Name: assessment of right ventricular structure and function in mouse model of pulmonary artery constriction by transthoracic echocardiography
Uploaded: 2014-02-03T14:45:00
Description: Watch this Scientific Journal Video about Assessment of Right Ventricular Structure and Function in Mouse Model of Pulmonary Artery Constriction by Transthoracic Echocardiography at JoVE.com

We thank Fred Roberts and Chris White for exemplary technical support. We thank Brigham Women&#8217;s Hospital Cardiovascular Physiology Core for providing with the instrumentation and the funds for this work. This work was supported in part by NHLBI grants HL093148, HL086967, and HL 088533(RL), K99HL107642 and the Ellison Foundation (SC).

Surgical Procedure
<ol>
	<li>Obtain 8 week-old male C57BL/6 mice and acclimate for one week before any experimental procedures are performed.</li>
	<li>Prior to imaging, pulmonary artery occlusion is performed as described previously14&#160;in accordance with AVMA guidelines and approved IACUC protocols. 
	Echocardiographic Images Acquisition and Measurements 
	All abbreviations used are summarized in Table 1.</li>
</ol>
1. Parasternal Long Axi...

<ol>
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We demonstrate that TTE provides a sensitive and reproducible methodology for routine assessment of RV structure and function in mice. Before the advent of TTE, studies of the RV largely focused on RVSP measurement via right heart catheterization, a terminal and invasive procedure6,9,11,17.
Prior reports have described a variety of techniques for performing right heart measurements3,4,11,17-19. However, the majority of previous studies reported RV size and structural data...

Historically, prognostic assessment of heart failure has focused on the LV, which is easy to image via echocardiography. Numerous studies on LV structure and function using echocardiography have led to the establishment of normal values for LV structure and function1,5,6. Measurements of LV size and systolic function obtained from two-dimensional and Color Doppler images are of great importance as they allow visual delineation of compartments and geometry in great detail for the LV7. M-Mode is often used for measuring LV dimensions and fractional shortening (FS) in mice. Inter-observer and intra-observer variability are low for diameter measurements using this mode, but wall thickness measurements tend to be quite variable7. Pulsed Doppler with color (PW or Color Doppler) has been used to evaluate valvular regurgitation8,9.
Similar to LV, the RV plays an important role and is a significant predictor of morbidity and mortality in patients afflicted with cardiopulmonary disease1,7,10. However, echocardiographic evaluation of RV is inherently challenging due to its complex shape5,11 and its retrosternal position that blocks the ultrasound waves8,9. RV is a crescent shaped structure wrapping around the LV and has a complex anatomy with thin walls that are accustomed to low pressure and resistance to pulmonary vasculature6. To overcome elevated vascular resistance (PVR), the RV first increases in size and undergoes hypertrophies. In chronic diseases like pulmonary hypertension or pulmonary vascular disease, RV undergoes progressive dilatation, eventually resulting in the deterioration of systolic and diastolic function4,5,10.
Echocardiography plays an important role in the screening and diagnosis of PAH despite some limitations present in its clinical diagnostic capability. The main advantage of TTE lies in that it is noninvasive and that it can be performed on lightly sedated, or even conscious animals9. TTE also provides a reasonable estimate of PA pressures, as well as an ongoing assessment of changes in RV structure and function12,13. Due to technical advances in TTE, which include the development of high-frequency mechanical probes, allowing axial resolution of approximately 50 &#956;m at a depth of 5-12 mm, high frame rates (greater than 300 frame/sec), and high sampling rates, echocardiography is a choice tool for imaging the rapidly contracting small sized mouse heart8,11.
Longitudinal monitoring of RV function using multiple views, including 2-dimensional (2D) short and long axis, M-mode and Doppler acoustic windows provide complementary information of RV anatomy and function. Collectively, this methodology permits complete longitudinal assessment of RV hemodynamics in physiology and pathological setting4,7.
Herein, we provide a detailed step-by-step methodology of using noninvasive TTE to characterize RV anatomical and functional changes secondary to PAC in mice.

<table border="0" cellpadding="0" cellspacing="0" width="609">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="61">
			<td height="61" style="height:61px;width:157px;">High Frequency Ultrasound</td>
			<td style="width:108px;">FUJIFILM VisualSonics, Inc.</td>
			<td style="width:96px;">Vevo 2100</td>
			<td style="width:248px;"></td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:157px;">High-frequency Mechanical Transducer</td>
			<td style="width:108px;">FUJIFILM VisualSonics, Inc.</td>
			<td style="width:96px;">MS250, MS550D, MS400</td>
			<td style="width:248px;"></td>
		</tr>
		<tr height="67">
			<td height="67" style="height:67px;width:157px;">Millar Mikro Pressure Catheter</td>
			<td style="width:108px;">Millar</td>
			<td style="width:96px;">SPR-1000</td>
			<td style="width:248px;"></td>
		</tr>
	</tbody>
</table>

assessment of right ventricular structure and function in mouse model of pulmonary artery constriction by transthoracic echocardiography

Emerging clinical data support the notion that RV dysfunction is critical to the pathogenesis of cardiovascular disease and heart failure1-3. Moreover, the RV is significantly affected in pulmonary diseases such as pulmonary artery hypertension (PAH). In addition, the RV is remarkably sensitive to cardiac pathologies, including left ventricular (LV) dysfunction, valvular disease or RV infarction4. To understand the role of RV in the pathogenesis of cardiac diseases, a reliable and noninvasive method to access the RV structurally and functionally is essential.
A noninvasive trans-thoracic echocardiography (TTE) based methodology was established and validated for monitoring dynamic changes in RV structure and function in adult mice. To impose RV stress, we employed a surgical model of pulmonary artery constriction (PAC) and measured the RV response over a 7-day period using a high-frequency ultrasound microimaging system. Sham operated mice were used as controls. Images were acquired in lightly anesthetized mice at baseline (before surgery), day 0 (immediately post-surgery), day 3, and day 7 (post-surgery). Data was analyzed offline using software.
Several acoustic windows (B, M, and Color Doppler modes), which can be consistently obtained in mice, allowed for reliable and reproducible measurement of RV structure (including RV wall thickness, end-diastolic&#160;and end-systolic dimensions), and function (fractional area change, fractional shortening, PA peak velocity, and peak pressure gradient) in normal mice and following PAC.
Using this method, the pressure-gradient resulting from PAC was accurately measured in real-time using Color Doppler mode and was comparable to direct pressure measurements performed with a Millar high-fidelity microtip catheter. Taken together, these data demonstrate that RV measurements obtained from various complimentary views using echocardiography are reliable, reproducible and can provide insights regarding RV structure and function. This method will enable a better understanding of the role of RV cardiac dysfunction.

In this study, baseline echocardiography was performed 48 hr&#160;prior to surgery. Mice were randomized into two groups. Mice received pulmonary artery occlusions (PAC) and sham operations (Sham). Echocardiography was performed at day 0, 3, and 7 following surgical procedure.&#160; The animals were euthanized immediately following the last echocardiography and hearts were harvested for histological assessment.&#160;Catheterization was conducted in subgroup (n=3 and 2 for day 0 and 7, respectively) of PAC mice to measure...

Watch this Scientific Journal Video about Assessment of Right Ventricular Structure and Function in Mouse Model of Pulmonary Artery Constriction by Transthoracic Echocardiography at JoVE.com

Assessment of Right Ventricular Structure and Function in Mouse Model of Pulmonary Artery Constriction by Transthoracic Echocardiography

Right ventricle (RV) dysfunction is critical to the pathogenesis of cardiovascular disease, yet limited methodologies are available for its evaluation. Recent advances in ultrasound imaging provide a noninvasive and accurate option for longitudinal RV study. Herein, we detail a step-by-step echocardiographic method using a murine model of RV pressure overload.

Emerging clinical data support the notion that RV dysfunction is critical to the pathogenesis of cardiovascular disease and heart failure1-3. Moreover, ...

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Transthoracic Echocardiography in Mice

In recent years, murine models have become the primary avenue for studying the molecular mechanisms of cardiac dysfunction resulting from changes in gene expression. Transgenic and gene targeting methods can be used to generate mice with altered cardiac size and function,1-3 and as a result, in vivo techniques are needed to evaluate their cardiac phenotype. Transthoracic echocardiography, pulse wave Doppler (PWD), and tissue Doppler imaging (TDI) can be used to provide dimensional measurements of the mouse heart and to quantify the degree of cardiac systolic and diastolic performance. Two-dimensional imaging is used to detect abnormal anatomy or movements of the left ventricle, whereas M-mode echo is used for quantification of cardiac dimensions and contractility.4,5 In addition, PWD is used to quantify localized velocity of turbulent flow,6 whereas TDI is used to measure the velocity of myocardial motion.7 Thus, transthoracic echocardiography offers a comprehensive method for the noninvasive evaluation of cardiac function in mice.

Transthoracic echocardiography offers a noninvasive method for the evaluation of cardiac function in mice. A combination of ultrasound and Doppler imaging modalities can be used to obtain dimensional measurements of the heart and intracardiac blood flow, which together provide an assessment of cardiac systolic and diastolic performance.

In recent years, murine models have become the primary avenue for studying the molecular mechanisms of cardiac dysfunction resulting from changes in gene ...

Echocardiographic Assessment of the Right Heart in Mice

Transgenic and toxic models of pulmonary arterial hypertension (PAH) are widely used to study the pathophysiology of PAH and to investigate potential therapies. Given the expense and time involved in creating animal models of disease, it is critical that researchers have tools to accurately assess phenotypic expression of disease. Right ventricular dysfunction is the major manifestation of pulmonary hypertension. Echocardiography is the mainstay of the noninvasive assessment of right ventricular function in rodent models and has the advantage of clear translation to humans in whom the same tool is used. Published echocardiography protocols in murine models of PAH are lacking.
In this article, we describe a protocol for assessing RV and pulmonary vascular function in a mouse model of PAH with a dominant negative BMPRII mutation; however, this protocol is applicable to any diseases affecting the pulmonary vasculature or right heart. We provide a detailed description of animal preparation, image acquisition and hemodynamic calculation of stroke volume, cardiac output and an estimate of pulmonary artery pressure.

This article provides a protocol for the echocardiographic assessment of right ventricular size and pulmonary hypertension in mice. Applications include phenotype determination and serial assessment in transgenic and toxin-induced mouse models of cardiomyopathy and pulmonary vascular disease.

Transgenic and toxic models of pulmonary arterial hypertension (PAH) are widely used to study the pathophysiology of PAH and to investigate potential ...

Chronic Thromboembolic Pulmonary Hypertension and Assessment of Right Ventricular Function in the Piglet

An original piglet model of Chronic Thromboembolic Pulmonary Hypertension (CTEPH) associated with chronic Right Ventricular (RV) dysfunction is described. Pulmonary Hypertension (PH) was induced in 3-week-old piglets by a progressive obstruction of the pulmonary vascular bed. A ligation of the left Pulmonary Artery (PA) was performed first through a mini-thoracotomy. Second, weekly embolizations of the right lower pulmonary lobe were done under fluoroscopic guidance with n-butyl-2-cyanoacrylate during 5 weeks. Mean Pulmonary Arterial Pressure (mPAP) measured by ritght heart catheterism, increased progressively, as well as Right Atrial pressure and Pulmonary Vascular Resistances (PVR) after 5 weeks compared to sham animals. Right Ventricular (RV) structural and functional remodeling were assessed by transthoracic echocardiography (RV diameters, RV wall thickness, RV systolic function). RV elastance and RV-pulmonary coupling were assessed by Pressure-Volume Loops (PVL) analysis with conductance method. Histologic study of the lung and the right ventricle were also performed. Molecular analyses on RV fresh tissues could be performed through repeated transcutaneous endomyocardial biopsies. Pulmonary microvascular disease in obstructed and unobstructed territories was studied from lung biopsies using molecular analyses and pathology. Furthermore, the reliability and the reproducibility was associated with a range of PH severity in animals. Most aspects of the human CTEPH disease were reproduced in this model, which allows new perspectives for the understanding of the underlying mechanisms (mitochondria, inflammation) and new therapeutic approaches (targeted, cellular or gene therapies) of the overloaded right ventricle but also pulmonary microvascular disease.

Chronic Thromboembolic Pulmonary Hypertension (CTEPH) and Right Ventricular (RV) dysfunction were induced in piglets by progressive obstruction of the pulmonary arteries. Consequences were remarkably similar to those observed in CTEPH patients. This animal model would be a very useful tool for pathophysiology and therapeutic experiments on CTEPH and RV failure.

An original piglet model of Chronic Thromboembolic Pulmonary Hypertension (CTEPH) associated with chronic Right Ventricular (RV) dysfunction is described. ...

Assessment of Cardiac Morphological and Functional Changes in Mouse Model of Transverse Aortic Constriction by Echocardiographic Imaging

Transverse aortic constriction (TAC) in mice has been used as a valuable model to study mechanisms of cardiac hypertrophy and heart failure1. A reliable noninvasive method is essential to assess real-time cardiac morphological and functional changes in animal models of heart disease. Transthoracic echocardiography represents an important tool for noninvasive assessment of cardiac structure and function2. Here we used a high-resolution ultrasound imaging system to monitor myocardial remodeling and heart failure progression over time in a mouse model of TAC. B-mode, M-mode, and Doppler imaging were used to precisely assess cardiac hypertrophy, ventricular dilatation, and functional deterioration in mice following TAC. Color and pulse wave (PW) Doppler imaging was used to noninvasively measure pressure gradient across the aortic constriction created by TAC and to assess transmitral blood flow in mice. Thus transthoracic echocardiographic imaging provides comprehensive noninvasive measurements of cardiac dimensions and function in mouse models of heart disease.

The goal of this protocol is to noninvasively assess cardiac structural and functional changes in a mouse model of heart disease created by transverse aortic constriction, using B- and M-mode echocardiography and color/pulse wave Doppler imaging.

Transverse aortic constriction (TAC) in mice has been used as a valuable model to study mechanisms of cardiac hypertrophy and heart failure1. A reliable ...

Transthoracic Speckle Tracking Echocardiography for the Quantitative Assessment of Left Ventricular Myocardial Deformation

The value of conventional echocardiography is limited by differences in inter-individual image interpretation and therefore largely dependent on the examiners&#39; expertise. Speckle tracking Echocardiography (STE) is a promising but technically challenging method that can be used to quantitatively assess regional and global systolic and diastolic myocardial performance. Myocardial strain and strain rate can be measured in all three dimensions&#160;&#8212; radial, circumferential, longitudinal &#8212; of myocardial deformation. Standard cross-sectional two-dimensional B-mode images are recorded and subsequently postprocessed by automated continuous frame-by-frame tracking and motion analysis of speckles within the myocardium. Images are recorded as digital loops and synchronized to a 3-lead EKG for timing purposes. Longitudinal deformation is assessed in the apical 4-, 3-, and 2-chamber views. Circumferential and radial deformation are measured in the parasternal short axis plane.
Optimal image quality and accurate tissue tracking are paramount for the correct determination of myocardial performance parameters. Utilizing transthoracic STE in a healthy volunteer, the present article is a detailed outline of the essential steps and potential pitfalls of quantitative echocardiographic myocardial deformation analysis.

Speckle tracking echocardiography is an emerging diagnostic imaging technique for the quantitative assessment of global and regional myocardial performance. Standard view echocardiographic motion images are recorded and deformation parameters are subsequently measured by automated continuous frame-by-frame tracking and motion analysis of speckles within the B-mode images of the myocardium.

The value of conventional echocardiography is limited by differences in inter-individual image interpretation and therefore largely dependent on the ...

Murine Echocardiography of Left Atrium, Aorta, and Pulmonary Artery

The present methodology teaches the investigator how to measure and use the LAV as a surrogate of chronic elevations in Left Ventricular diastolic pressure through echocardiography, as well as to obtain measurements of the Aorta and PA diameter in mice.
Mice older than 10 d of age can be analyzed using the present technique. The technique is composed of 3 main steps: set-up, image acquisition, and image analysis. The set-up step consists of getting the mouse anesthetized with 1% isoflurane, shaving it, and taping it in a supine position to a heated EKG board where the image acquisition will take place. The image acquisition step consists of learning to identify the cardiac structures and obtaining all the required images with its correspondent probe and axis in order to be able to calculate volumes and diameters. The image analysis step consists of measuring the previously acquired images with the aid of computer software.
Advantages of the proposed technique include a fast (15 min) procedure that would allow the researcher to evaluate interventions in a non-invasive, non-terminal approach and therefore follow the same mouse over time; each mouse can be used as its own control. This fact plus having the same operator perform all the acquisition and analysis for the entire experiment minimizes the limitation of operator-dependency. The present methodology is useful for mouse researchers in cardiovascular and pulmonary medicine.

The following protocol describes the methodology for the acquisition and analysis of echocardiographic images used to obtain the Left Atrial Volume (LAV), Aorta (Ao) diameter, and Pulmonary Artery (PA) diameter in mice. This technique is a non-invasive, non-terminal procedure that allows assessment of the cardiopulmonary function.

The present methodology teaches the investigator how to measure and use the LAV as a surrogate of chronic elevations in Left Ventricular diastolic ...

Echocardiographic Measurement of Right Ventricular Diastolic Parameters in Mouse

Diastolic dysfunction is a prominent feature of right ventricular (RV) remodeling associated with conditions of pressure overload. However, the RV diastolic function is rarely quantified in experimental studies. This might be due to technical difficulties in the visualization of the RV in the apical four-chamber view in rodents. Here we describe two positions facilitating the visualization of the apical four-chamber view in mice to assess the RV diastolic function.
The apical four-chamber view is enabled by tilting the mouse fixation platform to the left and caudally (LeCa) or to the right and cranially (RiCr). Both positions provide images of comparable quality. The results of the RV diastolic function obtained from two positions are not significantly different. Both positions are comparably easy to perform. This protocol can be incorporated into published protocols and enables detailed investigations of the RV function.

Here we describe and compare two positions for obtaining the apical four-chamber view in mice. These positions enable the quantification of the right ventricular function, provide comparable results, and can be used interchangeably.

Diastolic dysfunction is a prominent feature of right ventricular (RV) remodeling associated with conditions of pressure overload. However, the RV ...

A Pulmonary Trunk Banding Model of Pressure Overload Induced Right Ventricular Hypertrophy and Failure

Right ventricular (RV) failure induced by sustained pressure overload is a major contributor to morbidity and mortality in several cardiopulmonary disorders. Reliable and reproducible animal models of RV failure are therefore warranted in order to investigate disease mechanisms and effects of potential therapeutic strategies. Banding of the pulmonary trunk is a common method to induce isolated RV hypertrophy but in general, previously described models have not succeeded in creating a stable model of RV hypertrophy and failure.
We present a rat model of pressure overload induced RV hypertrophy caused by pulmonary trunk banding (PTB) that enables different phenotypes of RV hypertrophy with and without RV failure. We use a modified ligating clip applier to compress a titanium clip around the pulmonary trunk to a pre-set inner diameter. We use different clip diameters to induce different stages of disease progression from mild RV hypertrophy to decompensated RV failure.
RV hypertrophy develops consistently in rats subjected to the PTB procedure and depending on the diameter of the applied banding clip, we can accurately reproduce different disease severities ranging from compensated hypertrophy to severe decompensated RV failure with extra-cardiac manifestations.
The presented PTB model is a valid and robust model of pressure overload induced RV hypertrophy and failure that has several advantages to other banding models including high reproducibility and the possibility of inducing severe and decompensated RV failure.

We present a surgical method to induce right ventricular hypertrophy and failure in rats.

Right ventricular (RV) failure induced by sustained pressure overload is a major contributor to morbidity and mortality in several cardiopulmonary ...

Isometric Contractility Measurement of the Mouse Mesenteric Artery Using Wire Myography

The wire myograph technique is used to assess the contractility of vascular smooth muscles in response to depolarization, GPCR agonists/inhibitors and drugs. It is widely used in many studies on the physiological functions of vascular smooth muscle, the pathogenesis of vascular diseases such as hypertension, and the development of smooth muscle relaxant drugs. The mouse is a widely used model animal with a large pool of disease models and genetically modified strains. We introduced this method to measure the isometric contraction of mouse mesenteric artery in detail. A 1.4-mm segment of mouse mesenteric resistance artery was isolated and mounted on a myograph chamber by passing two steel wires through its lumen. After equilibration and normalization steps, the vessel segment was potentiated by a high-K+ solution twice prior to the contraction assay. As an example of the application of this method in drug development, we measured the relaxant effect of a novel natural substance, neoliensinine, isolated from a Chinese herb, embryos of the lotus seed (Nelumbo nucifera Gaertn.) on mouse mesenteric arteries. The vessel segments mounted on the myograph chamber were stimulated with a high-K+ solution. When the force tension reached a stable sustained phase, cumulative doses of neoliensinine were added to the chamber. We found that neoliensinine had a dose-dependent relaxant effect on smooth muscle contraction, thus suggesting that it bears potential activity against hypertension. In addition, as the vessel segment can survive at least 4 hours after mounting and maintain contractility induced by the high-K+ solution for many times, we suggest that the wire myograph system may be used for the time-consuming process of drug screening.

The wire myograph technique is used to investigate vascular smooth muscle functions and screen new drugs. We report a detailed protocol for measuring the isometric contractility of the mouse mesenteric artery and for screening new relaxants of vascular smooth muscle.

The wire myograph technique is used to assess the contractility of vascular smooth muscles in response to depolarization, GPCR agonists/inhibitors and ...

Invasive Hemodynamic Assessment for the Right Ventricular System and Hypoxia-Induced Pulmonary Arterial Hypertension in Mice

Pulmonary arterial hypertension (PAH) is a chronic and severe cardiopulmonary disorder. Mice are a popular animal model used to mimic this disease. However, the evaluation of right ventricular pressure (RVP) and pulmonary artery pressure (PAP) remains technically challenging in mice. RVP and PAP are more difficult to measure than left ventricular pressure because of the anatomical differences between the left and right heart systems. In this paper, we describe a stable right heart hemodynamic measurement method and its validation using healthy and PAH mice. This method is based on open-chest surgery and mechanical ventilation support. It is a complicated procedure compared to closed chest procedures. While a well-trained surgeon is required for this surgery, the advantage of this procedure is that it can generate both RVP and PAP parameters at the same time, so it is a preferable procedure for the evaluation of PAH models.

Here, we present a protocol to perform an invasive hemodynamic assessment of the right ventricle and pulmonary artery in mice using an open-chest surgery approach.

Pulmonary arterial hypertension (PAH) is a chronic and severe cardiopulmonary disorder. Mice are a popular animal model used to mimic this disease. ...