Left Ventricular Dyssynchrony

Assessment of Left Ventricular Dyssynchrony with Velocity-Encoded MRI

Jos J.M. Westenberg, Ph.D.

Introduction

Cardiac resynchronization therapy (CRT) is the proposed treatment in patients with severe heart failure, depressed left ventricular (LV) function and left bundle branch block (LBBB). Candidates who may benefit are mainly selected on ECG criteria. Still 20-30% of these patients does not respond to CRT, emphasizing the need for additional selection criteria.
Several studies demonstrated that the main predictor of CRT response may be the presence of LV dyssynchrony (i.e., mechanical delay between septum and lateral wall contraction), adequately assessed by echocardiography using tissue Doppler imaging (TDI). LV dyssynchrony assessment on TDI has not been compared directly with other imaging modalities. Velocity-encoded (VE) MRI potentially allows direct myocardial wall motion measurement similar to TDI.

Purpose

Comparing TDI with VE MRI for LV dyssynchrony assessment.

Methods

Twenty consecutive patients (15 men, mean age 57 ± 15 years) with heart failure, systolic LV dysfunction, QRS-duration >120 ms, interventricular conduction delay and idiopathic dilated cardiomyopathy were included. Ten normal individuals (8 men, mean age 57 ± 9 years) with QRS-duration <85 ms and normal LV function were evaluated for comparison.

TDI

Patients and normal individuals were imaged in the left lateral decubitus position using a commercially available system (Vingmed Vivid Seven, General Electric-Vingmed, Milwaukee, Wisconsin, USA). Images were obtained using a 3.5-MHz transducer at a depth of 16 cm in the parasternal and apical views (standard long-axis and two- and four-chamber images). Standard two-dimensional and color Doppler data, triggered to the QRS-complex, were saved in cine loop format. For TDI, color Doppler frame rates varied between 80 and 115 frames/s depending on the sector width of the range of interest; pulse repetition frequencies were between 500 Hz and 1 kHz, resulting in aliasing velocities between 16 and 32 cm/s. Intraventricular LV dyssynchrony was studied from the color Doppler images by off-line analysis using commercial software (Echopac 6.1, General Electric-Vingmed). The TDI data were analyzed by an experienced observer, blinded to the clinical and MRI data. Sample volumes were placed at the basal level in the septum and lateral wall (using the four-chamber images), to derive velocity graphs. From these data, the time from the beginning of the QRS-complex (on the ECG) to peak systolic velocities in the septum and lateral wall were assessed, and the difference between these two peak systolic velocities was calculated as measure of intraventricular dyssynchrony (referred to as the septal-to-lateral delay). In movie1, an example of the TDI is presented.

VE MRI

Within one week of the echocardiographic examination, MRI was performed using a 1.5 T MRI scanner (ACS-NT15 Gyroscan with the Powertrack 6000 gradient system; Philips Medical Systems, Best, The Netherlands). The body coil was used for transmission and a five-element phased-array synergy cardiac-coil was placed on the chest for signal reception. After scout images, standard two-chamber and four-chamber long-axis series for planning purposes (conform standard cardiac MR protocols, using balanced-FFE) and an LV short-axis series for LV function analysis were acquired, a three-directional VE MRIwas performed in the four-chamber orientation with a velocity sensitivity of 20 cm/s. Only the longitudinal velocity encoded in the direction parallel to the long-axis was analyzed. In movie2, an example of the VE MRI is presented.
The MRI data were analyzed by an experienced observer, blinded to the clinical and echocardiographic data. Sample volumes were placed at the basal level of the septum and lateral wall in the 30 phase images of the MRI with the velocity encoded in the direction of the long-axis of the LV. The mean velocity over the sample volume was measured, resulting in the myocardial wall velocity over one average cycle. During contraction and relaxation, the basal level moves, requiring manual correction for the placement of the sample volumes in each of the thirty phases. Intra- and inter-observer variations of the image analysis were determined by repeated analysis by one observer (blinded to the first analysis with an interval >1 month) and additional image analysis of a second observer (blinded to the results from the first observer).

Assessment of LV Function and LV Volumes with Cine MRI

LV function analysis was performed on the short-axis series using QMASS analytical software (Medis, Leiden, The Netherlands), yielding end-systolic and end-diastolic LV volumes, and LVEF was derived. In the presence of significant mitral regurgitation, he true left ventricular stroke volume was acquired by a velocity encoded sequence with a velocity sensitivity of 150 cm/s, measuring the flow in the ascending aorta. The aortic volume flow was determined using QFlow software (Medis, Leiden, The Netherlands).

Results

None of the normals showed LV dyssynchrony (mean -2 ± 15 ms on TDI; mean -5 ± 17 ms on MRI, p= non-significant (NS)). In patients, the mean LV dyssynchrony was 55 ± 37 ms on TDI, as compared to 49 ± 38 ms on MRI (p=NS).
In Figure 1, an example of the assessment of LV dyssynchrony in a normal individual is illustrated. In the color-coded TDI images (4-chamber view, Figure 1A), sample volumes are placed in the basal part of the septum and lateral wall. Velocity graphs are derived from the velocities measured in these sample volumes. In this normal individual, no LV dyssynchrony is present, as indicated by a septal-to-lateral delay in the timing of peak systolic velocity of 0 ms. In Figure 1B, the accompanying VE-MRI is presented. Similarly to TDI, sample volumes are placed at the basal level of the septum and lateral wall. The velocity graphs are presented in Figure 1C, confirming the absence of LV dyssynchrony (septal-to-lateral delay 0 ms).
In Figure 2, an example of the LV dyssynchrony assessment in a patient is presented. Figure 2A presents the color-coded TDI 4-chamber view. The velocity graphs are presented. There is a septal-to-lateral delay in peak systolic velocity of 115 ms. The accompanying VE-MRI and velocity graphs are presented in Figures 2B and 2C, respectively. The septal-to-lateral delay was 116 ms.
Intra- and inter-observer variations of LV dyssynchrony assessment with MRI were determined by repeated analysis by the same observer and one additional observer. The coefficient of variation (defined as the standard deviation of the differences between the two series of measurements divided by the mean of both measurements) was for both the intra- as well as the inter-observer variation 10%, with a confidence interval for both ranging from -11 ms to 8 ms. Differences in results for LV dyssynchrony measurement for the repeated analysis were statistically non-significant.
In Figure 3A, LV dyssynchrony measured by MRI is plotted versus LV dyssynchrony measured by TDI. Figure 3B shows the differences between both modalities in a Bland Altman graph. Good correlation between both modalities is observed (linear regression Y=aX+b, with a (± standard error SE) = 0.99 ± 0.04 and b ± SE = -5 ± 2, n=30, r=0.98, p<0.01). MRI exhibited a small, non-significant underestimation of 5 ± 8 ms for LV dyssynchrony as compared to TDI. The confidence intervals ranged from -22 ms to 11 ms.
Patients were categorized into three groups, according to the extent of LV dyssynchrony on TDI: minimal (<50 ms), intermediate (50-80 ms) and extensive LV dyssynchrony (>80 ms). The results are presented in a 3x3 table (Table 1). Excellent agreement between MRI and TDI classification was found (κ ± SE = 0.92 ± 0.07, p<0.01), 95% of the patients classification was identical.

Table 1. Agreement between LV dyssynchrony assessment with TDI and MRI.

MRI:

<50 ms

50-80 ms

>80 ms

minimal dyssynchrony (<50 ms)

8

0

0

TDI:

intermediate dyssynchrony (50-80 ms)

1

5

0

extensive dyssynchrony (>80 ms)

0

0

0

EDV: end-diastolic volume; ESV: end-systolic volume.

 

Figure 1
Figure 1.

Figure 2
Figure 2.

Figure 3
Figure 3.

Movie 1
Movie 1.

Movie 2
Movie 2.

Conclusion

Very strong correlation between MRI and TDI for LV dyssynchrony assessment, with both modalities producing almost similar results. The advantages of MRI over echocardiography (LV volumes, function, scar tissue and LV dyssynchrony are acquired in one examination, all potential markers for CRT response) makes this modality very suitable for CRT selection.

Publications

Westenberg JJM, Lamb HJ, van der Geest RJ, Bleeker GB, Holman ER, Schalij MJ, de Roos A, van der Wall EE, Reiber JHC, Bax JJ. Assessment of left ventricular dyssynchrony in patients with conduction delay and idiopathic dilated cardiomyopathy: head-to-head comparison between tissue doppler imaging and velocity-encoded magnetic resonance imaging. J Am Coll Cardiol 2006; 16 47(10): 2042-8.

Abstracts

Westenberg JJM, Lamb HJ, van der Geest RJ, Bleeker GB, Holman ER, Schalij MJ, de Roos A, van der Wall EE, Reiber JHC, Bax JJ. Dyssynchrony in left ventricular myocardial contraction assessed with tissue Doppler imaging and velocity-encoded MRI in patients with conduction delay and idiopathic dilated cardiomyopathy. Ninth Annual Meeting Society for Cardiac Magnetic Resonance, Miami , FL , January 20-22, 2006 (oral).

Westenberg JJM, Lamb HJ, van der Geest RJ, Bleeker GB, Holman ER, Schalij MJ, de Roos A, van der Wall EE, Reiber JHC, Bax JJ. Comparison between tissue Doppler imaging and velocity-encoded MRI for the assessment of left ventricular dyssynchrony. 34th Annual Meeting North American Society for Cardiac Imaging, Las Vegas , NV October 6-10, 2006 (poster).

Contact

Jos J.M. Westenberg, Ph.D.
Division of Image Processing
Department of Radiology, 1-C2S
Leiden University Medical Center
P.O. Box 9600
2300 RC Leiden
The Netherlands
Tel. +31 (0)71 526 4846
Fax. +31 (0)71 526 6801
e-mail: J.J.M.Westenberg@lumc.nl