Etiology
Congenital
- Usually at the level of the AV node
- Usually asymptomatic at rest, may be symptomatic with exertion (due to inability to increase heart rate)
- In the absence of structural abnormalities, congenital complete heart block may be associated with maternal SS-A (Ro) and SS-B (La) antibodies
Acquired
Degenerative Disease
- Lenègre Disease: sclerodegenerative process of the conduction system
- Lev Disease: calcification of the conduction system and valves
- Noncompaction Cardiomyopathy
- Nail-Patella Syndrome
- Mitochondrial Myopathy
Drugs
- Class Ia Antiarrhythmics
- Class Ic Antiarrhythmics
- Class II Antiarrhythmics
- Beta Blockerrs (see xxxx, [[]])
- Class III Antiarrhythmics
- Class IV Antiarrhythmics
- Calcium Channel Blockers (see xxxx, [[]])
- Digoxin or Other Cardiac Glycosides (see see Digoxin, [[Digoxin]])
Iatrogenic
- AV Nodal Slow/Fast Pathway Ablation
- Cardiac Surgery: complete heart block occurs in 1-5.7% of cases
- Risk Factors
- Aortic Valve Annular Calcification
- Aortic Valve Surgery
- Bicuspid Aortic Valve
- Female Gender
- Pre-Existing Conduction System Disease (RBBB or LBBB)
- Risk Factors
- Left Anterior Descending Coronary Artery Stenting
- Septal Alcohol Ablation
- Swan-Ganz Catheter Interference with Right Bundle Branch Conduction in Setting of Pre-Existing Left Bundle Branch Block (LBBB)
Infection
- Endocarditis with Valve Ring Abscess (see Endocarditis, [[Endocarditis]])
- Chagas Disease (see Chagas Disease, [[Chagas Disease]])
- Lyme Disease: in endemic regions
- Myocarditis (see Myocarditis, [[Myocarditis]])
- Aspergillus (see Aspergillus, [[Aspergillus]]
- Rheumatic Fever
- Trypanosomiasis (see Trypanosomiasis, [[Trypanosomiasis]]): Trypanosoma cruzi
- Varicella-Zoster Virus (see Varicella-Zoster Virus, [[Varicella-Zoster Virus]])
Infiltration
- Amyloidosis (see see Amyloidosis, [[Amyloidosis]])
- Hodgkin’s Disease see Hodgkin’s Disease, [[Hodgkins Disease]])
- Multiple Myeloma (see Multiple Myeloma, [[Multiple Myeloma]])
- Sarcoidosis (see Sarcoidosis, [[Sarcoidosis]])
- Tumors
Ischemia/Infarction
- General Comments
- Early revascularization has decreased the incidence of AV block from 5.3% to 3.7% of cases
- Occlusion of the right coronary artery is the most common source of AV block
- Proximal RCA occlusion has a high incidence of AV block (24% of cases) because there is involvement of not only the AV nodal artery, but also of the right superior descending artery (which originates from the proximal portion of the right coronary artery)
- Anterior Wall Myocardial Infarction with His-Purkinje (Infranodal) Block
- Inferior Wall Myocardial Infarction with AV Nodal Block: complete heart block occurs in <10% of cases
Metabolic Disorders
Neuromuscular Disease
- Becker Muscular Dystrophy
- Myotonic Muscular Dystrophy
Phase IV Block (Bradycardia-Related Block)
- xxxxx
Rheumatic Disease
- Ankylosing Spondylitis (see Ankylosing Spondylitis, [[Ankylosing Spondylitis]])
- Reiter’s Syndrome (see Reiter’s Syndrome, [[Reiters Syndrome]])
- Relapsing Polychondritis (see Relapsing Polychondritis, [[Relapsing Polychondritis]])
- Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis, [[Rheumatoid Arthritis]])
- Scleroderma (see Scleroderma, [[Scleroderma]])
Toxic
- Grayanotoxin (“Mad” Honey)
- Nerium Oleander (see Nerium Oleander, [[Nerium Oleander]]): contains oleandrin and other less well-studied cardiac glycosides
Physiology
- Complete Failure of Transmission of Sino-Atrial (SA) Node Firing to the Ventricle: absence of conduction, resulting in complete dissociation of atrial and ventricular electrical activity
- Site of Block: 61% of cases have block below the His bundle
- AV Node (20% of cases)
- Bundle of His (<20% of cases)
- Bundle Branch Purkinje System
- Origin of Escape Rhythm: the ventricular escape rhythm can originate anywhere from the AV node to the bundle branch Purkinje system
- Site of Block: 61% of cases have block below the His bundle
- AV Dissociation: while all cases of complete heart block have AV dissociation, not all cases of AV dissociation are due to complete heart block
- Example: AV dissociation can occur in ventricular tachycardia (VT), where ventricular rate is faster than the sinus rate
- Example: AV dissociation can occur in accelerated junctional tachycardia, where ventricular rate is faster than the sinus rate
Clinical Manifestations
Cardiac Manifestations
Bradycardia (see Bradycardia, [[Bradycardia]])
- Complete AV Dissociation: no relationship between P waves and QRS complexes
- Isorhythmic AV Dissociation: atrial and ventricular rates are so close to each other that the P waves appear to be normally conducting
- Diagnosis of this requires close inspection of a long rhythm strip (to detect P-R interval variation) or pharmacologic acceleration of the atrial/sinus rate
- Isorhythmic AV Dissociation: atrial and ventricular rates are so close to each other that the P waves appear to be normally conducting
- Absence of Fusion Complexes
- Variable QRS Duration: depends on the site of the block and the site of the escape rhythm pacemaker (pacemaker above His bundle produces a narrow-complex escape rhythm, while pacemaker at or below His bundle produces a wide-complex escape rhythm)
- Block at Level of AV Node: escape is typically junctional at around 45-60 beats per min
- Patient is usually hemodynamically stable
- Heart rate increases in response to exercise and atropine
- Block Below AV Node: escape arises from His bundle or bundle branch Purkinje system and is usually <45 beats per min
- Patient is usually hemodynamically unstable
- Heart rate does not increase in response to exercise and atropine
- Block at Level of AV Node: escape is typically junctional at around 45-60 beats per min
Hypotension (see Hypotension, [[Hypotension]])
- Variable, depending on site of block and escape rhythm
Treatment
General Management
- External/Transvenous Pacemaker: for emergent/short-term treatment
- Permanent Pacemaker: for long-term treatment
Treatment of Complete Heart Block Associated with Swan-Ganz Catheter Interference with Right Bundle Branch Conduction in Setting of Pre-Existing Left Bundle Branch Block
- Usually resolves with removal of catheter
Treatment of Complete Heart Block After Cardiac Surgery
- Time course for recovery is variable
- Many patients recover within 48 hrs of surgery
- If no recovery occurs by post-op day 4-5, a permanent pacemaker should be implanted
Treatment of Complete Heart Block Associated with Ischemia/Infarction
- Anterior Wall Myocardial Infarction with His-Purkinje (infranodal) Block: occlusion of the left anterior descending coronary artery (particularly proximal to the first septal perforator) usually requires permanent pacemaker implantation
- Inferior Wall Myocardial Infarction with AV Nodal Block: often resolves within hrs-days (particularly with early coronary revascularization)
References
- xxx