Study On Diagnosing Multivessel Disease In Patients With Coronary Artery Disease By Strain And Strain Rate Imaging

ObjectiveThe usage of tissue Doppler echocardiography with strain and strain rate imaging provides a new approach for quantitative analysis of longitudinal myocardial function.The aim of this study was to assess the diagnostic value of tissue Doppler echocardiographically-derived strain and strain rate imaging for multivessel coronary artery disease(CAD) by detecting changes in myocardial function due to myocardial ischemia.MethodsOne hundred eighteen patients without myocardial infarction were recruited in the study(mean age 59±11 years,76 male,42 female).Forty-three patients had multivessel, thirty-two had singlevessel and forty-three had 0-vessel disease.All the patients underwent selective coronary angiography using the Judkins technique within seven days of the echocardiography.Multiple views of each coronary artery were obtained.Stenoses in major epicardial vessels were assessed visually by two cardiologists.A maximal lumen diameter stenosis of≥50%in any plane was classified as significant.Stenosis location was evaluated by utilizing a simplified coronary tree schema with the left main coronary artery(LM),left anterior descending(LAD),left circumflex(LCX) and right coronary arteries(RCA) divided into proximal,middle and distal segments.For the purposes of analysis,distal segments of LAD and LCX were excluded from evaluated results.Proximal segments of large branches were classified as middle segments of LAD and LCX. Multivessel disease was defined as LM,two or three native vessels with significant disease. Patients were divided into normal angiography,singlevessel coronary artery disease(CAD) and multivessel CAD groups.Patients with normal angiography were selected as control group.All patients underwent conventional and color tissue Doppler imaging.Left ventricular ejection fraction was calculated with Simpson's method at the apical 2- and 4-chamber views.Left ventricle dimension and myocardial mass were obtained using M-mode.Strain(S) and strain rate(SR) measurements:Apical 2-chamber,4-chamber and long-axis views of color 2-dimensional tissue Doppler images were acquired during end-expiration at a frame rate of＞90 frames per second in the left recumbent position. The pulse repetition frequency was set to 1 to 1.5 kHz and second harmonic imaging was used.Sector size and depth were optimized for the highest possible frame rate(minimum sector size visualizing encompass entire left ventricle walls in each axis).The angle between the ultrasound beam and the left ventricular axis was less than 20℃.Images for at least three consecutive cardiac cycles averaged for each measurement were stored and analyzed off-line by internal analyzing software package.The strain length(distance for velocity gradient calculation) was 12mm.The sample volume was set to 10 mm in the longitudinal direction.The position of it was manually adjusted frame-by-frame to maintain its same position in the centre of myocardial segment throughout the cardiac cycle.Sample volumes were placed in the myocardium on the basal and mid segments of the left ventricle at the anterior,anteroseptal,inferoseptal,inferior,inferolateral,and anterolateral walls in the apical views.Thus,the left ventricle was divided into 12 segments.The parameters measured included peak PSS(S_PSS,SR_PSS),peak systolic S as well as SR(S_p,SR_s) and peak early diastolic SR(SR_E) in each segment.Each patient had 12 values of S_P,SR_S and SR_E;and average values of S_PSS,SR_PSS,S_P,,SR_S and SR_E were defined as S_PSS,SR_PSS,S_P,SR_S and SR_E indexes(S_PSSI,SR_PSSI,S_PI,SR_SI and SR_EI) to evaluate overall left ventricle longitudinal systolic and diastolic function;which were derived by dividing the summed value of S_PSS,SR_PSS,S_P,SR_S or SR_E by the number of assessable segments,respectively.The ratios of S_PSSI/S_PI.and SR_PSSI/SR_SI were also calculated to detect ischemic myocardium at the same time.Two independent observers determined the inter-observer variability of the strain and strain rate methods by comparing 30 randomly selected records.One observer,repeating the same analysis one month later, estimated the intra-observer variability.All results are expressed as mean±SD.Statistical significance was evaluated by ANOVA and Bonferroni adjustment in multiple comparison procedures or 2-tailed Student's t test for comparisons between the mean of 2 groups. Differences between 2 or 3 groups were assessed with x² test for categorical variables.The area under the receiver-operating characteristic(ROC) curve was used for the optimal ROC cut point which was defined as the value having the highest sum of sensitivity and specificity.The agreement in intra-observer or inter-observer for measurements was assessed by Kappa statistics.A value of P＜0.05 was considered statistically significant.ResultsThe absolute values of S_PI,SR_SI and SR_EI were significantly decreased in multivessel disease group(-14.6±4.4%,-0.86±0.24s^₁,0.84±0.32s^₁) compared with control (-19.5±4.1%,-1.21±0.35s^-1,1.22±0.38s^-1) group(P＜0.05).The value of SR_EI was significantly decreased in singlevessel disease(1.00±0.38s^-1) compared with control group (P＜0.05).The sensitivity and specificity of an optimal cut-off value of＞-15.0%for S_PI or＞-1.01s^-1 for SR_SI to detect multivessel disease were 65%,72%and 91%,74%, respectively.The Kappa value of S_PI for agreement in intra-observer or inter-observe for measurements was 0.46 and 0.53,respectively(P＜0.05).ConclusionLeft ventricular strain and strain rate are impaired at rest in patients with multivessel CAD, even when global systolic contraction is preserved.Strain and strain rate imaging is an accurate method for the detection of multivessel CAD.Further studies are needed to determine whether this approach will be clinically useful.