Aberrant Ventricular Conduction - Mechanisms

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Contents 1 Mechanisms 2 Phase 3 Aberration 3 Concealed Retrograde Invasion of a Bundle Branch 4 Phase 4 Block 5 Acceleration-Dependent Block

Mechanisms

1. Abrupt shortening of the ventricular cycle length (phase 3 aberration)
2. Retrograde penetration into a bundle branch (concealed retrograde conduction)
3. Prolongation of ventricular cycle length (phase 4 aberration or bradycardia dependent block)
4. Modest shortening of the ventricular cycle length (acceleration-dependent block)

Phase 3 Aberration

• Occurs in normal fibers if an impulse reaches the cell prematurely when refractory. Most commonly seen following long-short sequence because the beat following the long cycle length has a prolonged refractory period. This type of block is physiologic and not indicative of diseased tissue.

Concealed Retrograde Invasion of a Bundle Branch

• Common mechanism for aberration during SVT. Most often the initial aberration is due to phase 3 block, but the sustaining mechanism is concealed retrograde conduction into one of the bundles. Also physiologic form of block.

Phase 4 Block

• Phase 4 Block is a form of aberration that occurs following a prolongation of the cardiac cycle length. During a long pause, such as from delayed sinus beat, the conducting fibers within the His-Purkinje system experience a decrease in membrane potential and consequently block impulses with termination in the HPS. This form of block is seen only in diseased tissue.

Acceleration-Dependent Block

• Seen with modest increases in cycle length. Not initiated with phase 3 block because the slight increase in cycle length is longer than the refractory period of the bundle branch.