Fast tracking in cardiac surgery: is it safe?

Background

While fast track clinical pathways have been demonstrated to reduce resource utilization in patients undergoing cardiac surgery, it remains unclear as to whether they adversely affect post-operative outcomes. The purpose of this study was to determine the impact of fast tracking on post-operative outcomes following cardiac surgery.

Methods

In a retrospective study, all patients undergoing first-time, on-pump, non-emergent coronary artery bypass grafting, valve, or coronary artery bypass grafting + valve at a single centre between 2010 and 2017 were included. Patients were considered to have been fast tracked if they were extubated and transferred from intensive care to a step-down unit on the same day as their procedure. The risk-adjusted effect of fast tracking on a 30-day composite of all-cause mortality, stroke, renal failure, infection, atrial fibrillation, and readmission to hospital was determined. Furthermore, propensity score matching was used to match fasting track patients in a 1-to-1 manner with their nearest “neighbor” in the control group and subsequently compared in terms of 30-day post-operative outcomes.

Results

3252 patients formed the final study population (fast track: n = 245; control: n = 3007). Patients who were fast tracked experienced reduced time to initial extubation (4.3 vs. 5.6 h, p < 0.0001) and lower median initial intensive care unit length of stay (7.8 vs. 20.4 h, p < 0.0001). Fast tracked patients experienced lower 30-day rates of the composite outcome (42.4% vs. 51.5%, p = 0.008). However, following propensity score matching, fast tracked patients experienced similar 30-day rates of the composite outcome as the control group (42.4% vs. 44.5%, p = 0.72). After risk adjustment using multivariable regression modeling, fast tracking was predictive of an improved 30-day composite outcome (OR 0.75, 95% CI 0.57–0.98, p = 0.03).

Conclusion

Fast track clinical pathways was associated with reduced intensive care unit, overall length of stay and similar 30-day post-operative outcomes. These results suggest that fast tracking appropriate patients may reduce resource utilization, while maintaining patient safety.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13019-022-01815-9.

Virtual Care With Digital Technologies for Rural Canadians Living With Cardiovascular Disease

Canada is a wealthy nation with a geographically diverse population, seeking health innovations to better serve patients in accordance with the Canada Health Act. In this country, population and geography converge with social determinants, policy, procurement regulations, and technological advances with the goal to achieve equity in the management and distribution of health care. Rural and remote patients are a vulnerable population; when managing chronic conditions like cardiovascular disease, there is currently inequity to accessing specialist physicians at the recommended frequency-increasing the likelihood of poor health outcomes. Ensuring equitable care for this population is an unrealized priority of several provincial and federal government mandates. Virtual care technology might provide practical, economical, and innovative solutions to remedy this discrepancy. We conducted a scoping review of the literature pertaining to the use of virtual care technologies to monitor patients living in rural areas of Canada with cardiovascular disease. A search strategy was developed to identify the literature specific to this context across 3 bibliographic databases. Two hundred thirty-two unique citations were ultimately assessed for eligibility, of which 37 met the inclusion criteria. In our assessment of these articles, we provide a summary of the interventions studied, their reported effectiveness in reducing adverse events and mortality, the challenges to implementation, and the receptivity of these technologies among patients, providers, and policy-makers. Furthermore, we glean insight into the barriers and opportunities to ensure equitable care for rural patients and conclude that there is an ongoing need for clinical trials on virtual care technologies in this context.

Increased mast cell density is associated with decreased fibrosis in human atrial tissue

Fibrotic remodelling of the atria is poorly understood and can be regulated by myocardial immune cell populations after injury. Mast cells are resident immune sentinel cells present in the heart that respond to tissue damage and have been linked to fibrosis in other settings. The role of cardiac mast cells in fibrotic remodelling in response to human myocardial injury is controversial. In this study, we sought to determine the association between mast cells, atrial fibrosis, and outcomes in a heterogeneous population of cardiac surgical patients, including a substantial proportion of coronary artery bypass grafting patients. Atrial appendage from patients was assessed for collagen and mast cell density by histology and by droplet digital polymerase chain reaction (ddPCR) for mast cell associated transcripts. Clinical variables and outcomes were also followed. Mast cells were detected in human atrial tissue at varying densities. Histological and ddPCR assessment of mast cells in atrial tissue were closely correlated. Patients with high mast cell density had less fibrosis and lower severity of heart failure classification or incidence mortality than patients with low mast cell content. Analysis of a homogeneous population of coronary artery bypass graft patients yielded similar observations. Therefore, evidence from this study suggests that increased atrial mast cell populations are associated with decreased clinical cardiac fibrotic remodelling and improved outcomes, in cardiac surgery patients.

Variability in opioid prescribing practices among cardiac surgeons and trainees

BACKGROUND AND AIM

The opioid epidemic has become a major public health crisis in recent years. Discharge opioid prescription following cardiac surgery has been associated with opioid use disorder; however, ideal practices remain unclear. Our aim was to examine current practices in discharge opioid prescription among cardiac surgeons and trainees.

METHODS

A survey instrument with open- and closed-ended questions, developed through a 3-round Delphi method, was circulated to cardiac surgeons and trainees via the Canadian Society of Cardiac Surgeons. Survey questions focused on routine prescription practices including type, dosage and duration. Respondents were also asked about their perceptions of current education and guidelines surrounding opioid medication.

RESULTS

Eighty-one percent of respondents reported prescribing opioids at discharge following routine sternotomy-based procedures, however, there remained significant variability in the type and dose of medication prescribed. The median (interquartile range) number of pills prescribed was 30 (20-30) with a median total dose of 135 (113-200) Morphine Milligram Equivalents. Informal teaching was the most commonly reported primary influence on prescribing habits and a lack of formal education regarding opioid prescription was associated with a higher number of pills prescribed. A majority of respondents (91%) felt that there would be value in establishing practice guidelines for opioid prescription following cardiac surgery.

CONCLUSIONS

Significant variability exists with respect to routine opioid prescription at discharge following cardiac surgery. Education has come predominantly from informal sources and there is a desire for guidelines. Standardization in this area may have a role in combatting the opioid epidemic.

Transfusion Thresholds for Adult Respiratory Extracorporeal Life Support: An Expert Consensus Document

Severe acute respiratory distress syndrome (ARDS) can complicate novel pandemic coronavirus disease (COVID-19). Extracorporeal life support (ECLS) represents the final possible rescue strategy. Variations in practice, combined with a paucity of rigourous guidelines, may complicate blood-product resource availability and allocation during a pandemic. We conducted a literature review around venovenous extracorporeal membrane oxygenation (VV-ECMO) transfusion practices for platelets, packed red blood cells, fresh frozen plasma, prothrombin complex concentrate, and antithrombin. Pertinent society guidelines were examined, and the practice of Canadian ECLS experts was sampled through an environmental scan. This paper represents a synthesis of these explorations, combined with input from the Canadian Cardiovascular Critical Care (CANCARE) Society, Canadian Society of Cardiac Surgeons, and the Canadian Critical Care Society. We offer a pragmatic guidance document for restrictive transfusion thresholds in nonbleeding patients on VV-ECMO, which may attenuate transfusion-related complications and simultaneously shield national blood product inventory from strain during pandemic-induced activation of the National Plan for the Management of Shortages of Labile Blood Components.

Serum GDF15, a Promising Biomarker in Obese Patients Undergoing Heart Surgery

Background: Obesity is a risk factor that negatively impacts outcomes in patients undergoing heart surgery by mechanisms that are not well-defined nor predicated on BMI alone. This knowledge gap has fuelled a search for biomarkers associated with cardiovascular diseases that could provide clinical insight to surgeons. One such biomarker is growth differentiation factor15(GDF15), associated with inflammation, metabolism, and heart failure outcomes but not yet examined in the context of obesity and cardiac surgery outcomes.

Methods: Patients undergoing open-heart surgery were consented and enrolled for blood and tissue (atria) sampling at the time of surgery. Biomarker analysis was carried out using ELISA and western blot/qPCR, respectively. Biomarker screening was classified by inflammation(NLR, GDF15, Galectin3, ST2, TNFR2), heart failure(HF)/remodeling(NT-proBNP) and metabolism(glycemia, lipid profile). Patients were categorized based on BMI: obese group (BMI ≥30.0) and non-obese group(BMI 20.0–29.9). Subsequent stratification of GDF15 high patients was conservatively set as being in the 75th percentile.

Results: A total of 80 patients undergoing any open-heart surgical interventions were included in the study. Obese (mean BMI = 35.8, n = 38) and non-obese (mean BMI = 25.7, n = 42) groups had no significant differences in age, sex, or co-morbidities. Compared to other biomarkers, plasma GDF15 (mean 1,736 vs. 1,207 ng/l, p < 0.001) was significantly higher in obese patients compared to non-obese. Plasma GDF15 also displayed a significant linear correlation with BMI (R² = 0.097; p = 0.0049). Atria tissue was shown to be a significant source of GDF15 protein and tissue levels significantly correlated with plasma GDF15 (R² = 0.4, p = 0.0004). Obesity was not associated with early/late mortality at median follow-up >2years. However, patients with high GDF15 (>1,580 ng/l) had reduced survival (65%) compared to the remaining patients with lower GDF15 levels (95%) by Kaplan Meier Analysis (median >2 years; p = 0.007).

Conclusions: Circulating GDF15 is a salient biomarker likely sourced from heart tissue that appears to predict higher risk obese patients for adverse outcomes. More importantly, elevated GDF15 accounted for more sensitive outcome association than BMI at 2 years post-cardiac surgery, suggesting it heralds links to pathogenicity and should be actively studied prospectively and dynamically in a post-operative follow-up.

Trial number: NCT03248921.

Cardiac Rehabilitation During the COVID-19 Era: Guidance on Implementing Virtual Care

Cardiac rehabilitation programs across Canada have suspended in-person services as a result of large-scale physical distancing recommendations designed to flatten the COVID-19 pandemic curve. Virtual cardiac rehabilitation (VCR) offers an alternate mechanism of care delivery, capable of providing similar patient outcomes and safety profiles compared with centre-based programs. To minimize care gaps, all centres should consider developing and implementing a VCR program. The process of this rapid implementation, however, can be daunting. Centres should initially focus on the collation, utilization, and repurposing of existing resources, equipment, and technology. Once established, programs should then focus on ensuring that quality indicators are met and care processes are protocolized. This should be followed by the development of sustainable VCR solutions to account for care gaps that existed before COVID-19, and to improve cardiac rehabilitation delivery, moving forward. This article reviews the potential challenges and obstacles of this process and aims to provide pragmatic guidance to aid clinicians and administrators during this challenging time.

Guiding Cardiac Care During the COVID-19 Pandemic: How Ethics Shapes Our Health System Response

The COVID-19 pandemic has raised ethical questions for the cardiovascular leader and practitioner. Attention has been redirected from a system that focuses on individual patient benefit toward one that focuses on protecting society as a whole. Challenging resource allocation questions highlight the need for a clearly articulated ethics framework that integrates principled decision making into how different cardiovascular care services are prioritized. A practical application of the principles of harm minimisation, fairness, proportionality, respect, reciprocity, flexibility, and procedural justice is provided, and a model for prioritisation of the restoration of cardiovascular services is outlined. The prioritisation model may be used to determine how and when cardiovascular services should be continued or restored. There should be a focus on an iterative and responsive approach to broader health care system needs, such as other disease groups and local outbreaks.

Ramping Up the Delivery of Cardiac Surgery During the COVID-19 Pandemic: A Guidance Statement From the Canadian Society of Cardiac Surgeons

The coronavirus disease 2019 (COVID-19) has had a profound global effect. Its rapid transmissibility has forced whole countries to adopt strict measures to contain its spread. As part of necessary pandemic planning, most Canadian cardiac surgical programs have prioritized and delayed elective procedures in an effort to reduce the burden on the health care system and to mobilize resources in the event of a pandemic surge. While the number of COVID-19 cases continue to increase worldwide, new cases have begun to decline in many jurisdictions. This “flattening of the curve” has inevitably prompted discussions around reopening of the economy, relaxing some public health restrictions, and resuming nonurgent health care delivery. This document provides a template for cardiac surgical programs to begin to ramp-up the delivery of cardiac surgery in a deliberate and graded fashion as the COVID-19 pandemic burden begins to ease that is guided by 3 principles. First, all recommendations from public health authorities regarding COVID-19 containment must continue to be followed to minimize disease spread, ensure patient safety, and protect health care personnel. Second, patients awaiting elective cardiac surgery need to be proactively managed, reprioritizing those with high-risk anatomy or whose clinical status is deteriorating. Finally, case volumes should be steadily increased in a mutually agreed upon fashion and must balance the clinical needs of patients awaiting surgery against the overall requirements of the health care system.

Cardiac Surgery in Canada During the COVID-19 Pandemic: A Guidance Statement From the Canadian Society of Cardiac Surgeons

On March 11, 2020, the World Health Organization declared that COVID-19 was a pandemic.¹ At that time, only 118,000 cases had been reported globally, 90% of which had occurred in 4 countries.¹ Since then, the world landscape has changed dramatically. As of March 31, 2020, there are now nearly 800,000 cases, with truly global involvement.² Countries that were previously unaffected are currently experiencing mounting rates of the novel coronavirus infection with associated increases in COVID-19–related deaths. At present, Canada has more than 8000 cases of COVID-19, with considerable variation in rates of infection among provinces and territories.³ Amid concerns over growing resource constraints, cardiac surgeons from across Canada have been forced to make drastic changes to their clinical practices. From prioritizing and delaying elective cases to altering therapeutic strategies in high-risk patients, cardiac surgeons, along with their heart teams, are having to reconsider how best to manage their patients. It is with this in mind that the Canadian Society of Cardiac Surgeons (CSCS) and its Board of Directors have come together to formulate a series of guiding statements. With strong representation from across the country and the support of the Canadian Cardiovascular Society, the authors have attempted to provide guidance to their colleagues on the subjects of leadership roles that cardiac surgeons may assume during this pandemic: patient assessment and triage, risk reduction, and real-time sharing of expertise and experiences.

How Feasible is Extracorporeal Cardiopulmonary Resuscitation in a Medium Urban Population Centre?

Background

Patients suffering from out-of-hospital cardiac arrest (OHCA) experience poor survival and neurological outcomes, with rates remaining relatively unchanged despite advancements. Extracorporeal membrane oxygenation (ECMO), termed extracorporeal cardiopulmonary resuscitation (ECPR) in arrests, may offer improved outcomes. We developed local screening criteria for ECPR and then estimated the frequency of use by applying those criteria retrospectively to a cardiac arrest database. The purpose was to determine if an ECPR program is feasible in a medium urban population centre in Atlantic Canada.

Methods

A three-round modified Delphi survey, building upon data from a literature review, was conducted in collaboration with external experts. The resulting selection criteria for potential ECPR candidates were applied to a pre-existing local cardiac arrest database, supplemented by health records review, identifying potential candidates eligible for ECPR.

Results

Consensus inclusion criteria included witnessed cardiac arrest, age <70, refractory arrest, no-flow time <10min, total downtime <60min, and presumed cardiac or selected non-cardiac etiologies. Consensus exclusion criteria were an unwitnessed arrest, asystole, and select etiologies and comorbidities. Simplified criteria were developed to facilitate emergency medical services transport. Historically, 20.0% (95% CI 16.2-24.3%) of OHCA would be transported to the Emergency Department (ED), with 4.9% (95% CI 3.0% to 7.6%) qualifying for ECPR.

Conclusion

Despite conservative estimates based upon historically small numbers of select cardiac arrest patients meeting eligibility for transport and initiation of ECPR, a dedicated program may be feasible in our regional hospital setting. Patient care volumes suggest it would not be resource intensive yet would be sufficiently busy to maintain competency.

Introduction of an Extracorporeal Cardiopulmonary Resuscitation Eligibility Protocol for Paramedics in Atlantic Canada: A Pilot Knowledge Translation Project

Introduction

There is currently no protocol for the initiation of extracorporeal cardiopulmonary resuscitation (ECPR) for out of hospital cardiac arrest (OHCA) in Atlantic Canada. Advanced care paramedics (ACPs) perform advanced cardiac life support in the prehospital setting often completing the entire resuscitation on-scene. Implementation of ECPR will present a novel intervention that is only available at the receiving hospital. Our objective is to determine if an educational program can improve identification of ECPR candidates by paramedics. Establishing paramedic competence will ensure rapid transfer of eligible patients for a potentially life-saving intervention.

Methods

An educational program was delivered to paramedics including a short seminar and pocket card coupled with simulated OHCA cases. A before-and-after study design using a case-based survey was employed. Paramedics were scored on their ability to correctly identify patients suffering OHCA who met the inclusion criteria for our ECPR protocol. A Wilcoxon matched-pairs signed rank test was employed to compare paramedics’ scores before and after the education delivery. A six-month follow-up is planned to assess retention. Qualitative data was also collected from paramedics during simulation to help identify practical issues, potential barriers, and to refine inclusion and exclusion criteria prior to the implementation of our protocol in the prehospital setting.

Results

The median score pre-education was 10 (IQR: 9-10.5) compared to 14 (IQR: 13-15) after education delivery. The median difference between groups was 5. The Wilcoxon matched-pairs test demonstrated a significant improvement in the paramedics’ ability to correctly identify ECPR candidates after completing our educational program z = -2.67, p = 0.0039.

Conclusion

Paramedic training through a didactic session coupled with a pocket card and simulation appeared to be a feasible method of knowledge translation. Six-month follow-up data will help ensure knowledge retention is achieved.

Clinical outcomes of mitral valve intervention in patients with mitral annular calcification: A systematic review and meta-analysis

BACKGROUND

Mitral valve (MV) disease with mitral annular calcification (MAC) poses a surgical challenge and the clinical outcomes of MV surgery as well as transcatheter mitral valve replacement (TMVR) remain relatively unexplored. We performed a systematic review and meta-analysis to assess the effects of MAC on clinical outcomes following MV surgery and TMVR.

METHODS

We searched MEDLINE and EMBASE databases until February 2019 for studies comparing clinical outcomes of MV surgery or TMVR in patients with and without MAC. Data were extracted by two independent investigators. Outcomes were perioperative and midterm complications and mortality.

RESULTS

Seven observational studies enrolling 2902 patients were included. MAC patients were older, more likely to be female with greater chronic lung disease and kidney failure. Perioperative mortality was similar between patients with and without MAC undergoing MV surgery (risk ratio [RR], 1.15; 95% confidence interval [CI], 0.50-2.65; P = .74). MAC was associated with a higher risk of bleeding, permanent pacemaker implantation, and periprosthetic leak. Midterm mortality was greater in MAC patients undergoing MV surgery (incident rate ratio [IRR], 1.32; 95% CI, 1.05-1.67; P = .02). MAC patients undergoing TMVR had higher perioperative (RR, 4.65; 95% CI, 2.93-7.38; P < .01) and 1-year (RR, 5.44; 95% CI, 3.49-8.49; P < .01) mortality, decreased procedural success, greater left ventricular outflow tract obstruction and need for conversion to surgery when compared with patients undergoing TMVR for dysfunction of a bioprosthetic valve or annuloplasty ring.

CONCLUSION

MV procedures in patients with MAC are associated with higher mortality and morbidity. This is largely driven by the high-risk patient profile associated with MAC. TMVR holds promise but has important limitations and should be reserved for select patients.

Mast Cells in Cardiac Fibrosis: New Insights Suggest Opportunities for Intervention

Mast cells (MC) are innate immune cells present in virtually all body tissues with key roles in allergic disease and host defense. MCs recognize damage-associated molecular patterns (DAMPs) through expression of multiple receptors including Toll-like receptors and the IL-33 receptor ST2. MCs can be activated to degranulate and release pre-formed mediators, to synthesize and secrete cytokines and chemokines without degranulation, and/or to produce lipid mediators. MC numbers are generally increased at sites of fibrosis. They are potent, resident, effector cells producing mediators that regulate the fibrotic process. The nature of the secretory products produced by MCs depend on micro-environmental signals and can be both pro- and anti-fibrotic. MCs have been repeatedly implicated in the pathogenesis of cardiac fibrosis and in angiogenic responses in hypoxic tissues, but these findings are controversial. Several rodent studies have indicated a protective role for MCs. MC-deficient mice have been reported to have poorer outcomes after coronary artery ligation and increased cardiac function upon MC reconstitution. In contrast, MCs have also been implicated as key drivers of fibrosis. MC stabilization during a hypertensive rat model and an atrial fibrillation mouse model rescued associated fibrosis. Discrepancies in the literature could be related to problems with mouse models of MC deficiency. To further complicate the issue, mice generally have a much lower density of MCs in their cardiac tissue than humans, and as such comparing MC deficient and MC containing mouse models is not necessarily reflective of the role of MCs in human disease. In this review, we will evaluate the literature regarding the role of MCs in cardiac fibrosis with an emphasis on what is known about MC biology, in this context. MCs have been well-studied in allergic disease and multiple pharmacological tools are available to regulate their function. We will identify potential opportunities to manipulate human MC function and the impact of their mediators with a view to preventing or reducing harmful fibrosis. Important therapeutic opportunities could arise from increased understanding of the impact of such potent, resident immune cells, with the ability to profoundly alter long term fibrotic processes.

Regional differences in aortic valve replacements: Atlantic Canadian experience

BACKGROUND

Transcatheter aortic valve implantation (TAVI) is evolving rapidly and is increasingly being adopted in the treatment of aortic valve disease. The goal of this study was to examine regional differences in surgical aortic valve replacement (SAVR) and TAVI across Atlantic Canada.

METHODS

We identified all patients who underwent SAVR or TAVI between Jan. 1, 2010, and Dec. 31, 2014, in New Brunswick, Nova Scotia and Newfoundland and Labrador. Data obtained included patient demographic characteristics and surgical procedure details. We performed univariate descriptive analyses and calculated crude and age- and sex-adjusted incidence rates.

RESULTS

A total of 3042 patients underwent SAVR or TAVI during the study period, 1491 in Nova Scotia, 1042 in New Brunswick and 509 in Newfoundland and Labrador. Patient demographic characteristics were similar across regions. A much higher proportion of patients in Newfoundland and Labrador (43.6%) than in Nova Scotia (4.2%) or New Brunswick (13.6%) received a mechanical versus a bioprosthetic valve. Rates of TAVI increased over the study period, with New Brunswick adopting their program before Nova Scotia (144 v. 74 procedures). Adjusted rates of all AVR procedures remained stable in Nova Scotia (40-50 per 100 000 people). Adjusted rates were lower in New Brunswick and Newfoundland and Labrador than in Nova Scotia; they increased slowly in New Brunswick over the study period.

CONCLUSION

Despite geographical proximity and similar patient demographic characteristics, there existed regional differences in the management of aortic valve disease within Atlantic Canada. Further study is required to determine whether the observed differences in age- and sex-adjusted rates of AVR may be explained by geographical disease-related differences, varying practice patterns or barriers in access to care.

Effects of remote ischemic preconditioning in high-risk patients undergoing cardiac surgery (Remote IMPACT): a randomized controlled trial

BACKGROUND

Remote ischemic preconditioning is a simple therapy that may reduce cardiac and kidney injury. We undertook a randomized controlled trial to evaluate the effect of this therapy on markers of heart and kidney injury after cardiac surgery.

METHODS

Patients at high risk of death within 30 days after cardiac surgery were randomly assigned to undergo remote ischemic preconditioning or a sham procedure after induction of anesthesia. The preconditioning therapy was three 5-minute cycles of thigh ischemia, with 5 minutes of reperfusion between cycles. The sham procedure was identical except that ischemia was not induced. The primary outcome was peak creatine kinase-myocardial band (CK-MB) within 24 hours after surgery (expressed as multiples of the upper limit of normal, with log transformation). The secondary outcome was change in creatinine level within 4 days after surgery (expressed as log-transformed micromoles per litre). Patient-important outcomes were assessed up to 6 months after randomization.

RESULTS

We randomly assigned 128 patients to remote ischemic preconditioning and 130 to the sham therapy. There were no significant differences in postoperative CK-MB (absolute mean difference 0.15, 95% confidence interval [CI] -0.07 to 0.36) or creatinine (absolute mean difference 0.06, 95% CI -0.10 to 0.23). Other outcomes did not differ significantly for remote ischemic preconditioning relative to the sham therapy: for myocardial infarction, relative risk (RR) 1.35 (95% CI 0.85 to 2.17); for acute kidney injury, RR 1.10 (95% CI 0.68 to 1.78); for stroke, RR 1.02 (95% CI 0.34 to 3.07); and for death, RR 1.47 (95% CI 0.65 to 3.31).

INTERPRETATION

Remote ischemic precnditioning did not reduce myocardial or kidney injury during cardiac surgery. This type of therapy is unlikely to substantially improve patient-important outcomes in cardiac surgery.

TRIAL REGISTRATION

ClinicalTrials.gov, no. NCT01071265.

Development of a predictive model for major adverse cardiac events in a coronary artery bypass and valve population

BACKGROUND

Quality improvement initiatives in cardiac surgery largely rely on risk prediction models. Most often, these models include isolated populations and describe isolated end-points. However, with the changing clinical profile of the cardiac surgical patients, mixed populations models are required to accurately represent the majority of the surgical population. Also, composite model end-points of morbidity and mortality, better reflect outcomes experienced by patients.

METHODS

The model development cohort included 4,270 patients who underwent aortic or mitral valve replacement, or mitral valve repair with/without coronary artery bypass grafting, or isolated coronary artery bypass grafting. A composite end-point of infection, stroke, acute renal failure, or death was evaluated. Age, sex, surgical priority, and procedure were forced, a priori, into the model and then stepwise selection of candidate variables was utilized. Model performance was evaluated by concordance statistic, Hosmer-Lemeshow Goodness of Fit, and calibration plots. Bootstrap technique was employed to validate the model.

RESULTS

The model included 16 variables. Several variables were significant such as, emergent surgical priority (OR 4.3; 95% CI 2.9-7.4), CABG + Valve procedure (OR 2.3; 95% CI 1.8-3.0), and frailty (OR 1.7; 95% CI 1.2-2.5), among others. The concordance statistic for the major adverse cardiac events model in a mixed population was 0.764 (95% CL; 0.75-0.79) and had excellent calibration.

CONCLUSIONS

Development of predictive models with composite end-points and mixed procedure population can yield robust statistical and clinical validity. As they more accurately reflect current cardiac surgical profile, models such as this, are an essential tool in quality improvement efforts.

Assessing the risk of waiting for coronary artery bypass graft surgery among patients with stenosis of the left main coronary artery

BACKGROUND

Significant controversy remains over how urgently coronary artery bypass graft surgery (CABG) should be scheduled, particularly for patients with stenosis of the left main coronary artery. Our main objective was to evaluate the safety of waiting for CABG among patients with left main coronary artery disease using a standardized triage system.

METHODS

We identified 561 consecutive patients with stenosis of the left main coronary artery who were scheduled to undergo CABG between Apr. 1, 1999, and Mar. 31, 2003. Using standardized triage criteria, patients were assigned to 1 of 4 waiting queues: "emergent," "in-hospital urgent," "out-of-hospital semi-urgent A" and "out-of-hospital semi-urgent B." Postoperative outcome measures were in-hospital death from any cause and a composite outcome measure of in-hospital death from any cause, a prolonged requirement for postoperative mechanical ventilation (> 24 h) and a prolonged postoperative hospital stay (> 9 d). Waiting-time variables included the specific queue, whether patients waited longer than the standard time established for each queue and whether patients were upgraded to a more urgent queue. Logistic regression analysis was used to identify independent predictors of the composite outcome; propensity scores (probability of being assigned to a specific queue) were entered into the model to adjust for patient variability among queues.

RESULTS

Of the 561 patients, 65 (11.6%) were assigned to the emergent group, 343 (61.1%) to the in-hospital urgent group, 91 (16.2%) to the semi-urgent A queue and 62 (11.1%) to the semi-urgent B queue. Four patients (0.7%) died while waiting for surgery. The median waiting times were as follows: emergent group, 0 days; in-hospital urgent group, 2 days; 30 days in the semi-urgent A group and 49 days in the semi-urgent B group. A total of 52 patients (9.3%) were upgraded to a more urgent queue, and 147 patients (26.2%) waited longer than the standard times for their respective queue. The overall in-hospital mortality was 5.5% (n = 31), and the composite outcome was 32.6% (n = 183). Independent predictors of the composite outcome were myocardial infarction within 7 days before surgery, preoperative renal failure, ejection fraction of less than 40%, age greater than 70 years and stenosis of left main coronary artery greater than 70%. Waiting-time variables were associated with neither a significantly higher mortality nor morbidity outcome.

INTERPRETATION

For selected patients with stenosis of the left main coronary artery, waiting for CABG did not appear to be associated with increased mortality or morbidity.

Isolated pulmonic valve endocarditis

A 61-year-old man with no known cardiac history presented with septic arthritis of the right knee secondary to group B Streptococcus. During follow-up, echocardiography revealed a 1.8 cm x 1.2 cm mobile vegetation on the pulmonary valve. Despite parenteral antimicrobial therapy, the patient developed recurrent pulmonary emboli with enlargement of the vegetative mass, necessitating surgical debridement and replacement of the pulmonary valve. A diagnosis of pulmonic valve endocarditis should be considered in the differential diagnosis of any febrile patient with multiple pulmonary emboli.

Composite arterial grafts versus conventional grafting for coronary artery bypass grafting

OBJECTIVES

Composite arterial grafts for coronary artery bypass grafting surgery allow complete arterial revascularization but are limited by the inflow of a single internal thoracic artery supplying all the grafted vessels. We reviewed the safety of composite arterial grafts using either bilateral internal thoracic arteries or a single internal thoracic artery and radial artery.

METHODS

From January 1999 to July 2002, 402 consecutive patients receiving composite grafts only were compared to a control group of patients (n = 542) undergoing coronary artery bypass grafting with internal thoracic artery and saphenous veins operated upon by the same surgeons. Two different statistical approaches were used to compare groups in this retrospective analysis. First, propensity score analysis with greedy matching technique was used to match patients from each group. Second, a multivariate analysis was performed looking at a combined patient outcome of death, intra-aortic balloon counterpulsation utilization, myocardial infarction, stroke, and prolonged ventilation on all patients in both groups.

RESULTS

After matching by propensity score, the major clinical outcomes in composite arterial (n = 249) and control (n = 249) groups were found to be similar. The in-hospital mortality in the composite group was 1.2% as compared with 0.4% in matched patients (P =.62). However, patients in the composite group were found to have a significantly longer pump time (P <.0001), longer clamp time (P <.0001), increased incidence of prolonged mechanical ventilation (12.8% vs 4.8%; P =.002), and higher incidence of combined morbidity outcome (13.6% vs 6.4%; P =.007) as compared with matched patients. Multivariable analysis showed that composite arterial grafting was an independent predictor of the combined morbidity outcome with an odds ratio of 2.1 (1.2-3.7).

CONCLUSIONS

These findings suggest that composite arterial grafting may be associated with an increase in risk-adjusted patient morbidity when compared with a conventional coronary artery bypass grafting group, although a mortality difference was not demonstrable.

Preoperative prediction of prolonged mechanical ventilation following coronary artery bypass grafting

OBJECTIVE

Few studies have attempted to evaluate who would require prolonged mechanical ventilation following heart surgery. The objectives of this study were to identify predictors of prolonged ventilation in a large group of coronary artery bypass grafting (CABG) patients from a single institution.

METHODS

One thousand, eight hundred and twenty-nine consecutive patients undergoing CABG were reviewed retrospectively and evaluated for preoperative predictors of prolonged ventilation which included: age, gender, ejection fraction (EF), renal function, diabetes, angina status, New York Heart Association Class, number of diseased vessels, urgency of the procedure, re-operation, chronic lung disease (COPD) and intraoperative variables such as IABP, inotropes, stroke and myocardial infarction. Prolonged ventilation was defined as > or = 24 h. Stepwise logistic regression analysis was performed.

RESULTS

Patients were on average 65.4+/-10.6 years of age, 30% were diabetic, 80% had triple vessel disease and 93% were of functional class III/IV. The mean ejection fraction was 60+/-16 percent. Overall peri-operative mortality was 2.7%. There were 157 patients that required prolonged ventilation with a peri-operative mortality of 18.5% (P < 0.001). Preoperative independent predictors of prolonged ventilation were found to be: unstable angina (OR 5.6), EF < 50 (OR 2.3), COPD (OR 2.0), preop. renal failure (OR 1.9), female gender (OR 1.8) and age > 70 (OR 1.7). Based on these predictors, a model was created to estimate of the risk of prolonged ventilation in individual patients following CABG with results ranging from < or = 3% in patients without any risk factors to > or = 32% in patients with five or more independent risk factors. Certain intraoperative variables were strong predictors of prolonged ventilation and included: stroke (OR 12.3), re-operation for bleeding (OR 6.9) and perioperative MI (OR 5.8).

CONCLUSION

We were able to create a stable model where several preoperative and intra-operative variables were shown to be predictive of prolonged ventilation after CABG surgery. The ability to identify patients at increased risk for prolonged ventilation may allow the development of pre-emptive strategies and more effective resource allocation.

Prevention of allograft heart valve failure in a rat model

OBJECTIVE

Allograft heart valves are commonly used in cardiac surgery. Despite mounting evidence that these valves are immunogenic, leading to premature failure, current clinical practice does not attempt to minimize or control such a response. The objective of this study was to evaluate immune modulatory approaches to ameliorate allograft valve failure in a rat model.

METHOD

Aortic valve grafts were implanted infrarenally into Lewis rat recipients (n = 32). There were 4 transplant groups: syngeneic grafts (Lewis to Lewis), untreated allografts (Brown Norway to Lewis), allograft recipients treated with cyclosporine (INN: ciclosporin) (10 mg/kg per day for 7 or 28 days), and allograft recipients treated with anti-alpha4 integrin and anti-beta2 integrin monoclonal antibodies for 7 days. At 7 and 28 days the valves were examined for structural integrity and cellular infiltration.

RESULTS

Both cyclosporine and anti-alpha4/beta2 integrin treatment resulted in significant reduction in leaflet infiltration by macrophages (ED1(+)), T cells (CD3(+)), and CD8(+) T cells at 7 days with preservation of structural integrity when compared with control allografts. Twenty-eight days after implantation, daily treatment with cyclosporine preserved leaflet structural integrity and inhibited cellular infiltration. However, a short course of cyclosporine (7 days) failed to prevent destruction of the valves at 28 days.

CONCLUSIONS

Immune modulatory approaches aimed at T-cell activation or trafficking decrease leaflet cellular infiltration and prevent allograft valve structural failure. However, short-course therapy does not appear to be sufficient and must be maintained to allow long-term preservation of leaflet structural integrity (28 days).

Myocardial scintigraphy correlates poorly with coronary angiography in the screening of transplant arteriosclerosis

BACKGROUND

Coronary angiography remains an important screening tool for transplant coronary arteriosclerosis (TxCAD) after heart transplantation despite criticism that it underestimates the incidence of TxCAD. In an effort to improve TxCAD incidence estimation, several methods of screening have been proposed. In the present study, the incidence of TxCAD assessed by both yearly coronary angiography and stress myocardial scintigraphy imaging was reviewed.

PATIENTS AND METHODS

Ninety-nine consecutive primary heart transplantations were performed from 1988 to 1999. The standard immunosuppression protocol consisted of the introduction of antilymphocyte globulin and steroids, while maintenance therapy was with cyclosporine, imuran and steroids. Coronary angiography and a stress 2-methoxyisobutyl-isonitrile perfusion scan were performed yearly. TxCAD was defined by angiographic evidence of luminal abnormality by catheterization, or a perfusion abnormality at rest or after stress on myocardial scintigraphy.

RESULTS

The mean recipient age was 49+/-12 years and the mean donor age was 33+/-13 years. The etiology of heart failure was ischemic cardiomyopathy (50%), dilated cardiomyopathy (41%) and congenital heart disease (9%). The freedom from angiographic TxCAD was 92% at one year, 64% at five years and 35% at eight years. The freedom from nuclear imaging TxCAD was 92% at one year, 69% at five years and 44% at eight years. However, a diagnosis of TxCAD by angiography only correlated with a diagnosis of TxCAD by nuclear imaging 52.8% of the time in the same patient, with a median time between studies of one month.

CONCLUSION

The overall incidence of TxCAD diagnosed by angiography and nuclear imaging appears similar but correlates poorly in patients, casting doubt on the routine use of myocardial scintigraphy for screening TxCAD.

Aortic valve graft implantation in rats: a new functional model

BACKGROUND

Allograft heart valves used in cardiac surgery often fail at an unacceptable rate. Immune mechanisms contribute to this failure, but adequate and functional small-animal valve models to characterize this phenomenon are lacking. The objective of this study was to create native aortic valve insufficiency in recipient rats to provide for a functional abdominal aortic valve graft implant.

METHODS

Lewis recipient rats underwent single-leaflet injury of their native aortic valve through a right carotid catheter injury. Animals were allowed to recover for 28 days, at which time a Lewis aortic valve graft was implanted infrarenally. Echocardiography with color flow Doppler scanning was performed before aortic injury, 1 week after aortic injury, and after abdominal implantation of a valve graft in animals with native aortic insufficiency.

RESULTS

After aortic valve injury, all animals had moderate-to-severe aortic insufficiency with a significant increase in diastolic and systolic left ventricular dimensions. Color flow Doppler scanning revealed diastolic aortic flow reversal from the aortic valve extending to the infrarenal abdominal aorta. Aortic valve grafts were then implanted infrarenally in animals with created aortic valve insufficiency and resulted in 100% patency and preservation of leaflets at 4 weeks after implantation. Leaflet motion of the abdominal graft was visualized by means of M-mode echocardiography.

CONCLUSION

Compensated native aortic insufficiency results in aortic diastolic flow reversal distal to the infrarenal aorta, thus allowing normal motion of the infrarenal allograft leaflets. This functional model will provide an opportunity to investigate the role of immunologic valve injury in the failure of valve allografts.

CD8+ T lymphocytes mediate destruction of the vascular media in a model of chronic rejection

Allograft arteriosclerosis is an important characteristic of chronic graft rejection. In allograft arteriosclerosis there is a striking loss of medial smooth muscle cells (SMCs) before the development of a concentric intimal proliferative response. In this study we evaluated the role of CD8+ T lymphocytes in this medial SMC loss. Brown Norway aortic segments were transplanted into Lewis animals for 60 days (long allo-exposure) or 20 days (short allo-exposure). After 20 days allogeneic exposure aortic segments were transplanted back into syngeneic (Brown Norway) animals for 40 days. Experimental animals were treated with mAb to CD8. Apoptosis was measured by terminal dUTP nick-end labeling at 20 days and morphometry analyzed at 60 days to evaluate medial and intimal changes. Anti-CD8 treatment significantly lowered CD8+ T cell counts in peripheral blood, reduced medial SMC apoptosis at 20 days, and increased medial SMC counts at 60 days. Both short- and long-allogeneic exposure groups confirmed these findings and demonstrated that medial SMC loss is proportional to the length of allogeneic exposure. Antibody depletion of CD8+ T cells results in reduced medial SMC apoptosis and better medial SMC preservation. This supports the hypothesis that medial SMC loss occurs by apoptotic death and is driven by CD8+ T lymphocytes.

Ten-year heart transplantation experience at the MARITIME HEART CENTER: does volume affect results?

OBJECTIVE

To evaluate the experience of a small volume Canadian heart transplantation centre.

DESIGN

Ninety-four consecutive primary heart transplants were performed from 1988 to 1998 at the Maritime Heart Center, Halifax, Nova Scotia, with 100% follow-up. Kaplan-Meier survival analysis was used.

RESULTS

The mean recipient age was 48.5+/-12.3 years and donor age 33+/-13.2 years. Eighty per cent of recipients were men. The prevalence of elevated pulmonary vascular resistance (4 or more Wood units) was 20.2%. Etiology of heart failure was ischemic cardiomyopathy (50%), dilated cardiomyopathy (40.9%) and congenital heart disease (9.1%). Survival was 85.9% at one year (n=71), 75.3% at five years (n=33) and 60.5% at eight years (n=8). There was a trend toward survival benefit with human leukocyte antigen (HLA) -DR matching, body mass index ratio of donor to recipient greater than 0.8, ischemic time less than 90 mins and male donors. There was no effect on survival with donor or recipient age, recipient sex, diabetes, hypertension, hypercholesterolemia, elevated pulmonary vascular resistance and HLA-A/B mismatch.

CONCLUSIONS

Excellent survival at one and five years following heart transplantation is reported that compares favourably with results published by the International Society for Heart and Lung Transplantation.

Avoiding hyperoxemia at the start of cardiopulmonary bypass while optimizing gas flow and temperature

There seems to be a wide range of practice in relation to the optimum oxygen setting before, and at the start of, cardiopulmonary bypass. Even manufacturers of blood oxygenators vary in their suggestions for this phase of extracorporeal circulation. Most of these suggestions are based on peak performance, Association for the Advancement of Medical Instrumentation (AAMI) standards, experience, and legal considerations. Therefore, suggested gas:blood flow ratios will vary from no gas flow at the start of bypass, to a ratio setting of 1:1. On the other hand, suggested inspired oxygen concentrations will generally vary between 0.80 to 1.0 at the start of cardiopulmonary bypass. In regard to perfusate temperatures before going on bypass, there are no clearly defined standards other than those of clinical preference. The manufacturer of the oxygenator used in this study clearly states in the operating instructions that gas flow should be proportional to blood flow at the start of bypass, and gas flow should be turned off when there is no fluid flow through the oxygenator. The presence of hyperoxic perfusates and wide patient/perfusate temperature gradients at the start of bypass has been suspected in the appearance of gaseous microemboli during this critical period. Hyperoxemia during the bypass period is also implicated in the introduction of oxygen free radicals and nitric oxide into the hypoxic myocardium during cardioplegia delivery. Presented here are the results of a randomized clinical study involving 39 adult patients undergoing cardiopulmonary bypass for the surgical treatment of coronary artery disease. All patients were randomly selected into five groupings. The first group had 1 L of gas flow through the perfusate before bypass, and bypass was then started with an FIO2 of 0.80. The second two groups had no gas flow through the perfusate prior to bypass and a starting FIO2 of 0.21. Groups 4 and 5 had 1 L of gas flowing through the perfusate and a starting FIO2 of 0.21. Results indicate that gas flow through Normosol R/Albumin perfusates will prevent the acidosis that is found in this solution when the system is previously flushed with carbon dioxide. Also, suggested high FIO2 settings will produce hyperoxic perfusates at the start of cardiopulmonary bypass. However, the use of an FIO2 of 0.21 at the start of bypass will produce normoxemic conditions that are both safe and reliable for the conduct of initiating cardiopulmonary bypass.