Donald A. Palisaitis

Comparison of four tests to assess inhibition of platelet function by clopidogrel in stable coronary artery disease patients

AIMS We investigated the comparability of platelet function tests in quantifying platelet inhibition achieved by clopidogrel. METHODS AND RESULTS This pre-specified substudy of a randomized, double-blind trial included 116 patients with stable coronary artery disease requiring diagnostic angiography. Patients received clopidogrel for 1 (300 or 600 mg) or 7 days (300 + 75 or 150 mg daily) before the procedure. Blood samples obtained before clopidogrel initiation and before diagnostic coronary angiography were assayed using light transmission aggregometry [adenosine diphosphate (ADP) 5 and 20 microM as the agonist], whole-blood aggregometry (ADP 5 and 20 microM), PFA-100 (Collagen-ADP cartridge), and VerifyNow P2Y12. Although all assays studied were found sensitive to clopidogrel ingestion, none could distinguish categorically between patients who had, or not, ingested clopidogrel. Agreement between assays to identify patients with insufficient inhibition of platelet aggregation by clopidogrel was low. CONCLUSION The assessment of platelet function inhibition by clopidogrel is highly test-specific. Decision to increase clopidogrel dosage may vary on the basis of the assay used, thus highlighting the need for unambiguous guidelines with respect to assay selection, as platelet function assays are not interchangeable. At present, platelet function testing evaluating clopidogrel efficacy cannot be recommended in routine clinical practice.

New Body Surface Isopotential Map Evaluation Method to Detect Minor Potential Losses in Non–Q-Wave Myocardial Infarction

BACKGROUND Potential losses caused by stable non-Q-wave myocardial infarction (MI) are too small to diagnose with the use of standard ECG. The aim of the present study was to obtain accurate diagnostic criteria for this prognostically important disease with the help of body surface mapping. METHODS AND RESULTS Body surface potentials were recorded with the use of 63 unipolar leads in 45 patients with a non-Q-wave MI (41 to 75 years old); 24 healthy adults, 42 patients with unstable angina, and 70 patients with Q-wave MI served as reference groups. Qualitative pathological features of the isopotential maps, such as onset time and site and magnitude of the first right-anterior/anterior minimum, as well as pathological negativities at that time, were defined in non-Q-wave MI cases. These features, which account for the activation sequence and the body surface projections of specific cardiac regions (Selvester classification), showed a 91% sensitivity and an 88% specificity for the detection of non-Q-wave MI. In comparison, the different departure maps (first third QRS, QRS, and QRST isoarea) resulted in less favorable specificities (50% to 58%). Concordance between the isopotential maps and the acute-phase ECG (90%), hypokinesis (64%), fixed perfusion defects (59%), and significant stenosis of the infarct-related coronary artery (87%) supported the concept that these isopotential map changes correspond to the supposed sites of MI. There were pathological features in 69% of patients with unstable angina, with similar concordances as in non-Q-wave MI. CONCLUSIONS Isopotential maps revealed characteristic features that were suitable for the detection and localization of non-Q-wave MI in the clinical setting of unstable coronary artery disease.

Heterogeneity in platelet cyclooxygenase inhibition by aspirin in coronary artery disease

BACKGROUND Platelets, long believed to be incapable of de novo protein synthesis, may retain their ability to form the cyclooxygenase (COX) enzyme once it has been inactivated by aspirin. This may explain the inefficacy of the drug to induce sustained platelet inhibition in certain patients. We evaluated the stability of platelet inhibition following once-daily enteric-coated aspirin administration. METHODS Platelet responsiveness to aspirin was evaluated in 11 stable coronary artery disease patients on chronic aspirin therapy before and 1, 3, 8, and 24h after observed ingestion of 80-mg enteric-coated aspirin. Inhibition of the COX pathway was measured pharmacologically through plasma thromboxane (Tx) B(2) levels, and functionally by light transmission aggregometry in response to arachidonic acid. COX-independent platelet activity was measured in response to adenosine diphosphate, epinephrine and collagen. RESULTS Plasma TxB(2) levels showed profound inhibition of TxA(2) formation, which was stable throughout 24h, in all but 1 subject. This subject had optimal response to aspirin (inhibition of platelet TxA(2) production within 1h), but recovered the ability to synthesize TxA(2) within 24h of aspirin ingestion. Arachidonic acid-induced platelet aggregation closely mirrored TxB(2) formation in this patient, portraying a functional ability of the platelet to aggregate within 24h of aspirin ingestion. COX-independent platelet aggregation triggered TxA(2) production to a similar extent in all patients, likely through signal-dependent protein synthesis. CONCLUSIONS COX-dependent platelet activity is recovered in certain individuals within 24h of aspirin administration. Further research should consider increasing aspirin dosing frequency to twice daily, to allow sustained inhibition in such subjects.

Genetic determinants of response to aspirin: Appraisal of 4 candidate genes

INTRODUCTION Intersubject variability in platelet response to aspirin could be related to genetic factors that regulate platelet enzymes or receptors. This study evaluates the impact of the selected polymorphisms in the COX-1 gene, the CYP5A1 gene, the P2RY1 receptor gene, and the GPIIbIIIa receptor gene on platelet response to aspirin and risk of suffering from major adverse cardiovascular and cerebrovascular events (MACCE). MATERIALS AND METHODS 192 Caucasian patients with stable coronary artery disease treated with daily aspirin were recruited and followed for 3 years. Platelet aggregation was measured by light transmission aggregometry with arachidonic acid (1.6 mM) and adenosine diphosphate (5, 10 or 20 μM) used as agonists. Genotyping was performed by standard PCR methods. RESULTS Arachidonic acid-induced platelet aggregation was unaffected by the COX-1 22C/T and by the Pl(A1/A2) polymorphisms. However, carriers of the 1622 G/G genotype of the P2RY1 gene had significantly higher levels of arachidonic acid-induced platelet aggregation compared with non-carriers (AA 2.0%, AG 2.0% vs. GG 9.0%, p=0.047). Carrying the 1622 G/G genotype increased the risk of inadequate platelet response to aspirin, defined as arachidonic acid-induced aggregation ≥ 20%, by a factor of 8.5 (1.4 - 53.3, p=0.022) and the risk of 3-year MACCE by a factor of 7 (1.4 - 34.7, p=0.017). CONCLUSION The 1622A/G mutation of the P2RY1 gene could contribute to inadequate platelet response to aspirin and is associated with an increased risk of suffering from MACCE.

Platelet count, not oxidative stress, may contribute to inadequate platelet inhibition by aspirin

BACKGROUND Several patient characteristics have been shown to increase the risk of inadequate platelet inhibition by aspirin, yet underlying mechanisms remain mostly unknown. We explored whether oxidative stress, via isoprostane formation, was associated with inadequate platelet response to aspirin. Additionally, we sought to investigate whether individual pre-selected demographic, hematological or biochemical parameters further increased the risk of inadequate platelet response to aspirin. METHODS Two hundred consecutive subjects suffering from stable coronary artery disease and under daily aspirin therapy were enrolled in our study. Inadequate platelet response to aspirin was defined as residual platelet aggregation>or=20% per arachidonic acid-induced light transmission aggregometry. Morning urinary samples were used to determine levels of isoprostanes (8-iso-PGF2alpha) using an enzyme immunoassay. RESULTS Eight subjects were deemed to present inadequate platelet response to aspirin. Wide intersubject variability was observed in urinary 8-iso-PGF2alpha levels. However, levels were similar between aspirin responders and non-responders. Patients with inadequate platelet response to aspirin had higher platelet counts and received the lowest daily aspirin dose when compared to responders, suggesting subtherapeutic aspirin therapy due to increased platelet production. Only platelet count remained independently predictive of inadequate platelet response to aspirin in a multiple logistic regression model. CONCLUSIONS Urinary 8-iso-PGF2alpha levels, a reflection of systemic oxidative stress, did not appear to contribute to impaired platelet responsiveness to aspirin, while increased platelet production may partly explain this phenomenon.

Potential Anaphylactic Shock with Abciximab Readministration

A 46‐year‐old woman developed an anaphylactic reaction during percutaneous coronary intervention after she was pretreated with prednisone and diphenhydramine for a known allergy to iodine. She developed pruritus, edema, and nausea, which were followed by bradycardia and shock, minutes after administration of a bolus and standard‐dose infusion of abciximab. The reaction was treated successfully with epinephrine, methoxamine, hydrocortisone, atropine, furosemide, sodium bicarbonate, diphenhydramine, and ranitidine.

Evaluation of the platelet count drop method for assessment of platelet function in comparison with "gold standard" light transmission aggregometry.

INTRODUCTION Hyporesponsiveness to antiplatelet agents has been linked to an increased risk of major adverse cardiovascular events. However, light transmission aggregometry (LTA), the gold standard methodology for assessing platelet function, requires expertise and is labour-intensive, which render its use in clinical settings impractical. We assessed whether platelet count drop (PCD), a technique widely available in any haematology laboratory, could replace LTA in testing for inhibition of platelet aggregation induced by antiplatelet agents. MATERIALS AND METHODS One hundred and sixty-one coronary artery disease patients taking aspirin alone and 91 patients taking a combination of aspirin and clopidogrel were enrolled. Platelet aggregation was measured by LTA and PCD stimulated with 1.6 mM of arachidonic acid (AA) for aspirin and 5 and 20 microM of adenosine diphosphate (ADP) for clopidogrel. RESULTS Correlation between AA-induced LTA and PCD was nonexistent (r=-0.043, p=0.587), while correlation between ADP-induced LTA and PCD was low (r=0.374, p<0.0001 for ADP 5 microM and r=0.402, p<0001 for ADP 20 microM ). PCD, whether stimulated with AA or ADP, overestimated platelet aggregation as assessed by LTA, by 13-18%. The wide 95% limits of agreement suggest that the assays can disagree significantly in individual patients. CONCLUSIONS Although the PCD method is widely available in non-specialized laboratories, our results demonstrate that there is poor correlation with the current gold standard, i.e. LTA. Thus, PCD should not be used in replacement of LTA to assess antiplatelet responsiveness.

Prevalence of Unresponsiveness to Aspirin and/or Clopidogrel in Patients With Stable Coronary Heart Disease

This study sought to assess whether inadequate platelet responses to aspirin and clopidogrel are distinct phenomena caused by different mechanisms or different facets of the same phenomenon (i.e., general platelet hyperactivity). A total of 85 patients with stable coronary artery disease who were taking aspirin and clopidogrel daily for > or =3 months were enrolled in the present study. Platelet aggregation was measured by light transmission aggregometry (LTA) stimulated with 1.6 mM of arachidonic acid and 5, 10 and 20 microM of adenosine diphosphate, and by the VerifyNow Aspirin and VerifyNow P2Y12 point-of-care assays. An inadequate platelet response was defined as aggregation greater than or equal to the mean + 2 SDs. The prevalence of an inadequate platelet response varied greatly among the assays. For aspirin, the prevalence was 2.4% using arachidonic acid-induced LTA and 5.9% using the VerifyNow Aspirin assay. For clopidogrel, the prevalence varied from 1.2% to 3.9% using adenosine diphosphate-induced LTA and was 2.4% using the VerifyNow P2Y12 assay. The point-of-care assays did not select the same patients as LTA. No subject was unresponsive to both aspirin and clopidogrel, regardless of the assay used, suggesting that separate mechanisms govern platelet unresponsiveness to aspirin and clopidogrel. In conclusion, an inadequate platelet response to either aspirin or clopidogrel is rare, and the definition is dependent on the platelet function assay used. Because no subject was found to be unresponsive to both agents, the unresponsiveness is suspected to occur through distinct mechanisms of platelet activation.

Excellent outcomes for transcatheter aortic valve replacement within 1 year of opening a low-volume centre and consideration of requirements.

BACKGROUND After the approval of transcatheter aortic valve replacement (TAVR) for high-risk or inoperable patients with severe aortic stenosis (AS), many low- and moderate-volume TAVR programs were initiated. Contemporary outcomes from these newly initiated centres remain unknown. METHODS In March 2013, our institution was authorized by the Québec Ministry of Health to perform 30 TAVR procedures. After thorough clinical screening and imaging evaluation, suitable patients underwent transfemoral TAVR with the balloon-expandable SAPIEN XT (Edwards Lifesciences, Irvine, CA) transcatheter heart valve (THV). In-hospital and 30-day outcomes were prospectively collected and reported according to Valve Academic Research Consortium 2 guidelines. RESULTS From April 2013 to January 2014, 30 consecutive high-risk (n = 16 [53.3%]) or inoperable (n = 14 [46.7%]) patients (mean age, 84.6 years; mean Society of Thoracic Surgery score, 7) with symptomatic severe AS underwent transfemoral TAVR. No catastrophic intraprocedural complications such as annulus rupture, valve embolization, aortic dissection, or coronary occlusion occurred, and there were no deaths at 30 days. Disabling stroke occurred in 1 (3.3%) patient 48 hours after THV implantation. Major vascular complications and major bleeding occurred in 1 (3.3%) patient. No moderate or severe paravalvular leak was observed. The median length of stay was 2 (1-3) days, with 8 (26.7%) patients discharged within 24 hours after the procedure. CONCLUSIONS Excellent outcomes can be achieved in newly initiated relatively low-volume centres, which compares favorably to previously published large series. Important considerations include appropriate team training, rigorous patient screening, use of multimodality imaging techniques, a heart team approach, constant integration of lessons learned from larger published experiences, and maintaining a recommended minimum volume of 25 cases per year.

Insights into the interpretation of light transmission aggregometry for evaluation of platelet aggregation inhibition by clopidogrel

INTRODUCTION When studying the efficacy of clopidogrel to inhibit platelet aggregation by light transmission aggregometry, technical decisions must be taken prior to assessment or during analysis, including, but not limited to, concentration of agonist to use and timing of the evaluation of the response on the aggregation curve obtained (peak ADP-stimulated platelet aggregation vs. late aggregation). We investigated how some of these technical modalities affected the results of platelet aggregation obtained after clopidogrel administration. MATERIALS AND METHODS One hundred and twenty stable coronary artery disease patients requiring a diagnostic angiography were recruited prior to pre-treatment with clopidogrel. Blood samples were tested before clopidogrel initiation and immediately preceding coronary angiography using light transmission aggregometry with either 5 or 20 microM of ADP. Aggregation was measured at maximal amplitude (peak), and 5 minutes after agonist addition (late). RESULTS While measurements of platelet aggregation as either peak or late aggregation were strongly correlated, peak platelet aggregation was significantly higher than late aggregation, by 10.8% and by 10.3% with ADP 5 and 20 microM, respectively. Moreover, the use of ADP 20 microM resulted in less spontaneous disaggregation than 5 microM in the absence of clopidogrel (11.8% and 4.8% with ADP 5 microM and 20 microM, respectively). CONCLUSIONS When assessing platelet aggregation following clopidogrel, measurement of late aggregation after addition of ADP 20 microM should be preferred. Large clinical trials should be conducted to assess which parameter between residual aggregation or inhibition of platelet aggregation by clopidogrel best predicts clinical efficacy of the drug.