Experimental Study On Coronary Microembolization

Background:Coronary flow reserve(CFR) was the most commonly used index for evaluating coronary microcirculation at catheter lab. However, it was influenecd by hemodynamics. Coronary resistant indexes, which combined coronary pressure and coronary flow, will be better for evaluating coronary microcirculation.Objective:To investigate the changes of coronary resistant(CR) indexes and CFR at different time in swine models of coronary microembolization using catheterization techniques. And explore the relationship of CFR and endothelial function after coronary microembolization.Methods:The left anterior descending coronary artery(LAD) of 15 mini swines(21-25kg) were embolized by repetitive injections of 42μm microspheres through microcatheter. Intra-vascular ultrasound(IVUS) images, intracoronary doppler signals, intracoronary pressure signals and ECG signals were acquired at different time after microembolization using intracoronary ultrasound imaging catheter, Doppler flow wire and pressure wire at the middle segment of LAD. Systemic hemodynamics was measured at the same time. Serum ET-1 concentrations were measured by commercial available ELISA kits (R&D company). Baseline parameters were acquired in eight swines, as well as two hours' parameters in seven swines, six hours' parameters in six swines and one week' parameters in six swines.The curve of volume/pressure in cardiac cycle and CR indexes for coronary artery were established by the softwire of P C system. The CFR was calculated with the ratio of hyperemic average peak velocity(hAPV) and baseline average peak velocity(bAPV). Coronary resistance indexes included resting coronary resistance and minimal coronary resistance(min-CR), the first harmonic CR and min-CR. Statistical analysis was performed with use of SPSS 11.5 software. The change of coronary resistant indexes and hemodynamics at different time after coronary embolization were estimated by one-way ANOVA analysis. A P value less than 0.05 indicated a significant difference.Results:Changes of CFR were a biphasic pattern, first decreased then increased. CFR at base, 2 hours, 6 hours and 1 week were 1.77±0.30, 1.69±0.07, 1.24±0.10 and 1.58±0.22 respectively(6 hours compared with base P＜0.05). Resting CR were 2.448±1.891 at base, 3.229±2.872 at 2 hours, 3.197±3.227 at 6 hours and 3.466±2.683 at 1 week. First harmonic resting CR were 0.538±0.559 mmHg.ml^-1.s^-1 at base, 1.604±1.727 mmHg.ml^-1.s^-1 at 2 hours, 0.834±0.858 mmHg.ml^-1.s^-1 at 6 hours and 1.233±1.809 mmHg.ml^-1.s^-1 at 1 week. Minimal CR were 1.778±1.352 mmHg.ml^-1.s^-1 at base, 2.577±2.276 mmHg.ml^-1.s^-1 at 2 hours, 2.710±2.733 mmHg.ml^-1.s^-1 at 6 hours and 3.039±2.671 mmHg.ml^-1.s^-1 at 1 week. The changes of the resting CR, first harmonic resting CR and minimal CR had no difference at different time after coronary microembolization. First minimal harmonic CR were 0.388±0.395 mmHg.ml^-1.s^-1 at base, 0.947±0.844 mmHg.ml^-1.s^-1 at 2 hours, 1.639±1.9780 mmHg.ml^-1.s^-1 at 6 hours and 0.716±0.624 mmHg.ml^-1.s^-1 at 1 week (6 hours compared with base P＜0.05). Coronary resistance reserve were 1.463±0.235 at base, 1.265±0.105 at 2 hours, 1.160±0.068 at 6 hours and 1.276±0.266 at 1 week (6 hours compared with base P＜0.05). After adjustment, first harmonic minimal CR and coronary resistance reserve were the most sensitively parameters after coronary microembolization for evaluating microvascular function. The changes of the first minimal harmonic CR and coronary resistance reserve were similar to CFR at the same time after coronary microembolization.Concentration of ET-1 were 123.0±15.3 pg/ml at base, 138.5±8.2 pg/ml at 2 hours, 140.9±14.8 pg/ml at 6 hours and 119.0±15.6 pg/ml at 1 week(6 hours compared with base P＜0.05). Changes tendency of serum ET-1 was similar to CFR. Myocardial ischemia and microinfarcts was found after coronary microembolization which accompanied by leukocyte infiltration. Number of leukocyte infiltration was 103.0±49.4 at anterior myocardial and 43.9±24.0 at posterior(P＜0.05).Conclusion:CR decreased with time after coronary microembolization with 1.2×10⁶ 42μm microspheres. Coronary resistance reserve and first harmonic minimal CR reflect the coronary microvascular dysfunction better than other CR index. Serum concentration of ET-1 first decreased with time after coronary microembolization. Then it resumed after 1 week. Coronary microembolization was accompanied with microinfarct and leukocyte infiltration.BackgroundCoronary microembolization models was performed with open-chest preparation, which influences and contradicts the pathophysiology of coronary microembolization in vivo. In this study we will construct coronary microembolization animal model using intervention method and investigate changes of left ventricular remodeling and the mechanisms.ObjectiveCoronary microembolization is frequent in patients with coronary heart disease and especially in patients with percutaneous coronary intervention. Previous studies have shown that contractile dysfunction is related to changes of tumor necrosis factor-.(TNF-.). Then this paper is to test whether serum TNF-. correlated with left ventricular ejection fraction(LVEF) as well as changes of left ventricular remodeling and transforming growth factor-β1(TGF-β1) and its signal transduction after coronary microembolization.MethodsTwelve miniswines, of either sex(21-25 kg body weight), which divided as acute study (base, 2 hours, 6hours) and chronic study (base and 1 week), were studied. After coronary angiography, a 2.8F micro catheter(Cordis Inc., Johnson & Johnson) was placed in the LAD artery between the second and third diagonal branches for selective manual infusion of 1.2×10⁶ microspheres(42μm Dynospheres; Dyno Particles; Norway) into the LAD. LVEF was measured with transthoracic echocardiography using a GE VIVID 7 system with a 1.5-3.4MHz transducer. Regional myocardial blood flow was measured using colored microshperes(15μm, E-Z Trac company) injected into left ventricular while blood drawn from femoral artery with constant rate. After the study finished, the heart was removed and sectioned for analysis. Measurement of serum TNF-.,TGF-β1,MCP-1,P-selectin and VCAM-1were performed by ELISA kit. Reverse transcription polymerase chain reaction(RT-PCR) ofTNF-., TGFβ1 and MCP-1 in myocardial tissue were performed. TNF-. and TGFβ1 n myocardial tissue protein were measured using ELISA kit. ResultsIn the acute and chronic study, there were no changes for hemodynamics. LVEF (0.77±0.08 at base, 0.69±0.08 at 2 hours and 0.68±0.08 at six hours respectively; P＜0.05) decreased with time. And serum pro-BNP elevated with time (six hours compared with base P＜0.05). In the same time, serum TNF-. and TGF-β1,MCP-1,P-selectin and VCAM-1 elevated with time. In the chronic study, TNF-.,TGF-β1,P-selectin and VCAM-1 are still elevated(P＜0.05). But no changes were found for LVEF (0.699±0.06 at base and 0.691±0.063 at one week respectively, P＞0.05) and serum pro-BNP(P＞0.05). And left ventricular remodeling was observed at chronic study. Regional myocardial blood flow showed no significant changes at acute phase and chronic phase. Further analysis showed changes of serum TNF-. negatively correlated with changes of LVEF(-0.483, P＜0.05) at acute study but not at chronic study. And further RT-PCR analysis demonstrated that TNF-., TGF-β1, MCP-1 and Smad 4 only elevated six hours after microembolization at anterior myocardium compared with posterior myocardium(P＜0.05). Although Smad 7 decreased at six hours after microembolization, there was no significant difference(P＞0.05). And TNF-. and TGF-β1 protein elevated at 1 week after microembolization(P＜0.05).ConclusionLVEF decreases with time after microembolization at acute period and resumes one week later. LV remodeling is continued after one dose of microembolization. TNF-. plays a major role of myocaridal dysfunction after microembolization. TGFβ1 elevates after coronary microembolization. Signal transduction of TGF-β1 after microembolization is through Smad 4. BackgroudEchocardiography has limitations on evaluating left ventricular remodeling for lack of direct visualization myocardial infarction and ischemia changes after coronary microembolization. With the use of contrast enhanced magnetic imaging, we can solve these limitations.ObjectiveCoronary microembolization is frequent in patients with coronary heart disease, especially in patients wit h coronary intervention. And diagnosis of microembolization is of clinical importance for patients' prognosis. Contrast enhancement magnetic imaging (CeMRI) can not only distinguish the existence of myocardial infarction(MI) and measure the size of MI, but also discern the microvascular dysfunction with first pass perfusion technique. Also, assessment of left ventricular function is considered to be highly accurate and is considered to be the gold standard for the calculation of ventricular volumetric parameters such as left ventricular (LV) ejection fraction.MethodThree groups of eight mini swines were studied. Coronary microembolization model was made by injection of 120,000 microspheres (42μm) into left anterior descending coronary in six swines, 150,000 microspheres in one swine and 50,000 microshperes in one swine. Magnetic resonance imaging was performed at base, six hours and one week after microembolization using 1.5T Magnetom Avanto, Siemens AG, Erlangen, Germany. Transverse, two-chamber, and four-chamber left ventricular long-axis scout images were obtained to determine the final short-axis image plane. Cine MR images were acquired in contiguous short-axis planes from the apex to the base of the heart to observe the motion of ventricular wall. After the cine MR images were obtained, the swines received an intravenous bolus of 0.05 mmol/kg Gd-DTPA (Magnevist; Schering, Berlin, German) at a rate of 4 mL/s by means of an infusion pump followed by 10mL flush of saline at a rate of 4 mL/s. Three short-axis sections and a four-chamber long-axis of the left ventricle were used for myocardial perfusion analysis. Rest perfusion scanning acquired a series of 50 perfusion images for each slice. First-pass images were acquired by using a T1-weighted turbo fast low-angle shot sequence with a 90°saturation-recovery preparatory pulse. After 15 minutes, stressed first pass perfusion was performed using dipyridamole (0.56mg/kg) which was injection through vein within 4 minutes. After that, a second bolus of 0.15mmol mL/kg Gd-DTPA was given. After ten minutes, delayed images were acquired by using an Turbo_flash_T1WI_PSIR_segmented sequence. The inversion time was determined at 10 minutes with TI-Scout sequence. Results were analyzed at Siemens Syngo Leonardo workstation. After experiment finished, the heart was taken out for NBT staining to observe if there exists myocardial infarction.ResultsMyocardial infarction was observed only at papillary muscle level in the swine with 150,000 microshperes group at NBT staining.Left ventricular ejection fraction(LVEF) at six swines with 120,000 microspheres was 0.451±0.063 at base, 0.362±0.070 at six hours after microembolization and 0.431±0.053 at one week after microembolization (six hours compared with base P＜0.05). Left ventricular end diastolic volume(LVEDV) was 36.55±4.46ml at base, 37.18±4.48ml at six hours and 46.63±4.14ml at one week(six hours compared with base P＜0.05, one week compared with base P＜0.01). Left ventricular end systolic volume(LVESV) was 19.97±2.60ml at base, 23.59±2.83ml at six hours and 26.53±3.26ml at one week(six hours and one week compared with base P＜0.01, respectively). LVEF at swine with 150,000 microspheres was 0.452 at base, 0.391 at six hours and 0.419 at one week respectively. LVEDV was 35.85ml at base, 39.75ml at six hours and 44.85ml at one week respectively. LVESV was 19.65ml at base, 24.20ml at six hours and 26.06ml at one week. LVEF at swine with 50,000 microspheres was 0.500 at base, 0.428 at six hours and 0.478 at one week. LVEDV was 31.80ml at base, 32.40ml at six hours and 37.05ml at one week. LVESV was 15.90ml at base, 18.54ml at six hours and 19.33ml at one week.Hypoenhancement was not observed at first pass or stressed first pass perfusion images at six swines with 120,000 microshperes. Hyperenhancement was observed at six hours from papillary level to apex level at anterior wall, which disappeared one week later. Hypoenhancement was observed at first pass and stressed first pass perfusion images at the swine with 150,000 microshperes at papillary level at anterior wall at six hours, which dwindled one week later. And hyperenhancement was seen at the same site six hours and one week later, which corresponded to position displayed at NBT staining. Only hyperenhancement was observed at six hours at apex level at anterior wall in the swine with 50,000 microshperes. No hypoenhancement was observed at first pass or stressed first pass perfusion images.ConclusionOnly hyperenhancement is observed at low dose of microembolization which size was confined at apex level at acute phase and disappeared one week later. Hypoenhancement can be seen at first pass or stressed first pass perfusion images not only at acute phase but also lasted to chronic phase when microembolization increases. And hyperenhancement will also last to chronic phase when microembolization increases. Myocardial infarction will be visioned at NBT staining when microembolization increases which correspond to the position showed at CeMRI. LVEF decreases at acute phase and resumed one week later which accompanies left ventricular remodeling. CeMRI plays a major role in the diagnosis of coronary microembolization.