- Meeting abstract
- Open Access
142 Quantification of left ventricular internal flow from cardiac magnetic resonance images in patients with dyssynchronous heart failure
© Fornwalt et al; licensee BioMed Central Ltd. 2008
- Published: 22 October 2008
- Left Ventricle
- Cardiac Magnetic Resonance
- Cardiac Resynchronization Therapy
- Internal Flow
- Mechanical Dyssynchrony
Synchronous contraction of the left ventricle (LV) is required to optimize cardiac function. Regional timing of LV contraction is dyssynchronous in many patients with heart failure, and cardiac resynchronization therapy (CRT) is a treatment that can restore synchronous contraction. Patients are currently selected for CRT using surface electrocardiogram QRS duration as a measure of dyssynchrony. However, 30–40% of patients selected for CRT show no improvement. This poor response rate may be explained by the poor correlation between mechanical dyssynchrony and QRS duration. Better methods to quantify mechanical dyssynchrony in the heart may improve the poor CRT response rate. Dyssynchrony creates inefficient shifting of blood volume internally within the LV. This "internal flow" represents wasted energy due to the dyssynchronous motion of the LV walls. Measurement of internal flow may provide a better, more physiologic indication of dyssynchrony than existing methods, but there is currently no non-invasive method to quantify it.
LV internal flow can be quantified from cardiac magnetic resonance (CMR) images and will be significantly different in patients undergoing CRT compared to healthy volunteers.
The endocardial surface was detected with a semi-automated level-set approach. The 3-dimensional LV endocardial surface was reconstructed and divided into 18 regional volumes: 6 rotational wedge-shaped 60° volumes at each of the 3 longitudinal levels (basal, mid-ventricular and apical) (Figure 1A). The anterior RV insertion point was used as the origin of rotational segmentation. The wedges intersected at the vertical axis, which was defined as the line between the apex and the center of the mitral annulus. The volume of each wedge-shaped region was calculated for each time step and internal flow fraction was calculated from these 18 regional volume curves.
CMR images were obtained with a 1.5 T Philips Intera scanner using a 5-element phased array cardiac coil. Short-axis steady-state free procession (SSFP) cine images were acquired over the length of the LV during breath-holds. Slices were 8–10 mm thick with no gaps, and 20 time points were collected per cardiac cycle. Two-chamber and four-chamber long-axis images were also acquired.
CMR images were obtained from 5 patients undergoing CRT (class III-IV heart failure, EF<35% and QRS duration >150 ms). These patients have a high likelihood of mechanical dyssynchrony. Five healthy volunteers were also scanned for comparison (normal CMR and 12-lead ECG).
Internal flow fraction in the LV can be quantified from standard cardiac magnetic resonance images. Patients with dyssynchronous heart failure have 4 times the amount of internal flow within the LV compared to healthy controls. A threshold internal flow fraction of 10% discriminates normals from patients with dyssynchrony.
This article is published under license to BioMed Central Ltd.