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A rodent model of left heart volume overload from mitral regurgitation is reported. Mitral regurgitation of controlled severity is induced by advancing a needle of defined dimensions into the anterior leaflet of the mitral valve, in a beating heart, with ultrasound guidance.
Mitral regurgitation (MR) is a widely prevalent heart valve lesion, which causes cardiac remodeling and leads to congestive heart failure. Though the risks of uncorrected MR and its poor prognosis are known, the longitudinal changes in cardiac function, structure and remodeling are incompletely understood. This knowledge gap has limited our understanding of the optimal timing for MR correction, and the benefit that early versus late MR correction may have on the left ventricle. To investigate the molecular mechanisms that underlie left ventricular remodeling in the setting of MR, animal models are necessary. Traditionally, the aorto-caval fistula model has been used to induce volume overload, which differs from clinically relevant lesions such as MR. MR represents a low-pressure volume overload hemodynamic stressor, which requires animal models that mimic this condition. Herein, we describe a rodent model of severe MR in which the anterior leaflet of the rat mitral valve is perforated with a 23G needle, in a beating heart, with echocardiographic image guidance. The severity of MR is assessed and confirmed with echocardiography, and the reproducibility of the model is reported.
Mitral regurgitation (MR) is a common heart valve lesion, diagnosed in 1.7% of the general US population and in 9% of the elderly population greater than 65 years of age1. In this heart valve lesion, improper closure of the mitral valve leaflets in systole, causes regurgitation of blood from the left ventricle into the left atrium. MR can occur due to various etiologies; however, primary lesions of the mitral valve (primary MR) are diagnosed and treated more frequently compared to secondary MR2. Isolated primary MR is often a result of myxomatous degeneration of the mitral valve, resulting in elongation of the leaflets or chordae tendineae, or rupture of some chordae, all of which contribute to the loss of systolic coaptation of the valve.
MR resulting from such valve lesions elevates the blood volume filling the left ventricle in each heartbeat, increasing the end diastolic wall stress and providing a hemodynamic stressor that incites cardiac adaptation and remodeling. Cardiac remodeling in this lesion is often characterized by significant chamber enlargement3,4, mild wall hypertrophy, with preserved contractile function for prolonged periods of time. Since the ejection fraction is often preserved, correction of MR using surgical or transcatheter means is often delayed, until the onset of symptoms such as dyspnea, heart failure, and arrhythmias. However, uncorrected MR is associated with high risks of cardiac adverse events, though currently knowledge regarding the ultrastructural changes underlying these events are unknown.
Animal models of MR provide a valuable model to investigate such ultrastructural changes in the heart, and study longitudinal progression of the disease. Previously, researchers have induced MR in large animals including pigs, dogs, and sheep, by creating an external ventriculo-atrial shunt5, intracardiac chordal rupture6, or leaflet perforation7. While surgical techniques are easier in large animals, these studies have been limited to sub-chronic follow-up in a small sample size, due to the high costs of performing such studies in large animals. Furthermore, molecular analysis of tissue from these models is often challenging due to limited species-specific antibodies and annotated genome libraries for alignment.
Small animal models of MR can provide a suitable alternative to study this valve lesion and its impact on cardiac remodeling. Historically, the rat model of aorto-caval fistula (ACF) of cardiac volume overload has been used. First described in 1973 by Stumpe et al.8, an arterio-venous fistula is surgically created to bypass high pressure arterial blood from the descending aorta into the low pressure inferior vena cava. The high flow rate in the fistula induces a drastic volume overload on both sides of the heart, causing significant right and left ventricular hypertrophy and dysfunction occurring within days of creating the ACF9. Despite its success, ACF does not mimic the hemodynamics of MR, a low-pressure volume overload, which elevates preload but also reduces afterload. Due to such limitations of the ACF model, we sought to develop and characterize a model of MR that better mimics the low-pressure volume overload.
Herein, we describe the protocol for a model of mitral valve leaflet puncture to create severe MR in rats10,11. A hypodermic needle was introduced into the beating rat heart, and advanced into the anterior mitral valve leaflet under real-time echocardiographic guidance. The technique is highly reproducible and a relatively good model that mimics MR as seen in patients. MR severity is controlled by the size of the needle used to perforate the mitral leaflet and severity of MR can be assessed using transesophageal echocardiography (TEE).
Procedures were approved by the Animal Care and Use Program at Emory University under the protocol number EM63Rr, approval date 06/06/2017.
1. Pre-surgical preparation
2. Animal preparation
NOTE: Adult Sprague-Dawley male rats weighing 350-400 g were used in this study. The surgical techniques are amenable to slightly smaller or larger animals, if desired.
3. Left thoracotomy
4. Echo guided MR procedure (Figure 3 & Figure 4)
5. Animal recovery and post-operative care
6. Validation of MR severity with echocardiography (Figure 5)
7. Sham surgery
Feasibility and reproducibility
The proposed MR model is highly reproducible, with a well defined hole in the mitral leaflet achieved in 100% of the rats used in this study. Figure 6A depicts the direction of the needle as it is inserted into the mitral valve. Figure 6B depicts a hole in the mitral valve leaflet from a representative rat explanted at 2 weeks after the proce...
A reproducible rodent model of severe MR with good survival (93.75% survival after surgery) and without significant post-operative complications is reported. Real-time imaging with transesophageal echocardiography and introduction of a needle into the beating heart to puncture the mitral leaflet are feasible and can be taught. Severe MR was produced with the 23 G needle size in this study, which can be varied as desired using a smaller or larger needle. MR induced in this model creates a low-pressure volume overload on t...
M.P is an advisor to Heart Repair Technologies (HRT), for which he has received consulting fees. HRT did not have any role in this study, nor did it provide any funding to support this work.
This work was funded by grant 19PRE34380625 and 14SDG20380081 from the American Heart Association to D. Corporan and M. Padala respectively, grants HL135145, HL133667, and HL140325 from the National Institutes of Health to M. Padala, and infrastructure funding from the Carlyle Fraser Heart Center at Emory University Hospital Midtown to M. Padala.
Name | Company | Catalog Number | Comments |
23G needle | Mckesson | 16-N231 | |
25G needle, 5/8 inch | McKesson | 1031797 | |
4-0 vicryl | Ethicon | J496H | |
6-0 prolene | Ethicon | 8307H | |
70% ethanol | McKesson | 350600 | |
ACE Light Source | Schott | A20500 | |
ACUSON AcuNav Ultrasound probe | Biosense Webster | 10135936 | 8Fr Intracardiac echo probe |
ACUSON PRIME Ultrasound System | Siemens | SC2000 | |
Betadine | McKesson | 1073829 | |
Blunted microdissecting scissors | Roboz | RS5990 | |
Buprenorphine | Patterson Veterinary | 99628 | |
Carprofen | Patterson Veterinary | 7847425 | |
Chest tube (16G angiocath) | Terumo | SR-OX1651CA | |
Disposable Surgical drapes | Med-Vet | SMS40 | |
Electric Razor | Oster | 78400-XXX | |
Gentamycin | Patterson Veterinary | 78057791 | |
Heat lamp with table clamp | Braintree Scientific | HL-1 120V | |
Hemostatic forceps, curved | Roboz | RS7341 | |
Hemostatic forceps, straight | Roboz | RS7110 | |
Induction chamber | Braintree Scientific | EZ-1785 | |
Injection Plug, Cap, Luer Lock | Exel | 26539 | |
Isoflurane | Patterson Veterinary | 6679401725 | |
Mechanical ventilator | Harvard Apparatus | Inspira ASV | |
Microdissecting forceps | Roboz | RS5135 | |
Microdissecting spring scissors | Roboz | RS5603 | |
Needle holder | Roboz | RS6417 | |
No. 15 surgical blade | McKesson | 1642 | |
Non-woven sponges | McKesson | 446036 | |
Otoscope | Welch Allyn | 23862 | |
Oxygen | Airgas Healthcare | UN1072 | |
Pulse Oximeter | Nonin Medical | 2500A VET | |
Retractor, Blunt 4x4 | Roboz | RS6524 | |
Rodent Surgical Monitor | Indus Instruments | 113970 | The integrated platform allows for monitoring of vital signs and surgical warming |
Scale | Salter Brecknell | LPS 150 | |
Scalpel Handle | Roboz | RS9843 | |
Silk suture 3-0 | McKesson | 220263 | |
Small Animal Anesthesia System | Ohio Medical | AKDL03882 | |
Sterile saline (0.9%) | Baxter | 281322 | |
Sugical Mask | McKesson | 188696 | |
Surgical cap | McKesson | 852952 | |
Surgical gloves | McKesson | 854486 | |
Syringe 10mL | McKesson | 1031801 | |
Syringe 1mL | McKesson | 1031817 | |
Ultra-high frequency probe | Fujifilm Visualsonics | MS250 | |
Ultrasound gel | McKesson | 150690 | |
VEVO Ultrasound System | Fujifilm Visualsonics | VEVO 2100 |
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