Clinical Editor's Corner

Hemodynamic Data Collection at Square 1: From transducer to recorder

MORTON KERN, MD Clinical Editor Clinical Professor of Medicine Associate Chief Cardiology University of California Irvine Orange, California
MORTON KERN, MD Clinical Editor Clinical Professor of Medicine Associate Chief Cardiology University of California Irvine Orange, California
Hemodynamic studies require accurate data collection technique. For complex cases we record simultaneous pressure waveforms, working with multiple transducers. I have had some questions from our staff as to what is the best and easiest way to collect hemodynamic data. As a caveat, I am sure most of you already know that there is more than one way to do nearly everything in the lab, and that includes setting up and recording hemodynamics. Let’s spend a few moments addressing how we record hemodynamics in our cath lab. I tell our fellows, “if you’re going to do it (measure hemodynamics), spend the time to do it right. No data is better than wrong data.” Step 1. Check the cables: Transducer connections to the recorder. This step is one of the greatest points of confusion and frustration. It is generally an annoying experience for the nurses and technologists who come in to the laboratory to find all the cabling connecting the transducers to the table and the hemodynamic recorder unplugged and uncoiled, scattered over the catheter table and floor. We number and color code all cables and their inputs so that reconnections and match-ups can be made easily and quickly. Label clearly and read the labels when connecting. GE cables do not work in Prucka recorders. This problem of reconnecting cables has been a continuous battle, as our cleaning personnel unplug the cables for better access around the tables. In addition to clear labeling of the cables, an attachment device for the coiled cables to the tableside, such as Velcro strips or other tape, is also very helpful. On the sterile field, it is also worthwhile numbering and color-coding the transducers and tubing so that communications for recording the waveforms from the operators to the control room can proceed smoothly. For example, “Zeroing transducer number 1; pressure is up on number 1; number 1 is a femoral artery pressure.” Clear communications are always helpful and this is the best method to reduce frustration, save time and decrease confusion during hemodynamic measurements. Step 2. Set up the transducers: On the sterile field or on the injector device. To set up transducers for the sterile field, a small rack with transducer mounting brackets is placed opposite the operators and set at the patient’s mid-chest level. Transducers are connected electrically to the cath table sockets, sending the signals to the recorder. The transducers are flushed with saline through plastic tubing to be connected to the catheters on the sterile field. The transducers are flushed to ensure bubbles are eliminated. All connections to stopcocks and tubing should be flushed and tightened. If possible, the shortest and stiffest tubing should be used to produce the best pressure transmission pathway. After flushing, the tableside transducers are zeroed at the mid-chest level of the patient. The transducers are opened to atmosphere; the recording technologist zeros the signals on the hemodynamic recorder. The transducers are then closed. It may be necessary to reflush the transducers to be sure they are free of air bubbles. Any remaining bubbles may produce underdamped pressure waveforms. This setup applies for multiple transducers and will provide accurate hemodynamic measurements for all cases. In our laboratory, we also use the ACIST power injection system (Eden Prairie, MN), which has a built-in transducer. We like it very much for angiography but it has a minor limitation for pressure measurement. The ACIST transducer is mounted on a built-in bracket with rubber-padded backing through which the pressure is transmitted to an electrical sensor. Although the transducer on the ACIST device is accurate, because of the mechanical plate interface, the signal is delayed about 50 to 100 msec relative to the EKG. The computer-measured left ventricular end diastolic pressure (LVEDP) may be inaccurate, since the timing mark of the R wave from the EKG is out of synchrony with the pressure wave (please see Figure 1). For all simultaneous 2-pressure hemodynamic studies, or any study in which high accuracy is desired, we use tableside-mounted transducers. [Note: As of this month, ACIST has made available a connector to use your own transducer with the power injector. The next generation of this injector eliminates this problem with an incorporated transducer.] Recording Methodology I advocate using a standard routine for the three most common cath hemodynamic situations: left heart (aortic and LV only), right and left heart (2 simultaneous pressures with oxygen saturations and cardiac output), and right heart hemodynamics only. I know it is difficult to have all operators in the cath lab making measurements in the same way, but a common plan will help everybody and decreases procedure time. I reemphasize that communications from the operator’s field to the recording technologist should be clear in order to reduce frustration, confusion and errors. For example, we indicate chamber location, transducer number and then request a zero check. Each step is conveyed by verbal communications so the recording technologist knows where we are and what we are doing at the cath table. For accuracy, recording both phasic and mean tracings can be used and matched against the computer-generated numbers. Hemodynamics can be acquired as the catheter is moved through the right heart; for example, moving from right atrium to right ventricle to pulmonary capillary wedge and pulmonary artery (PA). Do not forget to obtain oxygen saturations during right heart catheterization to exclude unsuspected cardiac shunting and be used in a Fick O2 consumption calculation of cardiac output. Generally, four blood samples are required, one arterial, one from the inferior vena cava, one from the superior vena cava, and one from the PA. Should an increase in O2 saturation (step-up) exist of greater than 6% between chambers, one must ask whether or not there exists an atrial or ventricular level shunt. Cardiac output is then measured, followed by catheter pullback data recording from wedge to PA, right ventricle (RV) and right atrium (RA). Interpretation of the Pressure Waveforms It is important to review the waveforms as you collect them. The pressure waves should make sense for the catheter location, cardiac rhythm and clinical situation. The pressure waveform should be timed correctly with the EKG and should be of appropriate scale. For example, does an arterial pressure of 60/40 with a heart rate of 80bpm make sense in a perfectly comfortable, awake patient who is talking to you? First, check the patient. Then, check the scale factors on the recorder, then the connections and tubings again, and whether or not the pressure transducer is connected to the left- or right-sided catheter. Errors like this are a common source of confusion among inexperienced personnel. Unusual waveforms should correlate to pathophysiology. If not, suspect some error in the recording technique, such as a loose connection, an air bubble, clot in the line, a damped or kinked pressure tube or catheter, or a wrong recording scale and so on. These checkpoints are necessary to record good quality hemodynamics. Simultaneous Right and Left Heart Hemodynamics Usually, right heart hemodynamics are performed in conjunction with left heart hemodynamics to obtain a complete assessment of myocardial, pulmonary and valvular function. Normally, when performing simultaneous right and left heart hemodynamics, we place the right heart catheter through its normal route to the PA in the manner described above. After cardiac output is obtained, we insert the pigtail catheter in the LV via the femoral artery sheath and obtain LV hemodynamics and simultaneous wedge pressure to gauge mitral valve function. On pullback of the right heart catheter, we measure simultaneous right and left ventricular pressures in patients suspected of having constrictive or restrictive physiology. Finally, for all left heart hemodynamics, compare LV and femoral artery pressure (from the arterial sheath side arm) to evaluate aortic valve disease during pigtail catheter pullback. Right and left heart catheterizations performed in this manner will provide a complete hemodynamic assessment in 95% of all cases and provide an accurate understanding of aortic, mitral, tricuspid, and pulmonary valve disease with minimal extra maneuvers. These protocols have been described elsewhere.1 Finally as you review your own procedures in the cath lab, see where you can improve the precision, organization, clarity, and operational protocols to obtain better hemodynamic data.
1. Hemodynamic Data. In: Kern MJ. The Cardiac Catheterization Handbook. 4th ed. St. Louis, MO: Mosby; 2003:126-217.