Magnetic resonance imaging (MRI) with tissue tagging enables the quantification of multiple strain indices that can be combined through normalization into a single multiparametric index of regional myocardial contractile function. The aim of this study was to test the ability of multiparametric strain analysis to quantify regional differences in contractile function in an ovine model of myocardial injury. Regional variance in myocardial contractile function was induced in eight sheep by the ligation of the blood supply to the anterior and apical left ventricular myocardial walls. Left ventricular systolic strain was obtained from tissue tagged MRI images. A normal strain database (n = 50) defines all parameters of systolic strain and allows normalization of regional function at 15,300 left ventricular points by calculation of a Z-score. Multiparametric systolic strain Z-scores were therefore determined for 15,300 points in each injured sheep left ventricle. Multiparametric Z-scores were found to vary significantly by region (p < 0.001). Z-scores in regions remote to the infarct were found to be significantly smaller than those in the regions most likely to include infarcted myocardium. In this pre-clinical evaluation of MRI-based multiparametric strain analysis, it accurately quantified and visually defined regional differences in myocardial contractile function.

Background Global systolic strain has been described previously in patients with chronic aortic insufficiency (AI). This study explored regional differences in contractile injury. Methods Tagged magnetic resonance images of the left ventricle (LV) were acquired and analyzed to calculate systolic strain in 42 patients with chronic AI. Multiparametric systolic strain analysis was applied to relate cardiac function in AI patients to a normal strain database (N = 60). AI patients were classified as having normal or poor function based on their results. A two-way repeated-measures analysis of variance was applied to analyze regional differences in injury. Results The mean and standard deviation of raw strain values (circumferential strain, longitudinal strain, and minimum principal strain angle) are presented over the entire LV in our normal strain database. Of the 42 patients with AI, 15 could be defined as having poor function by multiparametric systolic strain analysis. In AI patients with poor function, statistical analysis showed significant differences in injury between standard LV regions (F369,44.33 = 3.47, p = 0.017) and levels (F1.49,17.88 = 4.41, p = 0.037) of the LV, whereas no significant differences were seen in the group with normal cardiac function. Conclusions Patients with poor function, as defined by multiparametric systolic strain z scores, exhibit a consistent, heterogeneous pattern of contractile injury in which the septum and posterior regions at the base are most injured.

The purpose of the current investigation was to characterize the early compensatory changes that occur in the right heart during chronic RV pressure overload before the development of chamber dilation. Magnetic resonance imaging with radiofrequency tissue tagging was performed on dogs at baseline and after 10 wk of pulmonary artery banding to yield either mild RV pressure overload (36% rise in RV pressure; n ϭ 5) or severe overload (250% rise in RV pressure; n ϭ 4). The RV free wall was divided into three segments within a midventricular plane, and circumferential myocardial strain was calculated for each segment, the septum, and the left ventricle. Chamber volumes were calculated from stacked MRI images, and RA mechanics were characterized by calculating the RA reservoir, conduit, and pump contribution to RV filling. With mild RV overload, there were no changes in RV strain or RA function. With severe RV overload, RV circumferential strain diminished by 62% anterior (P ϭ 0.04), 42% inferior (P ϭ 0.03), and 50% in the septum (P ϭ 0.02), with no change in the left ventricle (P ϭ 0.12). RV filling became more dependent on RA conduit function, which increased from 30 Ϯ 9 to 43 Ϯ 13% (P ϭ 0.01), than on RA reservoir function, which decreased from 47 Ϯ 6 to 33 Ϯ 4% (P ϭ 0.04), with no change in RA pump function (P ϭ 0.94). RA and RV volumes and RV ejection fraction were unchanged from baseline during either mild (P Ͼ 0.10) or severe RV pressure overload (P Ͼ 0.53). In response to severe RV pressure overload, RV myocardial strain is segmentally diminished and RV filling becomes more dependent on RA conduit rather than reservoir function. These compensatory mechanisms of the right heart occur early in chronic RV pressure overload before chamber dilation develops. pulmonary hypertension; hypertrophy; magnetic resonance imaging CHRONIC PULMONARY HYPERTENSION (CPH) ultimately leads to maladaptive right atrial (RA) and ventricular (RV) chamber dilation and right heart failure in most patients. However, the physiologic mechanisms responsible for the progression from compensated hypertrophy to decompensated end-stage disease are poorly understood (21,23,38). Previous studies (11,15,17,29,31,34) have identified alterations in RV strain patterns and systolic dynamics in patients with severe CPH and significant RV enlargement using tissue Doppler imaging, but little is known about the early adaptive response of the right heart before the development of myocardial hypertrophy and chamber dilation. Two recent clinical studies (16,20) have shown that even mild elevation in pulmonary arterial (PA) pressures, without the presence of gross RV dilation, can affect the mechanical properties of the ventricle and result in contractile dyssynchrony.In a canine model of chronic RV pressure overload, our laboratory (7) has previously demonstrated that RV diastolic mechanics are impaired and that the RA plays a compensatory role to maintain RV filling by augmenting contractility and increasing chamber compliance. Through ventricular interdep...

Background Guidelines for referral of chronic aortic insufficiency (AI) patients for aortic valve replacement (AVR) suggest that surgery can be delayed until symptoms or reduction in left ventricular (LV) contractile function occur. The frequent occurrence of reduced LV contractile function after AVR for chronic AI suggests that new contractile metrics for surgical referral are needed. Methods In 16 chronic AI patients, cardiac MRI tagged images were analyzed before and 21.5 ± 13.8 months after AVR to calculate LV systolic strain. Average measurements of three strain parameters were obtained for each of 72 LV regions, normalized using a normal human strain database (n=63), and combined into a composite index (multi-parametric strain z score [MSZ]) representing standard deviation from the normal regional average. Results Preoperative global MSZ (72-region average) correlated with post-AVR global MSZ (R2 = .825, p < .001). Preoperative global MSZ also predicts improvement of impaired regions (N=271 regions from 14 AI patients, R2 = .392, p < .001). Preoperative MRI-based left ventricular ejection fraction (LVEF) is also predictive (r = .410, p < .001). Although global preoperative MSZ had a significantly higher correlation than preoperative LVEF with improvement of injured regions (p < .001), both measures convey the same phenomenon. Conclusions Global preoperative MRI-based multi-parametric strain predicts global strain postoperatively, as well as improvement of regions (n=72/LV) with impaired contractile function. Global contractile function is an important correlate with improvement in regionally impaired contractile function, perhaps reflecting total AI volume-overload burden (severity/duration of AI).