Emergency Medicine Hub / Cardiovascular Emergencies • 3 min read • 3 sections

Bradycardias, Conduction Blocks & Emergency Cardiac Pacing

Emergency management of symptomatic bradycardias and high-grade atrioventricular (AV) blocks: sinus node dysfunction, 1st degree, Mobitz I, Mobitz II, 3rd degree (complete) heart block, trifascicular block, atropine dosing, chronotropic infusions (epinephrine/dopamine), transcutaneous pacing (TCP) technique, and transvenous pacing (TVP) catheter placement.

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Assess Instability

SBP < 90, altered mental status, ischemic chest discomfort, acute decompensated heart failure, or signs of shock.

Initial Pharmacotherapy

Atropine 1 mg IV push; repeat q3-5min up to max 3.0 mg. Note: Ineffective in heart transplant (denervated heart) and infranodal Mobitz II/3rd degree wide-complex blocks.

Second-Line Chronotropic Infusions

Epinephrine infusion 2-10 mcg/min OR Dopamine infusion 5-20 mcg/kg/min.

Transcutaneous Pacing (TCP)

Apply pacing pads in anterior-posterior orientation. Set rate to 60-80 bpm. Increase current (mA) from 0 until electrical capture is confirmed (wide QRS followed by broad T wave). VERIFY mechanical capture via femoral or right radial pulse palpation (do NOT check carotid pulse due to muscular twitches). Administer fentanyl/midazolam for sedation.

Trifascicular Block

Prolonged PR interval + Right Bundle Branch Block (RBBB) + Left Anterior Fascicular Block (LAFB) or Left Posterior Fascicular Block (LPFB). High risk of progression to complete heart block; requires admission for permanent pacemaker evaluation.

Transcutaneous & Transvenous Pacing

Transcutaneous pacing delivers pacing current via anterior-posterior pads; transvenous pacing involves catheter placement into RV via right IJ.

Bottom-Line Clinical Pearl

In symptomatic or unstable bradycardia (hypotension, AMS, chest pain, acute pulmonary edema), give Atropine 1 mg IV push q3-5min (max 3 mg). If infranodal block (Mobitz II or Complete Heart Block with wide escape) or no response to atropine, IMMEDIATELY initiate Transcutaneous Pacing while preparing a continuous Epinephrine infusion (2-10 mcg/min) or Transvenous Pacing.

CRITICAL WARNING: Electrical vs. Mechanical Capture in Pacing

Seeing pacing spikes followed by wide complexes on the cardiac monitor confirms electrical capture only. Muscle contractions of the chest wall can mimic a peripheral pulse. You MUST verify mechanical capture by manually palpating the right femoral pulse or observing a pulsatile arterial line/pulse oximeter plethysmograph waveform that matches the paced heart rate.

Atrioventricular Conduction Blocks: Localization & Treatment

Block Type	ECG Characteristics	Anatomic Level of Block	Response to Atropine	Definitive Management
1st Degree AV Block	PR interval > 200 ms (5 small boxes); every P wave conducted	AV Node	Responds (if needed)	Benign; observe unless associated with acute MI or medication toxicity
2nd Degree Mobitz I (Wenckebach)	Progressive PR prolongation until a P wave fails to conduct; grouped beating	AV Node (supra-Hisian)	Usually responds to atropine	Observe if asymptomatic; temporary pacing rare; treat reversible ischemia
2nd Degree Mobitz II	Constant PR interval before dropped QRS complexes; sudden non-conducted P waves	Bundle of His/Purkinje system (infranodal)	Rarely responds (may paradoxically worsen block)	High risk of sudden complete block; immediate transcutaneous pacing pads; cardiology consult for permanent pacemaker
3rd Degree (Complete) Heart Block	Complete AV dissociation; P-P intervals regular; R-R intervals regular; no relationship between P and QRS	AV node (narrow escape) or infranodal His-Purkinje (wide escape, rate 20-40 bpm)	Unreliable; poor in infranodal block	Transcutaneous pacing -> temporary transvenous pacing catheter -> permanent dual-chamber pacemaker
Trifascicular Block	RBBB + LAFB/LPFB + 1st degree AV block OR alternating RBBB and LBBB	Diffuse His-Purkinje conduction disease	Ineffective	Continuous telemetry monitoring, transcutaneous pacing on standby, admission for urgent electrophysiology pacemaker placement

Emergency Transvenous Pacing (TVP) Procedure Protocol

Indicated for hemodynamically unstable bradycardia refractory to medical therapy and transcutaneous pacing, or high-grade blocks with wide escape rhythms:

1. Vascular Access: Right internal jugular vein (preferred, direct anatomical line to tricuspid valve) or left subclavian vein using a 6 Fr cordis introducer sheath under ultrasound guidance. 2. Catheter Insertion: Advance the balloon-tipped bipolar pacing catheter through the cordis to 15-20 cm. Inflate the balloon with 1.5 mL of air. 3. Advancement & Capture: Connect pacing cable to pulse generator (set rate 80 bpm, output 20 mA, sensitivity asynchronous VOO or demand VVI). Advance catheter into right ventricle. Electrical capture is evidenced by immediate transition to a left bundle branch block (LBBB) morphology with negative QRS complexes in V1-V2 (confirming RV pacing). Deflate the balloon and secure catheter at depth (usually 40-45 cm from RIJ). 4. Threshold Testing: Lower mA until capture is lost (capture threshold); set permanent pacing output at 2.5 to 3 times the capture threshold.

Critical Electrophysiology Pitfalls

Giving atropine for wide-complex complete block: Atropine increases sinus node rate; in infranodal complete block, increasing atrial rate without improving AV conduction can worsen conduction block and induce ventricular standstill.
Relying on carotid pulse to check pacing capture: Violent pectoral muscle twitches from transcutaneous pacing transmit mechanical pulsation to the neck, falsely simulating carotid pulses; always check femoral pulse.
Giving beta-blockers or calcium channel blockers in Mobitz II: Precipitates complete heart block and asystole.

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