Background
There has been much recent interest in obtaining matched information by a single technique in clinical cardiology. This interest is continuously shown by the development of contrast agents and by the globalisation of marketing by companies involved in their market. As a consequence, echocardiography, nuclear cardiology and magnetic resonance compete not only on their main output, i.e. volume and motion for echocardiography/magnetic resonance and perfusion for nuclear cardiology, but also on the integrated information.
The need for such information in cardiology is particularly high because of the increasing incidence of dysfunctioning myocardium. In fact, more frequently than in the past, imaging techniques are asked to identify stunned and hibernated myocardium in which function recovery may occur after reflow. Although stunning is still a prognostically undefined syndrome, hibernation has a high impact on clinical decision-making and outcome.
Methodological considerations
The perfusion/function match originating from nuclear Single Photon Emission Tomography is the most reliable and widely used (1). In fact, almost all nuclear medicine labs use high tech digital cameras and specialised software that provide -at low additional cost- the perfusion pattern together with end-diastolic and end-systolic volumes, ejection fraction, regional wall motion and wall thickening. The super imposable segment-by-segment analysis, the favourable cost and the diffusion of SPECT are the main advantages of nuclear cardiology.
Echocardiography...
...is the most used imaging technique in cardiology, and it is continuously developing in the area of perfusion (2). “Bubble” technology is so advanced that it includes treatment beyond imaging and influences the evolution of backscatter technology in commercial devices. Power pulse inversion, power modulation or coherent imaging represents the state of the art of real time contrast echocardiography, with the intrinsic limitations of bi-dimensional imaging (it generates artefacts and does not provide the same accuracy in all myocardial segments).
Magnetic resonance...
...offers the best spatial resolution and for the first time connects the transmural distribution of ischemia and scar with acute and chronic coronary syndromes. There are virtually no limits to signal intensity except perhaps the elusive link between kinetic tracers and the dynamic response. In other words, a quantitative approach is still far from being obtained.
Clinical evaluation of the perfusion/function binomial
Clinically, a cardiological question should be answered using the more appropriate rather than the most available tool, and the combined flow/function assessment is not an exception to this rule. Furthermore, the wrong approach leads to higher costs and longer periods necessary for decision making, sometimes with significant discrepancies in terms of patients’ outcomes. Actually, the degree of ventricular dysfunction, of coronary artery disease and of emergency, condition the choice of the technique. In the case of advanced ischemic heart failure with an indication to revascularisation, nuclear cardiology will offer more information on flow/function match, i.e. and the segment by segment correlation among dyssynergic viable and necrotic segments beyond identification of ischemia. On the other hand, in patients with acute myocardial infarction undergoing revascularisation, contrast echocardiography will offer a repeatable evaluation of regional wall motion and perfusion, including the identification of the no reflow phenomenon, on a segmental although bi-dimensional matrix. Thus, limited availability of flow/function technology (echo provides mostly function and nuclear medicine perfusion), education (imaging specialist), diffusion (only major hospitals have nuclear medicine departments) and management (echocardiography belongs to cardiology, nuclear cardiology to nuclear medicine) influences the choice of the imaging technique. Magnetic resonance is behind the scenes, with a potential clinical role to be defined after some further confirmations.
To conclude, imaging techniques are developing toward an ideal “one stop shop”; technical progress is somewhat faster than clinical need, but the race goes on.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
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