Atrioventricular Block Workup
- Author: Chirag M Sandesara, MD; Chief Editor: Jeffrey N Rottman, MD more...
Laboratory testing is not usually indicated in patients with atrioventricular (AV) block. Levels of electrolytes and drugs (eg, digitalis) can be checked in the case of second-degree or third-degree AV block when suspicion of increased potassium level or drug toxicity exists. In cases when second-degree and third-degree AV block might be a manifestation of acute myocardial infarction, cardiac enzymes should be measured.
If clinical evaluation suggests systemic illness, appropriate directed laboratory studies for infection, myxedema, or connective tissue disease should be performed.
Routine electrocardiographic (ECG) recording and cardiac monitoring with careful evaluation of the relationship between P waves and QRS complexes are the standard tests leading to proper diagnosis of AV blocks.
Identifying episodes of transient AV block with sudden pauses and/or low heart rate causing syncopal episodes may require 24-hour Holter monitoring, multiple ECG recordings, event (loop) ECG recordings, or, in selected cases, monitoring with implantable loop recorders (Reveal, Medtronic, Inc; Confirm, St Jude Medical, Inc).
Electrophysiologic testing is indicated in a patient with suspected AV block as the cause of syncope. The invasive recording of AH (atrium-His) and HV (His-ventricle) intervals may determine the degree of conduction abnormality and may guide decision making for pacemaker therapy. As noted, in selected cases, invasive diagnostic procedures may include implantation of a loop recorder.
In general, routine imaging studies are not helpful in diagnosing AV blocks.
However, imaging studies (eg, echocardiography) might be useful in diagnosing underlying comorbid conditions, such as aortic valve stenosis with calcification, wall motion abnormalities in acute ischemia, cardiomyopathy, and congenital heart disease (eg, congenitally corrected transposition of the great vessels).
Advanced heart block, such as Mobitz II or third-degree AV block, may become more symptomatic with increased activity, where an actual increase in block and decrease in effective heart rate may occur.
Exercise may be used to evaluate 2:1 heart block and differentiate Mobitz I second-degree AV block (where the conducted rate increases) from Mobitz II AV block (where the block becomes more significant and often symptomatic).
[Guideline] Epstein AE, Dimarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: executive summary. Heart Rhythm. 2008 Jun. 5(6):934-55. [Medline].
[Guideline] Epstein AE, DiMarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, et al. 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2013 Jan 22. 61(3):e6-75. [Medline].
Schott JJ, Alshinawi C, Kyndt F, et al. Cardiac conduction defects associate with mutations in SCN5A. Nat Genet. 1999 Sep. 23(1):20-1. [Medline].
Nery PB, Beanlands RS, Nair GM, Green M, Yang J, McArdle BA, et al. Atrioventricular block as the initial manifestation of cardiac sarcoidosis in middle-aged adults. J Cardiovasc Electrophysiol. 2014 Aug. 25(8):875-81. [Medline].
Saleh F, Greene EA, Mathison D. Evaluation and management of atrioventricular block in children. Curr Opin Pediatr. 2014 Jun. 26(3):279-85. [Medline].
Crisel RK, Farzaneh-Far R, Na B, Whooley MA. First-degree atrioventricular block is associated with heart failure and death in persons with stable coronary artery disease: data from the Heart and Soul Study. Eur Heart J. 2011 Aug. 32(15):1875-80. [Medline].
Kuleva M, Le Bidois J, Decaudin A, et al. Clinical course and outcome of antenatally detected atrioventricular block: experience of a single tertiary centre and review of the literature. Prenat Diagn. 2014 Dec 8. [Medline].
Stiles S. BLOCK-HF: replace RV pacing with BiV in AV-block heart failure. Heartwire. Nov 8, 2012. [Full Text].