Intracardiac myocardial elastography in canines and humans in vivo

Abstract

Intracardiac echocardiography (ICE) is a useful imaging modality which is used during radiofrequency (RF) ablation procedures to help identify anatomical structures. Utilizing ICE in adjunct with myocardial elastography (ME) can provide additional information on the mechanical properties of cardiac tissue and provide information on mechanical changes due to ablation. The objective of this study was to demonstrate that ICE can be used at high frame rate using a diverging beam transmit sequence to image myocardial strain and differentiate myocardial tissue properties before, during and after ablation for a clinical ablation procedure. In this feasibility study, three normal canines and eight patients with atrial fibrillation (AF) were studied in vivo. A 5.8-MHz ICE transducer was used to image the heart with a diverging beam transmit method achieving 1200 frames per second (fps). Cumulative axial displacement estimation was performed using 1-D cross-correlation with a window size of 2.7mm and 95% overlap. Axial cumulative strains were estimated in left atrium (LA) and right atrium (RA) using a least-squares estimator with a kernel of 2mm on the axial displacements. In the canine case, radial thickening was detected in the lateral wall and in the interatrial septum during LA emptying. For AF patients, mean absolute strain in the ablated region was lower (6.7±3.1%) than before the ablation (17.4±9.3%) in LA at end LA emptying. In the cavotricuspid isthmus (CTI) region, mean absolute strain magnitude at end RA emptying was found to be higher during ablation (43.0±18.1%) compared to after ablation (33.7±15.8%). Myocardial strains in the LA of an AF patient were approximately 2.6 times lower in the ablated region than before ablation. This initial feasibility may suggest ME as a new imaging modality to be used in adjunct with ICE in RF ablation guidance and lesion monitoring.

Reproducibility and Angle Independence of Electromechanical Wave Imaging for the Measurement of Electromechanical Activation during Sinus Rhythm in Healthy Humans

“…An ongoing clinical study deals with arrhythmia patients undergoing electrophysiological EP studies and RF-ablation. Combination of EWI with Myocardial Elastography (Bunting et al 2016; Grondin et al 2015; Papadacci et al 2017) and their complementarities is also a topic of ongoing studies. In conjunction with the catheter-based electroanatomic mapping frequently used in the clinic, EWI could non-invasively help physicians for the early detection, diagnosis, treatment planning, monitoring and follow-up of patients with arrhythmia through ultrasound-based mapping of their electromechanical activation sequence.…”

“…EWI uses dynamic focusing in receive: the RF signal at each pixel is reconstructed by performing a standard sum and delay algorithm in post-processing. The latter consists of using the delayed channel data from each element of the probe and summing all the resulting RF signals (Grondin et al 2015). The reconstructed RF frames had an angular sampling of 0.7° (ie.…”

Evaluation of Coronary Artery Disease Using Myocardial Elastography with Diverging Wave Imaging: Validation against Myocardial Perfusion Imaging and Coronary Angiography

“…Channel radiofrequency (RF) data were acquired at 2000 Hz on the 64 elements of the probe during 2 s and sampled at 10 MHz. A standard delay-and-sum method was used to reconstruct the entire image for each single diverging beam transmit (Grondin, et al 2015). The image was reconstructed on a polar grid of 256 lines, sampled axially at 20 MHz (i.e.…”

“…Previous studies have shown that diverging wave imaging can be used to image the heart with high contrast at high temporal resolution (Papadacci, et al 2014) or follow the propagation of the electromechanical wave in the heart at high temporal resolution by estimating inter-frame strains (Provost, et al 2013) and was validated against electrical mapping (Grondin, et al 2016). Diverging wave imaging has also been used to image cardiac end-systolic cumulative axial strains in patients with an intracardiac transducer to differentiate healthy tissue from RF lesion (Grondin, et al 2015). The feasibility and precision of estimating axial and lateral cardiac strain using diverging wave imaging has also been shown in healthy volunteers but without accumulating the strain over systole (Bunting, et al 2014).…”

3D Myocardial Elastography <italic>In Vivo</italic>

“…One such method is Myocardial Elastography [6]. It has been used to estimate the local displacement and strain of the myocardium during a cardiac cycle and showed an interest in detection and diagnosis of infarct [7], [8], graded ischemia conditions [9] and radio-frequency lesions in patients [10]. Since this method originally enabled the estimation of the axial strain, several methods have been developed to assess the lateral strain component using radio-frequency cross-correlation based techniques in phantoms [11]–[17] as well as in the heart [18]–[20].…”