Optimizing platelet inhibition in peripheral artery disease: A comparison of mono-antiplatelet therapy and dual-antiplatelet therapy using thromboelastography

Abstract

Background

Antiplatelet therapy is used to prevent thrombosis in patients with peripheral artery disease (PAD) following revascularization. However, the current standard of care for these patients remains at the physician’s discretion, varying from mono-antiplatelet therapy (MAPT) to dual-antiplatelet therapy (DAPT). Viscoelastic assays such as Thromboelastography with Platelet Mapping (TEG-PM) provide insight into individual coagulation profiles and measure real-time platelet function. This prospective, observational study looks at the differences in platelet function for patients on MAPT versus DAPT using TEG-PM.

Methods

Patients with PAD undergoing revascularization were prospectively evaluated between December 2020 and June 2023. TEG-PM analysis compared platelet function for patients prescribed MAPT (aspirin or clopidogrel) at the initial encounter and DAPT (aspirin and clopidogrel) at the next visit. Platelet function measured in percent inhibition was evaluated at these visits, and within-group t-tests were performed.

Results

Of the 195 patients enrolled, 486 samples were analyzed by TEG-PM. Sixty-four patients met the study criteria. At the initial visit, 52 patients had been prescribed aspirin, and 12 patients had been prescribed clopidogrel. For patients initially prescribed aspirin MAPT, an increase of 96.8%in the mean ADP platelet inhibition was exhibited when transitioning to DAPT [22.0% vs. 43.3%, p < .01], as well as an increase of 34.6%in the mean AA platelet inhibition when transitioning to DAPT [60.9% vs. 82.0%, p < .01]. For patients prescribed initial clopidogrel MAPT, an increase of 100% in AA platelet inhibition was exhibited on DAPT compared to the MAPT state [42.3% vs. 84.6%, p < .01].

Conclusions

Patients on DAPT showed a significant increase in platelet inhibition when compared to initial aspirin MAPT. A significant difference in AA %platelet inhibition was shown for patients on DAPT when compared to initial clopidogrel MAPT. The results show that patients may benefit from DAPT post-revascularization. Personalizing antiplatelet therapy with objective viscoelastic testing to confirm adequate treatment may be the next step in optimizing patient outcomes to reduce thrombosis in PAD patients.

Keywords

Vascular surgery peripheral arterial disease antiplatelet therapy Thromboelastography

Introduction

Antiplatelet therapy, such as aspirin or clopidogrel, is commonly prescribed post-revascularization of the lower extremity of patients with peripheral artery disease to prevent the formation of blood clots in the newly revascularized vessel. The decision for the post-revascularization antiplatelet therapy depends on individual characteristics and type of revascularization procedure performed. Patients with low bleeding risk, MAPT can be considered for short-term use after certain peripheral vascular interventions such as balloon angioplasty without stenting or with the use of bare-metal stents where risk of reoccurring thrombotic events is low.¹ However, for patients exhibiting more complex lesions or at high risk of recurrent events, current guidelines recommend DAPT post-procedure.² The current American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for the management of PAD patients post-revascularization posits a Class IIb recommendation for DAPT (aspirin and clopidogrel) to reduce thrombotic events and further emphasizes the need for additional research to determined ideal antiplatelet dosage to prevent cardiovascular events.^3,4 Thus, post-revascularization antiplatelet prescription is at the physician’s discretion, varying from treatment with mono-antiplatelet therapy (MAPT) to dual-antiplatelet therapy (DAPT).^5,6

Although numerous studies exploring the superiority of DAPT to MAPT exist, research is still sparse and inconclusive. In the recent literature examining relevant trials following endovascular therapies in the realm of coronary, carotid and peripheral vascular patient population, it was observed that there were not substantial evidence in research to support either of DAPT versus MAPT solutions.⁷ While studies have shown MAPT confers a relative reduction in risk of vascular events in the PAD patient population post-revascularization, the role of DAPT in PAD has not been well established.⁸ Previous research has failed to demonstrate a significant benefit of DAPT over MAPT in preventing stroke, thrombotic events, and major adverse limb events (MALE) in patients with PAD.⁹ However, the actual change in percentage of platelet inhibition in patients taking DAPT versus MAPT has not been elucidated. This further emphasized the need for additional data on this subject matter to gain an accurate insight into which approach works best. Many of these studies have employed a longitudinal design to evaluate the response of different PAD patients to antiplatelet therapy over time, yet the PAD patient population is vast and diverse, and the variability among patients may affect the results of these studies.¹⁰ Thus, it is necessary to conduct further research to determine the individualized efficacy of pharmacological treatment in PAD patients. To personalize antiplatelet therapy, an understanding of the synergistic impact of DAPT as well as its use as a step-up agent in platelet function is required.

Recent published literature from a single-center prospective observational study of patients undergoing lower extremity revascularization reveals the significance of viscoelastic cut points such as platelet aggregation levels exceeding 70.8% and platelet inhibition levels below 29.2% to serve as crucial indicators for identifying patients at elevated thrombotic risk.¹¹ Specifically, it was found that for every 1% decrease in platelet inhibition, the risk of experiencing an event during a six-month period increased by 4%.¹¹ Therefore, it is imperative to thoroughly examine the effects of the medications administered to patients with PAD following revascularization in order to ascertain the extent to which these therapeutic agents influence platelet inhibition as well as to optimize treatment outcomes and prevent thrombotic complications in the post-revascularization period. An understanding of the medication induced alterations in platelet inhibition is indispensable for the effective management and care of PAD patients. By integrating our findings with a comprehensive assessment of DAPT’s efficacy as a step-up agent, we aim to facilitate the development of more targeted and efficacious treatment strategies for managing high-risk thrombotic patients.

We hypothesize that monitoring the subject-specific pharmacological efficacy of MAPT versus DAPT may provide insight into optimizing prescription strategies in PAD patients post-revascularization to prevent restenosis of patent vessels. Establishing antiplatelet efficacy metrics from revascularized patients may help in better establishing a guideline for post-revascularization prescription and potentially lead towards personalized medication management in this patient population. This prospective observational study aims to identify the impact in platelet inhibition in PAD patients prescribed MAPT versus DAPT.

Methods

Study population

All patients undergoing lower extremity revascularization for PAD in the Department of Vascular and Endovascular Surgery at Massachusetts General Hospital were prospectively enrolled from December 2020 to June 2023. Procedures included open surgical, endovascular, and hybrid procedures. Patients had to be prescribed MAPT at the initial visit and DAPT at the subsequent visit. Patients were excluded from the study if they were unable to provide informed consent, were pregnant, or were unable to comply with the blood sampling requirements for follow-up visits as per the established protocols. Patients who were unable to undergo successful revascularization due to a non-targetable lesion or inability to access a lesion endovascularly during the index procedure were deemed screen failures and therefore excluded from analysis. The study protocol was approved by the Institutional Review Board (IRB) at the Massachusetts General Hospital (Boston, MA). Written or electronic informed consent was obtained for each individual. All data were stored in a dedicated electronic study database.

Timing of procedures

Blood samples were collected from patients with PAD pre-operatively within 48 h, and post-operatively inpatient daily for up to 5 days depending on the procedure. Blood was collected at 1-month, 3-month and 6-month period if patient returned for standard of care visit. Blood was drawn by physicians, clinical staff, or research staff trained in phlebotomy as per completion of IRB-approved institutional courses. Blood was collected from existing intravenous access in a 10-cc discard syringe or a peripheral stick. Samples were drawn in a non-gel 4.0 mL sodium heparin Vacutainer tube. All blood samples were transported to the laboratory and processed at 30 min of incubation up to 2 h from the blood draw time. The TEG-PM assay was performed using the TEG 6s analyzer (Haemonetics Corporation, Braintree, MA, USA) according to the manufacturer’s instructions. Quality control measures were implemented to ensure the accuracy and reliability of the results.

Definition of variables

The independent variable in this study was the type of antiplatelet therapy prescribed at the visit (aspirin, clopidogrel, or both aspirin and clopidogrel). The dependent variable was a measure of medication efficacy measured as a percentage of platelet inhibition.

The use of antiplatelet medications was documented and observed in conjunction with TEG-Platelet Mapping results. Pre-operative and outpatient medication documentation was done by monitoring the last dose of medication by verbal report. Inpatient medication documentation was done by monitoring medical administration records documented by clinical staff. Patients were documented to be on aspirin if the last dose was reported to be within 7 days of the blood draw, and clopidogrel if the last dose was within 48 h of the blood draw.

Comparison groups

Antiplatelet reactivity

Patient samples were categorized by initial antiplatelet monotherapy (MAPT) as either aspirin or clopidogrel. All patients were then placed on dual-antiplatelet therapy (DAPT) with both aspirin and clopidogrel at the subsequent visit. Antiplatelet efficacy was measured in terms of percent platelet inhibition. Differences in platelet inhibition were compared between patients initially on MAPT and subsequently on DAPT.

Differences in aspirin and clopidogrel function in terms of percent platelet inhibition and responses of thromboxane A2 receptor agonist (AA) and adenosine diphosphate receptor agonist (ADP) were evaluated for medication efficacy within patients.

Antiplatelet reactivity – longitudinal comparison (1-month, 3-month, and 6-month)

We evaluated the sustained effects of DAPT on platelet function by measuring ADP % inhibition and AA % inhibition post-operatively on DAPT, and subsequently at one, three-, and six-months post-revascularization while on DAPT. This approach allowed us to map the trajectory of platelet reactivity over time and to investigate the potential sustained effect of DAPT and the development of tolerance to DAPT. These intervals were selected to provide snapshots of platelet function evolution during the critical initial period following surgical intervention when the risk of thrombotic events is heightened.

Antiplatelet reactivity – open and endovascular patients

We compared platelet reactivity in patients undergoing open versus endovascular procedures to elucidate the impact of procedural type on the response to dual-antiplatelet therapy (DAPT). Patients were stratified into groups based on the initial antiplatelet therapy (mono-antiplatelet therapy [MAPT] with either aspirin or clopidogrel) and subsequent transition to DAPT post-revascularization. Platelet function tests were conducted to measure ADP % aggregation and AA % aggregation at baseline on MAPT and after the initiation of DAPT, providing a comparative framework to assess the stepwise effect of antiplatelet therapy escalation.

Antiplatelet reactivity – Gender

This study reviewed the potential influence of gender on the efficacy of mono-antiplatelet (MAPT) and dual-antiplatelet therapy (DAPT). We conducted a thorough analysis of platelet aggregation responses in both male and female cohorts pre- and post-transition to DAPT. The study included patients originally on Aspirin and Clopidogrel MAPT, with subsequent monitoring after transitioning to DAPT. Platelet reactivity was quantified by measuring ADP % aggregation and AA % aggregation, with specific attention to any statistical differences between genders.

Clinical outcomes

This study tracked post-operative clinical events among patients who transitioned from mono-antiplatelet therapy (MAPT) with either aspirin or clopidogrel to dual-antiplatelet therapy (DAPT). We systematically documented occurrences of bypass/stent stenosis, wound complications, and bleeding events during hospitalization, at discharge, and at one, three, and more than six months post-operation.

Statistical analysis

Differences within treatment groups were formed with a paired Student’s t-test for pairwise analysis. The mean and range were calculated for each categorized group.

Results

Study population

Of the 195 patients enrolled in the study, 64 patients were initially prescribed MAPT and subsequently transitioned to DAPT at the next visit. A total of 128 samples were collected and analyzed by TEG-PM. Of those patients, 81.2% (52 patients) were prescribed aspirin as MAPT while 18.8% (12 patients) were prescribed clopidogrel as MAPT (Figure 1, Table 1)

Figure 1.

Identification of study population.

Table 1.

Demographics, comorbidities, and procedure type.

	Aspirin MAPT (N)	Clopidogrel MAPT (N)	p value
Coronary artery disease
Yes	26	8	0.35
No	26	4	0.35
Tobacco use
Current within the last year (> or = 1 pack a day)	6	1	0.75
Current within the last year (<1 pack a day)	9	1	0.44
None	7	3	0.32
Past, quit >10 year ago	20	4	0.74
Past, quit 1 to 10 years ago	10	3	0.29
Renal status
Normal	16	5	0.47
Evidence of renal dysfunction (GFR >90)	6	0	0.22
GFR 60 to 89	17	2	0.27
GFR 30 to 59	11	3	0.77
GFR 15 to 29	1	0	0.63
GFR <15 or patient is on dialysis	1	2	0.03
Statin
Atorvastatin	11	3	0.77
Pravastatin	6	1	0.75
Rosuvastatin	8	5	0.04
Simvastatin	3	1	0.74
None	24	2	0.06
Female vs male
Female	18	3	0.74
Male	34	9	0.74
Procedure type
Endovascular	29	9	0.22
Open	7	1	0.63
Combined	16	2	0.33

Abbreviations used: GFR, glomerular filtration rate; CAD, coronary artery disease.

Distribution of platelet reactivity

The quartile analysis of ADP and AA% inhibition demonstrated wide variability (Figure 2).

Figure 2.

Platelet inhibition with aspirin/clopidogrel MAPT and DAPT.

For patients on aspirin as MAPT, the median for ADP % inhibition is 18.7 with a range of 8.1–32 and IQR of 23.9. The median for AA % inhibition is 88.9 with a range of 46.5–99 and IQR of 52.9.

For patients on clopidogrel as MAPT the median for ADP % inhibition is 48.3 with a range of 15–89 and IQR of 74. The median for AA % inhibition is 95.4 with a range of 12.5–96.4 and IQR of 83.9.

For patients initially prescribed aspirin as MAPT, the median for DAPT ADP% inhibition is 29.4 with a range of 14.1–59.4 and IQR of 24.5. The median for DAPT AA% inhibition is 94 with a range of 72.4–96.9 and IQR of 24.5.

For patients initially prescribed clopidogrel as MAPT, the median for DAPT ADP% inhibition is 57.6 with a range of 15–89 and IQR of 86.7. The median for DAPT AA% inhibition is 95.5 with a range of 0–97.8 and IQR of 97.8.

Comparison of platelet reactivity between antiplatelet regimens

Among patients initially prescribed aspirin MAPT, there was an increase of 96.8% in the mean ADP platelet inhibition when transitioning to DAPT [22.0% vs. 43.3%, p < .01], as well as an increase of 34.6% in the mean AA platelet inhibition when transitioning to DAPT [60.9% vs. 82.0%, p < .01] (Figure 3, Table 2).

Figure 3.

Distribution of study population.

Table 2.

Events.

	Total	Aspirin MAPT (N)	Clopidogrel MAPT (N)	p value
Events
Total	25	18	7	1.00
Bypass/stent stenosis	16	11	5	.63
Worsening/enlarging wound	1	1	0	.52
Infection/dehiscence	6	4	2	.74
Bleeding event	2	2	0	.36

Among patients initially prescribed clopidogrel MAPT, an increase in the mean ADP platelet inhibition was exhibited on DAPT compared to the MAPT state [38.5% to 51.6%, p = .25]. As well as an increase of 100% in the mean AA antiplatelet inhibition was exhibited on DAPT compared to the MAPT state [42.3% to 84.6%, p < .01].

The results from the paired t-test show that among patients initially prescribed aspirin MAPT, there was a statistically significant increase in both ADP platelet inhibition and AA platelet inhibition when transitioning to DAPT. Among patients initially prescribed clopidogrel MAPT, there was a statistically significant increase in AA platelet inhibition when transitioning to DAPT.

Comparison of platelet reactivity at 1-month, 3 month, and 6-month

Post-operative DAPT showed an initial mean ADP % inhibition of 44.3, which slightly increased to 51.0 at the one-month mark (p = .37), suggesting a potential immediate enhancement of the DAPT effect. However, this effect did not sustain, as evidenced by a decrease to 48.7 at three months (p = .64), and further down to 36.6 at six months (p = .44), indicating a possible reduction in DAPT efficacy or emerging tolerance. For AA % inhibition, a significant reduction from the post-operative mean of 82.5 to 64.0 at three months (p = .02) was observed, followed by a partial rebound to 74.2 at six months (p = .34), reflecting a potential for transient fluctuations in platelet reactivity over time (Figure 4, Table 3).

Figure 4.

Longitudinal Analysis of Platelet Inhibition Over Time. This figure illustrates the comparison of (a) ADP percent inhibition and (b) AA percent inhibition at post-operative (N = 64), 1 month (N = 27), 3 months (N = 13), and 6 months’ (N = 11) time intervals, independent of the surgical procedure. Data points represent the mean values across all time points for patients on dual-antiplatelet therapy (DAPT). Differences in mean values over time provide insights into the potential attenuation of the DAPT effect or the development of tolerance. N-values indicate the number of patient samples analyzed at each time point.

Table 3.

Events stratified by time.

Event type	Post op (during hospitalization)	Discharge-1M	1M-3M	3M-6M	>6M post op
Infection/Dehiscence	1	3	2	0	0
Bleeding event	1	0	1	0	0
Bypass/Stent occlusion	2	2	8	2	2
Worsening/Enlarging wound	0	0	1	0	0

Comparison of platelet reactivity between endovascular and open procedures

For open surgery patients, the mean ADP % aggregation was 60.6 (29.6), and for endovascular patients, it was higher at 68.7 (30.1), although this difference was not statistically significant (p = .136). This trend continued when patients were stratified by MAPT and DAPT, with endovascular patients showing higher baseline ADP % aggregation 79.5 (25.4) compared to open surgery patients 68.4 (27.2) when on MAPT, and a reduction in platelet aggregation when transitioned to DAPT mean ADP % aggregation of 57.9 (30.9) for endovascular vs. 52.4 (29.4) for open surgery, with the latter reaching statistical significance (p = .002). Furthermore, the AA % aggregation showed a statistically significant difference in endovascular patients on MAPT 51.3% (39.7) versus those on DAPT 21.0% (28.7), p = .0001), suggesting that these patients have higher platelet reactivity and that DAPT is more effective in this group. In contrast, open surgery patients also demonstrated a significant reduction in AA % aggregation when on DAPT 12.0% (19.0) p = .002 (Figure 5, Table 4).

Figure 5.

Comparison of ADP % and AA % Aggregation Across Different Patient Groups and Therapies. This figure illustrates the differences in ADP % and AA % aggregation in various patient cohorts undergoing open surgery and endovascular interventions. The data is segmented into several comparisons: (a, b) ADP and AA% aggregation between open surgery (N = 52) and endovascular patients (N = 76) (c, d) Within the MAPT cohort, ADP and AA% aggregation between open surgery (N = 26) and endovascular patients (N = 38). (e, f) In the DAPT cohort, ADP and AA% aggregation between open surgery (N = 26) and endovascular patients (N = 38). (g, h) Comparison of MAPT (N = 26) and DAPT (N = 26) within the open intervention cohort (i, j) Comparison of MAPT (N = 38) and DAPT (N = 38) within the endovascular intervention cohort. N-values indicate the number of samples analyzed within each group. Error bars indicate standard deviation for each parameter.

Table 4.

Platelet inhibition with aspirin/clopidogrel MAPT and DAPT.

Aspirin MAPT
	MAPT	DAPT
ADP % aggregation	77.9 (±23.3) n = 51	56.7 (±30.1) n = 51
p-value	0.0002
AA % aggregation	40.6 (±33.5) n = 52	18.0 (±25.0) n = 52
p-value	0.0001

Aspirin MAPT
	MAPT	DAPT
ADP % inhibition	22.1 (±23.4) n = 51	43.3 (±30.4) n = 51
p-value	0.0002
AA % inhibition	60.9 (±33.1) n = 52	82.0 (±25.0) n = 52
p-value	0.0001

Clopidogrel MAPT
	MAPT	DAPT
ADP % aggregation	38.5 (±37.6) n = 12	51.6 (±31.6) n = 12
p-value	0.2521
AA % aggregation	57.7 (±43.8) n = 12	15.4 (±28.2) n = 12
p-value	0.0036

Clopidogrel MAPT
	MAPT	DAPT
ADP % inhibition	38.5 (±37.6) n = 12	48.4 (±31.6) n = 12
p-value	0.5664
AA % inhibition	42.3 (±43.8) n = 12	84.6(±28.2) n = 12
p-value	0.0036

Comparison of platelet reactivity between genders

In evaluating the gender-specific responses to MAPT and DAPT, our results indicated no statistically significant difference in ADP or AA % aggregation between females and males. Initially, on MAPT, females exhibited a mean ADP % aggregation of 83.8% compared to 70.7% in males (p = .07), and a mean AA % aggregation of 47% compared to 42.3% in males (p = .63), suggesting similar platelet reactivity across genders. This trend persisted when comparing the responses to DAPT; females had a mean ADP % aggregation of 46.4% while males had 60.3% (p = .08), and for AA % aggregation, females had a mean of 17.0% against 17.7% in males (p = .91). These findings were consistent across both Aspirin and Clopidogrel MAPT cohorts, indicating that gender does not significantly influence the antiplatelet effect of the therapies investigated. The data highlights that MAPT and DAPT are comparably effective across genders, which could be pivotal for personalized patient management strategies (Table 5).

Table 5.

Platelet inhibition with endovascular and open procedures.

Mean (±SD)
	Open	Endo	Open MAPT	Endo MAPT	Open DAPT	Endo DAPT	MAPT open	DAPT open	MAPT ENDO	DAPT ENDO
ADP % aggregation	60.6 (SD29.6)n = 52	68.7 (SD30.1) (n = 76)	68.4 (SD28.2)n = 26	79.5 (SD25.416)n = 38	52.4 (SD29.4)n = 26	57.9 (SD30.9)n = 38	68.4 (SD 28.2) n = 26	52.4 (SD29.4) n = 26	79.5 (SD25.4)n = 38	57.9 (SD30.9) n = 38
p-value	0.136		0.1052		0.4868		0.05		0.0015
AA % aggregation	22.6 (SD25.1) n = 52	36.2 (SD37.7) n = 76	32.877 (SD26.5)n = 26	51.3 (SD39.7)n = 38	12.3 (SD19.0)n = 26	21.0 (SD28.7) n = 38	32.9 (SD26.5) n = 26	12.3 (SD19.0)n = 26	51.3(SD 39.7)n = 38	21.0 (SD 28.7)n = 38
p-value	0.0243		0.0424		0.4868		0.0023		0.0001

Discussion

Even though the use of antiplatelet therapy is widespread in the management of PAD patients, the lack of standard guidelines for prescribing antiplatelet therapy for this population post-revascularization has led to variations in prescription patterns among physicians.⁹ As a result of this, many physicians prescribe antiplatelet therapy based on the type of surgery, leading to general uncertainty among providers regarding the optimal duration, dosing, and selection of antiplatelet agents for each patient.⁹ This approach fails to consider the unique needs and risk factors of each individual patient. While the utilization of antiplatelet therapy in patients with PAD following revascularization is crucial to prevent thrombosis, the risk of life-threatening thrombotic and hemorrhagic complications associated with improper prescription of antiplatelet therapy presents a significant challenge. The adoption of an individualized and objective approach to antiplatelet therapy is necessary and may lead to significant improvements in limb salvage outcomes for PAD patients undergoing revascularization procedures.

Our study compared the individualized response of patients taking DAPT to their response when taking MAPT with their initial MAPT state acting as a baseline measure. We evaluated differences in platelet function in PAD-prescribed MAPT and then DAPT using TEG-PM. Our results show that mean platelet reactivity was significantly higher when on DAPT than on MAPT. These findings suggest that DAPT may be more effective at inhibiting platelet function in PAD patients than MAPT.

In patients initially prescribed aspirin MAPT, the platelet inhibition working as an ADP inhibitor was noted to be 22.0% and AA inhibitor was noted to be at 60.9%. This finding is consistent with the existing literature that TEG-PM can identify the inhibition of the TxA₂ receptor after aspirin therapy.¹² The same patients who were then prescribed DAPT on their subsequent visit demonstrate platelet inhibition functioning as an ADP inhibitor at 43.3%, inhibition and AA inhibitor at 77.8% inhibition. This demonstrates a 96.8% increase in ADP platelet inhibition, with a 34.6% increase in AA platelet inhibition. The patients who transition to DAPT at the subsequent visit when initially prescribed aspirin MAPT benefit from the addition of a P2Y12 inhibitor with an increase in ADP platelet inhibition. However, an unexpected significant increase in the inhibition of the platelet TxA₂ receptor was observed upon the integration of clopidogrel to an existing aspirin MAPT. The cause for this observation is unknown, as both aspirin and clopidogrel employ parallel pathways to promote platelet inhibition. This peculiar observation was noted in other studies, which postulate that platelet receptor activation exhibits interdependence, and the effects of aspirin and clopidogrel may reciprocally influence the opposing receptor.¹²

Although statistically unproven, a trend towards an increase ADP percent inhibition was observed in patients on DAPT when initially prescribed clopidogrel MAPT. The limited sample size confers an initial, exploratory nature to the findings. Future studies aiming to understand differences in ADP and AA percent inhibition in patients who had initially been prescribed clopidogrel MAPT and then switched to DAPT may offer an opportunity to showcase the effect of aspirin on influencing clopidogrel ADP and AA platelet inhibition values.

Our investigation into the duration of DAPT’s platelet inhibitory effects reveals a complex pattern. Initially, a surge in ADP % inhibition at one-month post-surgery suggests an augmented response to DAPT, potentially due to improved medication adherence or a cumulative effect of treatment. However, this effect waned over the following months, with ADP % inhibition descending below post-operative levels by the six-month mark, hinting at the possibility of reduced DAPT efficacy or the emergence of tolerance. Similarly, AA % inhibition experienced a significant decrease at three months, yet partially rebounded by six months, suggesting variable influences on platelet reactivity over time, such as drug metabolism or changes in patient physiology. These trends underscore the need for personalized monitoring of DAPT efficacy and support the notion that patient-specific factors may modulate the long-term response to antiplatelet therapy.

Our findings suggest an interesting interplay between procedural type and antiplatelet therapy. While endovascular patients demonstrated higher baseline ADP % aggregation, potentially indicative of the procedure’s distinct vascular impact, the transition to DAPT resulted in a significant reduction in platelet aggregation for both procedural groups. Notably, open surgery patients on DAPT exhibited a more pronounced decrease in both ADP % and AA % aggregation compared to their endovascular counterparts. This trend may imply a differential efficacy of DAPT contingent on the type of surgical intervention. However, the lack of a discernible difference in ADP % aggregation between open and endovascular patients on DAPT marks the pivotal role of antiplatelet management. These results align with the concept that while procedural factors influence platelet reactivity, the choice and management of antiplatelet therapy are critical in mitigating thrombotic risk. Given the complexity of these interactions, further research is warranted to further investigate the relative contributions of procedural type and antiplatelet regimen to patient outcomes, particularly in light of the varying baseline reactivity and the potential for tailored antiplatelet strategies.

Our analysis investigated the potential differences in platelet reactivity to mono-antiplatelet (MAPT) and dual-antiplatelet therapy (DAPT) between male and female patients. The data revealed that, across both MAPT and DAPT cohorts, females did not significantly differ from males in ADP % aggregation or AA % aggregation. In the MAPT category, females had a slightly higher mean ADP % aggregation (83.843 vs. 70.698 for males, p = .066) and AA % aggregation (47 vs. 42.293 for males, p = .626), but these differences were not statistically significant. This trend remained consistent when patients were stratified into those who started with aspirin MAPT or clopidogrel MAPT, and when they transitioned to DAPT. Specifically, for those on aspirin MAPT, females had a mean ADP % aggregation of 86.172 compared to males’ 73.862 (p = .0681), and for those on clopidogrel MAPT, females had a mean ADP % aggregation of 69.867 compared to 58.744 for males (p = .6785). Even after transitioning to DAPT, females exhibited a mean ADP % aggregation of 46.4 and AA % aggregation of 16.99, which were comparable to males’ mean ADP % aggregation of 60.324 and AA % aggregation of 17.728, with p-values of 0.084 and 0.9142, respectively. The similar patterns in platelet reactivity suggest that the response to antiplatelet therapy is consistent between genders, which has important implications for the clinical management of thrombotic risks across diverse patient populations.

Post-operative clinical outcomes demonstrated variability dependent on the initial antiplatelet regimen. Among 25 total events, the majority (18) occurred in patients transitioning from aspirin MAPT to DAPT, which could imply a higher risk associated with aspirin monotherapy prior to DAPT compared to clopidogrel monotherapy. Bypass/stent stenosis was the most frequent complication, aligning with the known thrombotic risks associated with such procedures. The temporal pattern of events, with several graft occlusions spread across all post-operative phases, underscores the need for vigilant, long-term monitoring beyond the acute recovery phase. Notably, no bleeding events were observed in patients transitioning from clopidogrel MAPT to DAPT, suggesting a potential difference in bleeding risk profiles between the two therapeutic pathways.

The data indicates that patients on aspirin MAPT to DAPT have a 21.6% incidence rate of thrombosis (11 out of 51), resonating with established literature. Moreover, the clustering of infection/dehiscence events shortly after discharge highlights the critical period of the first month post-operation where enhanced patient care and follow-up might reduce complication rates. This pattern of clinical events, especially the late occurrences of stenosis or occlusion, accentuates the importance of a proactive, sustained approach to patient management to mitigate long-term risks associated with antiplatelet therapy transition (Tables 6 and 7).

Table 6.

Platelet inhibition over time.

1 month ADP % inhibition (p = .3665)
Post-op
Group	DAPT	1 month DAPT
Mean	44.3	51.0
SD	30.2	35.7
SEM	3.8	6.9
N	63	27

1 month AA % inhibition (p = .1366)
Post-op
Group	DAPT	1 month DAPT
Mean	82.5	72.9
SD	25.4	32.8
SEM	3.2	6.3
N	64	27

3 month ADP % inhibition (p = .6421)
Post-op
Group	DAPT	3 month DAPT
Mean	44.3	48.7
SD	30.2	32.1
SEM	3.8	8.9
N	63	13

3 month AA % inhibition (p = .02)
Post-op
Group	DAPT	3 month DAPT
Mean	82.5	64.0
SD	25.4	31.9
SEM	3.2	8.5
N	64	14

6 month ADP % inhibition (p = .4449)
Post-op
Group	DAPT	6 month DAPT
Mean	44.3	36.6
SD	30.2	33.5
SEM	3.8	10.1
N	63	11
6 month AA % inhibition (p = .3380)
Post-op
Group	DAPT	6 month DAPT
Mean	82.5	74.2
SD	25.4	32.9
SEM	3.2	9.9
N	64	11

Table 7.

Platelet inhibition by gender.

In light of the findings of our study, it is noteworthy to mention the results of previous research that have investigated the efficacy of antiplatelet therapy in peripheral artery disease (PAD) patients. Our findings align with several prior studies that have compared the efficacy of DAPT and MAPT in treating PAD. Previous studies have found that DAPT is associated with higher rates of primary patency and secondary patency compared to MAPT.^13,14 Furthermore, previous studies have found that the combination of aspirin and clopidogrel DAPT increase in efficacy than when compared to aspirin MAPT alone in preventing adverse limb events.^7,15 The MIRROR study assigned PAD patients to either a DAPT group (aspirin and clopidogrel) or an aspirin only MAPT control group. This was a double-blind trial that lasted for 6 months post-intervention. As part of the study, initial assessments of target lesion revascularization, stenosis rates, ankle-brachial index readings, and adverse events experienced were recorded from the study population of 80 participants. During the study, it was discovered that those who received DAPT had higher platelet inhibition and improved functional results in comparison to those using aspirin MAPT.¹⁶ Our study findings add a new dimension to the existing body of knowledge by demonstrating that DAPT has higher platelet inhibition TEG values than MAPT. This suggests that DAPT may be more effective in preventing thrombotic events, which could lead to higher rates of patency and better outcomes in PAD patients. Future studies may consider investigating the relationship between platelet inhibition TEG values and patency in PAD patients further to explore the potential benefits of DAPT over MAPT.

There is evidence to suggest that platelet mapping is a valuable predictor of the prothrombic state associated with poor wound healing in patients, and clinically relevant reference points were identified. From previously published data, a single-centered prospective observational study followed 162 patients up to 1-year post-revascularization to determine the platelet inhibition threshold related to thrombotic events. The analysis revealed the optimal platelet inhibition value as greater than 30% ADP inhibition and less than 70% ADP aggregation to prevent thrombotic events in PAD patients.¹⁷ Tailoring antiplatelet medications to maintain a platelet function threshold of greater 30% ADP platelet inhibition could significantly reduce the rate of thrombosis within the first year after revascularization. According to the study’s initial findings, patients maintained at this threshold experienced a thrombotic rate that was less than 50% of the reported rate. As a result, a guided approach to antiplatelet therapy rather than following the standard of care decreased the thrombotic rate from 20% to 10%. With the usage of DAPT post-revascularization when pre-operative patients present with a prescription of only aspirin MAPT, the benefit of prescribing DAPT may further increase the values of AA and ADP percent inhibition to a value that falls within the ideal range established above: greater than 30% platelet inhibition and less than a 70% value of platelet aggregation. Our study patients present an initial value of 22.0% ADP inhibition when on aspirin MAPT, and this value was increased to 43.3%, ADP inhibition after administration of aspirin and clopidogrel DAPT. This heightened ADP inhibition displays the synergistic effect of DAPT within 36 h post-operatively. These values are concordant with the TEG-PM viscoelastic cut points recommended for patients who are considered at high thrombotic risk.¹⁷ Further research can be conducted to determine if MALE is reduced in this specific subset of patients.

In conclusion, the current lack of standard guidelines for prescribing antiplatelet therapy post-revascularization presents a significant challenge in managing PAD patients. The utilization of TEG, which provides a comprehensive evaluation of the hemostatic system, offers the opportunity to identify individual responsiveness to antiplatelet medications and provide a more accurate view on patient-specific antiplatelet therapeutic regimens. Our study compared the individualized response of patients taking dual-antiplatelet therapy (DAPT) to their response when taking single antiplatelet medication (MAPT). Our results show that DAPT may be more effective at inhibiting platelet function in PAD patients than MAPT, as mean platelet reactivity was significantly higher when on DAPT. Our findings are in line with previous studies that recommend the combination of aspirin and clopidogrel may be more effective than aspirin alone in reducing adverse limb events in PAD patients. Further studies with larger sample sizes and longer follow-up periods are needed to confirm these functions and to determine the optimal antithrombotic regimen for PAD patients. A longitudinal analysis that follows patients with longitudinal testing with correlation to graft failure will best allow us to fill our knowledge gap to better understand optimal antiplatelet therapeutic management.

Limitations

It is important to note the several limitations in this study. First and foremost, the small sample size may affect the external validity. In addition, the study was conducted from a single institution, which further limits the generalizability of this study.

A notable limitation of this study is the potential for development of tolerance to DAPT over time, which was not directly measured. While the trends in ADP % inhibition and AA % inhibition suggest changes in the efficacy of DAPT, we cannot conclusively determine if these observations are due to tolerance, variable adherence, metabolic factors, or other patient-specific influences. Additionally, the small sample size at the six-month follow-up, particularly for the clopidogrel to DAPT transition group, limits the power of our statistical analysis and may not accurately reflect the broader patient population. The absence of a control group with continuous MAPT without transition to DAPT also restricts our ability to isolate the effects of the surgical procedure itself from the impact of DAPT on platelet function. Future studies should aim to address these limitations by including larger sample sizes, longer follow-up periods, and comprehensive baseline platelet function assessments to provide a more detailed understanding of the durability and variability of DAPT’s effect on platelet reactivity.

The study did not incorporate baseline platelet reactivity testing such as genetic assays for clopidogrel resistance or measurement of aspirin response, which represents a limitation in our methodology. The variable prevalence of clopidogrel resistance, reported to range from 5% to 44% in the literature, and the potential presence of aspirin resistance, highlighted in studies such as Goodman et al., could influence patient outcomes in response to antiplatelet therapy. In the absence of such testing, our results reflect the heterogeneity of a real-world patient population, which includes a spectrum of responders and non-responders to monotherapy, without selective exclusion. Future studies could benefit from incorporating such assessments to stratify patients more definitively and to potentially tailor antiplatelet strategies more precisely.

We did not investigate the effects of other P2Y12 receptor inhibitors, such as ticagrelor or prasugrel, on platelet inhibition. Both ticagrelor and prasugrel are known for their potent antiplatelet effects and are increasingly used in clinical practice for the prevention of thrombotic events in patients with post-revascularization. Their exclusion from this study represents a limitation in understanding the spectrum of antiplatelet therapy effects. This study’s findings are therefore specific to aspirin and clopidogrel, and conclusions may not be generalizable to other antiplatelet regimens. Future research should consider the inclusion of these agents to provide a broader view of platelet inhibition strategies, which could significantly enhance the applicability of the results to clinical practice where a variety of antiplatelet agents are employed.

One limitation of our study is the absence of baseline platelet reactivity data prior to the initiation of any antiplatelet therapy. Patients were compared to their own responses, transitioning from an established aspirin or clopidogrel monotherapy regimen to dual-antiplatelet therapy. Consequently, the study did not capture the initial platelet reactivity status without antiplatelet treatment, which would have offered a stepwise comparative analysis from no therapy through monotherapy to dual therapy. While this decision was based on the study’s specific design, future research might incorporate initial platelet reactivity measurements to enrich the understanding of the full impact of antiplatelet strategies on platelet function.

Our study’s design did not account for the possible confounding effects of anticoagulants, NSAIDs, or other medications that could influence platelet function and clinical outcomes. While our findings provide insights into the platelet reactivity in response to mono-antiplatelet and dual-antiplatelet therapies, they may not fully reflect the complex interplay of various medications in a real-world setting. This represents a limitation of our research and points to the need for further studies that include a broader range of concomitant medications to elucidate their potential impact on the effectiveness of antiplatelet strategies.

Lastly, this study only included the investigation of aspirin and clopidogrel antiplatelet therapies. Other antiplatelet agents were not included. Additional research with larger sample sizes across various sites and extended follow-up periods is required to further validate these findings and a better understanding of DAPT’s potential advantages and risks for PAD patients.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Grants and financial support: Grant support provided by the NIH R21 Federal Grant R21AG077310 & Haemonetics Corp, Boston, MA.

ORCID iDs

Ivy Lee

Monica Majumdar

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