venous thromboembolism and requires further in-depth study.