Bradycardia – Management

Acute Management

Approach to Management:

Hemodynamically Unstable Patient:

  1. Follow ACLS Algorithm
  2. Administer atropine 0.5mg IV q3-5 minutes for a total dose of 3mg.
    • Note: atropine increases sinus rate and can worsen infra-Hisian block due to increased activation of diseased tissue. 
    • Many cardiologists skip atropine administration
  3. Consider administrating ONE of the following chronotropic agents if the patient remains symptomatic despite atropine, and temporary pacing is not available or is unsuccessful.
    • Epinephrine 2-10 mcg/min IV infusion titrate to effect.
      • Usual dose is 0.1-0.5 mcg/kg/min.
    • Dopamine 2-20mcg/kg/min IV infusion, can titrate to a maximum of 50mcg/kg/min for response (note that doses >20mcg/kg/min may increase the risk of tachyarrhythmias)
    • Isoproterenol 2-10mcg/min continuous IV infusion, titrate to response.
  4. Initiate temporary cardiac pacing: (see below for indication for temporary pacing)
    1. Transcutaneous OR
    2. Transvenous

If drug toxicity is suspected, use the appropriate antidote.  See table.

AHA 2020 - Adult Bradycardia Algorithm
AHA 2018: Acute Medical Management of Bradycardia Attributable to SND or Atrioventricular Block

Transvenous / Transcutaneous Pacing

  • Indications: 
    • Medically refractory symptomatic or hemodynamically unstable bradycardia (includes markers of cardiogenic shock)
    • Bradycardia associated with a long QT
    • Unreliable escape rhythm
      • Junctional escape: more stable, usually faster escape rates (>40 BPM).  Identified by narrow QRS or QRS identical to prior sinus rhythm. Can defer temporary transvenous pacemaker if no other indication.
      • Ventricular escape: less reliable, Wide QRS, usually slower than 40bpm.  Almost always require a temporary transvenous pacemaker.
  • NOTE: Many patients with AV block or other bradycardias experience syncope or a cardiac arrest not from bradycardia itself, but secondary to the resultant long QT, which can lead to Torsades de pointes. (see ECG)
  • Transcutaneous pacing
    • Temporizing measure – energy is delivered through pads applied to the chest.
    • If the patient is conscious, they MUST be sedated because transcutaneous pacing can be very uncomfortable (i.e. midazolam and fentanyl)
    • Mechanical capture must be confirmed by palpating a central pulse.  Contraction of the chest wall muscles does not suggest capture of myocardium. 
  • Transvenous pacing
    • A central line with an electrical lead passed into the RV cavity. 
    • Two types exist:
      • Soft Balloon-Tipped Wire –  has an inflatable balloon, which can be floated with the bloodflow into the RV.  Fluroscopy/X-Ray is not required.  Patients with tricuspid regurgitation may be particularly challenging.
      • Hard Wire – Need intra-procedural fluoroscopy/X-Ray because the wire is stiff.  Hard wires are more stable, but can perforate the heart. 

Pacing Indications

  • The mainstay of treating bradycardia is pacemaker implantation
  • Any symptomatic bradycardia requires pacing.  Some bradycardias have a good prognosis (AV nodal), and risks/benefits of pacemaker for symptomatic relief need to be discussed. 
  • However, certain conditions carry a poor prognosis, marked by progressive conduction system disease.  For those conditions, symptoms are not required, and pacing is indicated prophylactically:
    • Infra-His block (i.e. Mobitz II, most complete AV block etc..), and alternating bundle branch blocks. 
    • Conditions must be irreversible
  • Can consider EP study or empiric pacing for syncope + bundle branch block
Summarized from AHA 2019 Pacing Guidelines
Indications for pacing
  1. Symptomatic bradycardia
  2. If NO symptoms:
    1. High-grade AV block
    2. Mobitz II 
    3. Complete AV Block
    4. Alternating bundle branch blocks (RBBB and LBBB)

***MUST BE IRREVERSIBLE

Myocardial Infarction and AV block

  • Class I Indications:
    • Patients presenting with an acute MI with Mobitz type II second-degree AV block, high-grade AV block, alternating bundle-branch block, or third-degree AV block (persistent or infranodal), permanent pacing is indicated after a waiting period.
  • NO pacing required (Class III) for:
    • Acute MI and transient AV block that resolves.
    • Acute MI with new BBB or isolated fascicular block in absence of second or third-degree AV block.
  • Patients with inferior (RCA) STEMI commonly present with AV block.  
    • The most common mechanism is Bezold–Jarisch reflex, which is a neurologically (vagal) mediated AV block at the level of the AV node. 
      • This is usually temporary and does not require pacing. 
      • Atropine can be used for temporary control if the patient is symptomatic.  
      • Chronotropic drugs need to be avoided because they can increase myocardial demand, which may increase infarct size.
      • Temporary transvenous pacing wires are avoided due to the theoretical risk of perforating an ischemic RV.  However, transvenous pacing may be required if the patient has hemodynamically unstable bradycardia.
    • An acute STEMI can cause AV nodal ischemia and result in AV block.  This usually resolves, and is very uncommon due to dual blood supply to the AV node. 

Pre-Pacemaker Workup

  • History/physical to rule out active infection and reversible causes
  • Echocardiogram to assess LVEF if the patient is a candidate for ICD/CRT, and rule out ASD/PFO.
  • Laboratory investigations to rule out reversible metabolic causes
  • ** Young patients with AV block must be carefully evaluated for secondary conditions, such as connective tissue diseases, autoimmune diseases, and sarcoidosis.
    • Sarcoidosis with cardiac involvement is an important cause of AV block.  A screening chest X-ray is reasonable and possibly a CT chest to assess for mediastinal lymphadenopathy.   Sarcoidosis can be confirmed with a cardiac MRI and/or biopsy.  
    • It is preferable to obtain a cardiac MRI prior to device implantation, as metal artifact can make interpretation challenging.
  • Authors: Drs. Yehia Fanous (MD, FRCPC, Internal Medicine Resident), Atul Jaidka (MD, FRCPC, Cardiology Fellow), Dr. Pavel Antiperovitch (MD, FRCPC, EP Fellow)
  • Staff Reviewer: Pending (MD, FRCPC[Cardiology])
  • Copy Editor: Pending 
  • Last Updated: February 25, 2021
  • Comments or questions please email feedback@cardioguide.ca