Antiplatelet therapy and clinical outcomes in cardiovascular diseases

Cardiovascular diseases (CVD) is a leading cause of death in the world. Despite effective treatment regimens for ischaemic heart disease (IHD) and ischaemic stroke, mortality and recurrence rates remain high. Antiplatelet therapy is on effective treatment and reduces the risk of recurrent heart attack and stroke. Nevertheless, there are patients who stopped or interrupted their antiplatelet therapy for certain reasons or some patients may be resistant or poor responders to antiplatelet therapy. Furthermore, there is evidence of rebound effect in platelet activity after antiplatelet cessation and this may associate with increased risk of cardiovascular event. This thesis is divided into five main chapters (chapters 3 to 7) which attempt to provide data to help resolve the uncertainty. Chapter 1 highlights the background of cardiovascular diseases and the global burden of cardiovascular and cerebrovascular diseases. The metabolism of platelets, antiplatelet therapy and current antiplatelet therapy guidelines are described, followed by discussion of the risk of cardiovascular event and changes in antiplatelet therapy. Chapter 2 describes the data source from Virtual International Stroke Trial Archive (VISTA) and National Health Service Greater Glasgow and Clyde (NHSGGC) Safe Haven, followed by definition of outcome measures. In chapter 3, Virtual International Stroke Trial Archive (VISTA) data was examined to test whether continue with the same antiplatelet therapy or changing to a new antiplatelet regimen reduces the risk of subsequent events in patients who experience a stroke whilst taking antiplatelet therapy. The findings indicate that subjects who switch to a new antiplatelet regimen after stroke did not have a lower early recurrence rate than subjects who continued with the same antiplatelet therapy. Observations on bleeding complications were similar in both groups. However, changing antiplatelet regimen after stroke was associated with more favourable functional outcome across a full scale modified Rankin Scale (mRS) at 90 days. In chapter 4, association between early or later initiation of antiplatelet with a recurrent ischaemic stroke and bleeding complications was assessed using VISTA data. The findings indicate that there was no association between a recurrent ischaemic stroke and timing of initiation of antiplatelet drug after stroke. However, early initiation was associated with increased risk of bleeding. In terms of functional outcomes, this study demonstrated that the mid-time and late initiation of antiplatelet therapy after acute stroke are associated with better functional outcomes compared with early initiation. In chapter 5, a nested case-control study was performed to explore the rate of antiplatelet cessation and interruption in a sample of patients with recent ischaemic stroke and to assess the risk of cardiovascular events associated with cessation and interruption of antiplatelet. It was found that there was no increased risk of cardiovascular event among patients who had early cessation or interrupted/stopped antiplatelet therapy within 90 days following acute ischaemic stroke. In chapter 6, the incidence and predictors of cardiovascular events after DAPT cessation were evaluated. The incidence of cardiovascular event while taking DAPT and following discontinuation of DAPT was 15.7% and 16.7% respectively. This study found that increasing age was associated with an increased risk of cardiovascular event, whereas, revascularization-treated patients and longer duration of DAPT, were each associated with a decreased risk. The duration of DAPT six months and less was associated a significantly higher risk for cardiovascular event. In chapter 7, an untargeted metabolomics analysis was performed while on DAPT (aspirin plus ticagrelor) and once they stopped ticagrelor to identify metabolite changes associated with cardiovascular events after stopping DAPT. Ten ACS patients were recruited in this study and data were analysed for seven patients. Three hundred eleven putative metabolites were identified. This study found 16 putative metabolites significantly altered following ticagrelor cessation. Of these, seven metabolites were from lipid pathway and down-regulated some up to 3-fold. On the other hand, adenosine, from nucleotide metabolism was upregulated up to 2.6-fold. It concluded that there are changes in numerous pathways following DAPT discontinuation and whether these changes differ in patients who have cardiovascular event after stopping DAPT warrant further investigation. In chapter 8, a summary of the findings of this thesis are presented as well as the future directions of research in this area

Cessation of dual antiplatelet therapy and cardiovascular events following acute coronary syndrome

Objective: To assess whether cardiovascular events are increased after cessation of dual antiplatelet therapy (DAPT) following acute coronary syndrome (ACS) and to explore predictors for recurrent events after DAPT cessation during long-term follow-up. Methods: We did a retrospective observational cohort study. We included consecutive people with ACS who were discharged from Scottish hospitals between January 2008 and December 2013 and who received DAPT after discharge followed by antiplatelet monotherapy. The rates of cardiovascular events were assessed during each 90-day period of DAPT treatment and 90-day period after stopping DAPT. Cardiovascular events were defined as a composite of death, ACS, transient ischaemic attack or stroke. Cox regression was used to identify predictors of cardiovascular events following DAPT cessation. Results: 1340 patients were included (62% male, mean age 64.9 (13.0) years). Cardiovascular events occurred in 15.7% (n=211) during the DAPT period (mean DAPT duration 175.1 (155.3) days) and in 16.7% (n=188) following DAPT cessation (mean of 2.7 years follow-up). Independent predictors for a cardiovascular event following DAPT cessation were age (HR 1.07; 95% CI 1.05 to 1.08; p<0.001), DAPT duration (HR 0.997; 95% CI 0.995 to 0.998; p<0.001) and having revascularisation therapy during the index admission (HR 0.58; 95% CI 0.39 to 0.85; p=0.005). Conclusions: The rate of cardiovascular events was not significantly increased in the early period post-DAPT cessation compared with later periods in this ACS population. Increasing age, DAPT duration and lack of revascularisation therapy were associated with increased risk of cardiovascular events during long-term follow-up after DAPT cessation

Interruption to antiplatelet therapy early after acute ischaemic stroke: a nested case-control study

Aims: Antiplatelet drugs are often discontinued early after ischaemic stroke, either because of poor compliance, complications or withdrawal of care. It is unclear whether this places patients at increased risk of recurrence. We explored the association between cardiovascular event rate and persistence with prescribed antiplatelet drugs. Methods: We used a matched case–control design using the Virtual International Stroke Trials Archive (VISTA). Cases were patients who had an acute coronary syndrome, recurrent stroke or transient ischaemic attack within 90 days post-stroke and were matched for age ± 10 years and sex with up to four controls. Antiplatelet use was categorized as persistent (used for >3 days and continued up to day 90), early cessation (used antiplatelet 3 days but stopped prior to day 90). These categories were compared in cases and controls using a conditional logistic regression model that adjusted for potential confounders. Results: A total of 970 patients were included, of whom 194 were cases and 776 were matched controls. At 90 days, 10 cases (5.2%) and 58 controls (7.5%) stopped/interrupted their antiplatelet. The risk of cardiovascular event was not different in stopped/interrupted users (adjusted odds ratio 0.70, 95% confidence interval 0.33, 1.48; P = 0.352) and early cessations (adjusted odds ratio 1.04, 95% confidence interval 0.62, 1.74; P = 0.876) when compared to persistent users. Conclusion: We found no increased risk in patients who stopped and interrupted antiplatelets early after stroke but the study was limited by a small sample size and further research is needed

Interruption to antiplatelet therapy early after acute ischaemic stroke: a nested case-control study

Aims: Antiplatelet drugs are often discontinued early after ischaemic stroke, either because of poor compliance, complications or withdrawal of care. It is unclear whether this places patients at increased risk of recurrence. We explored the association between cardiovascular event rate and persistence with prescribed antiplatelet drugs. Methods: We used a matched case–control design using the Virtual International Stroke Trials Archive (VISTA). Cases were patients who had an acute coronary syndrome, recurrent stroke or transient ischaemic attack within 90 days post-stroke and were matched for age ± 10 years and sex with up to four controls. Antiplatelet use was categorized as persistent (used for >3 days and continued up to day 90), early cessation (used antiplatelet 3 days but stopped prior to day 90). These categories were compared in cases and controls using a conditional logistic regression model that adjusted for potential confounders. Results: A total of 970 patients were included, of whom 194 were cases and 776 were matched controls. At 90 days, 10 cases (5.2%) and 58 controls (7.5%) stopped/interrupted their antiplatelet. The risk of cardiovascular event was not different in stopped/interrupted users (adjusted odds ratio 0.70, 95% confidence interval 0.33, 1.48; P = 0.352) and early cessations (adjusted odds ratio 1.04, 95% confidence interval 0.62, 1.74; P = 0.876) when compared to persistent users. Conclusion: We found no increased risk in patients who stopped and interrupted antiplatelets early after stroke but the study was limited by a small sample size and further research is needed

Antiplatelet therapy following ischaemic stroke: continue or change pre-existing therapy?

Introduction: Antiplatelet therapy is routinely prescribed early after ischaemic stroke. Many patients will already be taking antiplatelet therapy and it is unknown whether these patients should continue the same antiplatelet treatment or switch to a different regimen. Methods:We selected patients with ischaemic stroke from the Virtual International Stroke Trials Archive database who were prescribed antiplatelets both before and after their stroke and who had detailed records of adverse events after stroke. We compared patients who changed to a new antiplatelet regimen after their stroke to those who continued the same regimen. The primary outcome was recurrent ischaemic stroke within 90 days after their index stroke and the secondary outcome was intracranial haemorrhage (ICH) or extracranial haemorrhage (ECH). We used logistic regression analysis and adjusted for age and baseline NIHSS. Results: A total of 1129 participants were included. Of these, 538 subjects changed antiplatelet regimen post stroke and 591 continued the same regimen. A recurrent ischaemic event occurred in 4.1% of subjects who changed regimen and 4.3% who continued unchanged (adjusted OR¼0.93; 95% CI 0.54–1.75, p¼0.929). The incidence of ICH and ECH within the first 90 days was similar in both groups (2.4% vs. 2.6% (adjusted OR¼1.02; 95% CI 0.48–2.18, p¼0.955) and 4.7% vs. 2.9% (adjusted OR¼1.82; 95% CI 0.96–3.43, p¼0.065), respectively). Discussion: The analysis was performed using a non-randomised registry data. Conclusion: In patients who suffer ischaemic stroke whilst taking antiplatelets, a change in antiplatelet regimen was not associated with an altered risk of early recurrent ischaemic stroke rate or bleeding. However, the results must be interpreted in view of the low event rates

Assessing adherence and persistence to non-vitamin k antagonist oral anticoagulants (NOACs) among patients with atrial fibrillation in tertiary-care referral centers in Malaysia

Introduction: Non-vitamin K antagonist oral anticoagulants (NOACs), such as dabigatran and rivaroxaban, are now available for stroke prevention in patients with atrial fibrillation (AF) and are often clinically preferred over vitamin K antagonists (VKAs), such as warfarin. Data describing adherence and persistence to NOACs in real-life clinical practice in Malaysia are scarce. This study aimed to assess adherence and persistence to NOACs in patients with AF in two tertiary-care referral centers: Hospital Kuala Lumpur (HKL) and Hospital Serdang (HSDG). Materials and Methods: This was a retrospective cohort study that included all patients with AF who were treated with NOACs (dabigatran or rivaroxaban) in HKL and HSDG. Data were obtained from medical records and pharmacy databases. Adherence was assessed using proportion of days covered (PDC) over a 1-year duration. High adherence was defined as PDC ≥80%. A gap of >60 days between two consecutive refills was used to define non-persistence. Result: There were 281 patients who met the inclusion criteria, with 54.1% (n = 152) male. There were 75.1% (n = 211) patients on dabigatran and others on rivaroxaban. Only 66.9% (n = 188) of patients achieved high adherence with PDC ≥80% and 69.8% (n = 196) were persistence with >60-day gap over 12 months. Adherence and persistence were both influenced by treatment center, whereas polypharmacy only influenced adherence. Conclusion: Overall adherence and persistence to NOACs were suboptimal and varied between treatment centers, potentially due to institution-specific administrative and clinical practice differences. Clinical care and outcomes can potentially be optimized by identifying factors affecting adherence and persistence and by implementing interventions to improving the

Assessing adherence to direct oral anticoagulants (DOACs) among patients with atrial fibrillation in tertiary-care referral centers in Malaysia

INTRODUCTION Direct oral anticoagulants (DOACs), such as dabigatran and rivaroxaban, are now available for stroke prevention in patients with atrial fibrillation (AF) and are often clinically preferred over vitamin K antagonists (VKAs), such as warfarin. Data describing adherence to DOACs in real-life clinical practice in Malaysia are scarce. OBJECTIVES This study aimed to assess adherence to DOACs in patients with AF at Hospital Kuala Lumpur (HKL) and Hospital Serdang (HSDG), tertiary-care referral centers. METHODOLOGY This was a retrospective cohort study that included all AF patients who were treated with DOACs (dabigatran or rivaroxaban) in HKL and HSDG. Data were obtained from medical records and pharmacy database. Adherence was assessed by using proportion of days covered (PDC) over a 1-year duration and was calculated as the number of days that the medication was on hand over the total number of days in the time period. Good adherence was defined as PDC ≥80% RESULTS There were 281 patients who met the inclusion criteria, male 54.1% (n=152), with 75.1% (n=211) patients on dabigatran and others on rivaroxaban. The ethnic distribution was Chinese 49.8% (n=140), Malay 41.6% (n=117), and Indian 8.5% (n=24). Only 66.9% of patients achieved good adherence with PDC ≥ 80%. Adherence by institution was good in HKL with 85.2% (n=69/81) but poor in HSDG with 59.5% (n=119/200) [p<0.05]. CONCLUSION Overall adherence to DOACs was poor but it varied between institutions, potentially due to institution-specific administrative and clinical practice differences. Clinical care can potentially be optimized by identifying factors affecting adherence and implementing adherence-improving interventions

Non-linear Granger causality in currency futures returns

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