Abstract
Left bundle branch block (LBBB) causes left ventricular (LV) dyssynchrony which is often associated with heart failure. A significant proportion of heart failure patients do not demonstrate clinical improvement despite cardiac resynchronization therapy (CRT). How LBBB-related effects on LV diastolic function may contribute to those therapeutic failures has not been clarified. We hypothesized that LV hemodynamic forces calculated from 4D flow MRI could serve as a marker of diastolic mechanical dyssynchrony in LBBB hearts. MRI data were acquired in heart failure patients with LBBB or matched patients without LBBB. LV pressure gradients were calculated from the Navier-Stokes equations. Integration of the pressure gradients over the LV volume rendered the hemodynamic forces. The findings demonstrate that the LV filling forces are more orthogonal to the main LV flow direction in heart failure patients with LBBB compared to those without LBBB during early but not late diastole. The greater the conduction abnormality the greater the discordance of LV filling force with the predominant LV flow direction (r2 = 0.49). Such unique flow-specific measures of mechanical dyssynchrony may serve as an additional tool for considering the risks imposed by conduction abnormalities in heart failure patients and prove to be useful in predicting response to CRT.
Highlights
Heart failure is a common clinical problem and adverse cardiac remodeling is a key component in the deterioration of cardiac function, in the downward spiral leading towards heart failure
During systole the velocity is increased from apex towards the LVOT, the pressure gradient will be negative from apex to LVOT, i.e. the pressure will decrease in the flow direction and the hemodynamic force will be directed in the opposite direction
The short axis (SAx)/LAx-ratio, a measure of the deviation of the left ventricular (LV) hemodynamic forces from the main flow direction, was higher during the early diastolic filling phase in the patients with dyssynchronous LV relaxation (LBBB patients) compared to the matched patients, while no intergroup difference was observed during late diastolic filling
Summary
Heart failure is a common clinical problem and adverse cardiac remodeling is a key component in the deterioration of cardiac function, in the downward spiral leading towards heart failure. Previous studies have shown that the distributions of different flow components comprising the end diastolic volume (EDV) of LV may be markers of cardiac function[7,8,9,10,11] Another approach to assess intracardiac blood flow has been calculation of the kinetic energy of the blood[5, 7, 8]. The concept of LV hemodynamic force has been known for decades[16], but was only recently computed from 2D LV flow fields by Pedrizetti et al, using echocardiographic particle image velocimetry (echo-PIV)[17, 18] Using this technique, the directional distribution of hemodynamic forces in the LV of heart failure patients with cardiac resynchronization therapy (CRT) has been investigated[19]. In a heterogeneous group of dilated cardiomyopathy patients we found that the ratio of forces acting in the long- and short-directions was different from normal, especially during early filling, with a relative increase in the hemodynamic forces acting orthogonal to the main flow axis[20]
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