ABSTRACT
Inter atrial block (IAB) is a prevailing cardiac conduction abnormality that is under-recognized in clinical practice. IAB has strong association with atrial arrhythmia, left atrial enlargement, and electromechanical discordance, increasing the risk of atrial fibrillation (AF) and myocardial ischemia. IAB was generally believed to be caused by impaired conduction along the Bachmann bundle (BB). However, there are three other conduction pathways, including the fibers posteriorly in the vicinity of the right pulmonary veins (VRPV), transseptal fibers in the fossa ovalis (FO), and muscular bundles on the inferior atrial surface near the coronary sinus (CS). We hypothesized that the importance of BB on IAB might have been overestimated. To test this hypothesis, various combinations of conduction pathway blocks were simulated based on a realistic human atrial model to investigate their effects on the index of clinical diagnosis standard of IAB using a simulated 12-lead electrocardiogram (ECG). Firstly, the results showed that the BB block alone could not generate typical P wave morphology of IAB, and that the combination of BB and VRPV pathway block played important roles in the occurrence of IAB. Secondly, although single FO and CS pathways play subordinate roles in inter atrial conduction, their combination with BB and VRPV block could also produce severe IAB. In summary, this simulation study has demonstrated that the combinations of different inter atrial conduction pathways, rather than BB alone, resulted in ECG morphology of IAB. Attention needs to be paid to this in future pathophysiological and clinical studies of IAB.
Subject(s)
Adult , Humans , Male , Arrhythmias, Cardiac/physiopathology , Atrial Fibrillation/physiopathology , Computer Simulation , Coronary Sinus/physiopathology , Electrocardiography , Heart , Heart Atria , Models, Anatomic , Models, Cardiovascular , Pulmonary Veins/physiopathologyABSTRACT
Left anterior fascicular block (LAFB) is a heart disease identifiable from an abnormal electrocardiogram (ECG). It has been reported that LAFB is associated with an increased risk of heart failure. Non-specific intraventricular conduction delay due to the lesions of the conduction bundles and slow cell to cell conduction has also been considered as another cause of heart failure. Since the location and mechanism of conduction delay have notable variability between individual patients, we hypothesized that the impaired conduction in the ventricular myocardium may lead to abnormal ECGs similar to LAFB ECG patterns. To test this hypothesis, based on a computer model with a three dimensional whole-heart anatomical structure, we simulated the cardiac exciting sequence map and 12-lead ECG caused by the block in the left anterior fascicle and by the slowed conduction velocity in the ventricular myocardium. The simulation results showed that the typical LAFB ECG patterns can also be observed from cases with slowed conduction velocity in the ventricular myocardium. The main differences were the duration of QRS and wave amplitude. In conclusion, our simulations provide a promising starting point to further investigate the underlying mechanism of heart failure with LAFB, which would provide a potential reference for LAFB diagnosis.
Subject(s)
Adult , Humans , Male , Bundle-Branch Block/diagnostic imaging , Computer Simulation , Electrocardiography , Heart/diagnostic imaging , Heart Atria/diagnostic imaging , Heart Conduction System/physiopathology , Heart Failure/diagnostic imaging , Heart Ventricles/diagnostic imaging , Models, Anatomic , Models, Theoretical , Muscle Cells , Myocardium , Phantoms, Imaging , Poisson DistributionABSTRACT
Two clinical ablation protocols,2C3L and stepwise,have been routinely used in our group to treat atrial fibrillation (AF),but with a less than 60％ long-term arrhythmia-free outcome achieved in patients.The goal of this study was to examine the underlying mechanism of low success in clinical outcome.MRI images from one patient were used to reconstruct a human atrial anatomical model,and fibrotic tissue was manually added to represent the arrhythmia substrate.AF was induced with standard protocols used in clinical practice.2C3L and stepwise were then used to test the efficacy of arrhythmia termination in our model.The results showed that re-entries induced in our model could not be terminated by using either 2C3L or the stepwise protocol.Although some of the induced re-entries were terminated,others emerged in new areas.Ablation using only the 2C3L or stepwise method was not sufficient to terminate all re-entries in our model,which may partially explain the poor long-term arrhythmiafree outcomes in clinical practice.Our findings also suggest that computational heart modelling is an important tool to assist in the establishment of optimal ablation strategies.
ABSTRACT
Two clinical ablation protocols,2C3L and stepwise,have been routinely used in our group to treat atrial fibrillation (AF),but with a less than 60％ long-term arrhythmia-free outcome achieved in patients.The goal of this study was to examine the underlying mechanism of low success in clinical outcome.MRI images from one patient were used to reconstruct a human atrial anatomical model,and fibrotic tissue was manually added to represent the arrhythmia substrate.AF was induced with standard protocols used in clinical practice.2C3L and stepwise were then used to test the efficacy of arrhythmia termination in our model.The results showed that re-entries induced in our model could not be terminated by using either 2C3L or the stepwise protocol.Although some of the induced re-entries were terminated,others emerged in new areas.Ablation using only the 2C3L or stepwise method was not sufficient to terminate all re-entries in our model,which may partially explain the poor long-term arrhythmiafree outcomes in clinical practice.Our findings also suggest that computational heart modelling is an important tool to assist in the establishment of optimal ablation strategies.
