CHAPTER 8 Invasive Imaging and Haemodynamics
Direct catheter-based measurements of saturation and pressure in the various cardiac cavities allows full characterization of patient haemodynamics, including presence of intracardiac shunts, valve gradients and areas, and pulmonary and vascular resistances. The most important invasive haemodynamic assessment in today’s practice, however, is now performed in the coronary arteries using microsensor-tipped guidewires able to measure post-stenotic pressure. When measured after maximal vasodilation, fractional flow reserve offers reliable individual characterization of coronary lesions. Results from large randomized long-term studies have shown that this technique can be safely used to defer interventions in single vessel disease and to target only functionally significant lesions in multivessel disease.The diffuse practice of performing angioplasty immediately after diagnostic catheterization requires streamlined individualized coronary angiographic studies unfolding the relevant coronary segments in the projections that will optimally guide the angioplasty procedure. Tomographic high resolution images can be obtained with intravascular ultrasound (IVUS) or optical coherence tomography (OCT). The former does not require replacement of blood with crystalloids and measures the full thickness of the vessel wall encroachment (vessel or external elastic membrane diameter and area). IVUS has revolutionized our approach to stent deployment which became more aggressive using higher pressures for stent deployment or post-dilatation. However, convincing data on improved prognosis is still lacking for stent implantation, with the exception of non-randomized or small-scale studies in left main disease or small vessels and long lesions. OCT is limited by low penetration and the need to replace blood but has greater resolution compared with IVUS. At present, the main application is in the detection and quantification of malapposition and strut coverage. The clinical relevance of these findings is still under debate because no correlations are available between those parameters and long-term outcome after stenting.
Chapter 28)
