Two-dimensional transthoracic echocardiography (2D-TTE) is the reference technique for evaluating aortic stenosis (AS) but may be unreliable in some cases. We aimed to assess whether the use of a pressure wire to measure simultaneous transaortic gradient and aortic valve area (AVA) could be helpful in patients in whom initial noninvasive evaluations were considered doubtful for AS. Fifty-seven patients (mean age 76 years; 39 men) underwent cardiac catheterization with single arterial access for assessment of AVA with the Gorlin and Gorlin formula. Transaortic pressure was obtained by 2 invasive methods: (1) conventional pullback method (PM) from the left ventricle toward the aorta and (2) simultaneous method (SM) with transaortic pressure simultaneously recorded with a 0.014-inch pressure wire introduced into the left ventricle and with a diagnostic catheter placed in the ascending aorta. Reasons for inaccurate assessment by 2D-TTE were low flow states (88%) and/or atrial fibrillation (79%). Agreement for severe AS defined by AVA <0.6 cm²/m² between SM and 2D-TTE and between SM and PM was fair, with kappa coefficients of 0.38 (95% confidence interval [CI] 0.14–0.75) and 0.36 (95% CI 0.22–0.7) respectively; agreement was poor between 2D-TTE and PM (kappa: 0.23; 95% CI 0.002–0.36). SM led to a reclassification of the severity of AS in 9 patients (15.8%) compared with 2D-TTE and in 11 patients (19.3%) compared with PM. In conclusion, invasive evaluation of doubtful AS by measuring simultaneous transaortic gradient using a pressure wire may provide an attractive method that can lead to a change in therapeutic strategy in a substantial proportion of patients.
With the advent of transcatheter aortic valve implantation as an alternative to standard surgical aortic valve replacement, many patients suffering from severe aortic stenosis (AS) can now benefit from appropriate therapy. Accurate assessment of AS severity is crucial both to confirm that symptoms are related to AS and for optimal timing of valve repair. Two-dimensional transthoracic echocardiography (2D-TTE) currently represents the noninvasive investigation of choice for grading of AS but may be unreliable or biased in some cases (e.g., poor image quality, atrial fibrillation [AF] or low transvalvular flow regardless of left ventricular [LV] systolic function). In these situations, invasive evaluation by cardiac catheterization is the gold standard technique for measuring cardiac output and transvalvular gradient, from which aortic valve area (AVA) can then be calculated using the Gorlin and Gorlin formula. Transvalvular gradient is routinely assessed using the pullback method (PM), which involves measuring LV pressure, followed by ascending aortic pressure as the catheter is pulled backward. However, the results of the PM may suffer from some limitations. In an attempt to avoid these limitations, we hypothesized that a pressure wire, usually used for fractional flow reserve assessment, could prove helpful for the measurement of simultaneous transaortic pressure and AVA in patients with doubtful AS in whom initial evaluations with clinical data were considered nondiagnostic. We compared results with those obtained by the usual noninvasive (2D-TTE) and invasive (PM) methods.
Methods
We included all patients referred for cardiac catheterization due to symptoms possibly related to severe AS that could not be evaluated accurately by 2D-TTE. Patients were excluded if they had moderate or greater aortic regurgitation or previous aortic or mitral valve surgery or if they were hemodynamically unstable. All participants provided written informed consent.
The 2D-TTE images were acquired using a Vivid 7 scanner (GE Vingmed ultrasound, General Electric, Milwaukee, Wisconsin) and performed following the guidelines for the application of echocardiography. Mean transaortic gradient and aortic velocity time integral (VTI) were determined by continuous-wave Doppler and the modified Bernoulli equation. LV outflow tract (LVOT) VTI was measured by pulsed-wave Doppler just below the aortic valve. LVOT dimension was measured in the parasternal long axis view in midsystole, and LVOT area was calculated using the assumption of a circular LVOT. AVA was then calculated from the continuation equation (AVA = LVOT area × aortic VTI/LVOT VTI). Stroke volume index was calculated as the area of the LVOT multiplied by the LVOT VTI. In the presence of AF, aortic gradient and LVOT and aortic VTIs were taken from an average of 5 cycles. Preserved LV function was defined as a LV ejection fraction (LVEF) >50% and low flow as a stroke volume index <35 mL/m².
All pressures were measured with the zero reference level set at the midaxillary line. Right heart catheterization was performed via the femoral route with a 7-French Swan-Ganz catheter (Edwards Lifesciences, Irvine, California). Cardiac output was measured by thermodilution using 10-mL boluses of room temperature saline with an average of 3 samples. Left heart catheterization was performed using a femoral or radial approach, with 4- or 5-Fr diagnostic catheters (Pigtail, Judkins right-4 or Amplatz left-2, Cordis Corporation, Bridgewater, New Jersey) for the measure of the mean transaortic gradient. First, the catheter was placed across the aortic valve, and a 0.014-inch pressure wire (Radi Medical Systems, Uppsala, Sweden) was placed through the catheter into the LV. The diagnostic catheter and the pressure wire were both connected to pressure transducers. Leaving the pressure wire in the LV, the diagnostic catheter was first withdrawn into the ascending aorta and catheter pullback pressures were recorded. These values were recorded as the PM. Subsequently, the ventricular pressure from the pressure wire and aortic pressures from the diagnostic catheter were recorded simultaneously, and these values constituted the results of the SM. The measurements were made by tracing superimposed LV and aortic pressure from both SM and PM on an x-y digitizing table. The areas under the respective pressure curves represented the mean systolic LV and aortic pressures and allowed the calculation of the mean transaortic gradient. AVA for each method was calculated with the Gorlin & Gorlin formula, using the average gradient obtained with the respective technique.
Quantitative variables are presented as mean ± standard deviation (SD) and categorical variables are expressed as number and percentage. Measures of mean transaortic gradient and AVA were compared using the Bland-Altman method. Agreement between the 3 methods (2D-TTE, PM and SM) for severe aortic stenosis defined by an AVA <0.6 cm²/m² was assessed using the kappa coefficient. All significance tests were 2-sided, and a p-value <0.05 was considered significant. Statistical analyses were performed with SAS version 9.2. (SAS Institute, Cary, North Carolina).
Results
Between January 2007 and January 2012, 1420 patients were referred to our institution for evaluation of AS. 2D-TTE results revealed non-severe AS in 150 patients (10.5%) and severe AS in 1212 (85%). In 58 patients (4.5%), 2D-TTE was not sufficient to allow grading of AS and these patients were included in the present study for cardiac catheterization assessment. In one patient, retrograde crossing of the aortic valve with a diagnostic catheter failed. The remaining 57 patients comprise the study cohort. Baseline characteristics are summarized in Table 1 . Mean age was 76 years (range 60–88), the majority were male and a large proportion presented with dyspnea (79%).
| Variables | Value (n = 57) |
|---|---|
| Age (yrs) | 76.0 ± 6.8 |
| Men | 39 (68%) |
| New York Heart Association class | |
| I | 12 (21%) |
| II | 31 (54%) |
| III or IV | 14 (24%) |
| Cardiovascular risk factors | |
| Hypertension | 35 (60%) |
| Diabetes | 16 (27%) |
| Smoking | 20 (34%) |
| Obesity ∗ | 6 (10%) |
| Family history of coronary artery disease | 7 (12%) |
| Dyslipidemia † | 33 (56%) |
| Heart rate (beats/min) | 83.3 ± 21.6 |
| AF | 45 (79%) |
∗ Defined as body mass index ≥30 kg/m 2 .
2D-TTE measured the mean transaortic gradient at 28.8 ± 8.0 mmHg and estimated AVA at 0.48 ± 0.1 cm 2 /m 2 . The mean LVEF and the mean stroke volume index were respectively 48.2 ± 15.3% and 37.2 ± 11.4 mL/m². Finally, 2D-TTE was considered nonconclusive for evaluation of AS, and patients were referred to cardiac catheterization due to AF (n = 45 (79%)) and/or low flow states (n = 26 (47%) with LV dysfunction and n = 24 (43%) with preserved LVEF). Among the 50 patients with low flow state, 12 (21%) presented in sinus rhythm.
Average duration of cardiac catheterization was 68.0 ± 21.7 minutes and mean fluoroscopy time was 17.7 ± 7.9 minutes. Left heart catheterization was performed by the femoral approach in 45%, and radial approach in 55%. No adverse event related to catheterization occurred. Cardiac index was 2.08 ± 0.64 l/min/m² on average. An example of mean aortic-valve gradient measured by 2D-TTE, PM and SM is illustrated in Figure 1 .
The results of mean transaortic gradient and AVA calculated by SM were 30.5 ± 14.4 mmHg and 0.46 ± 0.2 cm 2 /m 2 respectively and by PM, 23.6 ± 9.9 mmHg and 0.5 ± 0.15 cm 2 /m 2 respectively. The results of Bland and Altman analysis comparing mean transaortic gradient as assessed by the three methods are shown in Figure 2 , and results of AVA between the three methods in Figure 3 . Bland and Altman analysis showed a lack of agreement between the three methods for the evaluation of both mean transaortic gradient and AVA, irrespective of whether patients had atrial fibrillation or were in sinus rhythm.
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