A Social Media Blueprint - Understanding What Makes the Optimal Social Media Account for Paediatric Surgical Families

BACKGROUND

Social media is one of the most common sources of information for parents seeking information on their child's health. The purpose of this study was to better understand the social media habits of parents of paediatric surgery patients through surveys and focus groups.

METHODS

An online survey was distributed to parents visiting paediatric surgery clinics at a tertiary care hospital. Surveys were distributed via QR code and social media. Two virtual focus groups were conducted with parents of paediatric patients. Descriptive statistics were used for survey analysis and focus group transcripts were thematically analyzed.

RESULTS

A total of 107 respondents completed the online survey. Median age of respondents was 36 (interquartile range: 32-41). 81.3% of the respondents were female. Facebook was the preferred social media platform (47.2%), followed by Instagram (41.5%) then other platforms (4.7%). Respondents indicated that their preferred length of video was 30 s (41.2%). When asked which type of video content they prefer, participants indicated animated video as most popular (66.0%) followed by a physician speaking (60.0%), and slides with voiceover (45.0%). The focus groups revealed themes of: (1) functionality and content; (2) branding, aesthetic and legitimacy; (3) unmasking of physicians; (4) peer and community support.

CONCLUSION

Creating a successful social media account for parents must take into consideration their social media habits. A Facebook account that features brief videos may be most likely to engage parents. Additionally, physicians need to establish credibility and legitimacy of their content to attract their target audience.

LEVEL OF EVIDENCE

III.

The Intersection of Family Planning and Perception of Career Advancement in General Surgery

INTRODUCTION

Women in surgery face unique challenges, particularly as it relates to family planning, parental leave, infant feeding, and career advancement. This study highlights disparities in present day general surgery training to tackle longstanding gender inequities.

METHODS

An open, anonymous online survey was distributed to Canadian residents, fellows, and practicing general surgeons through the Canadian Association of General Surgeons e-mail list from November 2021-March 2022. Data were analyzed descriptively and chi-square tests were performed to examine categorical outcomes across gender.

RESULTS

A total of 89 general surgery respondents (13.8% response rate) completed the survey (22 cisgender men; 65 cisgender women). Twenty six percent of participants had accessed fertility services or used assistive reproductive technologies. Of the participants with children, 36.4% of men and 100.0% of women took at least one parental leave during residency or clinical practice. A greater proportion of women compared to men agreed that their training/practice influenced their decision to have children (P = 0.002) and when to have children (P < 0.001). Similarly, a greater proportion of women indicated they had concerns about future family planning (P = 0.008), future fertility (P = 0.002), and future parental leave (P = 0.026). Fifty nine percent of women and zero men agreed that taking parental leave impacted their career advancement (P = 0.04).

CONCLUSIONS

Women surgeons and surgical trainees continue to face challenges with respect to family planning, parental leave, infant feeding, and career advancement. Further research is needed to explore the experiences of women surgeons. By providing surgeons with the support required to achieve their family planning goals, surgeons can accomplish their family and career goals with less conflict.

Parental perceptions and experiences of care in the surgical neonatal intensive care unit

BACKGROUND

Parents endure significant stress when their newborns require surgery while in the neonatal intensive care unit (NICU). Our study aims to explore the surgical NICU experience from the parents' perspective and identify areas that may improve this experience. A secondary objective was to integrate their feedback to refine the implementation strategy of the neonatal enhanced recovery after surgery (ERAS®) guideline.

METHODS

In December 2019, five surgical NICU parents participated in a focus group. Conversation surrounded parents' perspectives and experiences of the surgical NICU. Inductive analysis was performed to identify data, themes, and concepts that emerged from the discussion.

RESULTS

Participants identified four major interrelated themes that impacted the surgical parents' NICU experience. These themes include (1) parental state, both physical and emotional, (2) the altered parental caregiver role which necessitates identifying alternative meaningful parental experiences, (3) the care team dynamic, incorporating consistency and effective communication, and (4) the discharge process which may be significantly eased through graduated, hands-on training.

CONCLUSION

Key elements of the neonatal ERAS® guideline address major themes and stressors identified by parents. The parental perspective may help clinicians appreciate the parent surgical NICU experience and assist in improving family-centered care to surgical infants and their families.

Impact of implementing a fast-track protocol and standardized guideline for the management of pediatric appendicitis

Background:

In 2017, a provincial guideline was created to fast track and standardize care for pediatric appendicitis in Alberta. We conducted a study to determine the impact of implementation of the guideline at our institution on length of stay (LOS), antibiotic stewardship efforts and costs.

Methods:

We performed a retrospective review of the charts of all patients younger than 18 years of age who underwent appendectomy at our institution in 2 periods: before guideline implementation (Dec. 1, 2016, to May 31, 2017) and after implementation (Dec. 1, 2017, to May 31, 2018). We compared LOS, duration of antibiotic therapy, 30-day postdischarge complication rates and variable cost between the 2 cohorts.

Results:

Of the 276 total appendectomy procedures performed, 185 were for simple appendicitis (81 before guideline implementation and 104 after implementation), and 91 were for complicated appendicitis (44 and 47, respectively). The median LOS was shorter in the postimplementation cohort for both simple and complicated appendicitis (15.5 h [interquartile range (IQR) 12–19 h] v. 17.0 h [IQR 13–22 h], p = 0.03; and 3.0 d [IQR 2–4 d] v. 3.0 d [IQR 3–5 d], p = 0.05, respectively). Patients with complicated appendicitis had fewer antibiotic days after guideline implementation; the difference was statistically significant for patients without diffuse peritoneal contamination or abscess formation (p = 0.02). There were no differences between the cohorts with respect to 30-day rates of complications, including emergency department visits, readmission and surgical site infections. After guideline implementation, the average variable cost per patient was reduced by $230, equating to a total average annual cost savings of $75 842 for our institution.

Conclusion:

The implementation of a provincial guideline aimed at standardizing care in pediatric appendicitis at our institution was associated with shortened LOS, improved antibiotic stewardship efforts and reduced cost of care. Other institutions may replicate our model of a standardized pathway in the management of pediatric appendicitis in an effort to improve the quality of patient care and reduce health care costs.

Developing implementation strategies to adopt Enhanced Recovery After Surgery (ERAS®) guidelines

BACKGROUND

Strong implementation strategies are critical to the success of Enhanced Recovery after Surgery (ERAS®) guidelines, though little documentation exists on effective strategies, especially in complex clinical situations and unfamiliar contexts. This study outlines the process taken to adopt a novel neonatal ERAS® guideline.

METHODS

The implementation strategy was approached in a multi-pronged, concurrent but asynchronous fashion. Between September 2019 and January 2020, healthcare providers from various disciplines and different specialties as well as parents participated in the strategy. Multidisciplinary teams were created to consider existing literature and local contexts including potential facilitators and/or barriers. Task forces worked collaboratively to develop new care pathways. An audit system was developed to record outcomes and elicit feedback for revision.

RESULTS

32 healthcare providers representing 9 disciplines and 5 specialties as well as 8 parents participated. Care pathways and resources were created. Elements recommended for a successful implementation strategy included identification of champions, multidisciplinary stakeholder involvement, consideration of local contexts and insights, patient/family engagement, education, and creation of an audit system.

CONCLUSION

A multidisciplinary and structured process following principles of implementation science was used to develop an effective implementation strategy for initiating ERAS® guidelines.

Unusual case of coronal complete bladder duplication associated with rectoprostatic fistula to duplicated prostatic urethra

Anorectal malformations are a common congenital anomaly, while bladder duplication is rare. Bladder duplications are classified as complete or incomplete and sagittal or coronal. We present a rare case of coronal complete bladder duplication with rectoprostatic fistula to the blind ending prostatic urethra of the duplicated bladder.

Patients' blood pressure knowledge, perceptions and monitoring practices in community pharmacies

Hypertension is a modifiable risk factor for cardiovascular disease. Despite this, patients often cannot or inaccurately estimate their risk factors.

Objectives:

In order to improve pharmacist interventions, we sought to: 1) find out patients’ knowledge about blood pressure (BP) and their self-monitoring behaviors and 2) identify the relationships between these two elements. Specifically, if evaluation of BP control were related to knowledge of one’s BP level and self-monitoring habits, and if knowledge of one’s target and BP level varied with monitoring habits.

Methods:

Final year pharmacy students were trained and interviewed patients in community pharmacies as a required exercise in their pharmacy clerkship. Each student recruited a convenience sample of 5-10 patients who were on hypertension medication, and surveyed them regarding their BP targets, recent BP levels as well as monthly and home BP monitoring practices.

Results:

One third of the 449 patients interviewed were able to report a blood pressure target with 26% reporting a JNC 7 recognized target. Three quarters of patients who reported a blood pressure target were able to report a blood pressure level, with 12% being at their self-reported target. Roughly two thirds of patients perceived their BP to be “about right”, and slightly less than a third thought it to be “high”. Sixty percent of patients monitor their BP monthly, but less than 50% of patients practice home BP monitoring.

Conclusions:

This study along with others before it point to the knowledge and self-management gaps in patients with chronic conditions. Furthermore, pharmacy students were able to use a brief intervention to screen patients during routine care. Pharmacists can help improve patient understanding and promote increased self-management through regular BP monitoring.

Five-color-based high-information-content fingerprinting of bacterial artificial chromosome clones using type IIS restriction endonucleases

We have developed a high-information-content fingerprinting (HICF) system for bacterial artificial chromosome (BAC) clones using a Type IIS restriction endonuclease, HgaI, paired with a Type II restriction endonuclease, RsaI. In the method described, unknown five-base overhangs generated with HgaI are partially or fully sequenced by modified fluorescent dideoxy terminators. Using an in-lane size standard labeled with a fifth dye, fragments are characterized by both the size and the sequence of its terminal one to five bases. The enhanced information content associated with this approach significantly increases the accuracy and efficiency of detecting shared fragments among BAC clones. We have compared data obtained from this method to predicted HICF patterns of 10 fully sequenced BACs. We have further applied HICF to 555 BAC clones to assemble contigs spanning 16p11.2 to 16p13.1 of human chromosome 16.

Acute and delayed antithrombotic effects of alcohol in humans

Alcohol intake, especially in the form of red wine, has been shown to inhibit platelet function. However, whether alcohol in spirits may inhibit platelet-dependent thrombosis in humans up to 6 hours after ingestion is unknown and was assessed in this study. Platelet thrombus that is formed on exposure of an aortic media (simulating deep arterial injury or plaque rupture) to flowing blood was assessed in an ex vivo Badimon's superfusion chamber at shear rates of 754 or 2,546 seconds(-1) (simulating flow in normal or stenosed arteries). Twelve healthy subjects were studied before and at 20 minutes and 6 hours after consumption of 2 ounces of 40% alcohol. Blood alcohol level was 1.1+/-0. 1, 8.2+/-0.7, and 1.3+/-0.2 mmol/L at baseline, 20 minutes and 6 hours, respectively, after alcohol consumption (analysis of variance [ANOVA] p = 0.0001). Compared with baseline, platelet thrombus formation at the low shear rate flow was significantly decreased by 57% and 61% at 20 minutes and 6 hours, respectively, after alcohol intake (ANOVA p = 0.0001). Platelet thrombus deposition at the high shear rate was similarly inhibited to 68% and 64% of baseline values at 20 minutes and 6 hours, respectively (ANOVA p = 0.003). Men and women showed equal benefit. Thus, moderate alcohol intake in humans significantly inhibited platelet thrombus deposition under low and high shear rates of arterial flow conditions. This antithrombotic effect of a single alcohol drink, persisting for 6 hours and even after blood alcohol level has returned to baseline, may be clinically relevant to the cardioprotective effects of alcohol in men and women.

Nitroglycerin rebound associated with vascular, rather than platelet, hypersensitivity

OBJECTIVES

The purpose of this study was to determine whether acute withdrawal of nitroglycerin (NTG) during hemodynamic tolerance is associated with platelet hypersensitivity.

BACKGROUND

Nitroglycerin is an effective antianginal medication but its use is limited by the development of tolerance and rebound. We have previously demonstrated a sustained inhibition of platelet function during continued use of NTG, but whether cessation of NTG is associated with an increase in platelet function that may contribute to rebound is unknown.

METHODS

Normal porcine aortic media were exposed to flowing arterial blood from pigs (n = 8) treated continuously with NTG patches (Nitrodur 0.8 mg/h) for 48 h. Platelet function, blood pressure and the responses to angiotensin II infusion were evaluated before, during and after NTG treatment.

RESULTS

Mean arterial pressure fell by 15% after 3 h of treatment compared with control, returned to baseline by 48 h and increased significantly 2 h after drug removal. Autologous 51Cr-labelled platelet deposition on the aortic media was reduced by 30% after 48 h of continuous NTG administration compared with baseline (p = 0.02) and remained decreased 2 h after cessation of NTG therapy. Platelet aggregation to thrombin decreased in parallel to the decrease in platelet deposition. Blood pressure increase after intravenous injection of 10 microg of angiotensin II was blunted during treatment with NTG but increased significantly 2 h after cessation of nitrate therapy when compared with baseline.

CONCLUSIONS

Supersensitivity of the vessel wall to vasoconstrictors such as angiotensin 11, but not platelet hyperactivity, may contribute to the rebound phenomenon after acute nitrate withdrawal.

2-Carboxymethylendothal analogues as affinity probes for stabilized protein phosphatase 2A

Endothal (1diacid) and [3H]cantharidic acid ([3H]CA) bind with high affinity to the catalytic subunit of protein phosphatase 2A (PP2A). PP2A in liver cytosol was greatly stabilized with 30% glycerol as a preliminary step in the potential use of endothal-type derivatives for affinity chromatography. We report here the first introduction of a functionalizable group into endothal which allows retention of binding site affinity (assayed as [3H]CA binding in mouse liver cytosol). 2-Carboxymethylendothal anhydride (7) was prepared in two steps and 97% overall yield from cis-aconitic anhydride and furan. The potency of 7 was retained on conversion to two 2-carboxymethyl esters but not to two 2-(n-alkylcarboxamidomethyl) analogues.

Persistent inhibition of platelets during continuous nitroglycerin therapy despite hemodynamic tolerance

BACKGROUND

Nitroglycerin has been shown to possess antiplatelet properties in both animals and humans. Tolerance to the hemodynamic effects of nitroglycerin develops with continuous therapy, but it is unclear whether there is tolerance to its antiplatelet effect.

METHODS AND RESULTS

Tolerance to nitroglycerin was studied by exposing porcine aortic media to flowing arterial blood from control pigs (n = 9) or pigs treated with continuous nitroglycerin patches (Nitro-dur, 0.8 mg/h; n = 11) at a shear rate of 3397 s-1 for 3 minutes. Relative to baseline, mean arterial pressure fell by approximately 10% at 3 and 24 hours (P < .05) but returned to baseline at 48 hours of continuous nitroglycerin treatment, whereas no significant changes were observed in control animals. Autologous 51Cr-labeled platelet deposition (x 10(6)/cm2) on the aortic media at baseline and 3, 24, and 48 hours remained stable in control animals, with mean values of 94.8 +/- 5.9, 89.4 +/- 8.3, 89.3 +/- 8.8, and 84.3 +/- 5.7, respectively. However, in pigs treated continuously with nitroglycerin for 48 hours, platelet deposition was reduced significantly at 3 (65.9 +/- 4.8), 24 (63.8 +/- 6.4), and 48 hours (56.5 +/- 7.3) of nitroglycerin treatment compared with baseline (93.1 +/- 3.6). Platelet aggregation induced by thrombin also decreased at 3 (12.4 +/- 1.3), 24 (12.6 +/- 1.7), and 48 hours (10.8 +/- 1.6) of nitroglycerin treatment compared with baseline (16.3 +/- 1.4) but remained unchanged in the control group. Also, nitroglycerin treatment increased intraplatelet cGMP at 3, 24, and 48 hours compared with baseline.

CONCLUSIONS

This study demonstrates the persistent inhibition of platelet function and platelet deposition on an injured arterial wall by continuous nitroglycerin therapy despite hemodynamic tolerance.

Hyperlipidemia and coronary disease. Correction of the increased thrombogenic potential with cholesterol reduction

BACKGROUND

Hypercholesterolemia is a risk factor for coronary disease, and platelet reactivity is increased with hypercholesterolemia, suggesting a prethrombotic risk. The aim of this study was to measure mural platelet thrombus formation on an injured arterial wall in a model simulating vessel stenosis and plaque rupture in hypercholesterolemic coronary disease patients before and after cholesterol reduction.

METHODS AND RESULTS

Thirty-two patients with stable coronary disease were studied. Platelet thrombus formation and serum lipids were measured in 16 hypercholesterolemic patients (cholesterol > 5.2 mmol/L) before and after a mean of 2.5 months of pravastatin therapy (40 mg/d) and in 16 normocholesterolemic control patients. Thrombus formation was assessed by exposing porcine aortic media to the patient's flowing venous blood for 3 minutes at a shear rate of 754 or 2546 s-1 at 37 degrees C in an ex vivo superfusion chamber. Quantitative morphometric platelet thrombus formation at baseline was higher in the hypercholesterolemic patients at both the high and low shear rates: 4.8 +/- 1.0 and 3.3 +/- 0.7 micron 2/mm, respectively, compared with normocholesterolemic patients: 2.1 +/- 0.5 and 1.6 +/- 0.4 micron 2/mm (both P < .05). In the hypercholesterolemic patients, pravastatin decreased total cholesterol from 6.5 +/- 0.2 to 4.5 +/- 0.2 mmol/L and LDL cholesterol from 4.5 +/- 0.2 to 2.8 +/- 0.1 mmol/L (both P < .05). Platelet thrombus formation at high and low shear rates decreased to 2.0 +/- 0.3 and 1.3 +/- 0.3 micron 2/mm, respectively (both P < .05).

CONCLUSIONS

Thus, hypercholesterolemia is associated with an enhanced platelet thrombus formation on an injured artery, increasing the propensity for acute thrombosis. Platelet thrombus formation at both high and low shear rates decreased as total and LDL cholesterol levels were reduced with pravastatin. Cholesterol lowering may therefore reduce the risk of acute coronary events in part by reducing the thrombogenic risk.

Cigarette smoking acutely increases platelet thrombus formation in patients with coronary artery disease taking aspirin

BACKGROUND

Smoking is associated with an increased risk of myocardial infarction and sudden death. Platelet activation and thrombosis at sites of vessel stenosis and injury or plaque disruption play a crucial role in these acute coronary events. Thus, the aim of this study was to determine whether cigarette smoking acutely increases platelet thrombus formation on an injured arterial surface at local shear rates typical of a stenotic artery.

METHODS AND RESULTS

Twelve habitual smokers with stable coronary disease, on aspirin 325 mg/d, were studied immediately before and 5 minutes after smoking two cigarettes each. Ex vivo platelet thrombus formation on porcine arterial media (simulating deep arterial injury) was measured after exposure to the patient's circulating venous blood for 3 minutes in cylindrical flow chambers at 37 degrees C. The flow chambers were designed to produce shear rates of 754 or 2546 s-1, the latter being typical of the high shear rates produced by vessel stenosis. Plasma catecholamine, thromboxane B2, and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) levels and whole blood platelet aggregation responses to thrombin were also measured before and after smoking. Compared with before smoking, morphometrically measured platelet thrombus formation on arterial media at shear rates of 754 and 2546 s-1 increased by an average of 48% (P = .19) and 64% (P = .014), respectively, after smoking. Plasma epinephrine increased by more than twofold after smoking (P = .026). Plasma thromboxane B2 and 6-keto-PGF1 alpha levels did not change. Smoking also increased whole blood platelet aggregation to thrombin (P < or = .05).

CONCLUSIONS

These results suggest that smoking-enhanced platelet thrombosis may be an important contributory mechanism for acute coronary events in smokers that is not prevented by aspirin treatment. Catecholamine release and heightened platelet aggregation response to in vivo agonists may contribute to the prothrombotic effects of smoking.

Intramural delivery of agent via a novel drug-delivery sleeve. Histological and functional evaluation

BACKGROUND

The infusion sleeve is a novel drug-delivery catheter system designed to deliver an agent under controlled conditions into the arterial wall at the site of angioplasty. The purpose of the present study was to characterize the delivery agent via the infusion sleeve in ex vivo and in vivo models.

METHODS AND RESULTS

The delivery of horseradish peroxidase via the infusion sleeve was studied in a porcine explanted heart model. Under physiological conditions, arteries underwent balloon injury (approximately 10% overstretch), after which horseradish peroxidase (2.5 mL) was delivered at specific pressures. Cross-sectional analysis demonstrated greater staining when the agent was delivered at increasing pressures. The infusion sleeve was evaluated in an in vivo canine coronary model. With an infusion sleeve loaded over a standard dilatation catheter through a 9F guide, overstretch balloon injury was performed, after which fluoresceinated heparin was delivered. Animals were killed 2 hours after delivery. Fluoresceinated heparin-treated segments demonstrated high fluorescence signals, localizing with smooth muscle cell nuclei with less activity in the interstitium. The functional significance of intramural heparin delivery was studied in a porcine carotid model. In the presence of 111In-labeled platelets, arteries underwent overstretch injury followed by delivery of heparin (50 or 100 units/kg) or vehicle. Platelet deposition was reduced at 30 minutes (57%, P < .01) and 12 hours (39%, P = .06) compared with saline controls.

CONCLUSIONS

Agent delivery via the infusion sleeve is pressure dependent; transmural delivery is possible with minimal disruption of arterial wall architecture; the infusion sleeve is compatible with standard angioplasty equipment; and heparin delivery at the site of balloon injury significantly reduces platelet deposition in a porcine model for a minimum of 12 hours.

Increase of neutrophil adhesion and vasoconstriction with platelet deposition after deep arterial injury by angioplasty

Physiopathologic events after arterial injury are largely influenced by blood element reactions with the injured surface. To determine acute arterial reactivity to injury, simultaneous chromium 51-labeled platelet deposition and indium 111-labeled neutrophil adhesion were quantified at the site of different degrees of carotid arterial injury by balloon dilatation in 21 normal pigs. The degree of vasoconstriction distally to the dilated areas was also quantified angiographically. Arteries were classified histologically as (1) uninjured with intact endothelium; (2) mildly injured with endothelial desquamation; or (3) deeply injured with lesions extending beyond internal elastic lamina, exposing the media. We found that, compared to mild injury, deep injury was associated with greater platelet deposition (38.2 +/- 5.7 x 10(6)/cm2 vs 7.8 +/- 0.9 x 10(6)/cm2; p < 0.05), neutrophil adhesion (30.6 +/- 4.1 x 10(4)/cm2 vs 10.2 +/- 2.9 x 10(4)/cm2; p < 0.05), and vasoconstrictive response (45.5% +/- 3.2% vs 26.7% +/- 2.8%; p < 0.05). Although distally to both types of injuries, noninjured arterial segments with intact endothelium were thromboresistant to platelet deposition, neutrophil adhesion to intact endothelium was much higher after deep injury (2.2 +/- 0.4 x 10(4)/cm2) compared to mild injury (0.36 +/- 0.1 x 10(4)/cm2; p < 0.05). Like platelet deposition, neutrophil adhesion is influenced by the severity of arterial injury; both may therefore be implicated in thrombogenesis and vascular responsiveness after arterial injury in vivo.

Neutrophil implications in platelet deposition and vasoconstriction after deep arterial injury by angioplasty in pigs

BACKGROUND

Experimental studies in vitro suggest that neutrophils can modulate platelet function and vasomotor responses. In the present study, the interactions among neutrophils, platelets, and arterial responses to injury in vivo were assessed.

METHODS AND RESULTS

The acute thrombotic and vasomotor responses of porcine carotid arteries to balloon injury in vivo were evaluated in three groups of animals: neutropenic pigs treated (n = 11) or not treated (n = 12) with aspirin and healthy untreated control pigs (n = 15). Neutropenia was achieved by treatment with cyclophosphamide (50 mg/kg, 4 days before the experiment), which decreased circulating leukocyte count by 92% and almost abolished neutrophil aggregation to N-formyl-methionyl-leucyl-phenylalanine without affecting blood platelet count, hematocrit, hemoglobin concentration, or whole blood platelet aggregation to ADP. 51Cr platelet deposition on deeply injured and uninjured arterial segments was not statistically influenced by neutrophil depletion, whereas the angiographic vasoconstrictive response at the site of endothelial injury distally was significantly reduced by 41% from 46.3 +/- 2.9% in the control group to 27.2 +/- 4.1% in the neutropenic group (P < .05). Aspirin treatment in combination with neutropenia produced a 50% reduction in whole blood platelet aggregation, resulted in a significant inhibition of platelet deposition to deeply injured arteries, and decreased vasoconstriction by 66% to 15.6 +/- 3.0% (P < .05 versus control and neutropenic).

CONCLUSIONS

Neutrophils can influence the vasoconstrictive response at the site of endothelial injury in vivo. In addition to platelets, neutrophil interaction with the injured vessel wall may be implicated in the pathophysiological response to arterial injury in vivo.

Antithrombotic properties of transdermal nitroglycerin in stable angina pectoris

Nitroglycerin provides an external source of nitric oxide which stimulates guanylate cyclase and produces vasodilatation and inhibition of platelet function. The antithrombotic effects of intravenous nitroglycerin were recently documented in various experimental models and in patients with unstable angina. This protocol was designed to evaluate whether these effects could also be detected with transdermal nitroglycerin in patients with stable angina. In a randomized, double-blind, controlled parallel trial, 22 patients received transdermal nitroglycerin, 0.6 mg/hour (11 patients), or placebo (11 patients). Platelet aggregation to adenosine diphosphate (ADP) and to thrombin was measured in whole blood. Thrombus formation was assessed on porcine aortic media exposed to the patient's venous blood for 3 minutes at shear rates of 2,546 and 754 s-1. Platelet aggregation to ADP decreased from 7.7 +/- 0.8 to 5.3 +/- 0.8 ohms (p < 0.05) with nitroglycerin, and to thrombin from 15.6 +/- 1.2 to 12 +/- 1.2 ohms (p < 0.05). Thrombus size at the high-shear rate decreased from 2.8 +/- 0.7 to 1.0 +/- 0.3 microns 2 (p < 0.05), and at the low-shear rate from 2.5 +/- 0.5 to 1.0 +/- 0.2 microns 2 (p < 0.05). Placebo had no significant effect on platelet aggregation and platelet thrombus deposition. These parameters were all reduced by > or = 20% in 8 patients taking nitroglycerin but only in 3 patients taking placebo (p < 0.05). Transdermal nitroglycerin significantly inhibits platelet aggregation and mural thrombus formation in patients with angina pectoris.

Endothelium-derived nitric oxide attenuates neutrophil adhesion to endothelium under arterial flow conditions

Nitric oxide (NO) synthesized from cultured endothelial cells inhibits platelet aggregation and adhesion to subendothelial extracellular matrix and may contribute to the thromboresistance of the endothelium. NO has also been shown to inhibit neutrophil aggregation and adherence to postcapillary venules. Whether NO derived from the intact endothelium of an arterial wall can influence platelet and neutrophil adhesion under whole-blood arterial flow conditions was evaluated in this study. Porcine aortic segments with intact endothelium were exposed to flowing porcine arterial blood for 5 minutes at a shear rate of 424 sec-1. Pretreatment of the endothelium with the physiological precursor of NO, L-arginine (2 mmol/L), reduced 111In-labeled neutrophil adhesion by 32% from 10.2 +/- 1.6 to 6.9 +/- 1.3 x 10(3)/cm2 (P < .05), relative to control. This effect was reversed by the inhibitor of NO synthesis, N omega-nitro-L-arginine methyl ester (L-NAME, 5 mmol/L) (8.2 +/- 3.0 versus 8.6 +/- 3.2 x 10(3)/cm2 for control; P = NS). Pretreatment of the endothelium with D-arginine (2 mmol/L) did not influence neutrophil adhesion (8.7 +/- 2.0 versus 8.6 +/- 2.0 x 10(3)/cm2 for control; P = NS). The intact endothelium, which is normally thromboresistant, shows a low basal level of 51Cr activity, corresponding to a platelet adhesion less than 0.5 x 10(6)/cm2, and this thromboresistance was not significantly influenced by L-arginine. These results indicate that NO derived from an intact arterial endothelium under whole-blood arterial flow conditions may be an important modulator of neutrophil interaction with the intact endothelium.

Platelet aggregation, coronary artery disease progression and future coronary events

The platelet-aggregatory response, platelet-release factors and markers of thrombin generation in vivo were studied prospectively in 53 patients participating in a randomized clinical trial evaluating the influence of nicardipine on the progression of coronary atherosclerosis. Coronary lesions were measured quantitatively and progression was defined as a decrease in minimum diameter by > or = 0.4 mm. At repeat angiography 24 months after study entry, 20 of the 53 patients had progression of 28 coronary narrowings. Only thrombin-induced enhanced platelet aggregation differentiated patients with from those without coronary disease progression, with an estimated odds ratio of 2.49 (95% confidence interval 1.10 to 5.66). The aggregatory response to adenosine diphosphate, collagen, epinephrine and platelet-activating factor were not different in the 2 groups of patients, nor were measurements of platelet factor 4, beta-thromboglobulin, thromboxane B2, 6-keto-prostaglandin F1 alpha and fibrinopeptide A. During 46.8 months of follow-up after repeat angiography, coronary events occurred in 11 of the 20 with and 6 of the 33 without progression (difference 37%, p = 0.013, confidence interval 11 to 63%). Those with coronary disease progression and an enhanced thrombin-induced platelet aggregation had a worse prognosis than those with no disease progression and a low thrombin-induced platelet aggregation. Thus, patients with coronary disease progression and future coronary events have an enhanced thrombin-induced platelet aggregation. This platelet abnormality may be a marker of increased risk and may play a causative role in the development of coronary events.

Oral verapamil inhibits platelet thrombus formation in humans

BACKGROUND

Calcium antagonists such as verapamil are potent coronary and systemic vasodilators that are used in the treatment of coronary disease. They have also been shown to inhibit platelet aggregation in vitro, but whether they have beneficial antithrombotic effects in humans is unclear, and whether they can potentiate the antithrombotic effects of aspirin is unknown.

METHODS AND RESULTS

Platelet thrombus formation and whole blood platelet aggregation were measured in 18 stable coronary patients on three separate occasions: at baseline when receiving no active medications, after 7 days of receiving oral verapamil SR (240 mg/d), and after 7 days of receiving a combination of oral verapamil SR and aspirin (325 mg/d). Thrombus formation on porcine aortic media that were placed into cylindrical flow chambers and exposed to flowing antecubital venous blood for 3 minutes was assessed morphometrically at a shear rate of 2546 s-1, which is typical of arterial flow at sites of stenoses. Thrombus formation under basal conditions was 7.0 +/- 1.6 microns 2, and this was decreased to 3.1 +/- 0.5 microns 2 (P < .05) after 7 days of treatment with oral verapamil SR and to 2.6 +/- 0.5 microns 2 (P < .05) after 7 days of treatment with oral verapamil and aspirin. Whole blood platelet aggregation levels in response to 0.050 and 0.075 U of thrombin at baseline were 10.8 +/- 1.0 and 11.9 +/- 1.0 omega; aggregation was inhibited after 7 days of treatment with verapamil to 6.5 +/- 1.1 and 7.8 +/- 0.9 omega (P < .05 versus baseline) and after 7 days of treatment with verapamil and aspirin to 6.1 +/- 1.1 and 7.2 +/- 1.0 omega (P < .05), respectively.

CONCLUSIONS

The present study demonstrates that part of the benefit of verapamil in ischemic heart disease may occur by inhibition of platelet aggregation and thrombus formation. This beneficial antithrombotic effect may be important in preventing acute coronary ischemic events resulting from thrombus formation at sites of plaque rupture.

Effects of thrombocytopenia and shear rate on neutrophil and platelet deposition on endothelial and medial arterial surfaces

Both platelets and neutrophils interact with the injured vessel wall and may contribute to thrombosis and vasospasm. The effect of platelets on neutrophil interactions with the vessel wall was studied in normal and thrombocytopenic pigs. 51Cr-labeled platelet deposition (x10(6)) and 111In-labeled neutrophil deposition (x10(3)) on undamaged aortic strips with intact endothelium or damaged aortic strips with exposed media were quantified in superfusion flow chambers before and after platelet depletion by specific rabbit antisera. Arterial blood was drawn at a constant flow rate through the superfusion chambers at 37 degrees C. Under basal conditions, platelets did not adhere to the uninjured vessel wall with intact endothelium, whereas neutrophil interaction with the endothelium was low and constant at shear rates of 427, 853, and 1280 s-1 and did not change significantly after thrombocytopenia. On exposed aortic media simulating deep arterial injury, platelet deposition increased over these shear rates from 14.0 +/- 3.4 to 37.5 +/- 12.0 (P < .05) to 68.0 +/- 9.0, respectively (P < .05). Similarly, neutrophil deposition on the media increased from 48.7 +/- 8.7 to 73.7 +/- 14.3 (P < .05) to 118.3 +/- 22.9, respectively (P < .05). Platelet deposition on the media did not occur after thrombocytopenia (80% reduction in platelet count); however, neutrophil deposition persisted, but was less intense and was now independent of shear rates (23.3 +/- 5.2 at 427 s-1, 18.7 +/- 3.2 at 853 s-1, and 24.1 +/- 3.9 at 1280 s-1; not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Exogenous prostacyclin decreases vasoconstriction but not platelet thrombus deposition after arterial injury

OBJECTIVES

The aim of this study was to examine the in vivo effects of increasing doses of prostacyclin (PGI2) on arterial vasoconstriction, platelet deposition and their interrelation after balloon injury of porcine carotid arteries.

BACKGROUND

Extensive platelet deposition and localized vasoconstriction occur acutely after arterial injury in vivo. The platelet deposition and vasoconstriction are directly correlated, and previous studies suggest that platelets may mediate the vasoconstrictive response. However, it is unclear whether vasoconstriction contributes to platelet deposition.

METHODS

Seven pigs received an intravenous infusion of PGI2 at 10 ng/kg per min (PGI2 10), 8 pigs at 50 ng/kg per min (PGI2 50) and 4 pigs at 500 ng/kg per min (PGI2 500); 24 pigs with saline infusion served as a control group.

RESULTS

Vasoconstriction immediately proximal and distal to the balloon-dilated carotid arterial segment where selective endothelial injury occurred was directly related to indium-111-labeled platelet deposition within the dilated segment in both control pigs and PGI2-treated pigs. However, this relation was such that for any given level of platelet deposition relative to control, PGI2 decreased vasoconstriction in a dose-related manner. None of the treatments (PGI2 10, 50 or 500) decreased quantitative 111In-labeled platelet deposition or the proportion of deeply injured arteries with mural thrombus (91%, 70% or 75%, respectively, p = NS) compared with values in control pigs (81%). Thus, vasoconstriction was directly related to platelet deposition in control and PGI2-treated animals, but vasodilation alone did not decrease platelet deposition.

CONCLUSIONS

Intravenous infusion of PGI2 significantly decreases vasoconstriction but not platelet deposition or mural thrombosis after arterial injury by balloon dilation. It is therefore unlikely that vasoconstriction mediates platelet deposition in this model. At hemodynamically tolerated doses, PGI2 infusion probably will not prevent the thrombotic complications associated with angioplasty.

Methylene blue inhibits the antithrombotic effect of nitroglycerin

OBJECTIVES

The aim of this study was to examine whether cyclic guanosine monophosphate (GMP) may be involved in the antithrombotic action of nitroglycerin.

BACKGROUND

Nitroglycerin has been shown to inhibit platelet function in vitro by stimulating prostacyclin or inhibiting thromboxane A2 production, or both. Nitroglycerin has also been shown to possess potent antithrombotic properties in vivo. However, the mechanism of this antithrombotic effect is unclear.

METHODS

Nitroglycerin was infused to produce a 10% decrease in mean arterial pressure in 27 normal pigs by exposing their circulating arterial blood to porcine aortic media in an ex vivo perfusion chamber. Eight pigs received an infusion of nitroglycerin alone; eight received an infusion of methylene blue, a guanylate cyclase inhibitor, followed by nitroglycerin infusion and five pigs received an infusion of nitroglycerin followed by methylene blue and subsequent infusion of cyclic GMP.

RESULTS

With nitroglycerin alone, quantitative autologous indium-111-labeled platelet deposition (x10(6) on the aortic media was decreased to 63.9 +/- 10.4% (p = 0.01) of the baseline control platelet deposition. Methylene blue given before nitroglycerin tended to increase platelet deposition relative to baseline and platelet deposition after nitroglycerin was 142 +/- 35% (p = NS) of baseline value. In pigs that received all three agents, nitroglycerin reduced platelet deposition to 42.3 +/- 12.2% of baseline value; this decrease was then attenuated by subsequent methylene blue infusion but was enhanced by cyclic GMP infusion to 16.4 +/- 3.8% of baseline value (p = 0.006 vs. baseline control and p = 0.02 versus methylene blue infusion).

CONCLUSIONS

Guanylate cyclase inhibition with methylene blue abolishes the antithrombotic effect of nitroglycerin, which can be enhanced by cyclic GMP.

Cod liver oil alters platelet-arterial wall response to injury in pigs

In 36 normolipemic pigs randomized to a 4-week feeding with regular pig chow (n = 18, control group) or chow supplemented with cod liver oil (1 ml/kg per day) (n = 18, treated group), treatment with cod liver oil produced a significant decrease in serum cholesterol, low density lipoprotein cholesterol, and triglycerides. Deep carotid arterial wall injury (media exposed) by balloon angioplasty was associated with less 111In-labeled platelet deposition (24.6 +/- 4.8 x 10(6)/cm2 versus 62.5 +/- 17.0 x 10(6)/cm2, p less than 0.05; difference, -33.8 x 10(6)/cm2; 95% confidence interval [CI], -1.9 x 10(6)/cm2 to -73.9 x 10(6)/cm2) and injury-related vasoconstriction (21.3 +/- 2.2% versus 30.9 +/- 2.9%, p less than 0.05; difference, -9.6%; 95% CI, -2.2% to -17.0%) in the cod liver oil-treated group than in the control group; with mild injury (media not exposed), platelet deposition was low and unchanged (6.2 +/- 0.5 x 10(6)/cm2 versus 7.8 +/- 0.7 x 10(6)/cm2; difference, -1.6 x 10(6)/cm2; 95% CI, -1.1 x 10(6)/cm2 to +4.3 x 10(6)/cm2), but associated vasoconstriction was reduced respectively (16.3 +/- 2.0% versus 23.0 +/- 2.2%, p less than 0.05; difference, -6.7%; 95% CI, -0.6% to -12.8%). When arterial blood from cod liver oil-treated pigs superfused normal aortic media ex vivo, platelet deposition onto the normal aortic media was lower than when arterial blood from control pigs superfused the normal aortic media (43.7 +/- 8.8 x 10(6)/cm2 versus 66.8 +/- 13.0 x 10(6)/cm2, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cilazapril and early atherosclerotic changes after balloon injury of porcine carotid arteries

BACKGROUND

Cilazapril, a converting enzyme inhibitor, has been shown to significantly decrease the extent of intimal smooth muscle cell proliferation after arterial injury in a normotensive rat model.

METHODS AND RESULTS

To assess the influence of cilazapril on myofibrotic changes after balloon injury, control (n = 7) or cilazapril-treated (n = 9) (20 mg/kg b.i.d.) normal 3-month-old pigs underwent dilatation angioplasty of the right, and deendothelialization of the left common carotid artery. Carotid arteries isolated at 4 weeks were examined morphometrically with a computerized digitizer after in situ glutaraldehyde fixation. Both in the deendothelialized and dilated arteries, the surface area in square millimeters of the neointima and media were similar in the treated and control animals; therefore, the ratio of neointima to media was again not different. The neointimal changes included a combination of proliferative changes as well as organization of mural thrombus and were equally well distributed in the two groups of animals. At the time that the animals were killed, blood pressure (38.2 +/- 2.1 versus 56.8 +/- 4.8 mm Hg, p = 0.003) and plasma angiotensin converting enzyme activity (5.6 +/- 4.1 versus 182.3 +/- 70.4, p = 0.02) were lower in treated than in control pigs, but aortic media thrombogenicity (as assessed in an ex vivo perfusion flow chamber) and serum lipids were not different between groups.

CONCLUSIONS

In pigs, cilazapril did not alter the development of myofibrotic changes after mild or severe balloon injury despite plasma angiotensin converting enzyme activity inhibition.

[Not Available]

Antiplatelet agents are effective in reducing mortality and the incidence of infarction in patients with unstable angina and in reducing cardiovascular mortality and reinfarction in cases of acute myocardial infarction. Individuals with multiple risk factors who are likely to develop coronary disease could benefit from prophylactic treatment with these agents.

Antithrombotic therapy for deep arterial injury by angioplasty. Efficacy of common platelet inhibition compared with thrombin inhibition in pigs

BACKGROUND

Platelet-thrombus formation is a complication of arterial wall deep injury by balloon angioplasty that may lead to acute arterial occlusion and may contribute to restenosis.

METHODS AND RESULTS

Because common platelet-inhibitor drugs with a heparin bolus (100 units/kg) may be effective in inhibiting platelet-thrombus formation after arterial angioplasty, these were compared with a bolus of heparin alone (control), the specific thrombin inhibitor hirudin (1.0 mg/kg), and saline (hirudin control) in normal pigs after angioplasty of the common carotid arteries. In the presence of deep arterial wall injury (injury exposing the media), indium-111-labeled platelet deposition (x 10(6)/cm2) was 68.8 +/- 12.3 and 48.1 +/- 16.9 in the control animals. This was significantly reduced by pretreatment with low-dose aspirin (1 mg/kg/day), by high-dose aspirin (20 mg/kg/day) plus dipyridamole, and especially by thrombin inhibition with hirudin. Treatment regimens with aspirin alone (20 mg/kg/day), dipyridamole alone, or sulfinpyrazone were ineffective. Likewise, the incidence of mural thrombosis was 75% and 80% in deeply injured arteries of controls and was significantly reduced to 46% with aspirin plus dipyridamole, 25% with low-dose aspirin, and 0% with hirudin. The incidence of mural thrombosis was unchanged with high-dose aspirin (69%), dipyridamole (90%), or sulfinpyrazone (92%). This mural thrombosis could not be identified by angiography. In the presence of mild injury (deendothelialization), platelet deposition was low (less than 10 x 10(6)/cm2, a single layer) and was not changed by any therapy, including hirudin.

CONCLUSIONS

These therapies do not affect platelet adhesion to deeply or mildly injured artery. These data suggest a greater role for thrombin inhibition than with thromboxane or cyclooxygenase inhibition in the pathogenesis of platelet-rich mural thrombosis after deep injury during angioplasty. Antithrombotic therapy for arterial thrombosis by thrombin inhibition appears promising.

Effects of nitroglycerin at therapeutic doses on platelet aggregation in unstable angina pectoris and acute myocardial infarction

The platelet aggregation response to adenosine diphosphate (ADP) and to thrombin was quantified in 10 patients, 5 with unstable angina pectoris and 5 with acute myocardial infarction, before, during and after a 45-minute infusion of nitroglycerin. An impedance aggregometer allowing rapid bedside studies in whole blood was used. The reproducibility of the methods was documented to be within 10%. Doses of nitroglycerin were titrated for a 10 mm Hg decrease in mean arterial blood pressure with mean doses being 1.2 +/- 0.2 (standard error of the mean) micrograms/kg/min. Nitroglycerin decreased the area under the aggregation curve induced by ADP from 43 +/- 3.6 to 30 +/- 6.3 cm2 (p = 0.007) and by thrombin from 8.9 +/- 1.7 to 4.1 +/- 0.9 cm2 (p = 0.003). Peak responses to ADP were decreased from 13.3 +/- 1 to 9.1 +/- 1.7 ohms (p = 0.005) and to thrombin from 9.3 +/- 2 to 5.0 +/- 1.2 ohms (p = 0.003). All patients had greater than or equal to 50% inhibition with 1 agent or the other and the inhibition was greater than 50% with each of the 2 aggregating agents in 6 patients. Analyses performed on blood withdrawn 15 minutes after the discontinuation of nitroglycerin showed a return to baseline before nitroglycerin results. When analyses were delayed and performed on blood preserved at room temperature for 30 minutes, no effect of nitroglycerin could be detected. Thus, bedside platelet aggregation studies document a significant and reversible effect of nitroglycerin at therapeutic doses on platelet function.

Importance of adequate heparin dosage in arterial angioplasty in a porcine model

Acute occlusion after a successful angioplasty is a severe complication that has been reported in 2-12% of patients. Therefore, to determine whether there was a relation between the dosage of heparin and the presence of mural thrombosis, we studied in a pig model the relation between the dosage of heparin and acute platelet-thrombus deposition on the site of arterial injury. We retrospectively analyzed the effect of three heparin regimens on platelet deposition in 32 normal pigs (mean weight, 32.7 kg) that underwent bilateral carotid angioplasty and were sacrificed 90 +/- 26 minutes later. Pigs in protocol 1 (n = 7) received an intravenous bolus injection of 4,000 units heparin 10 minutes before angioplasty. Pigs in protocol 2 (n = 11) received two bolus injections of 4,000 units heparin 40 minutes apart; the angioplasty was performed immediately after the second bolus. Pigs in protocol 3 (n = 14) had an initial 4,000-unit bolus injection of heparin followed immediately by an infusion of 4,000 units/hr; angioplasty was performed 20 minutes after starting the infusion. 111In-labeled platelet deposition on deeply injured (torn into the media) arterial segments were 86.3 +/- 68, 56.2 +/- 56.9, and 37.7 +/- 37.7 X 10(6)/cm2 for protocols 1, 2, and 3, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelets, vasoconstriction, and nitroglycerin during arterial wall injury. A new antithrombotic role for an old drug

Endothelial injury in vivo is associated with platelet deposition and a localized platelet-dependent vasoconstrictive response. To assess the influence of nitroglycerin on platelets and vasoconstriction, quantitative 111In-labeled platelet deposition (no platelets x 10(6)/cm2) of the injured segment and the degree of angiographic vasoconstriction (percent diameter narrowing proximal and distal to the dilated segment) produced during injury by balloon angioplasty of the common carotid arteries were studied in heparinized normal pigs that were sacrificed immediately after the procedure. In deeply injured (injury extending through the internal elastic lamina) compared with mildly injured (deendothelialization only) arteries, there was both greater platelet deposition (63.8 vs. 6.9, p = 0.04) and more vasoconstriction (30% vs. 19%, p = 0.02). In the presence of deep arterial wall injury, nitroglycerin given intravenously at a dose sufficient to lower mean arterial pressure by 9 +/- 2% significantly decreased both platelet deposition (16.2 vs. 63.8, p less than 0.008) and the vasoconstrictive response (20 vs. 30%, p less than 0.02) relative to control. However, in the presence of mild arterial wall injury, nitroglycerin decreased vasoconstriction relative to control (10% vs. 19%, p less than 0.01) without causing a significant decrease in the already low level of platelet deposition (5.6 vs. 6.9, respectively; p = NS), suggesting a direct smooth muscle relaxant effect of nitroglycerin. This is the first reported in vivo effectiveness of nitroglycerin in the reduction of platelet deposition after deep arterial injury.

Safety and diagnostic accuracy of dipyridamole-thallium imaging in the elderly

The noninvasive diagnosis of coronary artery disease in the elderly can occasionally be difficult. Intravenous dipyridamole-thallium imaging is a potentially useful diagnostic test to determine presence and severity of coronary disease; however, the safety of the procedure has not been determined in an older population. The side effect profile and frequency of severe ischemic responses after 0.56 mg/kg of intravenous dipyridamole were compared in 101 patients greater than or equal to 70 years old and 236 patients less than 70 years old. There were no side effects in 64% and 62% of patients greater than or equal to 70 and less than 70 years old, respectively (p = NS). Among the 337 patients tested, there were no complications of myocardial infarction or death. The most common cardiac side effect was chest pain, which occurred in 21 (21%) of the 101 patients aged greater than or equal to 70 years and in 64 (27%) of the 236 patients less than 70 years (p = NS). Aminophylline was required to reverse cardiac or noncardiac side effects in 15 (15%) and 36 (15%) of the patients greater than or equal to 70 and less than 70 years old, respectively (p = NS). A severe ischemic response occurred in 2% and 2.5% of patients greater than or equal to 70 and less than 70 years old, respectively (p = NS). The sensitivity of intravenous dipyridamole-thallium imaging for obstructive coronary artery disease was 86% (25 of 29) and 83% (68 of 82) in older and younger patients, respectively (p = NS); the specificity was 75% (6 of 8) and 70% (16 of 23), respectively (p = NS). Thus, intravenous dipyridamole-thallium imaging is a safe noninvasive method for assessment of older patients with obstructive coronary disease; its side effect profile and diagnostic accuracy are similar to those seen in younger patients. The technique is associated with severe ischemic responses in only a small minority of patients.

Effects of dietary supplementation with cod-liver oil on endothelium-dependent responses in porcine coronary arteries

To study the effect of dietary supplementation with fish oil on endothelium-dependent responses, Yorkshire pigs were maintained on a normal diet or on a low (0.6 ml/kg/day) or a high (1.0 ml/kg/day) dose of cod-liver oil for 4 weeks. Endothelium-dependent responses were examined in vitro in rings of proximal left anterior descending coronary arteries taken from control and treated animals studied in parallel. Endothelium-dependent relaxations in response to bradykinin, serotonin, adenosine diphosphate, and thrombin were facilitated in arteries from treated but not in those from control animals, whereas the relaxations in response to A23187 were unaltered. The facilitated relaxations were not altered by indomethacin but significantly inhibited by methylene blue. Aggregating platelets from control and treated pigs induced comparable, facilitated endothelium-dependent relaxations in rings taken from treated pigs. The platelet-induced contractions were significantly reduced in rings with endothelium taken from treated pigs, and they were comparable in rings without endothelium in both groups. Aggregating platelets from control and treated pigs released comparable amounts of serotonin and thromboxane A2. Endothelium-dependent relaxations induced by arachidonic acid and eicosapentaenoic acid were unaltered, whereas transient endothelium-dependent contractions induced by arachidonic acid were significantly reduced by the treatment with cod-liver oil. Relaxations to sodium nitroprusside or isoproterenol,and contractions to potassium chloride or serotonin were not different in rings without endothelium from control or treated pigs. These results indicate that dietary supplementation with cod-liver oil facilitates endothelium-dependent relaxations and inhibits endothelium-dependent contractions in porcine coronary arteries.

Restenosis after arterial angioplasty: a hemorrheologic response to injury

Restenosis after arterial angioplasty appears to be a response to deep arterial injury, which is much more thrombogenic than superficial injury (endothelial denudation). Deep arterial injury exposes collagen, elastin and smooth muscle cells to circulating blood, releases tissue thromboplastin and causes immediate platelet-thrombus deposition as a result of activation of platelets and the clotting system, both of which mutually facilitate activation of the other. Regrowth of endothelium also is protective against platelet deposition. Platelet adherence to collagen, and thus to the arterial wall that is deeply injured, increases with shear rate (related inversely to the fourth power of luminal cross-sectional area and directly to blood flow); thus, the effect of shear rate increases the importance of adequate dilatation at the time of the procedure. Therapy that will reduce acute platelet-thrombus deposition appears to be an important factor for reduction of restenosis. Vasoconstriction occurs experimentally after arterial angioplasty in arterial segments proximal and distal to the dilated segment where there has been no necrosis of smooth muscle cells. The vasoconstriction is directly related to the severity of platelet deposition, can be reduced by reducing platelet deposition with low dose aspirin (1 mg/kg daily) and is probably mediated by vasoconstrictor substances from platelets (thromboxane A2, serotonin and other substances). Platelet-membrane receptor inhibitors to these substances reduce the vasoconstriction but do not reduce platelet deposition. Therapeutic intervention should probably involve both anticoagulation and platelet inhibition. Platelet-membrane receptor inhibition to the fibrinogen receptor, factor VIII-von Willebrand factor or both may be necessary acutely to sufficiently reduce acute platelet-thrombus deposition.

Is vasospasm related to platelet deposition? Relationship in a porcine preparation of arterial injury in vivo

Although aggregating platelets can release potent vasoactive substances in vitro, the importance of platelets in mediating naturally occurring or provoked spasm in vivo is not clear. To investigate the possible role of platelets in arterial spasm following arterial injury induced by angioplasty, quantitative platelet deposition of the dilated arterial segment and the degree of vasoconstriction (average percent diameter narrowing just proximal and distal to the dilated segment) produced during angioplasty of the common carotid arteries were studied in 42 heparinized normal pigs that were killed immediately after the angioplasty procedure. Angiographic films of the carotid arteries were taken before and after the dilatation to assess the vasoconstriction. Vasoconstriction was greater (40% vs 19%, p less than .002) when platelet deposition (X 10(6)/cm2) was in excess of 10, and the severity of vasoconstriction in vivo had a close positive exponential correlation (r = .77, p less than .001) with extent of platelet deposition in 24 untreated pigs. Platelet deposition and vasoconstriction were greater with severe arterial wall injury than with mild injury (58.8 versus 6.9, p less than .0001; 37% vs 21%, p less than .001, respectively). After severe injury in 18 pigs pretreated with 1 mg/kg/day aspirin, platelet deposition decreased (from 58.8 to 19.6, p less than .02) and vasoconstriction decreased (from 37% to 21%, p less than .003) relative to control. After mild injury, platelet deposition and vasoconstriction were mild and unchanged by aspirin. Thus, local vasoconstriction is influenced by the degree of platelet deposition.(ABSTRACT TRUNCATED AT 250 WORDS)

Deep arterial injury during experimental angioplasty: relation to a positive indium-111-labeled platelet scintigram, quantitative platelet deposition and mural thrombosis

Although it is not clear why coronary occlusion and restenosis occur after successful coronary angioplasty, factors related to the procedure may influence early and late results. The possible adverse effects of a medial tear documented histologically and produced during balloon angioplasty of the common carotid arteries were studied in 30 fully heparinized (100 U/kg body weight) normal pigs. Scanning electron microscopy showed endothelial denudation and extensive platelet deposition in all dilated arterial segments. Visible macroscopic mural thrombus was present within an hour of the procedure in 29 (91%) of the 32 arteries that had a medial tear documented by histologic study; the tear produced an indium-111-labeled platelet deposition of 116.4 +/- 26.5 X 10(6)/cm2 (mean +/- SE) and total thrombotic occlusion in 2 arteries (4%). None of the 24 arteries without a medial tear had a thrombus, and the mean platelet deposition in that group was 7.0 +/- 0.5 X 10(6)/cm2 (p less than 0.0008). In 12 pigs scanned with a gamma camera, visible thrombus was associated with platelet deposition in excess of 20 X 10(6)/cm2 in 12 arteries, 9 of which had a positive indium-111-labeled platelet scintigram. Thus, arterial angioplasty causes deep arterial injury, which appears to be a major cause of mural thrombosis, heavy platelet deposition, a positive indium-111-labeled platelet scintigram and acute arterial occlusion. A positive indium-111-labeled platelet scintigram was always associated with macroscopic thrombus of at least 20 > 10(6) platelets/cm2 and underlying deep arterial injury.

The pathogenesis and prevention of aortocoronary vein bypass graft occlusion and restenosis after arterial angioplasty: role of vascular injury and platelet thrombus deposition

Vascular injury during aortocoronary vein bypass graft surgery and arterial angioplasty initiates platelet thrombus deposition and mandates antithrombotic therapy, starting before the procedures to maximize protection against occlusion. This has been shown in studies in animals and in patients undergoing aortocoronary vein bypass graft operation where dipyridamole therapy was started before the operation, heparin was given intraoperatively and combined dipyridamole and aspirin therapy was started 7 hours after operation and markedly reduced vein graft occlusion in patients with grafts at both high and low risk for occlusion without increasing bleeding. Other alternative regimens, particularly preoperative dipyridamole followed postoperatively with aspirin alone, offer a promising future. Therapy should be continued for at least 1 year and perhaps indefinitely. Control of coronary risk factors appears important for long-term therapy to try to retard the atherosclerotic and occlusive process that leads to approximately 50% vein graft attrition by 10 years after operation. The possible role of cod liver oil and internal mammary artery bypass is discussed. Arterial angioplasty appears to cause deep arterial injury that activates both platelets and the coagulation system. These potentiate each other to form macroscopic mural thrombus within 1 hour in more than 90% of arteries that manifested deep arterial injury in pigs. Acute platelet thrombus deposition was retarded but not eliminated by only certain platelet-inhibitor agents. Implications for ongoing trials, current empiric therapy and future therapy are discussed.