Maximal Difference Of Time Research Articles

Abstract 1604: Response to Cardiac Resynchronization Therapy Differs Between Patients With and Without Previous Right Ventricular Pacing

Background: Previous large studies on the effects of cardiac resynchronization therapy (CRT) in patients with heart failure have generally excluded patients previously paced from the right ventricle (RV). Previously RV paced patients (RVp) can exhibit an iatrogenic cause of dyssynchrony and reduced systolic function and thus, may respond differently to CRT than patients not previously RV paced (nRVp). The purpose of this study was to test the hypothesis that RVp patients have greater improvements in left ventricular systolic function, volumes, and dyssynchrony in response to CRT than nRVp. Methods: Standard echocardiograms with tissue Doppler imaging were performed before and after chronic CRT in RVp (n = 21, 16 male) and nRVp (n = 70, 54 male) heart failure patients. Ejection fraction (EF), left ventricular end diastolic (LVEDV) and systolic (LVESV) volumes were calculated using the biplane Simpson’s method. Longitudinal dyssynchrony was calculated as the standard deviation of time to peak displacement (TT-12) of 12 segments in the apical views. Using mid-ventricular short axis views and speckle-tracking methods, radial dyssynchrony (Rad dys ) was calculated as the maximal time difference between six myocardial segments for peak radial strain. Echo response was defined as ≥ 15% reduction in LVESV. Results are reported as mean ± SD. Results: Significant baseline differences (p < 0.05) were observed between groups (RVp vs. nRVp) for age (74 ± 13 vs. 67 ± 13 year), follow-up time (6.1 ± 1.8 vs. 4.6 ± 2.1 months), LVEDV (154.3±50.8 vs.185.3±56.9 mL), and a trend for LVESV (112.4 ± 40.6 vs. 134.9 ± 47 mL, p = 0 .05). No differences were observed for EF, etiology of heart failure, and dyssynchrony measures between groups at baseline. Echo response rate was significantly ( p < 0.05) greater in RVp (76%) than nRVp (57%). After adjusting for baseline differences, RVp had greater improvement in EF (14 ± 9 vs. 8 ± 7%, p < 0.05) and LVESV (−33 ± 18 vs. −20 ± 21%, p < 0.05). After adjustment for follow-up time, no difference was observed for change in dyssynchrony between groups. Conclusion: RVp patients upgraded to CRT exhibit greater improvements in systolic function and ventricular remodeling as compared to nRVp patients.

Effects of Radial Left Ventricular Dyssynchrony on Cardiac Performance Using Quantitative Tissue Doppler Radial Strain Imaging

Our objective was to test the hypothesis that novel angle-corrected radial strain imaging can quantify left ventricular dyssynchrony associated with contractile impairment and improved with biventricular pacing. Eight open-chest dogs were studied by novel angle-corrected color-coded radial strain imaging and high-fidelity pressure-conductance catheters recording pressure-volume loops. Heart rate was controlled by right atrial pacing and all timing intervals were corrected by R-R interval (corrected interval = measured interval/(R-R interval)(1/2)). Left bundle branch block, simulated by right ventricular free wall pacing, resulted in marked radial dyssynchrony, which we defined as maximal time difference between peak segmental strain, from 39 +/- 17 to 354 +/- 49 milliseconds and stroke work decreased from 157 +/- 40 to 60 +/- 37 mJ, (P < .005 vs baseline). Depression of contractility by high-dose esmolol (end-systolic pressure-volume relationship from 5.7 +/- 2.4 to 3.6 +/- 1.0 mm Hg/mL) was associated with augmented dyssynchrony to 388 +/- 53 milliseconds (P < .05 vs baseline right ventricular pacing). Biventricular pacing improved dyssynchrony to 55 +/- 19 milliseconds and stroke work to 143 +/- 33 mJ (P < .05 vs right ventricular pacing). Changes in radial dyssynchrony correlated significantly with 6-site average regional strain (r = -0.93 +/- 0.05 individually, r = 0.80 overall) and stroke work (r = -0.88 +/- 0.12 individually, r = -0.82 overall). Angle-corrected radial strain imaging has clinical potential to quantify mechanical dyssynchrony and effects of biventricular pacing.