Clinical studyAssociation between elevated cerebrospinal fluid D-dimer levels and delayed cerebral ischaemia after aneurysmal subarachnoid haemorrhage
Introduction
The incidence of non-traumatic subarachnoid haemorrhage (SAH) in Australia is 10.3 cases per 100,000 person-years [1] and it is associated with significant morbidity and mortality. Delayed cerebral ischaemia (DCI), a post-ictus complication, is partly responsible for the high mortality and morbidity rates of aneurysmal subarachnoid haemorrhage (aSAH). Typically occurring between days 4 and 12 post-aSAH in approximately 46% of patients [2], DCI is often reversible but can also lead to infarction and significant morbidity and even death [3] despite maximal therapy (Table 1).
Although DCI has historically been associated with reversible cerebral angiographic vasospasm, current research shows that both can occur independently of each other [3] and a number of aetiologies have been proposed including microvascular dysfunction [4], microthrombosis [5], [6], spreading depolarization [7] and burden of clot in the subarachnoid space [8], [9]. Fisher et al., in 1980, first established that greater amounts of blood in the subarachnoid space, seen on CT, correlated with higher incidence of angiographic vasospasm [8]. The lysis of clots (fibrinolysis) begin within hours after SAH and complete clearance of blood by haemolysis from the CSF can range from 6 to 30 days [10]. Several metabolites of haemolysis have been associated with angiographic vasospasm including oxyhaemoglobin, eicosanoids and free radicals [11]. Hence, proteins in the fibrinolytic and haemolytic pathway may be potential biomarkers of delayed cerebral ischaemia.
Plasminogen is an inactive plasma zymogen produced in the liver. Normally the blood brain barrier excludes large proteins like plasminogen but in the event of SAH, plasminogen enters the subarachnoid space with arterial blood and is incorporated into the fibrinous meshwork complex. Plasminogen is activated primarily by plasminogen activators, forming plasmin. In SAH, the source of plasminogen activators is believed to be the arterial blood entering the subarachnoid space which is made conducive by the breakdown of blood brain barrier, inflamed meningeal blood vessels and platelets. Plasmin, then mediates several pathways that lead to fibrinolysis [12]. As plasmin is highly potent, it is normally stringently regulated by several mechanisms in the plasma [12], although the nature of these regulations in the subarachnoid space remain largely unknown. With fibrinolysis, several degradation products are released, including vasospastic factors like oxyhaemoglobin [11] and fibrin degradation product D-dimer, which is a surrogate marker of fibrinolytic activity [13].
Regulators of the fibrinolytic pathway have shown to be potential biomarkers of DCI [14], [15], however plasminogen itself has not been studied. CSF concentrations of D-dimer has also previously shown promise as a biomarker [16] although it was not investigated in the early days immediately after aSAH. Hence, it is useful to study the CSF concentrations of these potential biomarkers in the early stages post-aSAH.
Section snippets
Patient population
Ethics approval for this retrospective cohort study was obtained from Melbourne Health Human Research Ethics Committee (MH project number 2012.50). Patients presenting to the Royal Melbourne Hospital with confirmed aSAH from 2012 till 2018 were included as part of an ongoing database. Consecutive patients were recruited with informed consent, either from themselves or from their next of kin. Aneurysmal SAH was confirmed by blood on computed tomography or xanthochromia on lumbar puncture.
Patient characteristics
In this patient cohort, 47% were male and 53% were female. Median post-aSAH day of CSF collection was 2 and the mean age of patients was 58.6. Although the median admission WFNS score was higher for patients who developed DCI (non-DCI was grade 2, DCI was grade 3), gender, age and day of CSF collection were similar across both cohorts (DCI and non-DCI). A binary logistic regression analysis revealed that none of these variables significantly contributed to the incidence of DCI.
Discussion
Although the exact pathogenesis of DCI remains unclear, it has long been recognised that the higher the blood volume in the subarachnoid space the higher the risk of subsequent DCI and it is believed that toxic blood breakdown products such as oxyhaemoglobin and haem contribute to the development of DCI via oxidative stress [17], [18], [19], [20] and inflammation [4]. Fibrinolysis is one of the factors that determines the rate of resolution of subarachnoid clot and therefore the exposure to
Conclusion
Our study suggests CSF D-dimer levels and D-dimer/plasminogen ratio within the first 72 h post-aSAH are significantly elevated in patients that later develop DCI. We found that CSF levels of plasminogen within the same time frame did not correlate with incidence of DCI. In our sample population, D-dimer and D-dimer/plasminogen ratio shows good sensitivity and specificity for predicting DCI, however a larger prospective study is needed to validate these preliminary findings. Additionally, our
Declaration of Competing Interests
None.
Funding
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SJ, AA and JZ acknowledge funding from JT Reid Charitable Trust and Neuroscience Foundation for materials used in this research.
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JM acknowledges Fellowship support from the Australian National Health and Medical Research Council.
Acknowledgements
We would like to thank Dr Dalia Ponce Garcia for assistance with SDS-PAGE, western blotting, and imaging densitometry.
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