Future challenges to coronary angioplasty: perspectives on intracoronary imaging and physiology

Several intravascular techniques have been developed with the purpose of achieving optimal guidance for treatment during coronary angioplasty (PTCA). Although the coronary angiographic technique is well established, there are still some inherent limitations. Due to intimal rupture, tears, dissection and thrombus following PTCA treatment, angiography does not allow exact delineation of the true borders of the vessel. Coronary angioscopy is currently the most sensitive method to detect coronary thrombus and can also be used to classify atheromatous plaques. Furthermore, coronary dissection can be detected with more accuracy than with angiography. One limitation associated with angioscopy is the need to occlude the vessel during imaging, which may create myocardial ischaemia. Furthermore, there is presently no method for quantifying angioscopic findings. Intravascular ultrasound produces a cross-sectional image of the vessel, which permits analysis of the layers of the vascular wall. Characterization and classification of various types of plaque can be made because thrombus, lipid, fibrous tissue and calcium have different ultrasonic echogenicity. Flow velocity measurement with the Doppler technique is an interesting approach to the physiological assessment of coronary stenoses. Coronary flow reserve can be estimated with this method and monitoring of the flow signal following angioplasty will aid in the diagnosis of flow-limiting complications. The trans-stenotic pressure gradient is a valuable measure of the haemodynamic importance of a coronary lesion. Trans-stenotic gradients during maximal hyperaemia obtained with a miniaturized pressure transducer yield reliable information regarding the severity of the stenosis, and the pressure values may be used to calculate the relative coronary flow reserve. In conclusion, all of these intracoronary diagnostic techniques will to some extent play a role in the future of coronary angioplasty. Safety, cost and complexity are some of the factors which will determine the growth potential of each method.