The authors would like to acknowledge Dr. Wanchun Tang MD, MCCM, FCCP, FAHA and Jena Cahoon of the Weil Institute of Critical Care Medicine in Rancho Mirage, CA. for their contributions to the resuscitation protocol outline and for having helped train the rodent surgeon (LL). The preparation of this article was in part supported by a gift in memory of US Navy Retired SKC Robert W. Ply by Ms. Monica Ply for research in heart disease and Parkinson&#8217;s disease and by a discretionary fund from the Department of Medicine at Rosalind Franklin University of Medicine and Science.

The authors have nothing to disclose.

Critical Steps in the protocol
There are critical steps in the protocol. When mastered, the preparation and protocol proceed as succinctly described below. The surgical preparation is expeditious, advancing catheters rapidly through small incisions triggering minimal or no vessel spasm and positioning the catheter tips as intended, followed by successful tracheal intubation after a single or a few attempt(s); thus, completing the preparation in &#8776; 90 min from the initial pentobarbital dose to induction of VF with baseline measurements within reference values (Table 1). VF is electrically induced in every instance leading to spontaneously sustained VF after 3 min of uninterrupted electrical stimulation in &#62;95% of the instances. During chest compression, an aortic diastolic pressure &#8805;24 mm Hg and end-tidal CO2 &#8805;10 mm Hg is generated without exceeding a compression depth of 17 mm depth and without injuring intrathoracic organs. Implementation of a defibrillation protocol (e.g., as shown in Figure 3) occurs with ease and with &#60;5 sec interruptions in chest compression. Finally, return of spontaneous circulation occurs in &#62;60% of the experiments using the present protocol or similar ones leading to post-resuscitation myocardial dysfunction with a 240 min survival &#62;40% and metabolic abnormalities indicative of the systemic oxygen deficit that occurs during cardiac arrest and reverses in the post-resuscitation phase in survivors, as shown on Table 1.
Modifications and troubleshooting
The model is highly versatile, allowing for relatively simple adaptations to meet specific research objectives. Recently, use of PE25 size tubing was preferred over PE50 size tubing, which has been used in the past by other investigators, and found it easier to advance into proper position without compromising the fidelity of the pressure measurements. The left ventricle can been catheterized from a carotid artery to assess left ventricular function34,61 or to inject microspheres for measuring regional organ blood flow6,55. The trachea may be cannulated directly via tracheostomy instead of the oral &#8211; more challenging &#8211; technique featured in this article, especially in acute experiments without recovery from anesthesia. Other approaches to induce VF have been described including transcutaneous electrical epicardium stimulation74, current delivery to the entrance of the superior vena cava into the heart75, and electrical stimulation of the esophagus using a pacing electrode76. The method of chest compression may be varied by starting compression at the maximal depth, using lateral restraints, compressing at other rates and duty cycles, and also by using manual technique instead of a piston device. Ventilation can also be varied; the original description used a ventilatory rate of 100 min-1 synchronized 1:2 to compressions whereas the present model uses a ventilatory rate of 25 min-1 unsynchronized to compressions; consistent with the reduced ventilatory demands of CPR77 and current clinical recommendations against pausing for compressions after having established a secured airway. Ventilation can also be passive and promoted by chest compression provided the airway is patent20 or obviated while administering oxygen directly into the trachea25. If an experiment requires removal of large amounts of blood relative to the animal&#8217;s blood volume [BV(ml) = 0.06 x body weight (g) + 0.77]78; e.g., for blood collection for determining organ blood flow with microspheres6,55 or for repetitive measurement of blood analytes, blood may be transfused from a donor rat from the same colony6,55. Current analytical techniques, however, allow determination of multiple analytes in small samples and administration of equivalent amounts of normal saline or another accepted intravascular solution compensates for small blood losses. The model can also be used to study asphyxia as the mechanism of arrest9, which is typically accomplished by inducing neuromuscular blockade and occluding the airway.
Limitations of the technique
The model lacks underlying coronary artery disease and it is technically difficult to acutely induce coronary artery occlusion; conditions most commonly associated with sudden cardiac arrest in humans. The need to maintain the current to induce VF is not ideal and raises concerns of potential injury to the myocardium. Indeed minor thermal injury at the site of current delivery was recognized in the original study, and noted that it could be minimized by reducing the current to the minimum requirement during the 3 min interval needed to induced self-sustained VF4. In addition, the electrical current unintendedly triggers skeletal muscle contraction, which could contribute to lactic acid production. The calcium cycling physiology of the rat heart compared to other mammals is less dependent on the sodium-calcium exchanger79, and interpretation of related therapies should consider this aspect of the rat cardiac physiology. The rate of compression and ventilation exceeds that used in humans precluding direct extrapolation of related findings. The effects of anesthesia80 including cell protective effects81 should be considered when interpreting findings, although it is not clear that pentobarbital obfuscate findings compared to inhalant anesthetics which have cardioprotective effects81. Most of the studies reported in the literature have been conducted in male rats intended to minimize possible experimental confounders stemming from different timing within the estrous cycle. Further work is required to assess the effects of gender on resuscitation physiology and outcomes. Another important limitation is the reduced availability of genetically engineered rats relative to mice having to resort to customized genetic engineering or targeted gene manipulation of adult animals through introduction of genetic material (e.g., viral vectors and antisense oligonucleotides).
Significance of the technique with respect to existing/alternative methods
The model is best suited to explore new concepts, new interventions, and to challenge existing paradigms as part of a larger translational strategy that eventually includes focused studies in larger animal models, such as swine, before human trials. Studies in smaller animals (e.g., mice) are complicated by difficulties in inducing VF, limited surgical instrumentation, and the small blood volume that precludes repetitive blood analysis.
Future applications or directions after mastering this technique
The rat model was originally developed to simulate various aspects of human CPR after sudden cardiac arrest. As highlighted in the introduction, the model has been used by investigators to address several aspects of cardiac resuscitation, including its physiology, conventional determinant of outcomes, and mostly the effects of established and novel therapeutic interventions as referenced in this article. The Resuscitation Institute expects the reader to be inspired and use the model to address the many questions in resuscitation research that need further exploration given the disappointing outcomes with current resuscitation methods.

Close to 360,000 individuals in the United States1 and many more worldwide2 suffer an episode of sudden cardiac arrest every year. Attempts to restore life require not only that cardiac activity be reestablished but that damage to vital organs be prevented, minimized, or reversed. Current cardiopulmonary resuscitation techniques yield an initial resuscitation rate of approximately 30%; however, survival to hospital discharge is only 5%1. Myocardial dysfunction, neurological dysfunction, systemic inflammation, intercurrent illnesses, or a combination thereof occurring post-resuscitation account for the large proportion of patients who die in spite of initial return of circulation. Thus, greater understanding of the underlying pathophysiology and novel resuscitation approaches are urgently needed to increase the rate of initial resuscitation and subsequent survival with intact organ function.
Animal models of cardiac arrest play a critical role in the development of new resuscitation therapies by providing insights on the pathophysiology of cardiac arrest and resuscitation and offering practical means to conceptualize and test new interventions before they can be tested in humans3. The rat model of closed chest cardiopulmonary resuscitation (CPR) described here has played an important role. The model was developed in 1988 by Irene von Planta &#8211; a research fellow at the time &#8211; and her collaborators4 in the laboratory of late Professor Max Harry Weil M.D., Ph.D. at the University of Health Sciences (renamed Rosalind Franklin University of Medicine and Science in 2004) and has been extensively used in the field of resuscitation predominantly by fellows of Professor Weil and their trainees.
The model simulates an episode of sudden cardiac arrest with resuscitation attempted by conventional CPR techniques and thus includes induction of ventricular fibrillation (VF) by delivering an electrical current to the right ventricular endocardium and provision of closed chest CPR by a pneumatically driven piston device while concomitantly delivering positive pressure ventilation with oxygen-enriched gas. Termination of VF is accomplished by transthoracic delivery of electrical shocks. The rat model strikes a balance between models developed in large animals (e.g., swine) and models developed in smaller animals (e.g., mice) allowing exploration of new research concepts in a well-standardized, reproducible, and efficient manner with access to a robust inventory of pertinent measurements. The model is particularly useful in early stages of research to explore new concepts and examine the effects of confounders before conducting studies in larger animal models that are more costly, but of greater translational impact.
A Medline search for all peer-reviewed articles reporting a similar rat model having VF as the mechanism of cardiac arrest and some form of closed chest resuscitation revealed a total of 69 additional original studies using the model since it was first published in 19884. The research areas include pathophysiological aspects of resuscitation5-17, factors influencing outcomes18-30, the role of pharmacological interventions examining vasopressor agents31-43, buffer agents44, inotropic agents45, agents aimed at myocardial or cerebral protection46-70, and also the effects of mesenchymal stem cells71-73.
The model and protocol described in this article is currently being used at the Resuscitation Institute. Yet, there are multiple opportunities to &#8220;customize&#8221; the model based on the capabilities available to individual investigators and the goals of the studies.

<table><tbody><tr><td>Sodium pentobarbital</td><td>Sigma Aldrich</td><td>P3761</td><td>http://www.sigmaaldrich.com/catalog/product/sigma/p3761?lang=en&amp;amp;region=US</td></tr><tr><td>Rectal thermistor</td><td>BIOPAC Systems, INC</td><td>TSD202A</td><td>http://www.biopac.com/fast-response-thermistor</td></tr><tr><td>Needle electrode biopolar concentric 25 mm TP</td><td>BIOPAC Systems, INC</td><td>EL451</td><td>http://www.biopac.com/needle-electrode-concentric-25mm</td></tr><tr><td>PE25 polyethylene tubing&amp;nbsp;</td><td>Solomon Scientific</td><td>BPE-T25</td><td>http://www.solsci.com/products/polyethylene-pe-tubing</td></tr><tr><td>26GA female luer stub adapter</td><td>Access Technologies</td><td>LSA-26</td><td>http://www.norfolkaccess.com/needles.html</td></tr><tr><td>Stopcocks with luer connections; 3-way; male lock, non-sterile</td><td>Cole-Parmer</td><td>UX-30600-02</td><td>http://www.coleparmer.com/Product/Large_bore_3_way&lt;br/&gt; _male_lock_stopcocks&lt;br/&gt; _10_pack_Non_sterile/EW-30600-23</td></tr><tr><td>TruWave disposable pressure transducer</td><td>Edwards Lifesciences</td><td>PX600I&amp;nbsp;</td><td>http://www.edwards.com/products/pressuremonitoring/Pages/truwavemodels.aspx?truwave=1</td></tr><tr><td>Type-T thermocouple</td><td>Physitemp Instruments</td><td>IT-18</td><td>http://www.physitemp.com/products/probesandwire/flexprobes.html</td></tr><tr><td>Central venous pediatric catheter&amp;nbsp;</td><td>Cook Medical&amp;nbsp;</td><td>C-PUM-301J</td><td>https://www.cookmedical.com/product/-/catalog/display?ds=cc_pum1lp_webds</td></tr><tr><td>Abbocath-T subclavian I.V. catheter (14 g x 5 1/2&quot;)</td><td>Hospira</td><td>453527</td><td>http://www.hospira.com/products_and_services/iv_sets/045350427</td></tr><tr><td>Novametrix Medical Systems, Infrared CO2 monitor</td><td>Soma Technology, Inc.</td><td>7100 CO2SMO&amp;nbsp;</td><td>http://www.somatechnology.com/MedicalProducts/novametrix_respironics_co2smo_&lt;br/&gt; 7100.asp</td></tr><tr><td>Harvard Model 683 small animal ventilator</td><td>Harvard Apparatus</td><td>555282</td><td>http://www.harvardapparatus.com/webapp/wcs/stores/servlet/haisku2_10001_11051_44453_-1_&lt;br/&gt; HAI_ProductDetail_N_37322_37323</td></tr><tr><td>Double-flexible tipped wire guides</td><td>Cook Medical&amp;nbsp;</td><td>C-DOC-15-40-0-2</td><td>https://www.cookmedical.com/product/-/catalog/display?ds=cc_doc_webds</td></tr><tr><td>High accuracy AC LVDT displacement sensor</td><td>Omega Engineering</td><td>LD320-25</td><td>http://www.omega.com/pptst/LD320.html</td></tr><tr><td>HeartStart XL defibrillator/monitor</td><td>Phillips Medical Systems</td><td>M4735A</td><td>http://www.healthcare.philips.com/main/products/resuscitation/products/xl/</td></tr><tr><td>Graefe micro dissection forceps 4 inches</td><td>Roboz&amp;nbsp;</td><td>RS-5135</td><td>http://shopping.roboz.com/Surgical-Instrument-Online-Shopping?search=RS-5135</td></tr><tr><td>Graefe micro dissection forceps 4 inches with teeth</td><td>Roboz&amp;nbsp;</td><td>RS-5157</td><td>http://shopping.roboz.com/Surgical-Instrument-Online-Shopping?search=RS-5157</td></tr><tr><td>Extra fine micro dissection scissors 4 inches</td><td>Roboz&amp;nbsp;</td><td>RS-5882</td><td>http://shopping.roboz.com/micro-scissors-micro-forceps-groups/micro-dissecting-scissors/Micro-Dissecting-Scissors-4-Straight-Sharp-Sharp</td></tr><tr><td>Heiss tissue retractor</td><td>Fine Science Tools&amp;nbsp;</td><td>17011-10</td><td>http://www.finescience.com/Special-Pages/Products.aspx?ProductId=321&amp;amp;CategoryId=134&amp;amp;&lt;br/&gt; lang=en-US</td></tr><tr><td>Crile curve tip hemostats</td><td>Fine Science Tools&amp;nbsp;</td><td>13005-14</td><td>http://www.finescience.com/Special-Pages/Products.aspx?ProductId=372</td></tr><tr><td>Visistat skin stapler&amp;nbsp;</td><td>Teleflex Incorporated</td><td>528135</td><td>http://www.teleflexsurgicalcatalog.com/weck/products/9936</td></tr><tr><td>Braided silk suture, 3-0</td><td>Harvard Apparatus</td><td>517706</td><td>http://www.harvardapparatus.com/webapp/wcs/stores/servlet/haisku2_10001_11051_43051_-1_&lt;br/&gt; HAI_ProductDetail_N_37916_37936</td></tr><tr><td>Betadine solution</td><td>Butler Schein</td><td>3660</td><td>https://www.henryscheinvet.com/</td></tr><tr><td>Sterile saline, 250 ml bags</td><td>Fisher</td><td>50-700-069</td><td>http://www.fishersci.com/ecomm/servlet/itemdetail?catnum=50700069&amp;amp;storeId=10652</td></tr><tr><td>Heparin sodium injection, USP</td><td>Fresenius Kabi</td><td>504201</td><td>http://fkusa-products-catalog.com/files/assets/basic-html/page25.html</td></tr><tr><td>Loxicom (meloxicam)</td><td>Butler Schein</td><td>045-321</td><td>https://www.henryscheinvet.com/</td></tr><tr><td>Thermodilution cardiac output computer for small animals</td><td>N/A</td><td>N/A</td><td>Custom-developed at the Resuscitation Institute using National Instruments hardware and LabVIEW software</td></tr><tr><td>Analog-to-digital data acquisition and analysis system</td><td>N/A</td><td>N/A</td><td>Custom-developed at the Resuscitation Institute using National Instruments hardware and LabVIEW software</td></tr><tr><td>Pneumatically-driven and electronically controlled piston device for chest compression in small animals</td><td>N/A</td><td>N/A</td><td>Custom-developed at the Weil Institute of Critical Care Medicine</td></tr><tr><td>60 Hz alternating current generator</td><td>N/A</td><td>N/A</td><td>Custom-developed at the Weil Institute of Critical Care Medicine</td></tr></tbody></table>

a rat model of ventricular fibrillation and resuscitation by conventional closed-chest technique

A rat model of electrically-induced ventricular fibrillation followed by cardiac resuscitation using a closed chest technique that incorporates the basic components of cardiopulmonary resuscitation in humans is herein described. The model was developed in 1988 and has been used in approximately 70 peer-reviewed publications examining a myriad of resuscitation aspects including its physiology and pathophysiology, determinants of resuscitability, pharmacologic interventions, and even the effects of cell therapies. The model featured in this presentation includes: (1) vascular catheterization to measure aortic and right atrial pressures, to measure cardiac output by thermodilution, and to electrically induce ventricular fibrillation; and (2) tracheal intubation for positive pressure ventilation with oxygen enriched gas and assessment of the end-tidal CO2. A typical sequence of intervention entails: (1) electrical induction of ventricular fibrillation, (2) chest compression using a mechanical piston device concomitantly with positive pressure ventilation delivering oxygen-enriched gas, (3) electrical shocks to terminate ventricular fibrillation and reestablish cardiac activity, (4) assessment of post-resuscitation hemodynamic and metabolic function, and (5) assessment of survival and recovery of organ function. A robust inventory of measurements is available that includes &#8211; but is not limited to &#8211; hemodynamic, metabolic, and tissue measurements. The model has been highly effective in developing new resuscitation concepts and examining novel therapeutic interventions before their testing in larger and translationally more relevant animal models of cardiac arrest and resuscitation.

The rat model described here was recently used to compare the effects of two inhibitors of the sarcolemmal sodium-hydrogen exchanger isoform 1 (NHE-1) on myocardial and hemodynamic function during chest compression and post-resuscitation61. It was previously reported that NHE-1 inhibitors attenuate myocardial reperfusion injury by limiting sodium-induced cytosolic and mitochondrial calcium overload, and thereby help preserve left ventricular distensibility during chest compression and attenuate post-resuscitation myocardial dysfunction12. In this study, the NHE-1 inhibitor cariporide (1 mg/kg), which had been extensively investigated in the past, was compared with the newer compound AVE4454B (1 mg/kg) and vehicle control in three groups of 10 rats each, all subjected to 10 min of untreated VF followed by 8 min of chest compression before delivering electrical shocks. Either compound or vehicle control was randomized for administration into the right atrium immediately before starting chest compression with the investigators blind to the assignment. The effects of the NHE-1 inhibitors were analyzed individually and combined (i.e., against control). As shown in Figure 6, NHE-1 inhibition enabled attaining a predefined aortic diastolic pressure (between 26 mm Hg and 28 mm Hg) with less depth of compression consistent with preservation of left ventricular distensibility. When the coronary perfusion pressure was indexed to the depth of compression (CPP/Depth ratio) &#8211; an index of left ventricular distensibility &#8211; only rats treated with cariporide attained statistical significance. Post-resuscitation, both compounds ameliorated myocardial dysfunction and this effect was associated with greater survival as shown in Figure 7. It was concluded based on this study that cariporide is more effective than AVE4454B for resuscitation from cardiac arrest in this rat model.
<img alt="Figure 1" src="/files/ftp_upload/52413/52413fig1highres.jpg" /> 
Figure 1: Rat Instrumentation. Schematic rendition of the rat model of VF and closed-chest resuscitation illustrating the various instrumentations and devices used in the model to induce VF and perform cardiac resuscitation. AC = alternating current, ECG = electrocardiogram.
<img alt="Figure 2" src="/files/ftp_upload/52413/52413fig2highres.jpg" /> 
Figure 2: Representative Induction of Ventricular Fibrillation. Experiment depicting the ECG and the aortic pressure at baseline 6 min before inducing VF, at the start of the 60 Hz alternating current delivery to induce VF, and after turning the current off 3 min later. The current delivery typically masks the VF waveform superimposing a 60 Hz waveform, which is no longer seen after turning off the current, documenting sustained VF.
<img alt="Figure 3" src="/files/ftp_upload/52413/52413fig3highres.jpg" /> 
Figure 3: Defibrillation Protocol. Algorithm used to guide when to deliver electrical shocks and when to resume chest compression (CC) based on the electrical cardiac rhythm and the mean aortic pressure (MAP) level. VF = ventricular fibrillation, SHOCK = delivery of electrical shocks. The possible resuscitation outcomes include: (1) ROSC, return of spontaneous circulation defined as a MAP &#8805;40 mm Hg lasting &#62;5 min; (2) ROCA, return of cardiac activity defined as an organized rhythm with an aortic pulse pressure &#8805;5 mm Hg but MAP &#60;40 mm Hg; (3) refractory VF, defined as the persistency of VF upon completion of the 5th cycle; (4) PEA, pulseless electrical activity defined as an organized cardiac electrical activity with an aortic pulse pressure &#60;5 mm Hg; and (5) asystole, defined as the absence of electrical and mechanical cardiac activity.
<img alt="Figure 4" src="/files/ftp_upload/52413/52413fig4highres.jpg" /> 
Figure 4: Representative Defibrillation Protocol. Experiment depicting the ECG, the aortic pressure, and the piston displacement (Depth) at the end of chest compression and one additional cycle. Shown are the effects of chest compression (CC) on the aortic pressure while the heart is in VF followed by a pause in chest compression to deliver the initial electrical shock. The shock terminated VF but resulted in weak cardiac activity unable to sustain a mean aortic pressure &#8805;25 mm Hg prompting resumption of chest compression, this time yielding a pulsatile mean aortic pressure &#62;25 mm Hg which rapidly increased to &#62;40 mm Hg consistent with return of spontaneous circulation (ROSC).
<img alt="Figure 5" src="/files/ftp_upload/52413/52413fig5highres.jpg" /> 
Figure 5: Experimental Timeline. Timeline of a typical acute rat experiment showing interventions and measurements. Ao = aortic, BG = blood gases, Co-Ox = co-oximetry, ECG = electrocardiogram, FiO2 = fraction of inspired oxygen, Lac = lactate, RA = right atrium.
<img alt="Figure 6" src="/files/ftp_upload/52413/52413fig6highres.jpg" /> 
Figure 6: Effect of NHE-1 Inhibitors on CPR Efficiency. The depth of chest compression (Depth) and the ratio between coronary perfusion pressure and depth of compression (CPP/Depth) comparing the control solution (C) with AVE4454B (AVE) and cariporide (CRP) before chest compression. NHEI = AVE and CRP groups combined. Line graphs depict Depth and CPP/Depth throughout chest compression comparing NHEI (o) with controls (&#9679;). Numbers in brackets denote rats remaining in ventricular fibrillation. The bar graphs depict the same variables at the last min of chest compression. Values are means &#177; SEM. &#8224;p &#60;0.01, &#8225;p &#60;0.001 vs control by Student&#8217;s t-test; p &#60;0.01, p &#60;0.001 vs control by one-way ANOVA using Holm-Sidak&#8217;s test for multiple comparisons; p &#60;0.05 vs control by one-way ANOVA using Dunn&#8217;s test for multiple comparisons (This figure has been modified from Radhakrishnan et al.61).
<img alt="Figure 7" src="/files/ftp_upload/52413/52413fig7.jpg" /> 
Figure 7: Effect of NHE-1 Inhibitors on Survival. Kaplan-Meier curves in rats that received cariporide (CRP), AVE4454B (AVE), or vehicle control solution. Shown on the left are survival curves for all rats and on the right only those that had return of spontaneous circulation (ROSC). Upper graphs depict survival for the individual interventions and bottom graphs survival for the AVE and CRP groups combined (NHEI). p &#60;0.01 vs control by Gehan-Breslow analysis using Holm-Sidak&#8217;s test for multiple comparisons; &#8224;p = 0.01 vs control by Gehan-Breslow analysis (This figure has been modified from Radhakrishnan et al.61).
<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td rowspan="2">Variables&#160;</td>
			<td>Baseline&#160;</td>
			<td colspan="3">Post-Resuscitation&#160;</td>
		</tr>
		<tr>
			<td>-5 min</td>
			<td>60 min&#160;</td>
			<td>120 min&#160;</td>
			<td>180 min&#160;</td>
		</tr>
		<tr>
			<td>Temperature (&#176;C)</td>
			<td>36.9 &#177; 0.3 [12]</td>
			<td>36.9 &#177; 0.4 [6]</td>
			<td>36.7 &#177; 0.3 [6]</td>
			<td>37.0 &#177; 0.6 [5]</td>
		</tr>
		<tr>
			<td>HR (min-1)</td>
			<td>379 &#177; 30&#160;</td>
			<td>334 &#177; 27&#160;</td>
			<td>346 &#177; 21&#160;</td>
			<td>370 &#177; 35</td>
		</tr>
		<tr>
			<td>Cardiac Output (ml/min)</td>
			<td>87 &#177; 13&#160;</td>
			<td>48 &#177; 11</td>
			<td>33 &#177; 11</td>
			<td>30 &#177; 10</td>
		</tr>
		<tr>
			<td>Cardiac Index (ml/kg&#8729; min-1)</td>
			<td>175 &#177; 28&#160;</td>
			<td>93 &#177; 22</td>
			<td>65 &#177; 20</td>
			<td>58 &#177; 19</td>
		</tr>
		<tr>
			<td>Ao Sysolic Pressure (mmHg)</td>
			<td>162 &#177; 15&#160;</td>
			<td>108 &#177; 19</td>
			<td>107 &#177; 24</td>
			<td>102 &#177; 20</td>
		</tr>
		<tr>
			<td>Ao Diastolic Pressure (mmHg)</td>
			<td>130 &#177; 13&#160;</td>
			<td>84 &#177; 13</td>
			<td>86 &#177; 21</td>
			<td>82 &#177; 16</td>
		</tr>
		<tr>
			<td>Ao Mean Pressure (mmHg)</td>
			<td>141 &#177; 13&#160;</td>
			<td>92 &#177; 15</td>
			<td>93 &#177; 22</td>
			<td>89 &#177; 17</td>
		</tr>
		<tr>
			<td>RA Mean Pressure (mmHg)</td>
			<td>0 &#177; 1&#160;</td>
			<td>2 &#177; 1</td>
			<td>2 &#177; 2</td>
			<td>1 &#177; 2</td>
		</tr>
		<tr>
			<td>End-tidal CO2 (mmHg)</td>
			<td>37 &#177; 10&#160;</td>
			<td>34 &#177; 14</td>
			<td>24 &#177; 16</td>
			<td>24 &#177; 17</td>
		</tr>
		<tr>
			<td>pH, Aorta (unit)</td>
			<td>7.40 &#177; 0.04&#160;</td>
			<td>7.28 &#177; 0.11</td>
			<td>7.36 &#177; 0.10</td>
			<td>7.34 &#177; 0.08</td>
		</tr>
		<tr>
			<td>Lactate, Aorta (mmol/L)</td>
			<td>0.56 &#177; 0.32&#160;</td>
			<td>5.68 &#177; 2.64</td>
			<td>3.24 &#177; 1.63</td>
			<td>3.38 &#177; 2.15</td>
		</tr>
		<tr>
			<td>PO2, Aorta (mmHg)</td>
			<td>84 &#177; 8&#160;</td>
			<td>178 &#177; 18</td>
			<td>206 &#177; 9</td>
			<td>206 &#177; 25</td>
		</tr>
		<tr>
			<td>PCO2, Aorta (mmHg)</td>
			<td>40 &#177; 6&#160;</td>
			<td>30 &#177; 11</td>
			<td>29 &#177; 9</td>
			<td>24 &#177; 10</td>
		</tr>
	</tbody>
</table>
Table 1: Representative Hemodynamic and Metabolic Values. Baseline values were obtained in 12 male retired breeder Sprague-Dawley rats after completion of surgical instrumentation and before induction of ventricular fibrillation. Subsequent values were obtained at 60, 120, and 180 minutes post-resuscitation. Numbers in brackets denote rats that remained alive in the post-resuscitation interval. Data are shown as mean &#177; SD. Ao = aortic, HR = heart rate, RA = right atrial.

Watch this Scientific Journal Video about A Rat Model of Ventricular Fibrillation and Resuscitation by Conventional Closed-chest Technique at JoVE.com

A Rat Model of Ventricular Fibrillation and Resuscitation by Conventional Closed-chest Technique

This article describes a rat model of electrically-induced ventricular fibrillation and resuscitation by chest compression, ventilation, and delivery of electrical shocks that simulates an episode of sudden cardiac arrest and conventional cardiopulmonary resuscitation. The model enables gathering insights on the pathophysiology of cardiac arrest and exploration of new resuscitation strategies.

A rat model of electrically-induced ventricular fibrillation followed by cardiac resuscitation using a closed chest technique that incorporates the basic ...

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15.8K Views.  Rosalind Franklin University of Medicine and Science. This article describes a rat model of electrically-induced ventricular fibrillation and resuscitation by chest compression, ventilation, and delivery of electrical shocks that simulates an episode of sudden cardiac arrest and conventional cardiopulmonary resuscitation. The model enables gathering insights on the pathophysiology of cardiac arrest and exploration of new resuscitation strategies.

Video: A Rat Model of Ventricular Fibrillation and Resuscitation by Conventional Closed-chest Technique

Normothermic Cardiac Arrest and Cardiopulmonary Resuscitation: A Mouse Model of Ischemia-Reperfusion Injury

Acute Kidney Injury (AKI) is a common, highly lethal, complication of critical illness which has a high mortality1-4 and which is most 
frequently caused by whole-body hypoperfusion.5,6 Successful reproduction of whole-body hypoperfusion in rodent models has been fraught with 
difficulty.7-9,9,10 Models which employ focal ischemia have repeatedly demonstrated results which do not translate to the clinical setting, and larger 
animal models which allow for whole body hypoperfusion lack access to the full toolset of genetic manipulation possible in the mouse.11,12 However, in recent 
years a mouse model of cardiac arrest and cardiopulmonary resuscitation has emerged which can be adapted to model AKI.13 This model reliably reproduces 
physiologic, functional, anatomic, and histologic outcomes seen in clinical AKI, is rapidly repeatable, and offers all of the significant advantages of a murine surgical 
model, including access to genetic manipulative techniques, low cost relative to large animals, and ease of use. Our group has developed extensive experience 
with use of this model to assess a number of organ-specific outcomes in AKI.14,15

A powerful model for perioperative and critical care related acute kidney injury is presented. Using whole body hypoperfusion induced by cardiac arrest it is possible to nearly replicate the histologic and functional changes of clinical AKI.

Acute Kidney Injury (AKI) is a common, highly lethal, complication of critical illness which has a high mortality1-4 and which is most 
frequently caused ...

A Murine Closed-chest Model of Myocardial Ischemia and Reperfusion

Surgical trauma by thoracotomy in open-chest models of coronary ligation induces an immune response which modifies different mechanisms involved in ischemia and reperfusion. Immune response includes cytokine expression and release or secretion of endogenous ligands of innate immune receptors. Activation of innate immunity can potentially modulate infarct size. We have modified an existing murine closed-chest model using hanging weights which could be useful for studying myocardial pre- and postconditioning and the role of innate immunity in myocardial ischemia and reperfusion. This model allows animals to recover from surgical trauma before onset of myocardial ischemia.
Volatile anesthetics have been intensely studied and their preconditioning effect for the ischemic heart is well known. However, this protective effect precludes its use in open chest models of coronary artery ligation. Thus, another advantage could be the use of the well controllable volatile anesthetics for instrumentation in a chronic closed-chest model, since their preconditioning effect lasts up to 72 hours. Chronic heart diseases with intermittent ischemia and multiple hit models are other possible applications of this model.
For the chronic closed-chest model, intubated and ventilated mice undergo a lateral blunt thoracotomy via the 4th intercostal space. Following identification of the left anterior descending a ligature is passed underneath the vessel and both suture ends are threaded through an occluder. Then, both suture ends are passed through the chest wall, knotted to form a loop and left in the subcutaneous tissue. After chest closure and recovery for 5 days, mice are anesthetized again, chest skin is reopened and hanging weights are hooked up to the loop under ECG control.
At the end of the ischemia/reperfusion protocol, hearts can be stained with TTC for infarct size assessment or undergo perfusion fixation to allow morphometric studies in addition to histology and immunohistochemistry.

Surgical trauma induces an inflammatory response. Cytokines and endogenous ligands are known to modulate myocardial infarct size following ischemia and reperfusion. We present a modified closed-chest model of murine ischemia and reperfusion using hanging weights to minimize effects of thoracotomy.

Surgical trauma by thoracotomy in open-chest models of coronary ligation induces an immune response which modifies different mechanisms involved in ...

Testing the Efficacy of Pharmacological Agents in a Pericardial Target Delivery Model in the Swine

To date, many pharmacological agents used to treat or prevent arrhythmias in open-heart cases create undesired systemic side effects. For example, antiarrhythmic drugs administered intravenously can produce drops in systemic pressure in the already compromised cardiac patient. While performing open-heart procedures, surgeons will often either create a small port or form a pericardial cradle to create suitable fields for operation. This access yields opportunities for target pharmacological delivery (antiarrhythmic or ischemic preconditioning agents) directly to the myocardial tissue without undesired side effects.
We have developed a swine model for testing pharmacological agents for target delivery within the pericardial fluid. While fully anesthetized, each animal was instrumented with a Swan-Ganz catheter as well as left and right ventricle pressure catheters, and pacing leads were placed in the right atrial appendage and the right ventricle. A medial sternotomy was then performed and a pericardial access cradle was created; a plunge pacing lead was placed in the left atrial appendage and a bipolar pacing lead was placed in the left ventricle. Utilizing a programmer and a cardiac mapping system, the refractory period of the atrioventricular node (AVN), atria and ventricles was determined. In addition, atrial fibrillation (AF) induction was produced utilizing a Grass stimulator and time in AF was observed. These measurements were performed prior to treatment, as well as 30 min&#160;and 60 min&#160;after pericardial treatment. Additional time points were added for selected studies. The heart was then cardiopleged and reanimated in a four chamber working mode. Pressure measurements and function were recorded for 1 hr after reanimation. This treatment strategy model allowed us to observe the effects of pharmacological agents that may decrease the incidence of cardiac arrhythmias and/or ischemic damage, during and after open-heart surgery.

We have developed a swine model for the target delivery of pharmacological agents within the pericardial space/fluid. Using this approach, the relative benefits of administered agents on induced atrial fibrillation, relative refractory periods and/or ischemic protection can be investigated.

To date, many pharmacological agents used to treat or prevent arrhythmias in open-heart cases create undesired systemic side effects. For example, ...

Pre-clinical Model of Cardiac Donation after Circulatory Death

Cardiac transplantation demand is on the rise; nevertheless, organ availability is limited due to a paucity of suitable donors. Organ donation after circulatory death (DCD) is a solution to address this limited availability, but due to a period of prolonged warm ischemia and the risk of tissue injury, its routine use in cardiac transplantation is seldom seen. In this manuscript we provide a detailed protocol closely mimicking current clinical practices in the context of DCD with continuous monitoring of heart function, allowing for the evaluation of novel cardioprotective strategies and interventions to decrease ischemia-reperfusion injury.
In this model, the DCD protocol is initiated in anesthetized Lewis rats by stopping ventilation to induce circulatory death. When systolic blood pressure drops below 30 mmHg, the warm ischemic time is initiated. After a pre-set warm ischemic period, hearts are flushed with a normothermic cardioplegic solution, procured, and mounted onto a Langendorff ex vivo heart perfusion system. Following 10 min of initial reperfusion and stabilization, cardiac reconditioning is continuously evaluated for 60 min using intraventricular pressure monitoring. A heart injury is assessed by measuring cardiac troponin T and the infarct size is quantified by histological staining. The warm ischemic time can be modulated and tailored to develop the desired amount of structural and functional damage. This simple protocol allows for the evaluation of different cardioprotective conditioning strategies introduced at the moment of cardioplegia, initial reperfusion and/or during ex vivo perfusion. Findings obtained from this protocol can be reproduced in large models, facilitating clinical translation.

This protocol shows a simple and flexible approach for the evaluation of new conditioning agents or strategies to increase the feasibility of cardiac donation after circulatory death.

Cardiac transplantation demand is on the rise; nevertheless, organ availability is limited due to a paucity of suitable donors. Organ donation after ...

Standardized Model of Ventricular Fibrillation and Advanced Cardiac Life Support in Swine

Cardiopulmonary resuscitation after cardiac arrest, independent of its origin, is a regularly encountered medical emergency in hospitals as well as preclinical settings. Prospective randomized trials in human subjects are difficult to design and ethically ambiguous, which results in a lack of evidence-based therapies. The model presented in this report represents one of the most common causes of cardiac arrests, ventricular fibrillation, in a standardized setting in a large animal model. This allows for reproducible observations and various therapeutic interventions under clinically accurate conditions, hence facilitating the generation of better evidence and eventually the potential for improved medical treatment.

Cardiopulmonary resuscitation and defibrillation are the only effective therapeutic options during cardiac arrest caused by ventricular fibrillation. This model presents a standardized regimen to induce, assess, and treat this physiological state in a porcine model, thus providing a clinical approach with various opportunities for data collection and analysis.

Cardiopulmonary resuscitation after cardiac arrest, independent of its origin, is a regularly encountered medical emergency in hospitals as well as ...

Improved Rodent Model of Myocardial Ischemia and Reperfusion Injury

Myocardial ischemia and reperfusion injury (MIRI), induced by coronary heart disease (CHD), causes damage to the cardiomyocytes. Furthermore, evidence suggests that thrombolytic therapy or primary percutaneous coronary intervention (PPCI) does not prevent reperfusion injury. There is still no ideal animal model for MIRI. This study aims to improve the MIRI model in rats to make surgery easier and more feasible. A unique method for establishing MIRI is developed by using a soft tube during a key step of the ischemic period. To explore this method, thirty rats were randomly divided into three groups: sham group (n = 10); experimental model group (n = 10); and existing model group (n = 10). Findings of triphenyltetrazolium chloride staining, electrocardiography, and percent survival are compared to determine the accuracies and survival rates of the operations. Based on the study results, it has been concluded that the improved surgery method is associated with a higher survival rate, elevated ST-T segment, and larger infarct size, which is expected to mimic the pathology of MIRI better.

Myocardial ischemia-reperfusion model of rat heart is improved by using a self-made retractor, polyvinyl chloride tube, and a unique knotting method. Electrocardiogram, triphenyltetrazolium chloride and histological staining, and percent survival analysis results showed that the improved model group has higher success and survival rates than the already existing model group.

Myocardial ischemia and reperfusion injury (MIRI), induced by coronary heart disease (CHD), causes damage to the cardiomyocytes. Furthermore, evidence ...

Transthoracic Echocardiography to Assess Post-Resuscitation Left Ventricular Dysfunction After Acute Myocardial Infarction and Cardiac Arrest in Pigs

One of the main causes of out-of-hospital cardiac arrest is acute myocardial infarction (AMI). After successful resuscitation from cardiac arrest, approximately 70% of patients die before hospital discharge due to post-resuscitation myocardial and cerebral dysfunction. In experimental models, myocardial dysfunction after cardiac arrest, characterized by an impairment in both left ventricular (LV) systolic and diastolic function, has been described as reversible but very little data are available in cardiac arrest models associated with AMI in pigs. Transthoracic echocardiography is the first-line diagnostic test for the assessment of myocardial dysfunction, structural changes and/or AMI extension. In this pig model of ischemic cardiac arrest, echocardiography was done at baseline and 2-4 and 96 hours after resuscitation. In the acute phase, the examinations are done in anesthetized, mechanically ventilated pigs (weight 39.8 &#177; 0.6 kg) and ECG is recorded continuously. Mono- and bi-dimensional, Doppler and tissue Doppler recordings are acquired. Aortic and left atrium diameter, end-systolic and end-diastolic left ventricular wall thicknesses, end-diastolic and end-systolic diameters and shortening fraction (SF) are measured. Apical 2-, 3-, 4-, and 5-chamber views are acquired, LV volumes and ejection fraction are calculated. Segmental wall motion analysis is done to detect the localization and estimate the extent of myocardial infarction. Pulsed Wave Doppler echocardiography is used to record trans-mitral flow velocities from a 4-apical chamber view and trans-aortic flow from a 5-chamber view to calculate LV cardiac output (CO) and stroke volume (SV). Tissue Doppler Imaging (TDI) of LV lateral and septal mitral anulus is recorded (TDI septal and lateral s&#39;, e&#39;, a&#39; velocities). All the recordings and measurements are done according to the recommendations of the American and European Societies of Echocardiography Guidelines.

Transthoracic echocardiography is the first-line diagnostic test for post-resuscitation left ventricular dysfunction and structural changes in a pig model of cardiac arrest.

One of the main causes of out-of-hospital cardiac arrest is acute myocardial infarction (AMI). After successful resuscitation from cardiac arrest, ...

A Model of Long-Term Ventricular Fibrillation in Isolated Rat Hearts

Ventricular fibrillation (VF) is a fatal arrhythmia with a high incidence in cardiac patients, but VF arrest under perfusion is a neglected method of intraoperative arrest in the field of cardiac surgery. With recent advances in cardiac surgery, the demand for prolonged VF studies under perfusion has increased. However, the field lacks simple, reliable, and reproducible animal models of chronic ventricular fibrillation. This protocol induces long-term VF through alternating current (AC) electrical stimulation of the epicardium. Different conditions were used to induce VF, including continuous stimulation with a low or high voltage to induce long-term VF and stimulation for 5 min with a low or high voltage to induce spontaneous long-term VF. The success rates of the different conditions, as well as the rates of myocardial injury and recovery of cardiac function, were compared. The results showed that continuous low-voltage stimulation induced long-term VF and that 5 min of low-voltage stimulation induced spontaneous long-term VF with mild myocardial injury and a high rate of recovery of cardiac function. However, the low-voltage, continuously stimulated long-term VF model had a higher success rate. High-voltage stimulation provided a higher rate of VF induction but showed a low defibrillation success rate, poor recovery of cardiac function, and severe myocardial injury. On the basis of these results, continuous low-voltage epicardial AC stimulation is recommended for its high success rate, stability, reliability, reproducibility, low impact on cardiac function, and mild myocardial injury.

This protocol presents a model of long-term ventricular fibrillation in rat hearts induced by continuous stimulation with low-voltage alternating current. This model has a high success rate, is stable, reliable, and reproducible, has a low impact on cardiac function, and causes only mild myocardial injury.

Ventricular fibrillation (VF) is a fatal arrhythmia with a high incidence in cardiac patients, but VF arrest under perfusion is a neglected method of ...

Chronic Ovine Model of Right Ventricular Failure and Functional Tricuspid Regurgitation

The pathophysiology of severe functional tricuspid regurgitation (FTR) associated with right ventricular dysfunction is poorly understood, leading to suboptimal clinical results. We set out to establish a chronic ovine model of FTR and right heart failure to investigate the mechanisms of FTR. Twenty adult male sheep (6-12 months old, 62 &#177; 7 kg) underwent a left thoracotomy and baseline echocardiography. A pulmonary artery band (PAB) was placed and cinched around the main pulmonary artery (PA) to at least double the systolic pulmonary artery pressure (SPAP), inducing right ventricular (RV) pressure overload and signs of RV dilatation. PAB acutely increased the SPAP from 21 &#177; 2 mmHg to 62 &#177; 2 mmHg. The animals were followed for 8 weeks, symptoms of heart failure were treated with diuretics, and surveillance echocardiography was used to assess for pleural and abdominal fluid collection. Three animals died during the follow-up period due to stroke, hemorrhage, and acute heart failure. After 2 months, a median sternotomy and epicardial echocardiography were performed. Of the surviving 17 animals, 3 developed mild tricuspid regurgitation, 3 developed moderate tricuspid regurgitation, and 11 developed severe tricuspid regurgitation. Eight weeks of pulmonary artery banding resulted in a stable chronic ovine model of right ventricular dysfunction and significant FTR. This large animal platform can be used to further investigate the structural and molecular basis of RV failure and functional tricuspid regurgitation.

Right ventricular failure and functional tricuspid regurgitation are associated with left-sided heart disease and pulmonary hypertension, which contribute significantly to morbidity and mortality in patients. Establishing a chronic ovine model to study right ventricular failure and functional tricuspid regurgitation will help in understanding their mechanisms, progression, and possible treatments.

The pathophysiology of severe functional tricuspid regurgitation (FTR) associated with right ventricular dysfunction is poorly understood, leading to ...

Extracorporeal Cardiopulmonary Resuscitation in Animal Model After Cardiac Arrest

Pediatric Animal Model of Extracorporeal Cardiopulmonary Resuscitation After Prolonged Circulatory Arrest

Congenital heart disease (CHD) is the most prevalent congenital malformation, with about one million births impacted worldwide per year. Comprehensive investigation of this disease requires appropriate and validated animal models. Piglets are commonly used for translational research due to their analogous anatomy and physiology. This work aimed to describe and validate a neonatal piglet model of cardiopulmonary bypass (CPB) with circulatory and cardiac arrest (CA) as a tool for studying severe brain damage and other complications of cardiac surgery. In addition to including a list of materials, this work provides a roadmap for other investigators to plan and execute this protocol. After experienced practitioners performed several trials, the representative results of the model demonstrated a 92% success rate, with failures attributed to small piglet size and variant vessel anatomy. Furthermore, the model allowed practitioners to select from a wide variety of experimental conditions, including varying times in CA, temperature alterations, and pharmacologic interventions. In summary, this method uses materials readily available in most hospital settings, is reliable and reproducible, and can be widely employed to enhance translational research in children undergoing heart surgery.

Author Spotlight: Simulating Pediatric Cardiac Surgery Using a Neonatal Piglet Model

This protocol describes a neonatal porcine model of cardiopulmonary bypass (CPB), with circulatory and cardiac arrest as a tool for studying severe brain damage and other complications secondary to CPB.

Congenital heart disease (CHD) is the most prevalent congenital malformation, with about one million births impacted worldwide per year. Comprehensive ...

A Rat Model of Ventricular Fibrillation and Resuscitation by Conventional Closed-chest Technique

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