Related Experiment Video
Updated: May 23, 2026
Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
Published on: December 11, 2017
Conventional and biventricular pacing in patients with first-degree atrioventricular block
1Florida Heart Rhythm Institute, Tampa, FL, USA. ssbarold@aol.com
Insights
First-degree atrioventricular block may not be benign, potentially causing pacemaker syndrome and electrical desynchronization, especially during cardiac resynchronization therapy (CRT). Programming adjustments can mitigate risks, but AV junctional ablation may be needed in severe cases.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Devices
Background:
- First-degree atrioventricular block (AV block) is increasingly recognized as potentially serious.
- Conventional dual-chamber pacing can lead to functional atrial undersensing and pacemaker syndrome in patients with first-degree AV block.
- Cardiac resynchronization therapy (CRT) patients with prolonged PR intervals (≥200 ms) are more susceptible to electrical desynchronization.
Purpose of the Study:
- To evaluate the implications of first-degree AV block in patients undergoing cardiac pacing, particularly CRT.
- To identify risks associated with first-degree AV block, including pacemaker syndrome and electrical desynchronization.
- To discuss management strategies for first-degree AV block in the context of cardiac pacing.
Main Methods:
- Review of recent reports and clinical observations concerning first-degree AV block.
- Analysis of pacing parameters like PR interval, AV interval, and post-ventricular atrial refractory period (PVARP).
- Consideration of specific pacing modes and their impact on patients with first-degree AV block, including CRT.
Main Results:
- First-degree AV block can lead to functional atrial undersensing and pacemaker syndrome due to P-wave displacement into the PVARP.
- Patients with first-degree AV block undergoing CRT are at higher risk of electrical desynchronization, which is exacerbated during exercise.
- Shortening AV and PVARP intervals can prevent undersensing, but very long AV intervals in certain pacing modes may still cause issues.
Conclusions:
- First-degree AV block requires careful management to prevent complications like pacemaker syndrome and electrical desynchronization.
- Programming adjustments, including shorter AV and PVARP intervals, are crucial for managing patients with first-degree AV block.
- AV junctional ablation is a consideration for refractory cases of symptomatic undersensing or pacing disturbances during CRT.
Abstract:
Recent reports suggest that first-degree atrioventricular block is not benign. However, there is no evidence that shortening of the PR interval can improve outcome except for symptomatic patients with a very long PR interval ≥0.3 s. Because these patients require continual forced pacing, biventricular pacing should be used according to accepted guidelines for third-degree AV block. Functional atrial undersensing may occur in patients with conventional dual-chamber pacing and first-degree AV block because the sinus P-wave tends to be displaced into the post-ventricular atrial refractory period (PVARP) an arrangement that may cause a pacemaker syndrome. Prevention requires programming a shorter AV and PVARP that is feasible because retrograde conduction is rare in first-degree AV block patients. A relatively new pacing mode to minimize right ventricular stimulation has been designed by eliminating the traditional AV interval but with dual-chamber backup. This pacing mode permits the establishment of very long AV intervals that may cause pacemaker syndrome. About 50% of patients undergoing cardiac resynchronization therapy (CRT) have a PR interval ≥200 ms. The CRT patients with first-degree AV block are prone to develop electrical desynchronization more easily than those with a normal PR interval. The duration of desynchronization after exceeding the upper rate on exercise is also more pronounced. AV junctional ablation is rarely necessary in patients with first-degree AV block but should be considered for symptomatic functional atrial undersensing or when the disturbances caused by first-degree AV block during CRT cannot be managed by programming.
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