Quantitative analysis of intraventricular dyssynchrony using wall thickness by multidetector computed tomography

Abstract

Objectives: We sought to determine the feasibility of cardiac computed tomography (CT) to detect significant differences in the extent of left ventricular dyssynchrony in heart failure (HF) patients with wide QRS, HF patients with narrow QRS, and age-matched controls.

Background: The degree of mechanical dyssynchrony has been suggested as a predictor of response to cardiac resynchronization therapy. There have been no published reports of dyssynchrony assessment with the use of CT.

Methods: Thirty-eight subjects underwent electrocardiogram-gated contrast-enhanced 64-slice multidetector CT. The left ventricular endocardial and epicardial boundaries were delineated from short-axis images reconstructed at 10% phase increments of the cardiac cycle. Global and segmental CT dyssynchrony metrics that used changes in wall thickness, wall motion, and volume over time were assessed for reproducibility. We defined a global metric using changes in wall thickness as the dyssynchrony index (DI).

Results: The DI was the most reproducible metric (interobserver and intraobserver intraclass correlation coefficients >/=0.94, p < 0.0001) and was used to determine differences between the 3 groups: HF-wide QRS group (ejection fraction [EF] 22 +/- 8%, QRS 163 +/- 28 ms), HF-narrow QRS (EF 26 +/- 7%, QRS 96 +/- 11 ms), and age-matched control subjects (EF 64 +/- 5%, QRS 87 +/- 9 ms). Mean DI was significantly different between the 3 groups (HF-wide QRS: 152 +/- 44 ms, HF-narrow QRS: 121 +/- 58 ms, and control subjects: 65 +/- 12 ms; p < 0.0001) and greater in the HF-wide QRS (p < 0.0001) and HF-narrow QRS (p = 0.005) groups compared with control subjects. We found that DI had a good correlation with 2-dimensional (r = 0.65, p = 0.012) and 3-dimensional (r = 0.68, p = 0.008) echocardiographic dyssynchrony.

Conclusions: Quantitative assessment of global CT-derived DI, based on changes in wall thickness over time, is highly reproducible and renders significant differences between subjects most likely to have dyssynchrony and age-matched control subjects.

Keywords: dyssynchrony; heart failure; imaging; pacing; tomography.

Figure 1. Method of Assessing Dyssynchrony With Wall Thickness Analysis by Cardiac CT

(A) Left ventricular (LV) model displaying short axis slices with endocardial (white) and epicardial (red dots) casts. (B) Endocardial (red) and epicardial (green) tracing of 1 short-axis image, segmented into 6 standardized segments. Left ventricular wall thickness is depicted as the radial distance between the endocardial and epicardial contours (yellow lines). (C) Serial short axis images depicted at 10% phase increments of the cardiac cycle at 1 slice level of the mid-ventricle. Representative graphs showed the time-to-maximal LV wall thickness at 1 ventricular slice in (D) a healthy “control” with EF 66%; (E) “HF-narrow QRS patient” with nonischemic cardiomyopathy and EF 31%; (F) “HF-wide QRS patient” with ischemic cardiomyopathy, EF 33%, and LBBB; and (G) “HF-wide QRS patient” with nonischemic cardiomyopathy, EF 19%, and LBBB. The graphs displayed the wall thickness of the 6 standardized segments of the LV myocardium over 1 cardiac cycle at a single ventricular slice level. The time-to-maximal wall thickness of the 6 segments is more variable in the HF-wide QRS patients than control and HF-narrow QRS, suggesting a greater degree of dyssynchrony. A = anterior; AL = anterolateral; AS = anteroseptal; CT = computed tomography; EF = ejection fraction; HF = heart failure; I = inferior; IL = inferolateral; IS = inferoseptal; LBBB = left bundle branch block.

Figure 2. Interobserver Correlation and Bland-Altman Graphs of DI

(A) Interobserver correlation scatterplot of the individual DI measurements by Observer 1 and 2. The solid line is the linear regression line. (B) Bland-Altman graph plotted to assess for bias and limits of agreement between the measurements by Observer 1 and 2. The solid line is the bias (mean of the differences) between the measurements by Observer 1 and 2. The dashed lines are the upper and lower limits of agreement (bias ± 2 SD of bias). DI = dyssynchrony index.

Figure 3. Box and Whisker Plot of DI Using Changes in LV Wall Thickness of the 3 Groups

Mean DI was significantly different between the 3 groups and was greatest in the HF-wide QRS group, followed by the HF-narrow QRS, and then the control group (152 ± 44 ms vs. 121 ± 58 ms vs. 65 ± 12 ms, respectively; p < 0.0001). HF = heart failure; LV = left ventricular; other abbreviations, as in Figure 2.