Cath Lab Digest - February 2008 - (Page 50)

50 ASK THE CLINICAL INSTRUCTOR FEBRUARY 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. “I see we need to be prepared to calculate cardiac outputs on the RCIS exam. In what ways can we do that, and how does that apply to what we really do in the lab?” — RCIS Review Attendee T he registered cardiovascular invasive specialist (RCIS) exam does require the candidate to be familiar with a few different ways to calculate cardiac output. In reality, some are more reliable and accurate than others. It also appears that the emphasis on each varies slightly from hospital to hospital around the country. The predominate ways to calculate cardiac output in the cath lab are: 1. Angiographic 2. Thermodilution Cardiac Output 3. Fick Cardiac Output Some of our imaging systems will allow you to draw the systolic and diastolic outlines, and then provide some data for you. If you had to work it out on paper, and using the formulas and data provided above, the cardiac output for the above angiogram would be something like this: SV (systolic volume) = LVEDV (left ventricular end diastolic volume) – LVESV (left ventricular end systolic volume) SV = 148 – 84 (note: round numbers whenever possible) SV = 64ml We will hopefully know what the heart rate is, and if it is, say, 80 beats per minute, we can finish the cardiac output calculation as follows: Figure 1. Note that the diastolic volume is 147.8 and the systolic volume is 84.2. Generally, this is automatically calculated, based upon your drawing of the outline of each phase. As you practice, you will also notice that you can often get a different number with each series of drawings. Thermodilution Cardiac Output (TDCO) Unless you are a math whiz, you will likely rely on the computer equipment to provide the results you need from the data that you supply. The process is fairly simple, but the results are only as good as the accuracy of the technical aspects of the procedure. During a TDCO, an cool injectate of a known temperature is injected into the right atrium, and a temperature measurement occurs at the distal pulmonary artery (Figure 2). The time it takes for the temperature to return to normal is used to calculate the cardiac output. Essentially, the computer is looking for the CHANGE IN TEMPERATURE OVER TIME. Think of it this way (and keep this in mind for the next section as well)…the lower (or slower the flow) the cardiac output, the longer it will take for the temperature to change, because the blood is not moving as fast. The opposite is true for a higher cardiac output: the temperature will change quickly (Figure 3). This process is obtained by the use of a Swan-Ganz catheter specifically Angiographic We essentially do this on each left ventriculogram (LV gram) when we figure out the ejection fraction (EF). Sometimes you can just look at the LV gram and take a good guess at the EF, and as you become more experienced, your guesses become more and more accurate. However, to perform analysis of the cardiac output correctly, it requires a little bit of work, and unfortunately, a little bit of math. The basic calculation for determining cardiac output is: CO (cardiac output) = HR (heart rate) x SV CO = 80 x 64 CO = 5,120 ml or 5.12 liters per minute To take it further and figure out the ejection fraction, the formula is: CARDIAC OUTPUT = HEART RATE x STROKE VOLUME To figure out what the stroke volume is angiographically, we can use a simple formula: Ejection Fraction (EF) = (End Diastolic Volume [EDV] – End Systolic Volume [ESV]) / EDV x 100 If we use the numbers from the previous exercise, we have this calculation: The lower (or slower the flow) the cardiac output, the longer it will take for the temperature to change, because the blood is not moving as fast. The opposite is true for a higher cardiac output: the temperature will change quickly. STROKE VOLUME = LEFT VENTRICULAR END DIASTOLIC VOLUME – LEFT VENTRICULAR END SYSTOLIC VOLUME EF EF EF EF = = = = (148-84)/148 x 100 64/148 x 100 0.43 x 100 43%

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

Cath Lab Digest - February 2008 Bay Regional Medical Center ENDEAVOR IV: A Zotarolimus-Eluting Stent Versus a Paclitaxel-Eluting Stent in a Randomized Clinical Trial A 3D CT Vessel “Roadmap” Over Live Fluoroscopy for Chronic Total Occlusions Contents Clinical Editor’s Corner An Evaluation of Cath Lab Turnaround Time Commentary: An Evaluation of Cath Lab Turnaround Time Excerpts from Chapter 19. STEMI Interventions – Future Perspectives The Potential Clinical Utility of Intravascular Ultrasound Guidance in Patients Undergoing Percutaneous Coronary Intervention With Drug-Eluting Stents The Ten-Minute Interview with…Debbie Charlton, RN The Society of Invasive Cardiovascular Professionals (SICP) at Transcatheter Cardiovascular Therapeutics (TCT) 2007 The Cath Lab is a Business: Do You Have the Knowledge to Stay Afloat? Incidence and Predictors of Vascular Complications after Invasive Coronary Procedures: A Prospective Analysis Ask the Clinical Instructor: A Q&A Column for those New to the Cath Lab Volunteer Survey SICP* Section Meetings Calendar What Do You Think? CEU Education Center Clinical & Industry News Classifieds Advertisers Index

Cath Lab Digest - February 2008

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