Feasibility of a Pressure Wire and Single Arterial Puncture for Assessing Aortic Valve Area in Patients with Aortic Stenosis

Aortic stenosis (AS) is commonly encountered by cardiologists. Assessment of AS is routinely performed with Doppler echocardiography, but cardiac catheterization has an important role in the assessment of patients with inconclusive echocardiographic findings. The basis of invasive assessment is the Gorlin equation, which requires measurement of the transvalvular pressure gradient.¹ This gradient can be measured by using the pullback method, but simultaneous assessment of left ventricular pressure and aortic pressure is more accurate.² To obtain simultaneous pressure measurements, most catheterization laboratories use a two-catheter technique that requires two arterial punctures; one catheter is placed in the aorta, and another is placed into the left ventricle using a retrograde approach through the aortic valve. If a transseptal approach to the left ventricle is used, or if aortic pressure is measured through the side port of the femoral artery sheath or through a double-lumen pigtail catheter, a single arterial access site can be used.^2–4 Transseptal puncture, however, involves additional risks to the patient, and iliac stenosis, pressure amplification and timing delay of the pressure signal can produce inaccurate femoral pressure measurements.^2,3 Double-lumen pigtail catheters require precise catheter positioning4 and may yield falsely increased gradients from damping or partial occlusion of a smaller side lumen. The functional significance of epicardial coronary lesions is usually assessed with 0.014 inch pressure wires, which can be placed through a guiding catheter. We developed a method of using intracoronary pressure wires to safely, accurately and simultaneously measure transvalvular pressure gradients with a single arterial puncture. The purpose of this study was to assess the clinical feasibility of assessing AS with this novel technique. AVA and mean pressure gradients measured with transthoracic echocardiography (TTE) and calculated using the continuity equation were compared with measurements taken by cardiac catheterization using a pressure wire and single arterial puncture. Materials and Methods Study patients. From February 2002 through September 2005, 18 patients (mean age, 76 ± 9 years; 10 men) with AS underwent hemodynamic catheterization. Clinical characteristics of the study patients are shown in Table 1. The Mayo Foundation Institutional Review Board approved the study. Cardiac catheterization. Patients sequentially underwent catheterization of the left and right sides of the heart, as well as coronary angiography. Right femoral or radial artery puncture was performed with a 5 Fr to 6 Fr sheath system for catheterization and coronary angiography of the left side of the heart. Right femoral or antecubital vein puncture was performed with a 7 Fr sheath system for catheterization of the right side of the heart (Figure 1). A 5 Fr or 6 Fr multipurpose guiding catheter was placed in the left ventricle using a retrograde approach, and a 0.014 inch pressure wire (Radi Medical Systems, Uppsala, Sweden) was advanced through the guide into the left ventricle. The two pressure tracings from the guiding catheter and a pressure wire were matched for calibration, and the multipurpose guiding catheter was withdrawn into the ascending aorta. Pressure measurements of the ascending aorta and left ventricle were simultaneously recorded with the pressure tracing of the pulmonary artery and electrocardiographic (ECG) tracing (Figure 2). Cardiac output was determined by thermodilution using a 7 Fr Swan-Ganz catheter (average of 3 measurements). Last, diagnostic coronary angiography was performed to evaluate coronary artery disease. Analysis of hemodynamic data from cardiac catheterization. Hemodynamic data were analyzed using MacLab 7000 software (Version 5.2, General Electric Co., Milwaukee, Wisconsin). The mean transvalvular aortic pressure gradient was determined by automatic planimetry of the recorded pressure tracing. The systolic ejection period was determined and showed averaged data from 8 to 10 heartbeats. AVA was calculated using the Gorlin formula:1 AVA = cardiac output / (heart rate x systolic ejection period x 44.3 x pressure gradient 0.5) Transthoracic echocardiography. Left ventricular outflow tract diameter and continuous-wave Doppler echocardiographic data were recorded, and AVA was calculated using the continuity equation. TTE was performed within 2 weeks of cardiac catheterization. Statistical analysis. All analyses were performed using SPSS software (Version 12.0, SPSS Inc, Chicago, Illinois). Continuous variables were summarized as mean ± standard deviation. The Pearson correlation coefficient was used to evaluate the correlation between TTE and cardiac catheterization measurements of AVA and pressure gradients. Statistical significance was inferred at p Results Study patients. On the basis of AVA and clinical status, 9 of 18 patients underwent aortic valve replacement. Seven patients did not require surgery because of moderate AS, 1 patient refused surgery, and 1 patient could not undergo surgery because of generally poor health. Cardiac catheterization. Simultaneous measurement of left ventricular pressure and aortic pressure to determine the transvalvular pressure gradient was feasible for all patients. The mean procedural time from the injection of a local anesthetic to completion of pressure measurements was 36.4 ± 9.6 minutes. The mean time needed to finish all catheterization procedures, including coronary angiography, was 53.3 ± 18.6 minutes. No complications occurred. The mean AVA, measured by TTE and cardiac catheterization, was 1.07 ± 0.58 cm2 and 1.01 ± 0.43 cm2, respectively. The mean pressure gradient was 32.9 ± 12.1 mmHg and 27.5 ± 10.5 mmHg, respectively (Table 2). AVA and mean pressure gradients determined by cardiac catheterization were significantly correlated with those determined by TTE (AVA: r = 0.856; p Discussion This study shows that the use of a pressure wire with a single arterial access site is feasible for rapidly and accurately assessing aortic valve area and transvalvular pressure gradients in patients with AS. Moreover, this technique does not have the limitations or risks associated with transseptal puncture, a second arterial access site, a double-lumen catheter, or pullback of a single catheter. Comparison of techniques used to measure AVA. The Gorlin formula is the standard method for evaluation of AVA. Historically, the pressure gradient across the aortic valve has been measured with two catheters that required access through two arteries. One catheter is placed in the ascending aorta, and the other is usually placed through the aortic valve into the left ventricle. The disadvantages of this conventional technique include: 1) changes of arterial pressure induced by the catheter itself; 2) decrease of critical AVA by the catheter diameter; 3) possible aortic regurgitation; and 4) the need for 2 arterial access sites.^5,6 Several techniques have been developed that avoid using two arterial access sites when determining transvalvular pressure gradients. Simple pullback of a single catheter can be done, but is less accurate than simultaneous measurement;² the catheter bounce effect causes artifacts in the first few aortic pressure measurements after the pullback, and minor changes of heart rate may cause difficulty when aligning the aortic and left ventricular pressures.⁶ Transseptal puncture makes anterograde measurement of left ventricular pressure possible with only one arterial access site. This technique is typically employed for the invasive measurement of pressure gradients in patients with mechanical aortic valves,3 but requires substantial training and experience to perform accurately. Standard retrograde catheter access across a mechanical aortic valve prosthesis for left ventricular hemodynamic assessment is associated with complications attributable to catheter entrapment.⁷ However, a pressure wire has been safely used to assess left ventricular hemodynamics across a St. Jude Medical aortic prosthesis.⁸ Another method to measure the pressure gradient with a single arterial approach is the use of an arterial sheath 1 Fr size larger than the catheter used for left ventricular pressure measurement. Although convenient, this method is associated with errors due to pressure amplification in peripheral vessels (particularly in the elderly), timing delay of pressure signals, and pressure damping caused by torturous iliac vessels, sheath kinks or peripheral vascular disease.^2,9,10 Double-lumen catheters may also be used to measure pressure gradients across aortic valves with a single arterial access site;⁴ however, precise positioning of the catheter is required,⁴ and falsely increased gradient measurements may occur due to damping or partial occlusion of a smaller side lumen. Recent reports showed that a 0.014 inch pressure wire could be safely used to assess AVA in a small percentage of patients with AS or a bileaflet prosthetic aortic valve.^6,8,11 We were able to use this technique in 18 patients with AS; measurements were made in a relatively short time and without any complications. Unlike other measurement techniques, the 0.014 inch pressure wire method was not associated with dual arterial punctures, errors related to pressure damping, amplification, or timing delay, or changes of the pressure gradient caused by the catheter itself. Moreover, the pressure wire has an internal control for calibration. AVA measurements made with a pressure wire were highly correlated with those made with the pullback method,¹¹ but the pullback method itself is associated with changes of aortic pressure in patients with critical AS.5 Echocardiography (using the continuity equation) was the standard noninvasive method of determining AVA in this study. The correlation between AVA measurements by a pressure wire and echocardiographic measurements was significantly high. Study limitations. Although the pressure wire technique theoretically has many advantages over other techniques that use a single arterial access site, we did not perform, and thus cannot directly compare, all techniques that are used to assess AVA. In addition, the pressure wire method incurs greater costs and requires a certain degree of clinical experience. Conclusion This study shows that the use of a 0.014 inch pressure wire with a single arterial access site is feasible for the assessment of AVA in patients with AS. The measurements are accurate, and the procedure can be completed in a relatively short time. Acknowledgment. Editing, proofreading and reference verification were provided by the Section of Scientific Publications at our Clinic.

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