Fixed Volume-Intercept Approach for Serial Contractility Assessment with Closed-Chest Pressure-Volume Loops in a Porcine Model

Summary

This protocol aims to provide a feasible, closed-chest porcine protocol to serially quantify load-independent LV contractility by fixing V₀ and computing single-beat Ees, eliminating repeated IVC occlusions to enhance safety and stability in hemodynamically fragile, acute experiments.

Abstract

The end-systolic pressure–volume relationship (ESPVR) is widely regarded as the gold standard, load-independent descriptor of left-ventricular (LV) contractility. Practically, ESPVR is often approximated as a straight line defined by its slope - end-systolic elastance (Ees), a direct index of contractile state - and its volume-axis intercept (V₀), the theoretical LV volume at zero pressure. In vivo, ESPVR is classically derived from serial inferior vena cava (IVC) occlusions performed with simultaneous LV pressure–volume (PV) catheter monitoring. However, in disease states such as cardiogenic shock, the requisite preload depletion may provoke reflex tachyarrhythmias and transient or sustained hemodynamic instability, limiting feasibility and interpretability. Thus, methods for in vivo assessment of inotropy during hemodynamically fragile states are warranted.

This protocol aims to describe a practical experimental model in which V₀ is determined once under stable baseline conditions and then held fixed for subsequent, single-beat Ees estimation from LV PV loops. This approach, detailed step-by-step for use in acute large-animal studies, allows continuous serial assessment of contractility without repeated IVC occlusions. In a porcine cardiogenic shock model, it reliably tracked load-independent changes in myocardial performance while avoiding arrhythmias and hemodynamic instability otherwise provoked by preload reduction. The method is therefore well suited for acute, closed-chest experiments in which the ventricular geometry remains unchanged, and contractility primarily modulates the ESPVR slope rather than its intercept. Nonetheless, the fixed-V₀ assumption represents a methodological simplification that introduces deliberate systematic error and should only be applied when repeated preload manipulation is impractical or unsafe. When structural remodeling, profound LV dilation, or marked thoracic pressure changes occur, V₀ must be re-estimated. Overall, this protocol provides a feasible and physiologically sound approach for serial contractility assessment in unstable large-animal models, balancing methodological rigor with experimental safety and practicality.

Introduction

Left ventricular (LV) contractility is the intrinsic ability of myocardium to generate pressure independent of loading conditions^1,2,3. It is a critical determinant of cardiac stroke volume, cardiac output, and blood pressure. Hence, when suffering from acute myocardial ischemia, the heart may quickly lose contractility⁴. Thus, impaired myocardial contractility may cause acute heart failure and cardiogenic shock (CS)⁵. CS results in hypotension and inadequate organ perfusion, leading to high mortality (30%–50% in-hospital)....

Protocol

This protocol is approved by the Danish Animal Research Inspectorate (permit no: 2023–15–0201–01466, issued on 19/06–2023). Female Danish Landrace pigs of approximately 60 kg were used. This procedure is terminal, and the animals were euthanized at the end of the study with a lethal dose of pentobarbital (0.25 mL/kg IV of 400 mg/mL) under deep general anesthesia. The reagents and the equipment used are listed in the Table of Materials.

1. Anesthesia and ventilation

1. Pre-anesthetize the pig with intramuscular injection of anesthetic mix 1 mL/kg, containing 25 ....

Results

The instructions above present a protocol to derive Ees on a single-beat basis, keeping the theoretical volume of zero pressure generation, V₀, constant. This section presents data from two studies conducted in our lab. First, a separate pilot study was conducted to examine the development of V₀ and Ees following CS induction. Second, in a large dataset of 30 pigs included in previously published studies, the ischemic model of CS is presented⁴.

Discussion

This protocol describes a pragmatic, reproducible, and feasible strategy for serial, load-independent assessment of LV contractility, viable even in acute cardiac illness such as ischemic CS. The protocol uses a fixed volume-axis intercept, V₀, to estimate Ees from single beats, avoiding repetitive IVC occlusions and thus lowering the risk of arrhythmias and hypotension during vulnerable cardiovascular conditions. The methodological novelty of the present protocol lies in the explicit combination of empiricall.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.9% saline	Fresenius Kabi, Germany	921046	Microsphere suspension and flush
10 mL syringes	BD, USA	BD Plastipak 302143	Microsphere injection
12 Fr femoral venous sheath	Terumo, Japan	Radifocus Introducer II	For IVC occlusion balloon insertion
20 G venous catheter	BD, USA	BD Insyte 381223	Ear vein IV access
7 Fr femoral arterial sheath	Terumo, Japan	Radifocus Introducer II	Invasive arterial pressure monitoring
8 Fr carotid arterial sheath	Terumo, Japan	Radifocus Introducer II	Access for LV PV catheter
8 Fr jugular venous sheath	Terumo, Japan	Radifocus Introducer II	Pulmonary artery catheter access
Contour PVA microspheres	Boston Scientific, USA	Contour 355–500 µm	Induction of ischemic cardiogenic shock
Coronary guide catheter	Boston Scientific, USA	JL 3.5 / JR 4.0	Coronary access for microsphere injection
ECG electrodes (3-lead)	Ambu, Denmark	BlueSensor P	Continuous ECG monitoring
Endotracheal tube 7.5–8.0 mm	Smiths Medical, UK	Portex ETT	Tracheal intubation
Fentanyl (IV)	Hameln Pharma, Germany	Fentanyl Hameln	Continuous IV analgesia
Fluoroscopy system	-	-	Catheter guidance
Heated blankets	3M, USA	Bair Hugger Warming Unit	Maintenance of normothermia
Heparin	Leo Pharma, Denmark	Innohep	Anticoagulation if used
Iomeron contrast agent	Bracco Imaging, Italy	Iomeron 350	Coronary angiography and microsphere suspension
IVC occlusion balloon catheter	Fogarty / Edwards Lifesciences, USA	Fogarty Occlusion Balloon	Temporary preload reduction
LabChart 8 Pro software	ADInstruments, New Zealand	LabChart 8 Pro	PV loop acquisition and analysis
LV PV catheter (admittance)	Millar Inc., USA	MPVS Ultra PV Loop Catheter	Admittance-based LV pressure–volume measurement
Mechanical ventilator	GE Healthcare, USA	Datex Ohmeda S/5	Positive pressure ventilation
MPVS Module	ADInstruments, New Zealand	MPVS Ultra/Duo	Interface for PV catheter
PowerLab data acquisition system	ADInstruments, New Zealand	PowerLab 16/35	Signal acquisition
Propofol (IV)	Fresenius Kabi, Germany	Diprivan / Propofol-Lipuro	Continuous IV anesthesia
Pulmonary artery catheter 7.5 Fr	Edwards Lifesciences, USA	Swan-Ganz 131HF7	Thermodilution CO and PA pressure
Pulse oximeter	-	-	Peripheral oxygen saturation monitoring
Rectal temperature probe	-	-	Core temperature monitoring
Seldinger guidewires	Terumo, Japan	Radifocus Guide Wire M	Vascular access
Sterile saline flushes	Fresenius Kabi, Germany	0.9% NaCl	Sheath flushing
Suture material	Ethicon, USA	Vicryl 3-0	Fixation of sheaths
Syringe pumps	Becton Dickinson (BD), USA	BD Alaris	Continuous anesthetic infusion
Ultrasound system	-	-	Vascular access guidance
Urinary catheter	Teleflex, USA	Rüsch Foley catheter	Bladder drainage
Zoletil (tiletamine/zolazepam)	Virbac, France	Zoletil 100	Used for pre-anesthesia; mixed with butorphanol, ketamine, xylazine according to protocol