Adjunctive Diagnostic Instruments for PCI

Since the discovery of X-rays in 1895, there has been continuous development, first of imaging techniques, but over the last several decades, of therapeutics, to address the number-one killer of individuals in the industrialized world….heart disease. Since Andreas Gruentzig’s initial description of coronary angioplasty,¹ a whole host of additional percutaneous therapeutics have been developed. Along with percutaneous therapeutics, there has also been tremendous growth in percutaneous diagnostic techniques and equipment. As a testament to Gruentzig’s pioneering work, there are in excess of 20,000 citations in PubMed regarding the search term “PTCA”.²
Despite the maturity of coronary angiography including quantitative coronary angiography, the coronary angiogram, because it is an anatomic “lumenogram”, has several limitations. They include: 1) underestimation of the degree of stenosis and plaque burden; 2) a high interobserver variability, especially when quantitative coronary angiography is not used; 3) low sensitivity to detect calcification; and 4) it gives only an estimate, at best, of the physiologic significance of the visualized stenosis. Additional tools have been added to the interventionalist’s armamentarium to help in the assessment of coronary disease at the time of catheterization. I would like to briefly concentrate on: 1) fractional flow reserve (FFR); 2) intravascular ultrasound (IVUS); 3) angioscopy; and what these technologies have taught us, as well as what the future might bring with further development of technologies such as optical coherence tomography, computed tomographic coronary angiography (CTA) and magnetic resonance imaging (MRI).
Fractional flow reserve. Gruentzig identified very early the impact of balloon angioplasty on the gradient across the lesion and the positive impact on outcome of its improvement following the procedure.³ FFR represents a further refinement of his initial description and allows “on-the-fly” physiologic lesion assessment.⁴ It has taught us several things, among them:
• FFR is of help in the physiologic assessment of moderate stenosis (50–70%) and is superior to angiography in this lesion severity.
• A significant reduction in FFR is associated with a poorer patient outcome.
• Likewise, a more normal FFR is associated with a better outcome and can be used, as demonstrated in the DEFER trial,⁵ to determine which lesions can be successfully treated with medications alone.
• It can be used to determine a successful percutaneous coronary intervention (PCI) result over and above the angiographic result. Intravascular ultrasound. A tremendous body of literature has been generated using IVUS for the assessment of lesion severity, prediction of outcome, assessment of PCI results, and has yielded a more complete understanding of the atherosclerotic disease process. In addition it has taught us:
• Lesion composition, particularly the degree of calcification.⁶
• Percutaneous transluminal coronary angioplasty (PTCA) mechanisms of action.
• Proper stent and other device sizing; initial work in this area led Colombo to demonstrate that with proper stent sizing and delivery, warfarin anticoagulation was no longer necessary when using dual antiplatelet therapy.⁷
• Mechanism of PTCA and stent restenosis and the concepts of positive and negative remodeling.
Angioscopy. Although this is a tool that is used in only a few centers, it has nevertheless been a useful adjunct to angiography, particularly as it relates to intraluminal morphology and pathology. It has taught us the following:
• Lesion characteristics, particularly demonstrating the differences in acute versus non-acute presentations.
• The time course of stent endothelialization and differences between bare-metal and drug-eluting stents have been clearly demonstrated.⁸
Newer technologies. Many are being evaluated, but the final technology of choice will depend on the test of time. Of particular interest are:
• Optical coherence tomography, which has the ability to potentially further expand our understanding of lesion morphology due to its superior spatial resolution when compared to IVUS.^9,10
• Multislice CTA, currently at 64-slice, but moving rapidly higher. Although it has been touted as a replacement for catheter-based coronary angiography, in its present state it appears best suited to exclude significant disease when negative. Where it will ultimately fit in our diagnostic and therapeutic armamentarium is unclear, but it holds great promise.
• MRI, which produces images with a resolution that rivals anatomic pathology, but has failed, to date, to be a serious contender as a replacement for coronary angiography.
In summary, adjunctive diagnostic instruments for percutaneous intervention have: 1) improved our understanding of coronary disease and its response to PCI; 2) made lesion assessment more accurate compared to coronary angiography; 3) allowed improved assessment of PCI results; and 4) improved outcomes following PCI.
It is interesting to speculate on what Andreas Gruentzig would think of what has become of the balloon catheter that he developed on his kitchen table in Zurich now more than three decades ago. I think he would be delighted to see where we have taken the technology, but he would be pushing us to expand our knowledge of the revolutionary technique that he had the vision and courage to develop. As always, he would be teaching us.

References

1. Gruentzig AR. Transluminal dilatation of coronary-artery stenosis. Lancet 1978;1:263.
2. PubMed accessed September 1, 2007.
3. Gruentzig AR, Senning A, Siegenthaler WE. Non operative dilatation of coronary-artery stenosis. Percutaneous transluminal coronary angioplasty. N Engl J Med 1979;301:61–68.
4. Pijls NHJ. Is it time to measure fractional flow reserve in all patients? J Am Coll Cardiol 2003;41:1122–1124.
5. Pijls NH, van Schaardenburgh P, Manoharan G, et al. Percutaneous coronary intervention of functionally nonsignificant stenosis: 5-year follow-up of the DEFER study. J Am Coll Cardiol 2007;49:2105–2111.
6. Nicholls SJ, Tuzcu EM, Wolski K, et al. Coronary artery calcification and changes in atheroma burden in response to established medical therapies. J Am Coll Cardiol 2007;49:263–270.
7. Colombo A, Hall P, Nakamura S, et al. Intracoronary stenting without anticoagulation accomplished with intravascular ultrasound guidance. Circulation 1995;91:1676–1688.
8. Awata M, Kotani J, Uematsu M, et al. Serial angioscopic evidence of incomplete neointimal coverage after sirolimus-eluting stent implantation: Comparison with bare-metal stents. Circulation 2007;116:910–916.
9. Jang IK, Bouma BE, Kang DH, et al. Visualization of coronary atherosclerotic plaques in patients using optical coherence tomography: Comparison with intravascular ultrasound. J Am Coll Cardiol, 2002;39:604–609.
10. Kubo T, Imanishi T, Takarada S, et al. Assessment of culprit lesion morphology in acute myocardial infarction: Ability of optical coherence tomography compared with intravascular ultrasound and coronary angioscopy. J Am Coll Cardiol 2007;50:933–939.