Curriculum in interventional cardiology: coronary pressure and flow measurements in the cardiac catheterization laboratory

Cardiac magnetic resonance myocardial perfusion reserve index is reduced in women with coronary microvascular dysfunction. A National Heart, Lung, and Blood Institute-sponsored study from the Women's Ischemia Syndrome Evaluation

BACKGROUND

Women with signs and symptoms of ischemia and no obstructive coronary artery disease often have coronary microvascular dysfunction (CMD), diagnosed by invasive coronary reactivity testing (CRT). Although traditional noninvasive stress imaging is often normal in CMD, cardiac MRI may be able to detect CMD in this population.

METHODS AND RESULTS

Vasodilator stress cardiac MRI was performed in 118 women with suspected CMD who had undergone CRT and 21 asymptomatic reference subjects. Semi-quantitative evaluation of the first-pass perfusion images was completed to determine myocardial perfusion reserve index (MPRI). The relationship between CRT findings and MPRI was examined by Pearson correlations, logistic regression, and sensitivity/specificity. Symptomatic women had lower mean pharmacological stress MPRI compared with reference subjects (1.71±0.43 versus 2.23±0.37; P<0.0001). Lower MPRI was predictive of ≥1 abnormal CRT variables (odds ratio =0.78 [0.70, 0.88], P<0.0001, c-statistic 0.78 [0.68, 0.88]). An MPRI threshold of 1.84 predicted CRT abnormality with sensitivity 73% and specificity 74%.

CONCLUSIONS

Noninvasive cardiac MRI MPRI can detect CMD defined by invasive CRT. Further work is aimed to optimize the noninvasive identification and management of CMD patients.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00832702.

Intracoronary pressure and flow velocity for hemodynamic evaluation of coronary stenoses

Adequate patient selection for percutaneous coronary intervention is of utmost importance to minimize early and late complications. Consequently, objective evidence for myocardial ischemia is mandatory for the management of patients with coronary artery disease, in particular in multivessel disease and intermediate lesions (40-70% diameter stenosis on angiography). The use of sensor-equipped guide wires for the assessment of functional coronary lesion severity has become widespread in the catheterization laboratory. The indices derived from pressure or flow measurements, fractional flow reserve, coronary flow velocity reserve and relative coronary flow velocity reserve show a high agreement with noninvasive stress testing. However, while these indices are based on either intracoronary pressure or flow, they do not investigate the hemodynamics of the coronary circulation entirely, leading to ambiguous outcomes. Only the use of simultaneously measured pressure and flow will avoid any possible misinterpretation of the data.

Carotid artery stenosis near a bifurcation investigated by fluid dynamic analyses

Haemodynamic physical parameters play a role in determining endothelial cell phenotype and influence vascular remodelling. Accurate measurement of total pressure, velocity magnitude, and wall shear stress is vital for studies on the pathogenesis of atherosclerosis. This paper investigated a lesion-based computational fluid dynamic (CFD-Fluent) pilot analysis to understand the complex haemodynamic changes prevailing in patients with high-grade carotid artery stenosis (CS) 90%. All subjects were examined with colour-flow Doppler, power Doppler, and digital subtraction angiography to enable visualization of carotid stenosis and plaque surface morphology, and used to generate computational meshes. Two models were devised: the first without any stenosis and the second with an 82% grade of stenosis localized in the external carotid artery. The distribution of the principal parameters can be obtained by computational fluid dynamics (CFD-Fluent) using patient-specific geometries and flow analytical measurements. The total pressure distribution ranged between 16,000 and 8,000 Pa in the case of normal carotid artery and 16,000 and 5,500 Pa in the case of the stenosed artery. The velocity registered a peak in the stenosis region of 5 m/s. The mean wall shear stress within the stenosis region was 360 Pa. In conclusion, patient-based CFD-Fluent analysis of CS predicts a complex haemodynamic environment with large spatial haemodynamic parameter variations that occur very rapidly over short distances. Our results improve estimates of the flow changes and forces at the vessel wall in CS and the link between haemodynamic changes and stenosis pathophysiology.

Effect of Pulsatile Flow Waveform and Womersley Number on the Flow in Stenosed Arterial Geometry

The salient hemodynamic flow features in a stenosed artery depend not only on the degree of stenosis, but also on its location in the circulatory system and the physiological condition of the body. The nature of pulsatile flow waveform and local Womersley number vary in different regions of the arterial system and at different physiological state, which affects the local hemodynamic wall parameters, for example, the wall shear stress (WSS) and oscillatory shear index (OSI). Herein, we have numerically investigated the effects of different waveforms and Womersley numbers on the flow pattern and hemodynamic parameters in an axisymmetric stenosed arterial geometry with 50% diametral occlusion. Temporal evolution of the streamlines and hemodynamic parameters are investigated, and the time-averaged hemodynamic wall parameters are compared. Presence of the stenosis is found to increase the OSI of the flow even at the far-downstream side of the artery. At larger Womersley numbers, the instantaneous flow field in the stenosed region is found to have a stronger influence on the flow profiles of the previous time levels. The study delineates how an approximation in the assumption of inlet pulsatility profile may lead to significantly different prediction of hemodynamic wall parameters.

Particle depositions and related hemodynamic parameters in the multiple stenosed right coronary artery

BACKGROUND

Blood flow analysis of the human right coronary artery (RCA) has been carried out to investigate the effects of serial stenosis on coronary hemodynamics. A 3-D model of a serial stenosed RCA was reconstructed based on multislice computerized tomography images.

METHODS

A velocity waveform in the proximal RCA and a pressure waveform in the distal RCA of a patient with a severe stenosis were acquired with a catheter delivered wire probe and applied as boundary conditions. The numerical analysis examines closely the effect of a multiple serial stenosis on the hemodynamic characteristics such as flow separation, wall shear stress (WSS) and particle depositions.

RESULTS AND CONCLUSIONS

Energy loss associated with such flow expansion after each constriction will be large and consequently the pressure drop will be higher. Overall pressure drop increased from 1700 Pa (12.75 mmHg) at the end diastole to 11000 Pa (82.5 mmHg) at the peak systole. At the peak systole the WSS values reached 110 Pa in the stenosis with 28% diameter reduction and 210 Pa in the stenosis with 54% diameter reduction, which is high enough to damage the endothelial cells. However at the end of one cardiac cycle a percent of 1.4% (15 from 1063 particles release at the inlet section) remain inside the stenosed RCA.

Lack of correlation between noninvasive stress tests and invasive coronary vasomotor dysfunction in patients with nonobstructive coronary artery disease

BACKGROUND

Despite a nonobstructive coronary angiogram, many patients may still have an abnormal coronary vasomotor response to provocation and to myocardial demand during stress. The ability of noninvasive stress tests to predict coronary vasomotor dysfunction in patients with nonobstructive coronary artery disease is unknown.

METHODS AND RESULTS

All patients with nonobstructive coronary artery disease who had invasive coronary vasomotor assessment and a noninvasive stress test (exercise ECG, stress echocardiography, or stress nuclear imaging) within 6 months of the cardiac catheterization with provocation at our institution were identified (n=376). Coronary vasomotor dysfunction was defined as a percentage increase in coronary blood flow of <or=50% to intracoronary acetylcholine (endothelium-dependent dysfunction) and/or a coronary flow reserve ratio of <or=2.5 to intracoronary adenosine (endothelium-independent dysfunction). We determined the sensitivity and specificity of various noninvasive stress tests to predict coronary vasomotor dysfunction in these patients. On invasive testing, 233 patients (63%) had coronary vasomotor dysfunction, of which 187 patients (51%) had endothelium-dependent dysfunction, 109 patients (29%) had endothelium-independent dysfunction, and 63 patients (17%) had both. On noninvasive stress testing, 157 (42%) had a positive imaging study and 56 (15%) a positive ECG stress test. The noninvasive stress tests had limited diagnostic accuracy for predicting coronary vasomotor dysfunction (41% sensitivity [95% CI, 34 to 47] and 57% specificity [95% CI, 49 to 66]), endothelium-dependent dysfunction (41% sensitivity [95% CI, 34 to 49] and 58% specificity [95% CI, 50 to 65]), or endothelium-independent dysfunction (46% sensitivity [95% CI, 37 to 56] and 61% specificity [95% CI, 54 to 67]). The exercise ECG test was more specific but less sensitive than the imaging tests.

CONCLUSIONS

This study suggests that a negative noninvasive stress test does not rule out coronary vasomotor dysfunction in symptomatic patients with nonobstructive coronary artery disease. This underscores the need for invasive assessment or novel more sensitive noninvasive imaging for these patients.

The prognostic value of combined intracoronary pressure and blood flow velocity measurements after deferral of percutaneous coronary intervention

OBJECTIVES

We evaluated deferral of PCI of intermediate coronary lesions (IL) using fractional (FFR) and coronary flow reserve (CFR) hyperemic stenosis resistance index (HSR) in patients with a negative or nondiagnostic and noninvasive stress tests.

BACKGROUND

Outcome after deferral of PCI of IL with discordant results between FFR and CFR is unknown.

METHODS

PCI was deferred in 186 IL (mean diameter stenosis: 52%). Patients were divided according to the results of FFR and CFR in group A; FFR >or= 0.75 and CFR >or= 2.0 (n = 129), group B; FFR >or= 0.75 and CFR 2.0 (n = 28), group C; FFR 0.75 and CFR >or= 2.0 (n = 23) and group D; FFR 0.75 and CFR 2.0 (n = 6). Patients were followed for one year to document major adverse cardiac events (MACE).

RESULTS

Nineteen MACEs (0 deaths, 4 myocardial infarctions, 1 CABG, and 14 PCIs) occurred during a follow up of 323 +/- 88 days. MACE rate was lowest (4.7%) when FFR, CFR, and HSR were normal. A higher MACE rate was observed when concordant abnormal (group D) or discordant results between FFR and CFR (group B and C) were compared to concordant normal values (group A, 33.3% vs. 19.7% vs. 5.4%, P = 0.008). Multivariate regression analysis showed a higher predictive power for HSR than for FFR and CFR.

CONCLUSIONS

Abnormal FFR or abnormal CFR was documented in 31% of intermediate coronary lesions. Deferral of PCI in this group was associated with a high MACE rate, which underscores the rationale of combined pressure and flow measurements providing a stenosis resistance index that is better suited for clinical decision making in these lesions.

Relation of depression to coronary endothelial function

The purpose of this study was to determine the association between depression and coronary endothelial function and cardiac risk factors in men and women without obstructive coronary artery disease. Patients with no significant coronary artery disease who underwent invasive coronary endothelial function assessment with acetylcholine were studied. Men and women were divided into 2 groups: those with depression and those without. Endothelial function and risk factor profiles were compared between the 2 groups. Seven hundred fifty-nine patients were studied, 603 (79%) without depression and 156 (21%) with depression. Patients with depression were more likely to be women (71% vs 60%, p = 0.02), have greater body mass indexes (29.9 +/- 6.7 vs 28.2 +/- 5.9 kg/m(2), p = 0.002), and be diabetic (12% vs 6%, p = 0.02). Depressed patients also had higher levels of C-reactive protein (0.35 vs 0.30 mg/dl, p = 0.02). There was no difference in the change in coronary blood flow or diameter in response to acetylcholine between the 2 groups in men and women. In conclusion, the results of this study demonstrate that depression is not associated with coronary endothelial dysfunction in men and women without significant coronary artery disease. It is, however, associated with a cluster of cardiac risk factors that are linked to the progression of atherosclerotic disease.

Lipoprotein-associated phospholipase A2 is an independent marker for coronary endothelial dysfunction in humans

OBJECTIVE

The purpose of the current study was to determine whether lipoprotein-associated phospholipase A2 (Lp-PLA2) is associated with coronary endothelial dysfunction and is a predictor of endothelial dysfunction in humans.

METHODS AND RESULTS

Patients (172) with no significant coronary artery disease (<30% stenosis) undergoing assessment of coronary endothelial function were studied. Endothelial function was assessed by the change in coronary blood flow and coronary artery diameter in response to intracoronary acetylcholine. Plasma concentrations of Lp-PLA2 were measured, and patients were divided into tertiles. Patients in tertiles 2 and 3 had a significantly lower change in coronary blood flow (63.8+/-73.2 and 32.0+/-71.7 versus 78.4+/-73.2%; P<0.001) and greater epicardial coronary artery vasoconstriction (-14.1+/-14.7 and -23.3+/-25.1 versus -9.5+/-15.2% mean diameter change; P<0.001) in response to acetylcholine. Patients with coronary endothelial dysfunction had significantly higher serum concentrations of Lp-PLA2 than those with normal endothelial function (246.2+/-71.6 versus 209+/-56.7 ng/mL; P=0.001). The odds ratio for coronary endothelial dysfunction in patients with Lp-PLA2 in the highest tertile was 3.3 (95% CI, 1.6 to 6.6).

CONCLUSIONS

Lp-PLA2 is independently associated with coronary artery endothelial dysfunction and is a strong predictor of endothelial dysfunction in humans.

Computational Hemodynamics of an Implanted Coronary Stent Based on Three-Dimensional Cine Angiography Reconstruction

Coronary stents are supportive wire meshes that keep narrow coronary arteries patent, reducing the risk of restenosis. Despite the common use of coronary stents, approximately 20-35% of them fail due to restenosis. Flow phenomena adjacent to the stent may contribute to restenosis. Three-dimensional computational fluid dynamics (CFD) and reconstruction based on biplane cine angiography were used to assess coronary geometry and volumetric blood flows. A patient-specific left anterior descending (LAD) artery was reconstructed from single-plane x-ray imaging. With corresponding electrocardiographic signals, images from the same time phase were selected from the angiograms for dynamic three-dimensional reconstruction. The resultant three-dimensional LAD artery at end-diastole was adopted for detailed analysis. Both the geometries and flow fields, based on a computational model from CAE software (ANSYS and CATIA) and full three-dimensional Navier-Stroke equations in the CFD-ACE+ software, respectively, changed dramatically after stent placement. Flow fields showed a complex three-dimensional spiral motion due to arterial tortuosity. The corresponding wall shear stresses, pressure gradient, and flow field all varied significantly after stent placement. Combined angiography and CFD techniques allow more detailed investigation of flow patterns in various segments. The implanted stent(s) may be quantitatively studied from the proposed hemodynamic modeling approach.

Evaluation of in-stent stenosis by magnetic resonance phase-velocity mapping in nickel-titanium stents

PURPOSE

To evaluate different grades of in-stent stenosis in a nickel-titanium stent with MRI.

MATERIALS AND METHODS

Magnetic resonance phase velocity mapping (MR-PVM) was used to measure flow velocity through a 9-mm NiTi stent with three different degrees of stenosis in a phantom study. The tested stenotic geometries were 1) axisymmetric 75%, 2) axisymmetric 90%, and 3) asymmetric 50%. The MR-PVM data were subsequently compared with the velocities from computational fluid dynamic (CFD) simulations of identical conditions.

RESULTS

Good quantitative agreement in velocity distribution for the 50% and 75% stenoses was observed. The agreement was poor for the 90% stenosis, most likely due to turbulence and the high-velocity gradients found in the small luminal area relative to the pixel resolution in our imaging settings.

CONCLUSION

The accuracy of the MRI velocities inside the stented area renders MRI a modality that may be used to assess moderate to severe in-stent restenosis (ISR) in medium-sized vascular stents in peripheral vessels, such as the iliac, carotid, and femoral arteries. Advances in MR instrumentation may provide sufficient resolution to obtain adequate velocity information from smaller vessels, such as the coronary arteries, and allow MRI to substitute for invasive and expensive catheterization procedures currently in clinical use.

Magnetic resonance phase velocity mapping through NiTi stents in a flow phantom model

PURPOSE

To assess constant and pulsatile flow velocity within the lumen of a peripheral NiTi stent using phase velocity mapping for comparison with independent assessments of flow velocity in a phantom model.

MATERIALS AND METHODS

A 9 x 20-mm stent installed in flexible tubing was placed in a phantom filled with stationary fluid. Constant and pulsatile flow (produced by a pump programmed to produce a simulation of the carotid artery flow) was assessed using phase velocity mapping at 4.1 T (for constant flow) and at 1.5 T (for pulsatile flow). In all cases 256 x 256 gradient echo phase velocity maps were acquired. For the pulsatile flow condition, cine images with acquisition gated to the pump cycle were acquired with 40 msec temporal resolution across the simulated cardiac cycle. Computed flow volume rates were compared with fluid volume collection for the constant flow model, and with ultrasonic Doppler flow meter measurements for the pulsatile model.

RESULTS

The data showed that volume flow rate assessments by phase velocity mapping agreed with independent measurements within 10% to 15%.

CONCLUSION

Phase velocity mapping of the lumen of peripheral size NiTi stents is possible in an in vitro model.

Coronary flow: clinical considerations

In the measurement of coronary blood flow to determine the success of percutaneous coronary intervention, invasive techniques, coupled with plaque characterisation and other intracoronary imaging modalities, may prove invaluable.

The diastolic flow-pressure gradient relation in coronary stenoses in humans

OBJECTIVES

We assessed the feasibility and reproducibility of the instantaneous diastolic coronary flow velocity-pressure gradient relation to characterize different degrees of coronary stenoses.

BACKGROUND

Assessment of the hemodynamic significance of coronary stenoses can be difficult. Using sensor-tipped guidewires, various physiologic indexes can be determined in the catheterization laboratory. Each of the current methods, however, has limitations.

METHODS

After positioning a Doppler flow wire and a pressure wire distal of a coronary stenosis, the flow velocity signals and the proximal and distal pressure were sampled simultaneously, at baseline and after intracoronary administration of adenosine. The instantaneous diastolic flow velocity and pressure gradient of single cardiac cycles at baseline, at maximal and intermediate hyperemia were plotted. Data were fitted with a regression line using the equation: Delta P = 0 +kv+Sv(2). Measurements were performed in 11 normal coronary arteries, 20 intermediate stenoses and in 7 severe stenoses before and after percutaneous transluminal coronary angioplasty plus stenting.

RESULTS

We found significant differences between normal coronary arteries, intermediate and severe stenoses. Percutaneous transluminal coronary angioplasty nearly normalized the highly abnormal flow-pressure gradient relation in the severe stenoses. A high degree of reproducibility was observed. In 3% of the measurements, analysis was not possible due to the occurrence of pressure drift or bad flow velocity signals.

CONCLUSIONS

It is feasible to assess the diastolic flow velocity-pressure gradient relation over a wide range of stenoses. It characterizes the hemodynamics of epicardial coronary stenoses and allows discrimination between normal coronary arteries, intermediate and severe stenoses.