| ObjectiveRepeated ischemia and reperfusion may renders heart more resistant to the subsequent prolonged ischemia. The phenomenon was termed myocardial ische-mic preconditioning (IP). IP as a result of preinfarction angina (PA) can limit necrosis extent and guaranteeing greater myocardial functional recovery after a-cute myocardial infarction ( AMI). In the basic research we evaluated the protective effects of IP on Canine heart model with myocardial contrast echocardio-graphy (MCE) technique which can access myocardial peifusion state dynamically. The purpose of the clinical study was to evaluate the relationship between PA, microvascular reflow, and myocardial function using MCE and transthoracic coronary flow Doppler imaging ( TCFDI).MethodsPart 1: Thirteen mongrel dogs were divided into two groups; ischemia and reperfusion group (IR group) and the group preconditioned 4 cycles of 5 min ischemia followed by 5 min of reperfusion were conducted for preconditioning before left anterior descending artery ( LAD) occlusion (IP + IR group). LAD was occluded for 3 hours then the heart was reperfused for another 2 hours.MCE protocol: Open - chest power Doppler imaging was performed with acommercially available scanner (Intermittent harmonic imaging and angio mode, HP 5500 SONOS system). Machine settings included the following: large packet size, medium line density, pulse repetition frequency of 3.7 to 4.2 MHz, and a mechanical index of 1.6. The gain, the depth and focus were adjusted at the baseline and the myocardium was almost black and only endocardial borders could be visible. The adjustments were kept unchanged throughout the procedure. Left mid - papillary - muscle short - axis images were obtained at increasing pulsing intervals (ranging from 3 to 12 cycles) during continuous infusion of self - made contrast media and ECG - gated trigging at the point of R wave with the least cardiac motion. All of the data were stored on magnetic optic disk for later retrieval.Pathologic stain for infarction evaluation: At the completion of the experiment , the heart was arrested by intravenous administration of saturated KCL and then was excised. Evans blue dye was injected into left and right coronary artery and LAD was re - occluded. Then the heart was sectioned into 3 ~5mm - thick short - axis slices. The slice that corresponded to the echocardiographic imaging plane was immersed in a solution of 2% triphenyltetrazolium chloride ( TTC) at 37 C for 20min. The infracted myocardium (necrosis area, NA) was identified as the region of white color, while the risk area ( RA) was label with brick red. Both of NA and RA were calculated and NA/RA was also calculated.The following indices were measured and calculated: Peak velocity and velocity time integral both at baseline and 2 hours after reperfusion and their ratio ( Vmax/Vbase and VTImax/VTIbase) by TCFDI. Left ventricle ejection fraction (EF) was calculated at baseline, 3hours after ischemia and 2hours after reperfusion, respectively.Part2: In 42 patients with a first acute myocardial infarction, we noninva-sively assessed microvascular perfusion and coronary flow reserve (CFR) with intravenous myocardial contrast echocardiography and investigated myocardial contractile recovery with low -dose dobutamine echocardiography (LDSE) and 3 - month follow - up echocardiography. The percentage extent of contrast defect after MCE within the RA, CFR, wall motion score index (WMSI) and left ventricular volume were evaluated.ResultsParti: EF was decreased apparently both after occlusion and after reperfusion , but after reperfusion EF became better and EF in the IP group recovered more obviously than that of the IR group (P < 0. 0001). The infarction ration measured by MCE was well correlated with the result from pathological stain a-nalysis. NA/RA determined by MCE and pathologic staining were both larger in IR group than that in IP group( P < 0.001). CFR ( Vmax/Vbase and VTImax/ VTlbase) decreased at 2hours after reperfusion and CFR of IR group decreased much lower than that of IP group.Part2: Typical angina was present in 25 patients and absent in 26 patients during the 7 days preceding the myocardial infarction. Compared with those patients without PA, patients with PA showed a greater microvascular reflow extent and CFR, respectively (0. 26 0. 19 vs 0. 51 0. 23, P < 0. 05, and Vmax/ Vbase:2.91 ± 0.61 vs 1.67 ± 0.81, P < 0.0001; VTImax/VTIbase: 3.05±0.58 vs 1.81 ±0.76, P < 0.0001). The patients with PA had a better regional myocardial function expressed with WMSI in the risk area at LDSE (1. 71± 0.31 vs 2. 01 ± 0. 23, P < 0. 0001) and at follow - up echocardiography (1.69 ± 0.28 vs 2. 19 ± 0. 17, P < 0. 0001), despite being similar in the first echocardiogram (2.49 ± 0. 21 vs 2. 51 ±0. 19, P > 0. 05) , and significantly less pronounced left ventricular dilation at follow - up.ConclusionsThe protection effect of ischemic preconditioning on ischemic - reperfusion myocardium and coronary flow reserve can be objectively evaluated by myocardial contrast echocardiography and coronary flow Doppler imaging. Presence of preinfarction angina, because of the preconditioning effect, reduces myocardial damage and favors myocardial viability, limiting left ventricular remodeling. This beneficial effect seems to be at least partly mediated by the more preserved...
|
PDF Full Text Request