Terminal Harvest Procedure of a Large Animal Model of Chronic Myocardial Ischemia with Hemodynamic Characterization and Perfusion Analysis

Summary

The following surgical protocol represents the second and final procedure to thoroughly and reliably characterize the cardiac function and myocardial perfusion after successful induction of chronic myocardial ischemia in a swine model in an effort to investigate novel therapies.

Abstract

Reproducibility and research integrity are foundational tenets to scientific discovery, which are produced utilizing well-established, proven principles and protocols. Furthermore, with the ever-increasing prevalence and burden cardiovascular disease (CVD) places on individuals and society at large, it deems essential to cultivate robust and validated model for investigation. Our group utilizes a two-surgery protocol in a swine model that has been progressively refined over the last twenty years, in which we first induce chronic myocardial ischemia by placement of an ameroid constrictor mimicking the pathophysiology of coronary artery disease (CAD) in humans. The second and terminal procedure is a comprehensive and thoughtful collection of cardiac hemodynamic parameters as well as regional coronary perfusion, followed by beating heart euthanasia and detailed sectioning of the heart. Our lab uses isotope-labeled microspheres to analyze myocardial blood flow to the ischemic area as a powerful method to quantify collateralization due to experimental therapeutic agents. Furthermore, and likely the most important measurable cardiovascular outcome, we utilize left ventricular pressure-volume (PV) loop catheterization to measure a broad range of hemodynamic parameters. We hope by detailing the comprehensive cardiac analysis of our swine model of chronic myocardial ischemia, other researchers may improve and cultivate their own protocols and therapy investigation for the elimination of cardiovascular disease.

Introduction

In the United States, nearly half of individuals have at least one component of CVD, comprising a large group of disease states of the heart and blood vessels¹. By the year 2060, it is projected that the prevalence of multiple diagnoses comprising CVD will substantially increase compared to 2025. For instance, myocardial infarction is projected to increase by 30%, ischemic heart disease (IHD) by 31.3%, and heart failure by 33%². These staggering statistics are further worrisome when taken with similar predictions of cardiovascular risk factors, in which the number of individuals with diabetes mellitus is estimated to ris....

Protocol

The following surgical procedure was approved by the Institutional Animal Care and Use Committee of Rhode Island Hospital and Brown University (Protocol #23-08-0005).

1. Animal model

1. Choose Yorkshire swine that have previously undergone placement of an ameroid constrictor around the proximal left circumflex coronary artery (LCx), thereby inducing chronic myocardial ischemia, and subsequent treatment with an experimental therapeutic agent. Keep ~7 weeks between the first operation for ameroid placement and subsequent terminal harvest. Allow 2 weeks for ameroid closure and ensure the swine undergo an experimental ....

Results

First, by injecting isotope-labelled microspheres into the left atrial appendage, regional myocardial perfusion is measured. To calculate the myocardial blood flow, when a constant rate of blood withdrawal of 6.67 mL/min was utilized, the following equation can be applied: myocardial blood flow = (reference blood withdrawal [6.67 mL/min]/weight of tissue) (quantified tissue microsphere count/quantified blood reference microsphere count). Simply put, the ratio of measured microspheres in a.......

Discussion

This surgical procedure has four critical steps: exposure of the heart, femoral catheterization, microsphere injection for perfusional analysis, and pressure-volume loop acquisition. In regard to exposing the heart, an important consideration should be the possibility of encountering significant adhesions due to the first surgical procedure. When performing the median sternotomy, the pericardium may be adhered to the chest wall, which should be bluntly swept before starting the sternotomy. When approaching the latter one.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
#10 Scalpel	Medline	MDS15310
0.9% Saline	Dechra/Vetivex	17033-492-50	Rate: 5-10 mL/kg during case
18G Needles	Patterson Veterinary	78032793	For drawing medication/microspheres
2% Lidocaine	Phoenix	57319-533-05	Dosing: 2-5mg/kg
4-0 Polypropylene Suture	Covidien	D9H0436Y	For purse string
All Surgical Instruments	Steris and Medline	Requires Sales Representative	All Commonly Found in Hospital Operating Rooms
Analgesia: Buprenorphine	Hospira	Brand Name: Bupredine	Dosing: 0.03 mg/kg
Anesthesia: Telazol	Zoetis	(tiletamine and zolazepam)	Dosing: 4.4 mg/kg
Anesthesia: xylazine (Rompun)	Dechra	N/A	Dosing: 2.2 mg/kg
Arterial Sheath	Cordis	401-711M	Either 6F or 7F; requires two
Butterfly needle infusion set	Surflo	SV-25BLK	For microsphere injection; typically 23-25G
Chlorhexidine 4%	BD E-Z Scrub	371073	Surgical Prep, if preferred
Cuffed Endotracheal Tube	RUSCH	7-0 typically	May need different sizes depending on swine size and weight
ECG Monitoring System	MidMark	N/A	Multiparameter Monitor
Electrocautery	Bovie Specialist Pro	1250S	Typically set up 2 if possible
Isoflurane, USP	Dechra		Dosing: 0.75%-3.0%
Laptop	HP Microsoft	N/A	Can use any laptop preferred by individual
Lebsche Knife	Integra	300-425	N/A
Lutetium STERIspheres	BioPAL, Inc.	C-15E20	Amount: 5cc per surgery
Mini White Vessel Loops (X-ray Detectable)	DeRoyal	30-711	To isolate the femoral artery and IVC
Multiple 5cc Syringes	Terumo	SS-05L	For flushes and microsphere injections
Pacemaker	Osypka Medical	2428001	A temporary pacer
PV Loop Catheters	Transonic	Model: FDH-5018B-E3450 and S/N: 50-679	For PV Loop Acquisition
PV Loop Computer Program	Transonic Scisense	ADV500 Software	Program on your laptop
PV Loop Data Acquisition System	Transonic and ADInstruments	Models: FY097B and PowerLab 8/35	Connects the catheters and the computer
Samarium STERIspheres	BioPAL, Inc.	C-15A20	Amount: 5cc per surgery
Small Mallet	Integra	410-335	N/A
Sterile Gloves	Encore	820955	Would still recommend sterile gloves and gown
Sterile Saline	BAXTER	G171328	Dilute to make heparanized saline flushes
Suction System	GOMCO	4042	Better if Wall Suction of Own Facility
Suction tip: Yankauer	Medline	DYND50130	Important to keep the field clear when resecting the heart
Systemic Heparin	Covetrus	82496	Dosage: 80 IU/kg
Three-way stopcock	Jorgensen Laboratories, Inc.	200820	For microsphere injections
Warm Water Bath	Fisher		To warm the catheters before use
Withdrawal Pump	Harvard Apparatus	70-2002	To withdraw peripheral blood at constant rate
Yorkshire Swine	CBSET, Inc.	N/A	Swine will have already undergone the initial surgical procedure