Angio-CT and Antiplatelet Drugs Overview

Angio-CT

• Gold standard imaging test for pulmonary arteries

Platelet Aggregation

• Platelet aggregation is influenced by various factors:
  • Thromboxane A2 (TXA2)
  • Adenosine diphosphate (ADP)
  • Vasopressin (AVP)
  • von Willebrand factor
  • Collagen
  • Adrenergic system
  • Glycoprotein IIb/IIIa receptor

Antiplatelet Drugs

• Aspirin: Inhibits TXA2 synthesis (0.075 - 0.5 mg)
• Ticlopidine: Inhibits ADP (2 x 0.25 mg)
• Clopidogrel: Inhibits ADP (1 x 0.075 mg)
• Prasugrel: Inhibits ADP (loading dose 0.3 - 0.6 - 0.9 mg, maintenance 5 or 10 mg)
• Abciximab: Blocks GP IIb/IIIa receptor (0.25 mg/kg bolus, then 0.125 µg/kg/min)
• Tirofiban, Lamifiban, Fradofiban: Block GP IIb/IIIa receptor (0.01 mg/kg bolus, then 0.15 µg/kg/min)
• Eptifibatid: Blocks GP IIb/IIIa receptor (0.18 mg/kg bolus, then 2 µg/kg/min)
• Prostacyclin analogues: Inhibit platelet aggregation and vasoconstriction
• Ticagrelor: Inhibits ADP

Ticlopidine

• Oldest drug from thienopyridine group
• Side effects:
  • Diarrhea
  • Neutropenia
  • Hyperlipidemia

Anticoagulants

• Heparin: Inhibits thrombin and other coagulation factors (APTT monitoring)
• Low Molecular Weight Heparins (LMH): Enoxaparin, Dalteparin, Nadroparin
• Hirudin and synthetic analogues: Bivalirudin, Lepirudin (APTT monitoring)
• Polysaccharide group: Fondaparinux, Idraparinux
• Antagonists of Vitamin K: Warfarin (INR monitoring), Acenocumarol
• Non-Vitamin K Antagonist Oral Anticoagulants (NOACs):
  • Gatranes: Xymelagatran (liver toxicity), Dabigatran
  • Xabanes: Riwaroksaban, Apiksaban, Betriksaban, Endoksaban

Coagulation Cascade

• A series of enzymatic reactions leading to the formation of a fibrin clot:
  • Factors XIII, XII: Initiate the cascade
  • Factor Xa: Converts prothrombin (factor II) to thrombin (factor IIa)
  • Thrombin: Converts fibrinogen (factor I) to fibrin
  • Factor XIII: Stabilizes the fibrin clot

Anticoagulants and Coagulation Cascade

• Heparin, LMH, Polysaccharide group: Inhibit factor Xa
• Hirudin and analogues: Inhibit thrombin
• Xabanes: Inhibit factor Xa
• Gatranes: Inhibit thrombin

Oral Anticoagulants

• Vitamin K Antagonists: Inhibit the synthesis of coagulation factors II, VII, IX, X in the liver
• INR: International Normalized Ratio, used to monitor warfarin therapy (therapeutic range 2-3.5)
• NOACs: Well tolerated, fewer side effects, do not require INR monitoring

Thrombolytic (Fibrinolytic) Drugs

• Drugs that dissolve existing blood clots by breaking down fibrin
• Used to recanalize occluded blood vessels

Fibrinolytic Drugs

• Plasminogen: Converted to plasmin
• Plasmin: Breaks down fibrin

Fibrinolytic Drugs (Antigenicity)

• Streptokinase: Non-specific fibrinolytic drug
• Anistreplase: Modified streptokinase
• Urokinase: Non-specific fibrinolytic drug
• Alteplase (tPA): Tissue plasminogen activator, more specific fibrinolytic drug
• Tenecteplase (TNK–tPA): Modified tPA

Half-Life of Fibrinolytic Drugs

• Anistreplase: Shortest half-life
• Streptokinase: Moderate half-life
• Urokinase: Moderate half-life
• Alteplase (tPA): Moderate half-life
• Tenecteplase (TNK–tPA): Longest half-life

Therapeutic Uses of Fibrinolytic Drugs

• Acute ischemic stroke
• Acute myocardial infarction
• Acute pulmonary embolism
• Deep vein thrombosis
• Arterial thrombosis

Contraindications for Fibrinolytic Drugs

• Prior intracranial hemorrhage (ICH)
• Known cerebral vascular lesion
• Malignant neoplasm involving the intracranial cavity
• Ischemic stroke within the past 3 months
• Aortic dissection
• Active bleeding
• Pregnancy

This quiz covers key concepts related to Angio-CT as the gold standard for imaging pulmonary arteries, as well as factors influencing platelet aggregation and the various antiplatelet drugs. It examines the mechanisms and doses of medications such as Aspirin, Clopidogrel, and others used in inhibiting platelet aggregation. Test your understanding of these important topics in cardiology and hematology.