Patient assessment for cardiac resynchronization therapy: Past, present and future of imaging techniques

Abstract

It has been proposed that dyssynchrony assessment before cardiac resynchronization therapy (CRT) implantation could help predict response to CRT. It is known that up to 40% of patients who receive a CRT device for established indications do not respond to CRT. Great expectations came from the Predictors of Response to Cardiac Resynchronization Therapy (PROSPECT) study, which would finally identify the ultimate echocardiographic dyssynchrony criteria to help select responders. The recently published PROSPECT trial failed to identify an ideal parameter of dyssynchrony. Patient selection for CRT should involve a multimodal approach, and new promising tools are being investigated in that view. The present review integrated new data coming from the exciting field of imaging with currently available evidence to generate a stepwise approach to patient selection.

Figure 1)

Examples of simple dyssynchrony assessment using pulsed Doppler (left ejection pre-interval) and tissue Doppler imaging Q analysis septolateral delay. In this example, according to cited criteria, no dyssynchrony is identified

Figure 2)

A patient with ischemic cardiomyopathy who underwent cardiac resynchronization therapy. The upper left panel shows the pre-implantation colour-coded velocity curves derived from the basal septal (yellow) and lateral (green) segments. There is a delay of 90 ms between the septal and lateral peak systolic velocities, indicating left ventricular dyssynchrony. The upper right panel shows the corresponding tissue synchronization imaging (TSI) pre-implantation analysis. The red colour at the basal lateral wall indicates delay in mechanical activation. The automatically calculated difference in peak systolic velocities between the septal and lateral wall is 85 ms. The lower left panel shows the postimplantation velocity curves of the basal septal and lateral wall. No delay remains between the peak systolic velocities. The lower right panel shows the corresponding TSI analysis after implantation. The absence of late activation is evident. Pos vel Positive velocity. Reproduced with permission from reference

Figure 3)

Equations to calculate strain (1) and strain rate (2), where ΔL is an absolute change in length and L₀ is the baseline length

Figure 4)

Dyssynchrony using speckle-tracking strain. The left panel demonstrates time-strain curves of a patient without dyssynchrony at baseline. This patient did not show left ventricular (LV) remodelling during follow-up (LV end-systolic volume [LVESV] was 84 mL at baseline versus 73 mL at six-month follow-up). The right panel demonstrates time-strain curves of a patient with LV dyssynchrony at baseline (earliest activated segments: purple, green and dark blue; latest activated segments: light blue, yellow and red). This patient showed LV remodelling during follow-up (LVESV was 122 mL at baseline versus 77 mL at the six-month follow-up). Reproduced with permission from reference

Figure 5)

Three-dimensional echocardiography and left ventricular dyssynchrony. A Full volume acquisition. B Left ventricular cast produced by quantitative analysis. C Regional volume curves in normal systolic function. D Regional volume curves in severe intraventricular dyssynchrony. Reproduced with permission from reference

Figure 6)

Phase analysis with gated myocardial perfusion single-photon emission computed tomography (GMPS). A Example of a patient without left ventricular (LV) dyssynchrony on GMPS. The non-normalized (upper panel) and normalized (lower panel) phase distribution bull’s eyes are nearly uniform, and the corresponding phase histograms are highly peaked, narrow distributions (with a small SD). B Example of a patient with LV dyssynchrony derived from GMPS. The non-normalized (upper panel) and normalized (lower panel) phase distribution bull’s eyes show significant nonuniformity and the corresponding phase histograms are widely spread distributions (greater SD and bandwidth). Reproduced with permission from reference

Figure 7)

A gated blood pool single photon emission computed tomography reconstruction (A) is used to detect endocardial walls with 400 vertexes per ventricle (B). Normal vectors to the surface are used to analyze radial motion (C) of each vertex. A Fourier analysis is used to extract phase and amplitude of each motion curve, and create the phase diagram (D). Simple vectorial algebra is used to determine the contraction homogeneity index

Figure 8)

Dyssynchrony assessments through cardiac magnetic resonance imaging. A Division of the left ventricular (LV) myocardium into slices and segments. B The junction between the interventricular septum and the right ventricular (RV) free wall delimits the beginning of segment 1 and the end of segment 6, counting clockwise. C and D Representative graphs of radial wall motion of LV segments throughout the cardiac cycle in an LV basal slice in a control subject (C), and in a patient with heart failure (HF) and left bundle branch block (LBBB) (D). Polar maps are shown. Note the late contraction of the inferoposterior wall in the patient with HF and LBBB. Reproduced with permission from reference

Figure 9)

A multimodal approach (see text). 6MWT 6 min walk test distance in metres; CMR Cardiac magnetic resonance imaging; CRT Cardiac resynchronization therapy; EF Ejection fraction; IVMD Interventricular mechanical delay; LPEI Left ejection pre-interval; NYHA New York Heart Association; TSI Tissue synchronization imaging