Can shear wave imaging distinguish between diffuse interstitial and replacement myocardial fibrosis?

Funding Acknowledgements

Type of funding sources: None.

Background

  Diffuse interstitial or myocardial replacement fibrosis are common features of a large variety of cardiomyopathies. These alterations contribute to functional changes, particularly to an increased myocardial stiffness (MS). Histological examination is the gold standard for myocardial fibrosis quantification, however, it requires endomyocardial biopsy which is invasive and not without risks. Cardiac magnetic resonance (CMR) can characterize the extent of both diffuse and replacement fibrosis and may have prognostic value in various cardiomyopathies. Echocardiographic shear wave (SW) elastography is an emerging approach for measuring MS in vivo. SWs occur after mechanical excitation of the myocardium, e.g. after mitral valve closure (MVC), and their propagation velocity is directly related to MS, thus providing an opportunity to assess stiffness at end-diastole.

Purpose

The aim was to investigate if velocities of natural SW can distinguish between interstitial and replacement fibrosis. 

Methods

We prospectively enrolled 47 patients (22 patients after heart transplant [54.2 ± 15.8 years, 82.6% male] and 25 patients with established hypertrophic cardiomyopathy [54.0 ± 13.5 years, 80.0% male]) undergoing CMR during their check-up. We performed SW elastography in parasternal long axis views of the LV using a fully programmable experimental scanner (HD-PULSE) equipped with a clinical phased array transducer (Samsung Medison P2-5AC) at 1100 ± 250 frames per second. Tissue acceleration maps were extracted from an anatomical M-mode line along the midline of the LV septum. The SW propagation velocity at MVC was measured as the slope in the M-mode image. All patients underwent T1 mapping as well as late gadolinium enhancement (LGE) cardiac magnetic resonance at 1.5 T to assess the presence of diffuse or replacement fibrosis (Figure A). Therefore, patients were divided in three groups: no fibrosis, diffuse fibrosis and replacement fibrosis.

Results

Mechanical SW’s were observed in 46 subjects starting immediately after MVC and propagating from the LV base to the apex. SW propagation velocity at MVC correlated well with native myocardial T1 values (r = 0.65, p < 0.0001) and differed significantly among groups (p < 0.0001), with a significant post-test between any pair of groups (Figure B). SW velocities below a cut-off of 6.01 m/s showed the highest accuracy to identify patients without any type of fibrosis (sensitivity 88 %, specificity 89%, area under the curve = 0.93) (Figure C). A cut-off of 8.11 m/s could distinguish replacement fibrosis from diffuse fibrosis with a sensitivity and specificity of 59% and 92 %, respectively (area under the curve = 0.80) (Figure D).

Conclusions

  Shear wave velocities after mitral valve closure can distinguish between normal and pathological myocardium and can detect differences between diffuse and replacement fibrosis.

Abstract Figure.

Localizing myocardial scar on echocardiography. How good does it work in the presence of conduction delays?

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation - Flanders (FWO)

Introduction

Myocardial scar detection with echocardiography in patients with ischemic heart disease typically relies on semi-quantitative evaluation of regional systolic wall thickening. In patients scheduled for cardiac resynchronization therapy (CRT) however, such echo scar estimation is complicated by the presence of dyssynchronous contraction and differential regional remodelling. Visual assessment of myocardial shortening during systole may be an alternative approach. We tested this against cardiac magnetic resonance (CMR) with late gadolinium enhancement (LGE) in patients without and with conduction delay.

Methods

122 patients with ischemic heart disease were included (n = 58 without, and n = 64 with conduction delay). Scar burden of the LV was determined in all patients on a segmental level in both CMR and echo. Reading of echo was blinded for CMR data and vice versa. Myocardial scar was defined as LGE > 50% of transmural thickness. On echo, scar was assessed visually, and defined as thin, echogenic myocardium with no visible shortening during systole. Analysis was performed per segment (18 segment model), and per region (6 walls with basal and mid segment and the apex region consisting of all apical segments). An additional analysis was performed with a tolerance of one adjacent segment in order to account for potential image misalignment between modalities.

Results

2196 segments were available for comparison between echo and CMR. On CMR, 548 of those segments were defined as having >50% transmural scar. In echo, 565 segments were detected as having scar. On a segmental level, no difference was found for the correct assignment of segments by echo as having scar or not between patients without or with conduction delay (AUC 0.79 vs. 0.79; p = 0.968) (Figure, top panels). See Figure for sensitivity and specificity. If one segment tolerance was allowed, segments were correctly assigned with equal accuracy in both patient groups (AUC 0.98 vs. 0.96; p = 0.999) (see Figure; w. tolerance). Agreement on the level of LV regions was comparable. 295 regions had a scar on CMR while 286 regions were identified by echo. Echo correctly identified a scar in the same LV wall or apex as compared to CMR similarly in patients without or with conduction delay (AUC 0.79 vs. 0.77; p = 0.698). If one segment tolerance was allowed, correct identification improved further and was not different between both groups (AUC 0.93 vs. 0.91; p = 0.999). The extent of a scar was slightly underestimated (9%) by echocardiography in comparison to CMR in patients without, and slightly overestimated (3%) in patients with conduction delays.

Conclusions

Scars can be localized on echocardiography with good agreement to CMR-LGE as gold standard. The match between echo and CMR was similar for patients with and without conduction delay. Our findings demonstrate that echo can provide a valid impression of localization and extent of myocardial scar, even in the presence of conduction delays.

Abstract Figure.

P975 Echocardiography and nuclear medicine imaging techniques are insufficient for scar detection in patients referred for cardiac resynchronization therapy

Funding Acknowledgements

The study was supported by Center for Cardiological Innovation

Background

Many patients referred for cardiac resynchronization therapy (CRT) do not respond to the treatment. Scar either in septum or the left ventricular (LV) lateral wall, as well as global scar burden, influence the outcome negatively. Preoperative scar assessment is therefore recommended in this patient group. Late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) is considered reference standard for scar detection, but is not always available.

Purpose

To investigate the ability of advanced echocardiographic and nuclear imaging techniques to detect septal and left ventricular (LV) lateral wall scar in patients referred for CRT, compared to late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR).

Methods

Scar was quantified as percentage segmental LGE in 131 patients (age 66 ± 10, 66% male, QRS-width 164 ± 17ms) referred for CRT, 92% with left bundle branch block (LBBB). Longitudinal strain was assessed by speckle tracking echocardiography in 130 patients (641 septal and 630 LV lateral wall segments). Wall motion score index (WMSI) was assessed visually in all patients by an experienced operator, and graded from one to four. Glucose metabolism was assessed by 18F-fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) in 52 patients. Perfusion was assessed in 46 patients by either 13N-ammonia PET (n = 32) or Single Photon Emission Computed Tomography (SPECT) (n = 14). Metabolism and perfusion were reported as percentages of the segment with maximum tracer uptake. The ability of each parameter to identify scar was evaluated with receiver operating characteristic (ROC) curves with calculation of area under the curve (AUC) and 95% confidence interval (CI). AUC≥0.800 was considered reasonable agreement with LGE.

Results

Scar was present in 574 of total 2090 interpretable segments (79% ischemic etiology). Globally, perfusion (AUC = 0.845, 95% CI 0.777-0.914) and glucose metabolism (AUC = 0.807, 95% CI 0.758-0.855) adequately detected transmural scars, but not smaller scars (all AUC < 0.800). Echocardiographic parameters failed to detect global scars irrespective of size (all AUC < 0.800). However, the associations between echocardiographic/nuclear parameters and scars were highly dependent on myocardial region. In the LV lateral wall, glucose metabolism precisely detected transmural scars (AUC = 0.958, 95% CI 0.902-1.00) and WMSI proved reasonable agreement (AUC = 0.812, 95% CI 0.737-0.887), while the rest of the parameters did not (all AUC < 0.800). Smaller scars in this region was not detected by any parameter tested (all AUC < 0.800). No parameter adequately detected septal scars, not even those with transmural involvement (all AUC < 0.800) (Figure).

Conclusions

Neither echocardiographic nor nuclear imaging techniques can replace LGE-CMR in scar assessment prior to CRT. Septum is especially challenging, explained by LBBB-induced reduction in strain, metabolism and perfusion in this region.

Abstract P975 Figure. Detection of transmural septal scar

P6180Septal negative work correlates inversely with septal scar in patients referred for cardiac resynchronization therapy

Background

Myocardial scar is frequently present in patients with heart failure and left bundle branch block (LBBB), and associated with reduced response to cardiac resynchronization therapy (CRT). Furthermore, LBBB may be associated with markedly reduced strain, work, metabolism and perfusion in septum, even without septal ischemia. Therefore, it may be challenging to identify scar by functional imaging methods.

Purpose

To investigate the ability of advanced echocardiographic and nuclear imaging techniques to detect septal and left ventricular (LV) lateral wall scar in patients referred for CRT, compared to late gadolinium enhancement (LGE) cardiac magnetic resonance.

Methods

Scar was quantified as percentage LGE in five septal and five LV lateral wall segments of 131 patients (age 66±10, 66% male, QRS-width 164±17ms) referred for CRT, 92% with LBBB. Longitudinal strain was assessed by speckle tracking echocardiography in 130 patients (652 septal and 631 LV lateral wall segments). Myocardial work was calculated by LV pressure-strain analysis. Systolic shortening defined positive work, while systolic lengthening defined negative work. Glucose metabolism was assessed by 18F-fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) in 52 patients (260 septal and 260 LV lateral wall segments). Perfusion was assessed in 46 patients (230 septal and 230 LV lateral wall segments) by either 13N-ammonia PET (n=32) or Single Photon Emission Computed Tomography (SPECT) (n=14). Metabolism and perfusion were reported as percentages of the segment with maximum tracer uptake. We evaluated parameter relationship to scar with Spearman correlation (rs) and regression analysis.

Results

LGE was present in 198 septal (30%) and 136 LV lateral wall (21%) segments. In a multivariate regression model with negative work, metabolism, perfusion and peak strain, only the first three parameters showed a significant association with LGE percent in septum (p<0.001, p=0.022 and p<0.001, respectively), while peak strain did not (p=0.270). Negative work in septum correlated inversely with percentage septal LGE-uptake (rs=-0.33): increasing amount of scar was associated with less negative work (Figure).

In the LV lateral wall, however, negative work did not shown a significant association with percentage LGE in univariate regression analysis (p=0.109). In a multivariate regression model positive work, metabolism and perfusion correlated with percentage LGE (p=0.049, p=0.008 and p<0.001), while peak strain did not (p=0.607).

Two representative patients

Conclusions

Septal negative work correlates inversely with septal scar in patients referred for CRT. This finding is probably linked to LBBB, and may be explained by increased stiffness of scar tissue. Myocardial work, but not peak strain, reflects scar in the LV lateral wall. Future studies should explore the assessment of scar in the complete LV and how this relates to CRT response.