Cath Lab Digest

Figure 6 is a more typical example of distal pressure amplification artifact in the evaluation of aortic stenosis. The figure shows femoral artery pressure recorded from a sheath versus the central aortic pressure. This is from a 6 Fr 23 cm sheath with a 5 Fr diagnostic catheter. In contrast to the aortic pressure recorded from the sheath, the recording from the central aorta versus left ventricle in Figure 6 shows a significantly different picture. Depending on the cardiac output, the difference in gradient may represent the difference between a prosthetic valve or medical therapy.

Figure 7 is from a patient with an iliac origin stenosis just distal to the bifurcation of the aorta (angiogram inset). This was difficult to image because of the hip pin. The aortic pressure just above the iliac stenosis is falsely amplified, and below the stenosis it is decreased.

Figure 8A shows two traditional “gold standards” for gradient measurement in aortic stenosis.5 The left panel utilizes a double femoral puncture, with one catheter above the aortic valve and one in the left ventricle. This requires two arterial punctures. Figure 8B shows transseptal access to the left ventricle through a Hancock mitral valve prosthesis. There is a second catheter in the aortic root, passed retrograde via femoral access. The need for two arterial punctures or the use of transseptal access is more complicated than is needed or desirable in many cases. Use of a pressure wire passed through a diagnostic or guiding catheter is a method to obtain gradient measurements with a single arterial puncture, and has the advantage of placing the sampling points directly on either side of the target. Damping and amplification artifacts are thus minimized.
A double lumen pigtail catheter is also an option from a single femoral arterial puncture. The disadvantage is the need for a large 8F sheath. Older versions of the double lumen pigtail had a small caliber second lumen, which was subject to pressure damping. Current versions are better engineered, and provide good quality pressure tracings.

Figure 9 shows a pressure wire passed via a diagnostic catheter.⁶ This allows the pressure wire to sample left ventricular pressure, and the diagnostic catheter to sit in the aortic root, just above the valve, utilizing a single femoral arterial access. There is one critical trick needed to keep the wire in place in the left ventricle, which is to bend the wire into a large radius distal curve. If you only put a little coronary sized “j” on the end of the wire and place it into the ventricle through a diagnostic catheter, as soon as you pull the diagnostic catheter back out of the left ventricle over the wire, the pressure wire will be ejected. A large secondary bend in the wire will follow the basal inferior wall and stabilize the wire, as shown in the left two panels in Figure 9. I use a catheter that is made by Cook, which has an Amplatz-like shape, shown in Figure 9.7 This shape is easy to orient towards the aortic valve and has side holes to facilitate pressure measurement. The angiographic inset in Figure 9 shows how to deliver the pressure wire out of the 5 Fr catheter. The pressure tracings in Figure 10 show two left ventricular pressures from the 5 Fr fluid and the pressure wire. They are well matched. At that point, you back the diagnostic catheter out, put a little forward pressure on the pressure wire, and the wire lays along the basal inferior wall and the tip is curled backward in the left ventricular apex.

Figure 11 shows another recording from a patient with aortic stenosis. The femoral artery pressure measured from the sheath is amplified significantly. The diagnostic catheter is in the aorta right above the valve, showing central aortic pressure, and the pressure wire is in the left ventricle (LV). The difference between the gradient from sheath versus LV compared to central aorta versus LV is large enough to result in a discrepancy in valve area calculation. The difference in gradient is particularly important in the low output, low gradient setting.

Figure 12 is a case where the aortic valve measurement based on a sheath with aortic pressure amplification results in a diminished gradient, with a valve area of 0.9cm², which might warrant watchful waiting. The heart rate is irregular, so the gradient varies beat to beat. Simultaneous recording of LV and aortic pressure is thus necessary, but not necessarily sufficient. The pressure wire gives an unadulterated, accurate measure, and a calculated valve area of 0.7cm2, which is clearly treated with surgery in a symptomatic patient (Table 2).

Figure 13 shows pressure recorded from a 23 cm, 6 Fr sheath. The sheath flushes easily and is sitting above the bifurcation of the aorta in the descending aorta. It is damped, but this would not be apparent without another independent measure of the central aortic pressure. The damping likely results from tortuosity in the iliac, or possibly from thrombus in the sheath. There is no phase delay in the foot of the central aortic pressure recorded from the pressure wire, which distinguishes it as the correct measure.