Don't Judge a Book by Its Cover

Johnson, Nils P.; Davidson, Charles J.

doi:10.1161/circinterventions.110.960708

Cited by 2 publications

(1 citation statement)

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“…Specifically, anatomic imaging (IVUS, OCT, and CTA) should be performed rarely, if ever, when making a decision on the necessity of mechanical revascularization in stable patients but can be invaluable regarding its feasibility or procedural details. [113][114][115] Especially when instrumenting the coronary arteries, it makes little sense to perform IVUS or OCT instead of measuring FFR directly. ''Even the authors of a recent prospective IVUS study using FFR as the reference standard concluded that physicians should primarily use their clinical judgment and FFR because FFR is the most accurate tool to detect ischemia.…”

Section: Discussionmentioning

confidence: 99%

Coronary Anatomy to Predict Physiology

Johnson

Kirkeeide

Gould

2013

Circ: Cardiovascular Imaging

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A pproximately 40 years ago, we began to link coronary anatomy to its physiology. In those early experiments, percent diameter stenosis (%DS) provided a simple yet appropriate metric of anatomy because every lesion was created externally to an otherwise normal coronary artery by an adjustable, focal occluder of uniform length. 1 Since that time, a wide array of anatomic techniques has been proposed to predict physiological severity. But what insights have we gained from this work during the past 4 decades? Will we ever be able to predict physiology completely from anatomy? Or, like an isotope undergoing radioactive decay, must we content ourselves with a statistical and mechanistic understanding but without individual application?This review surveys the long and ongoing journey to predict physiology from anatomy in the coronary circulation. We begin with several general principles that apply to all techniques. Next we detail the 2 broad methods used for physiology prediction: single parameters (like %DS) and computational modeling. For each method, we explicitly provide the underlying assumptions. We compare the expected behavior between anatomy and physiology with representative experimental data from the literature. Although the concepts apply equally to animal models, we have chosen to present only results from humans to maximize clinical relevance.The data reveal a clear and simple message: Coronary anatomy alone will never be sufficient to predict physiological behavior at the level of a single patient. However, anatomic parameters and models will continue to provide a useful framework for understanding physiological behavior in general. General PrinciplesAn inaccurate prediction can result from only 2 general reasons. First, input parameters may contain uncertainty. The butterfly effect from weather forecasting, 2 whereby small changes in initial conditions can produce large downstream effects ("Does the flap of a butterfly's wings in Brazil set off a tornado in Texas?," provides a classic example). Second, the predictive model may contain inaccurate assumptions. For example, Ohm's empirical law relating current to potential difference in electric circuits does not apply to certain devices such as a diode or thermistor. Typically, our predictive assumptions reflect group behavior well but do not account for biological variability. Both of these general principles can be seen in using coronary anatomy to predict physiology. Uncertainty in Input ParametersThe Poiseuille equation relates pressure drop in a rigid tube to the fourth power of the vessel radius under certain conditions (a newtonian fluid during steady, fully developed, laminar flow). Therefore, a small uncertainty in the angiogram becomes magnified into a large uncertainty in model output.For example, assume a 4.4-mm reference diameter of the left main coronary artery with a 50% diameter stenosis such that the minimum lumen diameter (MLD) equals 4.4 mm×0.50=2.2 mm, equivalent to a radius of 1.1 mm. Current invasive angiographic technology provide...

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Section: Discussionmentioning

confidence: 99%