Second Degree Atrioventricular Block-Mobitz Type II

Definition of Atrioventricular Block

  • Atrioventricular Block: delayed/intermittent/completely absent transmission of the impulse from atria to the ventricles (either transiently or permanently) due to anatomical/functional impairment of the cardiac conduction system

Classification of Atrioventricular Blocks


Epidemiology

  • Fibrosis/Sclerosis of the Conduction System: accounts for 50% of cases of all atrioventricular blocks
  • Ischemic Heart Disease: accounts for 40% of cases of all atrioventricular blocks
  • Drugs: most patients with atrioventricular block who are taking drugs that can impair conduction probably have underlying conduction system disease

Etiology

Increased Vagal Tone

  • Athletic Training
  • Carotid Sinus Massage
  • Hypersensitive Carotid Sinus Syndrome
  • Pain
  • Sleep

Familial Atrioventricular Block

  • Cardiac Sodium Channnel (SCN5A) Gene Mutation: autosomal dominant
  • Cardiac Transcription Factor (CSX/NKX2-5) Gene Mutation

Hereditary Neuromuscular Degenerative Disease

  • Becker Muscular Dystrophy
  • Erb’s Dystrophy
  • Kearns-Sayre Syndrome
  • Myotonic Dystrophy (see Myotonic Dystrophy, [[Myotonic Dystrophy]])

Degenerative Conduction System Disease

  • Lenegre’s Disease
    • Epidemiology: occurs in younger patients (may be hereditary)
    • Physiology: progressive, fibrotic, sclerodegenerative disease of the conduction system
    • Clinical: frequently associated with slow progression to complete heart block
  • Lev’s Disease
    • Epidemiology: occurs in older patients
    • Physiology: fibrosis/calcification extending from any of the left-sided fibrous structures adjacent to the conduction system into the conduction system itself
      • Fibrosis of the Top of the Muscular Septum: commonly causes right bundle branch block with left anterior fascicular block
      • Calcification of the Mitral Valve Ring or the Central Fibrous Body: may be the most common cause of complete heart block with a narrow QRS complex
      • Aortic Valve Calcification: may invade the bundle of His, right bundle branch, left bundle branch, and/or left anterior fascicle -> QRS complex may be prolonged

Infiltrative Disease

Metabolic Abnormality

  • Hypercalcemia (see Hypercalcemia, [[Hypercalcemia]]): may occur with severe hypercalcemia
  • Hyperkalemia (see Hyperkalemia, [[Hyperkalemia]]): usually with plasma potassium >6.3 meq/L
  • Hypokalemia (see Hypokalemia, [[Hypokalemia]])
  • Hypoxia (see Hypoxemia, [[Hypoxemia]])

Ischemic Heart Disease

  • Acute Myocardial Ischemia/Infarction (see Coronary Artery Disease, [[Coronary Artery Disease]])
    • Epidemiology
      • Incidence of High-Degree Atrioventricular Block (data from 4 large randomized thrombolytic trials: GUSTO-I, GUSTO-III, ASSENT-II, and GUSTO-IIb) [MEDLINE]: 6.9% (inferior wall MI: 9.8%; anterior wall MI: 3.2%)
      • Incidence of Complete Heart Block (data from TRACE trial) [MEDLINE]: 5.1% (and 81% occurred within the first 2 days after acute MI)
      • Incidence of Bundle Branch Block (data from TRACE trial) [MEDLINE]: 8%
  • Chronic Ischemic Heart Disease

Myocarditis (see Myocarditis, [[Myocarditis]])

Rheumatologic Disease

Thyroid Disease

  • Hyperthyroidism (Severe)/Thyrotoxic Periodic Paralysis (see Hyperthyroidism, [[Hyperthyroidism]])
  • Hypothyroidism (Severe) (see Hypothyroidism, [[Hypothyroidism]])

Iatrogenic

  • Alcohol (Ethanol) Septal Ablation for Hypertrophic Cardiomyopathy (see Hypertrophic Cardiomyopathy, [[Hypertrophic Cardiomyopathy]])
    • Epidemiology: complete heart block occurs in 14-22% of cases
    • Physiology: ethanol infusion into the first septal perforating branch of the left anterior descending (LAD) coronary artery -> infarction/thinning of the proximal interventricular septum
  • Cardiac Surgery
    • Epidemiology: complete heart block occurs in 1-5.7% of cases
    • Risk Factors for Post-Cardiac Surgery Complete Heart Block
      • Aortic Valve Annular Calcification
      • Aortic Valve Surgery
      • Bicuspid Aortic Valve
      • Female Gender
      • Pre-Existing Conduction System Disease (RBBB or LBBB)
    • Procedures
      • Aortic Valve Replacement of a Calcified Aortic Valve
      • Closure of Ventricular Septal Defect (see Ventricular Septal Defect, [[Ventricular Septal Defect]])
      • Mitral Valve Replacement of a Calcified Mitral Valve
  • Catheter Ablation for Arrhythymia: following ablation for reentrant arrhythmias when the reentrant pathway lies within or near the AV node
  • Left Anterior Descending (LAD) Coronary Artery Stenting
    • Epidemiology: rare
    • Physiology: due to stent-related occlusion of septal perforator artery -> septal infarction
  • Swan-Ganz Catheter Interference with Right Bundle Branch Conduction in Setting of Pre-Existing Left Bundle Branch Block (LBBB) (see Swan-Ganz Catheter, [[Swan-Ganz Catheter]])
  • Trans-Catheter Aortic Valve Replacement (TAVR) (see Aortic Stenosis, [[Aortic Stenosis]])
    • Epidemiology: approximately 33% of patients require a permanent pacemaker within 30 days of TAVR
      • There may be a higher rate of atrioventricular block with self-expanding implanted aortic valves, as compared to balloon expandable versions
    • Predictors of Post-TAVR Atrioventricular Block
      • Pre-existing cardiac conduction disturbance
      • Narrow left ventricular outflow tract
      • Increased severity of mitral annular calcification appear to be predictors of this complication
  • Trans-Catheter Closure of Ventricular Septal Defect (VSD) (see Ventricular Septal Defect, [[Ventricular Septal Defect]])
    • Amplatzer Ventricular Septal Defect Occluder: likely due to the right ventricular retention disk overlapping the ventricular conduction system as it passes above or anterosuperiorly to the ventricular septal defect

Drugs/Toxins

  • Adenosine (Adenocard) (see Adenosine, [[Adenosine]])
  • Amiodarone (Cordarone) (see Amiodarone, [[Amiodarone]])
  • Beta Blockers (se eβ-Adrenergic Receptor Antagonists, [[β-Adrenergic Receptor Antagonists]])
    • Agents
      • Labetalol (Normodyne, Trandate) (see Labetalol, [[Labetalol]])
      • Metoprolol (Lopressor, Toprol) (see Metoprolol, [[Metoprolol]])
      • Propanolol (see Propanolol, [[Propanolol]])
    • Physiology: antagonism of catecholamine-induced increase in heart rate
  • Calcium Channel Blockers (see Calcium Channel Blockers, [[Calcium Channel Blockers]])
    • Agents
      • Diltiazem (Cardizem, Tiazac, Dilt-CD) (see Diltiazem, [[Diltiazem]])
      • Verapamil (Isoptin, Verelan, Verelan PM, Calan, Bosoptin, Covera-HS) (see Verapamil, [[Verapamil]]): probably the most common calcium channel blocker associated with atrioventricular blocks
    • Physiology: atrioventricular nodal blockade, since calcium channels are especially concentrated in the sinoatrial and atrioventricular nodes within the heart
  • Digitalis Intoxication (see Digitalis, [[Digitalis]])
    • Physiology: digitalis is a cardiac glycoside -> inhibits myocardial Na+/K+ ATPase and increases vagal activity
  • Digoxin (Lanoxin) (see Digoxin, [[Digoxin]])
    • Physiology: digoxin is a cardiac glycoside -> inhibits myocardial Na+/K+ ATPase and increases vagal activity
  • Disopyramide (Norpace) (see Disopyramide, [[Disopyramide]])
    • Physiology: modulates the sodium channel
    • Clinical: may produce block in the more distal His-Purkinje system
  • Mad Honey Intoxication (see Mad Honey, [[Mad Honey]])
    • Physiology: grayanotoxin-contaminated honey made from Rhododendron Ponticum and other plant species from the Ericaceae and Sapindaceae families -> increased cardiac sodium channel permeability
  • Nerium Oleander Intoxication (see Nerium Oleander, [[Nerium Oleander]])
    • Physiology: contains oleandrin and other less well-studied cardiac glycosides
  • Procainamide (Pronestyl) (see Procainamide, [[Procainamide]])
    • Physiology: modulates the sodium channel
    • Clinical: may produce block in the more distal His-Purkinje system
  • Quinidine (Quinaglute, Quinidex) (see Quinidine, [[Quinidine]])
    • Physiology: modulates the sodium channel
    • Clinical: may produce block in the more distal His-Purkinje system

Other

  • Cardiac Cysts
  • Cardiac Trauma
  • Cardiac Tumors
  • Cardiomyopathy (see Congestive Heart Failure, [[Congestive Heart Failure]])
  • Congenital Heart Disease (see Congenital Heart Disease, [[Congenital Heart Disease]])
  • Endocarditis with Valve Ring Abscess (see Endocarditis, [[Endocarditis]])
  • Mitochondrial Myopathy
  • Myocardial Bridging
  • Nail-Patella Syndrome
  • Neonatal Lupus Syndrome
    • Physiology: trans-placental passage of anti-Ro/SSA or anti-La/SSB antibodies from mother
  • Phase IV Block (Bradycardia-Related Block)

Physiology

Electrical Correlates of the Normal EKG

  • PR Interval
    • Depolarization of Atrium (P-Wave)
    • Conduction Through AV Node
    • Conduction Through His Bundle
    • Conduction Through Bundle Branches
    • Conduction Through Fascicles
    • Conduction Through Terminal Purkinje Fibers
  • QRS
    • Ventricular Depolarization
  • T-Wave
    • Ventricular Repolarization

CARDIAC CONDUCTION

Blood Supply to Cardiac Conduction System

  • Blood Supply to the Sinoatrial (SA) Node
    • Right Coronary Artery: 60% of patients
    • Left Circumflex Artery: 40% of patients
  • Blood Supply to the Atrioventricular (AV) Node
    • Right Coronary Artery: 90% of patients
    • Left Circumflex Artery: 10% of patients
  • Blood Supply to the His Bundle
    • Right Coronary Artery: main blood supply
    • Septal Perforators of the Left Anterior Descending Coronary Artery: minor contribution
  • Main/Proximal Left Bundle Branch
    • Left Anterior Descending Artery: main blood supply
    • Right Coronary Artery: collateral flow
    • Left Circumflex Artery: collateral flow
  • Left Anterior Fascicle
    • Septal Perforators of the Left Anterior Descending Coronary Artery: main blood supply
    • AV Nodal Artery: 50% of patients
    • Left Posterior Fascicle
    • Proximal Left Posterior Fascicle
      • AV Nodal Artery: main blood supply
      • Septal Perforators of the Left Anterior Descending Coronary Artery: in some cases
    • Distal Left Posterior Fascicle
      • Anterior and Posterior Septal Perforating Arteries (Dual Blood Supply)
  • Right Bundle Branch
    • Septal Perforators of the Left Anterior Descending Artery: main blood supply
    • Right Coronary Artery: some collateral flow (depending on dominance of the system)
    • Left Circumflex Artery: some collateral flow (depending on dominance of the system)

Diagnosis

  • EKG

Clinical Differentiation of Second Degree Atrioventricular Block-Mobitz Type I (Wenckebach) from Second Degree Atrioventricular Block-Mobitz Type II

  • General Comments: differentiation between Weckebach and Mobitz type II cannot be made in the setting of a 2:1 block (since every other beat is non-conducted and one cannot observe for possible PR prolongation that is observed in Wenkebach)
  • Second Degree Atrioventricular Block-Mobitz Type I (Wenckebach) (see Second Degree Atrioventricular Block-Mobitz Type I, [[Second Degree Atrioventricular Block-Mobitz Type I]]): progressive PR prolongation precedes the non-conducted P-wave
  • Second Degree Atrioventricular Block-Mobitz Type II: PR remains unchanged prior to the non-conducted P-wave

Clinical Manifestations

Cardiovascular Manifestations

  • xxxxx
  • xxxxx

Other Manifestations

  • xxx

Treatment

General Management

  • xxx

Treatment of Second Degree AV Block Associated with Myocardial Ischemia/Infarction

  • Second-degree AV block associated with bundle-branch block and in particular with alternating bundle-branch block is an indication for permanent pacing.

References

  • TRACE Trial: Prognostic importance of complete atrioventricular block complicating acute myocardial infarction. Am J Cardiol. 2003;92(7):853 [MEDLINE]
  • Incidence, predictors, and outcomes of high-degree atrioventricular block complicating acute myocardial infarction treated with thrombolytic therapy. Am Heart J. 2005;149(4):670 [MEDLINE]
  • Atrioventricular Block Induced by Mad-Honey Intoxication. Tex Heart Inst J. 2009; 36(4): 342–344 [MEDLINE]
  • Septal infarction and complete heart block following percutaneous coronary intervention of the left anterior descending coronary artery. J Invasive Cardiol. 2009 Mar;21(3):E48-50 [MEDLINE]
  • Irreversible delayed complete heart block secondary to jailed first septal perforator following PCI of the left anterior descending coronary artery. J Invasive Cardiol. 2012 Jan;24(1):E13-5 [MEDLINE]
  • Atrioventricular nodal dysfunction secondary to hyperparathyroidism. J Thorac Dis. 2013 Jun; 5(3): E90–E92 [MEDLINE]