Clinical implications of the 'no reflow' phenomenon. A predictor of complications and left ventricular remodeling in reperfused anterior wall myocardial infarction

Angiographic assessment of microvascular perfusion--myocardial blush in clinical practice

Assessment of myocardial "blush" by either Myocardial Blush Grade or TIMI Myocardial Perfusion Grade, is the angiographic method currently preferred to confirm myocardial tissue-level perfusion after primary percutaneous intervention. This review focuses on the utility of angiographic "blush" as a simple, widely available, and virtually costless technique for the immediate diagnosis of microvascular impairment at the time of acute catheterization. We comprehensively outline the available evidence behind the "blush," its use in clinical practice, and draw comparisons with other new technologies for assessment of microvascular integrity.

Comparison of the effects of nitroprusside versus nicorandil on the slow/no-reflow phenomenon during coronary interventions for acute myocardial infarction

Although slow/no-reflow is a serious problem complicating primary percutaneous coronary interventions (PCI) for acute myocardial infarction (AMI) and is associated with a poor prognosis, its efficacious treatment remains problematic. We compared the acute, in-hospital and long-term (1 year) effects of nitroprusside (NTP) with those of nicorandil (NC) on the slow/no-reflow phenomenon. Forty-nine of 442 consecutive patients with AMI who underwent primary PCI complicated by slow/no-reflow and who received intracoronary NTP (n = 25) or NC (n = 24) administration were studied. Both NTP and NC induced significant improvements in coronary flow, with increases in TIMI flow grade from 1.64 ± 0.62 to 2.74 ± 0.36 (p < 0.001) and 1.60 ± 0.86 to 2.23 ± 0.91 (p < 0.001), and in corrected TIMI frame count from 37.8 ± 15.1 to 13.7 ± 7.1 (p < 0.001) and 30.8 ± 20.7 to 19.3 ± 17.9 (p < 0.001), respectively. The degree of improvement in TIMI flow grade (post-pre/pre) and TIMI frame count (pre-post/pre) showed that NTP was more effective than NC (NTP vs. NC: 0.88 ± 0.79, 0.37 ± 0.37, p = 0.008; 0.59 ± 0.23, 0.36 ± 0.27, p = 0.003, respectively). Congestive heart failure did not tend to last beyond 3 days after onset in the NTP group, which was more than in the NC group, during hospitalization (1/25, 4/24, p = 0.143, respectively). At the 1-year follow-up, the NTP group tended to show more improvement than the NC group in MACE (5/25, 9/24, p = 0.175, respectively). NTP is a more effective treatment for slow/no-reflow associated with PCI in patients with AMI and may improve long-term clinical outcomes compared with NC.

Value of a new multiparametric score for prediction of microvascular obstruction lesions in ST-segment elevation myocardial infarction revascularized by percutaneous coronary intervention

BACKGROUND

Despite improvement in revascularization strategies, microvascular obstruction (MO) lesions remain associated with poor outcome after ST-segment elevation myocardial infarction (STEMI).

AIMS

To establish a bedside-available score for predicting MO lesions in STEMI, with cardiac magnetic resonance imaging (CMR) as the reference standard, and to test its prognostic value for clinical outcome.

METHODS

Patients with STEMI of<12 hours' evolution treated by percutaneous coronary intervention (PCI) were included. CMR was performed 4-8 days later, to measure myocardial infarction (MI) extent, left ventricular ejection fraction (LVEF) and volumes, and to identify MO lesions. An MO score was built from multivariable logistic regression results and included clinical, angiographic and electrocardiographic criteria. Adverse cardiovascular events were recorded prospectively after STEMI.

RESULTS

We analysed data from 112 patients. MO lesions were found in 63 (56%) patients and were associated with larger MI as assessed by higher peak creatine phosphokinase (3755 ± 351 vs 1467 ± 220 IU, p<0.001), lower LVEF (46.7 ± 1.5 vs 53.4 ± 1.6%, p<0.01) and larger MI extent (18.7 ± 1.2 vs 9.0 ± 1.3% LV, p<0.001) on CMR. MO score>4 accurately identified microcirculatory injuries (sensitivity 84%; specificity 82%) and independently predicted the presence of MO lesions on CMR. MO score>4 predicted adverse cardiovascular events during the first year after STEMI (relative risk 2.60 [1.10-6.60], p=0.03).

CONCLUSIONS

MO lesions are frequent in PCI-treated STEMI and are associated with larger MIs. MO score accurately predicted MO lesions and identified patients with poor outcome post-STEMI.

Shock wave-pretreated bone marrow cells further improve left ventricular function after myocardial infarction in rabbits

BACKGROUND

We tested whether shock wave (SW) offers additional benefits in improving left ventricular (LV) function after acute myocardial infarction (AMI) in rabbits receiving SW-treated autologous bone marrow-derived mononuclear cells (BMDMNCs) transplantation.

METHODS AND RESULTS

Saline (750 microL; group 2), BMDMNCs (1.0 x 10(7); group 3), or preimplant SW-treated BMDMNCs (group 4) were implanted into the infarct area of male rabbits 15 minutes after left coronary artery ligation, whereas eight rabbits without AMI served as controls (group 1; n = 8 per group). The results showed that in infarct area of LV, protein expressions of Cx43 and cytochrome C in mitochondria and endothelial nitric oxide synthase mRNA expression were lower in group 2 than in other groups, and decreased in group 3 as compared with groups 1 and 4 (all p values < 0.01). Conversely, mRNA expressions of endothelin-1 and matrix metalloproteinase-9, mitochondrial oxidative stress, and total fibrotic area were higher in group 2 than in other groups (all p values < 0.05). Furthermore, 6-month LV function by 2-D echo/angiogram showed significant impairment in group 2 than in other groups and in group 3 than in groups 1 and 4 (all p values < 0.005).

CONCLUSIONS

Application of SW-treated autologous BMDMNCs is superior to BMDMNCs alone for preserving LV function after AMI.

Early extracorporeal membrane oxygenator-assisted primary percutaneous coronary intervention improved 30-day clinical outcomes in patients with ST-segment elevation myocardial infarction complicated with profound cardiogenic shock

OBJECTIVES

This study tested the hypothesis that early extracorporeal membrane oxygenator offered additional benefits in improving 30-day outcomes in patients with acute ST-segment elevation myocardial infarction complicated with profound cardiogenic shock undergoing primary percutaneous coronary intervention.

METHODS

Between May 1993 and July 2002, 920 patients with acute ST-segment elevation myocardial infarction underwent primary percutaneous coronary intervention. Of these patients, 12.5% (115) with cardiogenic shock were enrolled in this study (group 1). Between August 2002 and December 2009, 1650 patients with acute ST-segment elevation myocardial infarction underwent primary percutaneous coronary intervention. Of these patients, 13.3% (219) complicated with cardiogenic shock were enrolled (group 2).

RESULTS

The incidence of profound shock (defined as systolic blood pressure remaining < or =75 mm Hg after intra-aortic balloon pump and inotropic agent supports) was similar in both groups (21.7% vs. 21.0%, p > .5). Extracorporeal membrane oxygenator support, which was available only for patients in group 2, was performed in the catheterization room. The results demonstrated that final thrombolysis in myocardial infarction grade 3 flow in infarct-related artery was similar between the two groups (p = .678). However, total 30-day mortality and the mortality of patients with profound shock were lower in group 2 than in group 1 (all p < .04). Additionally, the hospital survival time was remarkably longer in patients in group 2 than in patients in group 1 (p = .0005). Furthermore, multivariate analysis demonstrated that unsuccessful reperfusion, presence of advanced congestive heart failure, profound shock, and age were independent predictors of 30-day mortality (all p < .02).

CONCLUSION

Early extracorporeal membrane oxygenator-assisted primary percutaneous coronary intervention improved 30-day outcomes in patients with ST-segment elevation myocardial infarction with complicated with profound cardiogenic shock.

Injectable materials for the treatment of myocardial infarction and heart failure: the promise of decellularized matrices

Cardiovascular disease continues to be the leading cause of death, suggesting that new therapies are needed to treat the progression of heart failure post-myocardial infarction. As cardiac tissue has a limited ability to regenerate itself, experimental biomaterial therapies have focused on the replacement of necrotic cardiomyocytes and repair of the damaged extracellular matrix. While acellular and cellular cardiac patches are applied surgically to the epicardial surface of the heart, injectable materials offer the prospective advantage of minimally invasive delivery directly into the myocardium to either replace the damaged extracellular matrix or to act as a scaffold for cell delivery. Cardiac-specific decellularized matrices offer the further advantage of being biomimetic of the native biochemical and structural matrix composition, as well as the potential to be autologous therapies. This review will focus on the requirements of an ideal scaffold for catheter-based delivery as well as highlight the promise of decellularized matrices as injectable materials for cardiac repair.

Microvascular obstruction: underlying pathophysiology and clinical diagnosis

Successful restoration of epicardial coronary artery patency after prolonged occlusion might result in microvascular obstruction (MVO) and is observed both experimentally as well as clinically. In reperfused myocardium, myocytes appear edematous and swollen from osmotic overload. Endothelial cell changes usually accompany the alterations seen in myocytes but lag behind myocardial cell injury. Endothelial cells become voluminous, with large intraluminal endothelial protrusions into the vascular lumen, and together with swollen surrounding myocytes occlude capillaries. The infiltration and activation of neutrophils and platelets and the deposition of fibrin also play an important role in reperfusion-induced microvascular damage and obstruction. In addition to these ischemia-reperfusion-related events, coronary microembolization of atherosclerotic debris after percutaneous coronary intervention is responsible for a substantial part of clinically observed MVO. Microvascular flow after reperfusion is spatially and temporally complex. Regions of hyperemia, impaired vasodilatory flow reserve and very low flow coexist and these perfusion patterns vary over time as a result of reperfusion injury. The MVO first appears centrally in the infarct core extending toward the epicardium over time. Accurate detection of MVO is crucial, because it is independently associated with adverse ventricular remodeling and patient prognosis. Several techniques (coronary angiography, myocardial contrast echocardiography, cardiovascular magnetic resonance imaging, electrocardiography) measuring slightly different biological and functional parameters are used clinically and experimentally. Currently there is no consensus as to how and when MVO should be evaluated after acute myocardial infarction.

Predicting the no-reflow phenomenon following successful percutaneous coronary intervention

In the setting of acute myocardial infarction, early and adequate reopening of an infarct-related artery is not necessarily followed by a complete restoration of myocardial perfusion. This condition is usually defined as ‘no-reflow’. The pathophysiology of no-reflow is multifactorial since extravascular compression, microvascular vasoconstriction, embolization during percutaneous coronary intervention, and platelet and neutrophil aggregates are involved. In the clinical arena, angiographic findings and easily available clinical parameters can predict the risk of no-reflow. More recently, several studies have demonstrated that biomarkers, especially those related to the pathogenetic components of no-reflow, could also have a prognostic role in the prediction and in the full understanding of the multiple mechanisms of this phenomenon. Thus, in this article, we investigate the role of several biomarkers on admission in predicting the occurrence of no-reflow following successful percutaneous coronary intervention.

The assessment of microvascular flow and tissue perfusion using ultrasound imaging

Imaging microvascular flow is of diagnostic value for a wide range of diseases including cancer, inflammation, and cardiovascular disease. The introduction of microbubbles as ultrasound contrast agents offers significant signal enhancement to the otherwise weakly scattered signal from blood in the circulation. Microbubbles provide maximum impedance mismatch, but are not linear scatterers. Their complex response to ultrasound has generated research on both their behaviour and their scattered-signal processing. Nearly 20 years ago signal processing started with simple spectral filtering of harmonics showing contrast-enhanced images. More recent pulse encoding techniques have achieved good cancellation of tissue echoes. The good quality contrast-only images enabled ultrasound contrast-imaging applications to be established in microvascular measurements in the liver and the myocardium. The field promises to advance the quantification of microvascular flow kinetics.

Pathophysiology of myocardial injury and remodeling: implications for molecular imaging

Despite advances in reperfusion therapy, acute coronary syndromes can still result in myocardial injury and subsequent myocardial infarction (MI). Molecular, cellular, and interstitial events antecedent to the acute MI culminate in deleterious changes in the size, shape, and function of the left ventricle (LV), collectively termed LV remodeling. Three distinct anatomic and physiologic LV regions can be described after MI: the infarct, border zone, and remote regions. Given the complexity of post-MI remodeling, imaging modalities must be equally diverse to elucidate this process. The focus of this review will first be on cardiovascular MRI of the anatomic and pathophysiologic LV regions of greatest interest with regard to the natural history of the post-MI remodeling process. This review will then examine imaging modalities that provide translational and molecular insight into burgeoning treatment fields for the attenuation of post-MI remodeling, such as cardiac restraint devices and stem cell therapy.

High index of microcirculatory resistance level after successful primary percutaneous coronary intervention can be improved by intracoronary administration of nicorandil

BACKGROUND

Although microvascular dysfunction following percutaneous coronary intervention (PCI) can be evaluated with the index of microcirculatory resistance (IMR), no method of treatment has been established. We hypothesized that intracoronary administration of nicorandil can improve IMR after successful primary PCI in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS AND RESULTS

In 40 patients with first STEMI after successful primary PCI, IMR was measured using PressureWire(TM) Certus (St. Jude Medical, MN, USA). In 20 of the patients (Group N), IMR was measured at baseline and after intracoronary nicorandil (2 mg/10 ml). In the other 20 patients (Control), IMR was measured at baseline, after intracoronary saline (10 ml) and after intracoronary nicorandil (2 mg/10 ml). In Group N, IMR significantly decreased after intracoronary nicorandil (median IMR, 27.7-18.7 U, P<0.0001). In the Control group, IMR did not change after saline administration (median IMR, 24.3-23.8 U, P=0.8193), but was significantly decreased after intracoronary nicorandil (median IMR, 23.8-14.9 U, P<0.0001). Next, all 40 patients were divided into subgroups by tertile of baseline IMR. In those with intermediate to high IMR (baseline IMR > or =21), intracoronary nicorandil significantly decreased IMR, although it did not change IMR in those with low IMR (baseline IMR <21).

CONCLUSIONS

High IMR levels in patients with STEMI after successful primary PCI can be improved by intracoronary administration of nicorandil.

Cardiovascular magnetic resonance in patients with myocardial infarction: current and emerging applications

In patients with known or suspected myocardial infarction (MI), cardiovascular magnetic resonance (CMR) provides a comprehensive, multifaceted view of the heart. The data, including that from a recent multicenter clinical trial, indicate that delayed-enhancement cardiac magnetic resonance imaging (DE-CMR) is a well-validated, robust technique that can be easily implemented on scanners that are commonly available worldwide, with an effectiveness that clearly rivals the best available imaging techniques for the detection and assessment of acute and chronic MI. When patients present outside the diagnostic window of cardiac troponins, DE-CMR may be especially useful. Moreover, because DE-CMR can uniquely differentiate between ischemic and various nonischemic forms of myocardial injury, it may be helpful in cases of diagnostic uncertainty, such as in patients with classical features of MI in whom coronary angiography does not show a culprit lesion. Even after the diagnosis of MI has been made, CMR provides clinically relevant information by identifying residual viability, microvascular damage, stunning, and right ventricular infarction. In addition, post-MI sequelae, including left ventricular thrombus and pericarditis, are easily identified. Given that quantification of infarct size by DE-CMR is highly reproducible, this technique may provide a useful surrogate end point for clinical trials with appreciable reductions in sample size compared with alternative methods.

Long-term outcome after thrombectomy in acute myocardial infarction

BACKGROUND

Current data appear in favour of thrombectomy for ST-elevation myocardial infarction (STEMI). However, information on long-term outcome after thrombectomy is limited. We performed a retrospective long-term study to assess the risk of cardiac re-hospitalizations and survival after discharge from the index hospitalization for STEMI.

METHODS

Patients originally randomized to percutaneous coronary intervention (PCI) with thrombectomy vs. standard PCI were included in a retrospective long-term observational study. The primary study endpoint was the combined risk for all-cause death or cardiac re-hospitalization after index discharge under optimal medical therapy. The cumulative number of cardiac hospitalization days and ventricular remodelling assessed by echocardiography and plasma biomarkers were secondary endpoints.

RESULTS

Of 94 STEMI patients who had been randomized between 11/2000 and 03/2003, 89 patients consented to long-term follow-up. A total of 43 patients had been allocated to thrombectomy and 46 to standard primary PCI. The minimum follow-up time was 1115 days. There was a significantly lower risk for death or cardiac re-hospitalization for patients of the thrombectomy group (hazard ratio = 0.69, 95% CI: 0.49-0.98, P = 0.036). The incidence of recurrent myocardial infarction was not different (P = 0.343). No differences in cardiac remodelling were detected by echocardiography, with the exception that heart-type fatty acid binding protein at 53.2 +/- 17 months was lower in the thrombectomy group (P = 0.045).

CONCLUSION

Thrombectomy in STEMI may decrease the long-term risk for death or cardiac re-hospitalization.

Limitations and potential clinical application on contrast echocardiography

Myocardial contrast echocardiography (MCE) is a relatively simple myocardial perfusion imaging technique which should be used in different clinical settings. The ability of MCE to provide a comprehensive assessment of cardiac structure, function, and perfusion is likely to make it the technique of choice for non-invasive cardiac imaging.Contrast agents are encapsulated microbubbles (MB) filled with either air or high-molecular-weight gas. They are innocuous, biologically inert and when administered intravasculary, the sound backscatter from the blood poll is enhanced because MB have the enormous reflective ability due to a large acoustic impedance mismatch between the bubble gas and surrounding blood.MCE is an ideal imaging tool for the assessment of left heart contrast and the myocardial microcirculation. MCE detects contrast MB at the capillary level within the myocardium and, thus, has the potential to assess tissue viability and the duration of the contrast effect. MCE was equivalent to SPECT for the detection of CAD with a tendency toward higher sensitivity of MCE compared with SPECT in microvascular disease and CAD. MCE is also a bedside technique that can be used early in patients presenting with acute heart failure to rapidly assess LV function (regional and global) and perfusion (rest and stress).

Reperfusion injury components and manifestations determined by cardiovascular MR and MDCT imaging

Advances in magnetic resonance (MR) and computed tomography (CT) imaging have improved visualization of acute and scar infarct. Over the past decade, there have been and continues to be many significant technical advancements in cardiac MR and multi-detector computed tomography (MDCT) technologies. The strength of MR imaging relies on a variety of pulse sequences and the ability to noninvasively provide information on myocardial structure, function and perfusion in a single imaging session. The recent technical developments may also allow CT technologies to rise to the forefront for evaluating clinical ischemic heart disease. Components of reperfusion injury including myocardial edema, hemorrhage, calcium deposition and microvascular obstruction (MO) have been demonstrated using MR and CT technologies. MR imaging can be used serially and noninvasively in assessing acute and chronic consequences of reperfusion injury because there is no radiation exposure or administration of radioactive materials. MDCT is better suited for assessing coronary artery stenosis and as an alternative technique for assessing viability in patients where MR imaging is contraindicated. Changes in left ventricular (LV) volumes and function measured on cine MR are directly related to infarct size measured on delayed contrast enhanced images. Recent MR studies found that transmural infarct, MO and peri-infarct zone are excellent predictors of poor post-infarct recovery and mortality. Recent MR studies provided ample evidence that growth factor genes and stem cells delivered locally have beneficial effects on myocardial viability, perfusion and function. The significance of deposited calcium in acute infarct detected on MDCT requires further studies. Cardiac MR and MDCT imaging have the potential for assessing reperfusion injury components and manifestations.

Early electrocardiographic findings and MR imaging-verified microvascular injury and myocardial infarct size

OBJECTIVES

This study investigated early electrocardiographic findings in relation to left ventricular (LV) function, extent and size of infarction, and microvascular injury in patients with acute myocardial infarction (MI) treated with percutaneous coronary intervention (PCI).

BACKGROUND

The electrocardiogram (ECG) is the most used and simplest clinical method to evaluate the risk for patients immediately after reperfusion therapy for acute MI. ST-segment resolution and residual ST-segment elevation have been used for prognosis in acute MI, whereas Q waves are related to outcome in chronic MI. We hypothesized that the combination of these electrocardiographic measures early after primary PCI would enhance risk stratification.

METHODS

We prospectively included 180 patients with a first acute ST-segment elevation MI to assess ST-segment resolution, residual ST-segment elevation, and number of Q waves using the 12-lead ECG acquired on admission and 1 h after successful PCI. The ECG findings were related to LV function, infarction size and transmurality, and microvascular injury as assessed with cine and gadolinium-enhanced cardiac magnetic resonance 4 +/- 2 days after reperfusion therapy.

RESULTS

Residual ST-segment elevation (beta = -2.00, p = 0.004) and the number of Q waves (beta = -1.66, p = 0.005) were independent ECG predictors of LV ejection fraction. Although the number of Q waves was the only independent predictor of infarct size (beta = 2.01, p < 0.001) and transmural extent of infarction (beta = 0.60, p < 0.001), residual ST-segment elevation was the only independent predictor of microvascular injury (odds ratio: 19.1, 95% confidence interval: 2.4 to 154, p = 0.005) in multivariable analyses. The ST-segment resolution was neither associated with LV function, infarct size, or transmurality indexes, nor with microvascular injury in multivariable analysis.

CONCLUSIONS

In patients after successful coronary intervention for acute MI, residual ST-segment elevation and the number of Q waves on the post-procedural ECG offer valuable complementary information on prediction of myocardial function and necrosis and its microvascular status.

Comparison between myocardial contrast echocardiography and (99m)technetium sestamibi single photon emission computed tomography determined myocardial viability in predicting hard cardiac events following acute myocardial infarction

The extent of residual myocardial viability (MV) after acute myocardial infarction (AMI) is an important determinant of the outcome. Single photon emission computed tomography (SPECT) is widely used to assess MV after an AMI. However, myocardial contrast echocardiography (MCE), a relatively new technique for the assessment of MV, has better spatial and temporal resolution than SPECT. The present study evaluated whether MV determined by MCE is comparable to that determined using SPECT for the prediction of hard cardiac events after an AMI. Accordingly, 99 patients who had undergone simultaneous rest low-power MCE and nitrate-enhanced SPECT 7 days after an AMI were followed up for cardiac death and AMIs. Both MCE perfusion (1 = normal; 2 = reduced; and 3 = absent) and SPECT tracer uptake (0 = normal; 1 = mildly reduced; 2 = moderately reduced; 3 = severely reduced; and 4 = absent) were scored on a 16-segment left ventricular model. The contrast perfusion index and SPECT perfusion index were calculated by adding the respective scores in the 16 segments and dividing by 16. The contrast perfusion index and SPECT perfusion index were used as a measure of the residual MV on MCE and SPECT, respectively. Of the 99 patients recruited, 95 were available for the follow-up examination (follow-up 46 +/- 16 months). A total of 15 events (16%) occurred (8 cardiac deaths and 7 AMIs). Of the clinical, biochemical, echocardiographic, and SPECT markers of prognosis, the only independent predictors of cardiac death and cardiac death or AMI were age and MV as determined by MCE (p = 0.01 and p = 0.002, respectively). In conclusion, MV determined by MCE at rest was superior to nitrate-enhanced SPECT for the prediction of hard cardiac events after AMI.

Scintigraphic evaluation of routine filterwire distal protection in percutaneous coronary intervention for acute ST-segment elevation myocardial infarction: a randomized controlled trial

AIM

Distal embolization during primary percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction (STEMI) may result in reduced myocardial perfusion, infarct extension and impaired prognosis. In a prospective randomized trial, we assessed the effect of routine filterwire distal protection on scintigraphic estimated infarct size.

METHODS AND RESULTS

The effect of routine filterwire distal protection was evaluated in 344 patients with STEMI <12 hours undergoing primary PCI. Patients were randomized to distal protection with a filterwire or standard PCI. The primary endpoint was myocardial infarct size measured by Sestamibi SPECT after 30 days (%). Secondary endpoints included myocardial salvage, ST-segment resolution (STR), myocardial biomarker release and major adverse cardiac and cerebral events. Baseline characteristics including area at risk (estimated by Sestamibi SPECT) were similar. Final infarct size was not statistically different in the distal protection and the control groups (median [IQR], 6% [1-19] and 5% [1-14], P = .23). Also, secondary endpoints were similar in the two treatment groups.

CONCLUSION

Distal protection with a filterwire performed as routine therapy in primary PCI for STEMI did not reduce myocardial infarct size. The study does not support routine use of distal protection in primary PCI.

Appearance of microvascular obstruction on high resolution first-pass perfusion, early and late gadolinium enhancement CMR in patients with acute myocardial infarction

BACKGROUND

The presence and extent of microvascular obstruction (MO) after acute myocardial infarction can be measured by first-pass gadolinium-enhanced perfusion cardiovascular magnetic resonance (CMR) or after gadolinium injection with early or late enhancement (EGE/LGE) imaging. The volume of MO measured by these three methods may differ because contrast agent diffusion into the MO reduces its apparent extent over time. Theoretically, first-pass perfusion CMR should be the most accurate method to measure MO, but this technique has been limited by lower spatial resolution than EGE and LGE as well as incomplete cardiac coverage. These limitations of perfusion CMR can be overcome using spatio-temporal undersampling methods. The purpose of this study was to compare the extent of MO by high resolution first-pass k-t SENSE accelerated perfusion, EGE and LGE.

METHODS

34 patients with acute ST elevation myocardial infarction, treated successfully with primary percutaneous coronary intervention (PPCI), underwent CMR within 72 hours of admission. k-t SENSE accelerated first-pass perfusion MR (7 fold acceleration, spatial resolution 1.5 mm x 1.5 mm x 10 mm, 8 slices acquired over 2 RR intervals, 0.1 mmol/kg Gd-DTPA), EGE (14 minutes after injection with a fixed TI of 440 ms) and LGE images (1012 minutes after injection, TI determined by a Look-Locker scout) were acquired. MO volume was determined for each technique by manual planimetry and summation of discs methodology.

RESULTS

k-t SENSE first-pass perfusion detected more cases of MO than EGE and LGE (22 vs. 20 vs. 14, respectively). The extent of MO imaged by first-pass perfusion (median mass 4.7 g, IQR 6.7) was greater than by EGE (median mass 2.3 g, IQR 7.1, p = 0.002) and LGE (median mass 0.2 g, IQR 2.4, p = 0.0003). The correlation coefficient between MO mass measured by first-pass perfusion and EGE was 0.91 (p < 0.001).

CONCLUSION

The extent of MO following acute myocardial infarction appears larger on high-resolution first-pass perfusion CMR than on EGE and LGE. Given the inevitable time delay between gadolinium administration and acquisition of either EGE or LGE images, high resolution first-pass perfusion imaging may be the most accurate method to quantify MO.

Participation of mast cells in angiogenesis in the border zone of myocardial infarction in rats

BACKGROUND

We hypothesized that mast cells may participate in coronary angiogenesis in acute myocardial infarction, contributing to myocardial salvage.

METHODS

The left coronary artery was occluded in control (n = 30) and Ws rats (n = 30), which genetically lacked c-kit, resulting in a mast cell deficiency. Four weeks later, the infarct area, i.e., infarct core and surrounding infarct areas, and the non-infarct area were assessed histopathologically. The mast cell and small vessel densities were assessed using toluidine blue and alkaline phosphatase staining. Myocardial perfusion was assessed by myocardial contrast echocardiography (MCE).

RESULTS

In Ws rats, the percentage infarct core area increased (p < 0.05) compared with the controls, whereas the percentage surrounding infarct area decreased (p < 0.01). Mast cell density increased most in the surrounding infarct area (p < 0.01) in control rats, whereas mast cells were absent in Ws rats. Compared with the controls, coronary microvessel density decreased in the surrounding infarct area in Ws rats (p < 0.01). MCE showed that the percentage infarct core area, i.e., perfusion defect, increased (p < 0.05) and the percentage surrounding infarct area, i.e., reduced perfusion area, decreased (p < 0.01) in Ws rats.

CONCLUSION

Mast cells may participate in promoting coronary angiogenesis in the infarct area surrounding the infarct core, contributing to attenuation of left ventricular dysfunction.

Distal embolic protection during percutaneous coronary intervention in patients with acute coronary syndromes: The RUBY study

OBJECTIVE

To assess the safety and feasibility of the GuardWire system as an embolic protection device during percutaneous coronary intervention (PCI) in acute coronary syndromes (ACS).

BACKGROUND

Distal embolization occurs in approximately 15% of patients after primary angioplasty and is associated with reduced myocardial reperfusion, more extensive myocardial damage and a poor prognosis. Distal embolic protection could reduce the rate of embolic complications and improve outcome.

METHODS

329 patients (mean age 60+/-12 years) were included: 278 (84.5%) with ST-elevation myocardial infarction (STEMI), 50 (15.2%) with unstable angina/non-STEMI and 1 (0.3%) with post-infarction angina. Primary endpoint was the incidence of major adverse cardiac events (MACE) at 30 days. Secondary endpoints were the magnitude of ST-segment resolution at 90 and 180 min post-procedure, myocardial blush grade, and angiographically visible distal emboli.

RESULTS

The GuardWire system was successfully positioned in 99% of patients. Complete ST-elevation resolution (>70%) was observed in 28.5% immediately post-procedure, and in 35.4% and 41.6% at 90 and 180 min post-procedure. TIMI-3 flow grade was achieved by 89.8% of patients after intervention and mean corrected TIMI frame count was 20.2+/-13.2. Grade-3 myocardial blush was seen in 47.7% of patients and distal emboli were angiographically visible in 7.4%. Incidence of MACE at 30 days was 3.3% (death 1.2%; Q-wave MI 0.3%; non-Q-wave MI 0.3%; coronary artery bypass graft 0.6%; repeat PCI 0.9%).

CONCLUSION

The GuardWire system was successfully positioned in nearly all patients without complications. The use of this embolic protection device in ACS patients undergoing PCI was associated with low rates of distal embolization and 30-day MACE.

Relationship of admission hematological indexes with myocardial reperfusion abnormalities in acute ST segment elevation myocardial infarction patients treated with primary percutaneous coronary interventions

BACKGROUND

Elevated values of mean platelet volume (MPV) and elevated white blood cell (WBC) count are predictors of an unfavourable outcome among survivors of ST segment elevation myocardial infarction (STEMI). However, their relationship with reperfusion abnormalities is less clear.

OBJECTIVE

To evaluate the value of admission MPV and WBC count in predicting impaired reperfusion in patients with acute STEMI who are treated with primary percutaneous coronary intervention (PCI).

METHODS

Blood samples were obtained on admission from 368 STEMI patients who underwent successful PCI. According to the 60th minute ST segment resolution ratio, patients were divided into impaired reperfusion and reperfusion groups.

RESULTS

Impaired reperfusion was detected in 40% of study patients. Patients in the impaired reperfusion group had a higher admission MPV (9.8+/-1.3 fL versus 8.6+/-1.0 fL; P<0.001) and a higher WBC count (14.4+/-5.5 x 10(9)/L versus 12.1+/-3.8 x 10(9)/L; P<0.001) compared with the patients in the reperfusion group. In regression analysis, MPV (OR 2.21, 95% CI 1.69 to 2.91; P<0.001) and WBC count (OR 1.08, 95% CI 1.02 to 1.15; P=0.01) were found to be independently associated with impaired reperfusion. The best cut-off value of MPV for predicting impaired reperfusion was determined to be 9.05 fL, with a sensitivity of 74% and a specificity of 73%.

CONCLUSIONS

The results indicate that leukocytes and platelets have a role in the mediation of reperfusion injury. In patients with STEMI who are undergoing PCI, admission MPV may be valuable in discriminating a higher-risk patient subgroup and thus, may help in deciding the need for adjunctive therapy to improve the outcome.

The utilization of ultrasound and microbubbles for therapy in acute coronary syndromes

Ultrasound has become a useful high resolution imaging modality for examining the cardiac microcirculation. With the use of microbubbles as an ultrasound contrast agent, ultrasound can be utilized to image the microcirculation and detect capillary flow abnormalities in acute ischaemia. A wide range of ultrasound frequencies (including those used for diagnostic transthoracic imaging) have also been utilized therapeutically to augment the effectiveness of fibrinolytic therapy in ST-segment elevation myocardial infarction (STEMI). Ultrasound and microbubbles are now being explored as methods of improving both microcirculatory and epicardial flow in acute STEMI. This article will review the mechanisms by which ultrasound and microbubbles assist in thrombus detection and dissolution. In addition, the pre-clinical studies utilizing transthoracic ultrasound as a therapeutic entity in acute STEMI will be reviewed. Clinical studies, completed and ongoing, will also be presented.

Upfront thrombus aspiration in primary coronary intervention for patients with ST-segment elevation acute myocardial infarction: report of the VAMPIRE (VAcuuM asPIration thrombus REmoval) trial

OBJECTIVES

This study evaluated safety and efficacy of upfront thrombus aspiration during primary percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

Distal embolization during primary PCI results in reduced myocardial perfusion and poor clinical outcomes.

METHODS

The VAMPIRE (VAcuuM asPIration thrombus REmoval) study was a prospective, randomized, controlled multicenter trial conducted in 23 institutions. Patients (N = 355) presenting within 24 h of STEMI symptoms onset were randomized to primary PCI with (n = 180) or without (n = 175) upfront thrombus aspiration using Nipro's TransVascular Aspiration Catheter (Osaka, Japan).

RESULTS

The TransVascular Aspiration Catheter reached the lesion in 100% of cases. It successfully crossed the target obstruction in 86% without any delay in procedure time or time to reperfusion; whereas macroscopic thrombi were removed in 75% of the cases. Procedure success was similar between groups (98.9% vs. 98.3%). There was a trend toward lower incidence of slow or no reflow (primary end point-defined as a Thrombolysis In Myocardial Infarction flow grade <3) in patients treated with aspiration versus conventional primary PCI (12.4% vs. 19.4%, p = 0.07). Rate of myocardial blush grade 3 was higher in the aspiration group (46.0% vs. 20.5%, p < 0.001). Aspiration was most effective in patients presenting after 6 h of symptoms onset (slow flow rate: 8.1% vs. 37.6%, p = 0.01).

CONCLUSIONS

This study suggested the safety of primary PCI with upfront thrombectomy using a novel device in patients with STEMI. The study showed a trend toward improved myocardial perfusion and lower clinical events in patients treated with aspiration. Patients presenting late after STEMI appear to benefit the most from thrombectomy.

Dose-dependent effects of intravenous allogeneic mesenchymal stem cells in the infarcted porcine heart

Intravenous delivery of mesenchymal stem cells (MSCs) preserves myocardial function after infarction. This dose-escalating study was performed to examine pathologic remodeling and scar formation in a pig model of permanent coronary occlusion without restoration of reperfusion. MSCs labeled with fluorescent dye 48 h or saline (negative control, n = 8) were given intravenously 48 h post proximal left anterior descending artery occlusion. Animals received either autologous or allogeneic MSCs in doses from 1 x 10(3) up to 1 x 10(6) per kg bodyweight from an unrelated donor pig. Infarct size and myocardial function were assessed after 1 month. Morphologic analysis revealed that labeled autologous MSCs migrated in the peri-infarct region resulting in smaller infarct size (19 +/- 7% vs. 32 +/- 7%, p < 0.008) and higher fractional area shortening (33 +/- 7% vs. 21 +/- 3%, p < 0.001). Similarly, allogeneic MSCs had dose-dependent beneficial effects on cardiac function, statistically significant at 1 x 10(5) and 1 x 10(6) cells per kg bodyweight. Autologous as well as allogeneic MSCs specifically "home" to the heart after systemic delivery, leading to limited myocardial infarct size and improved functional outcome, even without coronary reperfusion. Therefore, intravenously administration of MSCs is an attractive minimal-invasive approach for cardiac tissue repair.

Major prognostic impact of persistent microvascular obstruction as assessed by contrast-enhanced cardiac magnetic resonance in reperfused acute myocardial infarction

The aim of this study was to compare the prognostic significance of microvascular obstruction (MO) and persistent microvascular obstruction (PMO) as assessed by cardiac magnetic resonance (CMR) in patients with acute myocardial infarction (AMI). CMR was performed in 184 patients within the week following successfully reperfused first AMI. First-pass images were performed to evaluate extent of MO and late gadolinium-enhanced images to assess PMO and infarct size (IS). Major adverse cardiac events (MACE) were collected at 1-year follow-up. MO and PMO were found in 127 (69%) and 87 (47%) patients, respectively. By using univariate logistic regression analysis, high Global Registry of Acute Coronary Events (GRACE) risk score (odds ratio [OR] 95% confidence interval [CI]: 3.6 [1.8-7.4], p < 0.001), IS greater than 10% (OR [95% CI]: 2.7 [1.1-6.9], p = 0.036), left ventricular ejection fraction less than 40% (OR [95% CI]: 2.4 [1.1-5.2], p = 0.027), presence of MO (OR [95% CI]: 3.1 [1.3-7.3], p = 0.004) and presence of PMO (OR [95% CI]:10 [4.1-23.9], p < 0.001) were shown to be significantly associated with the outcome. By using multivariate analysis, presence of MO (OR [95% CI]: 2.5 [1.0-6.2], p = 0.045) or of PMO (OR [95% CI]: 8.7 [3.6-21.1], p < 0.001), associated with GRACE score, were predictors of MACE. Presence of microvascular obstruction and persistent microvascular obstruction is very common in AMI patients even after successful reperfusion and is associated with a dramatically higher risk of subsequent cardiovascular events, beyond established prognostic markers. Moreover, our data suggest that the prognostic impact of PMO might be superior to MO.

Role of thrombectomy in acute myocardial infarction

Acute ST elevation myocardial infarction results from atherosclerotic plaque rupture with subsequent thrombus formation, leading to complete or near complete occlusion of an epicardial coronary artery. Minimization of the mechanical obstruction from this thrombus remains the main goal of therapy in ST elevation myocardial infarction. Primary percutaneous coronary intervention for an ST elevation myocardial infarction appears to be the preferred mode of revascularization over thrombolytic therapy if the door-to-balloon time target of 90 min is achievable. The idea of reducing the thrombus burden with the use of devices as an adjunct to percutaneous coronary intervention is an attractive one. Several thrombectomy devices have been studied in randomized clinical trials, but no definitive conclusions have emerged, owing to conflicting results and variable clinical end points. This article intends to shed further light on the potential role of thrombectomy in the treatment of acute myocardial infarction.