1Department of Heart Valve Defect, The Cardinal Stefan Wyszynski National Institute of Cardiology, Warszawa, Poland

2Krakow Center for Medical Research and Technologies, John Paul II Hospital, Kraków, Poland

3Institute of Cardiology, Jagiellonian University Medical College, Kraków, Poland

4Department of Coronary Artery Disease and Cardiac Rehabilitation, The Cardinal Stefan Wyszynski National Institute of Cardiology, Warszawa, Poland

INTRODUCTION

METHODS

Patients

To avoid potential confounding effects of other diseases on fibrin clot properties we excluded patients with a significant another valvular disease and epicardial or carotid artery stenosis requiring surgical or percutaneous treatment, infection, endocarditis, known cancer, autoimmune disorders, a history of thromboembolism or major bleeding during last 3 months.

The study was approved by Ethics Committee and the patients gave their informed written consent to participate in this study.

Laboratory investigations

Blood samples were taken after overnight fasting and 24 hours after oral anticoagulation (OAC) discontinuation. Lipid profile, fasting plasma glucose, creatinine, GFR, alanine aminotransferase (ALT) were determined by routine assays. Fibrinogen was measured by the von Clauss method (Siemens, Marburg, Germany).

Calibrated automated thrombogram

Clot permeability

Scanning electron microscopy (SEM)

Plasma fibrin clots from five randomly selected patients classified to SAVR or TAVI were analyzed. Fixation was performed after the permeability measurement using 2.5% glutaraldehyde in phosphate-buffered saline solution for 2 hours. Fixed clots were, washed with distilled water, and then dehydrated in graded ethanol solutions, dried by the critical point procedure, and sputter coated with gold. Samples were scanned in six different areas (microscope JEOL JCM-6000; JEOL Ltd., Tokyo, Japan). Images were analyzed in ImageJ (US National Institutes of Health, Bethesda, MD, USA).

Clot lysability

Statistical analysis

Data are presented as means ± standard deviation (SD) or medians and interquartile range (IQR: 25th to 75th) for continuous variables and as frequencies and percentages for categorical variables. The Kolmogorov-Smirnov test was used to verify the normality of distribution. Comparison between groups was performed using χ2 test or Fisher’s Exact test for categorical data and the independent t-test or the Mann-Whitney U test for continuous data as appropriate. In order to minimize the influence of age on coagulation and fibrinolysis parameters, the analysis of covariance with age as covariate was used. If appropriate, logarithmic transformation of non-normally distributed variables was performed. Univariate and multivariate logistic regression models were performed to identify variables which may influence the indication for TAVI. Demographic (age, gender, body mass index [BMI]) and clinical (comorbidities: atrial fibrillation [AF], hypertension, DM, CKD, coronary artery disease [CAD], COPD) characteristics, the severity of the defect (LV ejection fraction [EF], mean transvalvular gradient) were tested as potential explanatory variables. Variables that may influence the indication for TAVI with a significance level of P <0.2 in the bivariate models were selected for possible inclusion in the multivariate logistic regression models. The multivariate model was fitted using backward stepwise regression. Results are presented as odds ratios (OR) ± 95% confidence interval (CI). A 2-sided P <0.05 was considered statistically significant. All analyses were performed using SAS 9.4 (SAS Institute Inc., Cary, NC, USA).

RESULTS

Characteristics of the patients

A total of 104 patients with severe AS, who were mostly overweight and hypertensive were included to the study (Table 1).

Forty-five patients were scheduled for TAVI and 59 for SAVR. The patients referred to the SAVR were younger (Table 1). Patients qualified for TAVI had an increased estimated risk for surgery compared to SAVR (Euroscore II: 6.05% [3.38–8.49] vs 1.93% [1.60–3.50] and STS 4.01% [2.71–5.54] vs 2.05% [1.46–2.33], both P <0.0001, respectively) and more often had AF, CKD, DM, CAD, and hypercholesterolemia (Table 1). Due to the diagnosed AF, 3 subjects were treated with non-vitamin K antagonist oral anticoagulants (NOAC) and 9 with vitamin K antagonists (VKA) prior to hospitalization.

Within 30 days after TAVI or SAVR, we recorded 3 ischemic cerebrovascular events, i.e. 2 ischemic stroke episodes after TAVI (4%) and one stroke after SAVR (1.6%). No other cardiovascular events were observed within the first month.

Coagulation and fibrinolysis parameters

Thrombogram analysis showed that in our patient group, thrombin peak correlated with PVel (r = –0.5; P = 0.018), while lag time was correlated with PVel (r = 0.51; P = 0.015) and AVA (r = –0.2; P = 0.045). Analysis of the AS patients with individual comorbidities in terms of CAT parameters showed prolonged lag time in patients with DM (4.71 [3.97–7.95] vs 4.28 [3.55–5.00] minutes; P = 0.017) with no other differences.

Patients with AS referred to TAVI in comparison to those qualified for SAVR were characterized by delayed thrombin generation (Table 2). There were no intergroup differences in other thrombin generation parameters, such as ETP (Figure 2, Table 2).

Among TAVI patients with or without concomitant AF, CKD, DM, CAD, or EF <40% vs ≥40% there were no differences found in thrombin generation parameters (all P >0.05).

Fibrin network density, reflected by Ks, was 16% lower in the TAVI group compared with the SAVR group (Table 2), but after adjustment for age the difference was not significant (P = 0.17; Table 2). Increased clot density in TAVI compared to SAVR patients was confirmed on SEM images (Figure 3).

Image analysis showed that plasma fibrin clots from TAVI patients were composed of thinner fibrin fibers than those from SAVR patients (90.5 ± 3.3 vs 95.6 ± 4.7 nm, P = 0.012). Among TAVI patients, those with CKD, compared to the remainder, had Ks reduced by 13.2% (3.28 [2.71–4.36] vs 3.78 [3.56–4.87] × 10-9cm2; P = 0.035), while there was no impact of AF, DM, CAD, or EF <40% vs ≥40% on Ks (all P >0.05). After adjustment for age, the influence of CKD on Ks was no longer significant (P = 0.36).

In the whole cohort of AS patients , there were no associations of the AS severity measured as AVA or transvalvular gradients with Lys50 (all P >0.05). Of importance, the ana­lysis of fibrinolysis capacity induced by rtPA showed 10.8% longer Lys50 in TAVI patients compared to SAVR (Table 1). There were no differences in Lys50 between TAVI patients with or without concomitant AF, CKD, DM, CAD, or EF <40% vs ≥40% (all P >0.05).

In the univariate regression models predictors of indication for TAVI were: older age, concomitant CKD, DM, CAD, and prolonged Lys50 (all P <0.05), but not BMI, AF, hypertension, COPD, EF, or mean transvalvular gradient (all P >0.05).

The multivariate logistic regression analysis revealed that age, concomitant DM, CKD and prolonged Lys50 were independently associated with indication for TAVI in AS patients (Table 3).

DISCUSSION

The present study demonstrates for the first time that the impact of advanced age on prothrombotic fibrin clot properties in patients undergoing TAVI in comparison to those undergoing SAVR. We found a trend toward greater risk of the formation of denser fibrin networks in patients undergoing TAVI. It was identified that hypofibrinolysis is a key feature of the prothrombotic clot phenotype in patients scheduled for TAVI. The current study increases our knowledge on potential new mechanisms which might contribute to the risk of valve thrombosis as well as ischemic cerebrovascular events following TAVI. Our results provide a rationale for further studies assessing a predictive value of fibrin variables in AS patients. Furthermore, it is unknown whether any antithrombotic therapy after TAVI might reduce the prothrombotic tendency and this issue remains to be established.

Of note, this study showed that TAVI patients generated similar amounts of thrombin, i.e. peak thrombin and ETP, to those found in SAVR. However, the former group had slightly prolonged lag time in the CAT profiles than SAVR patients, indicating delayed onset of the propagation phase in thrombin generation capacity curves in TAVI patients. It might be concluded that patients with severe AS scheduled for TAVI had delayed prothrombin conversion to thrombin, but the final amount of thrombin generated is similar in TAVI and SAVT patients.

CONCLUSIONS

Patients who were scheduled for TAVI demonstrated preoperatively a prothrombotic fibrin clot phenotype characterized by impaired lysis of denser fibrin networks composed of thinner fibers. Our results suggest that prothrombotic clot features may have an impact on increased risk of thromboembolic episodes associated with TAVI in AS patients, providing the rationale for further research to optimize the effectiveness of antithrombotic treatment after TAVI.

Article information

Conflict of interest: None declared.

Open access: This article is available in open access under Creative Common Attribution-Non-Commercial-No Derivatives 4.0 International (CC BY-NC-ND 4.0) license, allowing to download articles and share them with others as long as they credit the authors and the publisher, but without permission to change them in any way or use them commercially. For commercial use, please contact the journal office at kardiologiapolska@ptkardio.pl.

How to cite: Jaworska-Wilczyńska M, Natorska J, Siudut J, et al. Patients scheduled for TAVI tend to form abnormal fibrin clots more resistant to lysis: the impact of age. Kardiol Pol. 2021; 79(7–8): 796–803, doi: 10.33963/KP.a2021.0005.

REFERENCES