Is there a future for coronary physiological evaluation in clinical decision making?

Most of our practice in interventional cardiology decision-making is still empirical and mainly guided by the immediate risk of the procedure and its long-term clinical benefits. The evolution of percutaneous coronary interventions, from balloons to stenting, is such an example. Although well established, the decision to perform a procedure is rarely based on critical knowledge of the anatomy and physiology beyond an angiographically significant stenosis. If coronary angiography depicts a lesion that could explain symptoms and abnormal noninvasive functional tests, why not perform a simple and inexpensive procedure and dilate that lesion or implant a stent, preferably in the same procedure? However, knowledge of anatomical features within the coronary artery and the importance of the physiological assessment of pressure and flow distal to a stenosis, has definitively helped the evolution of this form of therapy and the current state of the art of percutaneous coronary interventions. We cannot forget the importance of intravascular ultrasound, as a complement to angiography, in our understanding of atherosclerotic coronary disease, arterial remodelling, mechanisms of action of balloon angioplasty and other devices, correct stent apposition, restenotic process, etc. In the future, radiofrequency analysis may allow evaluation of plaque composition and guide us, eventually, to the best therapeutic option. In the same way, the physiological assessment of the influence of a stenosis on the distal arterial pressure–flow relationship can now be easily determined by sensor-tipped wires that measure absolute or relative coronary flow velocity reserve and pressure-derived fractional flow reserve. They have been used clinically, mainly on an individual basis, to decide if an intermediate grade stenosis should be treated, as was suggested by some clinical studies. Within research protocols they allow, for instance, the study of endothelial function and they are used to evaluate long-term pharmacological interventions. The reasons why these anatomical and physiological evaluations are not routinely or more often performed, continuing to be regarded as research tools, are mainly due to the fact that they can be time consuming and costly. Also, perhaps, because newcomers to interventional cardiology are too stent-oriented, not having been trained to question the reason for a clinical decision. The DEBATE study was the first multicentre trial to use Doppler absolute coronary flow velocity reserve, together with percent diameter stenosis by quantitative angiography, to assess their prognostic value after balloon angioplasty. The study defined as optimal cut-off criteria for predictors of clinical events, recurrence of symptoms, need for reintervention and restenosis rate, a post-procedural distal coronary flow reserve >2·5 and a residual stenosis of 35%. This historical trial initiated further studies to test the strategy of provisional stenting after balloon angioplasty. The work published by Piek et al. in the current issue is a post-hoc analysis of the DEBATE study, using a small and very selected population with absolute coronary blood flow velocity reserve determinations before, immediately after balloon angioplasty and at 6 months follow-up. It is a very interesting mechanistic physiological study, where coronary flow reserve and its components, baseline and hyperaemic average peak blood flow velocities, are used to help explain the rationale for future clinical events. The study confirms that a high proportion of patients (49%) do not reach a coronary flow reserve of 2·5 after balloon angioplasty, in spite of a good angiographic result (<35% residual stenosis). This impairment is exclusively due to haemodynamic factors before angioplasty and to an elevated baseline average peak flow velocity. In some patients there are coronary flow reserve alterations at follow-up which are determined by changes in hyperaemic blood flow velocity. Moreover, the study is the first to show that patients with impaired coronary flow reserve after optimal balloon angioplasty have increased recurrence of angina and higher target lesion revascularization, with a trend towards higher restenosis rates at 6 months. The explanations for these findings are discussed in the paper but some are speculative. The persistently low coronary flow reserve (due to elevated baseline blood flow velocity) after balloon angioplasty is probably secondary to increased shear stress, disturbed autoregulation and/or diffuse mild coronary atherosclerosis. The increase in impaired coronary flow reserve during follow-up could be due to normalization of autoregulation or epicardial remodelling.