ABSTRACT
A number of promising and highly technological echocardiographic imaging tools have recently been introduced to assess left ventricular diastolic function (i.e., the capacity of the ventricle to relax and fill). They permit quantification of distinct features of intraventricular blood flow velocity and pressure fields and myocardial tissue velocities. However, accurate interpretation of the new images and clinical indices is still cumbersome, as basic knowledge about intraventricular hemodynamics and ventricular wall mechanics is often insufficient. This review article provides a comprehensive and original overview of the hemodynamical and mechanical events that occur during diastole and discusses how this new information can be used in the clinical and research setting to evaluate diastolic function in the healthy and the diseased heart. It furthermore aims to explain the underpinnings of the techniques in such a way that the underlying biomechanical concepts (fluid dynamics and wall mechanics) become less obscure to cardiologists and echocardiographers and such that the biomedical engineers are given some insights into the avalanche of diastolic performance indices that currently exist.
Subject(s)
Echocardiography, Doppler/methods , Ventricular Function, Left/physiology , Atrioventricular Node/physiology , Blood Flow Velocity/physiology , Coronary Circulation/physiology , Diastole/physiology , Echocardiography, Doppler, Color/methods , Humans , Mitral Valve/physiology , Models, Cardiovascular , Ventricular Pressure/physiologyABSTRACT
Fractional flow reserve (FFR) is a commonly used index to assess the functional severity of a coronary artery stenosis. It is conventionally calculated as the ratio of the pressure distal (Pd) and proximal (Pa) to the stenosis (FFR= Pd/Pa). We hypothesize that the presence of a zero flow pressure (Pzf), requires a modification of this equation. Using a dynamic hydraulic bench model of the coronary circulation, which allows one to incorporate an adjustable Pzf, we studied the relation between pressure-derived FFR = Pdo/Pa, flow-derived true FFRQ = Qs/QN (= ratio of flow through a stenosed vessel to flow through a normal vessel), and the corrected pressure-derived FFRc = (Pd-Pzf)/(Pa-Pzf) under physiological aortic pressures (70 mmHg, 90 mmHg, and 110 mmHg). Imposed Pzf values varied between 0 mmHg and 30 mmHg. FFRc was in good agreement with FFRQ, whereas FFR consistently overestimated FFRQ. This overestimation increased when Pzf increased, or when Pa decreased, and could be as high as 56% (Pzf=30 mmHg and Pa =70 mmHg). According to our experimental study, calculating the corrected FFRC instead of FFR, if Pzf is known, provides a physiologically more accurate evaluation of the functional severity of a coronary artery stenosis.
