Optimal therapeutic strategies in the setting of post-infarct no reflow: the need for a pathogenetic classification

State of the Art: No-Reflow Phenomenon

Primary percutaneous coronary intervention is the preferred reperfusion strategy for the management of acute ST-segment elevation myocardial infarction. No reflow is characterized by the inadequate myocardial perfusion of a given segment without angiographic evidence of persistent mechanical obstruction of epicardial vessels. Both pharmacologic and device-based strategies have been tested to resolve coronary no reflow. This article provides an updated overview of the no-reflow phenomenon, discussing clinical evidence and ongoing investigations of existing and novel therapeutic strategies to counteract it.

Platelet/lymphocyte ratio for prediction of no-reflow phenomenon in ST-elevation myocardial infarction managed with primary percutaneous coronary intervention

Background

Coronary no-reflow phenomenon in ST-segment elevation myocardial infarction (STEMI) is associated with a poor clinical outcome. Although its pathophysiology is not fully understood, a deregulated systemic inflammatory response plays an important role. We aimed to explore the relationship between platelet\lymphocyte ratio (PLR) and no-reflow in patients with acute STEMI who were treated with a primary percutaneous coronary intervention (PPCI).

Methods

A total of 200 patients with STEMI undergoing PPCI were included in the study. Transthoracic echocardiographic examination was performed to assess left ventricular (LV) ejection fraction (EF) and wall motion score index. Blood samples were assayed for platelet and lymphocyte count before PPCI. No-reflow was defined as coronary blood flow thrombolysis in myocardial infarction grade ≤II.

Results

No-reflow was observed in 58 (29%) of STEMI patients following PPCI. PLR was significantly higher in hypertensive patients compared to normotensive patients (144.7±91.6 vs. 109.1±47.1, respectively, P<0.001) and in the no-reflow group compared to the normal reflow group (214±93 vs. 101.6±51.3, respectively, P<0.0001). Logistic regression analysis revealed that PLR (β: 0.485, 95% CI: -0.006-0.001, P<0.002) and LV EF (β: 0.272, 95% CI: 0.009-0.034, P<0.001) were independent predictors of no-reflow after PPCI.

Conclusion

Pre-procedural increase in PLR is predictive of the no-reflow phenomenon following PPCI in STEMI patients.

Relevance for Patients

No reflow phenomenon is an unfavorable complication following PPCI in patients with acute STEMI. High pre-procedural PLR is an independent predictor of reperfusion failure and helps to identify patients who require prophylactic treatment.

Effect of routine postdilatation on final coronary blood flow in primary percutaneous coronary intervention patients without angiographic stent expansion problems

Inadequate expansion of coronary stents is associated with stent thrombosis in early stage and with stent restenosis in later stages. Postdilatation (postD) performed using non-compliant balloons improves stent expansion. However, use of this ballooning strategy in primary percutaneous coronary intervention (PPCI) has not been evaluated adequately. Patients who presented with ST segment elevation myocardial infarction (STEMI) and underwent PPCI were included in the present study. Patients were randomized into two groups as those for whom postD was performed (n=62) and those for whom postD was not performed (n=62). Coronary blood flow was evaluated using the thrombolysis in myocardial infarction (TIMI) flow and TIMI frame count (TFC). Total of 124 patients with STEMI were included in the study. There was no difference with respect to baseline TIMI flow, culprit coronary artery and MI localization. However, slow-reflow rate (14.5% vs 35.5%, p=0.007) and final corrected TFC (28.9±16.9 vs 37.0±23.1, p=0.028) were significantly higher in the postD group. Multivariate regression analysis showed postD as an independent variable for slow reflow (OR 11.566, 95% CI 1.633 to 81.908, p=0.014). In our study, routine postD during PPCI was found to be associated with an increased risk of slow reflow in patients without angiographic stent expansion problems.

Intralesional versus intracoronary administration of glycoprotein IIb/IIIa inhibitors during percutaneous coronary intervention in patients with acute coronary syndromes: A meta-analysis of randomized controlled trials

BACKGROUND

Glycoprotein IIb/IIIa inhibitors (GPIs) have been regarded as an adjuvant regimen to deal with no-reflow. However, whether intralesional (IL) administration of GPIs improves myocardial reperfusion without increasing bleeding in patients with acute coronary syndrome (ACS) compared with intracoronary (IC) administration has not been well addressed. Our meta-analysis aimed to evaluate the efficacy and safety of IL versus IC administration of GPIs for patients with ACS during percutaneous coronary intervention.

METHODS

We systematically searched Medline, Embase, the Cochrane Central Register of Controlled Trials, and Cambridge Scientific Abstracts from January 2007 to May 2017. Thrombolysis in Myocardial Infarction (TIMI) 3 flow, corrected TIMI frame count (CTFC), and complete ST-segment resolution (>70%) were selected as the primary outcomes. Major adverse cardiac events (MACEs) were the secondary outcome, and major bleeding complications were the safety outcome. Data analysis was conducted using the Review Manager 5.3 software.

RESULTS

Six randomized controlled trials were included in our meta-analysis. Compared with IC, IL obtained better results in terms of TIMI grade 3 flow [odds ratio (OR) 2.29; 95% confidence intervals (CIs) 1.31-4.01; P = .004], CTFC [weighted mean difference (WMD) -4.63; 95% CI -8.82 to -0.43; P = .03], and complete ST-segment resolution (OR 1.55; 95% CI 1.12-2.14; P = .008). There was a trend toward decreased MACE in the IL administration groups, which was not of statistical significance (OR 0.63; 95% CI 0.30-1.31; P = .22). No significant difference was found between the two groups in terms of in-hospital major bleeding events (OR 2.52; 95% CI .66 to 9.62; P = .18).

CONCLUSION

IL administration yielded favorable outcomes in terms of myocardial tissue reperfusion as evidenced by the improved TIMI flow grade, CTFC, complete ST-segment resolution, and decreased MACE without increasing in-hospital major bleeding events. The IL administration of GPIs can be recommended as the preferred regimen to guard against no-reflow.

The Relation Between No-Reflow Phenomenon and Complete Blood Count Parameters

The no-reflow (NR) phenomenon represents an acute reduction in coronary blood flow without coronary vessel obstruction, coronary vessel dissection, spasm, or thrombosis. No reflow is an important complication among patients with acute ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (pPCI). The complete blood count (CBC) is one of the most frequently ordered laboratory tests in clinical practice. Various studies have evaluated the performance of CBC parameters to predict disease severity and mortality risk. Automated cell counters are routinely available in many clinical laboratories and can be used to determine red blood cell distrubiton width (RDW), platetecrit, platelet count, and and some ratios like the neutrophil-lymphocyte ratio and RDW-platelet ratio. These hematological markers have been reported to be independent predictors of impaired angiographic reperfusion and long-term mortality among patients with STEMI undergoing pPCI. In this context, we reviewed the role of admission CBC parameters for the prediction of NR in patients with STEMI undergoing pPCI.

No reflow phenomenon in percutaneous coronary interventions in ST-segment elevation myocardial infarction

Percutaneous coronary intervention (PCI) is effective in opening the infarct related artery and restoring thrombolysis in myocardial infarction flow 3 (TIMI-flow 3) in large majority of ST-elevation myocardial infarction (STEMI). However there remain a small but significant proportion of patients, who continue to manifest diminished myocardial reperfusion despite successful opening of the obstructed epicardial artery. This phenomenon is called no-reflow. Clinically it manifests with recurrence of chest pain and dyspnea and may progress to cardiogenic shock, cardiac arrest, serious arrhythmias and acute heart failure. No reflow is regarded as independent predictor of death or recurrent myocardial infarction. No reflow is a multi-factorial phenomenon. However micro embolization of atherothrombotic debris during PCI remains the principal mechanism responsible for microvascular obstruction. This review summarizes the pathogenesis, diagnostic methods and the results of various recent randomized trials and studies on the prevention and management of no-reflow.

Myocardial Hemorrhage After Acute Reperfused ST-Segment-Elevation Myocardial Infarction: Relation to Microvascular Obstruction and Prognostic Significance

Supplemental Digital Content is available in the text.

Background—

The success of coronary reperfusion therapy in ST-segment–elevation myocardial infarction (MI) is commonly limited by failure to restore microvascular perfusion.

Methods and Results—

We performed a prospective cohort study in patients with reperfused ST-segment–elevation MI who underwent cardiac magnetic resonance 2 days (n=286) and 6 months (n=228) post MI. A serial imaging time-course study was also performed (n=30 participants; 4 cardiac magnetic resonance scans): 4 to 12 hours, 2 days, 10 days, and 7 months post reperfusion. Myocardial hemorrhage was taken to represent a hypointense infarct core with a T2* value of <20 ms. Microvascular obstruction was assessed with late gadolinium enhancement. Adverse remodeling was defined as an increase in left ventricular end-diastolic volume ≥20% at 6 months. Cardiovascular death or heart failure events post discharge were assessed during follow-up. Two hundred forty-five patients had evaluable T2* data (mean±age, 58 [11] years; 76% men). Myocardial hemorrhage 2 days post MI was associated with clinical characteristics indicative of MI severity and inflammation. Myocardial hemorrhage was a multivariable associate of adverse remodeling (odds ratio [95% confidence interval]: 2.64 [1.07–6.49]; P=0.035). Ten (4%) patients had a cardiovascular cause of death or experienced a heart failure event post discharge, and myocardial hemorrhage, but not microvascular obstruction, was associated with this composite adverse outcome (hazard ratio, 5.89; 95% confidence interval, 1.25–27.74; P=0.025), including after adjustment for baseline left ventricular end-diastolic volume. In the serial imaging time-course study, myocardial hemorrhage occurred in 7 (23%), 13 (43%), 11 (33%), and 4 (13%) patients 4 to 12 hours, 2 days, 10 days, and 7 months post reperfusion. The amount of hemorrhage (median [interquartile range], 7.0 [4.9–7.5]; % left ventricular mass) peaked on day 2 (P<0.001), whereas microvascular obstruction decreased with time post reperfusion.

Conclusions—

Myocardial hemorrhage and microvascular obstruction follow distinct time courses post ST-segment–elevation MI. Myocardial hemorrhage was more closely associated with adverse outcomes than microvascular obstruction.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02072850.

New perspectives on the role of cardiac magnetic resonance imaging to evaluate myocardial salvage and myocardial hemorrhage after acute reperfused ST-elevation myocardial infarction

Cardiac magnetic resonance (CMR) imaging enables the assessment of left ventricular function and pathology. In addition to established contrast-enhanced methods for the assessment of infarct size and microvascular obstruction, other infarct pathologies, such as myocardial edema and myocardial hemorrhage, can be identified using innovative CMR techniques. The initial extent of myocardial edema revealed by T2-weighted CMR has to be stable for edema to be taken as a retrospective marker of the area-at-risk, which is used to calculate myocardial salvage. The timing of edema assessment is important and should be focused within 2 - 7 days post-reperfusion. Some recent investigations have called into question the diagnostic validity of edema imaging after acute STEMI. Considering the results of these studies, as well as results from our own laboratory, we conclude that the time-course of edema post-STEMI is unimodal, not bimodal. Myocardial hemorrhage is the final consequence of severe vascular injury and a progressive and prognostically important complication early post-MI. Myocardial hemorrhage is a therapeutic target to limit reperfusion injury and infarct size post-STEMI.

Temporal Evolution of Myocardial Hemorrhage and Edema in Patients After Acute ST-Segment Elevation Myocardial Infarction: Pathophysiological Insights and Clinical Implications

Background

The time course and relationships of myocardial hemorrhage and edema in patients after acute ST‐segment elevation myocardial infarction (STEMI) are uncertain.

Methods and Results

Patients with ST‐segment elevation myocardial infarction treated by primary percutaneous coronary intervention underwent cardiac magnetic resonance imaging on 4 occasions: at 4 to 12 hours, 3 days, 10 days, and 7 months after reperfusion. Myocardial edema (native T2) and hemorrhage (T2*) were measured in regions of interest in remote and injured myocardium. Myocardial hemorrhage was taken to represent a hypointense infarct core with a T2* value <20 ms. Thirty patients with ST‐segment elevation myocardial infarction (mean age 54 years; 25 [83%] male) gave informed consent. Myocardial hemorrhage occurred in 7 (23%), 13 (43%), 11 (33%), and 4 (13%) patients at 4 to 12 hours, 3 days, 10 days, and 7 months, respectively, consistent with a unimodal pattern. The corresponding median amounts of myocardial hemorrhage (percentage of left ventricular mass) during the first 10 days after myocardial infarction were 2.7% (interquartile range [IQR] 0.0–5.6%), 7.0% (IQR 4.9–7.5%), and 4.1% (IQR 2.6–5.5%; P<0.001). Similar unimodal temporal patterns were observed for myocardial edema (percentage of left ventricular mass) in all patients (P=0.001) and for infarct zone edema (T2, in ms: 62.1 [SD 2.9], 64.4 [SD 4.9], 65.9 [SD 5.3]; P<0.001) in patients without myocardial hemorrhage. Alternatively, in patients with myocardial hemorrhage, infarct zone edema was reduced at day 3 (T2, in ms: 51.8 [SD 4.6]; P<0.001), depicting a bimodal pattern. Left ventricular end‐diastolic volume increased from baseline to 7 months in patients with myocardial hemorrhage (P=0.001) but not in patients without hemorrhage (P=0.377).

Conclusions

The temporal evolutions of myocardial hemorrhage and edema are unimodal, whereas infarct zone edema (T2 value) has a bimodal pattern. Myocardial hemorrhage is prognostically important and represents a target for therapeutic interventions that are designed to preserve vascular integrity following coronary reperfusion.

Clinical Trial Registration

URL: https://clinicaltrials.gov/. Unique identifier: NCT02072850.

Short-Term Effects of Verapamil and Diltiazem in the Treatment of No Reflow Phenomenon: A Meta-Analysis of Randomized Controlled Trials

Currently, there is still a lack of an optimal treatment for no reflow phenomenon (NRP). We analyzed the efficacy and safety of using nondihydropyridine calcium channel antagonists (NDHP, verapamil/diltiazem) in patients suffering from NRP. Eight RCTs with 494 participants were eligible for analysis. The pooling analysis showed that intracoronary verapamil/diltiazem injection significantly decreased the occurrence of the coronary NRP (RR: 0.3, 95% CI: 0.16–0.57; P = 0.0002) and reduced corrected thrombolysis in myocardial infarction (TIMI) frame Count (WMD = −9.24, 95% CI −13.91–4.57; P = 0.0001) in patients with NRP. Moreover, verapamil/diltiazem treatment showed superiority in reducing wall motion index (WMI) compared to the control at day 1 (WMD = 0.11, 95% CI: 0.02–0.20; P = 0.02) (P < 0.05). There was also a significantly greater decline at occurrence of the major adverse cardiac events between verapamil/diltiazem and control groups (WMD: 0.4, 95% CI: 0.19–0.84; P = 0.02). However, using verapamil/diltiazem did not provide additional improvement of left ventricular ejection fraction post procedure (at 7 days, WMD, 0.1; 95% CI, −2.43–2.63; P = 0.94; at 30 days, WMD, 0.42; 95% CI, −2.09–2.92; P = 0.75). NDHP use is beneficial in attenuating NRP and reducing 6-month MACEs in patients with NRP.

Intracoronary administration of anisodamine and nicorandil in individuals undergoing primary percutaneous coronary intervention for acute inferior myocardial infarction: A randomized factorial trial

In acute inferior myocardial infarction (AIMI), numerous conventional drugs that are used to improve the myocardial microcirculation can significantly reduce blood pressure (BP) and coronary perfusion pressure, aggravate bradyarrhythmia and cause a deterioration in the hemodynamic state of the whole body, which greatly limits the application of these drugs in clinical settings. The aim of the present study was to assess the effect of anisodamine and nicorandil regimens on the prevention of no-reflow (NR) and the amelioration of myocardial reperfusion in patients with AIMI undergoing primary percutaneous coronary intervention (PCI). A total of 104 consecutive patients with AIMI were included in this study and randomly assigned to one of four groups: A (control group), B (anisodamine group), C (nicorandil group) and D (anisodamine and nicorandil group). Patients underwent PCI via transradial artery access and the angiographic results were evaluated. Coronary diastolic BP (DBP) and systolic and mean BPs were measured by invasive catheterization. The primary end-point was a post-PCI Thrombolysis In Myocardial Infarction (TIMI) myocardial perfusion grade (TMPG) of 3. Composite end-points (mortality + new MI + target vessel revascularization) were evaluated during the hospital stay and 30 days after discharge. Following the procedure, the proportion of patients achieving TMPG 3 was significantly higher in group D than that in the other groups (P=0.014); furthermore, the incidence of a postprocedural TIMI score of 3 was the highest in group D. Three days after the procedure, the peak creatine kinase-MB and cardiac troponin I levels were the lowest and the left ventricular ejection fraction was the highest in group D. A thrombus score of 3/4 and low DBP were the independent risk factors for poor myocardial reperfusion (expressed as TMPG <3), while 2 mg anisodamine plus 2 mg nicorandil prior to PCI was protective for optimal myocardial reperfusion following the procedure. The combination of anisodamine and nicorandil can effectively ameliorate myocardial reperfusion and protect cardiac function in patients with AIMI undergoing primary PCI.

The increased cardiovascular risk in patients affected by autoimmune diseases: review of the various manifestations

Cardiovascular and autoimmune diseases are among major health concerns in developed countries, and both represent a significant source of morbidity, mortality and economic costs. Despite they are thought to affect subjects at different ages, most of the deaths of patients affected by autoimmune diseases are represented by cardiovascular deaths. Several manifestations of cardiovascular diseases can be observed in patients with autoimmune diseases, such as endothelial dysfunction, accelerated atherosclerosis and an increase in the rate of acute coronary syndromes. Thus, people with autoimmune diseases have an increased cardiovascular risk and a worse outcome in the case of cardiovascular events. In this review, we will describe the correlations between the two spectra of diseases.

Concordance of angiographic and electrocardiographic indexes of microvascular obstruction: myocardial haemorrhage role

BACKGROUND

Angiographic and electrocardiographic (ECG) indexes of microvascular obstruction (MVO) have been described. We aimed at assessing by cardiac magnetic resonance (CMR) anatomical features underlying concordance between them.

METHODS

Forty-one patients were enrolled. Patients presented with neither angiographic nor ECG indexes of MVO (without MVO) (44%), with either angiographic or ECG indexes of MVO (discordant with MVO) (22%) or with both angiographic and ECG indexes of MVO (concordant with MVO) (34%). All patients underwent in-hospital CMR. Echocardiographic data obtained after 6 months were compared with those obtained in hospital.

RESULTS

Concordant patients with MVO had larger infarct size, lower myocardial salvage index and higher rate of myocardial haemorrhage (all assessed by CMR) [33% (25-41%), 15% (10-29%) and 88%, respectively] as compared with patients without MVO [12% (9-16%), 66% (52-79%) and 0%; Bonferroni-adjusted P < 0.001, Bonferroni-adjusted P < 0.001 and P < 0.001, respectively], or with discordant ones [25% (21-39%), 35% (20-48%) and 7%; Bonferroni-adjusted P = 0.03, Bonferroni-adjusted P = 0.002 and P = 0.04, respectively]. After 6 months, ejection fraction significantly decreased in concordant patients with MVO (P < 0.001) without significant changes in the other groups.

CONCLUSIONS

Concordance of angiographic and ECG indexes of MVO reflects more severe myocardial damage translating into unfavourable left ventricular remodelling.

Magnetic resonance imaging characterization of circumferential and longitudinal strain under various coronary interventions in swine

AIM: To compare the acute changes in circumferential and longitudinal strain after exposing a coronary artery to various interventions in swine.

METHODS: Percutaneous balloon angioplasty catheter was guided to location aid device (LAD) under X-ray fluoroscopy to create different patterns of ischemic insults. Pigs (n = 32) were equally divided into 4 groups: controls, 90 min LAD occlusion/reperfusion, LAD microembolization, and combined LAD occlusion/microembolization/reperfusion. Three days after interventions, cine, tagged and viability magnetic resonance imaging (MRI) were acquired to measure and compare left and right circumferential strain, longitudinal strain and myocardial viability, respectively. Measurements were obtained using HARP and semi-automated threshold method and statistically analyzed using unpaired t-test. Myocardial and vascular damage was characterized microscopically.

RESULTS: Coronary microemboli caused greater impairment in l left ventricular (LV) circumferential strain and dyssynchrony than LAD occlusion/reperfusion despite the significant difference in the extent of myocardial damage. Microemboli also caused significant decrease in peak systolic strain rate of remote myocardium and LV dyssynchrony. Cine MRI demonstrated the interaction between LV and right ventricular (RV) at 3 d after interventions. Compensatory increase in RV free wall longitudinal strain was seen in response to all interventions. Viability MRI, histochemical staining and microscopy revealed different patterns of myocardial damage and microvascular obstruction.

CONCLUSION: Cine MRI revealed subtle changes in LV strain caused by various ischemic insults. It also demonstrated the interaction between the right and left ventricles after coronary interventions. Coronary microemboli with and without acute myocardial infarction (AMI) cause complex myocardial injury and ventricular dysfunction that is not replicated in solely AMI.

Effects of intravenous diltiazem in a rat model of experimental coronary thrombotic microembolism

The aim of this study was to assess the feasibility of evaluating the therapeutic effects of intravenous diltiazem in a newly established rat model of coronary thrombotic micro-embolism (CME). CME was induced by injecting 0.199 ml saline containing 5 mg of automicrothrombotic particulates (∼10 μm) into the aorta of Sprague Dawley rats. The injection was carried out over 10 sec using a tuberculin syringe with a 28-gauge needle. The CME model rats were randomly divided into untreated (CME, n=38) and diltiazem-treated (CME+DIL, n=38) groups. Diltiazem (1 mg/ml, 50 μg/min/kg) was intravenously injected using an infusion pump through the tail vein for 175 min, 5 min following the injection of the automicrothrombotic particulates. Hemodynamic measurements, echocardiography and pathohistological examinations were performed at various time-points (3 h, 24 h and 7 and 28 days) postoperatively. Arteriolar thrombosis, multifocal myocardial necrosis, inflammatory cell infiltration with markedly increased myocardial tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) expression, reduced left ventricular (LV) systolic function and increased plasma von Willebrand factor (vWF), endothelin-1 (ET-1) and serum c-troponin I (c-TnI) levels (indicating vascular endothelial injury and myocardial necrosis) were observed in the CME model rats. These pathological responses in CME rats were partly attenuated by intravenous diltiazem treatment. The present CME model is suitable for evaluating the therapeutic effects of intravenous diltiazem; intravenous diltiazem treatment significantly improved cardiac function through alleviating inflammatory responses and microvascular thrombotic injury in this rat model of CME.

Telmisartan protects against microvascular dysfunction during myocardial ischemia/reperfusion injury by activation of peroxisome proliferator-activated receptor γ

Background

We investigated the potential of telmisartan to improve microvascular dysfunction induced by myocardial ischemia/reperfusion (I/R) injury by activating the peroxisome proliferator-activated receptor gamma (PPARG) pathway.

Methods

Forty-eight male rabbits were randomly allocated into sham-operated, I/R, GW9662, telmisartan, telmisartan–GW9662, or candesartan groups. Rabbits were anesthetized, and the left anterior descending coronary artery (LAD) was ligated for 60 minutes. Following reperfusion for 6 hours, angiotensin II content of the heart was determined using radioimmunoassay. Myocardial neutrophil accumulation and microvessel cross-sectional area were examined histologically. Myocardial capillaries were examined with transmission electron microscopy. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in the myocardium were measured using enzyme-linked immunosorbent assay. Western blot was utilized for investigating the expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and PPARG.

Results

Angiotensin II concentration was significantly increased in all treatment groups compared with the sham-operated group (P < 0.05, all). Accumulation of polymorphonuclear neutrophils was significantly lower, while microvessel cross-sectional area was significantly higher in the telmisartan, telmisartan-GW9662, and candesartan groups compared with the I/R group (P < 0.05). ICAM-1 and VCAM-1 levels were also significantly lower, and correlated with lower NF-κB expression in these groups. The effects were the most significant in the telmisartan group compared with the telmisartan–GW9662 and candesartan groups. Telmisartan significantly increased PPARG protein expression compared with all other groups (P < 0.05, all).

Conclusions

Except for the typical effects of angiotensin II-receptor blocker, telmisartan improved microvascular dysfunction during myocardial I/R injury via the PPARG pathway.

No-Reflow Phenomenon

No-reflow is responsible for 40% of the primary percutaneous coronary intervention without complete myocardial reperfusion despite successful reopening of the infarct-related artery. This review describes the main pathophysiological mechanisms of no-reflow, its clinical manifestation, including the strong association with increased in-hospital mortality, malignant arrhythmias, and cardiac failure as well as the diagnostic methods. The latter ranges from simple angiographic thrombolysis in myocardial infarction grade score to more complex angiographic indexes, imaging techniques such as myocardial contrast echo or cardiac magnetic resonance, and surrogate clinical end points such as ST-segment resolution. This review also summarizes the strategies of prevention and treatment of no-reflow, considering the most recent studies results regarding medical therapy and devices.

CMR of microvascular obstruction and hemorrhage in myocardial infarction

Microvascular obstruction (MO) or no-reflow phenomenon is an established complication of coronary reperfusion therapy for acute myocardial infarction. It is increasingly recognized as a poor prognostic indicator and marker of subsequent adverse LV remodeling. Although MO can be assessed using various imaging modalities including electrocardiography, myocardial contrast echocardiography, nuclear scintigraphy, and coronary angiography, evaluation by cardiovascular magnetic resonance (CMR) is particularly useful in enhancing its detection, diagnosis, and quantification, as well as following its subsequent effects on infarct evolution and healing. MO assessment has become a routine component of the CMR evaluation of acute myocardial infarction and will increasingly play a role in clinical trials of adjunctive reperfusion agents and strategies. This review will summarize the pathophysiology of MO, current CMR approaches to diagnosis, clinical implications, and future directions needed for improving our understanding of this common clinical problem.

Management of the no-reflow phenomenon

The lack of reperfusion of myocardium after prolonged ischaemia that may occur despite opening of the infarct-related artery is termed "no reflow". No reflow or slow flow occurs in 3-4% of all percutaneous coronary interventions, and is most common after emergency revascularization for acute myocardial infarction. In this setting no reflow is reported to occur in 30% to 40% of interventions when defined by myocardial perfusion techniques such as myocardial contrast echocardiography. No reflow is clinically important as it is independently associated with increased occurrence of malignant arrhythmias, cardiac failure, as well as in-hospital and long-term mortality. Previously the no-reflow phenomenon has been difficult to treat effectively, but recent advances in the understanding of the pathophysiology of no reflow have led to several novel treatment strategies. These include prophylactic use of vasodilator therapies, mechanical devices, ischaemic postconditioning and potent platelet inhibitors. As no reflow is a multifactorial process, a combination of these treatments is more likely to be effective than any of these alone. In this review we discuss the pathophysiology of no reflow and present the numerous recent advances in therapy for this important clinical problem.

Non-invasive evaluation of myocardial reperfusion by transthoracic Doppler echocardiography and single-photon emission computed tomography in patients with anterior acute myocardial infarction

BACKGROUND

The study was designed to evaluate whether the preserved coronary flow reserve (CFR) 72 hours after reperfused acute myocardial infarction (AMI) is associated with less microvascular dysfunction and is predictive of left ventricular (LV) functional recovery and the final infarct size at follow-up.

METHODS

In our study, CFR was assessed by transthoracic Doppler echocardiography (TDE) in 44 patients after the successful percutaneous coronary intervention during the acute AMI phase. CFR was correlated with contractile reserve assessed by low-dose dobutamine echocardiography and with the total perfusion defect measured by single-photon emission computed tomography 72 hours after reperfusion and at 5 months follow-up. The ROC analysis was performed to determine test sensitivity and specificity based on CFR. Categorical data were compared by an χ² analysis, continuous variables were analysed with the independent Student's t test. In order to analyse correlation between CFR and the parameters of LV function and perfusion, the Pearson correlation analysis was conducted. The linear regression analysis was used to assess the relationship between CFR and myocardial contractility as well as the final infarct size.

RESULTS

We estimated the CFR cut-off value of 1.75 as providing the maximal accuracy to distinguish between patients with preserved and impaired CFR during the acute AMI phase (sensitivity 91.7%, specificity 75%). Wall motion score index was better in the subgroup with preserved CFR as compared to the subgroup with reduced CFR: 1.74 (0.29) vs. 1.89 (0.17) (p < 0.001) during the acute phase and 1.47 (0.30) vs. 1.81 (0.20) (p < 0.001) at follow-up, respectively. LV ejection fraction was 47.78% (8.99) in preserved CFR group vs. 40.79% (7.25) in impaired CFR group (p = 0.007) 72 hours after reperfusion and 49.78% (8.70) vs. 40.36% (7.90) (p = 0.001) after 5 months at follow-up, respectively. The final infarct size was smaller in patients with preserved as compared to patients with reduced CFR: 5.26% (6.14) vs. 23.28% (12.19) (p < 0.001) at follow-up.

CONCLUSION

The early measurement of CFR by TDE can be of high value for the assessment of successful reperfusion in AMI and can be used to predict LV functional recovery, myocardial viability and the final infarct size.

Determinants of microvascular damage recovery after acute myocardial infarction: results from the acute myocardial infarction contrast imaging (AMICI) multi-centre study

AIMS

Microvascular damage (MD) occurring soon after primary percutaneous coronary intervention (PPCI) may reverse or remain sustained within the first week after ST-elevation myocardial infarction (STEMI). We investigated the incidence, determinants, and long-term clinical relevance of MD reversal after PPCI.

METHODS AND RESULTS

Serial two-dimensional echocardiograms (2DE) and a myocardial contrast study were obtained within 24 h of PPCI (T1) and at pre-discharge (T2) in 110 successfully re-perfused STEMI patients. Six months 2DE and 2-year clinical follow-up were obtained. After PPCI myocardial re-perfusion was normal at T1 only in 40 patients (36%, 'normal reflow'), recovered at T2 in 33 (30%, 'reversible MD'), and remained abnormal in 37 (34%, 'sustained MD'). At follow-up, normal reflow and reversible MD were coupled with a significant reduction in the infarct area, decrease in cardiac volumes, and a slight non-significant improvement in systolic function. Conversely, in the sustained MD group, the infarct area did not change and cardiac volumes significantly increased with a parallel worsening in systolic function. By multivariate analysis, independent predictors of reversible MD were: absence of family history of coronary artery disease (CAD), younger age, shorter time to re-perfusion, and absence of diabetes. The 2-year combined events rate was significantly lower in reversible MD (log-rank test P= 0.03) compared with sustained MD patients.

CONCLUSIONS

In STEMI patients treated according to the current guidelines, MD frequently occurs soon after re-perfusion but it is reversible in ~50% of cases and it is associated with a favourable functional and clinical outcome. Family history of CAD, aging, time to re-perfusion, and diabetes are independent predictors of MD reversibility.

Clinical Predictors of Incomplete ST-Segment Resolution in the Patients With Acute ST Segment Elevation Myocardial Infarction

Background and Objectives

The failure of ST-segment resolution (STR) after primary percutaneous coronary intervention (pPCI) is associated with adverse clinical outcomes. However, the clinical predictors on admission for incomplete STR are poorly known.

Subjects and Methods

Patients undergoing pPCI (n=101, 79 males and 22 females, mean age 60.0 years) were divided into complete STR group (≥70%, n=58) and incomplete STR group (<70%, n=43). The groups were compared according to clinical factors including history, electrocardiographic (ECG) patterns, angiographic features and laboratory data.

Results

The incomplete STR group contained more frequent hypertensive patients (p=0.04) and patients displaying longer tendency in total chest pain duration (p=0.08). This group was associated with worse clinical factors such as low ejection fraction (p=0.06), higher Killip class (p=0.08) and more death (p=0.042). Grade 3 ischemia pattern of ECG and precordial ST elevation (i,e anterior myocardial infarction) at admission were more frequent in the incomplete STR group (p=0.001 and 0.002, respectively). Initial troponin I, creatinin kinase -MB and brain natriuretic peptide levels were higher in the incomplete STR group (p=0.001, 0.002, and 0.043, respectively). Coronary angiography showed that culprit lesions were more frequent in left anterior descending artery than other arteries in the incomplete STR group of patients (p=0.002). Thrombolysis In Myocardial Infarction (TIMI) flow grades 2 or less before PCI was more frequent in the incomplete STR group (p=0.029). However, TIMI flow grade after PCI was not appreciably different between the two groups. Logistic regression analysis demonstrated that TIMI flow grade 2 or less was most powerful predictor for incomplete STR {odds ratio (OR)=12.12, 95% confidence interval (CI) 1.23-119.35, p=0.032}. Other independent predictors were anterior infarction (OR=3.39, CI 1.46-10.57, p=0.007), ischemia grade 3 ECG at admission (OR=3.87, CI 1.31-11.41, p=0.014), and hypertensive patients (OR=3.03, CI 1.13-8.15, p=0.027).

Conclusion

Incomplete STR after pPCI is associated with poor prognostic clinical factors. TIMI flow grade 2 or less before pPCI, ST elevation on precordial leads, ischemia grade 3 pattern of initial ECG, and hypertensive patients are independent predictors for incomplete STR in the early stage.

Management of 'no-reflow' complicating reperfusion therapy

No-reflow phenomenon, defined as inadequate myocardial perfusion of the adequately dilated target vessel without evidence of angiographic mechanical obstruction. It is a multifactorial, well-recognised, secondary phenomenon following reperfusion therapy such as thrombolysis or percutaneous coronary interventions (PCI). The pathophysiological mechanisms leading to the no-reflow state are incompletely understood. Embolization of the atheromatous material to the distal vasculature and intense arteriole vasospasm caused by microembolization of platelet-rich thrombi that release vasoactive agents resulting in microvascular obstructions are likely mechanisms. Current prophylaxis and management strategies are derived from limited clinical data. Intracoronary verapamil, adenosine and nitroprusside have been most frequently studied and administered for angiographic no-reflow during PCI for acute myocardial infarction or saphenous vein graft (SVG) lesions and have been shown to improve epicardial flow and microvascular perfusion. The use of distal embolic protection devices in SVG interventions also provide microvascular protection and improve clinical outcomes. However, by far the most important measures are prevention and anticipation during PCI as once no-reflow established, complete reversal of the situation may not be possible.

Carvedilol preserves endothelial junctions and reduces myocardial no-reflow after acute myocardial infarction and reperfusion

INTRODUCTION

Myocardial no-reflow, has been associated with alterations in endothelial junctions, which is regulated in part by endothelial dysfunction. Carvedilol is an alpha1 and nonselective beta-adrenergic receptor antagonist with antioxidative properties known to protect endothelial function. Therefore, we hypothesized that carvedilol might also have protective effects on myocardial no-reflow and endothelial junctions.

METHODS

Thirty-two mini-swines were randomized into 4 study groups: 8 in control, 8 pretreated with carvedilol (1 mg/kg/d) for 3 days, 8 in propranolol (nonselective beta-adrenergic receptor antagonist)-pretreated for 3 days and 8 in sham-operated. Acute myocardial infarction and reperfusion model was created with 3 h occlusion of the left anterior descending coronary artery followed by 1 h reperfusion. Coronary ligation area (LA) and area of no-reflow were determined with both myocardial contrast echocardiography (MCE) in vivo and pathological means (Path). Myocardial vascular endothelial (VE)-cadherin, beta-catenin and gamma-catenin were assessed by immunoblot.

RESULTS

Compared with the control group, carvedilol significantly improved ventricular function, increased coronary blood flow from 50.6+/-3.1% to 72.1+/-3.8% of the baseline at 1 h of reperfusion (P<0.01), decreased area of no-reflow (MCE: from 78.5+/-4.5% to 24.9+/-4.1%, Path: from 82.3+/-1.9% to 25.8+/-4.3% of LA respectively, all P<0.01), reduced necrosis area from 98.5+/-1.3% to 74.4+/-4.7% of LA (P<0.05). The levels of VE-cadherin, beta-catenin, and gamma-catenin in the reflow myocardium were significantly greater in the carvedilol group (all P<0.05). However, propranolol failed to significantly modify area of no-reflow, VE-cadherin, beta-catenin and gamma-catenin levels (all P>0.05).

CONCLUSION

Pretreatment with carvedilol preserves endothelial junctions and reduces myocardial no-reflow after acute myocardial infarction and reperfusion. The beneficial effect of carvedilol was not due to its beta-blocking action.

Different effects of adenosine and calcium channel blockade on myocardial no-reflow after acute myocardial infarction and reperfusion

BACKGROUND

Adenosine and calcium channel blockers have been used in the treatment of angiographic no-reflow directly after angioplasty for acute myocardial infarction (AMI). However, their effects on tissue perfusion after AMI and reperfusion are undefined. The present study was designed to compare the effect of adenosine with that of the calcium channel blockers diltiazem and verapamil on myocardial no-reflow.

MATERIALS AND METHODS

Coronary ligation area and area of no-reflow were determined with both myocardial contrast echocardiography in vivo and histopathological evaluation in 44 Yorkshire mini-swines randomized into five study groups: ten in control, eight in adenosine-treated, nine in diltiazem-treated, nine in verapamil-treated and eight in sham-operated. An acute myocardial infarction and reperfusion model was created with 3-h occlusion of the left anterior descending coronary artery followed by 1-h reperfusion.

RESULTS

Compared with the control group, adenosine significantly decreased the area of no-reflow measured with both methods from 78.5 and 82.3% to 20.7 and 21.5% of ligation area, respectively (both P < 0.01), reduced necrosis area, maintained VE-cadherin, beta-catenin and gamma-catenin levels in reflow myocardium (P < 0.05-0.01). Although diltiazem and verapamil also significantly decreased the area of no-reflow, they failed to significantly modify necrosis area, VE-cadherin, beta-catenin and gamma-catenin levels.

CONCLUSIONS

These findings support the concept that adenosine can reduce both structural and functional no-reflow, while calcium channel blockade can only reduce functional no-reflow.

Pretreatment with simvastatin reduces myocardial no-reflow by opening mitochondrial K(ATP) channel

BACKGROUND AND PURPOSE

Simvastatin, a cholesterol-lowering agent, can protect against endothelial dysfunction. However, the effects of simvastatin treatment on the restoration of blood flow to ischemic myocardium are not known. This study sought to assess such effects of simvastatin on an experimental model of myocardial no-reflow and to explore possible mechanisms.

EXPERIMENTAL APPROACH

Coronary ligation area and area of no-reflow were determined by myocardial contrast echocardiography in vivo and by histology in mini-pigs randomized into 7 study groups: controls, pretreated with simvastatin for 2 days, treated with 5-hydroxydecanoate (5-HD, the selective mitochondrial K(ATP) channel blocker), treated with simvastatin+5-HD, treated with HMR 1883 (the selective sarcolemmal K(ATP) channel blocker), treated with simvastatin+HMR 1883 and a sham-operated group. The myocardial no-reflow model was induced with 3 h occlusion of the left anterior descending coronary artery followed by 2 h reperfusion.

KEY RESULTS

Compared with the control group, simvastatin significantly increased coronary blood flow, decreased the area of no-reflow assessed echocardiographically and reduced the necrotic area, by histology. There was no significant difference in these outcomes between simvastatin and simvastatin+HMR 1883 groups. In contrast, 5-HD abolished the effect of simvastatin.

CONCLUSIONS AND IMPLICATIONS

Simvastatin can reduce the area and myocardial no-reflow after ischaemia and reperfusion. This beneficial effect is due to its activation of mitochondrial K(ATP) channels.

Post-infarction treatment with simvastatin reduces myocardial no-reflow by opening of the KATP channel

Simvastatin can prevent cardiac remodelling after myocardial infarction, though the exact mechanisms are uncertain. Myocardial no-reflow is associated with progressive cardiac remodelling. However, it remains unknown whether post-infarction treatment with simvastatin can also reduce myocardial no-reflow for which suppression of adenosine triphosphate-sensitive K+ (K(ATP)) channel opening is an important mechanism.

METHODS

Area at risk and the area of no-reflow were determined by myocardial contrast echocardiography (MCE) and by pathology in 45 mini-swine randomised into 5 groups: 10 control, 9 simvastatin, 9 glibenclamide, 9 simvastatin plus glibenclamide and 8 sham-operated. A myocardial infarction and reperfusion model was created by 3-h occlusion of the coronary artery followed by 4 weeks of reperfusion.

RESULTS

Compared with the control group, simvastatin significantly increased coronary blood volume (P<0.01) and decreased the area of no-reflow measured by MCE (78.5+/-4.5% to 43.7+/-4.3%) and pathological evaluation (82.3+/-1.9% to 45.2+/-3.8%) of area at risk (P<0.01). Simvastatin also increased the levels of K(ATP) channel proteins (SUR2 and Kir6.2) (P<0.05), but had no effect on necrosis area. The combination of simvastatin and glibenclamide had no significant effect on the above parameters.

CONCLUSIONS

Post-infarction treatment with simvastatin can reduce myocardial no-reflow. This beneficial effect is due to activation of the K(ATP) channel.

Microvascular obstruction after successful fibrinolytic therapy in acute myocardial infarction. Comparison of reteplase vs reteplase+abciximab: A cardiovascular magnetic resonance study

BACKGROUND.: About one third of patients with TIMI 3 after reperfusion have evidence of microvascular obstruction (MO) which represents an independent predictor of myocardial wall rupture. This explains all efforts made to prevent MO. Magnetic resonance imaging (MRI) has proved to be particularly useful in detecting MO. The aim of this study was to evaluate with MRI if different fibrinolytic regimens in acute myocardial infarction display different effects on left ventricle (LV) volumes and ejection fraction (EF), as well as on myocardial infarct size (MIsz) and MO. METHODS.: Twenty male patients, mean age 58 years, affected by acute myocardial infarction, ten anterior and ten inferior, were treated with: full dose reteplase in ten, and half dose reteplase plus full dose abciximab (R+Abcx) in the other ten patients. In the fourth day after hospital admission, MRI STIR T2 images were used to quantify MIsz, while 2dflash cineloops were used after the injection of gadolinium, to quantify LV volumes, EF and to detect MO. RESULTS.: LV EF was higher in R+Abcx 51±10 than in reteplase 41±8. MIsz was similar in both treatment groups: however a close relationship was present between MIsz and EF in the reteplase group indicating that the greater the MIsz the lower the EF. In R+Abcx this relationship was no longer present, suggesting a protective effect of the drug on microcirculation. In fact extensive MO was present in 25% of all cases, 80% of which in the reteplase group while only 20% in R+Abcx. CONCLUSION.: R+Abcx prevents MO: compared to traditional fibrinolytic therapy it allows better LV function and most likely improved long term survival.

The no-reflow phenomenon in coronary arteries

No reflow occurs when there is inadequate myocardial perfusion of a given segment of the coronary circulation without evidence of epicardial vessel obstruction. It is a rare but clinically significant condition associated with myocardial infarction and coronary interventions. Diagnosis is usually based on clinical signs of myocardial ischemia (symptoms and/or ECG changes) combined with coronary angiography. Management can be difficult and primarily consists of intracoronary administration of vasodilators. One interesting etiology is thromboembolism and this has become the focus for new potential treatments, including distal embolic protection devices.