Importance of Continuous Non-invasive Blood Pressure (CNBP) measurement in the calculation of Fractional Flow Reserve (FFR)

What is FFR

Measuring fractional flow reserve (FFR) is currently the ‘gold standard’ in the diagnostic assessment of coronary artery function. FFR measurement allows conclusions to be drawn about how the narrowing of the arterial lumen caused by the presence of atherosclerotic plaque influences the amount of blood – and thus oxygen – being supplied to the myocardium to enable it to work properly. This measurement can be performed by invasive and non-invasive methods.

The invasive method – measurement during coronary angiography (ICA)

FFR is calculated as the ratio of the pressure distal to the stenosis to the pressure proximal to it. The proximal pressure is measured at the coronary artery inlet and the distal pressure is measured downstream of the stenosis under maximum hyperaemia.

The non-invasive method – Hemolens Diagnostics’ breakthrough technology

Cardiolens FFR-CT Pro® by Hemolens Diagnostics is an innovative, non-invasive method for the diagnosis of coronary artery disease based on computer simulation of blood flow. The technology delivers precise anatomical and functional assessment of coronary arteries, enabling virtual FFR measurement.

Cardiolens FFR-CT Pro® analyses data obtained from two non-invasive diagnostic methods:

– coronary computed tomography angiography (CCTA),

– continuous non-invasive blood pressure monitoring (CNBP).

On this basis, Cardiolens FFR-CT Pro® generates a personalized, three-dimensional anatomical model of the patient’s coronary arteries. The model represents the lumen envelope of the coronary arteries as a set of connected vertex points (a surface mesh). A series of numerical simulations of blood flow are then performed inside the arterial model. From these calculations, a hemodynamic assessment is performed to evaluate the impact of stenosis in the coronary arteries by measuring FFR.

The diagnostic service offered by Hemolens Diagnostics® comes in handy if a significant coronary artery stenosis (≥50%) is suspected or if a CCTA test ordered by a cardiologist comes back inconclusive.

Calculation process in Cardiolens FFR-CT Pro® diagnostics

Proximal pressure (Pa) is measured by non-invasive pulse wave testing (CNBP) and is a unique value for each individual patient.

Continuous non-invasive blood pressure monitoring (CNBP) combines the advantages of two clinical “gold standards”:

– it measures blood pressure (BP) continuously in real time, like an invasive arterial catheter system (IBP),

– it is non-invasive, like a standard arm sphygmomanometer (NBP).

Recent developments in this field show promise in terms of accuracy, ease of use, and clinical acceptance. By measuring blood pressure with sensors applied to a finger and forearm, a personalized patient-specific CNBP measurement is fed into the system.

Distal pressure (Pd) is calculated using computational fluid dynamics (CFD). The calculation is performed in a patient-specific anatomical model of the coronary arteries, also taking into

account the patient’s individual aortic pressure signal derived from the measured CNBP signal. The result of the calculation is a blood pressure value that can be used to determine the FFR value at any point in the patient’s arterial model.

The technology of non-invasive virtual FFR testing features not only the analysis of functional data, but also anatomical data. The same degree of stenosis in two different patients may give a different FFR result due to anatomical differences in coronary artery structure, the site of the measurement or differences in proximal pressure. Our algorithms calculate the difference between the pressure in the aorta and downstream of the stenosis, showing the actual pressure drop across the stenosis.

Is the blood pressure measured at the level of the radial artery equal to the one in the aorta?

The flow of the arterial pressure wave measured at the level of the radial artery is not identical to that of the aorta. Its dynamics and maxima are different, while the minima are approximately equal in value. Thanks to advanced algorithms, the actual pressure waveform in the aorta is determined from the individual blood pressure (CNBP) measurement.