3 rd Degree AV block Jason Haag

Heart Block 1 st Degree AV Block one-to-one relationship exists between P waves and QRS complexes, but the PR interval is longer than 200 ms

Heart Block 2 nd Degree Mobitz Type I AV Block (Wenckebach) PR interval is prolonging with each P wave to the point when the P wave is no longer conducted

Heart Block 2 nd Degree Mobitz Type II AV Block PR interval is constant, but occasionally P waves are not followed by the QRS complexes

Heart Block 3 rd Degree Heart Block More P waves than the QRS complexes exist and no relationship exists between them

3 rd Degree Heart Block Block can be in AV node or infranodal conduction system AV node 2/3 escape rhythms have narrow QRS (junctional) Fascicular or bundle branches Wide QRS (subjunctional) Rate typically in low 40s

Frequency In the US: 0.02% Internationally: 0.04%. Age: Bimodal peak, at infancy given congenital complete AV block and at advance d age due to progressive fibrosis and ischemia

History Syncope, near-syncope, and lightheadedness Fatigue, dyspnea, and angina Asymptomatic Sudden cardiac death

Physical Vital Signs (stable vs. unstable, always check HR manually) Signs of heart failure – JVD, a waves, Pulmonary edema New murmurs or gallops Target lesions (Lyme) Splinter hemm, Osler nodes, etc (endocarditis) Neuromuscular changes (mytonic/muscular dystrophy)

Etiologies Idiopathic Progressive Cardiac Conduction Disease ½ of cases of AV block Lenegre’s disease Progressive, fibrotic, sclerodegeneration of the conduction system Younger individuals, may be hereditary Lev’s disease Calcification extending from fibrous structures (aortic/mitral rings) into the conduction system Older individuals, ? ESRD Fibrosis NOS Typically mitral and aortic rings Mitral  narrow QRS Aortic  wide QRS

Etiologies (cont.) Ischemic heart disease 40% of cases Either from chronic ischemia or acute MI Acute MI AV blocks (20% of patients) 1 st degree (8%) 2 nd degree (5%) 3 rd degree (6%) LBBB/RBBB (10-20%) AV nodal block (narrow QRS) associated with inferior wall MI Bundle blocks (wide QRS) associated with anterior wall MI Drugs Calcium channel blockers, beta blockers, digoxin, amiodarone, adenosine, quinidine, procainamide

Etiologies (cont.) Infection Lyme disease, endocarditis, Rheumatic fever, Chagas disease, myocarditis Rheumatic disease Ankylosing spondylitis, Reiter syndrome, relapsing polychondritis, rheumatoid arthritis, scleroderma Infiltrative disease Amyloidosis, sarcoidosis, multiple myeloma, hemachromatosis, Wilson’s disease

Etiologies Hyperthyroidism Metabolic Hypoxia, hyperkalemia Neuromuscular disease Muscular dystrophy, dermatomyositis

Treatment Correct underlying problem – if you can Correct K, stop AV blocking medications, etc. If unstable Transcutaneous pacing If stable Plan for permanent pacemaker placement

Permanent Pacemaker Class I - Conditions for which evidence and/or general agreement exists that a given procedure or treatment is beneficial, useful, and effective Third-degree AV block and advanced second-degree AV block at any anatomic level associated with any one of the following conditions: Bradycardia with symptoms, heart failure, arrhythmias, pauses greater than 3 seconds, escape rate < 40 bpm

Permanent Pacemaker Class IIa - Weight of evidence or opinion is in favor of usefulness or efficacy Asymptomatic third-degree AV block at any anatomic site with average awake ventricular rates of 40 bpm or faster, especially if cardiomegaly or left ventricular (LV) dysfunction is present

References Gregoratos G, Abrams J, Epstein AE, et al: ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices: summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation 2002 Oct 15; 106(16): Kojic EM, Hardarson T, Sigfusson N, Sigvaldason H: The prevalence and prognosis of third-degree atrioventricular conduction block: the Reykjavik study. J Intern Med 1999 Jul; 246(1): McEnvoy GK, ed: AHFS Drug Information Bethesda, Md: American Society of Health-System Pharmacists; 2000: Ostaner LD, Brandt RL, Kjelsberg MI, et al: Electrocardiographic findings among the adult population of a total natural community. 1965; 31: Rardon DA, Miles WM, Mitrani RD, et al: Electrocardiographic Recognition: Atrioventricular Block and Dissociation. In: Zipes DP, Jalife J, eds. Cardiac Electrophysiology From Cell to Bedside, 2nd ed. Philadelphia, Pa: WB Saunders; 1995.