Minimally Invasive Transverse Aortic Constriction in Mice

Summary

Minimally invasive transverse aortic constriction (MTAC) conserves the essentials of regular transverse aortic constriction (TAC) while eliminating the use of a ventilator with tracheal intubation. It proves to be a highly desirable method for high-throughput studies on left ventricular overload, particularly in translational studies.

Abstract

Minimally invasive transverse aortic constriction (MTAC) is a more desirable method for the constriction of the transverse aorta in mice than standard open-chest transverse aortic constriction (TAC). Although transverse aortic constriction is a highly functional method for the induction of high pressure in the left ventricle, it is a more difficult and lengthy procedure due to its use of artificial ventilation with tracheal intubation. TAC is oftentimes also less survivable, as the newer method, MTAC, neither requires the cutting of the ribs and intercostal muscles nor tracheal intubation with a ventilation setup. In MTAC, as opposed to a thoracotomy to access to the chest cavity, the aortic arch is reached through a midline incision in the anterior neck. The thyroid is pulled back to reveal the sternal notch. The sternum is subsequently cut down to the second rib level, and the aortic arch is reached simply by separating the connective tissues and thymus. From there, a suture can be wrapped around the arch and tied with a spacer, and then the sternal cut and skin can be closed. MTAC is a much faster and less invasive way to induce left ventricular hypertension and enables the possibility for high-throughput studies. The success of the constriction can be verified using high-frequency trans-thoracic echocardiography, particularly color Doppler and pulsed-wave Doppler, to determine the flow velocities of the aortic arch and left and right carotid arteries, the dimension of the blood vessels, and the left ventricular function and morphology. A successful constriction will also trigger significant histopathological changes, such as cardiac muscle cell hypertrophy with interstitial and perivascular fibrosis. Here, the procedure of MTAC is described, demonstrating how the resulting flow changes in the carotid arteries can be examined with echocardiography, gross morphology, and histopathological changes in the heart.

Introduction

The overall purpose of this article is to demonstrate how transverse aortic constriction (TAC) in mice can be modified to produce a simpler and more expedient surgery. TAC was first introduced in 1991¹ and enabled molecular biologists to study the cellular and molecular pathways that lead to hypertrophy in the left ventricle and to heart failure, particularly in small animals with manipulated genomes^2,3,4,5,6. Despite its efficacy at producing the desired pressure overload, the techn....

Protocol

The protocol follows the guidelines of the Committee on the Use of Live Animals in Teaching and Research (CULATR) at the University of Hong Kong.

1. Operation Site Preparation

1. Disinfect the operation site with 75% isopropyl alcohol. Adjust the heating pad temperature to 37 °C to avoid changes in heart and respiratory rates of the subject animal.
2. Use surgical instruments sterilized in a gravity displacement sterilizer at 121 °C for 30 min or by other appropriate methods.
3. Take 2 - 4 30-gauge needles and curve them with a needle holder, as seen in Figure 1, to make a tool for ligation ....

Results

MTAC enables the induction of significant hypertension in the left ventricle in a timely manner.

As seen in Figure 1, the preparation of the primary tools for the procedure is simple and minimal, requiring only 2 - 4 30-gauge needles to be bent and held in place with a polyurethane tube. The surgical procedure itself is also less complicated, as compared to TAC, and can be performed easily. Once the thyroid has .......

Discussion

Rockman and colleagues devised the first method for aortic banding as a method to study pressure overload in the heart. This enabled research to begin to uncover the cellular and molecular consequences of hypertension and heart failure¹. An improved method, minimally invasive transverse aortic constriction (MTAC), provides an amenable, time-dependent method for the induction of left ventricular pressure overload and heart failure, without the drawbacks of the conventional transverse aortic constri.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1 inch 30 Gauge Needles	BD, Franklin Lakes, NJ 07417, USA.	305128	Curved as in the procedure and Figure 1
27 Gauge Needle	BD, Franklin Lakes, NJ 07417, USA.	301629	Make blunt and smooth for spacer
6/0 Dafilon	B. Braun, 34212 Melsungen, Hessen, Germany.	C0933066
6/0 Silkam	B. Braun, 34212 Melsungen, Hessen, Germany.	C0762067
Sterile gloves	A.R. Medicom, Inc (Asia), Hong Kong.
Cotton Applicator	Mannings, Quarry Bay, Hong Kong.		Local Shopping Center
Depilatory Cream	Veet (Hong Kong), Kwun Tong, Kowloon, Hong Kong		Local Shopping Center
Lexer-Baby Scissor	FST, British Columbia V7H 0A6, Canada.	14078-10
Curved Iris Forcep	FST, British Columbia V7H 0A6, Canada.	11065-07
Micro Olsen-Hegar Needle Holder	WPI, Sarasota, FL 34240, USA.	501989
Stereo Micrioscope	WPI, Sarasota, FL 34240, USA.	PZMIII-BS
GenTeal Eye Gel	Novartis, East Hanover, NJ 07936, USA.		Local Pharmacy
Heating Pad	Kent Scientific Corporation, Torrington, CT 06790, USA.	DCT-20
Surgical tape	Laboratory Animal Unit
Ketamine and Xylazine	Laboratory Animal Unit
Betadine	Laboratory Animal Unit
Buprenorphine	Laboratory Animal Unit