Changes in electrical activation modify the orientation of left ventricular flow momentum: novel observations using echocardiographic particle image velocimetry

Abstract

Aims: Changes in electrical activation sequence are known to affect the timing of cardiac mechanical events. We aim to demonstrate that these also modify global properties of the intraventricular blood flow pattern. We also explore whether such global changes present a relationship with clinical outcome.

Methods and results: We investigated 30 heart failure patients followed up after cardiac resynchronization therapy (CRT). All subjects underwent echocardiography before implant and at follow-up after 6+ months. Left ventricular mechanics was investigated at follow-up during active CRT and was repeated after a temporary interruption <5 min later. Strain analysis, performed by speckle tracking, was used to assess the entity of contraction (global longitudinal strain) and its synchronicity (standard deviation of time to peak of radial strain). Intraventricular fluid dynamics, by echographic particle image velocimetry, was used to evaluate the directional distribution of global momentum associated with blood motion. The discontinuation of CRT pacing reflects into a reduction of deformation synchrony and into the deviation of blood flow momentum from the base-apex orientation with the development of transversal flow-mediated haemodynamic forces. The deviation of flow momentum presents a significant correlation with the degree of volumetric reduction after CRT.

Conclusion: Changes in electrical activation alter the orientation of blood flow momentum. The long-term CRT outcome correlates with the degree of re-alignment of haemodynamic forces. These preliminary results suggest that flow orientation could be used for optimizing the biventricular pacing setting. However, larger prospective studies are needed to confirm this hypothesis.

Keywords: cardiac fluid mechanics; cardiac mechanics; echo-PIV; electrical activation; haemodynamic forces.

Figure 1

Correlation between flow orientation changes and volumetric response. Correlation between change in the orientation of flow momentum from CRT-ON to CRT-OFF (δφ = φ_OFF – φ_ON) and relative volumetric reduction from pre-implant to follow-up of (A) end-diastolic volume (ΔEDV = EDV_post− EDV_pre) and (B) end-systolic volume (ΔESV = ESV_post− ESV_pre). The coloured green and red points indicate, respectively, the individual cases of SR and NR patients analysed in the text and in the subsequent pictures.

Figure 2

Directional distribution of flow momentum in SR and NR patients. Polar histograms show the orientation and relative magnitude of blood-induced intraventricular forces in four examples of SR patients and two examples of NRs. The left column shows the flow forces distribution under normal condition with CRT active (CRT-ON); the right column reports the same representation during temporary CRT deactivation (CRT-OFF). SR patients present a longitudinal alignment of haemodynamic forces that is lost when the therapeutic support is discontinued. Differently, NRs do not display a preferable longitudinal orientation either during active or inactive synchronization therapy.

Figure 3

Bland–Altman analysis of inter-observer agreement for the momentum orientation angle. Inter-operator agreement (A) in the repeated flow analysis of same recording (60 cases) and (B) in the flow analysis of second acquisitions (10 recordings).