Falk, Volkmar

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EDITORIALStay off-pump and do not touch the aorta!Volkmar Falk*Department of Cardiovascular Surgery, Institution, University of Zurich, Raemistr. 100, Zurich 8091, SwitzerlandOnline publish-ahead-of-print 3 December 2009This editorial refers to ‘Protecting the brain from gaseousand solid micro-emboli during coronary artery bypassgrafting: a randomized controlled trial’†, by T. Gerrietset al. on page 360One of the major drawbacks in contemporary on-pump coron-ary artery bypass surgery is the inherent risk of intraoperativestroke. In addition, neurophysiological dysfunction and neurobe-havioural changes have been reported in variable frequencies fol-lowing on-pump bypass surgery. Cardiopulmonary bypass (CPB)causes a systemic inflammatory response, haemodilution, changein vascular resistance, absence of pulsatile flow, and large volumeshifts. As a result, temporary cerebral oedema can be seen inmagnetic resonance imaging (MRI) studies early after on-pumpbypass surgery and has been identified as the substrate forwhat was termed ‘pump head’ in the past. Refinements of CPBcircuits using biocompatible surfaces, the use of less traumaticoxygenators, and the addition of filters as well as the establish-ment of standardized perfusion protocols have improved theresults of on-pump surgery. Despite these advances, CPBremains one major source for gaseous microembolization.1,2Retransfusion of shed mediastinal blood during on-pumpsurgery has long been recognized as an additional source ofembolization by fat particles and activation and derangement ofthe clotting cascade.Manipulation of the ascending aorta such as partial or totalclamping and cannulation required for installation of CPB cancause additional solid emboli especially in the presence of athero-sclerotic disease.3,4 Numerous studies have shown embolicshowers in transcranial Doppler during cannulation and clampingand declamping manoeuvres. The release of particulate embolicorrelates in particular with the release of the aortic cross-clamp.5Gerriets et al. have reported a randomized controlled trial todemonstrate the impact of two different methods to decreasethe embolic load during on-pump bypass surgery with partialaortic clamping in a low risk group of patients.6 As protectiondevices the Embol-X was used in 43 patients and a dynamicbubble-trap (DBT) in 50 patients. A control group (n ¼ 50)received no protection device.The primary endpoint was the 3 month cognitive outcomewhich showed better short-term memory and executive function-ing in the DBT group despite a general decline in the compositecognitive score in all groups. This finding, albeit statistically signifi-cant, may have only limited clinical implications, as numerousstudies have demonstrated complete recovery of peri-operativeneurocognitive decline over time. Intra-operatively, microembolicsignals (MES) were recorded with transcranial Doppler in only63% of the patients using transcranial Doppler sonography of themiddle cerebral arteries. While the total number of MES waslower in the DBT group, it was not different for the Embol-Xgroup as compared with controls. The numbers of event-relatedMES were higher with aortic clamping and filter insertion, butlower with declamping in the Embol-X group. In a multi-institutional randomized study on 1289 patients the efficacy ofthe Embol-X intra-aortic filter to reduce the embolic burdenwas demonstrated by the high capture rate (96.8%) of particulateemboli. Despite successful filtering of some solid emboli, there wasno difference for either the composite endpoint or the individualendpoints including stroke for the treatment group and thecontrol group.7 This is in line with the finding of Gerriets presentedhere who could not demonstrate a protective effect of theEmbol-X filter device.6In 17/125 patients (13.6%) undergoing post-operative cerebralMRI, asymptomatic acute ischaemic brain lesions (diffusion-weighted imaging lesions) were detected. There was no differencebetween groups, indicating that emboli do occur despite the use ofprotection devices, and visible lesions in MRI do not necessarilycorrelate with neurocognitive outcome 3 months after surgery.This confirms previous studies that have shown no associationbetween new focal brain lesions and impaired neuropsychologicalperformance and could not demonstrate a correlation betweenclinical variables and MRI findings. New ischaemic brain lesionson post-operative diffusion-weighted MRI per se do not appearto account for the mostly transient but sometimes persistentneurocognitive decline after on-pump bypass surgery.8Unfortunately, the authors did not comment on the extent ofaortic atherosclerotic disease within groups which largely deter-mines the risk for solid emboli and peri-operative stroke. OtherThe opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology.* Corresponding author. Tel: þ41 44 255 32 98, Fax: þ41 44 255 32 98, Email: volkmar.falk@usz.ch† doi:10.1093/eurheartj/ehp178Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2009. For permissions please email: journals.permissions@oxfordjournals.org.European Heart Journal (2010) 31, 278–280doi:10.1093/eurheartj/ehp527confounding factors such as peripheral artery disease, flow-limitingcarotid artery stenoses, previous stroke, age, diabetes, hyperten-sion, history of myocardial infarction, impaired left ventricular ejec-tion fraction and chronic renal failure have invariably beenidentified as potential risk factors for stroke unrelated to thetype of surgery. These confounding factors create a ‘backgroundnoise’ that is difficult to eliminate when discussingprocedure-related risks. Extended CPB times, high transfusionrequirements, peri-operative use of an intra-aortic balloon pump,as well as post-pump low cardiac output and atrial fibrillation areindependent determinants for post-operative stroke and mayalso contribute to the temporary neurocognitive decline followingon-pump surgery.While some risks such as gaseous embolization can be dimin-ished by the use of arterial line filters, adding devices is notalways without risk. For the Embol-X endoaortic filter endothelialdisruptions were found more frequently by epiaortic scanning in alarge multicentre trial .7In contrast, novel dispersion aortic cannulae or different cannu-lation sites can potentially reduce the number of particulate emboliby decreasing the ‘sandblasting’ effect of a highflow cannula facingthe wall of a calcified ascending aorta. Continuing this rationale,avoiding aorticmanipulation andCPB altogether seemsveryattractive.Off-pump coronary artery bypass surgery can potentially reducethe embolic load during coronary bypass surgery by eliminatingthe need for aortic cannulation and aortic cross-clamping(Figure 1). Avoidance of CPB reduces the systemic inflammatoryresponse and likelihood for gaseous emboli. Some studies havefound a decrease in the risk of stroke and cerebrovascular inci-dents after off-pump coronary artery bypass as compared withon-pump bypass surgery, especially in high risk groups.9,10 Aorticmanipulation can be avoided altogether if all arterial grafting is per-formed off-pump and no grafts to aorta anastomoses are per-formed (Figure 2). Most studies that could not find a differencebetween neurological complications after on- and off-pumpbypass procedures did not apply total arterial grafting and usedsite-biting clamps for performing the proximal anastomoses.However, even when a ‘no touch technique’ and the exclusiveuse of T-graft techniques are rigidly applied, the risk of peri-operative stroke cannot be completely eliminated,11,12 and ismost probably related to an underlying risk defined by thegeneral health condition of the patient. Interestingly, this alsoapplies to interventional revascularization procedures. Accordingto a recent meta-analysis the rate of procedural stroke (reportedin 15 randomized trials) is unarguably higher after coronaryartery bypass grafing (1.2%) than after percutaneous coronaryintervention (PCI) (0.6%) but is certainly not negligible afterPCI.13 The SYNTAX trial has highlighted once more the impor-tance of peri-operative stroke for the overall results after revascu-larization procedures.14Interestingly, in the bypass group, half of the events occurredperi- rather than intra-operatively and may be related to the highincidence of peri-operative atrial fibrillation and the lesser use ofantithrombotic drugs in the bypass group.To the best of our knowledge today, the combination ofoff-pump surgery and all arterial grafting may be the surgeon’sbest tool to avoid some but not all neurological complicationsafter bypass surgery. Prophylactic antiarhyhthmic and antithrombo-tic treatment as well as aggressive treatment of peri-operative atrialfibrillation may further reduce the incidence of neurological eventsafter bypass surgery.Conflict of interest: none declared.References1. Moody DM, Brown WR, Challa VR, Stump DA, Reboussin DM, Legault C. Brainmicroemboli associated with cardiopulmonary bypass: a histologic and magneticresonance imaging study. Ann Thorac Surg 1995;59:1304–1307.2. Borger MA, Peniston CM, Weisel RD, Vasiliou M, Green RE, Feindel CM. Neurop-sychologic impairment after coronary bypass surgery: effect of gaseous microem-boli during perfusionist interventions. J Thorac Cardiovasc Surg 2001:121:743–749.3. Patel NC, Deodhar AP, Grayson AD, Pullan DM, Keenan DJ, Hasan R, Fabri BM.Neurological outcomes in coronary surgery: independent effect of avoidingcardiopulmonary bypass. Ann Thorac Surg 2002;74:400–405.4. Sisillo E, Marino MR, Juliano G, Beverini C, Salvi L, Alamanni F. Comparison of onpump and off pump coronary surgery: risk factors for neurological outcome. Eur JCardiothorac Surg 2007;31:1076–1080.Figure 1 Standard coronary artery bypass procedure requiresaortic cannulation and clamping. Both manoevres can causeemboli especially in the setting of an atherosclerotic aorta (A).For off-pump coronary artery bypass grafting (B), the targetvessel is exposed applying a vacuum-assisted stabilizer thatallows for local immobilization (B). Cardiopulmonatry bypass isnot required since the procedure is performed on the beatingheart.Editorial 2795. Diegeler A, Hirsch R, Schneider F, Schilling LO, Falk V, Rauch T, Mohr FW.Neuromonitoring and neurocognitive outcome in off-pump versus conventionalcoronary bypass operation. Ann Thorac Surg 2000;69:1162–1166.6. Gerriets T, Schwarz N, Sammer G, Baehr J, Stolz E, Kaps M, Kloevekorn W-P,Bachmann G, Scho¨nburg M. Protecting the brain from gaseous and solid micro-emboli during coronary artery bypass grafting: a randomized controlled trial.Eur Heart J 2010;31:360–368. First published on 18 June 2009. doi:10.1093/eurheartj/ehp178.7. Banbury MK, Kouchoukos NT, Allen KB, Slaughter MS, Weissman NJ, Berry GJ,Horvath KA; ICEM 2000 Investigators. Emboli capture using the Embol-Xintraaortic filter in cardiac surgery: a multicentered randomized trial of 1,289patients. Ann Thorac Surg 2003;76:508–515.8. Knipp SC, Matatko N, Wilhelm H, Schlamann M, Massoudy P, Forsting M,Diener HC, Jakob H. Evaluation of brain injury after coronary artery bypass graft-ing. A prospective study using neuropsychological assessment and diffusionweighted magnetic resonance imaging. Eur J Cardiothorac Surg 2004;25, 791–800.9. Bucerius J, Gummert JF, Borger MA, Walther T, Doll N, Onnasch JF, Metz S,Falk V, Mohr FW. Stroke after cardiac surgery: a risk factor analysis of 16,184 con-secutive adult patients. Ann Thorac Surg 2003;75:472–478.10. Navia D, Vrancic M, Vaccarino G, Piccinini F, Raich H, Florit S, Hierer J. Totalarterial off-pump coronary revascularization using bilateral internal thoracicarteries in triple vessel disease: surgical technique and clinical outcome. AnnThorac Surg 2008;86:524–531.11. Vallely MP, Potger K, McMillan D, Hemli JM, Brady PW, Brereton RJ, Marshman D,Mathur MN, Ross DE. Anaortic techniques reduce neurological morbidity afteroff-pump coronary artery bypass surgery. Heart Lung Circ 2008;17:299–304.12. Holzhey DM, Jacobs S, Mochalski M, Walther T, Thiele H, Mohr FW, Falk V. Sevenyears follow-up after MIDCAB—experience with more than 1300 patients. AnnThorac Surg 2007;83:108–114.13. Bravata DM, Gienger AL, McDonald KM, Sundaram V, Perez MV, Varghese R,Kapoor JR, Ardehali R, Owens DK, Hlatky MA. Systematic review: the compara-tive effectiveness of percutaneous coronary interventions and coronary arterybypass graft surgery. Ann Intern Med 2007;147:703–716.14. Serruys PW, Morice MC, Kappetein AP, Colombo A, Holmes DR, Mack MJ,Sta˚hle E, Feldman TE, van den Brand M, Bass EJ, Van Dyck N, Leadley K,Dawkins KD, Mohr FW;SYNTAX Investigators. Percutaneous coronary interven-tion versus coronary-artery bypass grafting for severe coronary artery disease. NEngl J Med 2009;360:961–672.Figure 2 Total arterial grafting using both internal thoracic arteries and the radial artery allows complete revascularization without the needfor an aortic anastomosis (A). If this procedure is performed on the beating heart (a), the aorta is not touched (‘no touch technique’). If venousbypass grafts are used (B) manipulation of the ascending aorta is required to perform the proximal bypass graft anastomoses.Editorial280

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