Characterization of thrombogenic, endothelial and inflammatory markers in supraventricular tachycardia: a study in patients with structurally normal hearts.

Patients with atrial fibrillation (AF) are at an increased risk of thromboembolism and stroke primarily from the development of thrombi within the left atrium. Pathological changes in blood constituents and atrial endothelial damage promote left atrial thrombus formation. It is not known whether factors predisposing to left atrial thrombus formation in AF are disease specific or also evident within the normal heart. The present study examined whether there are differences in platelet reactivity, endothelial function and inflammation in blood samples obtained from intracardiac and peripheral sites in subjects within structurally normal hearts. Sixteen patients with diagnosed left-sided supraventricular tachycardia (SVT) undergoing a routine elective electrophysiological study and ablation were investigated. Blood samples were taken simultaneously from the femoral vein, right atrium and left atrium, immediately following trans-septal puncture and prior to heparin bolus administration. Between peripheral and atrial sample sites, patients with SVT showed no change in platelet reactivity or aggregation (P-selectin (CD62P) P = 0.91; platelet-derived soluble CD40 ligand P = 0.9), thrombus formation (thrombin-antithrombin complex; P = 0.55), endothelial function (von Willebrand factor P = 0.75; asymmetric dimethylarginine (ADMA) P = 0.97; nitric oxide P = 0.61), or inflammation (vascular cell adhesion molecule-1 P = 0.59; intercellular adhesion molecule-1 (ICAM-1) P = 0.69). However, SVT patients had lower ADMA and ICAM-1 levels than AF patients. The present study demonstrates, for the first time, that SVT subjects with structurally normal hearts have consistent haemostatic function between atrial and peripheral sites. These results suggest that the atria of SVT patients do not contain predisposing thrombogenic, endothelial or inflammatory factors that promote and/or initiate thrombus formation.

Clopidogrel improves microvascular endothelial function in subjects with stable coronary artery disease.

BACKGROUND: Clopidogrel therapy has recently been shown to reduce cardiovascular events in patients with stable vascular disease. This benefit may be due to effects not exclusively related to platelet aggregation. The aim of this study was to evaluate the effect of clopidogrel therapy on microvascular endothelial function in subjects with stable coronary artery disease (CAD). METHODS AND RESULTS: Forty subjects with stable CAD were randomised to clopidogrel therapy (75mg/day) or control. Blood and endothelial function testing occurred at baseline, one week and three months following randomisation. Microvascular endothelial function was assessed via reactive hyperaemic index (RHI). Platelet function was assessed by adenosine diphosphate (ADP)-induced whole blood aggregation and the VerifyNow™ system. Plasma markers of endothelial function (asymmetric dimethylarginine, ADMA) and oxidative stress (myeloperoxidase, MPO) were also tested. The primary endpoint was endothelial function assessment (RHI) at three months. At one week RHI increased by 20±10% in the clopidogrel group; this effect was maintained at three months (21±9% increase from baseline; P<0.01). A significant decrease in ADP-induced platelet aggregation and P2Y12 reaction units was observed in the clopidogrel therapy group (P<0.01). There was no correlation between endothelial function and platelet function testing in the clopidogrel therapy group. CONCLUSION: Clopidogrel therapy is associated with improved microvascular endothelial function in patients with stable CAD. This effect is independent of its effects on ADP-induced platelet reactivity.

Effect of atrial fibrillation on atrial thrombogenesis in humans: impact of rate and rhythm.

OBJECTIVES: We sought to assess the effect of atrial fibrillation (AF) on atrial thrombogenesis in humans by determining the impact of rate and rhythm. BACKGROUND: Although AF is known to increase the risk of thromboembolic stroke from the left atrium (LA), the exact mechanisms remain poorly understood. METHODS: We studied 55 patients with AF who underwent catheter ablation while in sinus rhythm; 20 patients were induced into AF, 20 patients were atrial paced at 150 beats/min, and 15 were control patients. Blood samples were taken from the LA, right atrium, and femoral vein at baseline and at 15 min in all 3 groups. Platelet activation (P-selectin) was measured by flow cytometry. Thrombin generation (thrombin-antithrombin [TAT] complex), endothelial dysfunction (asymmetric dimethylarginine [ADMA]), and platelet-derived inflammation (soluble CD40 ligand [sCD40L]) were measured using enzyme-linked immunosorbent assay. RESULTS: Platelet activation increased significantly in both the AF (p < 0.001) and pacing (p < 0.05) groups, but decreased in control patients (p < 0.001). Thrombin generation increased specifically in the LA compared with the periphery in both the AF (p < 0.01) and pacing (p < 0.01) groups, but decreased in control patients (p < 0.001). With AF, ADMA (p < 0.01) and sCD40L (p < 0.001) levels increased significantly at all sites, but were unchanged with pacing (ADMA, p = 0.5; sCD40L, p = 0.8) or in control patients (ADMA, p = 0.6; sCD40L, p = 0.9). CONCLUSIONS: Rapid atrial rates and AF in humans both result in increased platelet activation and thrombin generation. Prothrombotic activation occurs to a greater extent in the human LA compared with systemic circulation. AF additionally induces endothelial dysfunction and inflammation. These findings suggest that although rapid atrial rates increase the thrombogenic risk, AF may further potentiate this risk.

Ramipril sensitizes platelets to nitric oxide: implications for therapy in high-risk patients.

OBJECTIVES: Using 2 sequential studies in HOPE (Heart Outcomes Prevention Evaluation) study-type patients, the aims of this study were: 1) to test the hypothesis that ramipril improves platelet nitric oxide (NO) responsiveness: and 2) to explore biochemical and physiological effects of ramipril in a cohort selected on the basis of platelet NO resistance. BACKGROUND: Ramipril prevents cardiovascular events, but the bases for these effects remain uncertain. NO resistance at both the platelet and vascular levels is present in a substantial proportion of patients with diabetes or ischemic heart disease and is an independent risk factor for cardiovascular events. METHODS: Study 1 was a double-blind, randomized comparison of ramipril (10 mg) with placebo in a cohort of patients (n = 119) with ischemic heart disease or diabetes plus additional coronary risk factor(s), in which effects on platelet responsiveness to NO were compared. Study 2 was a subsequent short-term evaluation of the effects of ramipril in a cohort of subjects (n = 19) with impaired platelet NO responsiveness in whom additional mechanistic data were sought. RESULTS: In study 1, ramipril therapy increased platelet responsiveness to NO relative to the extent of aggregation (p < 0.001), but this effect occurred primarily in patients with severely impaired baseline NO responsiveness (n = 41). In study 2, ramipril also improved platelet NO responsiveness (p < 0.01), and this improvement was correlated directly with increased NO-stimulated platelet generation of cyclic guanosine monophosphate (p < 0.02) but not with changes in plasma thrombospondin-1 levels. CONCLUSIONS: Ramipril ameliorates platelet NO resistance in HOPE study-type patients, with associated increases in soluble guanylate cyclase responsiveness to NO. This effect is likely to contribute to treatment benefit and define patients in whom ramipril therapy is particularly effective.

Atrial platelet reactivity in patients with atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is associated with an increased risk of thrombus formation in the left but not the right atrium. The mechanisms underlying this differential effect on the atria are unknown. OBJECTIVE: The purpose of this study was to examine whether atrial-specific differences in platelet activation are present in patients with AF. METHODS: Nineteen patients (13 men and 6 women; age 60 +/- 2 years) with AF undergoing ablation in sinus rhythm were studied. Blood samples from the left atrium, right atrium, and femoral vein were obtained at the start of the procedure and analyzed by whole-blood flow cytometry for expression of platelet P-selectin (CD62P), vitronectin receptor (CD51/61), and active glycoprotein IIb/IIIa receptor (PAC-1). Platelet aggregation was evaluated using adenosine diphosphate (ADP)-induced whole-blood impedance aggregometry. Seven patients with left-sided accessory pathway also were studies as a reference group for the effect of transseptal puncture on platelet reactivity. RESULTS: Platelet P-selectin levels were significantly elevated in the left atrium compared to the right atrium (10.2% +/- 2.5% vs 8.6% +/- 2.3%, P <.05). CD51/61 and PAC-1 levels did not differ between sampling sites. ADP-induced platelet aggregation was significantly higher in the left atrium compared to the right atrium and femoral vein (P <.05 for both). Platelet P-selectin levels and ADP-induced platelet aggregation did not differ between sampling site in the reference group. CONCLUSION: In patients with AF, left atrial platelet reactivity is increased compared to the right atria and peripheral circulation. The study data suggest that the presence of chamber-specific platelet activation may explain, in part, the propensity for left atrial thrombus formation in patients with AF.

Detrimental effects of energy drink consumption on platelet and endothelial function.

BACKGROUND: Energy drink consumption has been anecdotally linked with sudden cardiac death and, more recently, myocardial infarction. As myocardial infarction is strongly associated with both platelet and endothelial dysfunction, we tested the hypothesis that energy drink consumption alters platelet and endothelial function. METHODS: Fifty healthy volunteers (34 male, aged 22+/-2 years) participated in the study. Platelet aggregation and endothelial function were tested before, and 1 hour after, the consumption of 250 mL (1 can) of a sugar-free energy drink. Platelet function was assessed by adenosine diphosphate-induced (1 micromol/L) optical aggregometry in platelet-rich plasma. Endothelial function was assessed via changes in peripheral arterial tonometry and expressed as the reactive hyperemia index (RHI). RESULTS: Compared with baseline values, there was a significant increase in platelet aggregation following energy drink consumption, while no change was observed with control (13.7+/-3.7% vs 0.3+/-0.8% aggregation, respectively, P <.01). Similarly, RHI decreased following energy drink consumption (-0.33+/-0.13 vs 0.07+/-0.12 RHI [control], P <.05). Mean arterial pressure significantly increased following energy drink consumption, compared with control (P <.05). Heart rate was unaffected by energy drink consumption. CONCLUSION: Energy drink consumption acutely increases platelet aggregation and decreases endothelial function in healthy young adults.

Determinants of occurrence of aortic sclerosis in an aging population.

OBJECTIVES: We sought to identify clinical, physiological, and biochemical correlates, including markers of endothelial dysfunction and of tissue nitric oxide (NO) responsiveness, of the presence of aortic sclerosis (ASc) in an aging population. BACKGROUND: Aortic sclerosis has been regarded predominantly as a precursor of hemodynamically significant aortic stenosis. However, ASc also represents an independent correlate of increased risk of cardiovascular morbidity and mortality; the basis of this association is incompletely understood. The assumption that the pathogenesis of aortic valve disease is similar to that of atherosclerosis has not been supported by recent studies; rather there has been increasing evidence of a pathogenetic role of inflammation and endothelial dysfunction. Furthermore, we have recently developed methodology for echocardiographic quantitation of early aortic valve disease. METHODS: Randomly selected subjects (n = 253) ages 51 to 77 years underwent transthoracic echocardiography; aortic valve ultrasonic backscatter score (AV(BS)) was used to quantitate echogenicity of the aortic valve. Conventional coronary risk factors were identified. Integrity of NO generation/response was assessed via: 1) plasma asymmetric dimethylarginine concentrations, as a marker of endothelial dysfunction; 2) inhibition of platelet aggregation by the NO donor sodium nitroprusside, as a measure of tissue NO responsiveness and also a coronary prognostic marker; and 3) aortic augmentation index, as a measure of arterial stiffness/wave reflection. All putative correlations with AV(BS) were examined by univariate and multiple linear regression analyses. RESULTS: On the basis of AV(BS) scores, ASc was present in 19.4% of subjects. The AV(BS) directly correlated with patients' age but inversely correlated with high-sensitivity C-reactive protein, creatinine clearance, and platelet NO responsiveness. On multiple linear regression, ASc was associated with impaired platelet NO responsiveness (beta = -0.16, p = 0.02), advancing age (beta = 0.21, p = 0.003), and low body mass index (beta = -0.23, p = 0.001). CONCLUSIONS: Aortic sclerosis is associated with platelet NO resistance rather than conventional coronary risk factors: this might explain the increased thrombotic risk in ASc.

Polycystic ovary syndrome is associated with severe platelet and endothelial dysfunction in both obese and lean subjects.

Platelet hyporesponsiveness to the anti-aggregatory effects of nitric oxide (NO) occurs commonly in association with myocardial ischemia and coronary risk factors, often co-exists with endothelial dysfunction and represents an independent marker of long-term cardiovascular risk. We sought to determine whether polycystic ovary syndrome (PCOS), which has been postulated as a cardiovascular risk factor in women, is independently associated with this phenomenon. Twenty-four young women with PCOS (mean age 32.1+/-1.3) were evaluated in lean (n=12) and obese (n=12) subgroups, and compared with age-matched lean normals (n=12). Platelet aggregation and its inhibition by the nitric oxide donor sodium nitroprusside (SNP) were assessed and compared with vascular endothelial function. Plasma concentrations of malondialdehyde (MDA), N(G),N(G)-dimethyl-L-arginine (ADMA) and hs-CRP were measured as markers of oxidative stress, endothelial dysfunction and inflammation, respectively. Circulating endothelial progenitor cell (EPC) counts were also documented. In both PCOS subgroups, which demonstrated hyperaggregability to ADP, responses to SNP inhibition of aggregation (the principal end-point of the study) were significantly impaired (P<0.01 for both), as were their endothelium-dependent vascular responses to salbutamol (P<0.05 for both). However, vasomotor responses to nitroglycerin and circulating EPC counts did not vary between groups. PCOS subjects also had significantly elevated ADMA, MDA and hs-CRP levels relative to normals (all P<0.05). Impairment of SNP response remained unaltered after mean 30+/-2.4 months follow-up in PCOS subjects. We conclude that in PCOS subjects, independent of obesity and associated insulin resistance, profound and reproducible impairment of platelet responsiveness to NO is an additional component of cardiovascular homeostatic disturbance.

Preservation of platelet responsiveness to nitroglycerine despite development of vascular nitrate tolerance.

AIMS: Organic nitrates, via nitric oxide (NO) release, induce vasodilatation and inhibit platelet aggregation. Development of nitrate tolerance in some vascular preparations may be associated with diminished responsiveness to NO. To date it is not known to what extent vascular tolerance to organic nitrates is associated with acquired platelet hypo-responsiveness to NO. In the current study we compared the acute and chronic effects of sustained release (SR) isosorbide 5' mono-nitrate (ISMN) and transdermal nitroglycerine (TD-NTG) on blood vessels (effects on apparent arterial stiffness) and platelets (effects on responsiveness to NO donors) in patients with stable angina pectoris (SAP). METHODS: Patients (n = 34) with SAP entered a blinded randomized crossover study of ISMN (120 mg) vs. intermittent TD-NTG (15 mg 24 h(-1)). Effects of each nitrate on pulse wave reflection (augmentation index (AIx)), platelet response to adenosine di-phosphate (ADP 1 micromol l(-1)), nitroglycerine (NTG 100 micromol l(-1)) and the non-nitrate NO donor sodium nitroprusside (SNP 10 micromol l(-1)), were measured pre-dose, 4 and 8 h post dose, on three occasions: 1) at the end of a pre-nitrate phase, 2) after dosing for 7 days and 3) following 14 days of full dose therapy with either nitrate. RESULTS: Acutely, both ISMN and TD-NTG markedly reduced AIx. After 14 days, these effects were significantly attenuated (ANOVA, P = 0.018) but not abolished, indicating development of nitrate tolerance. Neither nitrate preparation affected ADP (1 micromol l(-1))-induced platelet aggregation. Platelet responsiveness to NTG (100 micromol l(-1)) and SNP (10 micromol l(-1)) was not diminished during chronic nitrate therapy, and there was no evidence of 'rebound' hyper-aggregability during 'nitrate-free' periods. CONCLUSIONS: Chronic therapy with either ISMN or TD-NTG is associated with development of vascular tolerance. Despite the induction of vascular tolerance, platelet responsiveness to NTG and SNP remains unaffected. Therefore, development of vascular tolerance is unlikely to compromise the anti-aggregatory effects of organic nitrates, or those of endogenous NO.