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Approach to the Critical Patient
Immediate priorities
Unstable bradyarrhythmia approach
Airway compromise
If apnea or severe hypoventilation, bag valve mask and advanced airway pathway
Oxygenation and ventilation targets
SpO2 94 to 98 percent
Perfusion failure features
Hypotension
Altered mental status
Ischemic chest discomfort
Acute pulmonary edema
If perfusion failure features present, immediate ACLS bradycardia algorithm pathway
Monitoring and access
Cardiac monitor with pacing capability
Defibrillator pads in anterior posterior position
Noninvasive blood pressure cycling every 1 to 3 minutes
If shock or vasoactive infusion, arterial line when feasible
IV access
Two large bore peripheral IV lines
Point of care glucose
If hypoglycemia, immediate dextrose therapy
Rhythm confirmation workflow
12 lead ECG within 10 minutes
Rate
PR interval
QRS width
AV association
If bradycardia with wide QRS, high likelihood infranodal disease
Higher risk atropine failure
If second degree Mobitz II or third degree AV block, pacing first strategy
Atropine not relied on as definitive therapy
Rapid causes and reversible triggers
Immediate reversible causes screen
Ischemia or infarction
STEMI pathway if indicated
Drugs and toxicologic
Beta blockers
Calcium channel blockers
Digoxin
Antiarrhythmics
Opioids or sedatives
Hypoxia
Airway or ventilation failure
Electrolyte abnormality
Hyperkalemia
Hypothermia
Endocrine
Hypothyroidism myxedema
Increased vagal tone
Vomiting
Pain
Carotid sinus hypersensitivity
ECG based classification
Bradyarrhythmia patterns
Sinus bradycardia
P waves present with fixed PR
Junctional rhythm
Absent or inverted P waves
Ventricular escape rhythm
Wide QRS with very slow rate
First degree AV block
PR over 200 ms
Second degree AV block Mobitz I
Progressive PR prolongation then dropped QRS
Second degree AV block Mobitz II
Fixed PR with intermittent dropped QRS
High grade AV block
Two or more consecutive nonconducted P waves
Third degree AV block
AV dissociation with independent atrial and ventricular rates
History
Symptom pattern and timeline
Presenting syndrome
Syncope or near syncope
Exertional syncope
Supine syncope
Dizziness or lightheadedness
Positional association
Dyspnea
Orthopnea
Paroxysmal nocturnal dyspnea
Chest pain
Typical ischemic features
Palpitations with pauses
Post tachycardia pauses
Fatigue and exercise intolerance
New functional decline
Time course clues
Sudden onset minutes to hours
Ischemia
Drug ingestion
Subacute days to weeks
Myocarditis
Lyme disease exposure
Chronic months to years
Degenerative conduction disease
Sleep apnea related bradycardia
Risk factors and context
Conduction disease risks
Known structural heart disease
Prior MI
Cardiomyopathy
Prior cardiac surgery
Valve surgery
Transcatheter aortic valve implantation history
New conduction delay risk
Infiltrative or inflammatory disease
Sarcoidosis
Amyloidosis
Chagas disease
Medication and toxin exposures
Recent dose change
Beta blocker up titration
Calcium channel blocker up titration
Polypharmacy with AV nodal blockade
Beta blocker plus nondihydropyridine calcium channel blocker
Digoxin use
Renal dysfunction or dehydration
Infectious exposure
Tick exposure and rash
Lyme carditis concern
Viral prodrome
Myocarditis concern
Physical Exam
Hemodynamic and perfusion findings
Perfusion assessment
Blood pressure trend
MAP under 65 mmHg
Mental status
Confusion or decreased responsiveness
Skin
Cool clammy
Delayed capillary refill
Urine output history
Oliguria
Respiratory status
Work of breathing
Accessory muscle use
Lung exam
Rales suggesting pulmonary edema
Cardiac exam
Heart sounds
Cannon A waves suspicion with AV dissociation
JVP
Elevated with heart failure
Peripheral edema
Volume overload
Clues to cause
Ischemia clues
Diaphoresis
Associated chest discomfort
Toxicologic clues
Miosis
Opioid exposure
Wheeze or bronchospasm
Beta blocker toxicity
Endocrine and temperature
Hypothermia
Shivering or low measured temperature
Hypothyroid features
Dry skin
Periorbital edema
Neurologic
Focal deficits
Stroke pathway if present
Differential Diagnosis
Life threatening and time sensitive
Critical causes of bradycardia
Acute coronary syndrome with conduction involvement
Inferior MI with AV nodal ischemia
Anterior MI with infranodal block
Complete heart block
ICD 10 I44.2
High grade AV block
ICD 10 I44.1
Sick sinus syndrome
ICD 10 I49.5
Hyperkalemia
ICD 10 E87.5
Beta blocker poisoning
ICD 10 T44.7X1A
Calcium channel blocker poisoning
ICD 10 T46.1X1A
Digoxin toxicity
ICD 10 T46.0X1A
Myocarditis
ICD 10 I40.9
Cardiac tamponade
ICD 10 I31.4
Mimics and related syndromes
Non conduction etiologies presenting with low pulse
Frequent PVCs with pulse deficit
Apparent bradycardia on palpation
Atrial fibrillation with slow ventricular response
AV nodal blocker effect
Vasovagal syncope
Transient bradycardia
Increased intracranial pressure
Cushing response
Laboratory Tests
Core labs for unstable or symptomatic bradycardia
Initial laboratory panel
Electrolytes
Potassium in mmol/l
Magnesium in mmol/l
Calcium in mmol/l
Renal function
Creatinine for drug clearance risk
Glucose
Hypoglycemia as reversible cause
CBC
Anemia contributing to demand ischemia
Venous blood gas
pH
pCO2 in mmHg
Cardiac ischemia labs
High sensitivity troponin per local pathway
Rising pattern supporting ACS
BNP or NT proBNP if heart failure suspected
Volume overload correlation
Targeted labs by suspected cause
Cause directed labs
TSH if hypothyroidism suspected
Myxedema coma support
Digoxin level if digoxin exposure
Timing at least 6 hours after last dose if possible
Serum osmolality and tox screen when ingestion unclear
Co ingestants that worsen hypotension
Lyme serology when compatible exposure
ECG findings plus systemic signs
Pitfalls and interpretation
Laboratory limitations
Normal troponin does not exclude conduction system ischemia early
Serial testing with ECG trend
Potassium measurement delays in severe instability
Empiric hyperkalemia therapy when ECG suggests
Drug levels availability delays
Clinical toxidrome driven treatment
Diagnostic Tests
Scoring Systems
Risk stratification adjuncts
Syncope risk tools when syncope is presenting complaint
Canadian Syncope Risk Score framework use
Admission preference if high risk features
ECG risk features for malignant bradyarrhythmia
QRS 120 ms or more suggesting infranodal block
Escape rhythm under 40 per minute
Pauses 3 seconds or more with symptoms
MRI
Cardiac MRI indications
Suspected myocarditis
Conduction disease with viral prodrome
Suspected cardiac sarcoidosis
AV block in younger patient without other cause
Suspected amyloidosis
Low voltage ECG plus heart failure signs
MRI practical constraints
Hemodynamic instability
Deferred until stabilized
Temporary pacing hardware
MRI conditional device requirements
CT
CT indications related to bradycardia presentation
CT pulmonary angiography if PE suspected
Hypoxia with risk factors
CT head if new focal neurologic deficit or head trauma from syncope
Anticoagulation use increases bleed risk
CT chest for aortic pathology if suggestive chest pain and pulse deficit
Secondary conduction abnormalities possible with ischemia
CT limitations
Contrast nephropathy risk
Renal dysfunction mitigation
Ultrasound (or US)
Point of care ultrasound applications
Cardiac POCUS for shock with bradycardia
Pericardial effusion and tamponade physiology
Global LV systolic function
Lung ultrasound for dyspnea
B lines supporting pulmonary edema
IVC assessment
Volume status adjunct
POCUS pitfalls
Normal LV function does not exclude ischemia
ECG and troponin correlation
Disposition
Level of care decisions
Admission indications
Symptomatic bradycardia requiring intervention
Atropine response with recurrence risk
Mobitz II or high grade AV block
Telemetry and pacing capability
Third degree AV block
ICU or monitored unit with immediate pacing access
Suspected ACS
Cardiology admission pathway
ICU indications
Need for transcutaneous pacing
Frequent capture loss or high thresholds
Need for vasoactive infusion
Epinephrine or dopamine infusion
Need for transvenous pacing
Bridge to permanent pacemaker
Transfer and follow up
Transfer triggers
No transvenous pacing capability locally
Immediate transfer after stabilization
STEMI with bradyarrhythmia
PCI capable center transfer
Discharge criteria for benign bradycardia
Asymptomatic sinus bradycardia with stable vitals
Athlete baseline pattern
First degree AV block without symptoms
Outpatient follow up
Clear reversible medication cause corrected with stable observation period
Shared decision making and close follow up
Treatment
ACLS symptomatic bradycardia pathway
Initial temporizing therapy
Atropine
1 mg IV or IO bolus
Repeat every 3 to 5 minutes
Maximum total 3 mg
Lower expected efficacy in infranodal block
Mobitz II
Third degree AV block with wide QRS
Transcutaneous pacing
If unstable and atropine ineffective or inappropriate
Set rate 60 to 80 per minute
Increase mA until capture then 10 percent above threshold
Analgesia and sedation if conscious
Fentanyl IV titration in small aliquots
Close respiratory monitoring
Midazolam IV titration in small aliquots
Hypotension risk
Epinephrine infusion
2 to 10 microg per minute IV infusion
Titrate to perfusion targets
Tachyarrhythmia risk monitoring
Dopamine infusion
5 to 20 microg per kg per minute IV infusion
Titrate to perfusion targets
Extravasation precautions
Escalation therapy
Transvenous pacing
If high grade block with instability or refractory to above
Bridge to permanent pacing evaluation
Early cardiology and electrophysiology consultation
High grade AV block
Suspected pacemaker indication
Cause specific therapies
Hyperkalemia with ECG changes
Calcium gluconate IV
Repeat dosing guided by ECG response
Continuous ECG monitoring
Insulin with dextrose
Frequent glucose checks
Hypoglycemia prevention
Nebulized beta agonist
Tachycardia expected
Dialysis pathway for refractory or severe renal failure
Emergent nephrology activation
Beta blocker toxicity
Glucagon IV
Nausea and vomiting prophylaxis
High dose insulin euglycemia therapy
ICU monitoring required
Vasopressors
Epinephrine or norepinephrine titration
Calcium channel blocker toxicity
Calcium chloride or calcium gluconate IV
Repeat dosing guided by hemodynamics
High dose insulin euglycemia therapy
ICU monitoring required
Vasopressors
Norepinephrine titration
Digoxin toxicity
Digoxin specific antibody fragments
Indications
Life threatening arrhythmia
Severe hyperkalemia
Myxedema coma suspected
Levothyroxine IV per institutional protocol
Adrenal insufficiency coverage
Hydrocortisone IV before thyroid hormone
Permanent pacing indications overview
Permanent pacemaker considerations
Class I indications per guideline based recommendations
Symptomatic sinus node dysfunction with correlation
Syncope with documented pauses
Acquired Mobitz II second degree AV block not due to reversible cause
High risk progression
Acquired high grade AV block not due to reversible cause
Two or more consecutive nonconducted P waves
Acquired third degree AV block not due to reversible cause
Persistent AV dissociation
Reversible cause exclusion before permanent device
Medication effect corrected
Ischemia treated
Metabolic cause corrected
Special Populations
Pregnancy
Pregnancy specific considerations
Hemodynamic interpretation
Lower baseline blood pressure
Higher baseline heart rate
Pacing considerations
Transcutaneous pacing safe when indicated
Transvenous pacing with obstetric input for fluoroscopy minimization
Medication considerations
Atropine use for symptomatic bradycardia when indicated
Vasopressor infusion maternal fetal monitoring
Geriatric
Older adult considerations
Degenerative conduction disease prevalence
Higher risk Mobitz II and complete heart block
Polypharmacy risk
AV nodal blockers and drug interactions
Atypical presentation
Falls as syncope equivalent
Disposition bias toward observation or admission
Silent ischemia risk
Pediatrics
Pediatric considerations
Normal heart rate varies by age
Relative bradycardia definition age dependent
Common causes
Hypoxia
Hypothermia
Increased vagal tone
Pacing and medication pathways
Pediatric ACLS dosing differs from adult
Early pediatric critical care involvement
Background
Epidemiology
Frequency and distribution
Bradyarrhythmia common in older adults
Degenerative fibrosis of conduction system
Higher grade AV block risk with structural heart disease
Prior MI association
Sinus bradycardia common in athletes and during sleep
Often benign when asymptomatic
Pathophysiology
Mechanisms
Sinus node dysfunction
Failure of impulse initiation
Tachy brady syndrome with pauses
AV nodal conduction delay
First degree and Mobitz I patterns
Infranodal conduction disease
His Purkinje disease producing Mobitz II and wide QRS escape
Escape rhythms
Junctional escape typically narrow QRS
Ventricular escape typically wide QRS and less reliable
Therapeutic Considerations
Therapy principles
Symptom driven and perfusion driven escalation
Asymptomatic bradycardia often no acute therapy
Atropine mechanism
Antimuscarinic increasing SA and AV nodal conduction
Pacing as definitive temporization for high grade block
Transcutaneous then transvenous as needed
Guideline concept
Permanent pacing for symptomatic or high risk conduction disease not due to reversible cause
Patient Discharge Instructions
copy discharge instructions
Discharge guidance for low risk bradycardia
Medication plan
Do not restart held AV nodal blockers unless clinician advises
Bring all medications to follow up visit
Follow up
Primary care or cardiology within 3 to 7 days
Ambulatory monitoring plan if arranged
Return to ED now
Fainting or near fainting
Chest pain
Shortness of breath
New confusion or weakness
Palpitations with dizziness
Persistent heart rate under 50 per minute with symptoms
References
Clinical guidelines and algorithms
Key guidelines
AHA Adult Bradycardia With a Pulse Algorithm 2025
Atropine 1 mg IV IO bolus repeat every 3 to 5 minutes maximum 3 mg
Epinephrine infusion 2 to 10 microg per minute
Dopamine infusion 5 to 20 microg per kg per minute
2018 ACC AHA HRS Guideline on Bradycardia and Cardiac Conduction Delay
Permanent pacing indicated for acquired Mobitz II high grade or third degree AV block not due to reversible causes
2021 ESC Guidelines on Cardiac Pacing and Cardiac Resynchronization Therapy
Pacing recommendations for AV block and device strategies in structural heart disease
Coding references
Diagnostic coding anchors
Sinus bradycardia ICD 10 R00.1
SNOMED CT sinus bradycardia concept
First degree AV block ICD 10 I44.0
SNOMED CT first degree atrioventricular block concept
Second degree AV block ICD 10 I44.1
SNOMED CT second degree atrioventricular block concept
Complete heart block ICD 10 I44.2
SNOMED CT complete atrioventricular block concept
Sick sinus syndrome ICD 10 I49.5
SNOMED CT sinus node dysfunction concept
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.