Quantification of Absolute Myocardial Flow and Resistance by Continuous Thermodilution in Patients with Ischemia and Nonobstructive Coronary Artery Disease (INOCA)

Summary

Presented here is a protocol to measure absolute myocardial flow and resistance using continuous thermodilution in patients with ischemia and nonobstructive coronary artery disease.

Abstract

In approximately half of the patients undergoing coronary angiography for angina pectoris or for signs or symptoms suggestive of ischemic heart disease, no obstructive coronary artery disease is angiographically visible. The majority of these patients with angina or ischemia and no obstructive coronary artery disease (INOCA) have an underlying coronary vasomotor dysfunction, and current consensus documents recommend diagnostic invasive coronary vasomotor function testing (CFT).

During CFT, a variety of vasomotor dysfunction endotypes can be assessed, including vasospastic coronary dysfunction (epicardial or microvascular vasospasm), and/or microvascular vasodilatory dysfunction, including impaired vasodilatory capacity and increased microvascular resistance. The quantification of the continuous thermodilution derived absolute coronary blood flow and resistance might be a better measure compared to the currently used standard physiologic measures. This article provides an overview of this continuous thermodilution method.

Introduction

In approximately half of the patients undergoing coronary angiography for angina pectoris or for signs or symptoms suggestive of ischemic heart disease, no obstructive coronary artery disease is angiographically visible¹. The majority of these patients with angina or ischemia and no obstructive coronary artery disease (INOCA) have an underlying coronary vasomotor dysfunction, and current ESC guidelines and a recent ESC position paper on INOCA recommend diagnostic invasive coronary vasomotor function testing (CFT)^1,2.

During CFT, a variety of vasomotor dysfunc....

Protocol

The following protocol was approved by the local medical ethics committee at the Radboudumc hospital, Nijmegen, the Netherlands. The following steps should be followed when performing continuous thermodilution to calculate absolute flow and resistance.

1. Preparations

1. Withhold vasoactive medications for at least 24 hours (48 hours in case of calcium channel blockers).

2. Diagnostic Coronary Angiography

1. Inject local anesthesia (1 to 2 mL of 20 mg/mL lidocaine) either in proximity to the right radial artery or the left radial artery. In case radial access is not possible, inject local....

Results

Figure 2 shows a representative measurement performed in patient A with no obstructive CAD on coronary angiography. The LAD artery was measured using continuous thermodilution to calculate absolute Q and R. The red and green lines represent pressure measurements, and the blue line represents the temperature curve. The infusion rate was set at 20 mL/min (Qi) since the LAD artery was measured. At point 1, the infusion was started and the temperature measured at the distally placed pressure wir.......

Discussion

Continuous thermodilution is an accurate method to measure absolute coronary flow and resistance, which has been shown to strongly agree with the gold standard [¹⁵O₂]H₂O PET derived flow and resistance⁵. These measurements are of special interest in INOCA patients, with current clinical guidelines recommending the assessment of coronary flow and resistance in this group.

Fractional flow reserve (FFR), the ratio of the maximal myocardial .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Rayflow multipurpose infusion catheter	Hexacath	RFW61S	Only compatible with 6F guiding catheter
PressureWire X guidewire	Abbott	C12059	Wireless guidewire with distal temperature and pressure sensor
Coroventis CoroFlow Cardiovascular System software	Coroventis	N/A	Advanced platform to measure physiological indices
Illumena Neo injector or similar injector system	Liebel-Flarsheim	GU01181006-E	Any injector with pressure limit (600 psi) and adjustable flow and volume injection rate
100 ml NaCl 0.9% at room temperature