MCS XXXX-XXXX XXXX-XXXX Mechanical Circulatory Support Vol. 2, No. 0, March 2011, pp. 1–3 sici xxx PUBMED Abbreviation GiuseppeRescigno

*Giuseppe Rescigno, SOD Cardiochirurgia, Presidio Lancisi, Ospedali Riuniti di Ancona, Via Conca 71, 60020 Ancona, Italy

CarloAratari MarcoL. S.Matteucci FrancescoMassi FilippoCapestro AlessandroD'Alfonso LuciaTorracca Department of Cardiac Surgery Ospedali Riuniti di Ancona

AnconaItaly

Mechanical Circulatory Support CLINICAL RESEARCH ARTICLE Left ventricle venting during ECMO support Extracorporeal membrane oxygenation (ECMO) represents a temporary cardiac assist device. One important drawback of ECMO is related to the fact that inflow comes from the right heart and left ventricle unloading may be incomplete. Left venting is a possible solution that may be performed through apical cannulation. We present our technique management through the left ventricular venting apex. Keywords Extracorporeal membrane oxygenation (ECMO) may be considered a temporary short-term cardiac assist device 1. ECMO support may be useful in different conditions as postcardiotomy heart failure, acute heart failure due to myocarditis, severe myocardial ischemia, and so on. ECMO is particularly indicated when a sternotomy is not already present, allowing peripheral cannulation that may be done even at bedside. One of the main limitations of ECMO is related to the fact that blood drainage is performed on the right side of the heart; it has been clearly demonstrated that this does not achieve a full biventricular bypass and adequate decompression of the left ventricle 2. An excessively high LV pressure determines subendocardial ischemia and impairs LV recovery. This is extremely important in case of even mild aortic regurgitation or in the presence of a mechanical aortic valve. One option, in case of central cannulation, is to insert a standard LV venting catheter through the right superior pulmonary vein. However, when ECMO is established through a peripheral approach, there are several possible solutions to achieve LV decompression 345678. One of these is to directly cannulate the LV through the apex by means of a left minithoracotomy (9, 10). We have used this technique in three cases with good results. Insertion of a large cannula allows an effective drainage of the LV. However, this may create a shunt that reduces the true ECMO output. A simple mathematical formula may be used to calculate relative flow from the vent and modulate LV drainage accordingly in order to avoid this drawback. Transthoracic echo is used in order to precisely locate the LV apex on chest surface. Therefore, a minithoracotomy is performed accordingly. Cannulation is performed through the LV apex by means of a 28 Fr cannula (DLP, Medtronic Inc. Minneapolis, MN), originally designed for caval drainage in standard CPB. Hemostasis is obtained by two pledgetted purse string sutures. After careful air purging, the cannula is subsequently connected to a 3/8-inch line that joins the venous inflow of the ECMO device. The ECMO support is therefore started in a standard fashion, reaching the complete assist flow assessed by transesophageal echocardiography (Table 1). When the system is stabilized, three different blood samples are harvested: one from the left venting line, one from the femoral venous line as close as possible to the cannula itself, and the last from the ECMO inflow just proximal to the centrifugal head. The ECMO set-up as well as the blood sample sites is depicted in Fig. 1. By means of oxygen content values of the three samples, it is possible to calculate the percentage of incoming flow from the LV venting line and from the venous line (see formula in Fig. 2). Therefore, by partial clamping of the LV venting line and checking the LV decompression on transesophageal echo it is possible to optimize LV venting without creating excessive shunt. During ECMO weaning, venting line clamping may be increased observing the effect on hemodynamic parameters. Cannula removal is therefore easily accomplished.

ECMO venting setup and blood sample sites

Our personalized formula to estimate the percentage of flow coming from left ventricle and venous line

Patient no. BSA m² Inflow cannula Outflow cannula ECMO Flow l/min FiO₂ l/min O₂ l Mean BP mmHg Mean PAP mmHg 1 1.86 24 Fr Aortic Terumo Sarns 23 Fr Femoral Medtronic Biomedicus 4.4 0.7 3.0 70 12 2 1.67 20 Fr Femoral A. Medtronic EOPA 21 Fr Femoral V. Medtronic Biomedicus 4.0 0.65 2.0 75 11 3 2.04 20 Fr Femoral A. Medtronic EOPA 19 Fr Femoral V. Biomedicus 4.7 0.75 3.0 73 13 Ventricular assist devices are the only option in the surgical armamentarium when heart function is severely compromised and recovery cannot be achieved by standard clinical means. Among these supports, ECMO represents an effective, easy to manage, and relatively low-cost choice 1. There are well-known limitations represented by the short-term nature of its support, requiring weaning in a few weeks or shift to another assist device. Another drawback is related to the incomplete unloading of the LV; this may be overcome by direct venting of the LV through a minithoracotomy as previously described by others 10, or by alternative methods such as direct cannulation of the left atrium, trans-septal left atrial cannulation 1112, retrograde trans-aortic LV venting 13, or venting through the pulmonary artery by several devices 1415. Our technique may be performed in the operating room but it is feasible also at bedside in the Intensive care Unit (ICU), thus avoiding patient displacement. We have decided to use a large 28 Fr cannula instead of the classical 20 Fr LV venting catheter in order to gain the maximal discharging effectiveness. Line clamping can, therefore, be used to limit venting to the desired level. In our opinion, this technique is simpler than other endovascular alternatives requiring X-ray procedures. However, either shunting avoidance or proper weaning need a precise protocol of LV venting tapering by partial clamping of the venting line tube. Accurate venting is controlled by echo assessment and O₂ content values as described. In our limited experience, this adjunct has allowed an easier and faster recovery (unpublished results). Regardless the level of anticoagulation maintained during support, this solution requires a careful echo and direct inspection of the LV apex during weaning to exclude the presence of clots both before and especially following the removal of the vent. Future development of endoscopic devices for transapical aortic valve implantation that are currently under study could also be used in this setting in order to avoid the small left thoracotomy 16. There is no conflict of interest in the present study for any of the authors. 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