Dynamic cardiomyoplasty decreases myocardial workload as assessed by tissue tagged MRI

The effects of dynamic cardiomyoplasty (CMP) on global and regional left ve ntricular (LV) function in end-stage heart failure still remain unclear. MR I with tissue-tagging is a novel tool for studying intramyocardial motion a nd mechanics. To date, no studies have attempted to use MRI to simultaneous ly study global and regional cardiac function in a model of CMP. In this st udy, we used MRI with tissue-tagging and a custom designed MR compatible mu scle stimulating/pressure monitoring system to assess long axis regional st rain and displacement variations, as well as changes in global LV function in a model of dynamic cardiomyoplasty. Three dogs underwent rapid ventricul ar pacing (RVP; 215 BPM) For 10 weeks; after 4 weeks of RVP, a left posteri or CMP was performed. After 1 year of dynamic muscle stimulation, the dogs were imaged in a 1.5 T clinical MR scanner. Unstimulated and muscle stimula ted tagged long axis images were acquired. Quantitative 2-D regional image analysis was performed by dividing the hearts into three regions: apical, s eptal, and lateral. Maximum and minimum principal strains (lambda(1) and la mbda(2)) and displacement (D) were determined and pooled for each region. M R LV pressure-volume (PV) loops were also generated. Muscle stimulation pro duced a leftward shift of the PV loops in two of the three dogs, and an inc rease in the peak LV pressure, while stroke volume remained unchanged. With stimulation, lambda(1) decreased significantly (p < 0.05) in the lateral r egion, whereas lambda(2) increased significantly (p < 0.05) in both the lat eral and apical regions, indicating a decrease in strain resulting from sti mulation. D only increased significantly (p < 0.05) in the apical region. T he decrease in strain between unassisted and assisted states indicates the heart is performing less work, while maintaining stroke volume and increasi ng peak LV pressure. These findings demonstrate that the muscle wrap functi ons as an active assist, decreasing the workload of the heart, while preser ving total pump performance.