Profibrillatory effects of intracoronary thrombus in acute regional ischemia of the in situ porcine heart

Acetylsalicylic acid use is associated with reduced risk of out-of-hospital cardiac arrest in the general population: Real-world data from a population-based study

Aim

Activated blood platelet products facilitate myocardial intracellular Ca2+ overload, thereby provoking afterdepolarizations and increasing susceptibility of ischemic myocardium to ventricular fibrillation (VF). These effects are counteracted in vitro by acetylsalicylic acid (ASA), but no prior study investigated whether ASA is associated with decreased out-of-hospital cardiac arrest (OHCA) risk on a population level. Therefore, we studied whether ASA and other antiplatelet drugs (carbasalate calcium, clopidogrel) are associated with decreased risk of OHCA.

Methods

We conducted a population-based case-control study among individuals (772 OHCA-cases with documented VT/VF, 2444 non-OHCA-controls) who had used antiplatelet drugs in the year before index-date (OHCA-date), and studied the association between current antiplatelet drug use and OHCA-risk with multivariable logistic regression analysis.

Results

ASA use was associated with reduced OHCA-risk (adjusted odds ratio (ORadj) 0.6 [0.5–0.8]), and more so in women (ORadj 0.3 [0.2–0.6]) than in men (ORadj 0.7 [0.5–0.95], Pinteraction 0.021). Carbasalate calcium was associated with decreased OHCA-risk in women (ORadj 0.5 [0.3–0.9]), but not in men (ORadj 1.3 [0.96–1.7], Pinteraction 0.005). Clopidogrel was not associated with reduction in OHCA-risk. Risk reduction associated with ASA in patients with OHCA was similar in the presence of acute myocardial infarction (AMI) (ORadj 0.6 [0.4–0.9]) and in the absence of AMI (ORadj 0.7 [0.4–1.2]).

Conclusion

ASA use was associated with reduced OHCA-risk in both sexes, and more so in women, while carbasalate calcium only protected women. Clopidogrel was not associated with reduced OHCA-risk.

A Novel Large Animal Model of Thrombogenic Coronary Microembolization

Coronary microembolization is one of the main causes of the “no-reflow” phenomenon, which commonly occurs after reperfusion of an occluded coronary artery. Given its high incidence and the fact that it has been proven to be an independent predictor of cardiac morbidity and mortality, there is an imperative need to study its underlying mechanisms and pathophysiology. Large animal models are essential to perform translational studies. Currently there is no animal model that recapitulates a clinical scenario of thrombogenic microembolism with preceding myocardial ischemia. Therefore, the goal of this study was to develop and characterize a novel pig model of coronary microembolization using autologous thrombus injection (CMET). Twenty-three pigs underwent myocardial infarction through percutaneous balloon occlusion of the left anterior descending artery (LAD). Each animal was enrolled in one of two groups: (1) the CMET group, in which the LAD occlusion was followed by delivery of autologous clotted blood in the LAD (distal to the balloon occlusion) and reperfusion; (2) the ischemic reperfusion (I/R) group, in which the LAD ischemia was followed by reperfusion. Surviving animals underwent functional and morphological characterization at 1-week post-procedure. Three sham operated animals were used as a control. CMET resulted in impaired left ventricular function compared to I/R pigs at 1 week. Three-dimensional echocardiography demonstrated reduced ejection fraction in the CMET group (CMET vs. I/R: 35.6 ± 4.2% vs. 47.6 ± 2.4%, p = 0.028). Invasive hemodynamic measurements by Swan-Ganz and left ventricular pressure-volume catheters revealed that CMET impaired left ventricular contractility and diastolic function. This was confirmed by both load-dependent indices including cardiac output (CMET vs. I/R: 2.7 ± 0.2 l/min, vs. 4.0 ± 0.1 l/min, p = 0.002) and load independent indices including preload-recruitable stroke work (CMET vs. I/R: 25.8 ± 4.0 vs. 47.5 ± 6.5 mmHg, p = 0.05) and end-diastolic pressure-volume relationship (slope, 0.68 ± 0.07 vs. 0.40 ± 0.11 mmHg/ml, p = 0.01). Our unique closed-chest model of coronary microembolization using autologous thrombus injection resembles the clinical condition of thrombogenic coronary microembolization in I/R injury. This model offers opportunities to conduct translational studies for understanding and treating coronary microembolization in myocardial infarction.

[Sudden cardiac death related to coronary artery disease. Is the risk different for women?]

Sudden cardiac death is a major public health issue, with high incidence and disappointing survival. Therefore, prevention of sudden death and identification of high-risk patients are essential tools, especially in the field of coronary artery disease, which is the main cause of sudden death. Prevalence of coronary artery disease is higher among men, leading to a higher rate of coronary artery disease-related sudden cardiac death. The current issues are identification of gender-specificities regarding coronary artery disease, rhythmic complications and management.

Coronary microemboli effects in preexisting acute infarcts in a swine model: cardiac MR imaging indices, injury biomarkers, and histopathologic assessment

PURPOSE

To use cardiac magnetic resonance (MR) imaging indices, injury biomarkers, and microscopy for quantifying the effects of defined microemboli volume and sizes on viability, left ventricular (LV) function, and perfusion in preexisting acute myocardial infarcts in a swine model.

MATERIALS AND METHODS

Institutional approval was obtained to perform x-ray fluoroscopy and 90-minute left anterior descending coronary artery occlusion-reperfusion (single ischemic insult) in 16 pigs and coronary embolization in eight of the 16 pigs (32 mm(3), 40-120 μm microemboli) (double ischemic insults). Another eight pigs served as controls. Cardiac MR imaging results (viability, function, and perfusion), injury biomarkers (creatine-kinase-MB and troponin I), and histopathologic evaluations were quantified. Analysis of variance was performed, and a P value less than .02 was considered to indicate a significant difference.

RESULTS

Delayed contrast material-enhanced MR imaging allowed simultaneous visualization of hyperenhanced large infarcts, hypoenhanced microvascular obstruction (MVO) zones, and moderately enhanced patchy microinfarcts in border zones, which represent different degrees of contraction and perfusion in the respective regions, in pigs subjected to double ischemic insults. The increase in myocardial damage was smaller in pigs with double insults (15.7% ± 1.1% of total LV mass) than in those with a single insult (12.4% ± 1.2%, P < .02), but the reduction in LV ejection fraction was disproportional (32% ± 0.6% and 38% ± 1%, P < .02, respectively). Delayed contrast-enhanced imaging can allow quantification of the MVO zone but can result in underestimation of the extent of myocardial damage compared with microscopy in animals subjected to double insults (18.2 ± 1.6, P < .02). A significant increase in cardiac injury biomarkers was observed at 18-24 hours in both cohorts. The additional effect of microemboli on troponin I was demonstrated at 68-72 hours (3.2 ng/mL ± 0.85 [3.20 μg/L ± 0.85] vs 1.34 ng/mL ± 0.43 [1.34 μg/L ± 0.43], P < .02).

CONCLUSION

MR imaging has the potential to allow visualization of acute myocardial infarcts, MVO zones, and patchy microinfarcts simultaneously. The accentuated LV dysfunction caused by double ischemic insults was linked to expansion of the MVO zone, perfusion deficits, and myocardial damage.

Altered platelet contents in survivors of early ischemic ventricular fibrillation: preliminary findings

Early ischemic ventricular fibrillation (VF) in the setting of an acute myocardial infarction (AMI) due to thrombotic coronary occlusion remains a major health problem. Several animal studies have shown that platelet-dense granule contents released during thrombus formation can induce arrhythmias. We hypothesize that the platelet release reaction is involved in the predisposition to early ischemic VF. A case-control study was performed in patients who survived VF during a first AMI ("cases," n = 26) and in patients with one previous AMI without arrhythmias ("controls," n = 24). All patients were on aspirin 100 mg OD. Baseline platelet activation was assessed with flow cytometry. Response to activation was assessed with aggregometry, flow cytometry and PFA-100 analysis. Differences in platelet contents and content release were assessed by labeling platelet-dense granules with mepacrine and by measuring serotonin and ADP/ATP content. Patient and infarct characteristics and baseline platelet function tests were similar between groups. The mean time from event was 4.9 (±3.2) years among cases and 4.7 (±2.7) years among controls. Dense granule release was similar in cases versus controls. Platelet serotonin content in cases was higher than in controls (611 ± 118 ng/10E(9) platelets vs. 536 ± 141 ng/10(9), p = 0.048). Even years after the event, elevations in the platelet dense granule contents between VF survivors and controls may be detected. These preliminary findings shed new light on the pathophysiological mechanisms underlying ischemic VF, as platelet-dense granules may contain mediators of early ischemic VF risk.

Platelets and cardiac arrhythmia

Sudden cardiac death (SCD) remains one of the most prevalent modes of death in industrialized countries, and myocardial ischemia due to thrombotic coronary occlusion is its primary cause. The role of platelets in the occurrence of SCD extends beyond coronary flow impairment by clot formation. Here we review the substances released by platelets during clot formation and their arrhythmic properties. Platelet products are released from three types of platelet granules: dense core granules, alpha-granules, and platelet lysosomes. The physiologic properties of dense granule products are of special interest as a potential source of arrhythmic substances. They are released readily upon activation and contain high concentrations of serotonin, histamine, purines, pyrimidines, and ions such as calcium and magnesium. Potential arrhythmic mechanisms of these substances, e.g., serotonin and high energy phosphates, include induction of coronary constriction, calcium overloading, and induction of delayed after-depolarizations. Alpha-granules produce thromboxanes and other arachidonic-acid products with many potential arrhythmic effects mediated by interference with cardiac sodium, calcium, and potassium channels. Alpha-granules also contain hundreds of proteins that could potentially serve as ligands to receptors on cardiomyocytes. Lysosomal products probably do not have an important arrhythmic effect. Platelet products and ischemia can induce coronary permeability, thereby enhancing interaction with surrounding cardiomyocytes. Antiplatelet therapy is known to improve survival after myocardial infarction. Although an important part of this effect results from prevention of coronary clot formation, there is evidence to suggest that antiplatelet therapy also induces anti-arrhythmic effects during ischemia by preventing the release of platelet activation products.

Calcium-independent phospholipase A2-catalyzed plasmalogen hydrolysis in hypoxic human coronary artery endothelial cells

Thrombin stimulation of human coronary artery endothelial cells (HCAEC) results in activation of a membrane-associated, calcium-independent phospholipase A2(iPLA2) that selectively hydrolyzes membrane plasmalogen phospholipids. Rupture of an atherosclerotic plaque and occlusion of the coronary vasculature results in a coronary ischemic event in which HCAEC in the ischemic area would be exposed to dramatic decreases in oxygen tension in addition to thrombin exposure. We exposed HCAEC to hypoxia in the presence or absence of thrombin stimulation and measured iPLA2activation, membrane phospholipid hydrolysis, and the accumulation of biologically active phospholipid metabolites. HCAEC exposed to hypoxia, thrombin stimulation, or a combination of the two conditions demonstrated an increase in iPLA2activity and an increase in arachidonic acid release from plasmenylcholine. Thrombin stimulation of normoxic HCAEC did not result in an accumulation of choline lysophospholipids, but hypoxia alone and in combination with thrombin stimulation led to a significant accumulation of lysoplasmenylcholine (LPlsCho). We propose that the presence of hypoxia inhibits LPlsCho catabolism, at least in part, as a result of the accumulation of long-chain acylcarnitines. The combination of increased production and decreased catabolism of LPlsCho is necessary for its accumulation. Pretreatment with bromoenol lactone to inhibit iPLA2blocked membrane phospholipid hydrolysis and production of membrane phospholipid-derived metabolites. The increase in iPLA2activity and the subsequent accumulation of membrane phospholipid-derived metabolites in HCAEC exposed to hypoxia or thrombin stimulation alone, and particularly in combination, have important implications in inflammation and arrhythmogenesis in atherosclerosis/thrombosis and subsequent myocardial ischemia.

Assessment of markers of thrombin generation in patients with acute myocardial infarction complicated by ventricular fibrillation

BACKGROUND

In most cases, sudden cardiac death is triggered by ischemia-related ventricular tachyarrhythmias and accounts for 50% of deaths from cardiovascular disease in developed countries. Chronic elevation of indicators of coagulation activation has been found in patients with coronary heart disease, but a role of coagulation activation as a potential risk factor for ventricular fibrillation (VF) during acute myocardial infarction (MI) has not been investigated.

METHODS

We enrolled 50 patients with a history of MI, of whom 26 presented with VF in the acute phase of myocardial ischemia; 24 patients had an acute MI without ventricular tachyarrhythmias. Levels of thrombin-antithrombin complexes (TAT), prothrombin fragment F1 + 2 (F1 + 2), fibrinopeptide A (FPA), plasmin-antiplasmin complexes (PAP), protein C, antithrombin, activated partial thromboplastin time (aPTT), thromboplastin time, D-Dimer, fibrinogen, and high-sensitivity C-reactive protein (hs-CRP) were measured in plasma samples of all patients. Blood collection was obtained sequentially in two separate settings. Patients were studied at a median of 351 days after the acute coronary event.

RESULTS

Higher levels of TAT complexes (13.4 +/- 22.2 vs. 3.03 +/- 4.3 microg/l; p = 0.02), FPA (79.7 +/- 132.3 vs. 24.04 +/- 41.3 ng/ml; p = 0.04), and F1+2 (1.89 +/- 1.3 vs. 1.16 +/- 0.5 nmol/l; p = 0.01) were observed in patients with VF compared with patients without ventricular tachyarrhythmias during the acute phase of MI. D-Dimer levels displayed a trend without reaching statistical significance (0.69 +/- 0.48 vs. 0.48 +/- 0.24 mg/l; p = 0.06). No differences were found in hs-CRP (3.25 +/- 4.5 vs. 4.4 +/- 8.8 mg/l; p = 0.5) and fibrinogen (2.8 +/- 0.9 vs. 2.7 +/- 0.9 g/l; p = 0.6) measurements. Repeat assessment of markers of coagulation activation at a median of 847 days revealed a highly significant decrease in patients with VF.

CONCLUSIONS

Markers of thrombin generation are transiently increased in patients with VF during the acute phase of MI. These findings have implications for risk assessment and genetic screening of patients prone to VF during acute myocardial ischemia.

Tachyarrhythmias in percutaneous coronary interventions

Accompanying the clear benefits, there are certain risks of tachyarrhythmias in percutaneous coronary interventions (PCI), including serious ventricular arrhythmias and atrial fibrillation (AF). Ventricular arrhythmias may result from excess catheter manipulation, intracoronary dye injection, new ischemic events, or reperfusion. In patients with heart failure such kind of arrhythmias can occur more frequently. Atrial dysfunction, sino-atrial and nodal ischemia, congestive heart failure, sympathetic stimulation, iatrogenic factors are the possible causes of AF especially in patients undergoing primary PCI. Atrial fibrillation, on the other hand, can cause clinical squeal in the setting of a rapid ventricular response or if the loss of atrial systole results in hypotension, as in a patient with mitral stenosis or diastolic ventricular dysfunction. Majority of the ventricular arrhythmias and AF tend to revert spontaneously. However, the special treatment must be given, when necessary.

Coronary vasomotor and cardiac electrophysiologic effects of diadenosine polyphosphates and nonhydrolyzable analogs in the guinea pig

Platelet activation in heart disease is important owing to the effects of platelet-derived compounds on myocardial perfusion and cardiac electrophysiology. Diadenosine polyphosphates are secreted from platelets and present in the myocardium, but their electrophysiologic and vasomotor effects are incompletely understood. We used isolated guinea-pig hearts to study the effects of diadenosine triphosphate (Ap3A), tetraphosphate (Ap4A), pentaphosphate (Ap5A), and hexaphosphate (Ap6A) (10 pM-0.1 mM), comparing their actions to those of adenosine, adenosine triphosphate, and non-hydrolyzable Ap4A and Ap5A analogs. Diadenosine polyphosphates (0.1 nM-0.1 microM) transiently reduced coronary perfusion pressure, which recovered during the continued presence of the compounds. At concentrations greater than 0.1 microM effects were maximal and sustained (perfusion pressure decreased from 36.5+/-3.4 to 18.6+/-2.5 mm Hg, p < 0.001, with 1 microM Ap4A). The changes in action potential duration and refractory period developed slowly but were maintained (0.1 nM-1 microM). With 1 nM Ap4A, action potential duration increased from 170.6+/-2.6 to 187.3+/-3.8 ms, p < 0.05, and refractory period increased from 138.5+/-1.6 to 147.9+/-2.0 ms, p < 0.05. Ap4A and its analog reduced QRS duration (from 24.7+/-1.1 to 13.9+/-1.6 ms with 1 microM Ap4A, p < 0.05). P2-purinergic (adenosine triphosphate) receptor antagonism (suramin) reduced perfusion pressure but was without electrophysiologic effect. Other changes in coronary perfusion pressure and electrophysiologic variables associated with Ap4A were not seen in the presence of suramin. P1-(adenosine) antagonism (8-[p-sulfophenyl]theophylline) attenuated the electrophysiologic effects only. Diadenosine polyphosphates have potent cardiac electrophysiologic and coronary vasomotor effects via purinergic receptors, suggesting an important role during platelet activation in acute coronary syndromes.

Three-dimensional mapping of spontaneous ventricular arrhythmias in a canine thrombotic coronary occlusion model

INTRODUCTION

Ventricular tachycardia (VT) and ventricular fibrillation (VF) induced by thrombotic coronary occlusion were mapped in three dimensions in ten dogs.

METHODS AND RESULTS

Thrombotic occlusion was induced using a wire to deliver current to the proximal left circumflex artery (LCX). In nine dogs, nonsustained VT (NSVT) arose from numerous focal sites. Sustained VT was initiated in six dogs (VT group) by a focus near or in the ischemic region. VT was maintained by a focus in the ischemic border in three dogs and by macroreentry that involved both the ischemic and nonischemic regions in the other three dogs. In five dogs, VT degenerated into VF due to intramural reentry in different locations. Mean total activation time (AT), the time for activation to traverse the ventricles, for a sinus beat when LCX current was first applied was 40 +/- 4 msec. In the four dogs in which VT occurred 3 to 7 minutes after total occlusion, sinus AT increased to 98 to 146 msec just before VT. Sinus AT in the four dogs without VT was always <98 msec. Mean AT of the first ten cycles of VT was significantly longer in those VTs that degenerated into VF (169 +/- 29 msec) than in those that did not (81 +/- 12 msec).

CONCLUSION

Thrombotic LCX occlusion induced NSVT in 90%, VT in 60%, and VF in 50% of dogs. Focal mechanisms caused most NSVTs and VT initiation. VT was maintained by a focus near or in the ischemic region or by macroreentry involving both the ischemic and nonischemic regions. AT identified animals in which VT occurred soon after LCX occlusion and in which VT progressed to VF.

Cardiac ionic currents and acute ischemia: from channels to arrhythmias

The aim of this review is to provide basic information on the electrophysiological changes during acute ischemia and reperfusion from the level of ion channels up to the level of multicellular preparations. After an introduction, section II provides a general description of the ion channels and electrogenic transporters present in the heart, more specifically in the plasma membrane, in intracellular organelles of the sarcoplasmic reticulum and mitochondria, and in the gap junctions. The description is restricted to activation and permeation characterisitics, while modulation is incorporated in section III. This section (ischemic syndromes) describes the biochemical (lipids, radicals, hormones, neurotransmitters, metabolites) and ion concentration changes, the mechanisms involved, and the effect on channels and cells. Section IV (electrical changes and arrhythmias) is subdivided in two parts, with first a description of the electrical changes at the cellular and multicellular level, followed by an analysis of arrhythmias during ischemia and reperfusion. The last short section suggests possible developments in the study of ischemia-related phenomena.