Catheter Ablation Lesion Visualization With Intracardiac Strain Imaging in Canines and Humans

How to ablate the septo-pulmonary bundle: a case-based review of percutaneous ablation strategies to achieve roof line block

Electrical conduction through cardiac muscle fibres separated from the main myocardial wall by layers of interposed adipose tissue are notoriously difficult to target by endocardial ablation alone. They are a recognised important cause for procedural failure due to the difficulties of delivering sufficient energy via the endocardial radiofrequency catheter to reach the outer epicardial layer without risking adverse events of the otherwise thin walled atria. Left atrial ablations for atrial fibrillation (AF) and tachycardia are commonly affected by the presence of several epicardial structures, with the septo-pulmonary bundle (SPB), Bachmann's bundle, and the ligament of Marshall all posing substantial challenges for endocardial procedures. Delivery of a transmural lesion set is essential for sustained pulmonary vein isolation and for conduction block across linear atrial lines which in turn has been described to translate into a reduced AF/atrial tachycardia recurrence rate. To overcome the limitations of endocardial-only approaches, surgical ablation techniques for epicardial or combined hybrid endo-epicardial ablations have been described to successfully target these connections. Yet, these techniques confer an increase in procedure complexity, duration, cost, and morbidity. Alternatively, coronary venous system ethanol ablation has been successfully employed by sub-selecting the vein of Marshall to facilitate mitral isthmus line block, although this approach is naturally limited to this area by the coronary venous anatomy. Increased awareness of the pathophysiological relevance of these epicardial structures and their intracardiac conduction patterns in the era of high-resolution 3D electro-anatomical mapping technology has allowed greater understanding of their contribution to the persistence of AF as well as failure to achieve transmural block by traditional ablation approaches. This might translate into novel catheter ablation strategies with procedural success rates comparable to surgical 'cut-and-sew' techniques. This review aims to give an overview of percutaneous catheter ablation strategies to target the SPB, an important cause of failed block across the roof line and isolation of the left atrial posterior wall and/or the pulmonary veins. Existing and investigational technologies will be discussed and an outlook of future approaches provided.

Personalized biomechanical insights in atrial fibrillation: opportunities & challenges

INTRODUCTION

Atrial fibrillation (AF) is an increasingly prevalent and significant worldwide health problem. Manifested as an irregular atrial electrophysiological activation, it is associated with many serious health complications. AF affects the biomechanical function of the heart as contraction follows the electrical activation, subsequently leading to reduced blood flow. The underlying mechanisms behind AF are not fully understood, but it is known that AF is highly correlated with the presence of atrial fibrosis, and with a manifold increase in risk of stroke.

AREAS COVERED

In this review, we focus on biomechanical aspects in atrial fibrillation, current and emerging use of clinical images, and personalized computational models. We also discuss how these can be used to provide patient-specific care.

EXPERT OPINION

Understanding the connection betweenatrial fibrillation and atrial remodeling might lead to valuable understanding of stroke and heart failure pathophysiology. Established and emerging imaging modalities can bring us closer to this understanding, especially with continued advancements in processing accuracy, reproducibility, and clinical relevance of the associated technologies. Computational models of cardiac electromechanics can be used to glean additional insights on the roles of AF and remodeling in heart function.

Three‐dimensional and catheter‐based intracardiac echocardiographic characterization of the interatrial septum in 2 horses with suspicion of a patent foramen ovale

This case report describes the 2‐dimensional transthoracic (2D‐TTE), 3‐dimensional transthoracic (3D‐TTE) and intracardiac echocardiographic (ICE) characterization of the fossa ovalis region in 2 horses. The first case was presented for poor performance and showed an anechoic zone in the interatrial septum on 2D‐TTE. Based on 3D‐TTE a deepened fossa ovalis could be identified and using ICE the presence of an interatrial shunt could be excluded. The second case was referred for a cardiac murmur and the presence of turbulent flow in and around the interatrial septum on 2D‐TTE color flow Doppler. The complementary use of 2D‐TTE, 3D‐TTE, and ICE allowed detailed characterization of a patent foramen ovale, with evidence of a left‐to‐right shunt in a dorsocranial to ventrocaudal direction with limited hemodynamic implications. These 2 cases underline the feasibility of 3D‐TTE and ICE in horses and especially show the added value of ICE in a clinical setting.

Appropriate Window Function and Window Length in Multifrequency Velocity Estimator for Rapid Motion and Locality of Layered Myocardium

The heart wall has a multilayered structure and moves rapidly during ejection and rapid filling periods. Local strain rate (SR) measurements of each myocardial layer can contribute to accurate and sensitive evaluations of myocardial function. However, ultrasound-based velocity estimators using a single-frequency phase difference cannot realize these measurements owing to insufficient maximum detectable velocity, which is limited by a quadrature frequency. We previously proposed a velocity estimator using multifrequency phase differences to improve the maximum detectable velocity. However, the improvement is affected by a spatial discrete Fourier transform (DFT) window length that represents the locality of the velocity estimation. In this article, we theoretically describe that shortening the window increases the interference between different frequency components and decreases the maximum detectable velocity. The tradeoff between the maximum detectable velocity and the window length was confirmed through simulations and a water-tank experiment. Under the tradeoff, the Hanning window, which was used in previous studies, is not always appropriate for the local measurement of the velocity, which sometimes exceeds 100 mm [Formula: see text] depending on the subject, direction of the ultrasound beam to the heart wall, and cardiac periods. In the in vivo measurement with the short window, the Tukey window with a large flat part that has a high-frequency resolution and ameliorates the discontinuity at both edges of the windowed signal was appropriate to measure the maximum velocity. This study offers the potential for local measurements of each myocardial layer using the multifrequency velocity estimator with the appropriate window function and window length.

Cyclic Variation of Spectral Parameters for the Differentiation of Atrial Myocardium Before and Immediately Following Radiofrequency Ablation

Radiofrequency ablation (RFA) is a common treatment of atrial fibrillation. However, current treatment is associated with a greater than 20% recurrence rate, in part due to inadequate monitoring of tissue viability during ablation. Spectral parameters, in particular cyclic variation of integrated backscatter (CVIB), have shown promise as early indicators of myocardial recovery from ischemia. Our aim was to demonstrate the use of spectral parameters to differentiate atrial myocardium before and after radiofrequency ablation. An AcuNav 10 F catheter was used to collect radiofrequency signals from the posterior wall of the left atrium of patients before and immediately after RFA for AF. The normalized power spectrum was obtained and three spectral parameters (integrated backscatter [IB], slope, and intercept) were extracted across two continuous heart cycles. Parameters were gated for ventricular end-diastole and compared before and after ablation. Additionally, the cyclic variation of each of these three parameters was generated as an average of the variation across the two recorded heart cycles. Data from 14 patients before and after ablation demonstrated a significant difference in the magnitude of the cyclic variation of integrated backscatter (9.0 vs. 6.0 dB, p < .001) and cyclic variation of the intercept (14.0 vs. 11.5 dB, p = .04). No significant difference was noted in the magnitude of the cyclic variation of the slope. Among spectral parameters gated for end-diastole, significant differences were noted in the slope (-4.39 vs. -3.73 dB/MHz, p = .002) and intercept (16.8 vs. 11.9 dB, p = .002). No significant difference was noted in the integrated backscatter. Spectral parameters are able to differentiate atrial myocardium before and immediately following ablation and may be useful in monitoring atrial ablations.