Accuracy of coronary flow measurements performed by means of Doppler wires

doi:10.1016/S0301-5629(99)00133-7

Ultrasound in Medicine & Biology

Volume 26, Issue 2, February 2000, Pages 221-228

https://doi.org/10.1016/S0301-5629(99)00133-7 Get rights and content

Abstract

To estimate in patients the accuracy of coronary flow measurements performed by means of 0.014“ Doppler wires, the time-averaged maximal blood velocity (APV) was recorded in the 3 branches of 36 angiographically normal coronary artery bifurcations selected in 21 patients undergoing cardiac catheterization for various diseases. Contrast medium injections filmed under two incidences allowed identification of the 3 sample volume locations and computing of the 3 corresponding vessel cross-sectional areas (CSA) at subsequent data analysis. Multiplication of the velocities APV/2 (range: 3 to 20.5 cm/s) by the CSA (obtained by averaging the two calibrated vessel diameters; range: 1.6 to 5.4 mm) yielded 108 flow rates (range: 5.4 to 169 mL/min). The average relative flow error was then estimated using the continuity equation (Q_in = Q_out,1 + Q_out,2) and the central limit theorem. The result was that the relative flow error decreased from 30% at Q = 30 mL/min to 13% at Q = 160 mL/min. We conclude that coronary flow measurements are reasonably accurate, except perhaps for very low flows.

Introduction

Easy and selective measurements of coronary volume flow in patients has long been a dream. Methods based on thermodilution or angiography were available, but all had at least the drawback of being complicated. The development of Doppler catheters in the mid1980s represented, therefore, a major step. In 1992, Cardiometrics (Mountain View, California, USA) introduced the “FloWire®”, a disposable Doppler guide wire. This device, described in detail by Doucette et al. (1992), is now available with diameter 0.018″ or 0.014″ (0.46 mm or 0.36 mm). The piezoelectrical crystal situated at the tip of the 0.014″ wire emits ultrasonic bursts of frequency 15 MHz and duration 1.1 μs, at a repetition frequency of 15 to 117 kHz, depending on the selected blood velocity scale. The beam divergence is roughly 15^o (half angle); the range gate location is 4.2 mm and the sample volume width approximately 2 mm. The FloWire® is connected to an apparatus (FloMap®) that calculates every 10 ms the spectrum of the blood velocities by fast Fourier transform and the peak velocity (PV), which is the maximal blood velocity found in the spectrum (Fig. 1). The FloMap® also displays the average peak velocity (APV), which is the average value of the PV over the last two cardiac cycles. Evidently, the PV and the APV reflect the two corresponding true velocities only if these are permanently included in the sample volume.

The 0.018″ FloWire® has been validated in vitro and in dogs by Doucette et al. (1992). However, these authors still had to trace the envelope of the recorded velocity spectra manually. Furthermore, they pointed out that they “...did not accurately reproduce the conditions likely to be encountered clinically.” Velocity or flow rate measurements performed in patients during cardiac catheterization may, indeed, be not quite comparable to validation measurements in animals. For example, validation measurements are often limited to a single arterial branch, due to the necessity of measuring the flow simultaneously with a recognised “gold standard” (e.g., an electromagnetic flowmeter or the “beaker/stop-watch” method). Moreover, it is sometimes impossible in patients to position the transducer optimally. In general, the operator cannot be certain that the sample volume really includes the maximal velocity, especially in larger coronary arteries. These points may partly explain why there are already many Doppler wire publications dealing with flow velocities, but only a few involving volume flows (flow rates). For these and other reasons (see, for example, the Limitations section in Doucette et al. 1992), and because the Doppler wire is presently the most promising device available for selective and subselective flow measurements in coronary arteries, we wanted to investigate the accuracy of these measurements in patients. A direct approach with a “gold standard” being, of course, impossible, we have used an indirect method based on the fact that, at vessel bifurcations, the entry flow is equal to the sum of the two exit flows.

Section snippets

Data acquisition in patients

In 21 patients undergoing cardiac catheterization for various diseases, velocity measurements were performed in 1 or 2 (or exceptionally 3) coronary arterial bifurcations in the following manner. After the usual acquisition of the left and/or right diagnostic coronary angiograms, two more or less orthogonal projections that showed a vessel bifurcation composed of three angiographically normal segments without superposition with other opacified vessels (Fig. 2) were selected and reset on our

Results

Table 1 shows the ranges and mean values of the APV, CSA and flow rates Q. The heart rates ranged from 48 to 101 beats/min, and the aortic root pressures from 72 to 125 mmHg. The three mean heart rates associated with the first, the second, and the third velocity measurements at the 36 bifurcations were 73.5 ± 14.4 beats/min, 73.4 ± 15.0 beats/min, and 74.3 ± 14.7 beats/min. The three sets of heart rates were not significantly different (p = 0.96). The three mean aortic pressures were 97.5 ±

Discussion

Easy, selective and reliable measurements of coronary flow rates in patients may become important for basic or clinical studies, and for decisional purposes. For example, they would be the most direct way of assessing regional flow reserve, regional myocardial perfusion or steal phenomena. The present study was undertaken because the accuracy of coronary flow measurements in patients seemed to be controversial (although it had, to our knowledge, never been assessed). A direct accuracy

Conclusion

Coronary flow measurements performed in the cardiac catheterization laboratory by means of 0.014″ Doppler wires and biplane angiography appear to be reasonably accurate (except perhaps for very low flow rates).

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Cited by (14)

Characterizing momentum change and viscous loss of a hemodynamic endpoint in assessment of coronary lesions
2007, Journal of Biomechanics
Myocardial fractional flow reserve (FFR_myo) and coronary flow reserve (CFR), measured with guidewire, and quantitative angiography (QA) are widely used in combination to distinguish ischemic from non-ischemic coronary stenoses. Recent studies have shown that simultaneous measurements of FFR_myo and CFR are recommended to dissociate conduit epicardial coronary stenoses from distal resistance microvascular disease. In this study, a more comprehensive diagnostic parameter, named as lesion flow coefficient, $\tilde{c}$ , is proposed. The coefficient, $\tilde{c}$ , which accounts for mean pressure drop, $Δ \tilde{p}$ , mean coronary flow, $\tilde{Q}$ , and percentage area stenosis, can be used to assess the hemodynamic severity of a coronary artery stenoses. Importantly, the contribution of viscous loss and loss due to momentum change for several lesion sizes can be distinguished using $\tilde{c}$ .
FFR_myo, CFR and $\tilde{c}$ were calculated for pre-angioplasty, intermediate and post-angioplasty epicardial lesions, without microvascular disease. While hyperemic $\tilde{c}$ decreased from 0.65 for pre-angioplasty to 0.48 for post-angioplasty lesion with guidewire of size 0.35 mm, FFR_myo increased from 0.52 to 0.87, and CFR increased from 1.72 to 3.45, respectively. Thus, reduced loss produced by momentum change due to lower percentage area stenosis decreased $\tilde{c}$ . For post-angioplasty lesion, $\tilde{c}$ decreased from 0.55 to 0.48 with the insertion of guidewire. Hence, increased viscous loss due to the presence of guidewire decreased $\tilde{c}$ compared with a lesion without guidewire. Further, $\tilde{c}$ showed a linear relationship with FFR_myo, CFR and percentage area stenosis for pre-angioplasty, intermediate and post-angioplasty lesion. These baseline values of $\tilde{c}$ were developed from fluid dynamics fundamentals for focal lesions, and provided a single hemodynamic endpoint to evaluate coronary stenosis severity.
Quantitative IVUS blood flow: Validation in vitro, in animals and in patients
2003, Ultrasound in Medicine and Biology
In recent years, a new method to measure transverse blood flow based on the decorrelation of the radiofrequency (RF) signals of intravascular ultrasound (IVUS) rotating single-element scanners was introduced. We report here in vitro, animal and patient testing to evaluate the correlation-based method using an IVUS array catheter. A new correlation-based method to dynamically correct the correlation coefficients for noise is implemented. The decorrelation due to noise was estimated from the correlation coefficients from flowing blood obtained at increasing time lags. First, blood flow experiments were carried out with different catheters in a tissue-mimicking flow phantom with an inner diameter ranging from 3.0 to 5.0 mm. A calibrated electromagnetic flow meter (EMF, range: 0 to 250 cc/min) was used as a reference. Good linear relationships were found between the IVUS-derived flow and the calibrated EMF (all R²> 0.96). The catheter position within the flow phantom and the size of the ring-down were theoretically analyzed. These elements, and noise in the RF signals, have an important influence on the IVUS blood flow measurements reflected by the offset and the slope of the linear relationships. By placing the IVUS catheter outside the flow phantom, parabolic blood flow profiles were also measured. Second, IVUS blood flow measurements were performed in the carotid artery of two Yorkshire pigs, which showed linear relationships (all R²> 0.85) between the IVUS-derived flow and the calibrated EMF. Experimentally, the offset was lower than 3 mL/min and the slope was close to 1. Third, IVUS blood flow measurements were performed in coronary arteries in patients. Preliminary results for the coronary flow reserve (CFR = high flow/baseline flow) in patients using the decorrelation method of RF signals of an array IVUS scanner were comparable with CFR based on Doppler measurements. (E-mail: [email protected])
Shear stress and vascular remodeling: Study of cardiac allograft coronary artery disease as a model of diffuse atherosclerosis
2002, Journal of Heart and Lung Transplantation
The assessment of remodeling in diffuse atherosclerosis by intravascular ultrasound is hampered by the lack of an appropriate reference segment. Transplant coronary artery disease is an accepted model of diffuse atherosclerosis. Flow-dependent remodeling is regulated by shear stress. Thus, normal levels of shear stress at baseline flow reflect adequate regulation and provide a functional assessment of flow-dependent remodeling.
The approach was evaluated in 91 patients with transplant coronary artery disease and in 9 non-transplanted controls and 16 control transplant recipients. Quantitative coronary angiography, intracoronary ultrasound and intracoronary velocity studies were performed at baseline and after pharmacologic intervention. Calculated shear stress was compared between these groups and a sub-group with coronary angioplasty at follow-up (8 of 60 patients with control angiography after 23 ± 8 months). The relation of shear stress to flow, diameter, flow/area ratio and endothelial function was analyzed.
Normal shear stress was found in non-transplanted controls and transplant recipients without coronary artery disease. Patients with coronary angioplasty at follow-up had elevated shear stress and enhanced endothelial dysfunction on the initial investigation. Shear stress was not correlated with flow (r = 0.062, non-significant), but with diameter (r = −0.654), flow/area ratio (r = 0.814) and endothelial dysfunction (r = 0.722).
Calculated local shear stress appears to be useful for the assessment of the adequacy of flow-dependent macrovascular remodeling in diffuse atherosclerosis. Elevated blood flow/area ratio is a potential clinical marker of increased shear stress that reflects inadequate flow-dependent remodeling.
High shear stress after successful balloon angioplasty is associated with restenosis and target lesion revascularization
2002, American Heart Journal
Citation Excerpt :
WSS was computed proximal and distal to the lesion and in the lesion, before and after treatment, and at a 6-month repeat angiogram by use of the Hagen-Poiseuille formula14: WSS = 4μQ/πR3, with μ being blood viscosity, taken to be constant at 0.003 Ns/m2, Q being the volumetric blood flow in mL/s, and R being the radius of the coronary lumen at the site of the flow measurement. Volumetric flow was calculated from blood velocity (assuming parabolic flow) measured by means of intravascular Doppler scanning with the validated formula14,15: Q = CSA × APV/2, in which CSA is the cross-sectional area and APV is the baseline (before adenosine administration) average peak velocity. Minimal and reference vessel CSA were measured by means of videodensitometry with a computer-assisted quantitative coronary angiography analysis system (CAAS II system, Pie Medical Data, Maastricht, The Netherlands).
Background Vascular wall shear stress (WSS) has been implied in the pathogenesis of atherosclerosis and vascular remodeling. Our aim was to calculate WSS after balloon angioplasty and evaluate its predictive value for long-term outcome. Methods WSS was calculated proximal to, in, and distal to the lesion after angiographically successful balloon dilatation and at follow-up with the Hagen-Poiseuille formula (WSS = 4μQ/πR³) in 202 patients. Volumetric blood flow (Q) and lumen radius (R) were derived from Doppler scanning velocities and videodensitometric cross-sectional areas. Results Postprocedural proximal and in-lesion values were higher in vessels that developed restenosis (n = 72; 1.22 ± 0.61 N/m² and 3.61 ± 2.38 N/m², respectively) than in those without restenosis (n = 130, 1.05 ± 0.51 N/m² and 2.46 ± 1.39 N/m², respectively; P <.05). In-lesion WSS was revealed to be predictive of restenosis by means of logistic regression analysis (odds ratio [OR] = 1.42, P <.05), whereas WSS of the proximal segment was associated with an increased rate of target lesion revascularization (OR = 2.33, P <.005). In the multivariate regression model, WSS of the proximal segment was the only independent predictor when entered with known predictors such as diameter stenosis and coronary flow reserve (OR = 2.15, P <.05). Conclusions WSS in the lesion after balloon angioplasty is predictive of angiographic restenosis. Moreover, the proximal value is an independent predictor of target lesion revascularization. This study opens perspectives for the on-line use of WSS as a combined parameter of anatomy and physiology to assess the necessity of adjunctive therapy after successful balloon dilatation. (Am Heart J 2002;144:136-43.)
Effects of exercise training on vascular function and myocardial perfusion
2001, Cardiology Clinics
Citation Excerpt :
The accuracy and reproducibility of flow velocity measurements in patients has been recently assessed. When used with QCA, the relative flow error decreased from 30% at a flow of 30 mL/min to 13% at a flow of 160 mL/min.18 This implies that the accuracy of Doppler flow measurements increases with higher flow velocities.
The heart as an exclusively aerobic organ relies on a continuous supply of oxygen and nutrients by way of coronary circulation and on rapid adaptation of myocardial perfusion to metabolic demand. In the healthy individual, cardiac output can increase more than threefold during strenuous exercise. This increase in cardiac work is paralleled by an enhancement of myocardial perfusion from 0.8 mL/g⋅min at rest to 3.2 mL/g⋅min at peak exercise along with augmented oxygen extraction. Recent positron emission tomography studies have shown that the lowering of systolic blood pressure and heart rate associated with long-term exercise training improves myocardial flow reserve (the ratio of hyperemic and resting blood flow) by lowering resting coronary blood flow and increasing coronary vasodilatory capacity.¹⁵
It is precisely this ability of the coronary blood flow to increase in proportion to myocardial demand during physical exercise that is impaired in coronary artery disease (CAD). The mismatch between regional demand and perfusion causes ischemia and angina pectoris. Interventional cardiology has long accused stenoses of epicardial coronary conduit vessels as the prime etiologic factor for myocardial ischemia, which led to the approach of treating coronary artery disease by percutaneous transluminal coronary angioplasty (PTCA) and coronary stenting. When it comes to improvement of exercise capacity, freedom from angina, and improvement of myocardial perfusion,20, 71 however, exercise training therapy may be equally efficacious.⁸⁰ To understand the mechanisms involved in mediating these effects, one should look beyond the morphologic concepts of interventional cardiology.
Basically, regional myocardial hypoperfusion in anginal syndromes results from a combination of three basic pathogenetic components: (1) vascular stenosis, (2) microvascular dysfunction, and (3) hemostasis.⁴⁸ All three components may be affected by exercise training in stable CAD (Fig. 1).
- 1
  Vascular stenoses could be either reduced by regression of coronary atherosclerosis or bypassed by formation of new collaterals. The dynamic part of epicardial stenoses may be attenuated by improvement of endothelial function in coronary conduit vessels.
- 2
  Exercise training could improve exercise-induced flow through coronary resistance vessels and the microcirculation.
- 3
  Microrheology and platelet function may be positively influenced.
A dual-mode catheter for cardiac output monitoring
2020, IEEE International Ultrasonics Symposium, IUS

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Original ContributionsAccuracy of coronary flow measurements performed by means of Doppler wires

Abstract

Introduction

Section snippets

Data acquisition in patients

Results

Discussion

Conclusion

Am Heart J

Ultrasound Med Biol

Am Heart J

Validation of a Doppler guide wire for intravascular measurement of coronary artery flow velocity

Circulation

Position control of intravascular Doppler guidewireConcept of a tracking indicator and its clinical implications

Cathet Cardiovasc Diagn

Original Contributions
Accuracy of coronary flow measurements performed by means of Doppler wires