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Am J Physiol Heart Circ Physiol 292: H2349-H2355, 2007. First published January 12, 2007; doi:10.1152/ajpheart.01042.2006
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Effect of simultaneous intracoronary guidewires on the predictive accuracy of functional parameters of coronary lesion severity

Hein J. Verberne,1 Martijn Meuwissen,2 Steven A. J. Chamuleau,2 Bart-Jan Verhoeff,2 Berthe L. F. van Eck-Smit,1 Jos A. E. Spaan,3 Jan J. Piek,2 and Maria Siebes2,3

Departments of 1Nuclear Medicine, 2Cardiology, and 3Medical Physics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands

Submitted 22 September 2006 ; accepted in final form 9 January 2007


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
The aim of this study was to assess the influence of a second guidewire on the diagnostic accuracy of functional parameters of coronary lesion severity. Sixty-five patients with intermediate coronary lesions underwent myocardial perfusion scintigraphy. Fractional flow reserve (FFR), coronary flow velocity reserve (CFVR), and hyperemic stenosis resistance (HSR) index (HSR = stenosis pressure gradient ÷ velocity) were determined in 77 lesions. Distal pressure and velocity were acquired simultaneously (dual wire) and sequentially (single wire) with two sensor-equipped guidewires. Overall, functional parameters deteriorated from single- to dual-wire assessment. In patients without ischemia, the good diagnostic performance of FFR, CFVR, and HSR deteriorated significantly (P < 0.001) when assessed by dual wires, with an increase in the number of false-positive results. This trend was more pronounced for HSR, since the presence of a second wire reduced maximal velocity and increased the pressure gradient. The presence of two guidewires, especially across a myocardial perfusion scintigraphy-induced nonsignificant lesion, is associated with overestimation of the hemodynamically assessed lesion severity and, therefore, is likely to have a major impact on clinical decision making. This underscores the advantage of a dual-sensor-equipped guidewire for the evaluation of stenosis severity by combined pressure and velocity measurements.

hemodynamics; microcirculation; pressure; coronary disease; stenosis

PRESSURE-DERIVED MYOCARDIAL fractional flow reserve (FFR) and coronary flow velocity reserve (CFVR) have been evaluated as powerful predictors of inducible ischemia, as measured by noninvasive stress tests and adverse events after stent placement (21, 32). However, these parameters not only depend on stenosis resistance, but they are also affected by the prevailing microvascular resistance at full dilation, which may vary as result of heart rate, metabolic demand, or microvascular disease (15, 24, 26). These confounding factors affect FFR and CFVR in opposite directions (18, 20).

For assessment of epicardial and small-vessel disease, simultaneous measurement of hyperemic intracoronary pressure and blood flow velocity is mandatory (22). We previously showed that the diagnostic accuracy of the hyperemic stenosis resistance (HSR) index, assessed by combining stenosis pressure gradient and flow velocity, was significantly better than that of FFR or CFVR, especially in cases with discordant outcomes between these more traditional parameters (18, 19).

High-fidelity measurements of pressure and flow velocity distal to a coronary artery stenosis have necessitated the use of two single-sensor-equipped wires, which has hampered the investigation of stenosis hemodynamics in terms of the stenosis pressure gradient-velocity ({Delta}P-v) relation or combined FFR and CFVR assessment in patients (8, 9, 17). The recent availability of a dual-sensor-equipped 0.014-in. guidewire has made simultaneous measurement of phasic distal pressure and velocity feasible. HSR obtained with this dual-sensor guidewire was shown to be a sensitive measure of the functional gain achieved by percutaneous coronary intervention (PCI), and stenosis {Delta}P-v relations comprehensively visualized improvement in coronary hemodynamics after PCI (27).

On the basis of bench-top experiments or fluid dynamic models, it is generally assumed that the presence of a guidewire across a stenosis has a relevant hemodynamic effect only in the case of severe lesions that are already clinically significant and where the guidewire-to-minimal lesion diameter ratio approaches 0.5 (4, 7). However, this has not been tested in patients, where fixed threshold values are used for clinical decision making and where vessel curvature complicates the effect of wire presence beyond simple subtraction of wire area from lumen area and invalidates assumptions regarding the concentric location of the wire within the vessel lumen.

The purpose of this study was to test the effect of a second wire on functional parameters (i.e., CFVR, FFR, and HSR) and on their predictive accuracy in a group of patients with a wide range of lesion severities.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
In this retrospective analysis, digital recordings obtained in the course of earlier studies at our institution were used (5, 19). A total of 65 patients [59 yr (SD 10.1)] with anginal complaints and one- or two-vessel coronary artery disease eligible for PCI were studied. Measurements of pressure and Doppler velocity distal to the coronary artery stenosis were obtained with two separate guidewires, sequentially and simultaneously. Exclusion criteria were as follows: subtotal lesion or sequential stenosis in the target vessel, severe renal disease, significant left main stenosis, atrial fibrillation, recent (<6 wk) myocardial infarction, or previous coronary artery bypass grafting. The institutional ethics committee approved the study protocol. All patients gave written informed consent.

Myocardial perfusion scintigraphy. Patients were scheduled for myocardial perfusion scintigraphy (MPS) with single-photon-emission tomography (SPECT) during the week before cardiac catheterization with the use of ±500 MBq of 99mTc-labeled methoxyisobutylisonitrile or tetrofosmin according to a 2-day stress-rest protocol. All antianginal medication was discontinued ≥48 h before the stress test and resumed after the test. All patients were asked to fast on the day of SPECT and to abstain from any caffeine-related products for 24 h before the stress test. Stress was induced by dipyridamole (0.56 mg/kg iv for 6 min) or adenosine (140 µg·kg–1·min–1 iv for 6 min). A three-headed gamma camera (MultiSPECT-3, Siemens, Hoffman Estate, IL) equipped with low-energy high-resolution collimators was used to perform SPECT, with the patient in the prone position, starting 45–60 min after injection of the radiopharmaceutical. A 15% energy window was centered on the 140-keV photo peak of 99mTc. Data were collected over 360° in 20 views per camera head, for 60 s per view, in a 64 x 64 matrix, with the camera automated contour facility. Standard filtered backprojection was performed without correction for attenuation. Stress and rest tomographic images were reconstructed, reoriented, and displayed side-by-side in short axis, horizontal long axis, and vertical long axis. Short-axis slices were used to reconstruct polar plots (HERMES workstation, Nuclear Diagnostics, Stockholm, Sweden). Stress and rest perfusion images were scored in consensus by two experienced nuclear medicine physicians (HJV and BLFvE-S) using a five-point semiquantitative score for each of 17 myocardial segments. Perfusion defect severity was classified as follows: 0 (normal), 1 (equivocally abnormal), 2 (mildly abnormal), 3 (moderately abnormal), or 4 (severely abnormal). Subsequently, the summed stress score, the summed rest score, and the difference between the summed stress and summed rest scores (i.e., summed difference score) were calculated. Improvement at rest of ≥1 was considered to be reversible if present in more than one adjacent segment. A summed difference score ≥3 was considered to indicate clinically relevant ischemia. The result was considered positive when a reversible defect was allocated to the perfusion territory of the target vessel. The results were dichotomized into ischemia and no ischemia.

Cardiac catheterization. All antianginal and antiplatelet medication was continued until cardiac catheterization. Lorazepam (1 mg po) was administered before the procedure. Cardiac catheterization was performed by the percutaneous femoral approach. All patients received a bolus of heparin (7,500 IU iv) at the beginning of the procedure. Additional heparin was administered if the procedure lasted >90 min. Nitroglycerin (0.1 mg ic) was administered before coronary angiography and every 30 min throughout the procedure.

Hemodynamic measurements. All hemodynamic measurements were obtained at baseline and during maximum hyperemia induced by a bolus of adenosine (20–40 µg ic) (6). During the procedure, mean aortic pressure (Pao) was continuously measured through the guiding catheter. In 77 vessels, intracoronary pressure distal to the stenosis was measured with a 0.014-in. pressure-monitoring guidewire (Volcano Therapeutics, Rancho Cordova, CA). For simultaneous measurements of intracoronary pressure and flow velocity, a second, Doppler-tipped guidewire (Volcano Therapeutics) was also passed through the stenosis until the tip was at the location of the pressure sensor. The pressure-monitoring guidewire was then removed, and flow velocity was measured with the Doppler-tipped guidewire alone. For all flow velocity measurements, either combined with pressure measurements or alone, the Doppler sensor distal to the stenosis was manipulated until an optimal and stable velocity signal was obtained (11).

All signals were digitized at 120 Hz and recorded on a personal computer, and per-beat averages were obtained on the basis of the ECG.

FFR was calculated as the ratio of mean distal pressure to mean Pao during maximum hyperemia. CFVR was calculated as the ratio of average hyperemic to baseline flow velocity. HSR was calculated as mean stenosis pressure gradient ({Delta}P) divided by mean velocity (v) (19). All parameters were calculated from single-wire measurements (sequential measurements for HSR) and from simultaneous measurements obtained with two wires.

Angiographic data. Percent diameter stenosis, reference diameter, and minimal lumen diameter were obtained by quantitative analysis of the coronary angiograms with use of a validated automated contour detection algorithm (QCA-CMS version 5.02, MEDIS, Leiden, The Netherlands). The contrast-filled catheter was used for calibration. End-diastolic cine frames from two or more views were analyzed per lesion. The view with the most severe percent diameter stenosis was used for further analysis.

Statistical analysis. Continuous variables are expressed as means (SD). Means were compared for differences with an independent or a paired Student's t-test, Mann-Whitney test, or Fisher's exact test when appropriate. Categorical data were compared using a {chi}2 test (SPSS for Windows 11.5.1, SPSS, Chicago, IL). Receiver operating characteristic (ROC) curve analysis was used to compare the diagnostic performance of hemodynamically derived functional parameters of coronary artery stenosis severity with MPS. ROC curves were generated, and area under the curve (AUC) and differences between curves were calculated (MedCalc version 7.6.0.0 [EC] , Mariakerke, Belgium). Best cutoff values for FFR, CFVR, and HSR were defined as the value with the highest sum of sensitivity and specificity. Accuracy of the derived hemodynamic parameters to correctly predict the outcome of MPS was calculated for predefined and clinically used cutoff values (CFVR = 2.00, FFR = 0.75, and HSR = 0.80 mmHg·cm–1·s). It was defined as the sum of true-positive and true-negative results and expressed as a percentage of the total number of observations (16, 19). Accuracy to correctly predict the outcome of MPS was also determined using the best cutoff values of the present dataset. {kappa} Statistics were used to determine the agreement between the derived hemodynamic parameters and the results of MPS (SPSS for Windows 11.5.1). Systematic errors of measurement, as well as their degree of agreement between single-wire- and simultaneous dual-wire-based hemodynamic parameters, were assessed using Bland-Altman plots. P < 0.05 was considered to indicate a statistically significant difference.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Baseline clinical characteristics. Baseline clinical characteristics of the 65 patients (77 lesions) are displayed in Table 1. Most patients had moderate-to-severe anginal complaints [2% Canadian Cardiac Society (CCS) class 1, 19% CCS class 2, 58% CCS class 3, and 21% Braunwald class I–II]. MPS showed ischemia in 27 (35%) of the 77 regions of interest.


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  		Table 1. Baseline patient characteristics

 
Bland-Altman analysis. The mean differences between CFVR, FFR, and the HSR derived from dual- and single-wire measurements were –0.18 (95% limit of agreement = –0.70 to 1.11), –0.04 (95% limit of agreement = –0.08 to 0.16), and 0.45 mmHg·cm–1·s (95% limit of agreement = –1.91 to 0.99), respectively. The Bland-Altman analysis revealed neither trend nor bias between differences for each of the functional parameters (Fig. 1).


Figure 1
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  		Fig. 1. Bland-Altman plots with the mean of single-wire- and simultaneous dual-wire-assessed hemodynamic parameters on the horizontal axis and the respective differences on the vertical axis. Horizontal solid line, mean difference; horizontal dashed lines, 95% limits of agreement. CFVR, coronary flow velocity reserve; FFR, fractional flow reserve; HSR, hyperemic stenosis resistance (mmHg·cm–1·s).

 
Overall hemodynamic and angiographic parameters. Pao was slightly higher (4.4 mmHg, P < 0.05) for dual-wire measurements. A wide range of functional lesion severities was included. Hemodynamic parameters of functional severity and angiographic characteristics for all lesions are shown in Table 2; values were dichotomized by the presence or absence of scintigraphic myocardial ischemia. Coronary artery lesions were predominantly located in the left anterior descending coronary artery, followed by the right coronary and left circumflex arteries, with similar distribution between the ischemic and nonischemic groups (P = 0.83). Overall, functional parameters worsened from single- to dual-wire results. CFVR and FFR decreased (P < 0.001) and HSR increased from single- to dual-wire assessments (P < 0.001). The mean functional parameters worsened only in patients without scintigraphic ischemia (P < 0.001); in patients with scintigraphic ischemia, the single-wire-assessed CFVR, FFR, and HSR were not different from the dual-wire-assessed parameters (P = 0.41, P = 0.12, and P = 0.17, respectively).


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  		Table 2. Hemodynamic and angiographic parameters of coronary lesion severity

 
Diagnostic performance of functional parameters assessed by one or two guidewires. Table 3 displays the results of ROC analysis and the subsequently derived best cutoff values. The single-wire-assessed AUC (as obtained with ROC analysis) was significantly higher for HSR than for CFVR and FFR in both groups (both P < 0.001). The respective AUCs for CFVR and FFR were not significantly different (P = 0.11, CFVR vs. FFR). There were no differences between the AUCs for the dual-wire-derived parameters (P = 0.63, CFVR vs. FFR; P = 0.47, CFVR vs. HSR; P = 0.80, FFR vs. HSR). Overall fair-to-good agreement was obtained ({kappa} = 0.3–0.7) using the calculated best cutoff values (Table 3). {kappa} Values demonstrated the highest agreement for HSR assessed by sequential single-wire measurements. The use of predefined cutoff values did not change the agreement for parameters obtained by single- or dual-wire measurements, except for a decline in FFR assessed by dual-wire measurement (Table 4). Overall agreement was higher for HSR than for FFR and CFVR for single- and dual-wire assessment.


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  		Table 3. Results of ROC analysis

 

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  		Table 4. Diagnostic accuracy using predefined cutoff values

 
Separate effect for ischemic and nonischemic scintigraphic groups. Although there was a significant relation between single- and dual-wire-derived CFVR, FFR, and HSR (r = 0.805, P < 0.001; r = 0.874, P < 0.001; r = 0.665, P < 0.001, respectively), separation into ischemic and nonischemic groups revealed substantial differences in the effect of a second wire. Overall, a second guidewire worsened hemodynamic stenosis parameters (Fig. 2, Table 2). This effect was greater for HSR (Fig. 2C) because of the negative influence of the second wire on maximal velocity and pressure gradient. For each parameter, the consequence of a second guidewire was greater in the nonischemic group, thereby explaining the majority of false-positive results in the dual-wire group (Fig. 3). The difference in functional parameters resulting from the presence of a second guidewire was greatest for moderate-to-mild lesions (Fig. 4). At an essentially unchanged Pao and heart rate, the average {Delta}P increased due to the second wire in ischemic and nonischemic scintigraphic groups, as expected (Fig. 5). However, the second wire also reduced maximal hyperemic velocity, especially for the nonischemic group, with compounding consequences for diagnostic accuracy in this group.


Figure 2
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  		Fig. 2. Relations between simultaneous dual-wire- and single-wire-derived hemodynamic parameters. Gray line, line of identity.

 

Figure 3
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  		Fig. 3. Effect of a second wire on number of false-positive predictions in hemodynamic parameters.

 

Figure 4
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  		Fig. 4. Change in hemodynamic parameters compared with single-wire measurements. Vertical dashed line, predefined cutoff value.

 

Figure 5
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  		Fig. 5. Influence of a second wire on pressure gradient ({Delta}P, mmHg) and hyperemic flow velocity (cm/s) for nonischemic (neg) and ischemic (pos) groups. NS, not significant.

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The main findings of this study can be summarized as follows. 1) Overall, the presence of a second guidewire across the lesion significantly worsened CFVR, FFR, and HSR. 2) Separation into ischemic and nonischemic groups revealed substantial differences in the effect of a second wire. It was more pronounced for the nonischemic group, leading to an increase in false-positive results compared with MPS. A second wire especially worsened the hemodynamics for mild-to-moderate lesions as opposed to that of a more severe lesion. 3) Diagnostic performance of HSR was better than that of CFVR and FFR, whether assessed with dual wires or a single wire.

The evaluation of stenosis severity with pressure and Doppler sensor-equipped guidewires has become increasingly important for clinical decision making. However, the introduction of an intracoronary measuring device may negatively influence the derived parameters and, thereby, lead to an overestimation of the functional lesion severity (1–3, 25, 29). De Bruyne et al. (7) showed in an in vitro model that a single fluid-filled guidewire (0.015 in.) produced a significant overestimation of pressure drop only in cases of severe stenosis. This implies no effect of guidewire presence on clinical decision making and is consistent with the common assumption that, in moderately stenosed coronary arteries, the additional obstruction effect of the guidewire(s) can be neglected, since the ratio of the guidewire to the minimal lumen diameter of stenosis is small. The extrapolation of these in vitro findings to a clinical setting is hampered by the fact that the data were obtained under constant-flow conditions, whereas hyperemic flow velocity in vivo decreases as a result of the added resistance imposed by the second wire.

On the basis of fluid dynamic models applied to rigid axisymmetric stenosis geometries, Sinha Roy et al. (28, 29) also recently predicted that the added obstructive effect caused by the presence of a guidewire across a moderate stenosis may lead to an overestimation of lesion severity by FFR or CFVR. The guidewire was presumed to lie concentrically in the lesion, and the added pressure drop effect of the guidewire was computed for several time-averaged mean flow values. However, their numerical model did not take into account changes in microvascular resistance that occur physiologically due to a lower distending pressure caused by the guidewire-induced elevated proximal resistance (30, 31). The analysis of Sinha Roy et al. predicted a reduced maximal flow at an increased pressure gradient, progressively more so for more severe lesions. In contrast, our results demonstrate that the introduction of a second guidewire had a larger impact on clinical decision making for nonsignificant intermediate stenoses than for severe lesions because of the negative effect on maximal flow velocity, especially for milder lesions. This was also illustrated in a case study by Ruiz-Salmeron et al. (23) and is consistent with the proposition by Sinha Roy et al. (29) that the additional pressure drop due to a guidewire could have an important role in the clinical evaluation of intermediate stenoses.

Methodological considerations.

Insertion of a second guidewire could have had an impact on the more proximal vessel of the less diseased vessels in the nonischemic group by creating a so-called pseudostenosis through folding of the vessel wall after straightening of a tortuous vessel by the guidewire. This is a relatively rare phenomenon that is almost exclusively observed in the right coronary artery (10, 12). Coronary artery lesions in our study were predominantly located in the left anterior descending coronary artery, with a similar proportion of lesion location for the ischemic and nonischemic group (Table 2). The wires were highly flexible, and we did not observe marked straightening of the vessel or angiographic occurrence of new spurious lesions after wire insertion. Added resistance caused by creation of a pseudostenosis in the nonischemic group should have been visible as a positive intercept of the respective regression line in Fig. 2C, but the intercept was not different from zero (P = 0.7). We therefore believe that pseudostenosis is an unlikely culprit for worsened wire-related hemodynamics in the nonischemic group.

Wire positioning within the lesion could have contributed to a difference in the hemodynamic effect of a second guidewire between the groups. Wires may be more prone to be centrally located in milder lesions; i.e., the full wire area contributes to additional flow resistance. In contrast, severe lesions frequently have a more elliptical or slitlike lumen, which increases the possibility that the wire lies in a "corner" of the residual lumen. Such eccentric wire configuration can substantially reduce the hemodynamic effect of additional area reduction induced by a catheter or wire (2, 3).

Clinical implications.

Starting with the pioneering work by Young et al. (33) and Gould (13, 14), it has been demonstrated in vitro, in animals, and in patients that the relation between stenosis pressure drop ({Delta}P) and average flow velocity (v) is curvilinear and is described as follows: {Delta}P = av + bv2, where a and b are stenosis-specific constants. It is therefore understandable that the assessment of functional lesion severity based on only one of these two interdependent variables that make up the stenosis {Delta}P-v relation will be less successful in predicting perfusion deficits.

Stenosis resistance index, by definition, takes both parameters into account as the ratio of {Delta}P to flow at hyperemia, which implies that stenosis resistance increases linearly with flow (19, 20, 30). HSR shares two advantages with FFR over CFVR: 1) it is independent of baseline conditions, and 2) it has an unequivocal normal value of 0, because there is no appreciable pressure gradient without a stenosis. If we consider the better diagnostic performance of HSR (18, 19) and the limitations of simultaneous two-wire assessment with respect to cost, time for accurate wire placement, and possibility for complications associated with, e.g., wire entanglement, there is a need for combined single-wire measurements. {Delta}P-v relations measured with a recently introduced dual-sensor (pressure and Doppler velocity) guidewire (Volcano Therapeutics) have been shown to comprehensively demonstrate improvement in coronary hemodynamics after PCI and can be used to separately assess epicardial and microvascular disorders (27, 31). We used this dual-sensor wire to record simultaneous distal pressure and flow velocity signals in a pilot group of 19 patients who also underwent MPS. Although the number of patients was relatively small, the predictive diagnostic accuracy of the dual-sensor-wire-assessed hemodynamic parameters was similar to that of the sequential single-wire-assessed parameters (data not shown). These data further support the role for combined pressure and velocity measurements with a dual-sensor-equipped wire in clinical decision making.

In conclusion, in patients without scintigraphic evidence of ischemia, the presence of two single-sensor guidewires across a lesion is associated with overestimation of the hemodynamically assessed lesion severity. In contrast to generally accepted opinion, the presence of a second wire predominantly affects decision making for intermediate lesions. By combining velocity and pressure information, HSR is more accurate than FFR or CFVR in predicting ischemia, regardless of the number of wires used. This confirms the advantage of combined measurements with a dual-sensor wire for the evaluation of stenosis severity in the catheterization laboratory.


   GRANTS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This study was supported in part by Netherlands Heart Foundation Grants 96.020 and 2000.090.


   ACKNOWLEDGMENTS
 
The authors thank the technical and nursing staff of the Cardiac Catheterization Laboratory and the Department of Nuclear Medicine for skilled assistance.


   FOOTNOTES
 

Address for reprint requests and other correspondence: H. Verberne, Dept. of Nuclear Medicine, F2-238, Academic Medical Center, Meibergdreef 9, PO Box 22700, 1100 DE Amsterdam, The Netherlands (e-mail: h.j.verberne{at}amc.uva.nl)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
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 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

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