Coronary circulation: Pressure/flow parameters for assessment of ischemic heart disease.

Both invasive and non-invasive parameters have been reported for assessment of the physiological status of the coronary circulation. Fractional flow reserve and coronary (or myocardial) flow reserve may be obtained by invasive or non-invasive means. These metrics of coronary stenosis severity have achieved wide clinical acceptance for guiding revascularization decisions and risk stratification. Other indices are obtained invasively (e.g., instantaneous wave-free ratio, iFR; hyperemic stenosis resistance) or non-invasively (e.g., PET absolute myocardial blood flow (mL/min/g)) and have been used for the same purposes. Both iFR, and whole-cycle distal coronary to aortic mean pressure (Pd/Pa) are measured under basal condition and used for assessment of hemodynamic stenosis severity as is index of basal stenosis resistance (BSR). These metrics typically are dichotomized at an empirically derived cut point into "normal" and "abnormal" categories for purposes of clinical decision making and data analysis. Once dichotomized the indices do not always point in the same direction and so confusion may arise. This review, therefore, will present basic principles relevant to understanding commonly employed metrics of the physiological status of the coronary circulation, potential strengths and weaknesses, and hopefully an improved appreciation of the clinical information provided by each.

Anatomic versus physiologic assessment of coronary artery disease. Role of coronary flow reserve, fractional flow reserve, and positron emission tomography imaging in revascularization decision-making.

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.

PET measurement of adenosine stimulated absolute myocardial blood flow for physiological assessment of the coronary circulation.

Considerable awareness has been raised of late of the need to reduce radiation exposure and control costs of x-ray and radionuclide imaging procedures. PET/CT cameras are now widely available and in conjunction with appropriate radionuclides and commercially available software make quantitative measurement of absolute MBF feasible for routine clinical practice. Quantitative measurement of absolute MBF under condition of coronary vasodilation permits independent assessment of the functional status of each of the three major coronary perfusion zones and so obviates the need for rest MBF determination in the great majority of cases. Coronary microvascular function also may be assessed in this same way. Thus, the stress-only protocol with quantitative PET measurement of MBF provides essential information required for clinical decision making related to need for catheterization and intervention for patients with known or suspected ischemic heart disease. Moreover, the single PET determination of maximal MBF in contrast to the usual rest/stress procedure addresses both safety and cost concerns. The present review focuses on: (1) quantitative PET measurements of myocardial blood flow for physiological assessment of the coronary circulation and (2) the value and potential limitations of performing stress only imaging in the clinical context.

Comparison of positron emission tomography measurement of adenosine-stimulated absolute myocardial blood flow versus relative myocardial tracer content for physiological assessment of coronary artery stenosis severity and location.

OBJECTIVES: This study tests the hypothesis that absolute measurement of adenosine (Ado)-stimulated myocardial blood flow (MBFado) is superior to measurement of relative tracer uptake for identification of hemodynamically significant coronary artery disease (CAD). BACKGROUND: Positron emission tomography measurement of absolute myocardial blood flow (MBF) ((13)N-ammonia) with Ado has the capability to more accurately assess hemodynamic severity of CAD than measurement of relative tracer content (TC) (nCi/ml) during Ado, which by definition depends on at least 1 normal zone to which others are compared. METHODS: A total of 27 patients (20 male, 58 +/- 11 years, mean +/- SD) with known or suspected CAD and 21 normal subjects (13 male, 38 +/- 10 years) were studied. Parametric (K1) MBF images and TC sum images were analyzed. A stenosis > or =70% defined significant CAD. The receiver-operator characteristic curve (ROC) analysis area under the curve (AUC) compared MBF and TC results. Cut-point analysis for sensitivity, specificity, and accuracy showed the best MBF criteria for CAD as MBFado <1.85 ml/min/g and the best TC as <70% maximum. The myocardial blood flow reserve ratio (MBFR) (optimal <2.0x) also was studied. RESULTS: The ROC analysis of PET parameters showed that MBFado was superior to <70% maximum uptake for CAD detection (n = 144 vessels; AUC 0.900 vs. 0.690, respectively, p < 0.0001) and was marginally greater than MBFR (0.856; p = 0.10). For CAD cut-point analysis, MBFado accuracy exceeded TC (0.84 vs. 0.72, respectively, p = 0.005), as did sensitivity (0.81 vs. 0.48, respectively; p = 0.001). Specificity of MBFado for CAD classification (0.85) was comparable to TC (0.82; p = NS). Sensitivity, specificity, and predictive accuracy for MBFR were 0.62, 0.85, and 0.79, respectively. The difference in specificity was not significant versus MBFado. However, MBFado was more sensitive than MBFR (p = 0.01). The difference in predictive accuracy was borderline (p = 0.06) in favor of MBFado. CONCLUSIONS: Measurement of Ado-stimulated absolute MBF is superior to relative measurement of myocardial tracer retention for identification of CAD and can be accomplished with a single MBFado measurement.