A Q&A column for those new to the cath lab

“We have some physicians that do unusual things when trying to analyze valves. What is the correct way?” — RCIS Online student

Part I.
       There really isn’t a ‘right’ way to do it, as long as you get the proper information. However, there are some standard methodologies. The main valves we interrogate are the aortic and mitral valves. With the advancing technology of echocardiography, detailed valve analysis is no longer commonplace in the cath lab.

       Due to limitation in space, we will break our discussion into three parts. We will discuss aortic valve analysis in this month’s Part I column, and reserve the mitral valve analysis for next month. The month following that, we will briefly address a question on how stenotic valves are managed in the cath lab.
       Regardless of which valve is under examination, there are a couple of “absolutes” that we need to remember during our exercises:

1. To analyze a valve, you must know the pressure on each side of the valve.
2. Tricuspid and mitral valves are closed during systole and open during diastole.
3. Aortic and pulmonary valves are open during systole and closed during diastole.
4. Valves open and close due to pressure differences on either side.
5. Stenosis shows when valves are open.
6. Regurgitation shows when valves are closed.

       There are a few ways to analyze the patency of the aortic valve. While there are many different ways to get to the end result, following are the more common procedures. As with many methodologies that we have discussed in the past, each physician will have his or her own preferences and opinions on how these procedures are to be completed.

Left Ventricle to Femoral Sheath Comparison

Figure 2. With the catheter drawn back from the left ventricle to the aorta, we can see the transition line and that there is not a gradient.

Figure 1. In this procedure, a catheter is in the left ventricle (LV) and another transducer is simultaneously connected to the sheath that is in the femoral artery. Notice there is approximately a 70-80mmHg gradient between the two. However, we cannot appreciate any peripheral amplification that may be occurring in the distal circulation. This reading, however, would direct us to the need for a more detailed and accurate method of measuring the gradient.

       A pressure is obtained from the ventricle and also from the femoral sheath. It can be done separately or simultaneously, with the use of 2 transducers. However, because of peripheral amplification and delay, this method may bring the least reliable results. If a catheter is already in the ventricle, the next procedure may be more appropriate.

Left Ventricle to Aorta Pullback
       This is the most common method for valve analysis in the cath lab. After a left ventriculogram, the catheter can be pulled back sharply into the aorta. Staff would then look at the peak-to-peak comparisons to see if there is a difference (gradient) between the two. A problem can occur when a valve is potentially bad and the orifice of the valve can be very small, which can make the passage of a wire and catheter very difficult and time-consuming.

Dual Lumen Catheter

Figure 3. One issue that can occur is when the pigtail catheter is not completely drawn out of the left ventricle (LV), and a couple of the holes at the distal end of the catheter remain in the LV, while the proximal holes are in the aorta. This gives us a ‘mixed’ reading. Withdrawing the catheter back across the valve so nothing remains in the LV is the standard approach.

       There are a few companies that make a dual-lumen pigtail catheter. The Langston Dual-Lumen Pigtail catheter (Vascular Solutions, Inc., Minneapolis, MN), for example, is essentially a large catheter (6Fr) with a smaller catheter (4Fr) integrated within. There are ports on the proximal end of the catheter that can run to a transducer, and ports on the distal part of the catheter that are just like a pigtail catheter and can also be attached to a transducer. This process allows for both ventricular and aortic pressures to be analyzed at the same time without delay.

Two Catheters

Figure 4. From www.vascularsolutions.com. Courtesy of Vascular Solutions, Inc.

       Before the dual lumen catheters, physicians would sometimes ‘create’ their own dual lumen catheter. A short (60cm or so) 7Fr catheter could be placed in the aorta. This would generally rest somewhere near the aortic arch. It would be hooked up to a manifold to record its pressure. Then, a 4Fr pigtail catheter would be placed through the 7Fr catheter and placed into the ventricle. These pressures could then be read simultaneously. This process would provide the same function as the manufactured dual lumen catheter.
       If we know the gradient, then we can apply it to the Gorlin formula for calculation of valve area. Yes, it involves math, but as with other formulas presented in the past, it can be easy once you understand it. This will be presented in Part III, where intervention of a distressed valve is discussed.

       All of these methods can provide information concerning the status of the aortic valve. Of course, in doing this, we completed two of the theorems of valve analysis: “Knowing the pressure on each side of the valve” and “Stenosis occurs when valves are open.”

       Next month, we’ll talk about the more difficult analysis of the mitral valve.