Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA·2009
Understanding the intrinsic rate- and time-dependent properties of the atrioventricular (AV) node is crucial for characterizing cardiac conduction.
Previous studies have not fully elucidated how different heart rate (HR) stimulation paradigms influence AV interval (AVI) dynamics.
Purpose of the Study:
To investigate whether the AV interval (AVI) remains comparable at identical heart rates (HR) achieved through distinct stimulation protocols.
To characterize the rate- and time-dependent properties of the AV node under varying HR conditions.
Main Methods:
Compared AVI changes during incremental HR increases (five 30-s steps, 20 beats/min each) versus single-step protocols to identical HR levels.
Maintained HR at each level for extended durations (30-150 s) to control for time-dependent influences.
Utilized autonomically decentralized dogs (n=16) with continuous recording of electrocardiogram, blood pressure, and intracardiac electrograms.
Main Results:
Differences in AVI between single- and multiple-step protocols were most significant within the initial 15 seconds of atrial pacing.
AV node accommodation (change in AV conduction time with increased, constant HR) was observed in both protocols.
The time to the loss of 1:1 AV conduction was significantly shorter with the multiple-step HR increase protocol.
Conclusions:
The AV node's intrinsic response to HR alterations is influenced by the absolute HR level, the duration of the rate change, and prior cumulative HR effects.
AV node behavior exhibits both rate- and time-dependent characteristics that are sensitive to the method of HR manipulation.