Coronary microembolization

Peri-interventional coronary vasomotion

A percutaneous coronary intervention (PCI) is a unique condition to study the effects of ischemia and reperfusion in patients with severe coronary atherosclerosis when coronary vasomotor function is compromised by loss of endothelial and autoregulatory vasodilation. We studied the effects of intracoronary non-selective α-, as well as selective α(1)- and α(2)-blockade in counteracting the observed vasoconstriction in patients with stable and unstable angina and in patients with acute myocardial infarction. Coronary vasoconstriction in our studies was a diffuse phenomenon and involved not only the culprit lesion but also vessels with angiographically not visible plaques. Post-PCI vasoconstriction was reflected by increased coronary vascular resistance and associated with decreased LV-function. α (1)-Blockade with urapidil dilated epicardial coronary arteries, improved coronary flow reserve and counteracted LV dysfunction. Non-selective α-blockade with phentolamine induced epicardial and microvascular dilation, while selective α(2)-blockade with yohimbine had only minor vasodilator and functional effects. Intracoronary α-blockade also attenuated the no-reflow phenomenon following primary PCI. This article is part of a Special Issue entitled "Coronary Blood Flow".

TNFα in myocardial ischemia/reperfusion, remodeling and heart failure

TNFα is crucially involved in the pathogenesis and progression of myocardial ischemia/reperfusion injury and heart failure. The formation and release of TNFα and its downstream signal transduction cascade following activation of its two receptor subtypes are characterized. Myocardial TNFα and TNF receptor activation have an ambivalent role in myocardial ischemia/reperfusion injury and protection from it. Excessive TNFα expression and subsequent cardiomyocyte TNF receptor type 1 stimulation induce contractile dysfunction, hypertrophy, fibrosis and cell death, while a lower TNFα concentration and subsequent cardiomyocyte TNF receptor type 2 stimulation are protective. Apart from its concentration and receptor subtype, the myocardial action of TNFα depends on the duration of its exposure and its localization. While detrimental during sustained ischemia, TNFα contributes to ischemic preconditioning protection, no matter whether it is the first, second or third window of protection, and both TNF receptors are involved in the protective signal transduction cascade. Finally, the available clinical attempts to antagonize TNFα in cardiovascular disease, notably heart failure, are critically discussed.

Quantitative and qualitative characterization of the acute changes in myocardial structure and function after distal coronary microembolization using MDCT

RATIONALE AND OBJECTIVES

To determine the potential of multidetector computed tomography (MDCT) in assessing, at 72 hours, the effects of distal coronary microembolization on myocardial structure and function.

MATERIALS AND METHODS

Microembolic material (total volume=16 mm(3) of 40-120 μm diameter) was selectively delivered in the left anterior descending coronary artery under x-ray fluoroscopy (n = 6 pigs). After 72 hours, 64-slice MDCT was used to assess LV function, perfusion, and viability. For comparison between the measurements at 80 kV, 120 kV, and postmortem we used Bland-Altman and Pearson correlation. Histochemical and histopathological staining was used for quantitative and qualitative characterization of microinfarct.

RESULTS

Cine MDCT showed the deleterious effects of microembolization on systolic wall thickening, LV volumes, and ejection fraction. Perfusion parameters, such as max upslope, peak attenuation, and time to peak, differed between microinfarct territory and remote myocardium. Inconsistency in visualizing microinfarct was observed using tube voltages of 80 kV and 120 kV. The extent of heterogeneous microinfarct was 4.5 ± 1.0 % of LV mass at 80 kV, 6.1 ± 0.9% LV at 120 kV, and 5.9 ± 1.1% LV on postmortem. There was significant difference in the extent of microinfarct measured on 80 kV MDCT compared with 120 kV and postmortem. Microscopic examination revealed the random distribution of obstructed microvessels surrounded by myocardial necrosis and inflammatory cells in all animals.

CONCLUSION

Both visible and nonvisible microinfarct cause perfusion deficit and LV dysfunction. MDCT is sensitive for quantifying early functional changes in LV caused by microembolization. Further improvement in spatial resolution of this technology is needed to improve visualization of microinfarct.

Effects of distal embolization on the timing of platelet and inflammatory cell activation in interventional coronary no-reflow

INTRODUCTION

Myocardial hypoperfusion following percutaneous coronary intervention, termed "no-reflow", may be initiated by distal coronary embolization. This study examined the effects of distal embolization on the extent and timing of inflammation and platelet activation in an experimental model of coronary no-reflow.

MATERIAL AND METHODS

A no-reflow model was established in 9 Yorkshire pigs by injecting incremental doses of biologically inert polystyrene microspheres into the left anterior descending artery every 20 minutes via a transit catheter. A control group included 3 pigs that received corresponding intra-coronary boluses of normal saline. At predefined time points, coronary sinus blood samples were drawn and immediately analyzed by flow cytometry analysis for a panel of white blood cell and platelet activation markers, and the inflammatory cytokine TNFalpha.

RESULTS

No-reflow was achieved after delivery of 1,169,000+/-303,000 (range: 680,000 to 2,600,000) microspheres. In the distal embolization group, there were significant increases above baseline values in polymorphonuclear-platelet aggregates (146%-218%), in monocyte-platelet aggregates (51%-94%) and in TNFalpha levels (54%-84%) at multiple time points prior to no- reflow (15% cumulative dose and higher). For Annexin A5, there was a significant increase at 52% of cumulative dose (177% above baseline). Controls only showed one significant increase above baseline value for polymorphonuclear-platelet aggregates at the time of the last injection.

CONCLUSIONS

Widespread activation of interacting inflammatory and coagulation pathways following microsphere embolization occurred prior to the onset of angiographic no-reflow. This activation pattern cannot be attributed to prolonged coronary sinus instrumentation. Interactions between white blood cells (polymorphonuclears and monocytes) and platelets likely play an important role in the pathogenesis of no-reflow following distal embolization and may represent important therapeutic targets.

Establishment and characterization of an experimental model of coronary thrombotic microembolism in rats

To establish a model of coronary thrombotic microembolism in rats, either automicrothrombotic particulates (CM group) or saline control (SHAM group) was injected into temporarily clamped aortas of male Sprague-Dawley rats. After automicrothrombotic particulate injection, serum c-troponin I and von Willebrand factor levels, the no-flow area as evaluated by Thioflavin S, myocardial leukocyte infiltration levels, myocardial expressions of tumor necrosis factor alpha and interleukin-6, the percentage of arterioles obstructed by thrombosis, and myocardial fibrosis were all significantly increased whereas cardiac function as evaluated by echocardiography and hemodynamic measurements were significantly reduced compared with the sham group. Thus, aortic automicrothrombotic particulate injection could induce coronary microembolism in rats, and this model could be of value in improving the understanding of pathophysiology of coronary microembolism.

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.

Myocardial no-reflow in humans

In a variable proportion of patients presenting with ST-segment elevation myocardial infarction, ranging from 5% to 50%, primary percutaneous coronary intervention achieves epicardial coronary artery reperfusion but not myocardial reperfusion, a condition known as no-reflow. Of note, no-reflow is associated with a worse prognosis at follow-up. The phenomenon has a multifactorial pathogenesis including: distal embolization, ischemia-reperfusion injury, and individual predisposition of coronary microcirculation to injury. Moreover, it is spontaneously reversible in some patients, thus suggesting that it might be amenable to treatment also when we fail to prevent it. Several recent studies have shown that biomarkers and other easily available clinical parameters can predict the risk of no-reflow and can help in the assessment of the multiple mechanisms of the phenomenon. Several therapeutic strategies have been tested for the prevention and treatment of no-reflow. In particular, thrombus aspiration before stent implantation prevents distal embolization and has been recently shown to improve myocardial perfusion and clinical outcome as compared with the standard procedure. However, it is conceivable that the relevance of each pathogenetic component of no-reflow is different in different patients, thus explaining the occurrence of no-reflow despite the use of mechanical thrombus aspiration. Thus, in this review article, for the first time, we propose a personalized management of no-reflow on the basis of the assessment of the prevailing mechanisms of no-reflow operating in each patient.

Systematic analysis of functional and structural changes after coronary microembolization: a cardiac magnetic resonance imaging study

OBJECTIVES

Our study aimed to detect the morphological und functional effects of coronary microembolization (ME) in vivo by cardiac magnetic resonance (CMR) imaging in an established experimental animal model.

BACKGROUND

Post-mortem morphological alterations of coronary ME include perifocal inflammatory edema and focal microinfarcts. Clinically, the detection of ME after successful coronary interventions identifies a population with a worse long-term prognosis.

METHODS

In 18 minipigs, ME was performed by intracoronary infusion of microspheres followed by repetitive in vivo imaging on a 1.5-T MR system from 30 min to 8 h after ME. Additionally, corresponding ex vivo CMR imaging and histomorphology were performed.

RESULTS

Cine CMR imaging demonstrated a time-dependent increase of wall motion abnormalities from 9 of 18 animals after 30 min to all animals after 8 h (0.5 h, 50%; 2 h, 78%; 4 h, 75%; 8 h, 100%). Whereas T2 images were negative 30 min after ME, 4 of 18 animals showed myocardial edema at follow-up (0.5 h, 0%; 2 h, 6%; 4 h, 25%; 8 h, 17%). In vivo late gadolinium enhancement (LGE) was observed in none of the animals after 30 min, but in 33%, 50%, and 83% of animals at 2 h, 4 h, and 8 h, respectively, after ME. Ex vivo CMR imaging showed patchy areas of LGE in all but 1 animal (2 h, 83%; 4 h, 100%; 8 h, 100%). A significant correlation was seen between the maximum troponin I level and LGE in vivo (r = 0.63) and the spatial extent of ex vivo LGE (r = 0.76).

CONCLUSIONS

Our results show that in vivo contrast-enhanced CMR imaging allows us to detect functional and structural myocardial changes after ME with a high sensitivity. Ex vivo, the pattern of LGE of high-resolution, contrast-enhanced CMR imaging is different from the well-known pattern of LGE in compact myocardial damage. Thus, improvements in spatial resolution are thought to be necessary to improve its ability to visualize ME-induced structural alterations even in vivo.

How much myocardial damage is necessary to enable detection of focal late gadolinium enhancement at cardiac MR imaging?

PURPOSE

To assess the visibility of small myocardial lesions at magnetic resonance (MR) imaging and to estimate how much myocardial damage is necessary to enable detection of late gadolinium enhancement (LGE) in vivo.

MATERIALS AND METHODS

The study was approved by the local bioethics committee. Coronary microembolization was performed by injecting 300,000 microspheres into the distal portion of the left anterior descending artery in 18 anesthetized minipigs to create multifocal areas of myocardial damage. In vivo MR imaging was performed a mean of 6 hours after microembolization by using an inversion-recovery spoiled gradient-echo sequence (repetition time msec/echo time msec, 8/4; inversion time, 240-320 msec; flip angle, 20 degrees; spatial resolution, 1.3 x 1.7 x 5.0 mm(3)) after injection of 0.2 mmol gadopentetate dimeglumine per kilogram of body weight. High-spatial-resolution imaging of the explanted heart was performed by using the same sequence with a higher spatial resolution (0.5 x 0.5 x 2.0 mm(3)). Imaging results were verified with histologic examination. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of in vivo and ex vivo images were calculated, and a t test was used to analyze observed differences.

RESULTS

Multifocal myocardial damage was successfully induced in all animals. Areas of LGE with low SNR (mean, 36.3 +/- 29.4 [standard deviation]) and CNR (23.7 +/- 19.8) were observed in vivo in 12 (67%) of 18 animals, whereas ex vivo imaging revealed spotted to streaky areas of LGE with higher SNR (91.4 +/- 27.8, P < .0001) and CNR (72.1 +/- 25.4, P < .0001) among normal-appearing myocardium in all cases (100%). Focal myocardial lesions exceeding 5% of myocardium per slice at histologic examination were detected in vivo with a sensitivity of 83%.

CONCLUSION

Focal myocardial damage exceeding 5% of myocardium within the region of interest seems to be necessary for detection of LGE in vivo in an experimental model of coronary microembolization.

Transforming growth factor beta inhibition increases mortality and left ventricular dilatation after myocardial infarction

BACKGROUND

Transforming growth factor (TGF)-beta is a locally generated cytokine involved in healing processes and tissue fibrosis, all relevant for cardiac remodeling and the development of heart failure after myocardial infarction (MI). However, data regarding the function of TGF-beta after ischemic injury are inconclusive.

METHODS AND RESULTS

We tested the effect of TGF-beta inhibition by application of a blocking antibody in mice with MI. Starting 1 week before or 5 days after coronary artery ligation mice were treated with intraperitoneal injections of an anti-TGF-beta (5 mg/kg bodyweight 1D11, Genzyme) or control antibody. Mortality over 8 weeks was significantly higher in the groups treated with the anti-TGF-beta antibody. Both, pre or post MI treatments were associated with increased left ventricular dilatation after MI as determined by serial echocardiography. In anti-TGF-beta treated mice collagen production decreased and matrix-metalloproteinase expression increased. However, the expression of TGF pro-inflammatory cytokine TNF-alpha was not altered by the treatment. Anti-TGF-beta treatment before or after coronary artery ligation increases mortality and worsens left ventricular remodeling in mice with non-reperfused MI. The detrimental effects of TGF-beta inhibition may be mediated by alterations in extracellular matrix remodeling.

The association of coronary flow changes and inflammatory indices to ischaemia-reperfusion microvascular damage and left ventricular remodelling

BACKGROUND

The aim of this study was to investigate the effect of coronary flow (CF) changes and inflammatory indices on myocardial microcirculation--assessed by myocardial contrast echocardiography (MCE)--and on left ventricular remodelling, in an experimental ischaemia-reperfusion model.

METHODS

In 15 pigs, weighing 30 +/- 5 kg, ligation of the left anterior descending (LAD) coronary artery was performed, followed by reperfusion for 120 min. Peak, mean, duration and volume of systolic and diastolic components of CF distal to the LAD ligation were measured using a butterfly flowmeter and their ratio was calculated. The following two-dimensional echocardiography indices of LV geometry/function were measured from the apical four-chamber view: LV end-systolic (ESD) and end-diastolic (EDD) dimension long- (Ls, Ld) and short-axis (Ss, Sd) and their ratio (Ld/Sd, Ls/Ss, defined as the sphericity index). Interleukin (IL) 1beta, 6, 10 and tumour necrosis factor (TNF) were measured in samples obtained from the LV cavity and coronary sinus. A 0.5 ml/min injection slow bolus over 30 s of SonoVue was made into the left ventricle (LV) in order to assess myocardial perfusion by MCE. Standard apical four-chamber views were digitally acquired and stored for off-line analysis using the Echofit system. The peak intensity (Ac) of the microbubbles at the apex, distally to ligation, was normalised with respect to the peak intensity of the microbubbles in the LV cavity. All parameters were recorded at baseline, immediately after ligation and at 5, 15, 30, 60, 120 min during reperfusion. The percentage changes of CF indices, echocardiographic parameters, interleukins and Ac between baseline and reperfusion were calculated.

RESULTS

Mean systolic CF, systolic volume, peak and mean diastolic flow (MDF) changes and epicardial mean CF, Ld/Sd, Ls/Ss changes and coronary sinus IL-6 (IL-6 cs) were inversely correlated with Ac changes during reperfusion. At 5 and 15 min of reperfusion (hyperaemic phase), the greatest median increase of mean diastolic (172% and 86%), and mean systolic CF (713% and 344%) and the greatest reduction of Ac (-41% at 5 min) compared to baseline (P < 0.05) were observed. The maximum increase of IL-6 cs (40%) was detected at 120 min. ROC analysis showed that of all examined echocardiography indices an increase of mean diastolic CF > 22% was the best predictor of a >25% reduction of Ac with 76% sensitivity and 65% specificity (area 71%, CI 54%-85%, P = 0.02). In addition an >32% increase of IL-6 at 120 min of reperfusion predicted a >25% reduction of Ac with a 76% sensitivity and 65% specificity (area 71% CI 61%-97%, P = 0.01).

CONCLUSION

Changes of mean diastolic CF and IL-6 cs are associated with alterations in myocardial microvascular integrity after ischaemia-reperfusion and may be used as a predictor of myocardial dysfunction.

Platelet deposition in remote cardiac regions after coronary occlusion

BACKGROUND

Activated platelets might contribute to endothelial dysfunction in non-ischaemic territories during acute myocardial infarction. We assessed platelet deposition, coronary flow reserve and contractile function in remote cardiac regions after transient coronary occlusion and their association with systemic platelet activation.

MATERIALS AND METHODS

In 10 pigs (series A) subjected to 48-min occlusion of the left anterior descending coronary artery (LAD), 99mTc-platelet content in the right coronary artery (RCA) and its dependent myocardium was counted after reflow. In 10 pigs (series B) receiving the same occlusion of the RCA, the hyperaemic response at the LAD and systolic shortening in LAD-dependent myocardium were monitored after reperfusion. P-selectin expression on circulating platelets was assessed in both series by flow cytometry.

RESULTS

In series A, platelet counts in the RCA and non-ischaemic myocardium were correlated with platelet content, polymorphonuclear leukocyte infiltration and infarct size in the reperfused zone, as well as with the percentage of P-selectin-positive platelets after reflow. In series B, a transient reduction in peak hyperaemic response in the LAD and sustained contractile dysfunction in non-ischemic myocardium were observed after releasing the RCA occlusion, these changes being also correlated with platelet activation status.

CONCLUSIONS

Ischaemic injury triggers macro- and microvascular platelet deposition and causes an impairment in coronary flow reserve and contractile function in distant regions of the heart, which are related to activation of circulating platelets.

Effect of Distal Embolization on Myocardial Perfusion Reserve After Percutaneous Coronary Intervention

Background— Studies have shown that a subset of patients demonstrate persistent impairment in microcirculatory function after percutaneous coronary intervention (PCI). Distal embolization of plaque contents has been postulated as the main mechanism for this. We sought to investigate this further by evaluating PCI-induced changes in myocardial perfusion reserve index (MPRI) over time in segments with “distal-type” procedure-related myonecrosis using high-resolution quantitative cardiovascular magnetic resonance imaging.

Methods and Results— Forty patients undergoing PCI were studied with pre-PCI and 24-hour post-PCI delayed-enhancement magnetic resonance imaging and first-pass perfusion magnetic resonance imaging at rest and stress. Twenty patients underwent a third magnetic resonance imaging scan at 6 months. For perfusion imaging, 3 short-axis images were acquired during every heartbeat with a T1-weighted turboFLASH sequence. MPRI was calculated as the ratio of hyperemic to resting myocardial blood flow and subdivided according to the presence and location of new delayed hyperenhancement. Twenty-one patients demonstrated new distal hyperenhancement after PCI. Mean MPRI in revascularized myocardial segments not demonstrating new HE was significantly increased after the procedure (2.06 [95% CI, 1.99 to 2.13] before PCI and 2.52 [95% CI, 2.42 to 2.62] after PCI; P <0.001). In contrast, MPRI in segments with distal hyperenhancement was reduced after PCI (2.16 [95% CI, 1.95 to 2.37] before PCI; 2.00 [95% CI, 1.82 to 2.19] after PCI; mixed-model z =−4.82; P <0.001). Changes in mean MPRI 24 hours after PCI in segments upstream to new injury were not significantly different compared with perfusion changes in remote myocardium ( z =−0.68; P =0.50). At 6 months after the procedure, mean MPRI in segments with new injury improved significantly compared with MPRI measured in these segments at 24 hours after PCI.

Conclusions— MPRI is reduced in myocardial segments that demonstrate new distal irreversible injury at 24 hours after PCI. These reductions are confined to the segments with injury and do not affect the entire supply territory of the culprit vessel.

Characterization of the yeast tricalbins: membrane-bound multi-C2-domain proteins that form complexes involved in membrane trafficking

In a survey of yeast genomic sequences encoding calcium- and phospholipid-binding C2 domains, three homologous genes were identified that encode proteins that each have three C2 domains and an apparent transmembrane domain near the N terminus. The name tricalbins is suggested for these proteins, corresponding to the open reading frames YOR086c (TCB1), YNL087w (TCB2), and YML072c (TCB3). An antiserum was raised against the C-terminal portion of tricalbin 2 and used on Western blots to demonstrate that the corresponding protein is expressed in yeast and appears as a high-molecular-weight band at 130 kDa with smaller fragments at 39 kDa and 46 kDa. A fusion protein consisting of full length tricalbin 2 fused to the green fluorescent protein was expressed in cells and found to traffic from the cell surface to intracellular vesicles near the vacuole. A two-hybrid interaction screen with the C-terminal portion of tricalbin 2 indicated that tricalbin 2 binds the C-terminal portions of tricalbins 1 and 3 suggesting that the tricalbins may form heterodimers in vivo. Tricalbin 2 also interacted with the activation domain of the pleiotropic drug resistance transcription factor Pdr1p. Combinatorial disruptions of the tricalbin genes revealed that tcb2 single mutants or tcb1, tcb3 double mutants have an altered vacuole morphology and are hypersensitive to cycloheximide. A screen for single-copy suppressors of the cycloheximide sensitivity of tricalbin mutants yielded RSP5, which encodes a C2-domain-containing, ubiquitin-conjugating ligase essential for receptor-mediated and fluid phase endocytosis. The results suggest that the tricalbins function as multimers in membrane-trafficking events and may provide insights into the roles of multi-C2-domain proteins, such as the synaptotagmins, in other organisms.