Viscoelastic testing is improved following antivenom treatment in rattlesnake-envenomated equids.

Overview

• This study investigates changes in blood clotting abnormalities in horses and related animals (equids) after being bitten by rattlesnakes, and how antivenom treatment affects these changes.
• The research focuses on using viscoelastic testing to assess improvements in coagulation following antivenom administration.

Background and Objectives

• Rattlesnake bites can cause coagulopathies—disorders affecting the blood’s ability to clot properly—in equids.
• These coagulopathies can be complex, involving multiple factors like platelets, clotting times, and clot firmness.
• The study aims to:
  • Characterize coagulation abnormalities before and after administration of antivenom in equids envenomated by rattlesnakes.
  • Use viscoelastic testing to identify and monitor qualitative clotting abnormalities.
  • Correlate severity of envenomation with laboratory and clinical findings.

Study Design and Methods

• Client-owned equids envenomated by rattlesnakes and treated at Colorado State University between 2023 and 2024 were included.
• Measurements taken both on admission and approximately 24 hours after antivenom treatment included:
  • Rattlesnake Bite Severity Score (RBSS) – a clinical scale from 0 to 13 assessing severity of envenomation
  • Platelet count – evaluating the number of platelets in blood (important for clotting)
  • Prothrombin time (PT) and activated thromboplastin time (aPTT) – tests measuring how long it takes for blood to clot
  • D-dimers – markers of clot breakdown
  • Antithrombin activity – an inhibitor of clot formation
  • Viscoelastic testing variables:
    • Amplitude at 20 minutes (A20) – reflects clot strength after 20 minutes
    • Maximum Clot Firmness (MCF) – maximal clot strength
• The study included 7 acutely envenomated equids.
• Data analysis involved paired comparisons of variables between admission and recheck, and correlation of RBSS with lab parameters.
• Length of hospitalization and survival outcomes were recorded.

Key Findings

• Initial median RBSS was 7 out of 13, indicating moderate severity of envenomation.
• At admission, all animals showed coagulopathies, especially:
  • Thrombocytopenia (low platelet counts)
  • Elevated D-dimers (increased clot breakdown)
  • Abnormal clot strength measures (low A20 and MCF) via viscoelastic testing
• Approximately 24 hours after antivenom treatment:
  • RBSS significantly decreased to median 3, showing clinical improvement
  • A20 values improved from an average of 15.8 to 26.4, indicating stronger clot formation
  • MCF improved from an average of 18.7 to 28.8, further supporting improved clot firmness
• Strong correlations were observed between RBSS and:
  • Platelet count (negative correlation, i.e., higher severity linked with lower platelets)
  • Activated thromboplastin time (positive correlation, meaning more severe cases had longer clotting times)
  • Viscoelastic parameters A20 and MCF (negative correlations, with more severe cases having weaker clots)
• Median length of hospital stay was 2 days, and all animals survived (0% mortality).

Implications and Conclusions

• Coagulopathies are commonly induced by rattlesnake venom in equids and can be effectively identified with viscoelastic testing that assesses how clots form and stabilize over time.
• Antivenom treatment improves clotting function, as demonstrated by clinical improvement (decreased RBSS) and lab parameters (viscoelastic testing, platelet counts, clotting times).
• These improvements suggest that antivenom mitigates venom’s damaging effects on coagulation pathways.
• Effective treatment with antivenom can thereby reduce hospitalization duration and improve survival outcomes in envenomated equids.
• The study supports the use of viscoelastic testing as a useful monitoring tool for coagulopathies in snakebite cases, potentially guiding therapy and prognosis.