bradycardia

• related: syncope, Cardiology, Arrythmia
• tag: #note

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definition

• HR < 60

causes

• problems with
  • SA node
  • AV node or purkinje
  • extrinsic: vagal tones

SA node dysfunction

sinus bradycardia

• normal: trained athletes, sleep
• pathological:
  • right coronary ischemia
  • age related myocardial fibrosis
  • intracranial hypertension
  • postop scarring
  • infiltrative disease: sarcoidosis
  • sleep apnea: nocturnal bradycardia
  • electrolytes
  • hypothyroidism
  • medications
    • BB
    • donepezil, neostigmine, pyridostigmine
    • digoxin

Other types of sinus node dysfunction

• sinus arrest, junctional escape rhythm

• sinus with pauses

• tachy brady syndrome: SVT/af/aflutter, sinus node shut down from fibrosis/rate control blockade/suppression. At time of conversion, goes into long pauses

• sinoatrial exit block: failure of impulse to exit SA

• secondary sinoatrial exit block:

  • failure of p wave to form
    • 
  • p to p shortening, followed by drop beat

• Sx

  • usually asymptomatic, syncope, fatigue, lightheadedness, dyspnea

• Treatment

  • symptomatic patient: pacemaker
  • atrial based pacing support
  • most patient get RV lead for backup
  • high vagal tone: very dramatic bradycardia with normal HR between episodes
    • sinus slowing before bradycardia
    • 
    • nausea, vomiting, diaphoretic
  • SA node dysfunction: lower HR at baseline

AV nodal block

1st degree

• PR > 200 ms
• no treatment

3rd degree

• AV dissociation in HIS purkinje
• sx determined by rate of escape
• pause dependent VT: torsades de pointe => syncope

2nd degree

• AV node itself
• causes:
  • lupus
  • lyme
  • iatrogenic: AV ablation, pacemaker placement
• Mobitz 1: progressively longer PR, then dropped beat, regularly irregular
  • before/after drop beat, changes in PR the greatest
  • canon A waves, progressively softer 1st heart sound
  • 
• Mobitz 2: HIS purkingje
  • fixed PR
  • dropped beat
  • wide QRS
• 2:1 weckeback: Mobitz 1 has narrow QRS. Mobitz 2 has wide QRS
• walk the patient: increase sympathetic tone. Type 1 gets better on atropine. Type 2 does not change
• Type 2: prophylactic pacing

treatment

Inpatient

• symptomatic: give atropine first
• dopamine gtt second line
• epinephrine gtt 3rd line
• transcutaneous pacing or temporary pacing wire (preferred) placement if unstable or asystole

Outpatient

• pacemaker indications
  • symptomatic bradycardia with no reversible cause
  • permanent afib with symptomatic bradycardia
  • alternating BBB
  • 3rd degree block, Mobitz 2, high degree AV block (>1 nonconducted P)
• treat if EF < 40%
• biV pacemaker because RV pacing alone = worse EF
• Pace RV: wide QRS, LBBB
• if RBBB develops followed by pacing: biV pacemaker
• < 30%: ICD CRT biV pacing
• CXR: pacemaker = skinny. atrial = ventricular
• icd: coil at RV insertion
• Biv: 3rd lead, RV anterior, LV posterior