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Experimental His bundle escape rhythms
Insights
His bundle escape rhythms (HBER) often result from sino-atrial (S-A) node depression. Recovery time after overdrive stimulation is a key indicator of sinus node function and HBER sensitivity to sympathetic modulation.
Area of Science:
- Cardiovascular Physiology
- Cardiac Electrophysiology
Background:
- The sino-atrial (S-A) node is the primary pacemaker of the heart.
- His bundle escape rhythms (HBER) can occur when S-A node function is compromised.
Purpose of the Study:
- To investigate the interactions between the S-A node and HBER.
- To assess the impact of negative chronotropic agents on S-A node function and HBER.
Main Methods:
- Direct injection of negative chronotropic agents (verapamil, manganese, droperidol) into the canine S-A node artery.
- Assessment of S-A node depression and HBER using His bundle electrograms.
- Measurement of recovery times following atrial overdrive stimulation.
Main Results:
- HBER consistently followed S-A node depression.
- A strong correlation was observed between HBER and the initial S-A node rate.
- His bundle recovery time was significantly longer (50x) than S-A node recovery time after overdrive.
- HBER demonstrated greater sensitivity to sympathetic blockade compared to vagal influences.
Conclusions:
- Recovery time after overdrive stimulation is a reliable index of sinus nodal function.
- HBER frequently arises from selective S-A node depression, influenced by both rate and overdrive suppression.
- HBER exhibits heightened sensitivity to sympathetic modulation.
Abstract:
With the purpose of studying the interactions between sino-atrial (S-A) node and His bundle escape rhythms (HBER), negative chronotropic agents (verapamil, manganese and droperidol) were directly injected in the canine S-A node through its cannulated and autoperfused artery. HBER followed S-A node depression assessed by His bundle electrograms. A well established correlation was found between HBER and S-A node initial rate. His bundle recovery time following an atrial overdrive was 50 times larger than the S-A node recovery time. HBER was found to be more sensitive to sympathetic blockade than to vagal influences. It is concluded that 1) recovery time following overdrive stimulation is a valid index reflecting sinus nodal function; 2) HBER commonly results from selective depression of the S-A node not only depends on rate but also on overdrive suppression; 4) HBER is more sensitive to sympatheticmodulation.