View metadata, citation and similar papers at core.ac.uk brought to you by CORE EVOLVING TECHNOLOGY/BASIC SCIENCE provided by Elsevier - Publisher Connector Protecting the aged heart during cardiac surgery: Use of del Nido cardioplegia provides superior functional recovery in isolated hearts Arun Govindapillai, BSc,a Rui Hua, PhD,a Robert Rose, PhD,a Camille Hancock Friesen, MD,b,c,d and Stacy B. O’Blenes, MDa,b,c Objectives: Aged hearts are particularly vulnerable to ischemia-reperfusion injury. Our objective was to determine if del Nido cardioplegia, which contains lidocaine, less blood, and less calcium than our standard cardioplegia, provides superior protection for aged hearts. We also sought to determine if the lidocaine in del Nido cardioplegia is adequate to prevent Naþ influx via the window current. Methods: Sodium channel kinetics were measured in rat cardiomyocytes with and without lidocaine. Recovery after 60 minutes of cardioplegic arrest was assessed in isolated working senescent rat hearts. Del Nido cardioplegia was delivered as a single dose (n ¼ 8) because it is used clinically, and standard cardioplegia was delivered as an induction dose with re-dosing every 20 minutes (n ¼ 8). After 20 minutes of reperfusion, hearts were switched to working mode for 60 minutes. Flows were indexed to ventricular dry weight. Troponin release was assayed. Results: Sodium channel kinetics indicated that the lidocaine concentration in del Nido cardioplegia minimizes the potential for Naþ influx via the window current. Spontaneous contractions occurred in fewer hearts arrested with del Nido cardioplegia (88% vs 13%; P ¼ .01), and troponin release was reduced (0.24 vs 0.89 ng/mL; P ¼ .017). Cardiac output was approximately 90% of baseline in the del Nido group compared with À À approximately 50% in the standard group (173 Æ 14 vs 86 Æ 22 mL $ min 1 $ g 1; P ¼ .0008). Stroke work was higher in the del Nido group (93 Æ 6vs41Æ 10 mL $ mm Hg $ gÀ1; P ¼ .0002). Conclusions: Del Nido cardioplegia prevents spontaneous contractions during arrest, reduces troponin release, and results in superior myocardial function in isolated aged hearts. Del Nido cardioplegia has the potential to provide superior myocardial protection for older patients undergoing cardiac surgery. (J Thorac Cardiovasc Surg 2013;146:940-8) The growing number of elderly patients requiring cardiac Ca2þ, and contains lidocaine (Table 1). Del Nido cardiople- surgery is an important group at higher risk for cardiac gia usually is given as a single dose,9-11 whereas our dysfunction and death postoperatively.1,2 Aged hearts are standard cardioplegia is given as an induction dose particularly susceptible to reperfusion injury after the followed by maintenance doses approximately every ischemic periods that occur during cardiac surgery3-5 20 minutes. The del Nido cardioplegia strategy results in owing to changes in the way cardiomyocytes deal with lower postoperative troponin release in pediatric patients intracellular Ca2þ, particularly during ischemia.5-8 compared with our standard cardioplegia.9 Del Nido cardioplegia is used in several centers for Because elderly myocardium is similar to immature myocardial protection during pediatric cardiac surgery.9-11 myocardium in that both are particularly susceptible to þ Compared with the standard 4:1 blood cardioplegia we reperfusion injury related to Ca2 overload,3-8,12-14 we use in our adult practice, del Nido cardioplegia is more hypothesized that a del Nido cardioplegia strategy also dilute (1:4 blood:crystalloid), has approximately 75% less may be beneficial in the elderly. We previously showed, in cardiomyocytes from aged rats (z24 mo), that arrest with del Nido cardioplegia results in less activity during From the Departments of Physiology and Biophysics,a Surgery,c Pathology,d Dalhou- 2þ b the ischemic period, lower diastolic Ca during ischemia sie University, and IWK Health Centre, Halifax, Nova Scotia, Canada. 2þ Supported by grants form the Canadian Institutes for Health Research and the Heart and reperfusion, and avoidance of Ca -induced 15 and Stroke Foundation of Nova Scotia. Robert Rose is supported by a Canadian hypercontraction during early reperfusion. The objective Institutes for Health Research New Investigator Award. of this study was to determine if the beneficial effects Disclosures: Authors have nothing to disclose with regard to commercial support. Read at the 93rd Annual Meeting of The American Association for Thoracic seen with del Nido cardioplegia in aged cardiomyocytes Surgery, Minneapolis, Minnesota, May 4-8, 2013. translate into improved functional recovery in elderly whole Received for publication April 18, 2013; revisions received May 16, 2013; accepted ET/BS hearts. for publication May 20, 2013; available ahead of print Aug 19, 2013. Address for reprints: Stacy B. O’Blenes, MD, IWK Children’s Heart Centre, IWK Sodium influx is thought to be the main cause of 2þ Health Centre, 5850/5980 University Ave, PO Box 9700, Halifax, Nova Scotia intracellular Ca accumulation during ischemia by B3K 6R8, Canada (E-mail: [email protected]). driving reverse-mode Naþ/Ca2þ exchange.16,17 During 0022-5223/$36.00 Ó hyperkalemic cardioplegic arrest, membrane depolarization Copyright 2013 by The American Association for Thoracic Surgery þ http://dx.doi.org/10.1016/j.jtcvs.2013.05.032 opens a proportion of the voltage-gated Na channels 940 The Journal of Thoracic and Cardiovascular Surgery c October 2013 Govindapillai et al Evolving Technology/Basic Science Mg-adenosine triphosphate 4 mmol/L, Na-phosphocreatine 6.6 mmol/L, Abbreviation and Acronym Na-guanosine triphosphate 0.3 mmol/L, and HEPES 10 mmol/L, pH 7.2. ¼ The resistance of the borosilicate glass micropipettes (1.5 mm outer INa sodium current diameter, 0.75 mm inner diameter) was 3 to 5 MU, seal resistance was 2 to 15 GU, and rupturing the sarcolemma in the patch for voltage clamp experiments resulted in access resistances of 5 to 15 MU. Series resistance % % spanning the cell membrane. Most of these channels are compensation averaged 80 to 85 using an Axopatch 200B amplifier (Molecular Devices, Sunnyvale, Calif). Data were digitized using a inactivated rapidly, thereby preventing action potential Digidata 1440 and pCLAMP 10 software (Molecular Devices). generation and propagation, but a small fraction remain The voltage clamp protocol for measuring I current-voltage relation- þ Na tonically available and allow Na to flow into the cell via a ships and activation kinetics consisted of holding myocytes at -100 mVand 18-20 À þ window current. Lidocaine used as an additive to then giving a series of 20-ms, 10-mV steps from 80 to 60 mv. INa depolarizing cardioplegia may limit Naþ influx by activation kinetics were determined by calculating chord conductance (G) using the following equation: G ¼ I/(V ÀE ), where V represents blocking the window current, however, this has not been m rev m the depolarizing voltages and Erev is the reversal potential estimated well described. We investigated whether the concentration from the current-voltage relation of INa. The protocol for measuring INa of lidocaine present in del Nido cardioplegia is adequate to inactivation consisted of holding myocytes at À140 mVand giving a series minimize the potential for Naþ influx via thewindow current. of 500-ms voltage-clamp conditioning steps from À120 mV to À20 mV followed by a 20-ms voltage clamp test step to À20 mV. Activation and inactivation curves were generated by fitting normalized data with a MATERIALS AND METHODS Boltzmann function to determine the V1/2 of activation (V1/2[act]), and Experimental Animals and Anesthesia inactivation (V1/2[inact]) in the presence and absence (control) of lidocaine Experiments were performed in accordance with guidelines published 0.36 mmol/L, as found in del Nido cardioplegia. by the Canadian Council on Animal Care.21 Male Fisher 344 rats (3-4 mo for isolated cardiomyocyte studies, and 23-24 mo for isolated heart Isolated Working Heart studies) obtained from Charles River Laboratories (Saint-Constant, Hearts were cannulated via the aorta and pulmonary vein on a working Canada) were heparinized (intraperitoneally, 3000 U/kg; Pharmaceutical heart apparatus (Radnoti, Inc, Monrovia, Calif), and perfused retrograde Partners of Canada, Richmond, Ontario, Canada), and anesthetized with with Krebs-Henseleit buffer at 10 mL/min (37C). A temperature probe sodium pentobarbital (intraperitoneally, 160 mg/kg; Veterinary Medication and electrocardiogram electrode were placed through the pulmonary artery Distribution Centre; Saint-Hyacinthe, Quebec, Canada). Hearts were into the right ventricular outflow tract. Left atrial and aortic pressure and removed rapidly and placed in ice-cold Tyrode’s solution for isolated aortic flow (Transonic Systems, Inc, Ithaca, NY) were monitored cardiomyocyte studies (NaCl 140 mmol/L, KCl 5.4 mmol/L, Na HPO 1 2 4 continually using a PowerLab data acquisition system (ADI Instruments, mmol/L, CaCl 1 mmol/L, MgCl 1 mmol/L, glucose 10 mmol/L, HEPES 2 2 Colorado Springs, Colo). Coronary flow was measured by timed collection 5 mmol/L, pH 7.4), or Krebs-Henseleit buffer for isolated heart studies of effluent. After a 5-minute stabilization period, hearts were switched to (NaCl 118 mmol/L, KCl 4.71 mmol/L, NaHCO 25.0 mmol/L, KH PO 3 2 4 constant pressure mode (100 cm H O) for 5 minutes, and then into working 1.20 mmol/L, CaCl 2.50 mmol/L, MgSO 1.20 mmol/L, glucose 11 2 2 4 heart mode for 5 minutes (preload, 20 cm H O; afterload, 100 cm H O). mmol/L, ethylenediaminetetraacetic acid 0.5 mmol/L, equilibrated with 2 2 Only hearts that met the following predetermined baseline criteria were 95% O /5% CO , pH 7.4). 2 2 used in this study: heart rate greater than 200 bpm, regular rhythm, cardiac output greater than 25 mL/min, and coronary flow greater than 10 mL/ Cardiac Myocyte Isolation min.22 After the baseline working heart period, hearts were arrested with Ventricular cardiomyocytes were obtained by enzymatic dissociation.