Background: The interaction between regional left ventricular (LV) myocardial work and metabolism in remodeled hearts has not yet been well established. Our aim was to investigate the effect of inhomogeneous LV work distribution on regional metabolism and remodeling in our animal model with reversible dyssynchrony due to pacing. Methods: In 12 sheep, 8 weeks of right atrial and right ventricular free wall (DDD) pacing lead to LV dilatation, a thinned septum, and thickened lateral wall. Left bundle branch block–like dyssynchrony caused by DDD pacing could be acutely reverted by right atrial pacing (AAI) only. Invasive hemodynamics and echocardiography were used to assess regional work by stress-strain loop area and compared with regional glucose metabolism measured by 18 F-fluorodeoxyglucose positron emission tomography with and without improved spatial resolution by motion and anatomy correction on gated reconstructions. Results: Glucose metabolism by positron emission tomography with anatomic correction on gated positron emission tomography reconstruction showed a different regional distribution than with clinical reconstructions and correlated best and significantly with regional myocardial work. At baseline, work was homogeneously distributed with normal conduction (AAI pacing), whereas during dyssynchrony (DDD pacing), the lateral wall was more loaded, and the septum was unloaded. After 8 weeks of remodeling under DDD pacing, however, an almost homogeneous work distribution was found with DDD pacing, whereas with AAI pacing, the thin septum showed exaggerated loading and the lateral walls a low load. Our experimental observations were confirmed in 5 patient responders to cardiac resynchronization therapy. Conclusions: Regional LV glucose metabolism closely correlates with regional work. Our data indicate that regionally different LV remodeling after exposure to inhomogeneous loading conditions, such as during LV dyssynchrony, is an adaptive process that helps to equilibrate work distribution. Correction of the inhomogeneous loading conditions, such as during cardiac resynchronization therapy, then triggers a reverse LV remodeling through the same mechanism.
Aims Investigating the acute impact of cardiac resynchronization therapy (CRT) on regional myocardial work distribution in the left ventricle (LV) and to which extent it is related to long-term reverse remodelling. Methods and results One hundred and thirty heart failure patients, referred for CRT implantation, were recruited in our prospective multicentre study. Regional myocardial work was calculated from non-invasive segmental stress–strain loop area before and immediately after CRT. The magnitude of volumetric reverse remodelling was determined from the change in LV end-systolic volume, 11 ± 2 months after implantation. CRT caused acute redistribution of myocardial work across the LV, with an increase in septal work, and decrease in LV lateral wall work (all P < 0.05). Amongst all LV walls, the acute change in work in the septum and lateral wall of the four-chamber view correlated best and significantly with volumetric reverse remodelling (r = 0.62, P < 0.0001), with largest change seen in patients with most volumetric reverse remodelling. In multivariate linear regression analysis, including conventional parameters, such as pre-implant QRS morphology and duration, LV ejection fraction, ischaemic origin of cardiomyopathy, and the redistribution of work across the septal and lateral walls, the latter appeared as the strongest determinant of volumetric reverse remodelling after CRT (model R2 = 0.414, P < 0.0001). Conclusion The acute redistribution of regional myocardial work between the septal and lateral wall of the LV is an important determinant of reverse remodelling after CRT implantation. Our data suggest that the treatment of the loading imbalance should, therefore, be the main aim of CRT.
Major cardiovascular diseases are associated with (regional) dysfunction of the left ventricle. Despite the 3D nature of the heart and its dynamics, the assessment of myocardial function is still largely based on 2D ultrasound imaging thereby making diagnosis heavily susceptible to the operator's expertise. Unfortunately, to date, 3D echocardiography cannot provide an adequate spatio-temporal resolution in real-time. Hence, triplane imaging has been introduced as a compromise between 2D and true volumetric ultrasound imaging. However, tri-plane imaging typically requires high-end ultrasound systems equipped with fully populated matrix array probes embedded with expensive and little flexible electronics for two-stage beamforming. This paper presents an advanced ultrasound system for real-time, high frame rate, tri-plane echocardiography based on low element count sparse arrays, i.e. the so-called spiral arrays. The system was simulated, experimentally validated, and implemented for real-time operation on the ULA-OP 256 system. Five different array configurations were tested together with four different scan sequences, including multi-line and planar diverging wave transmission. In particular, the former can be exploited to achieve, in tri-plane imaging, the same temporal resolution currently used in clinical 2D echocardiography, at the expenses of contrast (−3.5dB) and signal-to-noise ratio (−8.7dB). On the other hand, the transmission of planar diverging waves boosts the frame rate up to 250 Hz, but further compromises contrast (−10.5dB), signal-to-noise ratio (−9.7dB), and lateral resolution (+46%). In conclusion, despite an unavoidable loss in image quality and sensitivity due to the limited number of elements, high frame rate tri-plane imaging with spiral arrays is shown to be feasible in real-time and may enable real-time functional analysis of all left ventricular segments of the heart. Index Terms-Cardiac imaging, high frame rate imaging, 3D imaging, tri-plane echocardiography, multiline transmission, diverging waves, spiral arrays, sparse arrays, real-time.
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