Effect of changes in contractility on pressure drop coefficient and fractional flow reserve in a porcine model.

OBJECTIVES AND BACKGROUND: Decisions based on invasive functional diagnostic measurements are often made in the setting of fluctuating hemodynamic variables that may alter resting or hyperemic measurements. The purpose of this investigation is to analyze the effect of myocardial contractility (CY) on invasive functional parameters. We hypothesize that the pressure drop coefficient (CDPe; ratio of pressure drop to distal dynamic pressure) and fractional flow reserve (FFR; ratio of average pressures distal and proximal to a stenosis) are not affected by fluctuations in CY and can distinguish between different severities of epicardial stenosis. METHODS: Simultaneous measurements of distal coronary-arterial pressure and velocity were performed in 10 pigs using a dual-sensor tipped guidewire for heart rate (HR) <110 bpm and HR >110 bpm, in the presence of coronary lesions of <50% area stenosis (AS) and >50% AS. Variations in myocardial function and vascular resistance were induced by atrial pacing, papaverine and balloon obstruction, respectively. The maximum rate of rise of left ventricular pressure ([dp/dt]max) was the index of contractility. The contractile function of the heart was empirically defined as CY >900 mm Hg/sec (higher) and CY <900 mm Hg/sec (normal). RESULTS: For CY >900 mm Hg/sec, under AS <50% and AS >50%, the mean values of FFR (0.91 ± 0.02 and 0.78 ± 0.02), and CDPe (15.6 ± 5.3 and 70.7 ± 24.7) were significantly different (P<.05). Similarly, for CY <900 mm Hg/sec, under AS <50% and AS >50%, the mean values of FFR (0.83 ± 0.04 and 0.63 ± 0.04), and CDPe (43.8 ± 14.9 and 191.8 ± 61.4) were also significantly different (P<.05). CONCLUSIONS: Both FFR and CDPe could effectively distinguish between stenosis severity at normal and higher levels of myocardial contractility.

Influence of heart rate on fractional flow reserve, pressure drop coefficient, and lesion flow coefficient for epicardial coronary stenosis in a porcine model.

A limitation in the use of invasive coronary diagnostic indexes is that fluctuations in hemodynamic factors such as heart rate (HR), blood pressure, and contractility may alter resting or hyperemic flow measurements and may introduce uncertainties in the interpretation of these indexes. In this study, we focused on the effect of fluctuations in HR and area stenosis (AS) on diagnostic indexes. We hypothesized that the pressure drop coefficient (CDP(e), ratio of transstenotic pressure drop and distal dynamic pressure), lesion flow coefficient (LFC, square root of ratio of limiting value CDP and CDP at site of stenosis) derived from fluid dynamics principles, and fractional flow reserve (FFR, ratio of average distal and proximal pressures) are independent of HR and can significantly differentiate between the severity of stenosis. Cardiac catheterization was performed on 11 Yorkshire pigs. Simultaneous measurements of distal coronary arterial pressure and flow were performed using a dual sensor-tipped guidewire for HR < 120 and HR > 120 beats/min, in the presence of epicardial coronary lesions of <50% AS and >50% AS. The mean values of FFR, CDP(e), and LFC were significantly different (P < 0.05) for lesions of <50% AS and >50% AS (0.88 ± 0.04, 0.76 ± 0.04; 62 ± 30, 151 ± 35, and 0.10 ± 0.02 and 0.16 ± 0.01, respectively). The mean values of FFR and CDP(e) were not significantly different (P > 0.05) for variable HR conditions of HR < 120 and HR > 120 beats/min (FFR, 0.81 ± 0.04 and 0.82 ± 0.04; and CDP(e), 95 ± 33 and 118 ± 36). The mean values of LFC do somewhat vary with HR (0.14 ± 0.01 and 0.12 ± 0.02). In conclusion, fluctuations in HR have no significant influence on the measured values of CDP(e) and FFR but have a marginal influence on the measured values of LFC. However, all three parameters can significantly differentiate between stenosis severities. These results suggest that the diagnostic parameters can be potentially used in a better assessment of coronary stenosis severity under a clinical setting.

Accuracy of fetal echocardiography: a cardiac segment-specific analysis.

OBJECTIVE: In patients with congenital heart disease, comprehensive, segment-specific analysis of cardiac anatomy has become 'the standard of care', largely as a result of improvements in cardiac imaging technology. Our aim was to apply segment-specific standards to assess the accuracy of fetal echocardiography. METHODS: This was a retrospective review of all fetal echocardiograms (n = 915) performed at our center between August 1998 and June 2003. Of these, 100 studies had congenital heart disease findings and corresponding postnatal studies on the same patients for comparison. An expert independent pediatric echocardiologist, using the standards of accuracy expected of postnatal echocardiography, assessed the studies for the following cardiac segments: abdominal situs, systemic venous return (VR), pulmonary VR, atria, atrioventricular valves, ventricular septum, ventricular hypoplasia, ventricular morphology, semilunar valves, great arterial relation and aortic arch. Sensitivity, specificity, and positive and negative predictive values were calculated for each segment. RESULTS: Specificity and negative predictive value were high for all cardiac segments (range, 82-100%). Sensitivity and positive predictive value were similarly high (range, 83-100%) for most cardiac segments, but were only 50-88% for systemic VR, pulmonary VR and aortic arch segments. CONCLUSIONS: Fetal echocardiography has excellent diagnostic accuracy in describing intracardiac anatomy. However, despite both technological advances and improved physician awareness, assessment of systemic VR, pulmonary VR, and aortic arch anatomy remain challenging.