Robert Gil

Slope of the instantaneous hyperemic diastolic coronary flow velocity-pressure relation. A new index for assessment of the physiological significance of coronary stenosis in humans.

Coronary flow reserve (CFR), the functional index of stenosis severity more frequently used in the catheterization laboratory, is greatly affected by the hemodynamic conditions at the time of measurement and cannot be applied in the immediate assessment of the outcome of coronary interventions. The aim of the present study was to establish the feasibility and reproducibility of the assessment of the slope of the instantaneous diastolic relation between coronary flow velocity and aortic pressure during maximal hyperemia (IHDVPS) using a spectral analysis of the intracoronary Doppler signal, to assess the sensitivity and specificity of this index in the detection of flow-limiting coronary stenoses in comparison with CFR, and to study the possibility of deter-mining the zero-flow pressure from the intercept of the velocity-pressure relation on the pressure axis during a con-trolled cardiac arrest. Methods and ResultsThe instantaneous peak coronary flow velocity measured after intracoronary papaverine with a Doppler guidewire was plotted against the simultaneously measured aortic pressure, and the slope of the velocity-pressure relation in the phase of progressive diastolic velocity decrease was calculated during four consecutive beats. In nine normal arteries, a controlled diastolic cardiac arrest was induced by an intracoronary bolus injection of 3 mg adenosine. The IHDVPS could be assessed in 79 of 95 patients (83%), with a moderate intraobserver variability (0.4±11% after independent selection of different beats during maximal hyperemia). The IHDVPS showed no significant correlation with heart rate, mean diastolic aortic pressure, type of vessel studied, and cross-sectional area at the site of the velocity recording. The IHDVPS was significantly lower in arteries with.30% diameter stenosis than in normal or near-normal arteries (0.71±0.48 versus 1.73±0.80 cm · s−1 · mm Hg−1, P<.0000002). In the stenosis group, both IHDVPS and CFR were significantly correlated with the minimal luminal cross-sectional area (r=.46, P<.05 and r=.62, P<.002, respectively). The study of the velocity-pressure relation during long diastolic pauses showed a curvilinear relation between velocity and pressure in the lower pressure range, with an upward concavity to the velocity axis and no intercept with the pressure axis in most cases. ConclusionsThe IHDVPS can distinguish between arteries with and without coronary stenoses and has a significant inverse correlation with the severity of the stenosis. Under the stable hemodynamic conditions of this study, the IHDVPS and CFR had similar sensitivities and specificities in distinguishing normal and stenotic vessels and demonstrated similar correlation with minimal luminal cross-sectional area. The curvilinearity of the velocity-pressure relation during long diastolic pauses, possibly due to a significant reduction of luminal cross-sectional area at low pressures, complicates the use of the flow velocity-pressure relation for the assessment of the zero-flow pressure.

Quantification of the minimal luminal cross-sectional area after coronary stenting by two-and three-dimensional intravascular ultrasound versus edge detection and videodensitometry

The use of 2-dimensional intravascular ultrasound (2-D IVUS) to improve the outcome of coronary stenting has gained clinical acceptance, and recently 3-D IVUS has been introduced to clinical practice. However, there have been no comprehensive studies comparing the measurements of the coronary dimensions after stenting obtained by the different approaches of IVUS and quantitative coronary angiography. We examined the minimal luminal cross-sectional area of 38 stents using 2-D IVUS, 3-D IVUS, and 2 standard methods of quantitative coronary angiography, edge detection (ED) and videodensitometry (VD). Correlations between 2-D IVUS and ED (r = 0.72; p < 0.0001), VD (r = 0.87; p < 0.0001), and 3-D IVUS (r = 0.81; p < 0.0001) were higher than the correlations seen between 3-D IVUS and ED (r = 0.58; p < 0.0005) and VD (r = 0.70; p < 0.0001). The measurements by 2-D and 3-D IVUS (8.32 +/- 2.50 mm2 and 8.05 +/- 2.66 mm2) were larger than the values obtained by the quantitative angiographic techniques ED and VD (7.55 +/- 2.22 mm2 and 7.27 +/- 2.21 mm2). Thus, concordance was seen among all of the 4 techniques, confirming the validity of using IVUS for determination of the minimal luminal cross-sectional area after coronary stenting. A particularly good correlation was found between VD and IVUS, perhaps because measurement of the luminal area is the basic quantification approach of both techniques, whereas the lower correlations of ED with IVUS and VD may be explained by the dependence of ED on the angiographic projections used, which is especially important in eccentric stent configurations.

Impact of plaque morphology and composition on the mechanisms of lumen enlargement using intracoronary ultrasound and quantitative angiography after balloon angioplasty

Limited information is provided by angiography on plaque morphology and composition before balloon angioplasty. Identification of plaques associated with reduced lumen gain or a high complication rate may provide the rationale for using alternative revascularization devices. We studied 60 patients with quantitative angiography and intracoronary ultrasound (ICUS) before and after balloon dilation. Angiography was used to measure transient wall stretch and elastic recoil. ICUS was used to investigate the mechanisms of lumen enlargement among different plaque compositions and in the presence of a disease-free wall (minimal thickness < or = 0.6 mm). Compared with ultrasound, angiography underestimated the presence of vessel calcification (13% vs 78%), lumen eccentricity (35% vs 62%), and wall dissection (32% vs 57%). ICUS measurements showed that balloon angioplasty increased lumen area from 1.82 +/- 0.51 to 4.81 +/- 1.43 mm2. Lumen enlargement was the result of the combined effect of an increase in the total cross-sectional area of the vessel (wall stretching, 43%) and of a reduction in the area occupied by the plaque (plaque compression or redistribution, 57%). Vessels with a disease-free wall had smaller lumen gain than other types of vessels (2.13 +/- 1.26 vs 3.59 +/- mm2, respectively, p < 0.01). Wall stretching was the most important mechanism of lumen enlargement in vessels with a disease-free wall (79% vs 37% in the other vessels). Angiography revealed a direct correlation between temporary stretch and elastic recoil that was responsible for 26% of the loss of the potential lumen gain. Thus, lumen enlargement after balloon angioplasty is the combined result of wall stretch and plaque compression or redistribution. ICUS indicates that vessels with a remnant arc of disease-free wall are dilated mainly by wall stretching compared with other types of vessels and are associated with a smaller lumen gain.

Maximal blood flow velocity in severe coronary stenoses measured with a Doppler guidewire: Limitations for the application of the continuity equation in the assessment of stenosis severity

In vitro and animal experiments have shown that the severity of coronary stenoses can be assessed using the continuity equation if the maximal blood flow velocity of the stenotic jet is measured. The large diameter and the low range of velocities measurable without frequency aliasing with the conventional intracoronary Doppler catheters precluded the clinical application of this method for hemodynamically significant coronary stenoses in humans. This article reports the results obtained using a 12 MHz steerable angioplasty guidewire in a consecutive series of 52 patients undergoing percutaneous coronary angioplasty (61 coronary stenoses). The ratio between coronary flow velocity in a reference segment and in the stenosis was used to estimate the percent cross-sectional area stenosis. A Doppler recording suitable for quantitation was obtained in the stenotic segment in only 10 of 61 arteries (16%). The time-averaged peak velocity increased from 15 +/- 5 to 115 +/- 26 cm/sec from the reference normal segment to the stenosis. Volumetric coronary flow calculated from the product of mean flow velocity and cross-sectional area was similar in the stenosis and in the reference segment (33.2 +/- 14.9 vs 33.5 +/- 17.0 mL/min, respectively, difference not significant). The percent cross-sectional area stenosis and minimal luminal cross-sectional area derived from the Doppler velocity measurements using the continuity equation and calculated with quantitative angiography were also similar (Doppler, 86.7 +/- 5.1% and 1.00 +/- 0.48 mm2; quantitative angiography, 85.9 +/- 7.9% and 1.02 +/- 0.50 mm2).(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of on-line three-dimensional reconstruction of intracoronary ultrasound for guidance of stent deployment

The additional information provided by automated on-line 3-dimensional (3-D) reconstruction of intracoronary ultrasound (ICUS) was assessed in 42 patients (62 stents) who underwent stent deployment after achieving an optimal quantitative angiographic result. In 10 of 42 patients, 3-D ICUS was also performed before stenting. ICUS images of stents and adjacent reference segments were acquired by using a motorized pullback at a constant speed (1 mm/s) and immediately processed in the catheterization laboratory. Optimal stent expansion was detected by 3-D ICUS in case of complete apposition of stent struts to the vessel wall. Furthermore, an attempt was made to maximize the intrastent lumen area to match lumen area of the reference segment and to cover with stents all the segments with residual significant lesions (plaque burden >50%). Three-dimensional automated reconstruction of ICUS was successful in 8 of 10 patients (80%) before, and in 36 of 42 patients (86%) after stent deployment. In all 8 patients who underwent successful 3-D ICUS assessment before stent implantation, the selection of stent length was facilitated by accurately measuring the lesion length. After stenting, 3-D ICUS modified the management strategy in 21 of 36 patients (58%), triggering additional high-pressure dilatations in 13 patients (36%) and additional stent deployment in 8 (22%). In conclusion, on-line 3-D ICUS facilitates stent selection and strongly modifies the revascularization strategy by accurately detecting stent underexpansion and presence of uncovered lesions.

Long-term reproducibility of coronary flow velocity measurements in patients with coronary artery disease

In conclusion, flow velocity measurements repeated after a 6-month interval show a variability, which is larger for baseline velocity and coronary flow reserve. This variability is correlated with the changes in heart rate and can be reduced by a normalization for the cross-sectional area at the site of the measurement (coronary flow) and for the aortic pressure at the time of the measurement (flow resistance).

Utilization of translesional hemodynamics: comparison of pressure and flow methods in stenosis assessment in patients with coronary artery disease.

Aim of this study is the assessment of feasibility and clinical usefulness of a new index of stenosis severity, the slope of the instantaneous transstenotic pressure gradient/velocity relationship. Twenty-one patients scheduled for percutaneous revascularization procedures were studied with simultaneous measurement of poststenotic coronary pressure and flow velocity, in basal condition and during maximal hyperemia induced with intracoronary papaverine. Reliable measurements of the transstenotic pressure gradient/velocity relationship could be obtained in 11 patients. In 64% of the cases, a quadratic equation showed the best fit for the data. Steeper increases of the transstenotic pressure gradient at any given velocity increase were observed in the lesions with the smallest cross-sectional area measured with quantitative angiography. A comparison of this new index with coronary flow reserved, maximal hyperemic velocity, stenosis flow reserve derived from quantitative angiography, basal and hyperemic transstenotic pressure gradient and fractional flow reserve is presented and the relative merits of all these parameters are discussed. This pilot experience suggests that the instantaneous relationship between pressure gradient and flow velocity changes during the cardiac cycle can accurately characterize the stenosis hemodynamics in the catheterization laboratory.

Response of conductance and resistance coronary vessels to scalar concentrations of acetylcholine: Assessment with quantitative angiography and intracoronary doppler echography in 29 patients with coronary artery disease

Abnormal vasoreactivity of the large conductance arteries has been observed in the presence of impaired endothelial function. More recently, experimental and clinical reports have shown that in early coronary atherosclerosis the impairment of the endothelium-mediated vasodilatation also involves the resistance arteries. The aim of this study is the correlation of endothelium-dependent vasodilatation of conductance and resistance vessels in coronary arteries without significant stenoses. In 29 patients (aged 57 +/- 9 years, 24 men and 5 women) undergoing coronary angioplasty, a Doppler guide wire and a perfusion catheter were introduced into the proximal segment of an artery with less than 30% diameter stenosis. Selective infusions of papaverine (bolus of 7 mg), acetylcholine (continuous infusion of 0.036, 0.36, and 3.6 micrograms/ml at a flow rate of 2 ml/min), and isosorbide dinitrate (bolus of 3 mg) were sequentially performed. Heart rate, aortic blood pressure, and blood flow velocity were continuously measured. Mean cross-sectional areas of a proximal and a distal arterial segment were measured in baseline conditions, at the end of each infusion of acetylcholine, and at the peak effect of isosorbide dinitrate with quantitative angiography (CAAS System; Pie Medical Data, Maastricht, The Netherlands). Coronary blood flow was calculated from the time-averaged flow velocity and the cross-sectional area at the site of the Doppler sample volume. Coronary flow resistance was calculated as mean aortic pressure divided by coronary flow. All of the concentrations of acetylcholine induced a significant vasoconstriction of the studied artery. At the maximal concentration of acetylcholine all but three patients (90%) showed a reduction of cross-sectional area (-24% +/- 20% and -22% +/- 20% for the proximal and distal segments, respectively, p < 0.00001). Flow velocity showed a significant increase only with the two highest concentrations of acetylcholine. The maximal concentration induced a 105% +/- 138% increase from the baseline flow velocity (p < 0.001). The coronary flow changes after acetylcholine showed a large interpatient variability, with a mean increase from baseline after the highest dose of +43% +/- 85% (range, -60% +/- 239%), with the presence of a flow reduction in 10 patients (35%). No clinical or angiographic variables showed a significant correlation with the cross-sectional area, flow velocity, and flow changes after infusion of acetylcholine.(ABSTRACT TRUNCATED AT 400 WORDS)

New concepts for interpretation of intracoronary velocity and pressure tracings.

The development of quantitative angiography and the introduction of new imaging techniques cannot replace functional methods of assessing the severity of stenosis. Measurement of transstenotic pressure gradient and poststenotic flow velocity using miniaturised sensors with guidewire technology offers an alternative to the conventional non-invasive methods that is immediately applicable in the catheterisation laboratory during interventional procedures. The complexity of the coronary circulation, however, makes it difficult to establish simple cut-off criteria to identify the presence of a flow-limiting stenosis. For intermediate lesions or in the presence of variable haemodynamic conditions, the accuracy of the assessment can be improved by the application of more complex indices proposed and validated in the laboratory animals. Two of these indices are myocardial fractional flow reserve and the slope of the instantaneous relation between pressure or pressure gradient and flow velocity.

Mechanism of high-speed rotational atherectomy and adjunctive balloon angioplasty revisited by quantitative coronary angiography: Edge detection versus videodensitometry

High-speed rotational coronary atherectomy (RA) is primarily used to treat complex lesions. Quantitative angiographic analysis of such complex lesions by edge detection is often unsuitable, whereas videodensitometry, measuring vessel dimensions independently of the target stenosis contours, may offer potential advantages. To gain insight into the operative mechanism of RA and to study the agreement between the two quantitative angiographic methods in measuring the minimal luminal cross-sectional area, the edge detection and videodensitometry techniques were applied to coronary angiograms of 21 lesions in 19 patients with symptoms who underwent successful RA and balloon angioplasty (BA). Obstruction diameter as determined by edge detection increased from 1.00 +/- 0.31 mm before intervention to 1.35 +/- 0.29 mm after RA (p < 0.001) and further increased to 1.74 +/- 0.33 mm after adjunctive BA (p > 0.001). The mean between-method difference (edge detection minus videodensitometry) was 0.34 mm2 before intervention, 0.13 mm2 after RA, and 0.09 mm2 after adjunctive BA (not significant). The standard deviation of the differences decreased from +/- 0.87 mm2 before intervention to +/- 0.80 mm2 after RA (not significant) and increased after BA significantly to +/- 1.21 mm2 (p < 0.05). Thus edge detection and videodensitometry provided equivalent immediate angiographic results after RA and adjunctive BA. The good agreement after RA may reflect the operative mechanism of RA, which by ablation of noncompliant plaque material yields a circular symmetric lumen with smooth surface. The increased dispersion of the between-method differences observed after adjunctive BA presumably results from dissections, plaque ruptures, and loss of luminal smoothness after balloon dilatation.