Complex AV nodal dynamics during ventricular-triggered atrial pacing in humans

Area of Science:

• Electrophysiology
• Cardiovascular Physiology
• Nonlinear Dynamics

Background:

• In vitro studies indicate increased atrioventricular nodal (AVN) conduction complexity with elevated heart rates.
• Clinical observations of complex AVN dynamics like alternans exist, but human responses during rapid pacing remain understudied.

Purpose of the Study:

• To systematically investigate human AVN conduction dynamics during rapid ventricular-triggered atrial pacing.
• To identify and characterize novel AVN conduction phenomena and their underlying mechanisms.

Main Methods:

• Ventricular-triggered atrial pacing was performed in 37 patients with normal AVN function.
• Atrial pacing was repeated in 12 patients following autonomic blockade.
• Observed dynamics included alternans and quasisinusoidal oscillations, analyzed for frequency and relation to pathway physiology and autonomic status.

Main Results:

• Alternans, linked to single pathway conduction, were observed in 18 patients.
• Quasisinusoidal AVN conduction oscillations (mean frequency 0.02 Hz) were identified in 16 patients, a novel finding.
• No significant differences in dynamics were found between patients with or without dual AVN pathways.
• Autonomic blockade facilitated alternans but inhibited oscillations.

Conclusions:

• Rapid AVN excitation in vivo can induce autonomically mediated conduction oscillations.
• Single pathway alternans occur in vivo and are influenced by inherent nonlinear dynamic properties of AVN tissue.
• Findings elucidate the complex interplay of physiological and autonomic factors in human AVN conduction dynamics.