Approach Considerations
Permanent pacing is the therapy of choice in patients with symptomatic atrioventricular (AV) block with bradycardia.
Temporary transcutaneous or transvenous pacing is required if a slow heart rate (or asystole) caused by AV block requires correction and permanent pacing is not immediately indicated or not available.
Activity restriction
Patients with AV block should have their activities restricted to reduce the risk of injury until they have been properly evaluated and treated.
Consultations
Consultation with a cardiologist and/or cardiac electrophysiologist is indicated in the case of advanced heart block or unexplained syncope. An electrophysiologist must be consulted when invasive electrophysiology testing is needed to determine the level and/or magnitude of the AV block.
Pacemaker Implantation
Pacemaker implantation (or a pacemaker defibrillator if there is ventricular dysfunction) is indicated for symptomatic, irreversible atrioventricular (AV) block. Pacemaker implantation may include ventricular (VVI) or dual chamber (DDD) modes of pacing. Chronic right ventricular (RV) pacing may worsen left ventricular (LV) function. Cardiac resynchronization therapy (CRT) may be necessary in certain cases in which long-term pacing is required with reduced LV function.
The BLOCK-HF (Biventricular Versus Right Ventricular Pacing in Patients With Left Ventricular Dysfunction and Atrioventricular Block) randomized trial evaluated the effect of CRT in heart failure patients with AV block and found that CRT caused LV reverse remodeling and improved ejection fraction. [24] In addition, CRT pacing reduced mortality and heart failure admissions compared to RV pacing. [24] Based on these findings, for patients with high-degree AV block, CRT pacing therapy could be considered for patients with New York Heart Association (NYHA) functional class I, II, or III symptoms, an ejection fraction below 50%, and when chronic RV pacing is required. However, this study was published after the 2008 pacemaker guidelines [1, 2] and is not currently incorporated into any guidelines.
An electrophysiologist should determine the pacing type and the optimal pacing mode based on the level of block.
Long-Term Monitoring
Patients with asymptomatic first-degree or Mobitz I atrioventricular (AV) block do not require long-term monitoring with repeated rhythm strips/electrocardiograms or an event monitor.
Patients with asymptomatic, intermittent second-degree Mobitz II, high-degree, or third-degree AV block benefit from long-term event monitoring to assess for symptoms, bradycardia, or periods of asystole, as this would affect the timing of pacemaker implantation.
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Atrioventricular Block. This rhythm strip shows first-degree atrioventricular block with a PR interval of 0.360 sec. Note the fixed prolonged PR interval.
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Atrioventricular Block. First-degree atrioventricular block. PR interval is constant and is 0.280 sec.
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Atrioventricular Block. Second-degree Mobitz type I atrioventricular block. Note the prolongation of the PR interval preceding the dropped beat and the shortened PR interval following the dropped beat.
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Atrioventricular Block. Second-degree atrioventricular block, Mobitz type I (Wenckebach). Note the prolongation of the PR interval preceding the dropped beat and the shortened PR interval following the dropped beat.
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Atrioventricular Block. Second-degree Mobitz II atrioventricular block. Note the fixed PR interval, but after the third beat, an atrial impulse fails to conduct to the ventricle. Courtesy of Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Second_degree_heart_block.png).
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Atrioventricular Block. Second-degree atrioventricular block, Mobitz type II. A constant PR interval in conducted beats is present. Intraventricular conduction delay is also present.
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Atrioventricular Block. A constant PP interval and normal PR interval in conducted beats is present. This progresses to 2:1 atrioventricular (AV) block. A 2:1 AV block can be present with conduction delay in the AV node or His-Purkinje system, but it is more likely to be in the AV node for all patients (with a greater chance of AV block in the His-Purkinje system if there is a bundle branch block). Review extended monitoring strips because Mobitz I or Mobitz II may be present at other times, and this might help to determine the level of the block.
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Atrioventricular Block. High-degree atrioventricular block is demonstrated with a 4:1 atrial-to-ventricular conduction ratio. Note the P wave prior to the QRS conducts whereas the others do not. Courtesy of Life in the Fast Lane (https://lifeinthefastlane.com/ecg-library/basics/high-grade-block/), Edward J Burns, MD, Sydney, Australia.
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Atrioventricular Block. This rhythm strip shows third-degree atrioventricular block (complete heart block). The atrial rate is faster than the ventricular rate, and no association exists between the atrial and ventricular activity. Courtesy of Life in the Fast Lane (https://lifeinthefastlane.com/ecg-library/basics/complete-heart-block/), Edward J Burns, MD, Sydney, Australia.
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Atrioventricular Block. Third-degree atrioventricular block (complete heart block). The atrial rate is faster than the ventricular rate, and no association exists between the atrial and ventricular activity.
