According to an old proverb, supposedly articulated in the 17 ^th century, but perhaps used first (although phrased differently) more than a hundred years earlier, “An old dog will learn no new tricks”. Interpreted literally, this aphorism tells us that an old dog, set in its ways after many years of experience, is not interested in learning how to do things differently. He knows how to do whatever it is that he does, presumably does it well enough to satisfy him, and views new challenges with an attitude of “why bother”. Applied to humans, “you can’t teach an old dog new tricks” means that a person who has done things in a certain manner for years is unlikely to embrace a new approach with great eagerness. The proverb is an oversimplification, of course, and does not always apply. However, the converse is certainly not true. As a lifelong dog lover, I know from experience that you can teach old tricks to a young dog— in fact, they pick them up quite quickly. And sometimes, old tricks are still very useful tricks; at an early age, my Labrador became very adept at sitting up on her hind legs and offering her paw; when she does this trick for my children, it almost always earns a treat for her.

In echocardiography, old tricks also can have great value. As an example, let’s consider M-mode echocardiography. I remember first learning M-mode echocardiography almost 40 years ago by reading the first edition of Dr. Harvey Feigenbaum’s textbook Echocardiography . In fact, some of my early experiences in using echocardiography to examine patients myself depended on my being able to recognize the meaning of the A-mode spikes, since the echocardiographic machine that was available to me had a malfunctioning oscilloscope. Therefore, I could not “see” the sweep of the spikes across the screen as echocardiographic targets moved toward and away from the transducer during the cardiac cycle, and was able to view the M-mode display only after I had completed the exam and taken the light-sensitive recording paper out into the hallway where, under the lights, the recordings finally became visible! Many readers will think that this story (which is true) is “quaint” but has little to do with their day-to-day activities. Didn’t we leave the “M-mode era” behind many years ago, when two-dimensional echocardiography (2D echo) became widely available and gave us the means to view the heart in tomographic format, rather than as what has been termed an “ice-pick view”? Clearly, views of the heart and great vessels using 2D echo provide important information about cardiovascular anatomy, dynamics, and function (both global and regional) that are important for proper diagnosis and patient management. And now, real-time three-dimensional echocardiography (3D echo) is a reality, for both transthoracic and transesophageal applications. Why would anybody bother with M-mode echo for examining the heart? Isn’t this an outmoded technique, perhaps of historical value so that old fogies can tell stories like the one recounted above, but surely of little practical use?

In this issue of the Journal of the American Society of Echocardiography (JASE), we are reminded that M-mode echocardiography is alive and well, and in some situations can be of enormous practical value. Dr. Harvey Feigenbaum, the first President of ASE and the founding editor of JASE, emphasizes— correctly, as usual—that M-mode echocardiography is not an anachronism. Instead, it can be very useful in many clinical situations. Even though current instruments are not optimized for M-mode examination, it is still possible to sample cardiac structures up to 1,000 times per second using M-mode echocardiography. This sampling rate is vastly superior to every other imaging modality; with 2D echo, we generally use sampling rates well below 100 frames per second, and 3D echo is even slower. So are angiography, magnetic resonance imaging (MRI), and computed tomographic (CT) imaging. If we want to examine structure motion, there is no substitute for the temporal resolution of M-mode echocardiography. For example, Dr. Feigenbaum illustrates quite persuasively how one can interrogate the timing of aortic valve motion in order to differentiate subaortic stenosis caused by a fixed membranous obstruction from that caused by dynamic narrowing of the left ventricular (LV) outflow tract by the mitral valve leaflet(s) moving toward a thickened ventricular septum in a patient with hypertrophic cardiomyopathy (HCM). He also demonstrates how the pattern of mitral valve motion can help identify high LV filling pressure, how pulmonic valve motion can help in documenting the presence of severe pulmonary hypertension, and how the pattern of ventricular septal motion may help identify differential filling of the left and right ventricles, abnormal septal activation in left bundle branch block, and dyssynchronous function of the septum and posterior LV walls in some patients with large, poorly contracting ventricles.

Of course, as economist Milton Friedman noted, “there is no such thing as a free lunch”. While M-mode echocardiography provides excellent temporal resolution, it is severely lacking in spatial resolution. That is to say, what one sees with M-mode echo is literally the position of an echocardiographic “target” along the axis of the ultrasound beam, as it changes with time. Distance measures are extremely accurate, but they depend upon the ultrasound beam traversing a desired path, and it is not easy to be certain of the path of the beam across a three dimensional structure such as the heart. In addition, since cardiac structures move within the chest during the cardiac and respiratory cycles, a fixed ultrasound beam, as is used in M-mode echocardiography, usually does not interrogate precisely the same structures during systole as during diastole. In addition, “motion” with M-mode echocardiography means motion along the axis of the ultrasound beam; it is not sensitive to motion perpendicular to the sound beam. One could observe, with some validity, that the strengths of M-mode and those of 2D echo imaging are complementary.

Back in the days when “echocardiography” meant M-mode echocardiography, the list of clinical uses of echocardiography was not as extensive as it is in 2010. Echocardiographers and cardiac sonographers had plenty of time to examine the heart and to pore over the recorded records. It seems to me that a good byword for that activity was “studying”, trying to understand the nuances of cardiac function and dysfunction, and how the findings might help establish what was wrong with the patient. With advances in technology, we now have at our disposal powerful techniques including Doppler hemodynamics, echocardiographic volumes (at least for the LV and left atrium) and related functional measures, and now methods (using strain imaging) for measuring myocardial shortening, lengthening, rotation, twisting, and torsion. There is no question that these modern techniques have made echocardiography even more versatile and powerful. Paradoxically, at the same time, economic pressures have forced all of us to do whatever we do more efficiently; the new byword has become “throughput”. In this environment, it is common to cut corners in an effort to get the needed information as quickly as possible in order to move right on to the next patient. It seems to me that newer graduates (both sonographers and physicians) have been taught not to waste time gathering “redundant” information; I believe that sometimes they are more intent than they should be on finishing the exam and not intent enough on documenting the findings as clearly as possible. From this perspective, an ideal transthoracic echocardiographic examination might be viewed as taking a single transducer, setting the instrument’s controls (depth, time-gain compensation, overall gain, and such) once, and doing the entire exam in an expeditious manner. Why take the time to record an M-mode through the aortic and mitral valves when they have been visualized adequately with 2D imaging? Why exchange the imaging transducer for a non-imaging continuous wave (CW) Doppler transducer (also known as a PEDOF transducer – more on that topic in another editor’s column ) in order to record high velocity jets such as in aortic stenosis, mitral regurgitation, ventricular septal defect, and a host of other conditions? One can do that with image-guided CW Doppler, which allows one to “see” the jet and align the examining cursor more rapidly.

In this regard, Dr. Feigenbaum’s concluding comments are most perceptive. As he states, “the most expensive test is one that produces wrong information. The second most expensive test is one that gives incomplete or non-diagnostic information”. I might take issue with the first part of that statement— in my view the most expensive test is the one that is not needed in the first place, such as the echocardiogram in the patient with longstanding non-ischemic cardiomyopathy, whose ejection fraction has been less than 30% for years, and who is admitted to the hospital with increasing fatigue and marked edema after stopping his diuretic therapy. Nonetheless, I agree completely with the notion that a test that gives incomplete or non-diagnostic information provides less “bang for the buck”. Using M-mode echocardiography is easy and quick, and it may provide definitive diagnostic evidence. For example, consider a patient with a systolic ejection murmur. Let’s imagine that color and CW Doppler demonstrate high velocity flow in the LV outflow tract and into the proximal aorta, but that the aortic leaflets clearly open well on parasternal 2D echocardiographic imaging. Taking a few moments to record aortic leaflet motion by M-mode might be of enormous value if it demonstrated a pattern such as illustrated in figure 9B of Dr. Feigenbaum’s article, and this might prompt a more careful search for the subaortic membrane that the examiner now knew must be present. Imagine another patient with a large right ventricle in whom the tricuspid valve was competent or the regurgitant waveform was faint and incomplete; an M-mode recording of pulmonic valve motion that demonstrated a pattern resembling figure 13B would establish the diagnosis of severe pulmonary hypertension and might guide further workup and treatment. Clearly, in these examples, using M-mode technique would add little time but would increase the value of the exam substantially.

Non-imaging CW Doppler also has some advantages over image –guided CW Doppler. While the latter is easier to implement, using an imaging probe to record CW Doppler velocities has several shortcomings. First, an imaging probe is not optimized for Doppler sensitivity; rather, its primary use is for imaging, which requires short pulses of alternating current to “ring” the transducer only for a few cycles. To optimize Doppler detection of frequency shifts in backscattered ultrasound, a longer series of ultrasonic compressions and rarefactions are ideal. A transducer that is used for “Doppler only” can be optimized for Doppler sensitivity, while an imaging probe that also can record Doppler cannot be optimized for both modalities. Second, the larger footprint of the imaging transducer makes it inherently more difficult to make small adjustments in probe angulation in order to achieve a co-axial Doppler intercept angle, and also makes it hard to use the probe from multiple windows. The non-imaging CW probe is optimized for Doppler data; it can also be placed in small interspaces and angulated easily.

I do not mean to suggest that every echocardiographic technique must be used for every possible application in every patient. It is, however, appropriate for cardiac sonographers and echocardiographers to remember that echocardiography is a family of related diagnostic techniques, and that one does not have to choose which technique to use. Used in conjunction with 2D (and 3D) imaging, older techniques such as M-mode interrogation and CW Doppler examination with a small, non-imaging probe can have great value in many circumstances. In my view it is imperative that “new dogs”, newer trainees in cardiac sonography and echocardiography, understand how “old tricks” work and when they may be useful, and that they take advantage of the strengths of these techniques when appropriate. In this manner, patients benefit from the most accurate and complete diagnostic examination, and that is good for everyone involved.

As always, if you have comments or suggestions, I can be reached at jaseeditor@asecho.org .