Treatment of Bradycardia

1. Initial Assessment

• Is the patient hemodynamically stable? (Signs of instability: hypotension, altered mental status, ischemic chest pain, acute heart failure, shock)
• Is the bradycardia symptomatic?
• Is there an identifiable, reversible cause?

2. Identify and Reverse Underlying Causes

• Washington Manual of Medical Therapeutics, p. 266
• Sabiston Textbook of Surgery, p. 2821

3. Pharmacologic Treatment

First-Line: Atropine

• Mechanism: Anticholinergic agent that blocks vagal tone
• Dose: 0.5-2.0 mg IV (adults); can repeat; avoid doses <0.5 mg (may cause paradoxical bradycardia)
• Indication: First-line for symptomatic bradycardia, vagally-induced bradycardia, primary AV block
• Works best for: Proximal conduction disease - sinus bradycardia, first-degree AV block, Mobitz I (Wenckebach) second-degree AV block
• Does NOT work for:
  • Junctional or ventricular bradycardia (AV nodal dysfunction) - atropine acts on the dysfunctional node and is ineffective
  • Dexmedetomidine-induced bradycardia (alpha-2 agonist mechanism)
  • Denervated heart (e.g., post-cardiac transplant)
  • Distal conduction disease can actually be worsened by atropine
• Washington Manual, p. 265-266
• Miller's Anesthesia, p. 11608
• Rosen's Emergency Medicine, p. 3213

Second-Line: Chronotropic Infusions

Special Case: Digoxin Toxicity

4. Electrical Therapy

Transcutaneous Pacing (TCP)

• Used when atropine fails or is contraindicated and the patient is hemodynamically unstable
• Immediate, non-invasive bridge therapy
• Limitation: unreliable capture and patient discomfort (second-line to transvenous)
• Washington Manual, p. 266

Temporary Transvenous Pacing (TVP)

• Preferred method for temporary pacing
• Indicated for:
  • Symptomatic second- or third-degree heart block from transient drug intoxication or electrolyte imbalance
  • Complete heart block or Mobitz II in the setting of acute MI
  • Junctional or ventricular bradycardia where atropine is ineffective
  • High cervical spinal cord injury with refractory bradycardia
• Sinus bradycardia, AF with slow ventricular response, or Mobitz I should only receive temporary pacing if significant symptoms or hemodynamic instability are present
• Washington Manual, p. 266

5. Permanent Pacemaker (PPM)

Class I Indications (PPM should be implanted):

• Acquired Mobitz II second-degree AV block (regardless of symptoms)
• High-grade AV block (2:1 or higher)
• Third-degree (complete) heart block that is not reversible or physiologic
• Symptomatic bradycardia with irreversible second- or third-degree AV block
• Asymptomatic complete heart block with HR ≤40 bpm, cardiac enlargement, or LV dysfunction

Class IIa Indications (reasonable to consider):

• Symptomatic Mobitz I (Wenckebach) in patients with neuromuscular disease
• Profound first-degree AV block with LV dysfunction where shorter AV interval improves hemodynamics
• Bifascicular/trifascicular block with syncope unexplained by other causes

AV block in acute MI:

• Temporary pacing is indicated for persistent second- or third-degree AV block, especially if symptomatic
• Inferior MI-related transient AV block usually resolves and typically does not require permanent pacing
• Harrison's Principles of Internal Medicine 22E, p. 429-435
• Washington Manual, p. 267-268

6. Summary Algorithm

Bradycardia HR < 60 bpm
        |
        v
Hemodynamically STABLE? ---YES---> Monitor, treat reversible cause, observe
        |
        NO
        v
Reversible cause? ------YES---> Correct cause (stop offending drug, 
        |                       treat hypothyroidism, etc.)
        NO
        v
ATROPINE 0.5-1 mg IV (repeat up to 3 mg)
        |
  ------+------
  |           |
Effective   Not effective
  |           |
Monitor    TCP or dopamine/epinephrine infusion
           + Transvenous pacing + Cardiology consult
                    |
                    v
        Permanent pacemaker (if irreversible)

Treatment of Krait (Bungarus) Snakebite

Understanding the Krait

Pathophysiology of Krait Venom

• Beta-bungarotoxin (presynaptic): Destroys motor nerve terminals, depletes synaptic vesicles, causes axonal degeneration - resulting in prolonged, irreversible neuromuscular block that does NOT respond to neostigmine
• Alpha-bungarotoxin (postsynaptic): Binds acetylcholine receptors at the motor end plate - may partially respond to neostigmine
• Minimal local tissue damage at bite site (unlike vipers/cobras) - this is a key diagnostic clue

Clinical Features

1. Ptosis (drooping eyelids) - earliest and most common sign
2. Ophthalmoplegia (extraocular muscle paralysis)
3. Facial/bulbar palsy - dysarthria, dysphagia, loss of gag reflex
4. Pooling of secretions in pharynx
5. Respiratory muscle paralysis - the leading cause of death

First Aid (Pre-hospital)

• Pressure-immobilization bandage (PIB): Apply a firm bandage over the entire bitten limb (lymphatic-obstructive pressure: 40-70 mmHg upper limb, 55-70 mmHg lower limb) - most effective for kraits and other elapids that do not cause local necrosis
• Immobilize the limb with a splint
• Keep patient still and calm
• Lay patient flat
• Rapid transport to hospital
• Mark bite time and bandage application time

• Cut, suck, or incise the wound
• Apply tourniquet (risk of distal ischemia)
• Apply ice/cryotherapy locally
• Give aspirin or NSAIDs
• Do not remove PIB until IV access is established and antivenom is ready
• Goldman-Cecil Medicine, p. 1224; P.C. Dikshit Textbook of Forensic Medicine, p. 498

Hospital Management

Step 1: Emergency Stabilization (ABCs)

• Assess airway, breathing, circulation immediately
• Establish IV access
• Monitor oxygen saturation continuously
• Anticipate rapid respiratory compromise - have intubation equipment ready
• Serial neurological assessments every 10-15 minutes

Step 2: Confirm Envenomation

• Clinical signs of neurotoxicity (ptosis, ophthalmoplegia) confirm krait envenomation
• 20-Minute Whole Blood Clotting Test (20WBCT): Non-clotting blood suggests viper envenomation; normal clotting supports elapid (krait/cobra) bite
• Baseline labs: CBC, renal function, LFTs, coagulation profile, creatine kinase, urinalysis (myoglobinuria)

Step 3: Antivenom (Anti-Snake Venom / ASV)

• Any signs of systemic envenomation: ptosis, ophthalmoplegia, dysphagia, respiratory distress

• WHO Guidelines for Management of Snakebites (SEARO)

1. Pre-medication: Subcutaneous/IM adrenaline (epinephrine) 0.25-0.5 mg SC before antivenom infusion to prevent anaphylaxis (do NOT perform skin test - it is unreliable)
2. Dilute antivenom in 500 mL normal saline; infuse IV over 1 hour
3. Keep adrenaline 1:1000 drawn up at bedside throughout infusion
4. Do NOT give as bolus IV push

Step 4: Respiratory Support - THE MOST CRITICAL INTERVENTION

"Antivenom treatment alone cannot be relied upon to save the life of a patient with bulbar and respiratory paralysis." - National Guidelines for Snakebite Management (Bhutan 2024)

• Loss of gag reflex
• Pooling of secretions
• Failure of cough reflex
• Respiratory distress or declining O₂ saturation
• Inability to swallow
• FVC < 15-20 mL/kg or deteriorating peak flow

• Often prolonged (mean 8 days in B. multicinctus series in Vietnam where antivenom was unavailable; 2-5 days even with antivenom)
• Recovery depends on nerve terminal regrowth, not just toxin clearance
• ICU stay mean 12 days in published series

Step 5: Anticholinesterase Trial (Neostigmine + Atropine)

• Atropine 0.3-0.6 mg IV first (to block muscarinic side effects of neostigmine)
• Then Neostigmine 0.01 mg/kg up to 0.5 mg IV or IM every 30 minutes
• Observe over 30-60 minutes for improvement: ptosis resolution, improved peak flow/FEV1

• Neostigmine 0.5-2.5 mg IM/IV/SC with atropine every 1-3 hours
• Maximum neostigmine: 10 mg/24 hours (adults)
• Children: Neostigmine 0.01-0.04 mg/kg every 2-4 hours; OR oral neostigmine 15 mg QID + oral atropine 0.6 mg BD

• Complete recovery from neuroparalysis
• Fasciculations or bradycardia develop (side effects)
• No improvement after 3 doses → probable KRAIT bite (presynaptic toxin; neostigmine generally ineffective in krait envenomation)

Key distinction: Neostigmine works well for cobra (postsynaptic neurotoxin) but does not help in krait (presynaptic beta-bungarotoxin has already destroyed nerve endings). Mechanical ventilation is the only life-saving intervention for respiratory paralysis from krait bites. - Nepal Snakebite Guidelines; Bhutan National Guidelines 2024

Step 6: Supportive Care

Step 7: Antivenom Reaction Management

Monitoring and Referral Criteria

• Patient requires respiratory support
• Deteriorating neurological status
• Worsening renal function
• Comorbidities (heart failure, CKD)

Summary Flowchart

Krait bite suspected
         |
First Aid: Pressure-immobilization bandage
Immobilize, transport to hospital
         |
Hospital: IV access, O₂, monitors
         |
Signs of envenomation? (ptosis, weakness)
   YES
    |
Give Antivenom IV (100 ml Indian polyvalent)
with pre-medication adrenaline
    |
Bulbar/respiratory signs? 
   YES ---> INTUBATE + Mechanical Ventilation
            (mainstay - may need 5-14 days)
    |
Trial of Neostigmine + Atropine
   Response? --NO--> Probable krait; continue ventilation
   YES (cobra)---> Maintain neostigmine schedule
         |
Supportive care, wound care, monitor for
antivenom reactions, renal function

Latest WHO Snakebite Management Protocols: 2024-2026

Overview of WHO's Snakebite Strategy

Key WHO Publications: 2023-2026 Timeline

Current WHO Clinical Management Protocol (2025 Internal Guidelines)

Step 1 - First Aid

• Remove patient from snake's territory; keep calm and still
• Pressure immobilization bandage (PIB): Recommended for elapid bites (kraits, cobras, mambas, sea snakes) that do NOT cause significant local necrosis
  • Elastic bandages, lymphatic-obstructive pressure (not venous)
  • Immobilize bitten limb with a splint
• Transport rapidly to hospital
• Do NOT remove PIB until IV access and antivenom are ready at hospital

• Cutting, sucking, electrocuting, or burning the wound
• Constricting tourniquets or circulation-reducing interventions
• Venom extractors or commercial snakebite kits
• Skin/test doses of antivenom - confirmed ineffective and not recommended

Step 2 - Rapid Clinical Assessment

• ABCDE primary survey
• 20-Minute Whole Blood Clotting Test (20WBCT): Simple bedside test - non-clotting blood at 20 min = viper envenomation with coagulopathy
• Bloods: FBC/CBC, RFTs, LFTs, coagulation studies (fibrinogen, PT, APTT)
• Creatine kinase + urine myoglobin (rhabdomyolysis screen)
• ABG, ECG, CXR in severe or hemodynamically unstable cases
• Reassess every 10-15 minutes for at least 8-12 hours

Step 3 - Antivenom Treatment

• Hemotoxicity: abnormal 20WBCT, spontaneous systemic bleeding, thrombocytopenia
• Neurotoxicity: ptosis, ophthalmoplegia, bulbar palsy, respiratory failure
• Cardiovascular: shock, hypotension, ECG changes
• Renal: oliguria, hematuria, rising creatinine
• Local envenomation: progressive swelling beyond the wrist/ankle, digital necrosis

• Dose is determined by snake species and venom load - NOT patient weight
• Same dose in adults and children - no pediatric dose reduction
• Choose monovalent antivenom where species is known; polyvalent when species is unknown
• Administer by IV infusion (diluted in normal saline), NOT IV bolus

• In patients with persistent or worsening bleeding: repeat dose within 1-2 hours
• In deteriorating neurotoxicity or cardiovascular signs: repeat initial dose after 1-2 hours
• For coagulopathy: give antivenom as long as evidence of coagulopathy persists (may be needed for up to 2 weeks in some viper bites)

• Antivenom is associated with high rates of allergic reactions, AND
• Capacity to manage anaphylaxis is limited (rural/low-resource settings)
• Evidence: limited but beneficial for prophylactic SC epinephrine before IV antivenom

Step 4 - Supportive Treatment

• Useful adjunct for postsynaptic neurotoxin envenomations (cobras, some elapids)
• Not effective for presynaptic neurotoxins (krait beta-bungarotoxin)
• Protocol: atropine first, then neostigmine; observe 30-60 min for response (ptosis improvement, better FEV1)

Step 5 - Wound Care

• Aspirate large tense bullae to prevent secondary infection
• Surgical debridement for gangrenous digits/limbs
• Skin grafting where indicated
• Fasciotomy: generally NOT indicated (compartment pressures rarely elevated beyond fascia depth) - exception: anterior tibial compartment

2025-2026: Novel Therapeutics Guidance (Major New Development)

1. Hospital-setting therapeutics: Products to be used in hospitals, as an adjunct to or replacement for conventional antivenom - applicable to any species of venomous snake
2. Pre-hospital/field therapeutics: Products usable in a post-bite, pre-hospital setting to either:
   • "Buy time" to transport victim to hospital, OR
   • Potentially abrogate the need to go to hospital at all

• Small molecule drugs (oral or injectable, heat-stable, affordable)
• Engineered antibody biologics (monoclonal antibodies, nanobodies - with improved species cross-reactivity and tissue penetration)

• In 2024, a Nature Communications study demonstrated a broadly neutralizing human monoclonal antibody cross-reacting with multiple elapid venoms
• October 2025 preprint introduced a nanobody-based candidate with improved tissue penetration
• No recombinant product has commercial approval yet, but the regulatory framework is now in place
• These TPPs complement earlier 2023 and 2024 documents for conventional antivenoms (sub-Saharan Africa and South Asian markets respectively)

WHO Category 1 vs. Category 2 Snake Classification

• Category 1: Highest medical importance - species causing high mortality/morbidity with proven antivenom available (e.g., Bungarus spp., Naja spp., Echis spp., Daboia spp., Dendroaspis spp.)
• Category 2: Important but lower priority - less well-characterized or with limited distribution

2024 WHO Emphasis: Data & Surveillance

• Chronic underreporting of snakebite cases globally
• Need for standardized national surveillance and mandatory hospital reporting
• Progress in snakebite envenomation data reporting reviewed in December 2024
• Data gaps undermine antivenom procurement, deployment, and health system planning

Summary: What's New vs. Unchanged

• WHO Improving Treatment for Snakebite Patients
• WHO Novel Therapeutics TPP - Feb 2026
• WHO Guidelines for Management of Snakebites, 2nd Ed. (core clinical reference)
• JTS Snakebite CPG v1.1 - April 2026
• Huang et al. (2025), heparin meta-analysis PMID: 39749494