J Am Coll Cardiol 2007;49:1715–21

Background Widespread use & recurrent improvements of the PCI method  significant reduction in early & late mortality Nonetheless, considerable variability in survival rate after PCI  accurate early risk stratification is of major clinical importance. Assessment of infarct size is important in risk stratification. - biochemical - electrocardiographic methods - scintigraphy - grayscale echocardiography - wall motion score index - contrast-enhanced MRI

MRI can quantify the extent of myocardial scarring after MI accurately  the use of MRI in the acute phase of AMI limited. Echocardiography - more easily available & feasible technique in the acute setting The use of strain by Doppler quantifies regional myocardial deformation & can demonstrate abnormal myocardial function due to ischemia.

J Am Soc Echocardiogr 2004;17:

Parameters Velocity [cm/s] peak systolic tissue Velocity (Vpeak sys) SR parameters [strain rate s-1] 1. SRpeak sys : peak systolic SR 2. peak SR E : early diastolic SR 3. peak SR A : late diastolic SR SR IVR : isovolumetric strain rate 6. Time to SRpeak sys Strain [%] 6. Eet : strain at end systole 7. EMAX : maximal strain 8. EPST = EMAX - Eet postsystolic thickening PSI = EPST / EMAX

J Am Soc Echocardiogr 2004;17:

Currently no established echocardiographic method to quantify infarcted myocardium immediately after revascularization therapy. A recent animal experiment  combining early systolic stretching & total shortening after reperfusion of MI can distinguish between viable or necrotic Myocardium. Circulation 2005;112:3901–10

Hypothesis Substantial negative strain value measured shortly after reperfusion indicates viability & potential for functional recovery. The average of total myocardial shortening in all LV segments reflects the total extent of necrotic myocardium & therefore may predict the final infarct size.

Methods Patient population - Thirty patients (23 men, 7 women, 54 9 years of age) with first AMI in the anterior LV wall were prospectively enrolled. All patients had typical chest pain & sustained ST-segment elevation demonstrated on ECG. Patients excluded if they had a previous history of MI

Twelve (40%) of the patients underwent a rescue procedure. The coronary angiography showed total (n 19) or subtotal (n 11) occlusion of the LAD & all underwent successful revascularization therapy. Seven (23%) of the patients had stenoses in 2 vessels. None had 3-vessel disease.

MRI Performed using a 1.5-T scanner & a phased array body coil. None of the patients had clinical evidence of recurrent coronary events in the period between the initial admission & the MRI scanning ( months after the AMI) Approximately 10 to 20 min after intravenous injection of 0.1 mmol/kg gadopentetate dimeglumine, late enhancement images were obtained from the long-axis & short axis views

Infarct defined as areas with pixel intensities 2 SD of the mean pixel intensity in normal myocardium in the same slice. In each segment, the infarct size was calculated as percentage of the total segment area. The total infarct size was reported as percent of LV mass & in units of grams of the infarcted myocardium

Echocardiography Performed with Vivid 7, GE Vingmed Ultrasound, Horten, Norway The patients examined within 2 h after revascularization TDI recordings of LV obtained from the apical long-axis, 4-C, & 2-C views A new echocardiographic study performed the same day as the MRI at 9 months after revascularization The echocardiographic recordings analyzed with Echopac

LVEF assessed by Simpson’s method WMSI was calculated from the same cine loops as used for the strain analyses, in a standard 16-segments model The strain value used in this study  the maximum negative strain magnitude during systole or early diastole Strain measurements from each segment were averaged to obtain a global strain value for the entire LV

ECG Standard 12-lead ECG was obtained from all patients before & after PCI as well as the following day. - The simplified Selvester score was used for an estimation of infarction size by ECG. ( developed to assess myocardial injury size, so that 1 point corresponds to a 3% loss of left ventricular mass ) Biochemistry - troponin I, serum glutamic oxaloacetic transaminase, creatine kinase-myocardial band & myoglobin before PCI & at 6, 12, & 24 h after the PCI procedure.

RESULT

Global strain was %. A total of 354 segments (81%) had sufficient image quality for strain analysis. Global strain nine months after revascularization was % (p NS from the acute measurement)

Peak negative strain was % in areas of complete transmural delayed enhancement whereas normal systolic shortening ( %) was found in remote areas (p ). Peak negative strain measured during early diastole in 58% of all segments ( ms after end-systole). This postsystolic shortening was observed in ischemic segments only. The magnitude of postsystolic shortening was % of total systolic shortening.

DISCUSSION

This study  global peak negative Doppler strain measured 1.5 h after revascularization therapy correlates well with final infarct size assessed by contrast enhanced MRI. This global strain was found to be a better predictor of the total extent of MI than LVEF. Global strain may thus add important information to early risk stratification after reperfusion of AMI

Infarct size is a major prognostic factor for cardiovascular death, reinfarction, congestive heart failure & stroke. Circulation 1998;97:765–72. LVEF has traditionally been used to assess the degree of myocardial damage & as a marker of early and late complications after MI. J Am Coll Cardiol 1984;4:1080 –7. In our study, LVEF showed a poor correlation to the infarct size by MRI

Significant correlation between infarct transmurality & strain in corresponding segments The relationship was not as good as between total infarct size & global strain.   size & position of each myocardial segment by MRI & echocardiography is not identical.

Study limitations The MRI examination performed several months after the acute phase of AMI whereas all other parameters were obtained during the acute phase. Not evident that global strain value is better than LVEF in assessing reduced myocardial function in diseases involving the whole LV. ( LVEF - a global parameter, whereas the global strain - calculated from regional measurements) Optimal strain measurements are not always easy to obtain in all parts of the myocardium.

Conclusion Assessment of regional & global strain at 1.5 h after reperfusion therapy correlates with size & transmural extent of MI as determined by contrast-enhanced MRI. The novel global strain parameter is a valuable predictor of the total extent of MI & may therefore be an important clinical tool for risk stratification in the acute phase of MI.