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Determinants of the ventricular rate during atrial fibrillation
1Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor.
Insights
The study found that the atrioventricular (AV) node
Area of Science:
- Cardiology
- Electrophysiology
Background:
- Atrial fibrillation (AF) is a common arrhythmia characterized by rapid, irregular ventricular responses.
- Understanding the determinants of ventricular rate during AF is crucial for patient management.
- The atrioventricular (AV) node plays a key role in regulating ventricular response during AF.
Purpose of the Study:
- To identify the primary determinants of ventricular cycle length during atrial fibrillation.
- To assess the predictive value of AV node properties and concealed conduction on ventricular response in AF.
Main Methods:
- Investigated 52 patients, some with structural heart disease.
- Measured AV node effective and functional refractory periods, 1:1 conduction limits, and conduction times.
- Assessed these parameters at baseline and after autonomic modulation (isoproterenol/propranolol).
- Induced AF via rapid atrial pacing and measured ventricular cycle lengths (mean, shortest, longest).
Main Results:
- AV node effective refractory period (ERP) strongly correlated with mean RR interval (r=0.93).
- AV node functional refractory period (FRP) and shortest 1:1 conduction cycle length also showed strong correlations (r=0.87, r=0.91).
- Concealed conduction measures did not significantly improve prediction of ventricular cycle lengths.
Conclusions:
- AV node refractory periods and conductivity are the most significant determinants of ventricular rate during AF.
- Concealed conduction is a less important factor in determining the mean ventricular rate in AF.
Abstract:
Determinants of the ventricular cycle length during atrial fibrillation were examined in 52 patients. Thirty-three patients had structural heart disease and none had an accessory atrioventricular (AV) connection. The AV node effective and functional refractory periods, the shortest atrial pacing cycle length associated with 1:1 conduction, the AV node conduction time and indexes of concealed conduction in the AV node were measured in the baseline state (36 patients) and after modification of sympathetic tone by infusion of isoproterenol or propranolol (8 patients each). Atrial fibrillation was then induced with rapid atrial pacing, and the mean, shortest and longest ventricular cycle lengths were measured. Variables that correlated most strongly with the mean RR interval during atrial fibrillation were the AV node effective refractory period (r = 0.93; p less than 0.001), AV node functional refractory period (r = 0.87; p less than 0.001) and shortest atrial pacing cycle length associated with 1:1 conduction (r = 0.91; p less than 0.001). The AH interval during sinus rhythm (r = 0.74; p less than 0.001) and during atrial pacing at the shortest cycle length with 1:1 conduction (r = 0.52; p less than 0.001) had weaker correlations. Measures of concealed conduction did not improve the prediction of the mean or longest ventricular cycle length during atrial fibrillation. In conclusion, the refractory periods and conductivity of the AV node are the best indicators of the potential of the node to transmit atrial impulses to the ventricles during atrial fibrillation. The degree of concealed conduction in the AV node is a less important determinant of the mean ventricular rate during atrial fibrillation.