Efficient identification of scars using heterogeneous model hierarchies

AIMS

Detection and quantification of myocardial scars are helpful for diagnosis of heart diseases and for personalized simulation models. Scar tissue is generally characterized by a different conduction of excitation. We aim at estimating conductivity-related parameters from endocardial mapping data. Solving this inverse problem requires computationally expensive monodomain simulations on fine discretizations. We aim at accelerating the estimation by combining electrophysiology models of different complexity.

METHODS AND RESULTS

Distributed parameter estimation is performed by minimizing the misfit between simulated and measured electrical activity on the endocardial surface, subject to the monodomain model and regularization. We formulate this optimization problem, including the modelling of scar tissue and different regularizations, and design an efficient solver. We consider grid hierarchies and monodomain-eikonal model hierarchies in a recursive multilevel trust-region method. With numerical examples, efficiency and estimation quality, depending on the data, are investigated. The multilevel solver is significantly faster than a comparable single level solver. Endocardial mapping data of realistic density appears to be sufficient to provide quantitatively reasonable estimates of location, size, and shape of scars close to the endocardial surface.

CONCLUSION

In several situations, scar reconstruction based on eikonal and monodomain models differ significantly, suggesting the use of the more involved monodomain model for this purpose. Eikonal models can accelerate the computations considerably, enabling the use of complex electrophysiology models for estimating myocardial scars from endocardial mapping data.

[Anatomic pitfalls and challenges of His bundle pacing]

Long-term right ventricular apical pacing is known to be deleterious for left ventricular function leading to the clinical picture of heart failure with all the possibly associated complications, ranging up to death of the affected patient. This led to the ambition to find alternative pacing sites such as pacing at the right ventricular outflow tract or septal pacing. An attractive alternative is selective His bundle pacing with the goal to use the physiologic His-Purkinje system in order to enable intrinsic conduction and physiologic myocardial contraction. To find and identify the His bundle poses a challenge for operators. For exact endocardial mapping, knowledge of the anatomic landmarks is as important as the ability to evaluate local electrocardiograms. The goal of this review is to characterize the anatomic landmarks to help physicians to identify these precise targets for His bundle pacing.

Mechanisms of torsade de pointes tachycardia in patients with spontaneous high-degree atrioventricular block: A modern look at old data

INTRODUCTION

The mechanisms of torsade de pointes tachycardia (TdP) are incompletely understood. We aimed to investigate the mechanisms underlying TdP tachycardia in patients with spontaneous high-degree atrioventricular block (AVB).

METHODS AND RESULTS

This retrospective study reviewed old TdP recordings after ventricular temporary pacing interruption in 16 patients with spontaneous high-degree AVB. Five of them had also bipolar endocardial right ventricular (RV) apex recordings. The QT interval during AVB at a mean heart rate of 38.9 ± 7.5 bpm was 653.0 ± 67.2 ms. The critical coupling interval (CCI) between the last escape QRS during AVB and the first premature ventricular complex (PVC) was significantly shorter before the onset of TdP than before single PVCs and couplets. A morphologic crescendo of the escape T wave was observed before the onset of TdP, followed by a rhythmic and morphologic crescendo of PVCs. The escape RV apex electrograms (EGMs) showed the constant pattern of a rapid deflection similar to a Purkinje potential 40 to 80 ms after the onset of the QRS, superimposed on a smooth low amplitude signal in 4 out of 5 patients.

CONCLUSIONS

The major endocardial T wave prolongation and augmentation (morphologic crescendo) of the escape beat prior to the first PVC suggests a phase 2 reentry mechanism due to early afterdepolarization. The induced TdP can be due to the changing outputs from one or two simultaneous RV moving reentry circuits between depressed fibers and fast conducting ones, possibly located in the thin crista supraventricularis structure which has several connections with the septum and the RV free wall.

Validation of the mapping accuracy of a novel non-invasive epicardial and endocardial electrophysiology system

Aims

Use of a non-invasive electrocardiographic mapping system may aid in rapid diagnosis of atrial or ventricular arrhythmias or the detection of ventricular dyssynchrony. The aim of the present study was to validate the mapping accuracy of a novel non-invasive epi- and endocardial electrophysiology system (NEEES).

Methods and results

Patients underwent pre-procedural computed tomography or magnetic resonance imaging of the heart and torso. Radiographic data were merged with the data obtained from the NEEES during pacing from implanted pacemaker leads or pacing from endocardial sites using an electroanatomical mapping system (CARTO 3, Biosense Webster). The earliest activation as denoted on the NEEES three-dimensional heart model was compared with the true anatomic location of the tip of the pacemaker lead or the annotated pacing site on the CARTO 3 map. Twenty-nine patients [mean age: 62 ± 11 years, 6/29 (11%) female, 21/29 (72%) with ischaemic cardiomyopathy] were enrolled into the pacemaker verification group. The mean distance from the non-invasively predicted pacing site to the anatomic reference site was 10.8 ± 5.4 mm for the right atrium, 7.7 ± 5.8 mm for the right ventricle, and 7.9 ± 5.7 mm for the left ventricle activated via the coronary sinus lead. Five patients [mean age 65 ± 4 years, 2 (33%) females] underwent CARTO 3 verification study. The mean distance between non-invasively reconstructed pacing site and the reference pacing site was 7.4 ± 2.7 mm for the right atrium, 6.9 ± 2.3 mm for the left atrium, 6.5 ± 2.1 mm for the right ventricle, and 6.4 ± 2.2 for the left ventricle, respectively.

Conclusion

The novel NEEES was able to correctly identify the site of pacing from various endo- and epicardial sites with high accuracy.