A Pacing-Controlled Procedure for the Assessment of Heart Rate-Dependent Diastolic Functions in Murine Heart Failure Models

Summary

The present protocol describes obtaining the pressure-volume relationship through transesophageal pacing, which serves as a valuable tool in evaluating diastolic function in mouse models of heart failure.

Abstract

Heart failure with preserved ejection fraction (HFpEF) is a condition characterized by diastolic dysfunction and exercise intolerance. While exercise-stressed hemodynamic tests or MRI can be used to detect diastolic dysfunction and diagnose HFpEF in humans, such modalities are limited in basic research using mouse models. A treadmill exercise test is commonly used for this purpose in mice, but its results can be influenced by body weight, skeletal muscle strength, and mental state. Here, we describe an atrial-pacing protocol to detect heart rate (HR)-dependent changes in diastolic performance and validate its usefulness in a mouse model of HFpEF. The method involves anesthetizing, intubating, and performing pressure-volume (PV) loop analysis concomitant with atrial pacing. In this work, a conductance catheter was inserted via a left ventricular apical approach, and an atrial pacing catheter was placed in the esophagus. Baseline PV loops were collected before the HR was slowed with ivabradine. PV loops were collected and analyzed at HR increments ranging from 400 bpm to 700 bpm via atrial pacing. Using this protocol, we clearly demonstrated HR-dependent diastolic impairment in a metabolically induced HFpEF model. Both the relaxation time constant (Tau) and the end-diastolic pressure-volume relationship (EDPVR) worsened as the HR increased compared to control mice. In conclusion, this atrial pacing-controlled protocol is useful for detecting HR-dependent cardiac dysfunctions. It provides a new way to study the underlying mechanisms of diastolic dysfunction in HFpEF mouse models and may help develop new treatments for this condition.

Introduction

Heart failure represents a leading cause of hospitalization and death across the globe, and heart failure with preserved ejection fraction (HFpEF) accounts for around 50% of all heart failure diagnoses. HFpEF is characterized by diastolic dysfunction and impaired exercise tolerance, and the associated hemodynamic abnormalities, such as diastolic dysfunction, can be clearly detected through exercise-stressed hemodynamic testing or MRI scans^1,2.

In experimental models, however, available modalities for assessing the physiological abnormalities related to HFpEF are limited

Protocol

This animal protocol was approved by the Institutional Animal Care and Use Committee and followed the regulations for animal experiments and related activities at the University of Tokyo. For the present study, 8-12 week old male C57/Bl6J mice were used. The animals were obtained from a commercial source (see the Table of Materials). A model of HFpEF was established by administering a high-fat diet for 15 weeks in conjunction with NG-nitro-L-arginine methyl ester, as described previously

Discussion

We present a methodology to assess pressure-volume relationships with the application of transesophageal pacing. Exercise intolerance is one of the key characteristics of HFpEF, yet there are no techniques available for the evaluation of cardiac function in mice during exercise. Our pacing protocol offers a valuable tool for detecting diastolic dysfunction, which may not be apparent under resting conditions.

To achieve a PV loop of accurate and consistent quality, the following steps must be m.......

Materials

Name	Company	Catalog Number	Comments
2-0 silk suture, sterlie	Alfresa Pharma Corporation, Osaka, Japan	62-9965-57	Surgical Supplies
2-Fr tetrapolar electrode catheter	Fukuda Denshi, Japan and UNIQUE MEDICAL, Japan	custom-made	Surgical Supplies
Albumin Bovine Serum	Nacalai Tesque, Inc., Kyoto, Japan	01859-47	Miscellaneous
C57/BI6J mouse	Jackson Laboratory		animals
Conductance catheter	Millar Instruments, Houston, TX	PVR 1035
Electrical cautery, Electrocautery Knife Kit	ellman-Japan,Osaka, Japan	1-1861-21	Surgical Supplies
Etomidate	Tokyo Chemical Industory Co., Ltd., Tokyo Japan	E0897	Anesthetic
Grass Instrument S44G Square Pulse Stimulator	Astro-Med, West Warwick, RI		Pacing equipment
Isoflurane	Viatris Inc., Tokyo, Japan	8803998	Anesthetic
Ivabradine	Tokyo Chemical Industory Co., Ltd., Tokyo Japan	I0847	Miscellaneous
LabChart software	ADInstruments, Sydney, Australia	LabChart 7	Hemodynamic equipment
MPVS Ultra	Millar Instruments, Houston, TX	PL3516B49	Hemodynamic equipment
Pancronium bromide	Sigma Aldrich Co., St. Louis, MO	15500-66-0	Anesthetic
PE10 polyethylene tube	Bio Research Center  Co. Ltd., Tokyo, Japan	62101010	Surgical Supplies
PowerLab 8/35	ADInstruments, Sydney, Australia	PL3508/P	Hemodynamic equipment
PVR 1035	Millar Instruments, Houston, TX	842-0002	Hemodynamic equipment
Urethane (Ethyl Carbamate)	Wako Pure Chemical Industries, Ltd., Osaka, Japan	050-05821	Anesthetic
Vascular Flow Probe	Transonic, Ithaca, NY	MA1PRB	Surgical Supplies