Effect of genetic variation in P2Y12 on TRAP-stimulated platelet response in healthy subjects.

In platelets, thrombin receptor signaling depends upon the release of adenosine diphosphate and subsequent activation at purinergic subtype Y (P2Y) receptors. The purpose of this study is to evaluate the influence of specific P2Y12 polymorphisms on platelet reactivity in healthy subjects mediated by thrombin receptor activating peptide (TRAP). We recruited a total of 29 healthy volunteers who had been previously genotyped for two polymorphisms of the P2Y12 receptor: the H2 haplotype (rs2046934) and 34C>T (rs6785930). Flow cytometry and the VerifyNow assay were used to assess platelet activation and aggregation stimulated by TRAP in the presence and absence of specific receptor antagonists for the P2Y1, P2Y12, and thromboxane A2 receptors. We identified a significant recessive effect of the P2Y12-receptor H2 haplotype on TRAP-induced flow cytometry. Specifically, H2/H2 carriers (n = 5) demonstrated a significant reduction in both glycoprotein IIb/IIIa receptor activation (p < 0.001) and CD62P expression (p = 0.035). While the VerifyNow assay did not reveal any effect of haplotype on TRAP-mediated platelet aggregation (p = 0.72), the H2/H2 subjects demonstrated greater platelet inhibition in the presence of cangrelor, a specific receptor antagonist for the P2Y12 receptor (p = 0.023). No consistent effects of the separate 34C>T genotype (rs6785930) were demonstrated under the conditions evaluated. The findings of this study suggest a potential association between P2Y12-receptor H2/H2 carriers and reduced platelet function mediated by TRAP in healthy volunteers.

Pharmacodynamic interplay of the P2Y(1), P2Y(12), and TxA(2) pathways in platelets: the potential of triple antiplatelet therapy with P2Y(1) receptor antagonism.

INTRODUCTION: Previous work suggests that the extent of platelet inhibition by P2Y(1) receptor antagonism may be underappreciated, particularly in the context of dual antiplatelet therapy with aspirin and clopidogrel. MATERIALS AND METHODS: Using P2Y(1), P2Y(12), and TxA(2) receptor antagonists individually and in combination, we assessed the incremental changes from baseline platelet reactivity in blood collected from healthy volunteers. RESULTS: The P2Y(1) receptor antagonist further inhibited platelet activation and aggregation in several assay conditions ex vivo when combined with P2Y(12) and/or TxA(2) receptor blockers. Collagen and TRAP-induced platelet aggregation measured by light transmittance aggregometry was inhibited to a greater extent with the triple combination relative to each of the antagonists alone. The triple combination of P2Y(1), P2Y(12), and TxA(2) receptor antagonists also significantly shifted adenosine diphosphate (ADP)-stimulated platelet glycoprotein IIb/IIIa receptor and P-selectin expression compared to individual or dual antagonists. CONCLUSIONS: These results substantiate that additional platelet inhibition occurs with the triple combination of P2Y(1), P2Y(12), and TxA(2) receptor antagonists and support further testing of P2Y(1) receptor antagonists as an option for alternative, synergistic, or triple antiplatelet therapy.

The dangers of gathering data: surgeon-specific outcomes revisited.

The accuracy of risk adjustment is important in developing surgeon profiles. As surgeon profiles are obtained from observational, nonrandomized data, we hypothesized that selection bias exists in how patients are matched with surgeons and that this bias might influence surgeon profiles. We used the Society of Thoracic Surgeons risk model to calculate observed to expected (O/E) mortality ratios for each of six cardiac surgeons at a single institution. Propensity scores evaluated selection bias that might influence development of risk-adjusted mortality profiles. Six surgeons (four high and two low O/E ratios) performed 2298 coronary artery bypass grafting (CABG) operations over 4 years. Multivariate predictors of operative mortality included preoperative shock, advanced age, and renal dysfunction, but not the surgeon performing CABG. When patients were stratified into quartiles based on the propensity score for operative death, 83% of operative deaths (50 of 60) were in the highest risk quartile. There were significant differences in the number of high-risk patients operated upon by each surgeon. One surgeon had significantly more patients in the highest risk quartile and two surgeons had significantly less patients in the highest risk quartile (p < 0.05 by chi-square). Our results show that high-risk patients are preferentially shunted to certain surgeons, and away from others, for unexplained (and unmeasured) reasons. Subtle unmeasured factors undoubtedly influence how cardiac surgery patients are matched with surgeons. Problems may arise when applying national database benchmarks to local situations because of this unmeasured selection bias.

Antiplatelet drugs: mechanisms and risks of bleeding following cardiac operations.

Preoperative antiplatelet drug use is common in patients undergoing coronary artery bypass grafting (CABG). The impact of these drugs on bleeding and blood transfusion varies. We hypothesize that review of available evidence regarding drug-related bleeding risk, underlying mechanisms of platelet dysfunction, and variations in patient response to antiplatelet drugs will aid surgeons as they assess preoperative risk and attempt to limit perioperative bleeding. The purpose of this review is to (1) examine the role that antiplatelet drugs play in excessive postoperative blood transfusion, (2) identify possible mechanisms to explain patient response to antiplatelet drugs, and (3) formulate a strategy to limit excessive blood product usage in these patients. We reviewed available published evidence regarding bleeding risk in patients taking preoperative antiplatelet drugs. In addition, we summarized our previous research into mechanisms of antiplatelet drug-related platelet dysfunction. Aspirin users have a slight but significant increase in blood product usage after CABG (0.5 U of nonautologous blood per treated patient). Platelet adenosine diphosphate (ADP) receptor inhibitors are more potent antiplatelet drugs than aspirin but have a half-life similar to aspirin, around 5 to 10 days. The American Heart Association/American College of Cardiology and the Society of Thoracic Surgeons guidelines recommend discontinuation, if possible, of ADP inhibitors 5 to 7 days before operation because of excessive bleeding risk, whereas aspirin should be continued during the entire perioperative period in most patients. Individual variability in response to aspirin and other antiplatelet drugs is common with both hyper- and hyporesponsiveness seen in 5 to 25% of patients. Use of preoperative antiplatelet drugs is a risk factor for increased perioperative bleeding and blood transfusion. Point-of-care tests can identify patients at high risk for perioperative bleeding and blood transfusion, although these tests have limitations. Available evidence suggests that multiple blood conservation techniques benefit high-risk patients taking antiplatelet drugs before operation. Guidelines for patients who take aspirin and/or thienopyridines before cardiac procedures include some or all of the following: (1) preoperative identification of high-risk patients using point-of-care testing; (2) withdrawal of aspirin or other antiplatelet drugs for a few days and delay of operation in patients at high risk for bleeding if clinical circumstances permit; (3) selective perioperative use of evidence-based blood conservation interventions (e.g., short-course erythropoietin, off-pump procedures, and use of intraoperative blood conservation techniques), especially in high-risk patients; and (4) platelet transfusions if clinical bleeding occurs.

The relationship between mortality and preexisting cardiac disease in 5,971 trauma patients.

BACKGROUND: We observed significant morbidity and mortality in patients with preexisting cardiac disease who suffer severe traumatic injuries. We wondered about the types of injury seen and about the cardiac risks factors that predispose to worse outcomes in these patients. Our hypothesis is that significant cardiac comorbidity is associated with adverse trauma outcomes. METHODS: We reviewed 10,144 trauma admissions to the University of Kentucky during a 5-year period (2002-2007) in patients 21 years or older. The types and extent of injuries were characterized, and risk factors for poor outcome were assessed. Propensity analysis assessed variable interaction and adjusted for important multivariate cardiovascular risk factors. RESULTS: Of the 10,144 adult trauma patients, there was adequate cardiovascular history before emergency treatment in 5,971 patients (58.9%). Of the 700 trauma deaths, 236 (33.7%) had adequate medical history to allow accurate assessment of cardiovascular disease. Significant multivariate predictors of trauma-related death included older age (odds ratio [OR] = 0.938), injury severity score (OR = 0.893 per unit score), major burn (OR = 5.907), assault with a weapon (OR = 3.205), systolic blood pressure divided by Glasgow coma score (OR = 0.958 per score unit), and female (OR = 1.629). In the cohort of 236 deaths with adequate medical history, severe head and chest injuries caused death in 187 patients (79.2%). Significant propensity-adjusted cardiovascular risks of trauma death included preinjury warfarin use (OR = 2.309, p = 0.001), congestive heart failure (CHF) (OR = 2.060, p = 0.011), and preinjury beta-blocker use (OR = 2.62, p = 0.001). The highest mortality rates occurred in patients with combinations of these cardiovascular risk factors. For example, patients on warfarin with CHF had a 26.3% mortality rate, whereas patients on warfarin and beta-blocker had a 27.3% mortality rate. CONCLUSIONS: Preinjury cardiac risk factors, especially preinjury warfarin, beta-blocker use, and CHF, are independent multivariate predictors of mortality in patients suffering significant trauma. Although head and chest injuries are the most frequent causes of death, patients with more than one preinjury cardiac risk factor have 5 to 10 times the mortality risk compared with those without cardiac risks.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline.

BACKGROUND: A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes. METHODS: We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme. RESULTS: Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions. CONCLUSIONS: Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

The preischemic combination of the sodium-hydrogen exchanger inhibitor cariporide and the adenosine agonist AMP579 acts additively to reduce porcine myocardial infarct size.

BACKGROUND: We tested whether the combination of two known cardioprotective agents, the type-1 sodium-hydrogen exchanger inhibitor cariporide plus the adenosine A(1)/A(2a) receptor agonist AMP579 ([1S-[1a,2b,3b, 4a(S*)]]-4-[7-[[2-(3-chloro-2-thienyl)-1-methylpropyl]amino]-[(3)H]-imidazo[4,5-b]pyridyl-3-yl]cyclopentane carboxamide), acted additively to reduce myocardial infarct size. STUDY DESIGN: Pigs underwent 1 hour of coronary artery occlusion and 3 hours reperfusion. Vehicle-treated controls were compared with animals treated before ischemia with low-dose and high-dose cariporide and AMP579, and low-dose cariporide plus AMP579. The effects of both agents, alone and in combination, were also tested in isolated porcine polymorphonuclear neutrophils (PMNs). The PMN respiratory burst was induced with phorbol 12-myristate 13-acetate and quantified by the increase in 2',7'-dichlorofluorescein fluorescence, measured by flow cytometry. RESULTS: Infarct size in the control pigs was 65 +/- 1% of the area at risk. Cariporide dose-dependently reduced infarct size to 39 +/- 2% and 24 +/- 3% in the low- and high-dose groups, respectively. Infarct size was 54 +/- 3% in the low-dose AMP579 group and 47 +/- 3% with high dose. The combination of low doses of cariporide and AMP579 reduced infarction to 25 +/- 6% of the area at risk. In the PMN studies, cariporide and AMP579 alone had no effect on 2',7'-dichlorofluorescein fluorescence, but the combination of the two agents reduced the PMN 2',7'-dichlorofluorescein increase to 79 +/- 5% of the vehicle control response. CONCLUSIONS: The preischemic combination of low doses of cariporide and AMP579 decreased myocardial infarct size more than either agent used alone in low concentration, indicating an additive effect of the two agents. Given the effects that cariporide plus AMP579 combination exerted on PMN activity, it appears that this combination has the potential to reduce PMN-mediated effects during myocardial reperfusion.

Assessing the medical literature: let the buyer beware.

As many as 30% of journal articles may contain errors. Most of these errors involve the use of simple statistical tests or elementary principles of research design. Assessment of the thoracic surgical literature involves cautious circumspection. This does not mean that it is necessary to have in-depth knowledge of sophisticated statistics, rather it means that common sense understanding of a few principles of research design and simple statistics are necessary to determine the usefulness and believability of literature publications.

Aspirin and postoperative bleeding after coronary artery bypass grafting.

OBJECTIVE: To evaluate the relationship between aspirin ingestion and postoperative bleeding complications, and to test the hypothesis that there is a subset of patients who are aspirin hyperresponders with a proclivity toward platelet dysfunction. SUMMARY BACKGROUND DATA: Despite numerous retrospective and prospective analyses, it is still controversial as to whether aspirin ingestion before coronary artery bypass grafting (CABG) is associated with significant postoperative bleeding. METHODS: Between January 1995 and December 1999, the records of 2,606 consecutive patients undergoing CABG were reviewed to identify patients with a history of aspirin ingestion up until the time of surgery. Aspirin ingestion was correlated with postoperative blood transfusion using multivariate analysis. In a subset of preoperative aspirin users (n = 40), bleeding times were measured before and after aspirin use. Flow cytometry was performed in another cohort of patients with known heart disease (n = 30) to determine the effect of aspirin on platelet surface receptors. RESULTS: During the 5-year study period, 63% of the CABG patients were identified as aspirin users. Among these, 23.1% required blood transfusions compared with 19% for the nonusers. Non-red blood cell transfusions were more common in aspirin users, as was reexploration for bleeding. Stratification of these results according to the frequency of aspirin use showed that aspirin is an independent multivariate predictor of postoperative blood transfusion only in high-risk patients. In the prospective studies, aspirin treatment resulted in a significant increase in the template bleeding time, an increase in platelet PAR-1 thrombin receptor activity, and a decrease in the binding of platelets to monocytes. CONCLUSIONS: The findings support the hypothesis that aspirin is associated with a greater likelihood of postoperative bleeding. A platelet function testing algorithm that combines preoperative risk factor assessment, template bleeding times, and flow cytometry may allow the identification of aspirin hyperresponders who are at increased risk for bleeding.