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Apparent bradycardia-dependent advanced second-degree atrioventricular block
Takakazu Katoh1, Shinji Kinoshita, Ichirou Ueji
1Katoh Cardiovascular Clinic, Ohtsu, Japan.
Journal of Electrocardiology
|April 16, 2002
Summary
This study reports a rare case of advanced second-degree atrioventricular block, presenting as intermittent bradycardia. The mechanism involves respiratory variations in vagal tone and concealed conduction, mimicking a previously undocumented condition.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Case Reports
Background:
- Atrioventricular (AV) block is a condition affecting the heart's electrical conduction system.
- Advanced second-degree AV block typically involves a higher ratio of blocked P waves to conducted QRS complexes.
- Understanding the mechanisms of rare cardiac arrhythmias is crucial for diagnosis and management.
Observation:
- A 65-year-old male presented with chest discomfort and dizziness.
- Continuous monitoring revealed a pattern of 4-5 conducted beats followed by 3-4 blocked P waves, with pulse pauses of approximately 4 seconds.
- Electrocardiogram (ECG) demonstrated sinus rhythm with intermittent failure of P wave conduction to the ventricles.
Findings:
- The observed bradycardia-dependent atrioventricular block was linked to respiratory variations in vagal tone.
- Shortening of PP intervals during inspiration facilitated impulse conduction.
- Lengthening of PP intervals during expiration led to successive P wave block, explained by concealed electrotonic conduction.
Implications:
- This case highlights a novel presentation of advanced second-degree AV block, potentially influenced by respiration.
- The findings suggest that periodic vagal tone changes and concealed conduction can precipitate unusual block patterns.
- Further research into such respiratory-modulated arrhythmias may improve understanding of complex cardiac conduction abnormalities.