# A Computer Simulation Research of Two Types of Cardiac Physiological Pacing
###### Abstract  
This manuscript adopted the cardiac modeling and simulation method to study the problems of physiological pacing in clinical application. A multiscale rabbit ventricular electrophysiological model was constructed. We simulated His-bundle pacing (HBP) treatment for left bundle branch block (LBBB) and atrioventricular block (AVB), and left bundle branch pacing (LBBP) treatment for LBBB by setting various moments of the stimulus. The synthetic ECGs and detailed electrical activities were analyzed. Our electrophysiological model accurately simulated the normal state, HBP, and LBBP. The synthetic ECG showed that QRS duration was narrowed by 30% after HBP correction for LBBB. For LBBB correction with LBBP, the synthetic ECGs of LBBP starting before 30 ms (if the end of atrial excitation is set as 0 ms) presented right bundle branch block (RBBB), and those of LBBP starting at 30-38 ms were synchronous, while those of LBBP starting after 42 ms possessed LBBB morphologies. The best pacing results were obtained when LBBP started at 34 ms. This manuscript verified the feasibility of the constructed ventricular model, and studied the physiological pacing mechanism. The results showed that HBP realized correction for AVB and high LBBB. The performance of LBBP can be improved by applying the stimulus within a specific period of time (0-8 ms) after atrial excitation.  
cardiac modeling; computer simulation; is-bundle pacing; left bundle branch pacing; left bundle branch block; atrioventricular block +
Footnote †: journal: Medical Medical Imaging  
doi: 10.1146/1.  
Indications for physiological pacing include the atrioventricular block (AVB) and bundle branch block. Although LBBP has become a new popular treatment, it still has some limitations compared with HBP. For example, the conduction through the right bundle was abandoned, the excitation of the left ventricle is often too much earlier than that of the right ventricle. Additionally, the right bundle branch block (RBBB) often occurs following the use of LBBP for the correction of both the left bundle branch block (LBBB) [5, 8] and AVB [9], which may result in right heart insufficiency in the long run.  
Therefore, the key problems that need to be solved in the clinical application of physiological pacing include (a) the detailed internal mechanism of HBP and LBBP, (b) the setting of the pacing parameters to achieve biventricular synchronization in LBBP, such as release time of stimulus pulse. In clinical practice, the performance of physiological pacing can only be evaluated by clinical features, such as the electrocardiogram (ECG), ejection fraction, and others. The internal principles of electrical activities can hardly be explored and clarified in detail through clinical experiments. These years, computer modeling has become an effective way to study cardiac electrophysiology and has been applied in many studies [10, 11]. This method can simulate the process of action potential conduction on a heart model that accounts for the electrophysiological characteristics of cells and tissues. Recently, this method has begun to be used in the study of physiological pacing [12].  
This manuscript adopted the method of cardiac modeling and simulation to conduct research related to pathological problems in the clinical application of physiological pacing. First, we constructed a detailed, multiscale, rabbit ventricular electrophysiological model, which contained myocardial segmentation, cellular heterogeneity, and His-Purkinje system. We compared the synthetic ECG with the real ECG dataset to verify the correctness of the model. The HBP treatment for LBBB and AVB was then simulated, and the internal mechanism was explored, which also further verified the feasibility of the modeling simulation method for physiological pacing research. Finally, LBBP treatment for LBBB was simulated, we investigated the different effects of the release time of stimulus pulse, and determined how to improve pacing efficiency of LBBP.