Contrast echocardiography for assessment of myocardial perfusion

It has been suggested that the myocardial perfusion can be qualitatively and quantitatively assessed by different ultrasound contrast techniques. It has been reported that the intracoronary or intraaortic administration of the ultrasound contrast agents can be used to visualize perfusion defects or to analyze the coronary flow reserve. The perfusion analysis after intracoronary injection of ultrasound contrast agents seems to be established, but there are a lot of open questions. A topographic (qualitative) perfusion analysis with visualization of perfusion defects and perfusion areas or analysis of collaterals has been demonstrated. A quantitative analysis of myocardial blood flow has been described but the existing studies are inconsistent. It is not known which parameters of the contrast wash-out curves should be used for perfusion analysis and if the Stewart-Hamilton curve analysis can be transferred to all ultrasound contrast agents as a model for quantitative myocardial blood flow assessment. The development of the transpulmonary contrast agents for echocardiographic evaluation of left ventricular cavity has the impact for myocardial perfusion imaging. The increase of myocardial intensity does not mean that a qualitative or quantitative perfusion analysis can be clinically used. In this field we have to differentiate between the possibilities of qualitative discrimination of perfusion defects and quantitative perfusion (myocardial blood flow) analysis. The different scanning conditions, the poor transthoracic ultrasound window and insufficient enhancement of the myocardial intensity make it problematic to quantify the myocardial perfusion. At the moment myocardial intensity will be increased after intravenous injection of transpulmonary contrast agents, but the value for perfusion analysis has not been shown. New ultrasound technologies such as second harmonic imaging, power-mode and raw data analysis have to show the clinical importance of these techniques for perfusion analysis in daily clinical routine. The open questions of the perfusion analysis by contrast echocardiography will be discussed in this review article.