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Second-Degree AV Block (Mobitz II)
Cardiovascular Presentations
Abdominal aortic aneurysm
Acute coronary syndrome (NSTEMI)
Acute coronary syndrome (STEMI)
Acute decompensated heart failure
Acute limb ischemia
Acute mesenteric ischemia
Aortic dissection
Aortic stenosis
Atrial fibrillation and flutter
Bradyarrhythmia and heart block
Cardiac arrest
Deep vein thrombosis
Myocarditis
Pericarditis
Pulmonary embolism
Stable angina
Superficial thrombophlebitis
Superior vena cava syndrome
Supraventricular tachycardia
Syncope (cardiogenic)
Unstable angina
Ventricular tachycardia
Respiratory Presentations
Acute bronchitis
Acute respiratory failure
Aspiration pneumonia
Asthma exacerbation
Bronchiolitis
Community-acquired pneumonia
COVID-19 pneumonia
COPD exacerbation
Croup
Croup (laryngotracheobronchitis)
Epiglottitis
Hemothorax
Hospital-acquired pneumonia
Pleural effusion
Pneumothorax (traumatic)
Pulmonary contusion
Spontaneous pneumothorax
Neurological Presentations
Bell's palsy
Benign paroxysmal positional vertigo
Brain abscess
Cauda equina syndrome
Cervical radiculopathy
Concussion (mild traumatic brain injury)
Encephalitis
Guillain-Barré syndrome
Hemorrhagic stroke (intracerebral)
Ischemic stroke
Lumbar radiculopathy
Malignant spinal cord compression
Migraine
Peripheral neuropathy (acute)
Retropharyngeal abscess
Schizophrenia (acute exacerbation)
Seizure (breakthrough:known epilepsy)
Seizure (first-time)
Spinal cord injury
Status epilepticus
Subarachnoid hemorrhage
Tension headache
Transient ischemic attack
Traumatic brain injury (moderate-severe)
Vestibular neuritis
Viral meningitis
Gastrointestinal Presentations
Acute appendicitis
Acute cholecystitis
Acute diverticulitis
Acute pancreatitis
Anal fissure
Choledocholithiasis and cholangitis
Clostridioides difficile colitis
Gastritis
Gastroenteritis (viral and bacterial)
Gastroesophageal reflux disease
Incarcerated or strangulated hernia
Inflammatory bowel disease flare
Large bowel obstruction
Lower GI hemorrhage
Peptic ulcer disease
Perforated viscus
Small bowel obstruction
Upper GI hemorrhage
Genitourinary and Reproductive Presentations
Acute prostatitis
Acute urinary retention
Ectopic pregnancy
Epididymitis
Orchitis
Ovarian torsion
Paraphimosis
Pelvic inflammatory disease
Priapism
Pyelonephritis
Renal laceration
Ruptured ovarian cyst
Testicular torsion
Tubo-ovarian abscess
Urinary tract infection (uncomplicated)
Urolithiasis (renal colic)
Vaginal bleeding (non-pregnant)
Infectious Disease Presentations
Acute sinusitis
Acute tonsillitis
Acute upper respiratory infection
Animal bite
Bacterial meningitis
Cellulitis
Conjunctivitis (bacterial)
Dental abscess
Endocarditis
Febrile neutropenia
Fournier gangrene
Hand-foot-mouth disease
Hepatitis (acute)
Herpes zoster
HIV-related illness
Human bite
Impetigo
Infected diabetic foot ulcer
Infectious mononucleosis
Influenza
Necrotizing fasciitis
Osteomyelitis
Otitis externa
Parasitic infection
Periorbital cellulitis
Peritonsillar abscess
Scabies
Sepsis
Septic arthritis
Spontaneous bacterial peritonitis
Tick-borne illness (Lyme disease)
Tinea infection
Tuberculosis
Viral exanthem
Wound infection
Trauma Presentations
Achilles tendon rupture
ACL and mceniscus tear
Ankle fracture
Ankle sprain
Burn
Calcaneus fracture
Cervical spine fracture
Clavicle fracture
Dental avulsion
Distal radius fracture
Drowning
Elbow fracture and dislocation
Electrical injury
Facial bone fracture
Facial laceration
Femur fracture
Fingertip amputation
Forearm fracture (radius and ulna)
Frostbite
Hand:finger laceration
Heat exhaustion
Heat stroke
Hip fracture
Humeral shaft fracture
Knee dislocation
Knee sprain
Lightning injury
Mandible fracture
Metacarpal fracture
Metatarsal fracture
Muscle strain
Nasal fracture
Non-accidental trauma
Orbital fracture
Patella fracture
Phalanx fracture (finger)
Proximal humerus fracture
Pulmonary contusion
Rib fracture
Rotator cuff tear (acute traumatic)
Scalp laceration
Scaphoid fracture
Shoulder dislocation
Skull fracture
Splenic laceration
Sternal fracture
Supracondylar pediatric fracture
Tendon laceration (hand:wrist)
Thoracic and lumbar spine fracture
Tibia:fibula fracture
Tibial plateau fracture
Toe fracture
Traumatic epistaxis
Traumatic hyphema
Toxicologic Presentations
Acetaminophen toxicity
Alcohol intoxication
Alcohol withdrawal
Anticholinergic toxicity
Anticoagulant overdose
Benzodiazepine overdose
Benzodiazepine:sedative overdose
Beta-blocker and calcium channel blocker toxicity
Carbon monoxide poisoning
Caustic ingestion
Digoxin toxicity
Drug eruption
Foreign body ingestion
Opioid intoxication
Opioid overdose
Opioid withdrawal
Organophosphate
Salicylate toxicity
Serotonin syndrome
Stimulant intoxication (cocaine, methamphetamine)
Tricyclic antidepressant overdose
Psychiatric Presentations
Acute anxiety
Acute psychosis
Agitation:behavioral emergency
Bipolar disorder
Conversion disorder
Major depressive episode
Neuroleptic malignant syndrome
Suicidal ideation and attempt
Musculoskeletal and Rheumatologic Presentations
Acute low back pain (mechanical)
Bursitis
Cervical radiculopathy
Costochondritis
Gout (acute)
Lumbar radiculopathy
Pseudogout
Tendinitis
Dermatology Presentations
Acute eczema (Eczema acute flare)
Allergic contact dermatitis
Erythema multiforme
Henoch-Schönlein purpura
Pressure injury
Psoriasis (acute flare)
Stevens-Johnson syndrome
Toxic epidermal necrolysis
Urticaria (acute)
Environmental and Exposure Presentations
Envenomation (snake, spider, insect)
High-altitude illness
Hypothermia
Hematologic and Oncologic Presentations
Acute chest syndrome
Coagulopathy
Hyperviscosity syndrome
Sickle cell crisis (vaso-occlusive)
Symptomatic anemia
Thrombocytopenia (severe)
Tumor lysis syndrome
Pediatric-Specific Presentations
Bronchiolitis
Croup
Emergency delivery
Febrile seizure
Kawasaki disease
Neonatal jaundice
Neonatal sepsis
Nursemaid's elbow
Pediatric fever 0 to 28 days
Pediatric fever 29 to 60 days
Pediatric fever 61 to 90 days
Pyloric stenosis
Slipped capital femoral epiphysis
Intussusception
Endocrine and Metabolic Presentations
Adrenal crisis
Diabetic ketoacidosis
Hypercalcemia
Hyperosmolar hyperglycemic state
Hypertensive emergency
Hypertensive urgency
Hypoglycemia
Myasthenia gravis crisis
Myxedema coma
Severe hyperkalemia
Severe hyponatremia
Thyroid storm
ENT and Maxillofacial Presentations
Acute laryngitis
Acute otitis media
Acute pharyngitis
Cerumen impaction
Epistaxis (anterior)
Nasal foreign body
Otitis externa
Tympanic membrane perforation
Ophthalmologic Presentations
Acute angle-closure glaucoma
Central retinal artery occlusion
Chemical eye injury
Corneal abrasion
Corneal ulcer
Globe rupture
Ocular foreign body
Orbital cellulitis
Retinal detachment
Obstetric Presentations
Hyperemesis gravidarum
Painful vaginal bleeding in pregnancy
Placenta previa
Placental abruption
Preeclampsia:eclampsia
Preterm labor
Threatened:inevitable:incomplete abortion
Systemic and Miscellaneous Presentations
Anaphylaxis
Angioedema
Cannabis-induced hyperemesis
Second-Degree AV Block (Mobitz II)
POCUS
Procedures
Calculators
Resuscitation
ECG Guide
Back
Clinical Assessment Checklist
Browse categories and answer follow-up questions to refine your symptom profile.
Approach to the Critical Patient
Immediate stabilization
Hemodynamic instability triggers
▶
Hypotension (SBP < 90 mmHg) with bradycardia
▶
Transcutaneous pacing pads applied immediately
Activate transcutaneous pacing if hemodynamically unstable
Target rate 60-80 beats/min with transcutaneous pacing
Altered mental status or syncope with bradycardia
▶
Place patient supine with legs elevated
IV access x2 large bore
Signs of cardiogenic shock
▶
Hypoperfusion with cool extremities
Elevated lactate >= 2 mmol/l
Airway and oxygenation targets
▶
SpO2 target >= 94%
Supplemental oxygen for hypoxic patients
Intubation readiness if altered mental status or hemodynamic collapse
Rhythm identification priorities
▶
12-lead ECG within 10 minutes of arrival
▶
Fixed PR interval in conducted beats
Intermittent dropped QRS without preceding PR prolongation
Wide vs. narrow QRS determination critical for risk stratification
Continuous telemetry monitoring mandatory
▶
AHA Class I recommendation for hospital ECG monitoring in high-grade block
Distinguish from other AV block types immediately
Critical decision points
Pacing urgency stratification
▶
Emergent transcutaneous pacing
▶
Hemodynamic instability despite initial resuscitation
Syncope with documented Mobitz II on ECG
Progression to complete heart block
Urgent temporary transvenous pacing
▶
Symptomatic bradycardia not responding to transcutaneous pacing
Planned bridge to permanent pacemaker in unstable patient
Class I recommendation per ACC/AHA/HRS 2018 guidelines
Expedited permanent pacemaker planning
▶
All confirmed Mobitz II without reversible cause
Regardless of symptom status
Atropine avoidance
▶
Atropine generally ineffective for infranodal block
▶
May paradoxically worsen block by increasing sinus rate
Overwhelms diseased His-Purkinje system
If temporizing pharmacotherapy needed
▶
Isoproterenol infusion (if no ischemia)
Dopamine infusion
Epinephrine infusion
Class IIb for these agents per ACC/AHA/HRS 2018
Monitoring and consults
Monitoring requirements
▶
Continuous telemetry in monitored bed
▶
AHA scientific statement on ECG monitoring standards
Detect progression to high-grade or complete AV block
Vital signs every 15-30 minutes until stable
Repeat 12-lead ECG with any symptom change
Immediate consultation
▶
Cardiology/electrophysiology for all confirmed Mobitz II
▶
Permanent pacemaker planning
Level of block determination if uncertain
Critical care/ICU for hemodynamically unstable patients
Cardiac surgery standby if temporary pacing fails
History
Presenting symptoms
Cardinal symptoms
▶
Syncope or Stokes-Adams attacks
▶
Abrupt onset without prodrome distinguishes from vasovagal
Hallmark symptom noted by Mobitz in original description
Presyncope and dizziness
▶
Lightheadedness with positional changes
Graying of vision
Palpitations
▶
Awareness of skipped beats or pauses
Sensation of heart stopping
Associated symptoms
▶
Fatigue and exercise intolerance
▶
Reduced cardiac output with bradycardia
Exertional worsening suggests infranodal disease
Dyspnea
▶
Exertional dyspnea
Orthopnea or PND if heart failure present
Chest pain
▶
Ischemic etiology must be excluded
Anterior MI supplies His bundle and bundle branches via LAD
Timeline and context
Symptom duration and pattern
▶
Episodic vs. persistent symptoms
Exertional worsening vs. rest occurrence
Prior episodes of syncope or documented bradycardia
Triggering or preceding events
▶
Recent medication changes
▶
New beta-blocker, calcium channel blocker, digoxin
New antiarrhythmic initiation
Recent cardiac procedures
▶
Cardiac surgery
Catheterization or ablation
TAVR (high risk for conduction disturbance)
Recent viral illness or flu-like prodrome
▶
Myocarditis possibility
Tick exposure or travel to Lyme-endemic areas
▶
Lyme carditis is reversible cause
Risk factors and medical history
Cardiac history
▶
Prior MI especially anterior wall
▶
LAD territory supplies His bundle and proximal bundle branches
Known coronary artery disease
Structural heart disease or cardiomyopathy
Valvular heart disease
Prior bundle branch block (RBBB or LBBB)
▶
Strongest ECG predictor of progression to complete heart block
Bifascicular block history
Systemic conditions
▶
Degenerative fibrosis of conduction system (age-related, most common cause)
Chronic hypertension
Diabetes mellitus
▶
Both associated with AV block in JAMA Network Open 2019 registry study
Infiltrative cardiomyopathy
▶
Cardiac sarcoidosis
Cardiac amyloidosis
Autoimmune/inflammatory
▶
Systemic lupus erythematosus
Rheumatoid arthritis
Infectious endocarditis
▶
Perivalvular abscess extending to conduction system
Neuromuscular diseases
▶
Myotonic dystrophy type 1
Emery-Dreifuss muscular dystrophy
Limb-girdle muscular dystrophy
Kearns-Sayre syndrome
▶
All associated with progressive conduction system disease per ACC/AHA/HRS 2018
Medications review
AV nodal blocking agents
▶
Beta-blockers
▶
Primarily slow AV nodal conduction
Mobitz II on these agents often reveals severe underlying infranodal disease
Non-dihydropyridine calcium channel blockers
▶
Verapamil
Diltiazem
Digoxin
▶
Therapeutic level does not exclude toxicity as contributing factor
Antiarrhythmic agents
▶
Class Ic agents
▶
Flecainide
Propafenone
Class III agents
▶
Amiodarone
Sotalol
Drug-induced vs. drug-revealed distinction
▶
~50% of patients have block recurrence after drug discontinuation
Per ACC/AHA/HRS: reasonable to pace without waiting for washout if medically necessary (Class IIa)
Other implicated agents
▶
Fingolimod (sphingosine-1-phosphate receptor modulator)
Family and social history
Family history
▶
Sudden cardiac death in first-degree relatives
Pacemaker implantation in young family members
Known hereditary conduction disease
Lamin A/C gene mutations
▶
Associated with progressive AV block and sudden death risk
Social history
▶
Outdoor activities in tick-endemic areas
IV drug use (endocarditis risk)
Alcohol use (cardiomyopathy, electrolyte disturbances)
Physical Exam
Vital signs
Cardiovascular vital sign assessment
▶
Heart rate
▶
Bradycardia with regular rhythm interrupted by pauses
Rate may be deceivingly normal in 2:1 block
Blood pressure
▶
Hypotension indicates hemodynamic compromise
Pulse pressure narrowing with low cardiac output
Respiratory rate
▶
Tachypnea may indicate pulmonary edema or low output state
SpO2 on room air
Cardiovascular exam
Pulse and rhythm
▶
Irregular pulse with intermittent pauses
▶
Pause duration equals exactly 2 PP intervals
Distinguishes from PAC-induced pauses
Pulse deficit assessment
Radial vs. apical pulse comparison
Jugular venous pulsations
▶
Cannon A waves
▶
Occur when atria contract against closed tricuspid valve during blocked beat
Intermittent rather than regular (unlike complete heart block)
Elevated JVP suggests right heart failure or pericardial disease
Cardiac auscultation
▶
Variable S1 intensity (less variable than complete heart block, PR is fixed in conducted beats)
S3 gallop suggests left ventricular dysfunction
Murmurs
▶
Aortic stenosis as structural cause
Mitral regurgitation in cardiomyopathy
Peripheral perfusion
▶
Capillary refill time
Skin temperature and mottling
Peripheral edema
Pulmonary exam
Respiratory findings
▶
Bilateral crackles at bases suggest pulmonary edema
Respiratory effort assessment
Pleural effusion signs with heart failure
Neurological exam
Mental status
▶
GCS or AVPU baseline
Confusion or altered consciousness from low cardiac output
Neuromuscular disease screening
▶
Myotonia (grip or percussion myotonia)
Ptosis or external ophthalmoplegia (Kearns-Sayre)
Proximal muscle weakness and wasting
Facial weakness
Skin and other findings
Dermatologic clues
▶
Erythema migrans rash (pathognomonic for Lyme disease)
Lupus rash (malar, discoid)
Pallor suggesting anemia with underlying cardiac disease
Signs of infiltrative disease
▶
Lymphadenopathy (sarcoidosis)
Hepatosplenomegaly (amyloidosis)
Differential Diagnosis
High-grade AV block variants
Mobitz Type I (Wenckebach) AV block
▶
ICD-10: I44.1
Progressive PR prolongation before dropped beat
Generally benign, AV nodal in origin
Responds to atropine unlike Mobitz II
Differentiating feature: PR not fixed between conducted beats
Complete (Third-Degree) AV block
▶
ICD-10: I44.2
Complete AV dissociation, no relationship between P waves and QRS
Escape rhythm maintains ventricular rate independently
May be the outcome of untreated or progressed Mobitz II
High-Grade (Advanced) AV block
▶
ICD-10: I44.30
Two or more consecutive non-conducted P waves
Treated similarly to Mobitz II per ACC/AHA/HRS 2018
ECG mimics
2:1 AV block
▶
Cannot be classified as Mobitz I or II from a single ECG strip
Requires longer monitoring or maneuvers to reveal true block pattern
Exercise test or carotid sinus massage may unmask pattern
Pseudo-Mobitz II
▶
Vagally mediated block with sinus slowing before dropped beat
Distinguishing feature: sinus rate is NOT constant (true Mobitz II has constant PP intervals)
Generally benign and responds to atropine
Blocked premature atrial complexes
▶
ICD-10: I49.1
P waves hidden within preceding T waves mimicking dropped beats
Careful T wave morphology analysis on multiple leads required
Structural and conduction causes
First-Degree AV block
▶
ICD-10: I44.0
PR interval > 200 ms in all beats, no dropped beats
Can coexist with Mobitz II in bifascicular disease
Sick sinus syndrome
▶
ICD-10: I49.5
Sinus node dysfunction producing bradycardia and pauses
AV conduction typically intact
Bundle branch block without AV block
▶
ICD-10: I45.x
Pre-existing BBB predicts future Mobitz II but is distinct
Lyme carditis
▶
ICD-10: A69.20
Reversible AV block in appropriate epidemiologic context
All degrees of block possible, often rapidly fluctuating
Acute anterior MI with new AV block
▶
ICD-10: I21.0x + I44.30
Infranodal block from ischemia of His bundle or bundle branches
Emergency revascularization may restore conduction
Noncardiac causes of syncope
Vasovagal syncope
▶
ICD-10: R55
Prodrome distinguishes from sudden Stokes-Adams attack
Triggered by specific stimuli, positional
Pulmonary embolism with syncope
▶
ICD-10: I26.09
Tachycardia more typical than bradycardia
Right heart strain pattern on ECG
Laboratory Tests
Cardiac biomarkers
Troponin
▶
Troponin I or T (high-sensitivity preferred)
▶
Elevated in acute MI as etiology of Mobitz II
Anterior MI may cause infranodal block via LAD territory ischemia
Serial troponins 0 and 3 hours if ischemia suspected
BNP or NT-proBNP
▶
Elevated with associated heart failure
Guides level-of-care decisions
Metabolic panel
Basic metabolic panel
▶
Potassium
▶
Hyperkalemia can exacerbate conduction disease
Target 4.0-5.0 mmol/l
Calcium
▶
Hypercalcemia may affect AV conduction
Magnesium
▶
Hypomagnesemia can worsen conduction disturbances
Target 0.75-1.0 mmol/l
Creatinine and eGFR
▶
Renal function affects drug dosing for temporizing agents
Glucose
▶
Hypoglycemia may mimic syncope
Complete blood count
▶
Hemoglobin
▶
Anemia worsens cardiac output compromise
White blood cell count
▶
Leukocytosis with infectious etiology (Lyme, endocarditis)
Drug levels and toxicology
Digoxin level
▶
All patients on digoxin
▶
Therapeutic level does not exclude toxicity-mediated block
Level > 2 ng/mL concerning for toxicity
Toxicity may require Fab fragment treatment
Serum drug levels for other antiarrhythmics if applicable
▶
Amiodarone
Flecainide
Endocrine and inflammatory
Thyroid-stimulating hormone
▶
Hypothyroidism can contribute to conduction disease
Required per ACC/AHA/HRS 2018 initial workup
Inflammatory markers
▶
ESR and CRP
▶
Elevated in inflammatory/infiltrative etiologies
Sarcoidosis, myocarditis, Lyme carditis
ACE level
▶
Elevated in active sarcoidosis (sensitivity ~60%)
Not specific; must correlate with imaging
Infectious and autoimmune
Lyme serology
▶
Borrelia burgdorferi IgM and IgG (ELISA with Western blot confirmation)
Indicated in Lyme-endemic areas or suggestive history
▶
Erythema migrans, tick exposure, summer presentation
Lyme carditis: reversible cause of all grades of AV block
ANA and complement
▶
If SLE or autoimmune etiology suspected
Neuromuscular labs
▶
Creatine kinase and aldolase
▶
Elevated in muscular dystrophies causing conduction disease
Lactate and pyruvate
▶
Mitochondrial disease (Kearns-Sayre syndrome)
Diagnostic Tests
Scoring Systems
AV block risk stratification
▶
Wide QRS (> 120 ms) with Mobitz II
▶
Indicates diffuse His-Purkinje disease
Highest risk of sudden progression to complete heart block
Class I indication for pacemaker regardless of symptoms per ACC/AHA/HRS 2018
Narrow QRS Mobitz II
▶
Less common; may represent intra-Hisian block
Class IIa indication for pacemaker per ACC/AHA/HRS 2018
2018 ACC/AHA/HRS Bradycardia Guideline Algorithm
▶
Identifies reversible causes before committing to permanent pacing
Stratifies by symptoms, QRS width, and LV function
LVEF thresholds for device selection
▶
LVEF > 35%
▶
Standard dual-chamber pacemaker appropriate
LVEF <= 35% with anticipated RV pacing > 40%
▶
Cardiac resynchronization therapy (CRT) preferred
CRT-D if concomitant SCD risk
HV interval on electrophysiology study
▶
HV >= 70 ms indicates significant infranodal disease
Supports pacemaker implantation even with ambiguous surface ECG
MRI
Cardiac MRI indications
▶
Suspected infiltrative cardiomyopathy
▶
Cardiac sarcoidosis: patchy mid-myocardial or subepicardial late gadolinium enhancement
Cardiac amyloidosis: diffuse subendocardial or transmural LGE with characteristic kinetics
Myocarditis evaluation
▶
Lake Louise criteria: T2-weighted edema, LGE, T1 mapping
Protocol considerations
▶
LGE sequences for fibrosis detection
T1 and T2 mapping for diffuse myocardial disease
Native T1 elevation in amyloidosis
Pacemaker compatibility
▶
MRI conditional devices require specific protocol
Discuss with device manufacturer and imager if pacemaker already implanted
Brain MRI
▶
If syncope with atypical features suggesting neurologic etiology
Not primary investigation for confirmed Mobitz II with typical presentation
CT
Coronary CT angiography
▶
Ischemic etiology evaluation when troponin negative or equivocal
▶
Rules out significant coronary artery disease non-invasively
Sensitivity ~95-97% for significant CAD (> 50% stenosis)
Not indicated as first-line when acute MI confirmed; proceed to coronary angiography
Chest CT
▶
Sarcoidosis evaluation
▶
Bilateral hilar lymphadenopathy
Perilymphatic nodules
CT-guided biopsy planning
Pulmonary edema severity assessment if chest X-ray equivocal
CT pulmonary angiography
▶
If pulmonary embolism is on differential
Tachycardia more typical in PE; indicated when clinical probability warrants
Ultrasound
Transthoracic echocardiography
▶
Essential in all patients with Mobitz II
▶
LV systolic function (LVEF)
Wall motion abnormalities suggesting ischemia
Valvular disease assessment
Pericardial effusion
Infiltrative pattern recognition
▶
Increased echogenicity (sparkling) in amyloidosis
Granulomatous pattern in sarcoidosis
Required before pacemaker to determine CRT vs. standard device
▶
Class I per ACC/AHA/HRS 2018
Transesophageal echocardiography
▶
Suspected endocarditis with perivalvular abscess
▶
Superior sensitivity for abscess (sensitivity ~90% vs. ~50% TTE)
Better visualization of posterior structures
Point-of-care ultrasound (POCUS)
▶
Rapid assessment of global LV function in ED
IVC assessment for volume status
Pericardial effusion exclusion
B-lines for pulmonary edema
Disposition
Admission criteria
Mandatory admission for all confirmed Mobitz II
▶
ACC/AHA/HRS 2018: all patients with Mobitz II require monitored admission until pacemaker implantation
▶
Risk of sudden unpredictable progression to complete heart block
Stokes-Adams attacks and sudden death without warning
Continuous telemetry monitoring throughout admission
▶
AHA scientific statement on ECG monitoring standards
ICU/CCU level care indications
▶
Hemodynamic instability
▶
Hypotension requiring vasopressors
Cardiogenic shock
Active transcutaneous or transvenous pacing requirement
Frequent or prolonged symptomatic pauses
Concurrent STEMI with infranodal block
Monitored bed criteria
Stepdown or telemetry unit
▶
Hemodynamically stable symptomatic patients
▶
Syncope or presyncope without current instability
Awaiting electrophysiology consultation and pacemaker planning
Asymptomatic Mobitz II confirmed on ECG
▶
Still requires monitored admission; block is unpredictable
Discharge criteria
Copy
Only following one of:
▶
Permanent pacemaker implanted with confirmed appropriate device function
▶
Device interrogation confirms appropriate sensing and pacing thresholds
Reversible cause fully treated with documented resolution of AV block
▶
Lyme carditis: documented return to normal conduction after antibiotics
Drug toxicity: block resolved after washout with close follow-up arranged
Never discharge with active Mobitz II without a definitive plan
Transfer criteria
Transfer to tertiary center if
▶
Electrophysiology and device implantation not available at current facility
Hemodynamic instability requiring temporary pacing beyond local capability
Complex device decision (CRT-D, subcutaneous ICD)
Follow-up planning
Copy
Post-pacemaker surveillance
▶
Device check within 2-12 weeks of implantation
Subsequent checks every 6-12 months
Annual echocardiography if RV pacing burden > 40%
▶
Monitor for pacing-induced cardiomyopathy
Wound check at 1-2 weeks post-implantation
Cardiology/EP outpatient follow-up
▶
Underlying etiology management (CAD, sarcoidosis, Lyme)
Medication optimization
Treatment
Immediate bridging therapies
Transcutaneous pacing
▶
Indications
▶
Hemodynamic instability
Symptomatic high-degree or complete AV block
Immediate bridge while transvenous pacing is prepared
Technique
▶
Pads placed anteroposteriorly (preferred) or anterior-lateral
Rate set at 60-80 beats/min
Output titrated from low to threshold for capture
Confirm electrical and mechanical capture
Sedation/analgesia
▶
Fentanyl 25-50 mcg IV for pain
Midazolam 1-2 mg IV for sedation
Ketamine 0.5-1 mg/kg IV if hypotensive
Temporary transvenous pacing
▶
Indications
▶
Hemodynamic compromise not resolved by transcutaneous pacing
Bridge to permanent pacemaker in unstable patient
Class I per ACC/AHA/HRS 2018
Access
▶
Right internal jugular or left subclavian preferred for stability
Femoral route if other access not feasible
Parameters
▶
Rate 60-80 beats/min
Output at 2x threshold for reliable capture
Sensitivity at appropriate setting to avoid undersensing
Pharmacologic temporizing agents
Isoproterenol
▶
Mechanism: beta-1 and beta-2 agonist increasing His-Purkinje automaticity
Indication: temporizing if pacing unavailable and no ischemia risk
Dosing
▶
2-10 mcg/min IV infusion
Titrate to achieve adequate ventricular rate
Avoid in ischemic heart disease (increases myocardial oxygen demand)
Class IIb recommendation per ACC/AHA/HRS 2018
Dopamine
▶
Dosing
▶
2-20 mcg/kg/min IV infusion
Titrate to heart rate and blood pressure targets
Alternative if isoproterenol unavailable or ischemia concern
Epinephrine
▶
Dosing
▶
2-10 mcg/min IV infusion
Titrate to hemodynamic response
Last resort agent for refractory hemodynamic collapse with bradycardia
Atropine
▶
Generally NOT recommended in Mobitz II
▶
Ineffective for infranodal block
May paradoxically worsen block
By increasing sinus rate, overwhelms diseased His-Purkinje system
Consider only if Mobitz I (Wenckebach) cannot be excluded
Aminophylline
▶
IV aminophylline 250 mg over 20 minutes
▶
Considered in acute inferior MI with bradycardia
Adenosine antagonism may improve AV conduction
Evidence limited; use as adjunct only
Reversible cause treatment
Lyme carditis
▶
High-degree block: IV ceftriaxone 2g daily for 14-21 days
▶
Temporary pacing while awaiting antibiotic response
Do not implant permanent pacemaker until block fails to resolve
Lower-degree block: oral doxycycline 100 mg twice daily for 14-21 days
Block typically resolves within days to weeks
Drug toxicity
▶
Digoxin toxicity: digoxin-specific Fab fragments (Digibind/DigiFab)
▶
Dose calculated from serum level or total body load
40 mg vial neutralizes approximately 0.5 mg digoxin
Discontinue offending AV-blocking agents
Electrolyte correction
▶
Potassium target 4.0-5.0 mmol/l
Magnesium target >= 0.75 mmol/l
Acute MI
▶
Emergency revascularization (PCI) for STEMI with infranodal block
Anterior MI: LAD revascularization may not restore conduction if His-Purkinje permanently damaged
Temporary pacing until conduction assessment post-revascularization
Definitive treatment: permanent pacemaker
Class I indications (per ACC/AHA/HRS 2018)
▶
Acquired Mobitz II not attributable to reversible or physiologic causes
▶
Regardless of symptoms
Asymptomatic Mobitz II with wide QRS (> 120 ms)
▶
High risk of sudden unpredictable progression
Symptomatic Mobitz II regardless of QRS width
Class IIa indications
▶
Asymptomatic Mobitz II with narrow QRS
▶
Less common; intra-Hisian disease possible
Device selection
▶
Standard dual-chamber pacemaker (DDD)
▶
LVEF > 35% with expected low RV pacing burden
Maintains AV synchrony
Cardiac resynchronization therapy (CRT or CRT-D)
▶
LVEF <= 35% with anticipated RV pacing > 40%
Prevents pacing-induced cardiomyopathy
CRT-D if SCD risk stratification warrants defibrillator
Pacemaker with defibrillator (ICD or CRT-D)
▶
Infiltrative cardiomyopathy (sarcoidosis, amyloidosis)
Lamin A/C mutation carriers
His bundle pacing or left bundle branch area pacing
▶
Alternative to RV pacing to preserve physiologic conduction
Emerging evidence; consider in appropriate anatomy
Post-implant management
▶
Device interrogation before discharge
Sensing and pacing threshold confirmation
Arm movement restrictions for 2-4 weeks (pectoral implant)
Avoid electromagnetic interference sources
Special Populations
Pregnancy
Incidence and risk in pregnancy
▶
Mobitz II in pregnancy is rare; most conduction disease in pregnancy is first-degree
Lyme carditis and drug-induced block are important reversible causes
Peripartum cardiomyopathy may occasionally produce conduction disease
Physiologic changes affecting management
▶
Increased heart rate in normal pregnancy (10-15 bpm above baseline)
▶
May partially mask bradycardia in mild cases
Increased plasma volume and cardiac output demands
▶
Poorly tolerated bradycardia relative to non-pregnant state
Aortocaval compression in supine position
▶
Left lateral decubitus positioning required
Treatment modifications
▶
Transcutaneous and transvenous pacing safe in pregnancy
▶
Preferred over pharmacotherapy in hemodynamically significant block
Isoproterenol: use with extreme caution
▶
May cause uterine relaxation
Avoid in first trimester; limited data
Permanent pacemaker implantation
▶
Can be performed in pregnancy with appropriate radiation minimization
Fluoroscopy time minimized; lead-lined apron
ICE guidance or echocardiographic guidance to reduce fluoroscopy
Lyme treatment in pregnancy
▶
IV ceftriaxone 2g daily preferred over doxycycline
Doxycycline contraindicated in second and third trimesters
Delivery planning
▶
Multidisciplinary team: cardiology, maternal-fetal medicine, anesthesia
Continuous telemetry during labor and delivery
Transcutaneous pacing pads applied
Geriatric
Epidemiology in older adults
▶
Degenerative fibrosis (Lev disease, Lenegre disease) most common etiology in elderly
▶
Progressive fibrocalcification of conduction system with aging
No underlying structural heart disease required
Age > 65 years is an independent risk factor for AV block
Comorbidity burden
▶
Multiple comorbidities increase procedural risk
▶
Frailty assessment before pacemaker implantation
CGA (comprehensive geriatric assessment) in complex cases
Polypharmacy
▶
Review all AV-nodal blocking agents
Drug interactions increasing digoxin toxicity risk (e.g., amiodarone, clarithromycin)
Renal impairment
▶
Reduces digoxin and other drug clearance
Dose adjustments for temporizing agents
Atypical presentations
▶
Fatigue and functional decline rather than classic syncope
Falls as presentation of hemodynamically significant pauses
Cognitive decline from chronic low cardiac output
Device considerations
▶
Pacemaker implantation remains indicated regardless of age
▶
Significant symptom burden and mortality benefit
MRI-conditional devices preferred
▶
Elderly patients more likely to need future MRI
Subcutaneous ICD generally avoided in very elderly
▶
Pacing function available with transvenous systems
CRT consideration
▶
Benefits may persist even in elderly with reduced LVEF
Pediatrics
Incidence and causes in children
▶
Mobitz II is rare in pediatric population
▶
Congenital complete heart block more common than acquired Mobitz II
Most common pediatric causes
▶
Myocarditis (viral)
Post-cardiac surgery (especially AV canal repair, VSD repair, AVSD)
Lyme carditis in endemic areas
Neuromuscular diseases
Congenital heart disease
▶
Post-surgical AV block
▶
Incidence depends on procedure proximity to AV node
Most post-surgical block resolves within 7-10 days
Persistent block > 7-14 days warrants permanent pacemaker
Presentation differences
▶
Infants: poor feeding, pallor, tachypnea rather than syncope
Children: exercise intolerance, syncope with exertion
Neonates: hydrops fetalis if very slow ventricular rate
Treatment in children
▶
Transcutaneous pacing
▶
Pediatric pads for < 15 kg or < 8 years
Adult pads acceptable for larger children
Temporary transvenous pacing
▶
Fluoroscopy guidance preferred
Smaller sheaths and leads based on patient size
Permanent pacemaker indications
▶
Same threshold as adults: Mobitz II regardless of symptoms
Lead selection based on patient size and anatomy
Epicardial leads preferred in very small children or those with intracardiac shunts
Pharmacologic doses
▶
Atropine 0.02 mg/kg IV (minimum 0.1 mg, maximum 0.5 mg per dose)
▶
May attempt once while recognizing likely ineffective for infranodal block
Isoproterenol 0.01-0.5 mcg/kg/min IV infusion
Epinephrine 0.01-0.1 mcg/kg/min IV infusion
Background
Epidemiology
Incidence and prevalence
▶
Exact prevalence of Mobitz II is uncertain due to intermittent nature
▶
Estimated 1-2% of all AV blocks presenting to cardiology referral centers
Age distribution
▶
Most common in older adults (> 60 years)
Degenerative fibrosis predominates in this age group
Younger patients more likely to have structural or infiltrative disease
Risk factor epidemiology
▶
JAMA Network Open 2019 registry study (Kerola et al.)
▶
Chronic hypertension: OR ~1.8 for AV block
Diabetes mellitus: OR ~1.5 for AV block
Pre-existing BBB is strongest predictor of progression
Sex distribution
▶
Slightly more common in males
Female predominance in autoimmune etiologies
Mortality and prognosis without treatment
▶
Significant risk of sudden cardiac death without pacemaker
▶
Progression to complete heart block unpredictable and often sudden
Stokes-Adams attacks in up to 40-50% of untreated patients
Post-pacemaker prognosis
▶
Survival determined primarily by underlying heart disease
Conduction disease per se does not independently worsen prognosis after pacing
ICD-10 coding
▶
Mobitz II: I44.1 (Second-degree atrioventricular block)
With complete heart block: I44.2
Cardiac pacemaker status: Z95.0
Pathophysiology
Anatomic basis
▶
Infranodal location of block
▶
Below the AV node in the His bundle or bundle branches
Contrasts with Mobitz I (Wenckebach) which is AV nodal
Results in wide QRS in most cases (bundle branch disease)
Narrow QRS Mobitz II
▶
Rare; intra-Hisian block within the His bundle itself
QRS narrow because both bundle branches still conduct
His bundle anatomy
▶
His bundle penetrates the central fibrous body
Receives blood from AV nodal artery (RCA territory) and LAD
Right bundle branch: LAD territory; left bundle: LAD + RCA
Mechanism of block
▶
All-or-none failure of infranodal conduction
▶
Unlike Wenckebach which shows incremental fatigue of AV node
Diseased His-Purkinje tissue conducts or fails completely
Results in fixed PR before dropped beat (no incremental delay)
Why PR is fixed
▶
AV node conducts normally; delay occurs below
Conduction time above the block remains constant
Only the infranodal segment fails intermittently
Etiologic mechanisms
▶
Degenerative fibrosis (Lev and Lenegre disease)
▶
Progressive fibrocalcification replacing conduction tissue
Most common cause in elderly without structural disease
Ischemic
▶
Anterior MI: LAD supplies right bundle and anterior left bundle
Inferior MI less commonly causes infranodal block
Infiltrative
▶
Sarcoid granulomas replacing conduction tissue
Amyloid fibrils disrupting conduction cell architecture
Inflammatory/infectious
▶
Borrelia burgdorferi spirochetes causing local inflammation at AV junction
Myocarditis with cellular infiltrate
Neuromuscular
▶
Dystrophin gene mutations causing conduction cell loss
Mitochondrial dysfunction in Kearns-Sayre syndrome
Post-procedural
▶
Direct trauma to conduction tissue during cardiac surgery
Inflammatory edema post-ablation or TAVR
Therapeutic Considerations
Pacemaker evidence base
▶
ACC/AHA/HRS 2018 Bradycardia Guidelines (Kusumoto et al.)
▶
Class I: permanent pacing for acquired Mobitz II not due to reversible cause
Based on observational data and expert consensus
Level of Evidence C (expert opinion with supporting data)
ACC/AHA/HRS 2012 Device Therapy Guidelines (Epstein et al.)
▶
Class I: asymptomatic Mobitz II with wide QRS
Class IIa: asymptomatic Mobitz II with narrow QRS
Evidence for CRT
▶
BLOCK HF trial: CRT superior to RV pacing in reduced LVEF
Reduces pacing-induced cardiomyopathy risk
His bundle and left bundle branch area pacing
▶
Physiologic pacing alternatives to RV apical pacing
▶
Recruit native His-Purkinje system
Preserve mechanical synchrony
His bundle pacing
▶
Success rate 80-90% in experienced centers
Higher capture thresholds may affect battery longevity
Left bundle branch area pacing
▶
Higher success rate than His bundle pacing
Emerging as preferred physiologic pacing strategy
Drug-induced AV block considerations
▶
Journal of Cardiovascular Electrophysiology 2025 (Sfairopoulos et al.)
▶
Drug-induced vs. drug-revealed AV block distinction
~50% recurrence after drug discontinuation
Supports early pacemaker in most cases
ACC/AHA/HRS 2018: Class IIa for pacing without drug washout when medically necessary
Monitoring technology
▶
Implantable loop recorder
▶
For suspected intermittent block not yet captured on surface ECG
Provides years of continuous monitoring
AHA 2017 ECG monitoring standards
▶
Category I conditions for continuous monitoring include high-degree AV block
Defines monitoring duration requirements
Patient Discharge Instructions
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Diagnosis and key information
▶
Diagnosed with Second-Degree AV Block (Mobitz Type II)
▶
A serious heart rhythm disorder where your heart skips beats due to a block in the electrical system
This condition carries a significant risk of sudden progression to a complete block
A pacemaker is the definitive treatment and is life-saving in most cases
Activity restrictions before pacemaker
▶
Activity limitations
▶
No driving until pacemaker is implanted and confirmed functioning
Avoid strenuous physical activity
Avoid lifting > 5 kg
Avoid operating heavy machinery
Follow up urgently with your cardiologist or electrophysiologist if discharged before pacemaker
After pacemaker implantation
▶
Wound care
▶
Keep incision clean and dry for 5-7 days
Watch for redness, swelling, warmth, or discharge at site
No submerging wound in water (bathing vs. showering restrictions per your team)
Activity restrictions post-pacemaker
▶
Avoid raising implant-side arm above shoulder for 2-4 weeks
Avoid heavy lifting on implant side for 4-6 weeks
Most patients return to full activity within 4-6 weeks
Device precautions
▶
Carry pacemaker identification card at all times
Notify all healthcare providers of your pacemaker
Security screening at airports: inform security, request hand wand
Keep cell phones > 15 cm from device
MRI: notify MRI team; MRI-conditional devices require specific protocol
Avoid strong magnetic fields (industrial, MRI without clearance)
Follow-up appointments
▶
Device check within 2-12 weeks of implantation
Wound check at 1-2 weeks
Then device checks every 6-12 months
Return to emergency department immediately if
▶
Syncope (fainting) or near-fainting episodes
Prolonged dizziness or lightheadedness
Chest pain or pressure
Significant shortness of breath
Palpitations or sensation of heart racing or stopping
Signs of wound infection (redness, warmth, pus, fever)
Hiccups that will not stop (may indicate pacemaker lead displacement)
Muscle twitching in chest or abdomen (may indicate lead displacement)
Lifestyle guidance
▶
Electrolyte-rich diet and adequate hydration
Avoid excessive alcohol and caffeine
Continue all prescribed medications unless told otherwise by your cardiologist
Do NOT restart any beta-blockers, calcium channel blockers, or digoxin without explicit cardiology guidance
References
Guidelines and key sources
2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay
▶
Kusumoto FM, Schoenfeld MH, et al.
Heart Rhythm. 2019
Class I permanent pacing for acquired Mobitz II regardless of symptoms
https://doi.org/10.1016/j.hrthm.2018.10.037
2018 ACC/AHA/HRS Guideline Executive Summary
▶
Kusumoto FM, Schoenfeld MH, et al.
Journal of the American College of Cardiology. 2019
Temporizing pacing strategies and device selection guidance
https://pubmed.ncbi.nlm.nih.gov/30412710
2012 ACCF/AHA/HRS Focused Update for Device-Based Therapy
▶
Epstein AE, DiMarco JP, Ellenbogen KA, et al.
Journal of the American College of Cardiology. 2013
Class I and IIa indications by QRS width
https://doi.org/10.1016/j.jacc.2012.11.007
AHA Update to Practice Standards for ECG Monitoring
▶
Sandau KE, Funk M, Auerbach A, et al.
Circulation. 2017
Category I monitoring recommendation for high-degree AV block
https://www.ahajournals.org/doi/10.1161/CIR.0000000000000527
Centennial of Mobitz Type II second-degree AV block
▶
Barold SS, Herweg B.
Journal of Cardiovascular Electrophysiology. 2024
Historical and mechanistic review
https://onlinelibrary.wiley.com/doi/10.1111/jce.16199
Clinical Significance of Drug-Associated AV Block
▶
Sfairopoulos D, Bazoukis G, Sideris S, et al.
Journal of Cardiovascular Electrophysiology. 2025
Drug-induced vs. drug-revealed AV block; 50% recurrence after drug withdrawal
https://onlinelibrary.wiley.com/doi/10.1111/jce.16697
Drug-Induced Arrhythmias: AHA Scientific Statement
▶
Tisdale JE, Chung MK, Campbell KB, et al.
Circulation. 2020
https://www.ahajournals.org/doi/abs/10.1161/CIR.0000000000000905
Risk Factors Associated With Atrioventricular Block
▶
Kerola T, Eranti A, Aro AL, et al.
JAMA Network Open. 2019
Hypertension, diabetes, BBB as risk factors
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/10.1001/jamanetworkopen.2019.4176
Pacemakers (Review)
▶
Aldaas OM, Roberge-Lacharite AS, Birgersdotter-Green U.
NEJM Evidence. 2025
Contemporary device selection and physiologic pacing strategies
https://www.nejm.org/doi/full/10.1056/EVIDra2400323
Atrioventricular Conduction Block (Chapter)
▶
Mitchell SH, Hudson KB, Brady WJ.
The Electrocardiogram in Emergency and Acute Care. 2023
ECG diagnosis and classification of AV block
https://onlinelibrary.wiley.com/doi/10.1002/9781119266938.ch9
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.
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Management Protocols
Second-Degree AV Block (Mobitz II)