Three dimensional colour Doppler echocardiography for the characterisation and quantification of cardiac flow events.

The accurate non-invasive quantification of cardiac flow volumes is an important goal in clinical cardiology. Computation of laminar volume flow through the ventricular outflow tracts would allow direct measurement of stroke volume and cardiac output. Grading of valvar regurgitation and follow up of patients with regurgitant lesions may be more accurately performed through calculation of regurgitant volume and fraction, and regurgitant orifice area. While estimates of these parameters can be made by conventional two dimensional (2D) echocardiographic techniques, these methods may be unreliable when applied to complex, dynamic, three dimensional (3D) flow events (table 1). The advent of three dimensional echocardiography (3DE) provides a solution to this basic limitation. 3DE generates a scan volume (as opposed to a two dimensional scan sector) which produces a three dimensional dataset containing entire cardiac structures. 15 Surface rendering may then be performed to produce an image with feature contours and depth perspective. Such an approach has proved useful in the representation of complex cardiac structural pathology and in the generation of images which reflect typical “surgeon’s eye” views of the heart. In addition, the 3D dataset may be transected by cut planes orientated in any direction within the volume (“anyplane imaging”). As the entire structure under study is encompassed in the dataset, volume calculations may be made without the need to make geometric assumptions regarding its morphology. A number of studies have confirmed the accuracy of 3D echocardiography for the calculation of cardiac chamber volumes. 3D flow quantitation methods are currently under development and it seems reasonable to assume that these will be superior to the 2D methods listed in table 1. We review these new approaches to the quantification of cardiac flow events and indicate how they may ultimately be integrated into clinical practice.