Derek A. Fyfe, MD

Tissue Doppler Imaging (TDI) is an emerging ultrasound technology that measures heart function without the invasive and painful elements of cardiac catheterization and biopsy. Derek A. Fyfe, MD, PhD and researchers from Sibley Heart Center at Children's Healthcare of Atlanta, are conducting a study testing TDI on pediatric heart-transplant patients. Children’s Healthcare of Atlanta is one of the largest pediatric healthcare systems in the United States; it is also only one of four hospitals in the nation that is testing TDI on these patients. Their results are showing that TDI, when used in conjunction with traditional echocardiography, can detect signs of terminal heart failure up to 12 months before the child's heart actually fails. Researchers are also finding that TDI can effectively measure the deterioration of the right ventricle, as well as possibly be able to detect signs of rejection. In this special interview, Dr. Fyfe reports his findings with EP Lab Digest.

What are some of the benefits of Tissue Doppler? How does it work?
Tissue Doppler Imaging (TDI) uses the same technology as conventional echocardiograms and medical ultrasounds. Energy impulses, which are not felt by the patient, are transmitted into the area being studied. Some of this energy is reflected or "bounced" back to the machine by the underlying organs. Based on these reflections, a 2-dimensional image is created. In conventional heart ultrasounds, this technology can also be used to measure the velocity of blood as it flows through the heart. This is called the Doppler principle. Tissue Doppler, however, measures the velocity of the heart muscle itself, rather than that of the blood. This is beneficial for a number of reasons. First, it is a direct measurement of heart function. Second, it is easy to perform and available on most current echocardiographic machines. Finally, it is not affected by factors such as anemia, fluid overload, and valve leakage, all of which can cause inaccurate measurements with conventional blood flow Doppler.

What is new in Tissue Doppler technology? Describe the work in Tissue Doppler being done at Children's Healthcare of Atlanta.
Tissue Doppler Imaging is an exciting new area of ultrasound with many applications. Most recently, TDI has been studied at Children’s in patients following heart transplantation to monitor their heart function. It is being studied as a method of predicting or identifying patients in rejection. Another study at Children’s uses TDI to evaluate heart function in patients with permanent pacemakers. These patients’ pacemakers are programmed in various ways, and the function is assessed with TDI to determine the most efficient method of pacing. In other centers, TDI has been used to identify various genetic conditions which affect the heart before it becomes apparent with conventional ultrasound.

When did you begin using TDI on pediatric patients?
Two years ago, we began using it as a research tool. This fall, we will begin using it routinely to evaluate heart function in some patients.

Figure 1

The figure shows the velocity tracing of TDI. The marks show #1: the systolic (s); #2: the early diastolic (E); and #3: the late diastolic (A) velocities.

What results have you seen so far? How many pediatric patients have used TDI? What is the clinical significance of this technology?
The results have been promising. TDI can be used to identify pediatric transplant patients who are at high risk for death within the next 12 months. There have been a total of 59 patients involved in our TDI studies so far. Clinically, this technology will be useful because of its ease, availability, and non-invasiveness. It will be used as an adjunct to current ultrasound measurements in the evaluation of heart function in patients with heart failure, transplantation, pacemakers, and others.

How does TDI compare with other technologies (cath or biopsy) currently being used for heart function in pediatric patients?
TDI gives us different information than these other modalities so it is unlikely to replace all of these procedures. Whereas TDI measures contraction or function of the heart, catheterization typically measures pressure and oxygen levels throughout the heart. Biopsies are routinely done in patients who have had heart transplantations in order to monitor for rejection. It is our hope that with TDI, we will be able to predict rejection and perhaps limit the number of necessary biopsy procedures these patients are subjected to.

How accurate is TDI?
TDI has proven to be an accurate measurement of heart function in both adults and pediatrics.

What are other possible uses for TDI? How might this be a promising tool for measuring RV function or in evaluating patients with biventricular pacing?
Right ventricular function has traditionally been difficult to quantify. TDI is a non-invasive, easy, available, and accurate means of quantifying RV function. In patients with biventricular pacing, it may prove beneficial to maximize pacer settings or perhaps lead placement to attain the maximal velocity of muscle contraction.

Who else benefits from TDI? Is TDI already used in adult patients?
TDI has been used for a number of years in the adult population. All patients who require quantification of heart function will benefit from Tissue Doppler Imaging.

Tell us more about the Sibley Heart Center at Children’s. How long have you been there? What other research in pediatric health care is being done there?
The Sibley Heart Center at Children’s is one of the largest pediatric cardiac programs in the country. We were recently named one of the top five programs by Child magazine. We perform 900 surgeries, including 10–15 heart transplants, each year. In August, we performed three transplants in one day and reached a milestone – we have performed 150 heart transplants, one of only seven centers in the country to have done this. We have 26 cardiologists and care for children from all over the United States.

Is there anything else you would like to add?
The families of children with heart disease have generously contributed to all of our research by allowing their children to participate. We are all indebted to them for this.