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Tachycardia and bradycardia-dependent bundle branch block alternans: clinical observations

H C Cohen, I D'Cruz, E R Arbel

    Circulation
    |February 1, 1977
    PubMed

    Insights

    This study classifies bundle branch block (BBB) alternans based on heart rate. Tachycardia-dependent BBB alternans results from rapid rates, while bradycardia-dependent BBB alternans stems from slower rates and varying refractoriness.

    Area of Science:

    • Cardiology
    • Electrophysiology
    • Medical Sciences

    Background:

    • Bundle branch block (BBB) alternans is a complex phenomenon affecting cardiac conduction.
    • Understanding the mechanisms of BBB alternans is crucial for diagnosing and managing arrhythmias.
    • Previous classifications have not fully elucidated the rate-dependent nature of BBB alternans.

    Purpose of the Study:

    • To classify and elucidate the mechanisms of bundle branch block (BBB) alternans based on heart rate dependency.
    • To differentiate between tachycardia-dependent, bradycardia-dependent, and pseudobradycardia-dependent BBB alternans.

    Main Methods:

    • Study of eleven patients exhibiting bundle branch block (BBB) alternans.
    • Classification based on initiation of alternans relative to heart rate changes (acceleration or pause termination).
    • Analysis of conduction patterns, including 2:1 bidirectional block and alternating bundle branch cycle lengths.

    Main Results:

    • Identified three types of BBB alternans: tachycardia-dependent, bradycardia-dependent, and pseudobradycardia-dependent.
    • Tachycardia-dependent BBB alternans is linked to rapid heart rates and bidirectional block.
    • Bradycardia-dependent BBB alternans involves alternating refractoriness and cycle lengths, potentially due to retrograde conduction.

    Conclusions:

    • BBB alternans can be accurately classified based on its relationship with heart rate.
    • Tachycardia-dependent BBB alternans is characterized by a 2:1 block at faster rates.
    • Pseudobradycardia-dependent BBB alternans, while appearing rate-dependent, ultimately demonstrates underlying tachycardia-dependence.

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