Toronto, ON - New data presented during the American Society of Echocardiography 2008 Scientific Sessions suggest that a new noninvasive ultrasound technique can replace the bulk of endomyocardial biopsies in heart-transplant recipients [1]. One expert who spoke with heartwire after the meeting said that the imaging tool, known as two-dimensional ultrasound speckle-tracking imaging, is already widely available, easy to do, and being studied in a wide range of applications, particularly as a screening tool for various cardiomyopathies.

Dr Judy Mangion

"This technique is fairly well researched and well studied at this point in different subsets of heart-disease patients, but this particular study, looking at its application in heart-transplant patients, is relatively novel," Dr Judy Mangion (Brigham and Women's Hospital, Boston MA), who was not involved in the study, told heartwire. "It's just a matter of getting the word out to physicians and patients that the technique and the technology are available."

Endomyocardial biopsies are an essential tool in the early detection of transplant rejection, but "they are not without risk," Mangion pointed out. In addition to the risk of infection, the bioptome, which snips out a piece of myocardium for analysis, can cause a rupture in the thin wall of the right heart and can lead to hematomas, which in turn can cause cardiac tamponade, and, if positioned improperly, it can damage the chordal apparatus of the tricuspid valve, she noted. The search for new noninvasive methods for detecting transplant rejection, using everything from blood tests, to different imaging modalities, to breathalyzers, has been dubbed the holy grail of transplant medicine.

Dr Soo Jin Cho and colleagues presented the results of their study during a poster session at the meeting. "Ultrasound speckle-tracking imaging will be an important tool as scientists continue to search for alternatives to invasive right ventricular endomyocardial biopsies," Cho commented in a press release.

For their study, Cho et al performed conventional echocardiograms and apical imaging at a high frame rate for speckle-tracking imaging in 17 consecutive heart-transplant patients who had also recently undergone a total of 42 endomyocardial biopsies. On biopsy, 26 samples showed no evidence of transplant rejection, whereas 16 indicated rejection of some degree. Echocardiograms showed no regional wall-motion abnormalities or changes in ejection fraction, but peak systolic longitudinal strain (PSLS), seen on speckle tracking, was reduced in all of the segments from patients diagnosed with rejection on biopsy, compared with those who had no evidence of rejection (-17.3%±2.2% vs -14.8%±1.6%; p<0.001).

"PSLS is one of the measurements that can be made with this speckle-tracking technology," Mangion explained. "Basically, strain is a measure of what happens to the myocardium when it contracts; the shortening during systole is what you're measuring during strain, and it shortens less if there is some form of rejection. In this study, the investigators saw less longitudinal strain when they looked at all the segments, and the mid and apical segments, in particular, were lower in these patients who had subacute rejection."

According to Cho et al, a receiver-operating characteristic analysis suggested that an average PSLS in all segments of less than -15.8% could predict rejection with a sensitivity and specificity of 78%.

Mangion pointed out that this sensitivity and specificity is as good as or better than some of the noninvasive tests regularly used in cardiovascular medicine.

"There's a lot of noninvasive testing that is routinely used that has specificity and sensitivity even lower than what we're seeing here," she said. "Plain old exercise-stress testing has a sensitivity of about 70% to 75% for picking up coronary disease and a specificity in the mid-70s as well."

Mangion noted that the four major cardiac ultrasound vendors already offer the ability to perform speckle-tracking imaging on their top-of-the-line machines; Toshiba is the first manufacturer to provide a 3D version of the technology.

"I think that this could replace a lot of biopsies," she said. "It would be valuable if you knew that your patient had perfectly normal PSLS of all segments and that the likelihood of rejection would be extremely low. If you had a patient who had evidence of rejection both clinically and echocardiographically, you might just go ahead and treat that patient without performing a biopsy. And if you had an asymptomatic patient who underwent this noninvasive technology and it suggested rejection, you could then subject the patient to a biopsy before aggressively treating them for that rejection."