Perioperative outcomes of hypertrophic cardiomyopathy: An insight from the National Readmission Database

BACKGROUND

Data regarding hypertrophic obstructive cardiomyopathy (HOCM) patients undergoing noncardiac surgery is lacking. We sought to examine the perioperative outcomes of HOCM patients undergoing noncardiac surgery using a national database.

METHODS

We used the National readmission database from 2016 to 2019. We identified HOCM, heart undergoing noncardiac surgery using ICD 10 codes. We examined hospital outcomes as well as 90 days readmission outcomes.

RESULTS

We identified 16,098 HOCM patients and 21,895,699 non-HOCM patients undergoing noncardiac surgery. The HOCM group had more comorbidities at baseline. After adjustment for major clinical predictors, the HOCM group experienced more in-hospital death, odds ratio (OR) 1.33 (1.216-1.47), P < 0.001, acute myocardial infarction (AMI), OR 1.18 (1.077-1.292), P < 0.001, acute heart failure odds ratio OR 1.3 to (1.220-1.431), P < 0.001, 90 days readmission OR 1.237 (1.069-1.432), P < 0.01, cardiogenic shock OR 2.094 (1.855-2.363), P < 0.001. Cardiac arrhythmia was the most common cause of readmission, out of the arrhythmias atrial fibrillation was the most prevalent. Acute heart failure was the most common complication of readmission. There was no difference in major adverse cardiovascular events (MACE), and AMI between both groups and readmission.

CONCLUSION

HOCM patients undergoing noncardiac surgery may be at increased risk of in-hospital and readmission events. Acute heart failure was the most common complication during index admission, while cardiac arrhythmias were the most common complication during readmission. More research is needed to address this patient population further.

A low-dose thrombolytic infusion protocol for safe and successful treatment of left ventricular assist device thrombosis: a case series

Background

Pump thrombosis is a serious complication of continuous-flow left ventricular assist device (CF-LVAD) therapy. In this study, we aim to report a novel protocol of an intermittent, low-dose, and slow infusion of tissue plasminogen activator (alteplase).

Case summary

We treated seven LVAD pump thrombosis events (HeartMate® II and HeartWare) in four patients with a median age of 52 years (31-63), and all were female. The protocol was applied from January 2015 to December 2018, and it consisted of an intermittent, low-dose, and slow infusion of systemic thrombolytic therapy in the intensive care unit. This therapy resulted in successful resolution of pump thrombosis in six out of seven events. Bleeding complication occurred in one patient, which included a ruptured haemorrhagic ovarian cyst and a small cerebellar intra-parenchymal haemorrhage. All patients were discharged home in a stable condition, except one patient who died during hospitalization because of severe sepsis, pump thrombosis with subsequent pump exchange, and multi-organ failure.

Discussion

A low-dose, prolonged, and systemic thrombolytic infusion protocol is an effective and relatively safe treatment that can lead to a sustained resolution of pump thrombosis with low bleeding complications and failure rates.

Cardiac Contractility Modulation in Patients with Advanced Heart Failure: A Comprehensive Review of Literature

Heart failure is a significant cause of morbidity and mortality worldwide. Despite advancements in guideline-directed medical therapy and improvements in device-based therapies, patients with advanced heart failure have high rates of mortality regardless of ejection fraction. For patients with reduced ejection fraction who meet criteria, cardiac resynchronization therapy or implantable cardiac defibrillators are options available to improve outcomes. However, not all heart failure patients meet those criteria. Cardiac contractility modulation is an innovative therapy that serves to improve functional outcomes and quality of life, while also modifying pathologic gene expression and preventing further remodeling. In this article, we aim to discuss the major clinical trials investigating cardiac contractility modulation as a suitable therapy for patients with advanced heart failure.

Atrial Speckle Tracking Echocardiography for Detecting Atrial Fibrillation in Cryptogenic Stroke: A Meta-Analysis

Cryptogenic stroke (CS) accounts for approximately 25% of ischemic stroke cases, with atrial fibrillation (AF) accounting for 30% of CS cases. We investigated the utility of left atrial (LA) speckle-tracking echocardiography in identifying patients at high risk of AF after CS and potentially guiding patients who will benefit from long-term rhythm monitoring devices. Cochrane Library, MEDLINE, and EMBASE were searched for relevant studies. We included studies that examined patients with new CS without a history of AF and further examined LA strain parameters (peak and/or reservoir strain). Continuous data were pooled as a mean difference (MD) comparing patients who developed AF vs no AF.  We used the inverse variance method with the DerSimonian-Laird estimator for tau2 and Hartung-Knapp adjustment for random effect analysis. I2 was used to assess heterogeneity. Thirteen observational studies met our criteria and included 3031 patients with new CS. Of those, 420 patients developed AF on follow-up, and 2611 patients did not develop AF. The AF group vs. no AF had significantly reduced LA reservoir strain (LARS) [MD: -8.61; 95% CI: -10.76, -6.47, I2 = 85%, p < 0.01] at presentation. LARS is significantly lower in patients who developed AF after CS. More studies are needed to validate this data.

Characteristics and Outcomes of Early vs Late Initiation of Mechanical Circulatory Support in Non-Acute Myocardial Infarction related Cardiogenic Shock: An Analysis of the National Inpatient Sample Database

Cardiogenic shock (CS) is significant cause of mortality. The use of mechanical circulatory support (MCS) in patients with non-acute myocardial infarction (Non-AMI) CS is lacking. We inquired data regarding the trends and outcomes early vs late initiation of MCS in non-AMI CS. We investigated National Inpatient Sample database between October 2015-December 2018, identifying hospitalizations with CS, either complicated by AMI or Non-AMI. Patients were divided into 2 cohorts, early initiation of MCS (<48 hours) and late initiation of MCS (>48 hours). The primary analysis included death within first 24 hours. A secondary analysis was adjusted after excluding patients who died in first 24 hours. A total of 85,318 patients with non-AMI-related CS with MCS placement were identified. Among this cohort, 54.6% (n=46,579) underwent early initiation of MCS within 48 hours, and 45.4% (n=38,739) underwent late initiation of MCS after 48 hours. In primary analysis, early MCS initiation was associated with more in-hospital mortality in primary outcome of all-cause hospital mortality (35.72% vs 27.63%, P<0.0001, OR 1.44, 95% CI: 1.40-1.49, P<0.0001), however, adjusted secondary analysis showed a statistically significant decrease in all-cause hospital mortality (23.63% vs 27.63%, P<0.0001, OR 0.80, 95% CI: 0.78-0.83, P<0.0001). In non-AMI-related CS and based on survival to 24 hours after admission, early initiation of MCS had statistically significant decrease in all-cause hospital mortality, with less incidence of vascular and renal complications, and shorter hospital stay. Late initiation of MCS was associated with a higher incidence of advanced therapies, including LVAD and transplant.

Percutaneous Coronary Intervention Outcomes in Patients With Prior Thoracic Radiation Therapy: A Systematic Review and Meta-Analysis

Background

Thoracic radiation predisposes patients to accelerated coronary artery disease. There is a paucity of data in both short-term and long-term outcomes following revascularization in patients who have undergone thoracic radiation.

Methods

We performed a search of the Medline, Cochrane, and Scopus databases for studies that compared outcomes in cancer patients who have undergone thoracic radiation and percutaneous coronary intervention (PCI). The primary outcome of our meta-analysis was all-cause mortality. Secondary outcomes included cardiac mortality, myocardial infarction (MI), and restenosis.

Results

The analysis included four observational studies with a total of 13,941 patients for the primary outcome of all-cause mortality. There were a total of 1,322 patients analyzed for cardiac mortality, 13,103 for MI, and 10,530 for restenosis. The longest follow-up for the primary outcome was 16 years. There was statistically significant higher risk of all-cause mortality in patients who underwent thoracic radiation (risk ratio (RR): 1.29, 95% confidence interval (CI): 1.08 - 1.54, P = 0.004). There was no statistically significant difference in cardiac mortality (RR: 1.15, 95% CI: 0.83 - 1.61, P = 0.40), MI (RR: 1.01, 95% CI: 0.20 - 5.08, P = 0.99), and restenosis (RR: 1.92, 95% CI: 0.24 - 15.35, P = 0.54).

Conclusion

In this meta-analysis, we found a higher risk of all-cause mortality in patients with a history of thoracic radiation undergoing PCI, likely from underlying malignancy itself.

Coronary Artery Disease and Aspirin Intolerance: Background and Insights on Current Management

Aspirin is one of the most widely used medications across the global healthcare system and is the foundation in treating ischemic heart disease, as well as secondary prevention for ischemic and valvular heart disease. Challenges arise in treating patients with cardiovascular disease who have concomitant aspirin intolerance. Through an extensive review of the literature, we provide a comprehensive background on the pharmacology of aspirin, the mechanisms behind aspirin intolerance, the importance of aspirin in cardiovascular disease, and the management of aspirin intolerance in both acute coronary syndrome and stable coronary artery disease. Our review includes a multidisciplinary approach from the internist, allergist/immunologist, and cardiologist when evaluating this important patient population.

Coronary Microvascular Disease

Coronary microvascular disease or dysfunction (CMVD) has been associated with adverse cardiovascular outcomes. Despite a growing prevalence, guidelines on definitive treatment are lacking. Proposed mechanisms of endothelial dysfunction and resultant inflammation have been demonstrated as the underlying cause. Imaging modalities such as echocardiography, cardiac MRI, PET, and in some instances CT, have been shown to be useful in diagnosing CMVD mainly through assessment of coronary blood flow. Invasive measurements through thermodilution and pressure sensor-guided Doppler microcatheters have also been utilized. Treatment options are directed at targeting inflammatory pathways and angina. In our review, we highlight the current literature on the background of CMVD, diagnostic modalities, and management of this disease.

Native and Prosthetic Valve Staphylococcus capitis Endocarditis: A Review of the Literature

Infective endocarditis (IE) is a rare but serious disease. Coagulase-negative staphylococci (CoNS) are among the least prevalent causes of IE. Staphylococcus capitis, a species of CoNS, although described in the literature before has only been seen in a few cases. Even with such few cases, complications and mortality have still been demonstrated. In our review, we look at the epidemiology, diagnosis, management, and literature prevalence of CoNS in native and prosthetic valve IE.

Age-specific trends and outcomes of hospitalizations with acute heart failure in the United States

OBJECTIVE

To analyze the age-specific temporal trends, in-hospital outcomes and readmissions for acute heart failure (HF).

BACKGROUND

There is a paucity of data on the age-specific differences in the trends and outcomes of hospitalizations with acute HF.

METHODS

The National Inpatients Sample database years 2002-2016 and the National Readmissions Database years 2013-2016 were used to identify primary hospitalizations for acute HF. We analyzed the age-specific temporal trends, in-hospital outcomes, and readmissions for acute HF.

RESULTS

The annual rate of hospitalizations for acute HF declined from 456 per 100,000 people in 2002 to 356 per 100,000 people in 2016 (P_trend < 0.001). The decline was observed among all age groups, except those aged 18-44 years. There was a decline in in-hospital mortality among all age groups, except for those aged 18-34 years. Compared with 18-34 years, adjusted in-hospital mortality was lower among 35-44 years (odds ratio 0.78, 95% confidence interval [CI] 0.74-0.82) and 45-54 years (OR 0.87; 95% CI 0.83-0.91) but higher among 55-64 years (OR 1.60; 95% CI 1.54-1.67) and ≥ 75 year (OR 2.54; 95% CI 2.44-2.64). Compared with 18-34 years, 30-day HF-related readmissions were significantly lower in older age groups (>34 years).

CONCLUSIONS

This nationwide contemporary analysis demonstrated a decline in the annual rates of hospitalizations with acute HF across all age categories except those aged 18-44 years. There was a reduction in rates of in-hospital mortality among middle-aged and older patients, but not in those aged 18-34. In-hospital mortality exhibited a dichotomous relationship with age. There was an inverse relationship between age and 30-days HF readmissions.

Outcomes of transcatheter versus surgical aortic valve replacement among solid organ transplant recipients

BACKGROUND

There is a paucity of data regarding the outcomes of transcatheter aortic valve replacement (TAVR) versus surgical aortic valve replacement (SAVR) among solid-organ transplant recipients.

METHODS

Temporal trends in hospitalizations for aortic valve replacement among solid-organ transplant recipients were determined using the National Inpatient Sample database years 2012-2017. Propensity matching was conducted to compare admissions who underwent TAVR versus SAVR. The primary outcome was in-hospital mortality.

RESULTS

The analysis included 1,730 hospitalizations for isolated AVR; 920 (53.2%) underwent TAVR and 810 (46.7%) underwent SAVR. TAVR was increasingly utilized for solid-organ transplant recipients (P_trend = 0.01), while there was no change in the number of SAVR procedures (P_trend = 0.20). The predictors of undergoing TAVR for solid-organ transplant recipients included older age, diabetes, and prior coronary artery bypass surgery, while TAVR was less likely utilized in small-sized hospitals. TAVR was associated with lower in-hospital mortality after matching (0.9 vs. 4.7%, odds ratio [OR] 0.19; 95% confidence interval [CI] 0.11-0.35, p < .001) and after multivariable adjustment (OR 0.07; 95% CI 0.03-0.21, p < .001). TAVR was associated with lower rate of acute kidney injury, acute stroke, postoperative bleeding, blood transfusion, vascular complications, discharge to nursing facilities, and shorter median length of hospital stay. There was no difference between both groups in the use of mechanical circulatory support, hemodialysis, arrhythmias, or pacemaker insertion.

CONCLUSION

This contemporary observational nationwide analysis showed that TAVR is increasingly performed among solid-organ transplant recipients. Compared with SAVR, TAVR was associated with lower in-hospital mortality, complications, and shorter length of stay.

In-Hospital acute ischemic stroke following ST-elevation myocardial infarction

BACKGROUND

In-hospital ischemic stroke following acute ST-elevation myocardial infarction (STEMI) has not been evaluated on a national scale in the United States.

METHODS

We used 2003 to 2014 Nationwide Inpatient Sample data to identify adults with a principal diagnosis of STEMI. Patients were divided into two groups defined by presence or absence of ischemic stroke. Clinical characteristics and in-hospital outcomes were studied using relevant statistics. Multiple linear and logistic regression models identified factors associated with ischemic stroke, national trend of in-hospital stroke incidence and in-hospital mortality.

RESULTS

Of 1,842,529 STEMI patients hospitalized from 2003 to 2014, 22,268 (1.2%) developed acute in-hospital ischemic stroke. Those with acute strokes were older (age ≥ 65 years: 70% vs 46%), more likely female (51% vs 33%), and had higher rates of atrial fibrillation (28.9% vs 12.2%) and heart failure (40.5% vs 21.1%). Age and gender adjusted incidence of in-hospital ischemic stroke following STEMI remained stable; 1.4% in 2003 and 1.5% in 2014 (P trend = 0.50). However, age and gender adjusted in-hospital mortality declined in STEMI patients with and without in-hospital ischemic stroke [AOR 0.97 (0.95-0.99) P trend = 0.03, and AOR 0.98 (0.98-0.99) P trend < 0.001, respectively]. Patients with ischemic strokes had higher in-hospital mortality (25.7% Vs 7.2%, p < 0.001), [AOR 2.11, 95% CI (1.92-2.32)].

CONCLUSION

In the United States, the incidence of acute in-hospital stroke remained stable from 2003 to 2014 following STEMI with significant decrease of in-hospital mortality trends. Despite slight improvement in mortality trends, in-hospital mortality rates remained elevated calling for interventions to optimize health care delivery.

Aortic Stenosis Complicated by Gastrointestinal Arteriovenous Malformations: It is not Always Heyde Syndrome

Aortic stenosis (AS) and arteriovenous malformations (AVM) are a common coexisting pathology in the elderly. When both pathologies are combined, Heyde syndrome is a differential that is widely explored among clinicians. Unfortunately, this may not always be the case. We present a case of an 82-year-old female admitted for acute gastrointestinal (GI) bleeding with a history of AVMs and AS, as well as, an algorithm in diagnosing elderly patients with both pathologies.

In-hospital left ventricular thrombus following ST-elevation myocardial infarction

BACKGROUND

In-hospital left ventricular (LV) thrombus following acute ST-elevation myocardial infarction (STEMI) has not been evaluated on a national scale and was the focus of this investigation.

METHODS

We used the 2003 to 2013 Nationwide Inpatient Sample database to identify adults ≥18 years old with a principal diagnosis code of ST-elevation myocardial infarction. Patients were divided into two groups defined by the presence or absence of LV thrombus. Clinical characteristics and in-hospital outcomes were studied using relevant statistics. Multiple linear and logistic regression models were conducted to identify factors associated with LV thrombus.

RESULTS

Of 1,035,888 STEMI patients hospitalized in the U. S from 2003 to 2013, 1982 (0.2%) developed acute in-hospital LV thrombus. Compared to no LV thrombus, patients with LV thrombus were more likely to have in-hospital complications; acute ischemic and hemorrhagic stroke, acute renal failure, gastrointestinal bleed, cardiogenic shock, in-hospital cardiac arrest and mortality. They also had longer mean length of stay and higher hospital charges. Factors associated with LV thrombus included: anterior/anterolateral STEMI, acute or chronic heart failure with reduced ejection fraction, atrial fibrillation, LV aneurysm, Left heart valvular disease, acute or chronic deep venous thrombosis/pulmonary embolism and alcohol abuse. Patients with LV thrombus were less likely to be female [AOR 0.66, 95% CI (0.51-0.84)].

CONCLUSION

The identification of factors associated with early development of LV thrombus following STEMI, will help direct resources for specific high-risk group and prompt cost-effective therapies. Gender variability in LV thrombus development warrants further investigations.

Interleukin-1 receptor type I signaling critically regulates infarct healing and cardiac remodeling

The proinflammatory cytokine interleukin (IL)-1 signals exclusively through the type I IL-1 receptor (IL-1RI). IL-1 expression is markedly induced in the infarcted heart; however, its role in cardiac injury and repair remains controversial. We examined the effects of disrupted IL-1 signaling on infarct healing and cardiac remodeling using IL-1RI(-/-) mice. After reperfused infarction IL-1RI-null mice exhibited decreased infiltration of the infarcted myocardium with neutrophils and macrophages and reduced chemokine and cytokine expression. In the absence of IL-1 signaling, suppressed inflammation was followed by an attenuated fibrotic response. Infarcted IL-1RI(-/-) mice had decreased myofibroblast infiltration and reduced collagen deposition in the infarcted and remodeling myocardium. IL-1RI deficiency protected against the development of adverse remodeling; however, infarct size was comparable between groups suggesting that the beneficial effects of IL-1RI gene disruption were not attributable to decreased cardiomyocyte injury. Reduced chamber dilation in IL-1RI-null animals was associated with decreased collagen deposition and attenuated matrix metalloproteinase (MMP)-2 and MMP-3 expression in the peri-infarct area, suggesting decreased fibrotic remodeling of the noninfarcted heart. IL-1beta stimulated MMP mRNA synthesis in wild-type, but not in IL-1RI-null cardiac fibroblasts. In conclusion, IL-1 signaling is essential for activation of inflammatory and fibrogenic pathways in the healing infarct, playing an important role in the pathogenesis of remodeling after infarction. Thus, interventional therapeutics targeting the IL-1 system may have great benefits in myocardial infarction.

Aging-related defects are associated with adverse cardiac remodeling in a mouse model of reperfused myocardial infarction

OBJECTIVES

The purpose of this study was to study aging-associated alterations in the inflammatory and reparative response after myocardial infarction (MI) and their involvement in adverse post-infarction remodeling of the senescent heart.

BACKGROUND

Advanced age is a predictor of death and ventricular dilation in patients with MI; however, the cellular mechanisms responsible for increased remodeling of the infarcted senescent heart remain poorly understood.

METHODS

Histomorphometric, molecular, and echocardiographic end points were compared between young and senescent mice undergoing reperfused infarction protocols. The response of young and senescent mouse cardiac fibroblasts to transforming growth factor (TGF)-beta stimulation was examined.

RESULTS

Senescence was associated with decreased and delayed neutrophil and macrophage infiltration, markedly reduced cytokine and chemokine expression in the infarcted myocardium, and impaired phagocytosis of dead cardiomyocytes. Reduced inflammation in senescent mouse infarcts was followed by decreased myofibroblast density and markedly diminished collagen deposition in the scar. The healing defects in senescent animals were associated with enhanced dilative and hypertrophic remodeling and worse systolic dysfunction. Fibroblasts isolated from senescent mouse hearts showed a blunted response to TGF-beta1.

CONCLUSIONS

Although young mice exhibit a robust post-infarction inflammatory response and form dense collagenous scars, senescent mice show suppressed inflammation, delayed granulation tissue formation, and markedly reduced collagen deposition. These defects might contribute to adverse remodeling. These observations suggest that caution is necessary when attempting to therapeutically target the post-infarction inflammatory response in patients with reperfused MI. The injurious potential of inflammatory mediators might have been overstated, owing to extrapolation of experimental findings from young animals to older human patients.

CD44 is critically involved in infarct healing by regulating the inflammatory and fibrotic response

Infarct healing is dependent on an inflammatory reaction that results in leukocyte infiltration and clearance of the wound from dead cells and matrix debris. However, optimal infarct healing requires timely activation of "stop signals" that suppress inflammatory mediator synthesis and mediate resolution of the inflammatory infiltrate, promoting formation of a scar. A growing body of evidence suggests that interactions involving the transmembrane receptor CD44 may play an important role in resolution of inflammation and migration of fibroblasts in injured tissues. We examined the role of CD44 signaling in infarct healing and cardiac remodeling using a mouse model of reperfused infarction. CD44 expression was markedly induced in the infarcted myocardium and was localized on infiltrating leukocytes, wound myofibroblasts, and vascular cells. In comparison with wild-type mice, CD44(-/-) animals showed enhanced and prolonged neutrophil and macrophage infiltration and increased expression of proinflammatory cytokines following myocardial infarction. In CD44(null) infarcts, the enhanced inflammatory phase was followed by decreased fibroblast infiltration, reduced collagen deposition, and diminished proliferative activity. Isolated CD44(null) cardiac fibroblasts had reduced proliferation upon stimulation with serum and decreased collagen synthesis in response to TGF-beta in comparison to wild-type fibroblasts. The healing defects in CD44(-/-) mice were associated with enhanced dilative remodeling of the infarcted ventricle, without affecting the size of the infarct. Our findings suggest that CD44-mediated interactions are critically involved in infarct healing. CD44 signaling is important for resolution of the postinfarction inflammatory reaction and regulates fibroblast function.

The role of the thrombospondins in healing myocardial infarcts

The five current members of the thrombospondin (TSP) family can be divided in two subgroups according to their molecular architecture. TSP-1 and -2 (subgroup A) are trimeric matricellular proteins that do not contribute directly to tissue integrity, but influence cell function by modulating cell-matrix interactions, whereas TSP-3, -4 and -5 (subgroup B) are pentameric proteins. TSP-1 and TSP-2 are markedly induced in healing wounds and may regulate cellular responses important for tissue repair. TSP-1 is a crucial activator of TGF-beta, whereas both TSP-1 and TSP-2 inhibit angiogenesis. This manuscript reviews our current knowledge on the expression and role of the TSPs in healing myocardial infarcts. In both canine and murine infarcts, TSP-1 shows a strikingly selective localization in the infarct border zone. In the absence of injury, TSP-1 -/- mice exhibit normal cardiac morphology and show no evidence of myocardial inflammation. Infarcted TSP-1 -/- mice have an enhanced and protracted inflammatory response with subsequent expansion of granulation tissue in the non-infarcted area, resulting in myofibroblast infiltration into the viable myocardium neighboring the infarct. Infarcted TSP-1 -/- animals have enhanced left ventricular remodeling compared with their wildtype littermates. We suggest that TSP-1 is a critical component of the protective mechanisms induced in the infarct border zone in order to limit expansion of fibrosis into the non-infarcted myocardium. Localized TSP-1 expression may suppress expansion of the inflammatory process by activating TGF-beta or by inhibiting local angiogenesis. In addition, TSP-1-mediated inhibition of MMP activity may decrease adverse remodeling. TSP-2, on the other hand, appears to be a crucial regulator of the integrity of the cardiac matrix that is necessary for the myocardium to cope with increased loading. The expression and potential role of the pentameric TSPs in the infarcted heart remain unknown. Understanding the specific mechanisms responsible for the protective effects of TSP-1 and TSP-2 in healing infarcts may lead to novel therapeutic interventions aiming at attenuating adverse left ventricular remodeling.

The role of platelet-derived growth factor signaling in healing myocardial infarcts

OBJECTIVES

This study sought to examine the role of platelet-derived growth factor (PDGF) signaling in healing myocardial infarcts.

BACKGROUND

Platelet-derived growth factor isoforms exert potent fibrogenic effects through interactions with PDGF receptor (PDGFR)-alpha and PDGFR-beta. In addition, PDGFR-beta signaling mediates coating of developing vessels with mural cells, leading to the formation of a mature vasculature. We hypothesized that PDGFR activation may regulate fibrosis and vascular maturation in healing myocardial infarcts.

METHODS

Mice undergoing reperfused infarction protocols were injected daily with a neutralizing anti-PDGFR-beta antibody (APB5), an anti-PDGFR-alpha antibody (APA5), or control immunoglobulin G, and were killed after 7 days of reperfusion.

RESULTS

The PDGF-B, PDGFR-alpha, and PDGFR-beta mRNA expression was induced in reperfused mouse infarcts. Perivascular cells expressing phosphorylated PDGFR-beta were identified in the infarct after 7 days of reperfusion, indicating activation of the PDGF-BB/PDGFR-beta pathway. The PDGFR-beta blockade resulted in impaired maturation of the infarct vasculature, enhanced capillary density, and formation of dilated uncoated vessels. Defective vascular maturation in antibody-treated mice was associated with increased and prolonged extravasation of red blood cells and monocyte/macrophages, suggesting increased permeability. These defects resulted in decreased collagen content in the healing infarct. In contrast, PDGFR-alpha inhibition did not affect vascular maturation, but significantly decreased collagen deposition in the infarct.

CONCLUSIONS

Platelet-derived growth factor signaling critically regulates postinfarction repair. Both PDGFR-beta- and PDGFR-alpha-mediated pathways promote collagen deposition in the infarct. Activation of PDGF-B/PDGFR-beta is also involved in recruitment of mural cells by neovessels, regulating maturation of the infarct vasculature. Acquisition of a mural coat and maturation of the vasculature promotes resolution of inflammation and stabilization of the scar.

Ultraviolet-B Radiation Effects on the Structure and Function of Lower Trophic Levels of the Marine Planktonic Food Web

The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (approximately 70-80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with approximately 90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed.

The Responses of a Natural Bacterioplankton Community to Different Levels of Ultraviolet-B Radiation: A Food Web Perspective

With the continuing increase of ultraviolet-B radiation (UVBR: 280-320 nm) fluxes toward the Earth's surface, there is concern regarding a possible negative impact on heterotrophic bacterioplankton. The effects of enhanced UVBR on a natural bacterioplankton community were studied during a 7-day experiment conducted in mesocosms (1500 L). Four light regimes were tested: natural light, 280 to 313 nm excluded UVBR, and two levels of UVBR enhancement. During the first 3 days of the experiment characterized by high inorganic nutrient concentrations (nitrates > 1 µmol L-1 and ammonium > 0.1 µmol L-l), UVBR had no effect on both bacterial abundances and activities. From day 4 to the end of the experiment, nitrate concentrations remained low (

An endogenous periodicity exhibited in the activity of a natural bacterioplankton community isolated in mesocosms

In July 1996, bacterial abundance and incorporation of [3H]thymidine (3H-TdR) were determined every 4 h during a mesocosm experiment initially designed to study the effects of different intensities of ultraviolet-B (UVB) radiation on the summer planktonic community of the lower St. Lawrence Estuary. Water was obtained from the quay of the Maurice Lamontagne Institute (Mont-joli, Qué.) and incubated in experimental mesocosms (1500 L total volume, n = 8) with continuous mixing provided by a pumping system. During 72 h, different UVB intensities showed no significant effects on the bacterial incorporation of3H-TdR. This indicates that in the presence of other trophic levels and with continuous mixing, bacterioplankton responses to UVB are substantially different from those reported in axenic bacterial cultures or even whole-water incubations exposed to UVB at fixed depths. In conjunction with this observation,3H-TdR incorporation exhibited a significant periodic variation within all experimental treatments. The periodicity consisted of a 16-h cycle occurring independently of the time of the day. When the3H-TdR incorporation was normalized to cell abundance, the resulting cell-specific thymidine incorporation exhibited the same periodic oscillatory pattern. On the other hand, other factors suspected of inducing such a variability showed no consistent oscillation. In addition to suggesting an endogenously controlled activity of the studied bacterial community, the results of the present study indicate that failure of taking temporal variations of bacterial activity into account may introduce an error of almost 50% in the estimation of the daily thymidine incorporation rates. This represents a considerable error, because several studies rely on this measurement to estimate bacterial carbon production and to establish carbon budgets within different oceanic provinces.Key words: bacterioplankton, [3H]thymidine, ultraviolet-B radiation, periodicity, endogenous cycles, St. Lawrence Estuary.