The coronary flow reserve (CFR) represents an important functional parameter to assess epicardial coronary stenosis and to evaluate the integrity of coronary microcirculation (Kern, 2000; Sadamatsu, Tashiro, Maehira, & Yamamoto, 2000). CFR can be measured, during adenosine or dipyridamole infusion, as the ratio of maximal (pharmacologically stimulated) to baseline (resting) diastolic coronary blood flow peak. Even in absence of stenosis in epicardial coronary artery, the CFR may be decreased when coronary microvascular circulation is compromised by arterial hypertension with or without left ventricular hypertrophy, diabetes mellitus, hypercholesterolemia, syndrome X, hypertrophic cardiomyopathy, and connective tissue diseases (Dimitrow, 2003; Strauer, Motz, Vogt, & Schwartzkopff, 1997). Several methods have been established for measuring CFR: invasive (intracoronary Doppler flow wire) (Caiati, Montaldo, Zedda, Bina, & Iliceto, 1999b; Lethen, Tries, Brechtken, Kersting, & Lambertz, 2003a; Lethen, Tries, Kersting, & Lambertz, 2003b), semi-invasive and scarcely feasible (transesophageal Doppler echocardiography) (Hirabayashi, Morita, Mizushige, Yamada, Ohmori, & Tanimoto, 1991; Iliceto, Marangelli, Memmola, & Rizzon, 1991; Lethen, Tries, Michel, & Lambertz, 2002; Redberg, Sobol, Chou, Malloy, Kumar, & Botvinick, 1995), or extremely expensive and scarcely available methods (PET, SPECT, MRI) (Caiati, Cioglia, Montaldo, Zedda, Rubini, & Pirisi, 1999a; Daimon, Watanabe, Yamagishi, Muro, Akioka, & Hirata, 2001; Koskenvuo, Saraste, Niemi, Knuuti, Sakuma, & Toikka, 2003; Laubenbacher, Rothley, Sitomer, Beanlands, Sawada, & Sutor, 1993; Picano, Parodi, Lattanzi, Sambuceti, Andrade, & Marzullo, 1994; Saraste, Koskenvuo, Knuuti, Toikka, Laine, & Niemi, 2001; Williams, Mullani, Jansen, & Anderson, 1994), thus their clinical use is limited (Dimitrow, 2003). In addition, PET and intracoronary Doppler flow wire involve radiation exposure, with inherent risk, environmental impact, and biohazard connected with use of ionizing testing (Picano, 2003a). In the last decade, the development of new ultrasound equipments and probes has made possible the noninvasive evaluation of coronary blood velocity by Doppler echocardiography, using a transthoracic approach. In this way, the peak diastolic coronary flow velocity reserve (CFVR) can be estimated as the ratio of the maximal (pharmacologically stimulated) to baseline (resting) diastolic coronary blood flow velocity peak measured from the Doppler tracings. Several studies have shown that peak diastolic CFVR, computed in the distal portion of the left anterior descending (LAD) coronary artery, correlates with CFR obtained by more invasive techniques. This provided a reliable and non invasive tool for the diagnosis of LAD coronary artery disease (Caiati et al., 1999b; Caiati, Montaldo, Zedda, Montisci, Ruscazio, & Lai, 1999c; Hozumi, Yoshida, Akasaka, Asami, Ogata, & Takagi, 1998; Koskenvuo et al., 2003; Saraste et al., 2001).
Key Terms in this Chapter
Transthoracic Doppler Echocardiography: Noninvasive evaluation of coronary blood velocity by Doppler echocardiography, using a transthoracic approach.
Coronary Flow Reserve: Functional clinical parameter, computed as the ratio of maximal (pharmacologically stimulated) to baseline (resting) diastolic coronary blood flow peak, used to assess epicardial coronary stenosis and to evaluate the integrity of coronary microcirculation.
Dipyridamole: Drug that inhibits platelet aggregation and causes vasodilation. It is used in cardiac stress testing as a coronary vasodilator to induce the maximal stress condition.
Local Adaptive Thresholding Algorithm: Technique based on the computation of a locally dependent threshold in a determined region of interest, by which the object contour is then detected by thresholding.
Bland-Altman Analysis: Statistical method which allows to compare measurements obtained in the same subjects by two different techniques. The Bland-Altman graph plots the difference between the two measurements against their average, for each subject.
Image Processing: The process of applying algorithms to images in order to improve their quality reducing artefacts, to enhance characteristics, to detect object contours.
Thresholding: The process of detecting object contours based on the computation of a binary image in which pixel values are set to one, in correspondence to a videointensity value of the corresponding pixel position in the analyzed image greater than the threshold, and to zero if the videointensity is lower than the threshold. The threshold can be constant for all image, or can be adaptive and spatially dependent.
Left Anterior Descending Coronary Artery: One of the two branches (together with the circumflex (Circ) coronary artery) in which the left main coronary artery divides into.