| Objection:In order to find an easy and practical way to evaluate viable myocardium, we detected the strain (ε) and strain rate(SR) change of normal and abnormal myocardial segment in baseline and with dobutamine stress; to evaluate the predicting value of strain rate imaging(SRI) combining with low dose dobutamine echocardiography (LDDSE) in identification of viable myocardium; to see the differences of 2D-strain and strain rate between viable myocardium and nonviable myocardium in baseline.Method:We studied 74 normal segments (A group) according to the normal of wall motion during LDDSE and their related coronary arteries also showed normal in the coronary angiography and 109 segments had motion dysfunction in 21 patients.52 segments showed improvement of wall motion both during LDDSE and at follow-up were defined as viable segments (B group); 44 segments showed no change both during LDDSE and at follow-up were defined as nonviable segments (C group). We used SRI which is developed from the tissue velocity imaging (TVI) and provides a new noninvasive way to access regional myocardial function together with LDDSE measured the regional contraction and relaxation function quantitatively. We measured theε, peak systolic strain rate (SRs), early diastolic peak strain rate(SRe), last diastolic peak strain rate(SRa), isovolumic relaxation period peak strain rate(IVRsr) and time to the compression/expansion crossover(T-CEC). We measured the 2D-strain and 2D-SR of both normal and abnormal segments before LDDSE. 2D-strain rate imaging based on 2D pattern tracking and it is not affected by the angle of ultrasound beam, can measure the regional myocardial strain and strain rate more accurate.Results:1. The anatomy M-mode of SRI has 3 bars in normal segments, with the injection of Dobutamine, the color of the bars in normal group turned bright and the T-CEC shortened. Theε, SRs, SRe, SRa of normal myocardium increased with the increasing of dobutamine, the peak value of SRs, SRe, SRa andεwere measured at dobutamine 17.5 micro-gram per kilogram body weight per minute (μg/kg/min). The |PSS| of normal group indicated no significant differences during LDDSE. 2. Compared with the baseline, the SRs of viable group increased with the increasing of dobutamine from 2.5μg/kg/min to 15μg/kg/min, then it began to decrease when the dose of dobutamine continue to grow. SRa andεof viable myocardium increased at dobutamine 5μg/kg/min, they reach the top value at dobutamine 17.5μg/kg/min. The SRe only had statistic difference between baseline and 15μg/kg/min. The systolic peak velocity (Vs) to go up at Dob 10μg/kg/min, and it began to drop at the grade of dobutamine 15μg/kg/min. There are no significant changes between baseline and stress in Ve and Va. The |PSS| of viable group decrease at low dose dobutamine stress (2.5-5μg/kg/min), it began to increase when the dose of dobutamine to go up.3. The SRs andεof infarct group incline to increase at the beginning of LDDSE, and then they incline to decrease, but both the data lack statistical significance. SRe, SRa, IVRsr and the velocity index (Vs, Ve, Va) showed no regular change during LDDSE. 4.△SRs,△ε,△T-CEC,△Vs were equal to the value of SRs,ε, T-CEC, Vs measured at each Dob level minus the value measured at baseline, as new indexes to identify viable and nonviable myocardium. The△SRs of B group was higher than C group at each grades. The△SRs of A group was lower than B group when Dob at 2.5μg/kg/min-5μg/kg/min,the state changed when Dob continued to go up.△SRe was no differences at each level during A, B and C groups. The△SRa of C group lower than A and B groups.△εof B group was higher than C group at each grade. The△Vs of C group was lower than A and B groups. The changes of△Ve and△Va during the 3 groups were meaningless. The△T-CEC of both A, B groups was shortened, but there was no change in C group.5. The differences of△SRs and△εwere more obviously between B and C group. The sensitivity, specificity and accuracy are 92.3%, 88.6%, 90.6% respectivly when△SRs≥0.2 s-1 at Dob 10μg/kg/min is used as a standard to detect viable myocardium. When△ε≥3% at Dob 10μg/kg/min is used as a standard to detect viable myocardium, the sensitivity, specificity and accuracy are 75.0%, 90.9%, 82.3% respectivly.6. Three month after LDDSE, SRs, SRa,ε, T-CEC of viable group showed statistical significance compared with at rest time 3 month before. Other indexes showed no significant changes. All indexes of infarct group showed no changes compared with 3 month before. There are significant differences of△SRs,△ε,△T-CEC,△SRa between B and C group three month later. The mean△SRs of B group was 0.17 s-1 in follow up, 40 segments out of the 48 segments which△SRs≥0.2 s-1 at Dob 10μg/kg/min reach this standard, and only 1 segment which didn't reach 0.2 s-1 at Dob 10μg/kg/min reach this standard. The mean△εof B group in follow up was 3.29%, 37 segments out of the 39 segments which△ε≥3% at Dob 10μg/kg/min reach this standard.7. Thirteen segments out of infarct group and thirty segments out of viable group had been undergone percutaneous coronary intervention (PCI). According to whether underwent PCI, both A and B groups were devided into two subgroups. The PCI subgroup and the conservative treatment subgroup in the infarct group showed no differences between flow-up and 3 month before. While in the viable group, the indexes of SRs,εand T-CEC showed improvement in both the two subgroups.8. In the baseline, 2D-strain and 2D-strain rate were different obviously between B group and C group. The percent of appearance of post systolic shortening (PSS) were 67.3%, 70.5% in the B and C group. But the |PSS| of the B group was significant lower then the C group.Conclusion:1. SRI combining with LDDSE is a safe, convenient and practical method in evaluating viable myocardium. SRs,ε, PSS and T-CEC are main parameters.2. The first time to raise the standard to detect viable myocardium by using△SRs≥0.2 s-1 and△ε≥3% at the grade of Dob 10μg/kg/min. The sensitivity, specificity and accuracy of using△SRs≥0.2 s-1 are 92.3%, 88.6%, 90.6% respectivly. And the sensitivity, specificity and accuracy of using△ε≥3% are 75.0%, 90.9%, 82.3% respectivly.3. The differences between viable and nonviable myocardium were obvious at the level of Dob10μg/kg/min, indicate LDDSE can be achieved at even lower doses, so more people can tolerance this test.4. In this study, PCI treatment didn't show better than tradition treatment. A large sample research is needed to answer the question how to choose the righe way to help viable myocardium to recover.5.2D-strain rate imaging may become a more accurate and more convenient way in predicting viable myocardium, but it needs further research to demonstrate. |
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