When cheating turns into a stabilizing mechanism of plant-pollinator communities.

Mutualistic interactions, such as plant-mycorrhizal or plant-pollinator interactions, are widespread in ecological communities and frequently exploited by cheaters, species that profit from interactions without providing benefits in return. Cheating usually negatively affects the fitness of the individuals that are cheated on, but the effects of cheating at the community level remains poorly understood. Here, we describe 2 different kinds of cheating in mutualistic networks and use a generalized Lotka-Volterra model to show that they have very different consequences for the persistence of the community. Conservative cheating, where a species cheats on its mutualistic partners to escape the cost of mutualistic interactions, negatively affects community persistence. In contrast, innovative cheating occurs with species with whom legitimate interactions are not possible, because of a physiological or morphological barrier. Innovative cheating can enhance community persistence under some conditions: when cheaters have few mutualistic partners, cheat at low or intermediate frequency and the cost associated with mutualism is not too high. Under these conditions, the negative effects of cheating on partner persistence are overcompensated at the community level by the positive feedback loops that arise in diverse mutualistic communities. Using an empirical dataset of plant-bird interactions (hummingbirds and flowerpiercers), we found that observed cheating patterns are highly consistent with theoretical cheating patterns found to increase community persistence. This result suggests that the cheating patterns observed in nature could contribute to promote species coexistence in mutualistic communities, instead of necessarily destabilizing them.

Efficacy of maintaining low-tidal volume mechanical ventilation as compared to resting lung strategy during coronary artery bypass graft cardiopulmonary bypass surgery: A post-hoc analysis of the MECANO trial.

STUDY OBJECTIVE: To compare a low-tidal-volume with positive end-expiratory pressure strategy (VENT strategy) to a resting-lung-strategy (i.e., no-ventilation (noV) strategy) during cardiopulmonary bypass for coronary artery bypass graft surgery on the incidence of postoperative pulmonary complications. DESIGN: Post-hoc analysis of the MECANO trial which was a prospective single-center, blind, randomized, parallel-group controlled trial. SETTING: Tertiary care cardiac surgery center. PATIENTS: Patients who underwent isolated on-pump coronary bypass surgery were randomized either to VENT or noV group. INTERVENTION: During the cardiopulmonary bypass phase of the cardiac surgery procedure, mechanical ventilation in the VENT group consisted of a tidal volume of 3 mL/kg, a respiratory rate of 5 per minute and a positive end-expiratory pressure of 5 cmH2O. Patients in the noV group received no ventilation during this phase. MEASUREMENTS: Primary composite outcome combining death, early respiratory failure, ventilation support beyond day 2 and reintubation. MAIN RESULTS: In this post-hoc analysis, we retained 725 patients who underwent isolated CABG surgery, from the 1501 patients included in the original study. There were 352 in the VENT group and 373 patients in the noV group. Post-hoc comparison yielded no differences in baseline characteristics between these two groups. The primary outcome occurred less frequently in the VENT group than in the noV group, with 44 (12.5%) and 76 (20.4%) respectively (odds-ratio (OR) = 0.56 (0.37-0.84), p = 0.004). There were fewer early respiratory dysfunctions and prolonged respiratory support in the VENT group (respectively, OR = 0.34 (0.12-0.96) p = 0.033 and OR = 0.51 (0.27-0.94) p = 0.029). Complications related to mechanical ventilation were similar in the two groups. CONCLUSIONS: In this post-hoc analysis, maintaining low-tidal ventilation compared to a resting-lung strategy was associated with fewer pulmonary postoperative complications in patients who underwent isolated CABG procedures.

Efficacy of parasternal block to decrease intraoperative opioid use in coronary artery bypass surgery via sternotomy: a randomized controlled trial.

OBJECTIVE: This study aims to assess the effect of a preoperative parasternal plane block (PSB) on opioid consumption required to maintain hemodynamic stability during sternotomy for coronary artery bypass graft surgery. METHODS: This double-blind, randomized, placebo-controlled trial prospectively enrolled 35 patients scheduled for coronary artery bypass graft surgery under general anesthesia with propofol and remifentanil. Patients were randomized to receive preoperative PSB using either ropivacaine (PSB group) or saline solution (placebo group) (1:1 ratio). The primary endpoint was the maximal effect-site concentration of remifentanil required to maintain heart rate and blood pressure within the recommended ranges during sternotomy. RESULTS: Median maximum concentration of remifentanil necessary to maintain adequate hemodynamic status during sternotomy was significantly reduced in PSB group (4.2 (2.5-6.0) ng/mL) compared with placebo group (7.0 (5.2-8.0) ng/mL) (p=0.02). Mean maximum concentration of propofol used to control depth of anesthesia was also reduced (3.9±1.1 µg/mL vs 5.0±1.5 µg/mL, PSB vs placebo, respectively; p=0.02). This reduction in propofol consumption during sternotomy enabled a more adequate level of sedation to be maintained in patients (minimum patient state index was 11.7±8.7 in placebo group and 18.3±6.8 in PSB group; p=0.02). PSB reduced postoperative inflammatory response by limiting concentrations of proinflammatory cytokines IL-8, IL-18, IL-23, IL-33 and MCP-1 measured in the first 7-day after surgery (p<0.05). CONCLUSIONS: Preoperative PSB reduced the maximum concentrations of remifentanil and propofol required to maintain hemodynamic stability and depth of anesthesia during sternotomy. TRIAL REGISTRATION NUMBER: NCT03734159.Sébastien Bloc, M.D.1,2; Brieuc P. Pérot, Ph.D.3; Hadrien Gibert, M.D.1; Jean-Dominique Law Koune, M.D.1; Yannick Burg, M.D.1; Didier Leclerc, M.D.1; Anne-Sophie Vuitton, M.D.1; Christophe De La Jonquière, M.D.1; Marine Luka, L.S.3; Thierry Waldmann, M.D.4; Nicolas Vistarini, M.D.4; Stéphane Aubert, M.D.4; Mickaël M. Ménager, Ph.D.3; Messaouda Merzoug, Ph.D.2; Cécile Naudin, Ph.D.2; Pierre Squara, M.D.2,5.

Low Tidal Volume Mechanical Ventilation Against No Ventilation During Cardiopulmonary Bypass in Heart Surgery (MECANO): A Randomized Controlled Trial.

BACKGROUND: Postoperative pulmonary complications are common after cardiac surgery and have been related to lung collapse during cardiopulmonary bypass (CPB). No consensus exists regarding the effects of maintaining mechanical ventilation during CPB to decrease these complications. RESEARCH QUESTION: To determine whether maintaining low-tidal ventilation (3 mL/kg 5 times/min, with positive end expiratory pressure of 5 cm H2O) during CPB (ventilation strategy) was superior to a resting-lung strategy with no ventilation (no ventilation strategy) regarding postoperative pulmonary complications, including mortality. STUDY DESIGN AND METHODS: In a randomized controlled trial, patients undergoing cardiac surgery at a single center from May 2017 through August 2019 were randomized to the ventilation or no ventilation strategy during CPB (1:1 ratio). Apart from the CPB phase, perioperative ventilation procedures were standardized. RESULTS: The study included 1,501 patients (mean age, 68.8 ± 10.3 years; 1,152 (76.7%) men; mean EuroSCORE II, 2.3 ± 2.7). Seven hundred fifty-six patients were in the ventilation strategy group, and no differences existed in baseline characteristics and types of procedures between the two groups. An intention-to-treat analysis yielded no significant difference between the ventilation and no ventilation groups regarding incidence of the primary composite outcome combining death, early respiratory failure, ventilation support beyond day 2, and reintubation, with 112 of 756 patients (14.8%) in the ventilation group vs 133 of 745 patients (17.9%) in the no ventilation group (OR, 0.80; 95% CI, 0.61-1.05; P = .11). Strict per-protocol analyses of 1,338 patients (89.1%) with equally distributed preoperative characteristics yielded similar results (OR, 0.81; 95% CI, 0.60-1.09; P = .16). Post hoc analysis of the subgroup who underwent isolated coronary artery bypass graft procedures (n = 725) showed that the ventilation strategy was superior to the no ventilation strategy regarding the primary outcome (OR, 0.56; 95% CI, 0.37-0.84; P = .005). INTERPRETATION: Among patients undergoing cardiac surgery with CPB, continuation of low tidal volume ventilation was not superior to no ventilation during CPB with respect to postoperative complications, including death, early respiratory failure, ventilation support beyond day 2, and reintubation. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT03098524; URL: www.clinicaltrials.gov.

Low tidal volume mechanical ventilation against no ventilation during cardiopulmonary bypass heart surgery (MECANO): study protocol for a randomized controlled trial.

BACKGROUND: Postoperative pulmonary complications are a leading cause of morbidity and mortality after cardiac surgery. There are no recommendations on mechanical ventilation associated with cardiopulmonary bypass (CPB) during surgery and anesthesiologists perform either no ventilation (noV) at all during CPB or maintain low tidal volume (LTV) ventilation. Indirect evidence points towards better pulmonary outcomes when LTV is performed but no large-scale prospective trial has yet been published in cardiac surgery. DESIGN: The MECANO trial is a single-center, double-blind, randomized, controlled trial comparing two mechanical ventilation strategies, noV and LTV, during cardiac surgery with CPB. In total, 1500 patients are expected to be included, without any restrictions. They will be randomized between noV and LTV on a 1:1 ratio. The noV group will receive no ventilation during CPB. The LTV group will receive 5 breaths/minute with a tidal volume of 3 mL/kg and positive end-expiratory pressure of 5 cmH2O. The primary endpoint will be a composite of all-cause mortality, early respiratory failure defined as a ratio of partial pressure of oxygen/fraction of inspired oxygen <200 mmHg at 1 hour after arrival in the ICU, heavy oxygenation support (defined as a patient requiring either non-invasive ventilation, mechanical ventilation or high-flow oxygen) at 2 days after arrival in the ICU or ventilator-acquired pneumonia defined by the Center of Disease Control. Lung recruitment maneuvers will be performed in the noV and LTV groups at the end of surgery and at arrival in ICU with an insufflation at +30 cmH20 for 5 seconds. Secondary endpoints are those composing the primary endpoint with the addition of pneumothorax, CPB duration, quantity of postoperative bleeding, red blood cell transfusions, revision surgery requirements, length of stay in the ICU and in the hospital and total hospitalization costs. Patients will be followed until hospital discharge. DISCUSSION: The MECANO trial is the first of its kind to compare in a double-blind design, a no-ventilation to a low-tidal volume strategy for mechanical ventilation during cardiac surgery with CPB, with a primary composite outcome including death, respiratory failure and postoperative pneumonia. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03098524 . Registered on 27 February 2017.

First experimental use of magnets in cardiac valve repair.

BACKGROUND AND AIM OF THE STUDY: Valve repair is currently performed to treat mitral regurgitation, but aortic valve repair remains a surgical challenge. In contrast, aortic valve replacement leads to complications and constraints on the patients' quality of life and valve durability. The mechanisms that produce malcoaptation of the aortic leaflets, with resultant insufficiency, are mainly due to prolapse or retraction of the leaflets. Thus, a new strategy has been proposed to correct valvular insufficiency, using magnetic force. METHODS: Low-profile permanent magnets were implanted in seven sheep, under cardiopulmonary bypass (CPB), through a transverse aortotomy, and maintained in place for three months. No aortic insufficiency was created in these first experiments. Two-dimensional color Doppler echocardiography was used to assess the function and safeguarding of the aortic valve. Blood samples were withdrawn to assess hemolysis, and histopathologic examinations performed at necropsy. RESULTS: Direct implantation of the three permanent magnets was possible in all seven animals, but the surgical procedure resulted in major complications in three cases. Only five animals could be weaned from CPB, and only four survived the procedure at three months. One magnet was also shown to have migrated postoperatively. Echocardiography confirmed the stability of the aortic leaflet contours. The biocompatibility of the implanted magnets (i.e., absence of hemolytic reaction) was found to be satisfactory, without a need for postoperative anticoagulation. CONCLUSION: The use of magnetic force to correct valvular insufficiency has not previously been reported, and is an interesting field of investigation. Whilst these experiments are at an early stage of development, future changes in magnet design and surgical approach are indicated.

Is an anterior mitral leaflet prolapse still a challenge?

Quadrangular resection is the gold standard in the treatment of posterior leaflet prolapse. Anterior leaflet prolapse has been considered a more challenging problem; several techniques are available to treat it, all with the same goal - mitral valve competency. Nowadays, good long-term results are reported, similar to those for posterior leaflet prolapse. Certain improvements may explain these results, especially improvements in transesophageal echocardiography (including three-dimensional echocardiography), which allow the detection of atypical mitral regurgitation and its mechanism.

Extra-corporeal membrane oxygenation temporary support for early graft failure after cardiac transplantation.

OBJECTIVE: Early graft failure (EGF) is a major risk for death after heart transplantation. We studied the impact of an extra-corporeal membrane oxygenation (ECMO) temporary support on the operative mortality and the mean-term survival after EGF. MATERIALS AND METHODS: Between January 2000 and December 2006, 394 patients underwent orthotopic heart transplantation at our institution. EGF was observed in 90 (23%) patients. Fifty-four patients (14%) were treated with ECMO support, eight (2%) with other assisting devices, and 28 (7%) received maximal inotropic drug support only. RESULTS: The overall mortality was 21% (83 patients). EGF was a major risk for death: 13% (35 patients) without EGF versus 58% (49 patients) with EGF, p<0001. Among patients supported with ECMO, 36 (67%) were weaned from the assisting device and 27 (50%) were discharged from the hospital. Overall survival was 73% at 1 year and 66% at 5 years. Absence of EGF improved long-term survival: 78% at 1 year and 70% at 5 years without EGF versus 37% at 1 year and 35% at 5 years with EGF. Patients treated with ECMO have the same 1-year conditional survival as patients not having suffered EGF: 94% at 3 years. CONCLUSIONS: ECMO support is a reliable therapeutic option in severe EGF after cardiac transplantation; furthermore, patients treated with ECMO have the same 1-year conditional survival as patients not having suffered EGF.

Gaping cleft or commissure--an under-rated cause of residual mitral insufficiency following valve repair: case reports.

Naturally occurring clefts in the posterior leaflet of the mitral valve and/or the mitral commissures themselves may become the foci of residual mitral regurgitation when distorted by an adjacent rigid suture line. Herein are reported the details of three cases in which cleft/commissure closure resolved such leaks. The anatomical substrate which predisposed to this problem is also discussed.

Revisiting the localisation of Zn(2+) cations sorbed on pathological apatite calcifications made through X-ray absorption spectroscopy.

The role of oligo-elements such as Zn in the genesis of pathological calcifications is widely debated in the literature. An essential element of discussion is given by their localisation either at the surface or within the Ca apatite crystalline network. To determine the localisation, X-ray absorption experiments have been performed at SOLEIL. The Exafs results suggest that Zn atoms, present in the Zn(2+) form, are bound to about 4 O atoms at a distance of 2.00 A, while the interatomic distance R(CaO) ranges between 2.35 A and 2.71 A. Taking into account the content of Zn (around 1000 ppm) and the difference in ionic radius between Zn(2+) (0.074 nm) and Ca(2+) (0.099 nm), a significant longer interatomic distance would be expected in the case of Zn replacing Ca within the apatite crystalline network. We thus conclude that Zn atoms are localised at the surface and not in the apatite nanocrystal structure. Such structural result has essential biological implications for at least two reasons. Some oligoelements have a marked effect on the transformation of chemical phases, and may modify the morphology of crystals. These are both major issues because, in the case of kidney stones, the medical treatment depends strongly on the precise chemical phase and on the morphology of the biological entities at both macroscopic and mesoscopic scales.

A simplified surgical approach for aortic valve replacement after previous coronary artery bypass grafting.

Aortic valve replacement (AVR) in patients who have undergone previous coronary artery bypass grafting (CABG) is a challenging redo surgery. We undertook this study to evaluate the early and late outcomes of patients operated upon using a simplified surgical approach. Between January 2001 and December 2005, 2238 patients underwent AVR in our institution. We reviewed retrospectively the 57 patients who had AVR following previous CABG. All patients underwent cardiopulmonary bypass with a mild-to-moderate systemic hypothermia (mean temperature: 29.7 +/- 2.5 degrees C). Patent internal thoracic artery (IMA) grafts were never dissected, controlled or clamped. A mechanical or biological prosthesis was implanted considering the patient's age. The mean cardiopulmonary bypass (CPB) time was 93 +/- 29 min (median: 80 min, range: 43-244 min) and the mean aortic cross-clamp (AoX) time was 63 +/- 18 min (median: 59 min, range: 31-125 min). The early mortality was 10.5% and the late mortality was 9.8% (mean follow-up time: 38 months). The survival was 81% at 5 years and the freedom from major cardiac events was 77%. In conclusion, from our experience, the operating quickness and a simplified approach ('open IMA technique', anterograde cardioplegia, mild-to-moderate hypothermia and minimal dissection of the mediastinal structures) represent two fundamental choices to perform this type of surgery easily, safely and with optimal results.

Paracorporeal pulsatile biventricular assist device versus extracorporal membrane oxygenation-extracorporal life support in adult fulminant myocarditis.

OBJECTIVE: Biventricular assist device support with a paracorporeal pulsatile device is known to be an efficient bridge to recovery for patients with fulminant myocarditis-related cardiogenic shock. Whether these patients can be as efficiently supported with femorofemoral extracorporeal membrane oxygenation remains unclear. METHODS: From 2001 to 2006, 11 patients were referred to our cardiac surgery department for fulminant myocarditis-related cardiogenic shock. The first 5 patients (mean age, 32 +/- 2 years) were supported with a biventricular assist device (Thoratec, Pleasanton, Calif; group I), whereas the remaining patients (40 +/- 4 years) were supported with femorofemoral extracorporeal membrane oxygenation (group II). Preimplantation probability of death was calculated by using the APACHE II score, which was 11 +/- 9 in group I versus 24 +/- 18 in group II. RESULTS: One patient in each group died while receiving support. In group I the death occurred after 18 days of support in a patient who had 45 minutes of external resuscitation before biventricular assist device implantation. In group II a patient who remained unstable during extracorporeal membrane oxygenation was switched to a biventricular assist device 13 days later and eventually died of tamponade after 45 days. All other patients were weaned from the device after a mean duration of support of 21 +/- 5 days in group I versus 13 +/- 4 days in group II. At hospital discharge, the mean ejection fraction was 45% +/- 5% in both groups, and at 6 months' follow-up, it was 65% and 75%, respectively, in groups I and II. CONCLUSION: In our experience extracorporeal membrane oxygenation is as efficient as use of a biventricular assist device as a bridge to recovery for patients with fulminant myocarditis-related cardiogenic shock and facilitates renal and hepatic recovery on support.

Circumflex coronary artery injury following mitral annuloplasty treated by emergency angioplasty.

Iatrogenic injury to the circumflex coronary artery following mitral annuloplasty is a potentially fatal complication. It can be clinically silent or else be responsible for a cardiogenic shock. The diagnosis should be suspected on EKG changes with segmental dysfunction of the lateral wall on the intraoperative echography. The author reports one case whose recognition relied on emergency angiography; the patient was successfully treated by angioplasty and stenting. The management of this complication remains controversial and the various treatment modalities are discussed.

[Cardiac transplantation in 2008]. / La transplantation cardiaque en 2008.

The number of heart transplants in France has begun to increase again in the past few years, albeit slowly. Indications for transplants must be discussed on a case-by-case basis and no contraindication should be considered absolute. Heart transplant results have not been modified by the expansion of the selection criteria for donors. The "super-urgent" list makes it possible to provide transplants for the patients at highest risk of imminent death, with encouraging results. The repercussions of "super-urgent" transplants must be analyzed regularly. Quality of life must be taken into account in the analysis of heart transplant results, just like survival. New circulatory assist devices can be offered to some patients as an alternative to transplantation.

A safe option to perform an apparent difficult redo surgery.

A 50-year-old female operated of Bentall five years before was referred to our hospital for an aneurysm of both right subclavian artery and brachiocephalic trunk associated with a false anastomotic aneurysm on the insertion of the left coronary artery. The procedure was performed under moderate hypothermic circulatory arrest; the false aneurysm was repaired, the brachiocephalic trunk and the subclavian aneurysm were resected, an aorto-carotid and axillary bypass were finally performed. The postoperative course was uneventful. She was discharged to home on postoperative day 7. At six-month follow-up, she was still asymptomatic.

Surgery for infective endocarditis on mitral annulus calcification.

BACKGROUND AND AIM OF THE STUDY: The study aim was to assess the characteristics of bacterial endocarditis complicating mitral annulus calcification, and to evaluate the surgical results. METHODS: Twenty-four patients (mean age 64 years) underwent surgery for mitral insufficiency secondary to mitral endocarditis with annulus calcification (acute, n = 18; healed, n = 6). Surgery was performed as an emergency in seven cases for septic (n = 3) or cardiogenic (n = 4) shock. An aortic prosthesis had previously been placed in three cases. Comorbidities noted included chronic renal insufficiency/dialysis (n = 8), cancer (n = 6), coronary disease (n = 6), and obstructive cardiomyopathy (n = 1). Nine patients suffered an embolic complication, such as stroke (n = 7, of which three had coma), splenic (n = 3), or lower limb (n = 1). The microorganism present was identified as Staphylococcus aureus (n = 9), Streptococcus/ Enterococcus sp. (n = 12), or others (n = 3). The left atrial diameter was 48 mm, the ejection fraction 63%, and the septal thickness 13 mm. RESULTS: The mean severity score of annulus calcifications (range: 1 to 5) was 1.9. The anatomical lesions included: vegetations (n = 16, of which eight were > 10 mm), leaflet perforation (n = 9), chordae rupture (n = 9), aortic abscess (n = 2) and mitral annular abscess (n = 9), and one fistulation into the pericardium. The valve was repaired in 15 cases, and replaced in nine (seven bioprostheses, two mechanical). Associated procedures included aortic valve replacement (n = 7) and coronary artery bypass (n = 3). The in-hospital mortality was 29% (n = 7); all patients who died were operated on during the acute phase. All patients who presented with septic shock or coma died. After a mean follow up of 46 months, six patients had died (overall survival was 46% at 33 months), and 11 were in NYHA class I/II. One recurrence of endocarditis was treated medically. CONCLUSION: Bacterial endocarditis complicating mitral annulus calcification has a poor prognosis due to the frequent comorbidity and severity of the infectious complications. Patients in septic shock or coma do not appear to be suitable candidates for surgery. Valve repair was possible in two-thirds of the present patients; otherwise, a bioprosthetic replacement was the option of choice.