Cath Lab Digest - May 2008 - (Page 40)

40 ASK THE CLINICAL INSTRUCTOR MAY 2008 Ask the Clinical Instructor A Q&A column for those new to the cath lab Questions are answered by: Todd Ginapp, EMT-P, RCIS, FSICP Todd is the Cardiology Manager for Memorial Hermann Southeast in Houston, Texas. He also teaches an online RCIS Review course for Spokane Community College, in Spokane, Washington, and regularly presents with RCIS Review Courses. “We have some physicians that do unusual things when trying to analyze valves. What is the correct way?” — RCIS Online student Part II. In the April issue (Part I), we presented some ideas about how to interrogate the aortic valve. In this month’s article, we will cover mitral valve analysis. Many of the same principles apply as with the aortic valve. Let’s review some of the principles of mitral valve analysis: 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 valves are closed. when Figure 2. In this snapshot, we can see that the left ventricular end diastolic pressure (LVEDP) and the pulmonary capillary wedge (PCW) mean match fairly well. Remember, to eyeball the LVEDP, come straight down from the QRS complex and intersect it with the LV waveform. Any gradient in these waveforms is insignificant. As with the aortic valve, we must know the pressures on each side of the valve to establish the gradient, which is the challenge with mitral valve analysis. The options available to obtain the pressures on each side of the valve are limited. Ventricle Pressure and Wedge Pressure We already are comfortable with knowing that a pressure can be obtained from a ventricle by placing a catheter in it. But how do we get the pressure on the “other” side of the mitral valve, or from the left atrium (LA)? We’ll discuss how to obtain a direct pressure reading from the LA in a moment, but it is not a common procedure. The best we can do is to obtain a distant reading that mimics the LA. If we go back to some basic hemodynamics, we should recall that we use a SwanGanz catheter to obtain pulmonary capillary wedge (PCW) pressures (Figure 1). In the normal patient, we can also “see” all the way to the left ventricle, specifically, the left ventricular end diastolic pressure (LVEDP). Once the tip of the Swan-Ganz catheter is ‘wedged,’ it creates a continuous, fluid-filled pathway from the tip of the catheter to the ventricle. Since the mitral valve is open during diastole (Principle #2), we “see” the ventricle during diastole, and the moment just before contraction is when we see the LVEDP (Figure 2). You might be wondering how we would know the LA pressure when looking at the ventricle. Refer to Principle #2. If the valve is open, and the ventricle is in diastole, then before it contracts, the pressures between the LA and the LV must be equal, since the valve is open. Refer to Principle #4. Once the pressure is high in the LV, it will close the mitral valve. Therefore, it can easily be remembered that: PCW = LA (mean) = LVEDP the pressures within the lung beds. If that is the case, you cannot reliably use this process. Now that we have the necessary information, what do we do with it? First, you have to allow your monitoring system to help. With the aortic analysis, we looked at peak-topeak gradients (systole). With mitral valve analysis, we are looking for diastolic filling, so we have to look at the area underneath the pressure gradient. This is more difficult and we rely on the computers to figure it out. One thing that must happen is that the tracings must be adjusted to correctly line up. When reading the PCW compared to the LV, there will be a delay in the PCW reading, because of the time it takes for the pressure wave to reach the tip of the Swan-Ganz catheter. You would need to move the tracing over to line it up, as shown in Figure 3a. After you complete this task, obtain the information from your computer. Once you know the gradient of the valve, you can apply it to the Gorlin Formula to obtain your valve area (to be discussed in the next issue). Direct LA Pressure Reading This means that we CAN know what the pressure is in the LA by using the PCW pressure and obtaining the mean from the LA. However, this does not apply to patients who have pulmonary hypertension, or other pathologies that create disturbances in More difficult, and done less often, is the transeptal procedure to obtain a direct pressure reading from the LA. We described this procedure in detail in a previous column (November 2006; available online at http://cathlabdigest.com/ article/6459). Figure 1. Courtesy of Wes Todd (www.westodd.com) http://www.cathlabdigest.com/ http://www.westodd.com http://www.cathlabdigest.com/

Table of Contents Feed for the Digital Edition of Cath Lab Digest - May 2008

Cath Lab Digest - May 2008 The King Faisal Specialist Hospital and Research Centre Cell Therapy in the Cath Lab for Heart Failure: A Look at MyoCell® Therapy and the SEISMIC Trial Performance Improvement Strategies Speed Up Treatment Times in the Management of ST-Elevation Myocardial Infarction (STEMI) Patients Contents Clinical Editor’s Corner Commentary: Performance Improvement Strategies Speed Up Treatment Times in the Management of ST-Elevation Myocardial Infarction (STEMI) Patients Ask the STEMI Expert Comparing Drug-Eluting Stents and Bare-Metal Stents SICP: The Ten-Minute Interview with… Christopher Kambak, RT(R) Cardiac Cath Lab Economics in a Public Hospital of a Developing Country Keeping Your Heart & Vascular Employees: Proven Ideas for an Effective Retention Plan Unspoken Words Ask the Clinical Instructor Society of Invasive Cardiovascular Professionals Meetings Calendar Education Center What Do You Think? Clinical & Industry News Classifieds Advertisers Index

Cath Lab Digest - May 2008

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