Alan D. Waggoner, MHS, RDCS, FASE

This month’s Sonography Council Yellow Pages mark a bitter-sweet moment in the history of echocardiography. One of our beloved colleagues, Alan Waggoner, has decided that it is time to retire. Al is one of the most respected, most experienced, and certainly most published sonographers in our community, and his contributions to the field are tremendous. He has been a sonographer for over 38 years and has seen cardiac sonography grow from its infancy to its current state. Al has been a mentor to many of us, and he has worked hard to raise the level of professionalism to where we are today. He has served as chair of the Sonography Council, associate editor of the JASE, received the ASE Distinguished Teacher Award, and had the Alan D. Waggoner Sonographer Student Scholarship named after him to recognize his contributions. This month, I asked Al to try to summarize the past, present and future of cardiovascular ultrasound.

On behalf of myself and all members of the ASE. I would like to send heartfelt thanks to Al and we wish him the best in his retirement.

The council chair asked me to write about the evolution of echocardiography and where we are headed, so here is my personal perspective as a “senior” clinical sonographer and a research scientist. When I look back over 38 years I was fortunate to be in the right place and the right time as echocardiography evolved, working in echo labs at Baylor College of Medicine, Houston, TX and Washington University in St. Louis, MO. My interest in echocardiography has always related to its role as a non-invasive method through which to assess the patient’s clinical presentation, how the results affected the patient’s management, and the impact on clinical outcomes. I am skeptical, when a new technology is introduced, about whether new methods will make the “cut” for widespread clinical application.

M mode and then 2D echo were introduced for clinical use during the early and mid-1970s, respectively. Pulsed Doppler and CW Doppler emerged at the same time as 2D, but were stand-alone units. These fundamental components of echocardiography were ultimately integrated into a single ultrasound system by the 1980s. Phased array-based ultrasound systems provided simultaneous real-time 2D/M-mode and Doppler information. 2D echocardiographic-derived measurements of LV size and volumes, ejection fraction, LV wall thickness and mass were validated in subsequent studies, and then extended to other cardiac chambers and the great vessels. The role of Doppler for the determination of valvular gradients and valve areas, intracardiac pressures (i.e., RV systolic pressure and RA pressures) and LV diastolic function was established in the 80s and early 90s to become an established component of an echocardiography examination that no other imaging modality could provide.

The development of color flow imaging (aka, multi-gate Doppler, color flow mapping) for the assessment of spatial intracardiac flow dynamics evolved and rapidly became part of the standard echo exam during the mid to late 1980s. The detection of regurgitant valves and presence of intracardiac shunts were distinct advantages of color flow imaging. Early methods to quantify severity of regurgitant valves based on jet area, length, and width had pitfalls due to inherent limitations of 2D imaging, eccentric regurgitant jets, and other technical factors. Later investigations have addressed this by combining pulsed and CW Doppler with color flow determined flow convergence to better determine the severity of valvular regurgitation.

Intravenous injections of contrast agents were used in the early years of M-mode to define cardiac chambers. Agitated normal saline was later employed for 2D imaging to detect intracardiac and intrapulmonary shunts and is widely used today as an important application for detection of interatrial shunts. In the 1990s, transpulmonary contrast agents were developed to improve LV endocardial border detection in patients with suboptimal 2D images. This remains valuable today in selected patients and for stress echo. Novel methods have been reported for the assessment of myocardial perfusion. However, this extension of contrast agents has not evolved for routine use to determine myocardial perfusion due to multiple factors, notwithstanding the competition with nuclear imaging that has been the gold standard for many years. The issue with widespread use of left heart contrast agents remains the availability of qualified personnel (i.e., sonographers, RNs) to perform IV injections, and the recent FDA “boxed” warnings, although now revised, have left many echocardiographers less than enthusiastic. Interestingly, harmonic imaging for 2D is now widely employed (ironically developed for improved contrast imaging) and has markedly improved LV endocardial border detection and may also have affected the use of contrast agents.

Tissue Doppler imaging emerged in the 1990s when echocardiographers reported that placement of a pulsed wave Doppler sample volume at the base of the mitral annulus displayed unique waveforms of systolic and diastolic myocardial velocities that represented regional systolic contraction and diastolic relaxation. This method ultimately became an integral component for echocardiography studies to determine LV relaxation and to estimate LV filling pressures beyond conventional pulsed Doppler mitral inflow.

Pulsed Doppler, and later 2D-derived, strain measurements are now in the spotlight for assessment of myocardial function. Early research began in 2000 with pulsed Doppler sampling in myocardial regions in the apical views (i.e., longitudinal planes) to determine systolic and diastolic myocardial strain and strain rate. However, it became evident that pulsed Doppler-derived strain measurements were angle dependent, affected by translation and tethering to ischemic segments, and a fixed sample volume that did not track the myocardial region of interest. 2D-derived strain, based on speckle tracking, has now become the preferred method to determine longitudinal strain, and also radial/circumferential strain (i.e., parasternal short axis views) that addresses the limitation of the pulsed Doppler method. Strain is reported to be preload independent, but some investigators have suggested that correction for LV length and LV volume may be necessary. It is also influenced by LV systolic function and LV mass. The value of strain measurements is primarily to identify myocardial ischemia and/or fibrosis, or subclinical myocardial dysfunction, despite normal LV wall motion. This new technology requires further study, particularly with regard to clinical outcomes and relative benefit compared to conventional 2D imaging.

3D echo technology began in the early 80s but was hampered by transducer design, online availability and sufficient software for over 20 years. This has been addressed with matrix transducers, newer ultrasound systems and better online/offline software that requires less time for analysis. 3D clearly provides better assessment of LV volumes, RV structure, valvular and congenital heart defects, but still has not been widely adapted for use by many echocardiographers. In some respects, it is a paradigm shift for sonographers and echocardiographers that requires additional time for image acquisition, reconstruction, and interpretation, in addition to performing conventional 2D imaging. 3D is affected by image quality and has lower frame rates. How this technology will evolve to routine daily use remains a hot topic of investigation.

The future of echocardiography depends on attention to standards for the use of established 2D-Doppler methods for patient management and its value in clinical outcomes. Second, it is important to determine whether newer methods (i.e., 3D and strain) demonstrate incremental value and impact on clinical outcomes. Finally, I encourage you to strengthen the bonds with physicians and fellow sonographers with whom you work, and with those you meet during educational events such as the ASE scientific sessions. There is a unique partnership in echocardiography, unlike in other professions, and it is the foundation of ASE. It has certainly benefitted me over my long career.