Snakebite at 12 Hours - Bradycardia (HR 40 bpm) with No Neuro/Hematological Signs

Key Clinical Issue: HR 40 is NOT a Benign Finding

"Cardiovascular abnormalities: hypotension, shock, cardiac arrhythmia, abnormal ECG"

Why Is Bradycardia Happening?

Immediate Management

1. Do an ECG RIGHT NOW

• Look for: sinus bradycardia, AV blocks (1st/2nd/3rd degree), ST-T changes, prolonged PR/QT, signs of hyperkalemia (peaked T waves, wide QRS)
• ECG abnormalities in snakebite include: sinus bradycardia, varying degrees of AV block, ST-T changes, arrhythmias

2. Administer ASV - This Patient Qualifies

• Cardiac arrhythmia (HR 40) = systemic envenomation = indication for ASV
• Indian polyvalent ASV covers the "Big Four": Naja naja, Bungarus caeruleus, Daboia russelii, Echis carinatus
• Give ASV IV slowly (initial rate 2 mL/min), after premedication with subcutaneous adrenaline 0.25 mg (adults) to reduce anaphylaxis risk

3. Treat the Bradycardia Directly

• Per WHO guidelines: "In hypotension with bradycardia, try Atropine"
• Atropine 0.6 mg IV, repeat as needed (titrate to response)
• If refractory to atropine: consider transcutaneous pacing

4. Urgent Labs

• 20WBCT (20-minute whole blood clotting test) - must be done to rule out coagulopathy even if clinically no bleeding
• CBC, BMP (electrolytes - rule out hyperkalemia), serum creatinine
• Cardiac enzymes (Troponin, CK-MB) - direct myocardial damage can occur
• PT/INR, fibrinogen
• Urine dipstick (hemoglobinuria/myoglobinuria)

5. IV Access and Monitoring

• Two large-bore IVs
• Continuous cardiac monitoring (ECG monitoring)
• Pulse oximetry
• Frequent BP monitoring every 15-30 minutes
• Watch for hemodynamic deterioration

Why "No Neuro/Hematological Signs at 12 hrs" Does NOT Reassure Completely

• Neurological signs of krait (Bungarus) envenomation are notoriously delayed - ptosis can appear 6-24 hours post-bite; the patient may not have peaked yet
• Coagulopathy from viper venom is present subclinically before spontaneous bleeding - the 20WBCT is essential
• Bradycardia is the early cardiac sign - more severe arrhythmias or hemodynamic collapse can follow without treatment

Disposition

• Cardiac monitoring
• Immediate access to atropine, vasopressors, and temporary pacing capability
• Repeat 20WBCT every 1 hour for 3 hours, then every 6 hours
• Repeat clinical neuro assessment (test for ptosis, swallowing, grip strength) every 1-2 hours

When the Patient Has Pre-Existing Sinus Bradycardia

The Core Problem: How Do You Distinguish the Two?

Clinical Clues That Suggest Venom-Induced Bradycardia (Not Pre-Existing)

• HR further decreased from patient's known baseline (e.g., usual HR 50, now 40)
• New ECG changes: sinus node dysfunction, junctional escape rhythm, retrograde P waves, AV blocks, ST-T changes - these do NOT occur in benign athletic sinus bradycardia
• Hemodynamic instability: hypotension, dizziness, presyncope - a fit athlete with HR 40 is usually asymptomatic
• Rising cardiac enzymes: Troponin or CK-MB elevation indicates direct myocardial damage
• Symptoms: new fatigue, near-syncope, altered sensorium accompanying the bradycardia
• Evidence of systemic envenomation in other systems (even subclinical coagulopathy on 20WBCT)

The ECG Is the Key Differentiator

Decision Framework

Patient with snakebite + HR 40 + known sinus bradycardia
          |
          v
  Get 12-lead ECG immediately
          |
   ┌──────┴──────┐
Normal ECG         Abnormal ECG
(same as baseline) (new changes: AV block,
                    junctional rhythm, ST changes)
          |                    |
          v                    v
Check trend of HR         VENOM-INDUCED
+ cardiac enzymes         → Give ASV now
+ 20WBCT
          |
  HR worsening OR         HR stable at
  enzymes rising OR       known baseline +
  20WBCT non-clotting     normal enzymes +
          |               clotting normal
          v                    |
    Give ASV                   v
                      Cautious observation
                      with close monitoring
                      (30-min vitals, serial ECG)

Important Notes

1. The 20WBCT is still mandatory - coagulopathy is a separate envenomation indicator independent of the cardiac picture. If the blood doesn't clot at 20 minutes, give ASV regardless of the bradycardia etiology.
2. "Every snakebite should be assumed dangerous to the cardiovascular system until proven otherwise" - per published review on arrhythmias in snakebite. This is sound clinical practice.
3. Pre-existing first-degree AV block is actually an independent risk factor for developing atrial fibrillation in envenomed patients - so a patient with any pre-existing conduction abnormality warrants even more vigilant monitoring.
4. Serial ECGs are essential - even if the first ECG looks like the patient's baseline, repeat at 1, 3, 6, and 12 hours. Venom-induced arrhythmias may appear late (reported up to 3 hours post-envenomation in some cases).
5. Atropine threshold: In a patient with pre-existing bradycardia, you would use atropine only if there is hemodynamic compromise (hypotension, syncope, altered sensorium) - not just for the rate number alone.

Troponin I in Venom-Induced Cardiotoxicity

Short Answer: Yes, Troponin I is Positive - But Not Always

• 13.8% had adverse cardiovascular events (ACVEs)
• 10.8% had elevated high-sensitivity Troponin I (hs-TnI)
• Median hs-TnI elevation was 0.063 ng/mL (max: 3.0 ng/mL)
• Patients with elevated TnI also had higher bleeding rates (33.3% vs 5.4%)

• cTnI levels were significantly higher in severe envenomation vs mild (p < 0.01)
• cTnI correlated negatively with global longitudinal strain (GLS) on echo - meaning higher troponin = worse cardiac function
• Subclinical cardiotoxicity occurred even with normal LVEF - troponin caught it when clinical exam missed it

Mechanisms Behind Troponin Release in Snakebite

What Troponin Tells You Clinically

Critical Point: Troponin Positive Does NOT Mean Treat Like a Normal MI

• Do NOT give thrombolytics - venom-induced coagulopathy + thrombocytopenia makes bleeding catastrophic
• Do NOT give antiplatelet agents (aspirin, clopidogrel) routinely - same bleeding risk
• Coronary angiography - reported cases show normal coronary arteries despite troponin elevation + ST changes, suggesting vasospasm or direct toxicity, not atherosclerotic plaque rupture
• Primary treatment is ASV - antivenom neutralizes the toxin causing the myocardial injury; this is fundamentally different from atherosclerotic MI

Practical Algorithm for This Patient

Snakebite + HR 40 + Suspicion of cardiotoxicity
              |
              v
        Send hs-Troponin I NOW
        + Repeat at 3 hrs and 6 hrs
              |
    ┌─────────┴──────────┐
  Negative              Positive
    |                      |
    v                      v
Still monitor         Confirms myocardial
Serial ECG            injury from venom
Check 20WBCT          ↓
                  Give ASV (cardiac arrhythmia
                  + positive Troponin = clear
                  systemic envenomation)
                  ↓
                  Supportive: atropine for
                  bradycardia, avoid ACS drugs
                  ↓
                  Echo to assess LVEF + wall
                  motion abnormalities
                  ↓
                  ICU monitoring

Key Takeaway