Deferral of PCI of a functionally non-significant stenosis is associated with a favourable very long-term follow-up without signs of late 'catch-up' phenomenon.

This comprehensive core laboratory analysis comparing iFR and Pd/Pa with FFR demonstrated an overall accuracy of ~80% for both nonhyperemic indices, which can be improved to ≥90% in a subset of lesions. Clinical outcome studies are required to determine whether the use of iFR or Pd/Pa might obviate the need for hyperemia in selected patients.

CFR is linearly related to FFR for progressive stenosis superimposed on diffuse narrowing. The relative contributions of focal and diffuse disease define the slope and values along the linear CFR and FFR relationship. Discordant CFR and FFR values reflect divergent extremes of focal and diffuse disease, not failure of either tool. With such discordance observed by invasive and noninvasive techniques and also fitting fluid dynamic predictions, it reflects clinically relevant basic coronary pathophysiology, not methodology.

Cardiac PET combined with CT is rapidly expanding despite artifactual defects and false-positive results due to misregistration of PET and CT attenuation correction data-the frequency, cause, and correction of which remain undetermined. Methods: Two hundred fifty-nine consecutive patients underwent diagnostic rest-dipyridamole myocardial perfusion PET/CT using 82 Rb, a 16-slice PET/CT scanner, helical CT attenuation correction with breathing and also at end-expiratory breath-hold, and averaged cine CT data during breathing. Misregistration on superimposed PET/CT fusion images was objectively measured in millimeters and correlated with associated quantitative size and severity of PET defects. Misregistration artifacts were defined as PET defects with corresponding misregistration on helical CT-PET fusion images that resolved after correct coregistration using a repeat CT scan, cine CT averaged attenuation during normal breathing, or shifted cine CT data that coregistered with PET data. Results: Misregistration of standard helical CT PET images caused artifactual PET defects in 103 of 259 (40%) patients that were moderate to severe in 59 (23%) (P 5 0.0000) and quantitatively normalized on cine or shifted cine CT PET (P 5 0.0000). Quantitative misregistration was a powerful predictor of artifact size and severity (P 5 0.0000), particularly for transaxial misregistration .6 mm occurring in anterior or lateral areas in 76%, in inferior areas in 16%, and at the apex in 8% of 103 artifactual defects. Conclusion: Misregistration of helical CT attenuation and PET emission images causes artifactual defects with falsepositive results in 40% of patients that normalize on cine CT PET using averaged CT attenuation data during normal breathing comparable to normal breathing during PET emission scanning and shifting cine CT images to coregister visually with PET.

Noninvasive, absolute myocardial perfusion and coronary flow reserve (CFR) can be imaged by many techniques. However, such data must be interpreted for clinical application regardless of its source. Currently, no guide exists for physiological integration. Therefore, we propose 2-dimensional scatter plots of stress flow and CFR with superimposed thresholds for normal flow, reduced flow without ischemia, definite ischemia, and transmural infarction to allow for automatic and objective classification. Application of this schema to 1,500 studies demonstrates that flow capacity relates inversely to risk factors and atherosclerotic burden. Interpreting stress flow to make clinical decisions requires rest flow or CFR for broad application to all patients. Although relative uptake images alone are adequate for some patients, it can either under- or over-estimate flow capacity in many persons. Our standardized framework could prompt future studies leading to a trial of revascularization guided by absolute flow measurements.

Angiographic severity of coronary artery stenosis has historically been the primary guide to revascularization or medical management of coronary artery disease. However, physiologic severity defined by coronary pressure and/or flow has resurged into clinical prominence as a potential, fundamental change from anatomically to physiologically guided management. This review addresses clinical coronary physiology-pressure and flow-as clinical tools for treating patients. We clarify the basic concepts that hold true for whatever technology measures coronary physiology directly and reliably, here focusing on positron emission tomography and its interplay with intracoronary measurements.

FFR demonstrates a continuous and independent relationship with subsequent outcomes, modulated by medical therapy versus revascularization. Lesions with lower FFR values receive larger absolute benefits from revascularization. Measurement of FFR immediately after stenting also shows an inverse gradient of risk, likely from residual diffuse disease. An FFR-guided revascularization strategy significantly reduces events and increases freedom from angina with fewer procedures than an anatomy-based strategy.

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