Feasibility Assessment of Aortic Valve Area in Patients with Aortic Stenosis Using a Pressure Wire through a 4 French System and

Stefan C. Bertog, MD, Andrew Smith, MD, Carmelo J. Panetta, MD
Stefan C. Bertog, MD, Andrew Smith, MD, Carmelo J. Panetta, MD
Symptomatic aortic stenosis can be associated with significant morbidity and mortality.1 Accurate assessment of the severity is important both to determine the association of symptoms with aortic stenosis and for optimal timing of surgical repair. In the majority of patients, the aortic valve area can be assessed noninvasively with accuracy by transthoracic echocardiography. However, due to poor images or other technical limitations with echocardiography, cardiac catheterization is occasionally necessary for valve area assessment. Calculation of the aortic valve area (AVA) relies on measurements of the transvalvular gradient across the aortic valve, cardiac output and application of the Gorlin equation.2 Transvalvular gradient measurement is ideally performed with two catheters, one above and one below the aortic valve. To save time and avoid additional access site puncture, the assessment of the transvalvular gradient is frequently done using the pullback method. The pullback method involves measuring the left ventricular pressure and then the ascending aortic pressure after the catheter is pulled backwards. The tracings are then overlapped either with tracing paper or by means of the computer, and the transvalvular gradient is calculated. Results of the pullback method may be inaccurate in the setting of irregular rhythms such as atrial fibrillation or due to variation in systolic pressure as seen with frequent premature ventricular contractions. Alternatively, simultaneous recording of left ventricular and ascending aortic pressure can be achieved by transduction of pressures from a larger diameter sized arterial sheath relative to the catheter in the left ventricle. This method requires a sheath size large enough to avoid obstruction by the catheter and is complicated by time delay of arterial pressure tracings that could lead to overestimation or, if the time delay is corrected by realignment of the pressure tracings, underestimation of the true gradient.3 Another approach includes the use of a 7 French long (35 cm) sheath in the femoral artery that minimizes temporal delays. Unfortunately, in the setting of severe aortic stenosis, with this and previously mentioned methods, inaccuracies may result from partial obstruction by the catheter of an already narrow orifice, or the Carabello effect.4 We therefore sought to determine the safety, technical success and accuracy of using a pressure wire to determine the aortic valve area in patients with aortic stenosis by simultaneous left ventricular and ascending aortic pressure recording, along with cardiac output measurement. This novel method would avoid potential inaccuracies and risks associated with two access sites and large arterial sheaths, allowing single arterial access, a 4 French arterial sheath size and a pressure measurement device that greatly reduces partial obstruction of the aortic valve orifice. Materials and Methods Four patients underwent cardiac catheterization both to determine the presence and extent of coronary artery disease and to assess the severity of aortic stenosis. Baseline clinical characteristics were obtained by database review of cardiovascular information services. Right heart catheterization with a Swan Ganz catheter (Baxter Healthcare Corporation, Irvine, California) was performed and the tip of the catheter left in the pulmonary artery in preparation for cardiac output measurements. Arterial access with a 4 French sheath was obtained in the femoral artery. A 4 French diagnostic catheter (Pigtail, Judkins right-4 or Multipurpose catheter) was advanced to the ascending aorta over a straight or curved 0.035 inch guidewire. The catheter was placed across the aortic valve into the left ventricle either with or without advancing a guidewire in front. A 0.014 inch pressure wire (Radi Medical Systems, Uppsala, Sweden) was placed through the diagnostic catheter into the left ventricle. The diagnostic catheter and the pressure wire were then connected to pressure transducers and the equalized and left ventricular pressure were recorded both by the pressure wire and the diagnostic catheter. Leaving the pressure wire in the left ventricle, the diagnostic catheter was then withdrawn into the ascending aorta and catheter pullback pressures were first recorded from the catheter alone. Subsequently, the ventricular pressure from the pressure wire and aortic pressure from the catheter pressures were recorded simultaneously. The transvalvular gradient was determined by computerized overlapping of pressure tracings from both the pullback method and the simultaneous recordings. Cardiac output was measured using the thermodilution method. Applying the Gorlin equation, aortic valve areas were calculated using the transvalvular gradient determined by the simultaneous recording through pressure wire and diagnostic catheter and the pullback methods, respectively. Of note, patients with significant arrhythmias, such as atrial fibrillation or frequent atrial or ventricular premature contractions, were excluded to maintain accuracy of the comparison method (pullback method). Statistical analysis. Analysis of data for correlation of valve areas was performed with SAS software (Version 8.2, SAS Institute, Inc., Cary, North Carolina). Results The procedures were accomplished without complications or significant technical difficulties (see baseline characteristics in Table 1). All hemodynamic parameters were successfully obtained in all four patients. There were no procedure-related complications. There was no significant difference in mean gradients between the pressure wire method and the pullback method. Table 1 lists the AVA for each patient. There was a significant correlation between the pullback method and use of the pressure wire (n = 4, r = 0.983, p = 0.017). An example is shown in Figure 1. Discussion The results demonstrate the feasibility, accuracy and safety of using a pressure wire to assess the severity of aortic stenosis. When compared to the frequently used alternative pullback method, using a pressure wire with simultaneous pressure recording appears to have the same accuracy. Furthermore, this method has several advantages. First, it avoids potential errors caused by partial aortic valve orifice obstruction by the diagnostic catheter (Carabello effect). Second, it can be performed through a 4 French single arterial sheath, thereby reducing potential complications associated with larger arterial sheaths or two separate arterial access sites, which is particularly important in patients with significant peripheral vascular disease. Finally, although patients with significant arrhythmias were excluded in our study (see below), it may avoid potential inaccuracies in these patients caused by the nonsimultaneous pressure recording with the pullback method. Study limitations. Our study has several limitations. First, use of the pressure wire in the leftventricle with simultaneous aortic catheter pressure measurement was compared to the pullback method, given that it is the most convenient and frequently used method in our cardiac catheterization laboratories, with acceptable accuracy in the absence of significant arrhythmias (e.g., atrial fibrillation). Use of simultaneous pressure recording by catheters in the aorta and left ventricle respectively requiring bilateral femoral access or, alternatively, simultaneous pressure recording of left ventricular pressure and femoral, brachial or radial pressure as a substitute for aortic pressure could be used instead of the pullback method. This would require either second arterial access (with minor increase in risk for vascular complication) or larger sheath size (associated with inaccuracies caused by the time delay of femoral, brachial and radial pressures with respect to left ventricular pressure typically causing gradient overestimation in the absence of realignment and gradient underestimation after realignment). In the setting of arrhythmias, however, further studies are needed in this subset of patients to compare the pressure wire method with the method using bilateral access and two catheters for simultaneous recording to prove noninferiority. Second, assembly and set-up of the necessary equipment is time-consuming and requires physician and support staff experience. In addition, pullback of the diagnostic catheter while leaving the pressure wire in place can be technically challenging, but can be overcome with experience. Third, additional costs associated with the use of the pressure wire (approximately $600) may limit this method to specific patient subsets such as those with significant peripheral arterial disease or, if accuracy is confirmed in future studies, with significant arrhythmias. Finally, the number of patients was limited in this case series, and further studies are needed to confirm noninferiority. Conclusion In conclusion, the novel use of the pressure wire to assist in determining the aortic valve area appears feasible, safe and accurate. The technique could be important in patients with severe peripheral arterial disease in whom a second arterial access is not desirable.
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