Dedicated Continuous Wave Doppler Transducer

Blind CW Probe... Dedicated CW Probe... Pedoff... Aux Probe... However you refer to it . . . use of a dedicated continuous wave Doppler transducer significantly increases the accuracy of the hemodynamic assessment. As part of the 2006 ICAEL Standards released this Spring, a significant revision to the Adult Transthoracic testing section was incorporated under Primary Instrumentation: Cardiac Ultrasound Systems. The change requires a dedicated continuous wave Doppler transducer. In previous versions of the Standards, availability of this transducer was simply suggested, whereas now it is required: 1) At least two imaging transducers, one of low frequency (2 - 2.5 MHz) and one of high frequency (3.5 MHz or higher); or a multi-frequency transducer which includes these frequencies. A transducer dedicated to the performance of continuous wave Doppler studies must be available for each study. Since publishing the 2006 Standards, the ICAEL has received numerous inquiries from laboratories throughout the United States and Canada asking for clarification on the use of this transducer and the rationale for why the ICAEL has deemed it a necessary component.

What is it?

A dedicated continuous wave Doppler transducer has two elements, one that continuously transmits and the other that continuously receives the Doppler signal (no images). Since it does not share bandwidth with imaging components, this specialized transducer has the capability to detect significantly higher velocities, thus providing more accurate measurements.

Where is it used?

Within the ICAEL Standards, under Components of the Transthoracic Echocardiogram, the following guidelines are provided:

3.2.2 The complete examination must include (except where technically unobtainable), but not be limited to:

C) The following standard Doppler flow evaluations:

2) For aortic stenosis, the highest systolic velocity must be multiple transducer positions (e.g., apical, suprasternal/parasternal). When necessary this should include interrogation from multiple views with a dedicated standoff continuous wave transducer

3) Also use of non-imaging Doppler Transducer to assess stenotic valves, valvular regurgitation or whenever indicated

The small size of this transducer gives the sonographer the ability to obtain Doppler signals in technically difficult patients with small acoustic windows, and it allows for excellent apical, suprasternal, right parasternal, and subcostal access. In cases where it is difficult to get a 2-D image (with an imaging transducer), the dedicated CW probe can still provide useful Doppler information.

Why is it used?

The flow through a stenotic valve (or a prosthetic valve) may be principally directed in any number of spatial planes. In order to ensure that the highest velocity across the valve has been obtained, the sonographer should interrogate a stenotic valve from multiple tranducer positions using the dedicated continuous wave Doppler transducer. To avoid errors, only clearly defined Doppler envelopes should be used for quantification.

Geoffrey A. Rose, MD, FACC, FASE, ICAEL Board member and Director of the Cardiac Ultrasound Laboratory at Sanger Clinic/Carolinas Medical Center in Charlotte, North Carolina, commented on the ICAEL's recent addition of the requirement for a dedicated continuous wave Doppler probe. "Use of a dedicated continuous wave Doppler probe remains vital for the accurate evaluation of stenotic valvular lesions, as well as for assessing other high velocity lesions, such as VSDs and PDAs," stated Dr. Rose. "Not only does this type of probe provide the temporal resolution to record these high velocities accurately (without aliasing), the small footprint characteristic of this type of transducer allows interrogation from multiple locations, many of which are ill-suited to use with a standard imaging probe. Since the specific direction of the highest velocity jet is unpredictable in stenotic lesions, careful evaluation from multiple sites is imperative for accurate quantification. For these reasons, a continuous wave transducer is an essential tool for laboratories committed to providing a complete echocardiographic evaluation of patients with stenotic lesions."

In recent years some ultrasound programs, unfortunately, have not emphasized the importance of using the dedicated continuous wave Doppler transducer. Developing this skill is essential; it increases the accuracy of the hemodynamic assessment, ultimately leading to improved patient care.

The most recent version of the ICAEL Standards is available for viewing and download from the website, at www.icael.org/icael/apply/standards.htm. For more information about the ICAEL Standards, please contact the ICAEL toll-free at 800-838-2110 or email Bev Gorman, ICAEL Technical Manager, at gorman@intersocietal.org.

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