Effect of aspirin on cholesterol crystallization: A potential mechanism for plaque stabilization.

Background and aims: Cholesterol crystals (CCs) have been found to be critical in the evolution and progression of atherosclerotic plaque leading up to rupture. This includes triggering inflammation and mechanically traumatizing the plaque and surrounding tissues. Thus, inhibition of crystal formation and degrading the crystals could be an important therapeutic approach in the prevention of cardiovascular events. Because of its physico-chemical properties we examined the effect of aspirin (ASA) on cholesterol crystallization. Methods: A first experiment tested three amounts of cholesterol (1, 2, 3 g) with a wide range of ASA (0-60 mg) on cholesterol crystallization and volume expansion. A second experiment tested the effect of CCs with and without ASA in perforation of fibrous membrane during crystallization. A third experiment evaluated the effect of ASA on melting CCs in human atherosclerotic plaques. Scanning electron microscopy (SEM) was used to evaluate crystal morphology. Results: Aspirin significantly inhibited cholesterol crystallization and volume expansion in a dose related fashion and even at physiologic levels (0.3 mg/ml). Moreover, ASA prevented perforation of fibrous membranes. By SEM, crystals in human atherosclerotic plaques were found melted with ASA. Conclusions: Cholesterol volume expansion during crystallization was significantly inhibited and CCs were dissolved in the presence of ASA. Fibrous membranes were not perforated with ASA because of both these effects.

Plaque rupture and thrombosis are reduced by lowering cholesterol levels and crystallization with ezetimibe and are correlated with fluorodeoxyglucose positron emission tomography.

OBJECTIVE: This study evaluated effects of lipid lowering with ezetimibe on plaque burden and associated cholesterol crystallization and inflammation in a rabbit model of plaque disruption and thrombosis. METHODS AND RESULTS: Atherosclerotic rabbits (Group I, n=10 without; Group II, n=12 with ezetimibe, 1 mg/kg per day) were pharmacologically triggered for plaque disruption. Fluorodeoxyglucose positron emission tomography, RAM 11 macrophage staining, and serum inflammatory markers detected arterial inflammation. Serum and aortic wall cholesterol levels were measured, and thrombus area was planimetered. Cholesterol crystal density on aortic surface was scored (0 to +3) by scanning electron microscopy. Serum and aortic wall cholesterol, plaque area, and thrombosis area were significantly lower in Group II versus Group I (83.4±106.4 versus 608±386 mg/dL, P=0.002; 3.12±1.40 versus 9.39±5.60 mg/g, P=0.003; 10.84±1.6 versus 17.48±1.8 mm(2), P<0.001; and 0.05±0.15 versus 0.72±0.58 mm(2), P=0.01, respectively). There were significant correlations between crystal density and plaque area (r=0.75, P<0.003) and between crystal density and RAM 11 (r=0.82, P<0.001). Scanning electron microscopy demonstrated that there were fewer crystals in Group II versus Group I (+1.2±0.61 versus +2.4±0.63, P<0.001) and less inflammation detected by fluorodeoxyglucose positron emission tomography and RAM 11 (P<0.004 and P<0.04, respectively). CONCLUSIONS: Lowering cholesterol levels with ezetimibe reduced plaque burden, crystallization, and inflammation, preventing plaque disruption and thrombosis.

Effect of statins on cholesterol crystallization and atherosclerotic plaque stabilization.

Pleiotropic effects of statins have not been fully elucidated. Recently we demonstrated that cholesterol expands when crystallizing and may trigger plaque rupture. The present study evaluated the potential direct effects of statins in altering cholesterol crystallization as a possible mechanism for plaque stabilization independent of cholesterol lowering. Cholesterol powder was dissolved in oil with and without pravastatin, simvastatin, or atorvastatin (10 to 90 mg) and then allowed to crystallize to measure peak volume expansion (ΔVE) in graduated cylinders. Effect of ΔVE on fibrous membrane damage was also evaluated. Human coronary, carotid, and peripheral arterial plaques (65 plaques from 55 patients) were incubated with statin or saline solution using matched plaque segments to evaluate direct effects of statins on preformed crystals. Also, the effect of in vivo use of oral statins on crystal structure was examined by scanning electron microscopy and crystal content in plaques scored from 0 to +3. For all statins, ΔVE decreased significantly in a dose-dependent fashion (0.76 ± 0.1 vs 0 ml at 60 mg, p <0.001). By scanning electron microscopy crystal structure with statins had loss of pointed tip geometries, averting fibrous membrane damage. Cholesterol crystal density was markedly decreased and appeared dissolved in human plaques incubated with statins (+2.1 ± 1.1 vs +1.3 ± 1.0, p = 0.0001). Also, plaques from patients taking oral statins compared to controls had significantly more dissolving crystals (p = 0.03). In conclusion, statins decreased ΔVE by altering cholesterol crystallization and blunting sharp-tipped crystal structure and dissolving cholesterol crystals in human arteries in vivo and in vitro, providing plaque stabilization.

Successful staged neonatal repair of tetralogy of Fallot with long-segment hypoplasia of the aorta.

We describe an extremely rare combination of tetralogy of Fallot (TOF), right-sided cervical aortic arch with long-segment hypoplasia, and other vascular anomalies. A two-stage surgical approach included aortic arch reconstruction followed by right ventricular muscle bundle division and ventricular septal defect closure a few weeks later. The initial clinical presentation, perioperative course, and imaging studies are presented along with a review of the relevant literature. This is the first report of successful neonatal repair of TOF with long-segment hypoplasia of the aorta.

Hypercholesterolemia and myocardial function evaluated via tissue doppler imaging.

OBJECTIVE: To establish a link between hypercholesterolemia and myocardial dysfunction. BACKGROUND: Heart failure is a complex disease involving changes in systolic and diastolic function. Newer echocardiographic imaging modalities may be able to detect discreet changes in myocardial function associated with hypercholesterolemia. Therefore we sought to establish a link between hypercholesterolemia and myocardial dysfunction with tissue Doppler imaging (TDI). METHODS: Twenty-seven rabbits were studied: 7 were fed normal chow (group 1) and 20 a high cholesterol diet (10 with ezetimibe, 1 mg/kg/day; group 2 and 10 without, group 3). Echocardiographic images were obtained under general anesthesia. Serum cholesterol levels were obtained at baseline, 3 and 6 months and myocardial cholesterol levels measured following euthanasia. RESULTS: Doppler measurements, including E/A, E'/A' and S' were significantly lower in group 3 compared to both groups 1 and 2 but no significant differences were noted in chamber sizes or ejection fraction among the groups. Average serum cholesterol was higher in group 3 compared to groups 1 and 2 respectively (495 +/- 305 mg/dl vs. 114 +/- 95 mg/dl and 87 +/- 37 mg/dl; p < 0.01). Myocardial cholesterol content was also higher in group 3 compared to group 2 (0.10 +/- 0.04 vs. 0.06 mg/dl +/- 0.02; p = 0.05). There was significant correlation between S', E'/A', E/E' and serum cholesterol (r2 = 0.17 p = 0.04, r2 = 0.37 p = 0.001 and r2 = 0.24 p = 0.01). CONCLUSION: Cholesterol load in the serum and myocardium was significantly associated with decreased systolic and diastolic function by TDI. Moreover, lipid lowering was protective.

Impact of prior statin therapy on arrhythmic events in patients with acute coronary syndromes (from the Global Registry of Acute Coronary Events [GRACE]).

Animal models of myocardial ischemia have demonstrated reduction in arrhythmias using statins. It was hypothesized that previous statin therapy before hospitalization might be associated with reductions of in-hospital arrhythmic events in patients with acute coronary syndromes. In this multinational, prospective, observational study (the Global Registry of Acute Coronary Events [GRACE]), data from 64,679 patients hospitalized for suspected acute coronary syndromes (from 1999 to 2007) were analyzed. The primary outcome of interest was in-hospital arrhythmic events in previous statin users compared with nonusers. The 2 primary end points were atrial fibrillation and the composite end point of ventricular tachycardia, ventricular fibrillation, and/or cardiac arrest. In-hospital death was also examined. Of the 64,679 patients, 17,636 (27%) had received previous statin therapy. Those taking statins had higher crude rates of histories of angina (69% vs 46%), diabetes (34% vs 22%), heart failure (15% vs 8.4%), hypertension (74% vs 58%), atrial fibrillation (9.3% vs 7.0%), and dyslipidemia (85% vs 35%). Patients previously taking statins were less likely to have in-hospital arrhythmias. In propensity-adjusted multivariable models, previous statin use was associated with a lower risk for ventricular tachycardia, ventricular fibrillation, or cardiac arrest (odds ratio 0.81, 95% confidence interval 0.72 to 0.96, p = 0.002); atrial fibrillation (odds ratio 0.81, 95% confidence interval 0.73 to 0.89, p <0.0001); and death (odds ratio 0.82, 95% confidence interval 0.70 to 0.95, p = 0.010). In conclusion, patients previously taking statins had a lower incidence of in-hospital arrhythmic events after acute coronary syndrome than those not previously taking statins. Our study suggests another possible benefit from appropriate primary and secondary prevention therapy with statins.

Prophylaxis to prevent infective endocarditis: to use or not to use?

The American Heart Association (AHA) published their revised guidelines in 2007 in which they markedly limited the recommendations for the use of antimicrobial prophylaxis for the prevention of infective endocarditis (IE), except for patients who are at highest risk of adverse outcomes. A recent focused update on valvular heart diseases changed the recommendation for antibiotic use for patients with many underlying heart conditions including mitral valve prolapse (MVP) which were considered as "low risk" heart defects. In this article, we argue that antibiotic prophylaxis should be considered until concrete clinical evidence is provided to dispute against the use of this strategy, especially for patients with MVP. This approach is cost efficient, and provides a chance to prevent a dreadful disease. We have also enlisted 2 clinical cases to support our argument. These are not uncommon clinical scenarios, and emphasize that IE can be fatal in spite of optimum treatment. Patients have the right to make the final decision, and they should be allowed to participate in choosing for or against this approach until adequate clinical evidence is available.

Effect of cholesterol crystals on plaques and intima in arteries of patients with acute coronary and cerebrovascular syndromes.

Plaque disruption (PD) causes most acute cardiovascular events. Although cholesterol crystals (CCs) have been observed in plaques, their role in PD was unknown. However, cholesterol expands with crystallization tearing and perforating fibrous tissues. This study tested the hypothesis that CCs can damage plaques and intima, triggering PD, as observed in tissues prepared without ethanol solvents that dissolve CCs. Coronary arteries of patients who died of acute coronary syndrome (n = 19) and non-acute coronary syndrome causes (n = 12) and carotid plaques from patients with (n = 51) and without (n = 19) neurologic symptoms were studied. Samples were examined for CCs perforating the intima using light and scanning electron microscopy (SEM) with ethanol or vacuum dehydration. In addition, fresh unfixed carotid plaques were examined at 37 degrees C using confocal microscopy. Crystal content using SEM was scored from 0 to +3. SEM using vacuum dehydration had significantly higher crystal content compared with SEM using ethanol dehydration (+2.5 +/- 0.53 vs +0.25 +/- 0.46; p <0.0003), with enhanced detection of CC perforations. The presence of CCs using SEM and confocal microscopy was similar, suggesting that CC perforation can occur in vivo at 37 degrees C. All patients with acute coronary syndrome had perforating CCs, but none was present in patients without acute coronary syndrome (p = 0.0001). For all plaques, there were strong associations of CCs with PD, thrombus, symptoms (p <0.0001), and plaque size (p <0.02). Crystal content was an independent predictor of thrombus and symptoms. In conclusion, by avoiding ethanol in tissue preparation, CCs perforating the intima were shown to be associated with PD. Crystal content was significantly associated with clinical events, suggesting that cholesterol crystallization may have a role in PD.

Physical factors that trigger cholesterol crystallization leading to plaque rupture.

BACKGROUND: Triggers of plaque rupture have been elusive. Recently it was demonstrated that cholesterol expands when transforming from a liquid to a crystal state, disrupting overlying plaque. This study examined the effect of physical conditions including saturation, temperature, hydration, pH on cholesterol crystallization. METHODS: Graduated cylinders were filled with varying amount of cholesterol powder (1, 2 and 3g) and dissolved in corn oil at 37 degrees C. Change in volume expansion (DeltaVE) and time to crystallization were measured for each saturation. The same was repeated while varying temperature (22-44 degrees C); hydration (1-3ml H(2)O); pH (5-8.4) and combination of saturation and temperature. Scanning electron microscopy was performed to evaluate crystal morphology and X-ray diffractometry to assess molecular structure of cholesterol. RESULTS: Increasing saturation raised both DeltaVE (3g: 0.53+/-0.1ml vs. 1g: 0.14+/-0.02ml and 2g: 0.3+/-0.1ml; p<0.0001; p<0.01) and rate of change over 3min (3g: 60% vs. 1g: 14%). Crystal morphology was the same seen with crystals perforating human plaques. Temperature drop increased DeltaVE (44 degrees C: 0.05+/-0.01ml vs. 22 degrees C: 0.5+/-0.07ml; p<0.0001) and initiated earlier crystallization. Hydration resulted in greater DeltaVE (3ml: 0.7+/-0.07 vs. 0ml: 0.1+/-0.05; p<0.001) with corresponding changes in cholesterol molecular structure. Rising pH was associated with increased DeltaVE (1.3+/-0.03ml vs. 0.1+/-0.02ml; p<0.001). Combined increase in saturation and temperature had greater DeltaVE than expected from the sum of each alone. CONCLUSIONS: Physical factors influenced both volume and rate of cholesterol crystallization. This suggests that local factors may play an important role in triggering plaque rupture. Combination of several factors may even be a more powerful trigger for acute cardiovascular events.

Dual antiplatelet agent failure: a new syndrome or clinical nonentity?

BACKGROUND: Aspirin resistance is a well-documented laboratory finding, but the effects of clinical aspirin (ASA) failure on patients with acute coronary syndrome (ACS) have been debated. Likewise, there is recognition of clopidogrel resistance, but the clinical effects of clopidogrel failure are not well understood. We sought to determine the 6-month outcomes of patients who developed an ACS while on ASA or dual antiplatelet agents. METHODS: Of all patients admitted to the University of Michigan, Ann Arbor, between 1999 and 2005 with a diagnosis of ACS, 6-month follow-up data were available for 3126. The cohort was divided into 3 groups based on medication history: no prior antiplatelet agent, ASA only, and ASA with clopidogrel (or ticlopidine). Primary end point was the rate of death, myocardial infarction, and stroke, or composite major adverse cardiac events (MACEs) at 6 months. RESULTS: Aside from a lower rate of myocardial infarction in patients without any prior antiplatelet agent use, there were no significant differences in 6-month stroke, death, or MACE between the 3 medication cohorts. In the propensity-adjusted model, whereas dual antiplatelet status was not an independent predictor of 6-month mortality or MACE, there was a trend toward lower 6-month death rates for patients with prior ASA use (odds ratio 0.72, 95% CI 0.51-1.04, P = .08). CONCLUSIONS: Patients who "fail" antiplatelet therapy do not have overall worse prognosis. Our data do not support ASA or dual antiplatelet agent failure as a distinct clinical entity.