Cardiology Notes - 29 Bradycardia

29.1 Note

# Bradycardia
- Defined as non-physiologic sinus rate of less than 50 bpm and/or sinus pauses of >3 s (2018 Guidelines)
- Symptomatic?
  - If not, no increased risk for incident CVD/mortality (Dharod et al., 2016); no need for further Tx or ppm
  - If Sx, risk for syncope, incident AFib, and HF -> if chronic Sx sinus node dysfunction, will need ppm
    - Atropine: first dose is 0.5 mg bolus; can repeat q3-5 mins (max = 3g, i.e. 6x)
- History and evaluation to identify potential reversible causes
- Medication review: ***
- 12-lead ECG
  - look for structural heart dz, conduction disturbance (e.g. AV block), etc.
  - Development of LBBB is assoc w/ structural heart disease and ↑ mortality
- Echo
  - Class I rec if new LBBB, Mobitz Type II AV block, high grade AV block or complete AV block
- If HD unstable or risk of asystole -> temporary pacing may be needed
- Consider ambulatory ECG monitoring to establish Dx or identify Sx-rhythm correlation
- Consider exercise testing if Sx are temporally related to exercise, ASx 2nd degree AV block, or suspected chronotropic incompetence
- Treat/Evaluate for sleep-disordered breathing
  - Class I rec if nocturnal bradycardia and documented/suspected sleep-disordered breathing
  - Tx of sleep apnea can result in 90% reduction in bradycardia events (Becker et al., 1995)
- Labs:
  - TSH w/ reflex
  - CMP
  - Lyme titers
- Defer genetic testing at this time as yield likely to be low
  - If suspected inherited condition, can consider w/ assistance of genetic counselor

See different types of heart monitors in Chapter 13.
Check for end-organ perfusion
BP - check for hypOtension, HD instability
QRS
- if wide, suggests escape rhythm (bad!)
  - May need to get the dopamine going and begin coordinating for pacing
- if narrow, good (relatively)
Syncope - bad if present

29.2 Overnight Treatment Options

Atropine
- unlikely to be successful if block below AV node
- rarely useful in complete heart block
Transcutaneous pacing
- temporary measure
- uncomfortable for patient
- can be used transiently if HD unstable
Chronotropic medications, e.g. dopamine, dobutamine, and isoproterenol
Transvenous pacing

29.3 Temporary transvenous pacemaker

1. Venous access

2. Setting up your generator

3. Floating the pacer wire

4. Ensure pacemaker capture and adjustment

1. Rate: usually 20 above intrinsic (80 bpm)

2. Output: once ECG capture, decrease mA to find minimum threshold for capture, then increase 2-3 times that

3. Sensitivity (mV): the higher the sensitivity, the lower threshold to pick up intrinsic rhythm. Usually decrease to half of the sensitvity threshold.

Instructions and details on bedside placemet at Taming the SRU

29.4 Symptoms

Common symptoms of bradycardia include syncope, presyncope, transient dizziness or lightheadedness, fatigue, dyspnea on exertion, heart failure symptoms, or confusion resulting from cerebral hypoperfusion. (Sidhu and Marine 2020)

29.5 Causes

Sinus brady occurs in 15-25% of pts w/ acute MI (See Chapter 19), particular if it involves the RCA because it supplies the SA node in ~60% of folks.

Conditions associated with bradycardia and conduction disorders. (Sidhu & Marine, 2020)
General cause	Conditions
Autonomic dysfunction	Carotid sinus hypersensitivity Neurally-mediated syncope Situational syncope
Cardiomyopathy	Ischemic Non-ischemic Infiltrative
Congenital ❤️ disease \| \| \| \| \|
Degenerative
Infection	Lyme disease Infective endocarditis Chagas disease
Ischemia/Infarction - esp. inferior MI
Meds/Drugs	anti-HTN: BBs, verapamil, diltiazem anti-arrhythmics: amio, dronedarone, sotalol, digoxin psychoactive: phenothiazines, opioids, TCAs
Metabolic/Endocrine	Acidosis hypO- or hyperK hypOthyroid, hypOadrenal state hypOthermia hypOxia
Rheumatologic	RA Scleroderma SLE
Surgical/traumatic	Catheter ablation Surgical correction of congenital ❤️ dz \| Valve surgery Septal myectomy/Alcohol septal ablation

29.5.1 Drugs associated with Bradycardia

Very comprehensive list of Drug-Induced Arrhythmias (AHA Scientific Statement) (Tisdale et al. 2020)

Drugs that may cause/exacerbate Sinus Bradycardia/AV Block
Drug Class	Drug(s)	MOA
Acetylcholinesterase Inhibitor	Donepezil, Neostigmine, Physostigmine, Pyridostigmine	Stimulation of activity of the parasympathetic nervous system, leading to inhibition of automaticity of sinus node
Anesthetic	Bupivacaine, Propofol	Reduction in sympathetic activity
Antiarrhythmic	Adenosine, Amiodarone, Disopyramide, Dronedarone, Flecainide, Ivabradine, Propafenone, Quinidine, Sotalol	Node inhibition
Anticancer	Thalidomide
Antidepressant	Citalopram, Escitalopram, Fluoxetine	Na⁺ and Ca²⁺ inhibition
Antihypertensive	Clonidine, β-Blockers (including eye drops), Diltiazem, Verapamil	Clonidine: Stimulation of central α₂-receptors, reducing release of norepinephrine β-Blockers and non-DHP CCBs: inhibition of automaticity of sinus node
Inotrope	Digoxin	↑ vagal tone
Sphingosine 1-phosphate receptor modulator	Fingolimod	Modulation of the sphingosine 1-phosphate receptors
Vasodilator/antiplatelet	Dipyridamole	Increased adenosine leading to direct sinoatrial/atrioventricular node inhibition

29.6 Pharmacotherapy

Medications to treat bradycardia (Sidhu & Marine, 2020)
Medication	Utility
Atropine	A parasympatholytic drug that can affect sinoatrial conduction, sinus node automaticity, and AV conduction.
Isoprotenerol, Dopamine, Dobutamine, Epinephrine	Direct stimulation of beta-receptors to increase sinus node automaticity and AV conduction. Should use with caution if concerned for coronary ischemia.
Intravenous calcium	Can be used if bradycardia is attributed to calcium channel blocker overdose.
Glucagon	Can be used if bradycardia is attributed to calcium channel blocker or beta-blocker overdose. May cause nausea and vomiting.
High dose insulin	Can be used if bradycardia is attributed to calcium channel blocker or beta-blocker overdose. Risk of hypoglycemia.
Aminophylline	Can be used in heart transplant patients, spinal cord injury, or inferior MI with AV block.