Murine Isolated Heart Model of Myocardial Stunning Associated with Cardioplegic Arrest

Summary

The goal of this protocol to assess myocardial stunning following ischemic cardioplegic arrest in rodents.

Abstract

The following protocol is of use to evaluate impaired cardiac function or myocardial stunning following moderate ischemic insults. The technique is useful for modeling ischemic injury associated with numerous clinically relevant phenomenon including cardiac surgery with cardioplegic arrest and cardiopulmonary bypass, off-pump CABG, transplant, angina, brief ischemia, etc. The protocol presents a general method to model hypothermic hyperkalemic cardioplegic arrest and reperfusion in rodent hearts focusing on measurement of myocardial contractile function. In brief, a mouse heart is perfused in langendorff mode, instrumented with an intraventricular balloon, and baseline cardiac functional parameters are recorded. Following stabilization, the heart is then subject to brief infusion of a cardioprotective hypothermic cardioplegia solution to initiate diastolic arrest. Cardioplegia is delivered intermittently over 2 hr. The heart is then reperfused and warmed to normothermic temperatures and recovery of myocardial function is monitored. Use of this protocol results in reliable depressed cardiac contractile function free from gross myocardial tissue damage in rodents.

Introduction

Myocardial stunning is defined as reversible reduced contractile activity despite restoration of adequate blood flow following a brief period of ischemia or prolonged periods of ischemic insults with cardioprotection^1,2,3,4,5. The method presented is specifically used to model clinically relevant ischemic insults which can result in reversible impairments in contractile function (i.e., ischemic insults associated with cardiac surgery utilizing cardioplegic arrest, brief periods of ischemia, angina, etc.). In contrast to severe ischemia studies (myocardial infarction, necrosis) this protocol was developed to evaluate myocardial functional r....

Protocol

NOTE: All Procedures were approved by the Lifespan Institutional Animal Care and Use Committee and all animals and procedures according to the National research Council Guide for Care and Use of Laboratory Animals¹⁰.

1. Balloon Fabrication and Left Ventricular Pressure Monitoring Circuit

1. Construct LV balloons according to Miller et al.¹¹ In a beaker with a stir bar, mix 9.5 ml of distilled water, 14.2 ml of light corn syrup and 33.8 g of sucrose, and heat on a hot plate, mix until the sugar is dissolved. Continue heating solution until it reaches approximately 150 ºC.
   NOTE: Numerous met....

Results

Figure 1 presents typical results from one mouse experiment. LVP (red line), dP/dt (green line), and temperature (purple line) were continusouly recorded over ~3 hr. Letters indicate a - baseline measurement, b, c, d, e - delivery of cardioplegia solution, f - start of reperfusion, g, h, i, j - measurement of cornary flow during reperfusion. Note, depressed LVDP and dP/dt upon reperfusion compared to baseline. Figure 1B includes the data from A recorded over ~2 sec. Note, the decrease in.......

Discussion

The preceding protocol details methods to evaluate myocardial stunning secondary to global ischemia associated with cardioplegic arrest. In our hands this protocol produces an approximate ~40% reduction in cardiac function (LVDP, +/- dP/dt) with minimal changes in heart rate at the 30 min post-reperfusion time point. As the heart is reperfused and rewarmed all parameters of cardiac function are reduced at initial time points with a greatly reduced heart rate before stabilizing between 20 and 30 min. Coronary flow is gene.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Cardioplegia Solution (St Thomas II)			Symbol / Concentrations (mM)
Sodium Chloride			NaCl; 110
Potassium chloride			KCl; 16
Calcium Chloride			CaCL2; 1.5
Magnesium Chloride			MgCL2; 16
Sodium Bicarbonate			NaHCO3; 10
Krebs-Heinslet Buffer
Sodium Chloride			NaCl; 118
Potassium Chloride			KCl; 4.8
Magnesium Sulfate			MgSO4; 1.7
Sodium Bicarbonate			NaHCO3; 24.9
Potassium Phosphate (monobasic)			KH2PO4; 1.2
Calcium Chloride			CaCL2; 1.4
Sodium Pyruvate			Na pyruvate; 2
Glucose			C6H12O6; 6
Balloon reagents
Corn Syrup
Spaghetti
Silicon Dispersion Gel
styrofoam block
lab oven/incubator ( 50C)
Langendorff Perfusion equipment
Isolated perfused heart sytem (IH-SR (Hugo-Sachs) or equivalent)
Data acquisition system (DSI, ADinstruments or equivalent)
Heated water circulator
Cooling water circulator
Perfusion pump capable of 2-30 ml/min
Inline perfusion filters - 1 um glass fiber
Pressure sensors and amplifiers for LVP and perfusion pressure
Small graduated cylinder (~10 mL)
Small temperature probe and thermometer (Werner or equivalent)
perfusion resevoir (1L)
cardioplegia resevoir (~200 mL)
gas bubbler
95/5 O2/CO2 mix
Surgical tools and reagents
Metzenbaum and Potz surgical scissors
two Dumont size 5 forceps
ketamine
xylazine
heparin
small clamp with soft sides to hold aorta (i.e. terminal clamp with taped ends)
Silk 2-0 and 4-0 sutures