| The evaluation of functional severity of coronary stenoses has been a subject of intense study for the past several decades. With the advent of small diameter guidewire, newer diagnostic endpoints were introduced. Among them, coronary flow reserve (CFR) and myocardial fractional flow reserve (FFR myo) were most widely accepted. However, CFR was affected by several parameters such as the presence of collaterals, Doppler sensor inaccuracy, attainment of maximum hyperemia, microvascular impairment. Similarly, FFR myo was affected by the presence of microvascular impairment. Simultaneous measurement of FFRmyo and CFR was recommended for coronary stenoses and microvascular impairment. The sensor guidewire introduces an additional "artifactual" resistance to blood flow, which affects CFR and FFRmyo measurement.;In this thesis, the effect of guidewire on CFR and FFRmyo measurement was studied. The effect of the guidewire was presented in the form of linear correlations between FFRmyo and FFRmyog [subscript g: guidewire], and CFR and CFRg for 2 different guidewire sizes of 0.35 and 0.46 mm. A strong linear correlation was found between CFR and CFRg (0.46 mm: CFR = CFRgx0.689 + 1.271 (R 2=0.99); 0.35 mm: CFR = CFRgx0.757 + 1.004 (R2=0.99)), and between FFRmyo and FFRmyog (0.46 mm: FFRmyo = FFRmyogx0.737 + 0.263 (R2=0.99); 0.35 mm: FFRmyo = FFRmyogx0.790 + 0.210 (R2=0.99)). These correlations were developed for focal stenoses and could prove useful to estimate the true values of CFR and FFRmyo, delineating the guidewire flow obstruction effect.;Further, a new diagnostic parameter, named Lesion flow coefficient (LFC), was developed. This invasive parameter enables simultaneous evaluation of mean pressure drop across a stenosis, mean blood flow measured by guidewire and minimum area of the stenoses relative to the area of the non-diseased blood vessel. Thus is similar to the idea of Simultaneous measurement of FFRmyo and CFR was recommended for coronary stenoses and microvascular impairment. The in vivo data from animal experiments has shown strong linear correlation between Lesion flow coefficient and CFRg (r = 0.88, p < 0.001) and FFRmyog (r = 0.75, p < 0.001). When Lesion flow coefficient was correlated simultaneously with FFR and CFR, the correlation coefficient increased to 0.90 (LFC = 0.0912xFFRmyog + 0.0644xCFRg + 0.0282; p < 0.001, Type II error: p < 0.01). The significant linear correlations between LFC, FFRmyog and CFRg are interesting considering the non-linear form of LFC in comparison to FFRmyog and CFR g, which are simply ratios of pressure and flow velocity, respectively. Additionally the effect of compliance of healthy vessel on LFC was evaluated. It was seen that the compliance significantly affected the LFC as compared to non-compliant vessels as seen in diseased (atherosclerotic) arteries. |
