Abstract:

Ablation strategies to prevent episodes of paroxysmal atrial fibrillation (AF) have been subject to many clinical studies. The issues mainly concern pattern and transmurality of the lesions. This paper investigates ten different ablation strategies on a multilayered 3-D anatomical model of the atria with respect to 23 different setups of AF initiation in a biophysical computer model. There were 495 simulations carried out showing that circumferential lesions around the pulmonary veins (PVs) yield the highest success rate if at least two additional linear lesions are carried out. The findings compare with clinical studies as well as with other computer simulations. The anatomy and the setup of ectopic beats play an important role in the initiation and maintenance of AF as well as the resulting therapy. The computer model presented in this paper is a suitable tool to investigate different ablation strategies. By including individual patient anatomy and electrophysiological measurement, the model could be parameterized to yield an effective tool for future investigation of tailored ablation strategies and their effects on atrial fibrillation.

Abstract:

Reduced cardiac output, dysfunction of the conduction system, atrio-ventricular block, bundle branch blocks and remodeling of the chambers are results of congestive heart failure (CHF). Biventricular pacing as Cardiac Resynchronization Therapy (CRT) is a recognized therapy for the treatment of heart failure. The present paper investigates an automated non-invasive strategy to optimize CRT with respect to electrode positioning and timing delays based on a complex threedimensional computer model of the human heart. The anatomical model chosen for this study was the segmented data set of the Visible Man and a set of patient data with dilated ventricles and left bundle branch block. The excitation propagation and intra-ventricular conduction were simulated with Ten Tusscher electrophysiological cell model and adaptive cellular automaton. The pathologies simulated were a total atrioventricular (AV) block and a left bundle branch block (LBBB) in conjunction with reduced interventricular conduction velocities. The simulated activation times of different myocytes in the healthy and diseased heart model are compared in terms of root mean square error. The outcomes of the investigation show that the positioning of the electrodes, with respect to proper timing delay influences the efficiency of the resynchronization therapy. The proposed method may assist the surgeon in therapy planning.

Abstract:

BackgroundMultiple wavelets and rotors are accused of maintaining atrial fibrillation (AF). However, snake-like excitation patterns have recently been observed in AF. So far, computer models have investigated AF in a simplified anatomical model. In this work, pulmonary vein firing is simulated to investigate the initiation and maintenance of AF in a realistic anatomical model.Methods and ResultsThirty-five ectopic foci situated around all pulmonary veins were simulated by a unidirectional conduction block. The excitation propagation was simulated by an adaptive cellular automaton on a realistic 3-dimensional atrial anatomy. Atrial fibrillation was initiated in 65.7% of the simulations. Stable excitation patterns were broken up in anatomically heterogeneous regions, creating a streak-like excitation pattern similar to snakes. Multiple wavelets and rotors could be observed in anatomically smooth areas at the atria's roofs.ConclusionsThe influence of macroscopic anatomical structures on the course of AF seems to play an important role in the excitation propagation in AF. The computer simulations indicate that multiple mechanisms contribute to the maintenance of AF.

Abstract:

An optimal electrode position, atrio-ventricular (AV) and interventricular (VV) delay in cardiac resynchronization therapy (CRT) improves its success. An optimization strategy does not yet exist. A computer model of the Visible Man and a patient heart was used to simulate an atrio-ventricular and a left bundle branch block with 0%, 20% and 40% reduction in interventricular conduction velocity, respectively. The minimum error between physiological excitation and pathology/therapy was automatically computed for 12 different electrode positions. AV and VV delay timing was adjusted accordingly. The results show the importance of individually adjusting the electrode position as well as the timing delays to the patient's anatomy and pathology, which is in accordance with current clinical studies. The presented methods and strategy offer the opportunity to carry out non-invasive, automatic optimization of CRT preoperatively. The model is subject to validation in future clinical studies.

Abstract:

OBJECTIVE: Optimization of cardiac resynchronization therapy (CRT) is still unsolved. It has been shown that optimal electrode position,atrioventricular (AV) and interventricular (VV) delays improve the success of CRT and reduce the number of non-responders. However, no automatic, noninvasive optimization strategy exists to date. METHODS: Cardiac resynchronization therapy was simulated on the Visible Man and a patient data-set including fiber orientation and ventricular heterogeneity. A cellular automaton was used for fast computation of ventricular excitation. An AV block and a left bundle branch block were simulated with 100%, 80% and 60% interventricular conduction velocity. A right apical and 12 left ventricular lead positions were set. Sequential optimization and optimization with the downhill simplex algorithm (DSA) were carried out. The minimal error between isochrones of the physiologic excitation and the therapy was computed automatically and leads to an optimal lead position and timing. RESULTS: Up to 1512 simulations were carried out per pathology per patient. One simulation took 4 minutes on an Apple Macintosh 2 GHz PowerPC G5. For each electrode pair an optimal pacemaker delay was found. The DSA reduced the number of simulations by an order of magnitude and the AV-delay and VV - delay were determined with a much higher resolution. The findings are well comparable with clinical studies. CONCLUSION: The presented computer model of CRT automatically evaluates an optimal lead position and AV-delay and VV-delay, which can be used to noninvasively plan an optimal therapy for an individual patient. The application of the DSA reduces the simulation time so that the strategy is suitable for pre-operative planning in clinical routine. Future work will focus on clinical evaluation of the computer models and integration of patient data for individualized therapy planning and optimization.

Abstract:

Congestive heart failure (CHF) is affecting more than 15 million people in the western population with an increasing number. Biventricular pacing as Cardiac Resynchronization Therapy (CRT) is a recognized therapy for the treatment of heart failure. The present paper investigates the optimal pacing sites and stimuli delays for stimulation, based on a complex three-dimensional computer model of the human heart. The anatomical features were derived from the Visible Man data set. The excitation propagation and intraventricular conduction were simulated with Ten Tusscher electrophysiological cell model and an adaptive cellular automaton. Biventricular pacing in AV block III and LBBB with different interventricular conduction delays were investigated. The simulated activation times of different myocytes in the healthy and diseased heart model are compared in terms of root mean square error (ERMS). The outcomes of the investigation underline that the positioning of the electrodes considering a proper atrioventricular and intraventricular delay influences the efficiency of the resynchronization therapy. The results of this optimization strategy may assist the surgeon in therapy planning.

Abstract:

Heart Failure is the most common cardiac disease worldwide; supraventricular arrhythmia the most common cardiac arrhythmia. The understanding of these diseases advances treatment options. Ablation therapy is a well accepted non-pharmacological option in the treatment of atrial fibrillation. Cardiac resynchronization therapy with biventricular pacing devices has been shown successful in patients with severe heart failure. However, an optimization or even individual therapy planning is not standard or not even carried out today. These non-pharmacological treatments can be investigated and optimized with the help of computer models of the heart. Different ablation strategies are applied to terminate the arrhythmia in the virtual environment and a comparison of strategies can be carried out. With respect to cardiac resynchronization therapy, the computer model allows for automatic and non-invasive optimization of electrode positions and timing delays. With clinical validation, the presented computer models and methods have the potential to contribute to individualized therapy planning.

Abstract:

Question: The mechanisms responsible for atrial fibrillation (AF) are not completely understood. Various conduction velocities and realistic anatomical structures of the atria are implemented into a computer model showing the influence of complex anatomical structures on the initiation and maintenance of AF.Method Used: In a computer model of the Visible Female heart (National Library of Medicine, Bethseda, Maryland, USA), the initiation of AF was simulated by pulmonary vein (PV) firing. The anatomical model had a resolution of 1,696,740 tissue voxel with 0.33 mm voxel side length. 32 foci around all pulmonary veins were set. The excitation propagation was simulated using an adaptive cellular automaton. Electrophysiological parameters depending on different tissue types can be set. In this work, only the conduction velocity was reduced compared to physiological data.Results: The initiation of AF through ectopic foci creates re-entrant circuits and quasi-chaotic excitation pattern in the computer model. 8 of 16 foci in the left superior, 3 of 4 foci in the left inferior, 5 of 8 foci in the right superior and 4 of 4 foci in the right inferior PV created AF after only 1.5 s. The excitation pattern shows stable re-entrant circuits as well as chaotic behavior. A breakup of stable re-entrant circuits was also observed when simulating the pathology for 17.5 s. The other foci caused self-terminating rotors.Conclusion: Computer models of the excitation propagation of the heart can be used to simulate AF initiated by triggers in the PV. A reduction in conduction velocity caused the establishment of re-entrant circuits and quasi-chaotic behavior. The complex model of the Visible Female heart showed the importance of anatomical structures in the maintenance of AF. Future work will include an improvement of the computer model by incorporating heterogeneities of atrial tissue and an implementation of individual patient models for therapy planning.

Abstract:

Atrial Fibrillation (AF) is the most common cardiac arrhythmia with overall prevalence of almost 1%. Treatment options range from pharmacological to surgical options. While ablation strategies are the most common thera- pies, it has been testified that overdrive stimulation can prevent AF successfully. The presented work suggests an approach to simulate the excitation propagation with various overdrive pacing frequencies based on a detailed cell model in a simplified anatomical structure. Through simulations, a relationship between the overdrive pac- ing position and its frequency with respect to the onset of AF was shown. The method applied in this work can be used to further develop optimization strategies for overdrive pacing. In the long run, the application trans- ferred to individual patient data might be used to increase the success rate of overdrive pacing in terminating atrial fibrillation.