| Background and objectivesStrain rate and strain imaging (SRI and SI) by ultrasound are newly developed echocardiographic modality based on Doppler tissue velocity imaging (TVI) allowing quantitative assessment of regional myocardial wall deformation. SRI/SI have theoretic advantages over TVI in those SRI/SI are relatively immune to cardiac translational motion and tethering; their temporal and spatial resolutions are very high. Therefore, SRI/SI can depict and quantify systolic and diastolic deformation of regional myocardium accurately during the entire cardiac cycle. Initial studies indicate that SRI/SI may be superior to conventional echocardiography and TVI in quantitative assessment of regional myocardial function and interrogation of myocardial ischemia of coronary heart disease (CHD). However, the studies of SRI/SI are at their beginning and most of them are animal experiments, in contrast to clinical application studies on this subject which are few up to now. It is needed to carry out a lot of systemic studies on both normal and pathologic myocardium by SRI/SI. The objectives of this study are.- (1) to observe the characteristicsof myocardial strain rate(SR)and strain(e) systematically in normal subjects; (2)to assess regional systolic and diastolic function and the features of postsystolic contraction (PSC) of ischemic myocardium quantitatively in patients with CHD by SRI/SI, and investigate the clinical feasibility of SRI/SI. (3 )to investigate the optimal cutoff points of SRI, SI and TVI parameters for recognition of myocardial ischemia according to the results of coronary angiography , and compare the clinical value of these three techniques in the diagnosis of CHD. Methods and results1. Study on characteristics of myocardial SR and ε in normal subjects Sixty healthy individuals were enrolled in the study. Radial and longitudinal peak SR and e of left ventricular walls (LVW) during systole, rapid filling phase and atrial systolic phase (SRs, SRe, SRAand εs, εe, εa) were measured. Results: Radial SR and 8 of the posterior wall (PW) were significantly larger than those of the anterior interventricular septum (AS). During systolic phase and rapid filling period, SR and 8 were found significantly higher in the basal and mid segments than in the apical segments of PW. But no significant differences were found among SRa, εa of PW and SR, 8 of AS at three different levels. Longitudinal SR and 8 of LVW were not uniformly distributed over the wall. During systolic phase and rapid filling period, for several free wall, SR and 8 were found significantly larger in the basal segments than in the middle and/or apical segments of the same wall; by contrast SR and 8 of AS were significantly smaller in the basal segments than in the middle and apical segments. Significant differences among SR or 8 of all LVW were often found at basal level, and SR, 8 of AS were the lowest in all LVW. Age had no significant influence on SRs and εs on the whole. Longitudinal SRe and εe in some segments were correlated negatively withage, indicating age had a certain amount of influence on SRe and sE. All radial SRA in AS and PW, most of the longitudinal SRA and many eA in LV W were correlated positively with age, signifying age had significant influence on SRA and SA.2. Study on myocardial ischemia of coronary heart disease using SRI and SI The study population included 55 patients with CHD and 42 age-matched normal controls. Radial and longitudinal peak SR and s parameters of LVW during systolic phase, rapid filling period and atrial systolic phase were measured; radial and longitudinal peak velocities during systolic phase and rapid filling period, peak SR and e of post-systolic contraction (SRpsc and 8psc) of LVW were measured too. According to the results of coronary angiography, the parameters in ischemic segments of CHD and in normal segments of controls were compared; the optimal cutoff points of parameters for detection of ischemia were analyzed using receiver operating characteristic analysis (ROC) and the sensitivity (Se) and specificity (Sp) of every parameter to detect ischemia were obtained. Then the clinical value of these three techniques in the diagnosis of CHD was compared. Results: (1) During systolic phase and rapid filling period, color M-mode SRI showed the color in ischemic segments became lighter, disappeared, or even exhibited the antiphase color, indicating that SR of ischemic segments decreased, disappeared, or even showed inversion. (2) Radial and longitudinal SR, 8, and velocity indexes in ischemic segment s during systolic phase and rapid filling period reduced significantly than those in corresponding normal segments of controls. On the whole, no significant differences were found in SRA and eA between ischemic segments of CHD and corresponding normal segments of controls. (3) The incidence of PSC in ischemic segments of CHD was significantly higher than that in corresponding normal segments ofcontrols (radial PSC: 67.0 % vs 14.3 %, PO.01; longitudinal PSC: 66.2 % vs 17.2 %, P<0.01). SRpsc/SRs in ischemic segments of all LVW was significantly larger than that in corresponding normal segments of controls (P<0.05). Except for the longitudinal 8psc in basal segments, all 8psc in ischemic segments were significantly larger than those in corresponding normal segments of controls (/><0.05). Longitudinal SRpsc at apical ischemic segment was significantly larger than that in corresponding normal segment of controls (P<0.05), and no statistical differences were found for SRpsc between other ischemic segments of CHD and corresponding normal segments of controls. (4) For the same parameter, cutoff points among different segments were different. Sp of radial SRs and SRe for recognition of ischemic segments were significantly higher than those of Vsand Ve respectively (0.83±0.06 vs 0.71±0.05, 0.80±0.10 vs 0.73±0.07, respectively, both PO.05). Se, Sp of longitudinal SRs and Ss for detection of ischemic segments were significantly higher than those of Vs (Se: 0.83±0.06 and 0.77±0.07 vs 0.71±0.07, PO.01. Sp: 0.80±0.07 vs 0.68±0.08, P<0.01; 0.74±0.07 vs 0.68±0.08, P<0.05. respectively). Se, Sp of longitudinal SRs for detection of ischemic segments were significantly higher than those of 8s (P<0.01 and 0.05, respectively). No statistical differences were found among Se or Sp of longitudinal SRe, ￡e and VE(P>0.05). Conclusions(1) Spatial distribution of myocardial SR and 8 in normal LV are heterogeneous. The main characteristics are as follows: Radial SR and 8 of the posterior wall (PW) are significantly larger than those of AS; during systolic phase and rapid filling period, SR and 8 are found significantly higher in the basal and mid segments than in the apical segments of PW. During systolic phase and rapid filling period, for several free wall, longitudinal SR and 8 arefound significantly larger in the basal segments than in the middle and/or apical segments of the same wall; by contrast SR and s of AS are significantly smaller in the basal segments than in the middle and apical segments. Significant differences among SR or 8 of all LVW are often found at basal level. Age has obvious influence on SR and 8 during diastolic phase.(2) During systolic phase and rapid filling period, SR and 8 in ischemic segments of CHD decrease significantly, disappear, or even show inversion. Whether there are significant differences for SRa and Sa between ischemic segments of CHDs and corresponding normal segments of controls mainly depend on the functional status of left atrium and complaisance of LV.(3) The incidence of PSC in ischemic segments of CHD is significantly higher than that in corresponding normal segments of controls. SRpsc/SRs in ischemic segments of all LVW are significantly larger than those in corresponding normal segments of controls (P<0.05). Most of the Spsc in ischemic segments are significantly larger than those in corresponding normal segments of controls. This result indicates that PSC is a common sign for myocardial ischemia of CHD, and ischemic PSC has obvious features by which it could be distinguished from physiological PSC. Characteristics of ischemic PSC may be correlated with the extent of ischemic myocardial injury.(4) SRI/SI can evaluate regional myocardial deformation function in radial and longitudinal direction noninvasively and quantitatively, and could be used as new technique for detecting myocardial ischemia of CHD. The suitable criteria must be selected according to different segment for the diagnosis of myocardial ischemia using SRI/SI and TVI. Se and Sp of SRI/SI for detecting myocardial ischemia are higher than those of TVI, indicating that SRI/SI have important clinical application values. SRI appears superior to SI... |
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