Impact of Imaging in Optimizing Outcomes After Angioplasty, Health News, ET HealthWorld
Over the past several decades, improvements in equipment, stents, procedures, and pharmaceutical therapy have dramatically improved short- and long-term clinical outcomes after percutaneous coronary intervention (PCI). Because image guidance is an integral part of every step of PCI, including assessment of lesion severity, pre-procedural planning (selection of appropriate stent strategy, stent size , landing zones), optimization (stent expansion, malposition, light gain) and management of immediate complications, it is one of the key determinants of operative results (dissection, thrombus, tissue prolapse, compromise of the lateral branches). Imaging helps in the diagnosis and management of stent failure mechanisms during follow-up (restenosis, thrombosis).
The current gold standard for imaging during percutaneous coronary procedures is angiography, although it has serious drawbacks. Catheter-based intravascular imaging techniques, such as intravascular ultrasound and, more recently, optical coherence tomography, have the potential to overcome these constraints and improve clinical outcomes. We have discussed current applications of available imaging modalities, existing evidence, unmet needs and possible areas of research in this update.
Functional assessment of the vessel pre and post angioplasty:
The instantaneous waveless ratio (iFR) is a measure of the severity of coronary artery stenosis. In small trials, the index has been compared to fractional flow reserve (FFR), and the two measures have been found to have similar diagnostic accuracy. However, there are no clinical outcome studies related to the use of iFR.
Whether instantaneous wave-free ratio (iFR)-guided coronary revascularization strategies are generally non-inferior to those guided by fractional flow reserve (FFR) in terms of rates of major adverse cardiac events at one-year follow-up in patients With stable angina or acute coronary syndrome, the overall accuracy of iFR diagnosis in large cohorts of patients is approximately 80% compared to FFR diagnosis. The variables that contribute to the diagnostic gap between iFR and FFR are still unknown. Given the fixed severity of coronary artery stenosis, worsening aortic valve disease (eg, regurgitation or stenosis) causes a significant decrease in iFR and a slight increase in FFR, and this increase in coronary microvascular resistance resulted in a significant increase in both iFR and FFR, but the degree of increase in iFR was less than that of FFR. In patients with severe aortic valve disease or coronary microcirculatory dysfunction, there is a substantial risk of discordant diagnosis between iFR and FFR.
Role of intracoronary ultrasound or IVUS vs optimal coherence tomography:
Intracoronary imaging can help the interventional cardiologist determine the shape of atherosclerotic plaques, optimize stent sizing, and reduce the risks associated with PCI. Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) are common imaging techniques, while other spectroscopic techniques are under development.
Unlike IVUS, OCT uses near infrared light to obtain intracoronary imaging. The initial generation of OCT imaging used time domain (TD) imaging, which was based on occlusive balloon technology. Frequency domain (FD) imaging, also known as Fourier domain spectral imaging, has now overtaken TD imaging in popularity.
Although angiographic guidance is the accepted standard of care during PCI, new intravascular imaging techniques such as optical coherence tomography (OCT) have potential advantages over angiography in assessing lesion characteristics and optimize the results of the procedure. OCT has been proven to identify plaque morphologies that are linked to a worse outcome in acute coronary syndrome (ACS). Beyond plaque characterization, OCT can reveal procedural features not visible with angiography alone, such as proper lesion coverage, stent expansion, or apposition. After treatments deemed ideal by angiographic standards, abnormal OCT imaging findings are common, and OCT criteria of inadequate stent expansion have been associated with an elevated risk of significant adverse cardiac events.
Commercially available OCT software automatically recognizes lumen, allows frame marking, and provides user-defined proximal and distal reference frames with measurements. Each coronary artery indent can also be seen in cross-sectional frames, longitudinal views, and lumen profile views. 3D reconstruction is possible and can aid in the assessment of bifurcation lesions and optimization of PCI results. Co-registration of OCT and angiography can help locate anatomical lesions more precisely, minimizing the risk of geographic error.
The safety profile of IVUS and the current generation of FD-OCT has been demonstrated. The feasibility, procedure, and long-term safety of OCT and IVUS in patients with ST-segment elevation MI (STEMI) with primary PCI were investigated in an integrated substudy of biomarkers and imaging.
The requirement of a bloodless field for good imaging was one of the drawbacks of early TD-OCT imaging. This was accomplished by occluding the coronary artery proximally with a semi-conforming balloon and flushing it with Ringer’s lactate solution. Minor problems such as transient ST-segment elevation with concomitant chest pain were common, despite the fact that this approach was not associated with major complications. Moreover, with a recoil speed of only 0.5 to 3.0 mm/s, the acquisition time was longer. In contrast, contemporary FD-OCT imaging does not require blockage of a coronary artery with a balloon and can achieve a bloodless field with higher withdrawal rates.
Dr Rajpal Singh, Director and Interventional Cardiologist, Department of Cardiology, Fortis Hospitals Bannerghatta Road
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