Relationship between conductivity and functional refractoriness of atrioventricular node in man

Area of Science:

• Cardiology
• Electrophysiology

Background:

• The atrial extrastimulus technique is commonly used to assess atrioventricular node (AVN) refractoriness.
• Limitations in measuring AVN refractoriness using this technique have been noted.

Purpose of the Study:

• To evaluate the limitations of the atrial extrastimulus technique for measuring AVN refractoriness in humans.
• To determine the relationship between AVN conductivity and functional refractoriness (FRP).

Main Methods:

• Studied 81 patients to assess AVN refractoriness measurement limitations.
• Defined AVN conduction patterns and analyzed H1H2 vs. A2A2 plots.
• Applied a mathematical formula derived from canine studies to relate conductivity and FRP.

Main Results:

• The atrial extrastimulus technique failed to determine AVN FRP in 13% of patients and 46% of basic cycle lengths.
• A strong agreement (r=0.97) was found between measured and calculated FRP using a derived algorithm.
• The calculation of FRP was independent of patient-specific variables.

Conclusions:

• The atrial extrastimulus technique is often inadequate for measuring human AVN refractoriness.
• A consistent relationship between AVN conductivity and FRP exists, similar to canine models.
• Calculating FRP from conductivity measurements is recommended for efficiency and data yield.