Intravascular ultrasound--the new gold standard?

Abstract

Intravascular ultrasound (IVUS) has evolved to a research tool to an intrinsic part of modern invasive cardiology. The main reason is the capability to obtain "in-vivo" micro anatomy by means of miniaturized echo-transducers with an outer diameter of 2.9-3.5 French. For the first time it is possible to base decisions not only on lumenograms but also on vessel wall assessment. The capabilities of IVUS can be divided in its diagnostic and intervention associated potentials. The diagnostic strength of IVUS is the ability to monitor compensatory coronary artery enlargement as a response to arteriosclerosis, to assess intermediate lesions, to reveal occult left main stem disease, and angiographically "silent" arteriosclerosis. In conjunction with the estimation of intracoronary flow reserve, patients with the diagnosis of coronary "syndrome X" can be better classified into those with or without early signs of arteriosclerosis. Additionally, IVUS is at present the only method allowing the classification of coronary artery lesions according to the AHA/ACC Stary classification. The intervention associated potentials of IVUS are the ability to allow optimal device selection, i.e. rotablators in calcified lesions or atherectomy devices in large plaque burden. The effects of PTCA on vessel wall morphology can be studied in great detail and the effect on luminal gain can be assessed almost on-line. The correlation between IVUS and angiography for estimation of luminal dimensions is inferior, because angiography is not able to describe complex luminal geometries. Several groups showed that the residual plaque area even after angiographically successful PTCA lies still in the range of 60%. A significant reduction of this number may influence long-term outcome after PTCA. Minimal luminal areas and residual plaque area after PTCA seem to be an indicator of restenosis, while the presence or absence of dissections seem to be less predictive. Additionally, the main mechanism of restenosis after PTCA is vessel shrinkage, not intimal hyperplasia. Intravascular monitoring of stent expansion led to high-pressure stent deployment with significant increase in post-procedural luminal diameters and finally the ability to withhold anticoagulation in patients with optimal stent deployment and to lower subacute stent thrombosis rates. First results for IVUS guided PTCA show a superior gain in post procedural free lumen without an increased complication rate. In the future, integrated devices, like balloons on IVUS catheters, steerable catheters, integrated flow and pressure transducers, tissue characterisation, and 0.018 inch IVUS guidewires will further enhance the usefulness of IVUS.