Antiplatelet agents in cardiology: the choice of therapy

Therapeutic hypothermia in combination with percutaneous coronary intervention in out-of-hospital cardiac arrest due to left main coronary artery disease

A 59-year-old man had a witnessed collapse while driving a car. Approximately 10 min after the call to emergency services, paramedics arrived and initiated cardiopulmonary resuscitation. The first electrocardiogram (ECG) obtained by paramedics showed pulseless electrical activity. Review of his prehospital records documented that he experienced approximately 13 min of no flow or low flow before return of spontaneous circulation. On admission, he was still comatose with midrange dilated pupils. Electrocardiogram showed sinus rhythm, ST segment elevation in lead aVR, and ST segment depression in leads I, II, and V4-6. Coronary angiography showed 99% narrowing of the left main coronary artery (LMCA), but did not show any disease in the right coronary artery. A bare-metal stent was placed in the LMCA, and postdilated at 20 atmospheres. Immediately after return to the coronary care unit, therapeutic hypothermia was initiated. Hypothermia with a target temperature of 33.0 degrees C was maintained for 30 h. During this period, no significant hemodynamic instability occurred under intra-aortic balloon pumping (IABP) and intravenous catecholamines. Subsequently, he was slowly rewarmed at a rate of 0.3 degrees C/h up to 36.0 degrees C. Next day, the neurological condition improved and IABP was stopped. Creatine kinase increased to 2182 IU/l. Stent thrombosis did not occur despite the ad hoc loading of antiplatelet drugs. Follow-up echocardiography 9 days later showed mild hypokinesia of the anterior wall with an ejection fraction of 77%. He was discharged with no neurologic complications 18 days later.

Management of antiplatelet therapy for minimization of bleeding risk before cardiac surgery

Antiplatelet therapy is commonly administered for primary and secondary prevention of stroke, recurrent angina, myocardial infarction, and death in patients with cardiovascular disorders. It also is associated with an increased risk of bleeding. We describe the management of antiplatelet therapy in patients undergoing coronary artery bypass graft surgery. In addition, we provide basic information about the mechanisms of action by which the most common antiplatelet agents inhibit platelet function. This information is integrated with results from pharmacologic studies and clinical trials. Determining the net effect in patients undergoing coronary artery bypass graft surgery requires knowledge about the pharmacokinetics, pharmacodynamics, and clinical efficacy of each drug, and an estimation of the absolute thrombotic versus hemorrhagic risk for each patient.

Plasma asymmetric dimethylarginine concentrations in newly diagnosed patients with acute myocardial infarction or unstable angina pectoris during two weeks of medical treatment

A high concentration of plasma asymmetric dimethylarginine (ADMA) has been associated with several risk factors for atherosclerosis, and this may increase the risk for acute coronary syndromes (ACSs). We measured plasma ADMA concentrations in patients who had newly diagnosed ACS (n = 48), and we followed the changes in ADMA concentrations during these patients' short-term medical therapy, which included various combination of drugs with or without percutaneous coronary interventions according to the needs of each patient. Concentrations of plasma ADMA were found to be high in patients who had ACS compared with 48 age-matched healthy control subjects (3.13 +/- 0.85 vs 1.57 +/- 0.85 mumol/L, p <0.0001). Follow-up measurements of ADMA showed dramatic decreases in plasma ADMA concentrations over 2 weeks of medical therapy for ACS (from 3.27 +/- 0.87 to 1.52 +/- 0.47 mumol/L, p <0.0001). Plasma ADMA at baseline showed a significant positive correlation with serum C-reactive protein and plasma insulin and a significant negative correlation with serum levels of high-density lipoprotein and plasma alpha-tocopherol. During therapy, changes in plasma ADMA concentrations were significantly correlated with changes in the ratio of total cholesterol to high-density lipoprotein cholesterol and in serum C-reactive protein concentrations but not with changes in insulin levels. This study provides the first evidence that plasma ADMA concentrations are significantly high in patients who have ACS and that ADMA concentrations rapidly decrease after short-term medical therapy.

Antiplatelet effects and pharmacodynamics of clopidogrel in cats

OBJECTIVE

To evaluate antiplatelet effects and pharmacodynamics of clopidogrel in cats.

DESIGN

Original study.

ANIMALS

5 purpose-bred domestic cats.

PROCEDURE

Clopidogrel was administered at dosages of 75 mg, p.o., every 24 hours for 10 days; 37.5 mg, p.o., every 24 hours for 10 days; and 18.75 mg, p.o., every 24 hours for 7 days. In all cats, treatments were administered in this order, with at least 2 weeks between treatments. Platelet aggregation in response to ADP and collagen and oral mucosal bleeding times (OMBTs) were measured before and 3, 7, and 10 days (75 and 37.5 mg) or 7 days (18.75 mg) after initiation of drug administration. Serotonin concentration in plasma following stimulation of platelets with ADP or collagen was measured before and on the last day of drug administration. Platelet aggregation, OMBT, and serotonin concentration were evaluated at various times after drug administration was discontinued to determine when drug effects were lost.

RESULTS

For all 3 dosages, platelet aggregation in response to ADP platelet aggregation in response to collagen, and serotonin concentration were significantly reduced and OMBT was significantly increased at all measurement times during drug administration periods. All values returned to baseline values by 7 days after drug administration was discontinued. No significant differences were identified between doses. None of the cats developed adverse effects associated with drug administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that administration of clopidogrel at dosages ranging from 18.75 to 75 mg, p.o., every 24 hours, results in significant antiplatelet effects in cats.

Central venous catheter occlusion and thrombosis

Central venous catheters are widely used in children with critical illness and chronic disease. These devices are often essential in the delivery of medications and intravenous fluids and in hemodynamic monitoring. Central venous catheter occlusion and thrombosis are common problems in patients using these devices. This article reviews the background, pathophysiology, and incidence of catheter occlusion and catheter-related thrombosis. Diagnostic, preventive, and treatment strategies, along with future research directions, are addressed.

Complications related to off-pump bypass grafting

Surgical myocardial revascularization is a technique undergoing critical reevaluation in an attempt to reduce operative morbidity and mortality. As the age and number of comorbidities in the surgical population presenting for bypass increases, improved strategies to lessen operative risk have evolved. The use of off-pump bypass grafting to avoid the detrimental effects of extracorporeal circulation demonstrates great promise in reducing operative complications. However, with new techniques come new challenges. Avoidance of the cardiopulmonary bypass circuit has been linked to the development of a hypercoagulable state postoperatively. Complications related to the unique management of the ascending aorta and target vessels during the performance of beating heart surgery are also being reported. Moreover, despite increasing experience in a number of centers, hemodynamic collapse does occur during off-pump bypass, thereby requiring rapid institution of cardiopulmonary bypass. Continued scientific investigation and research should provide the tools to manage the unique obstacles encountered with off-pump coronary artery bypass.

The effects of platelet inhibitors on blood use in cardiac surgery

Platelet inhibition via glycoprotein (GP) IIb/IIIa receptor antagonists has greatly reduced the need for emergent cardiac surgery. However, this change has come at a cost to both the patient and the cardiac surgical team in terms of increased bleeding risk. Current guidelines for patients requiring coronary artery bypass surgery include: 1) cessation of GP IIb/IIIa inhibitor; 2) delay of surgery for up to 12 h if abciximab, tirofiban, or eptafibitide is used; 3) utilization of ultrafiltration via zero balance technique; 4) maintenance of standard heparin dosing despite elevated bleeding times; and 5) transfusion of platelets as needed, rather than prophylactically. These agents present cardiac surgery teams with increased risk during CABG, although overall risk may be diminished by the substantial benefits to patients with acute coronary syndromes and percutaneous interventions, i.e., reduced infarction rates and improved vessel patency. With judicious planning, urgent coronary artery bypass can be safely performed on patients who have been treated with GP IIb/IIIa receptor inhibitors.