Discussion:
The REQUEST trial reported that the use of high-frequency ultrasound (HFUS) is not only helpful for evaluating coronary targets, but that physicians should consider incorporating it into their usual practice for CABG surgery.(1) Higher frequency probes (55 Mhz) have been used to examine temporal arteries in the setting of Giant Cell disease, with greater resolution allowing for accurate assessment of intima layer thickness that correlated with histological diagnosis.(3)
As the probe frequency increases, image resolution improves while sound penetration decreases.(2) Therefore, the use of UFHUS for epicoronary scanning presents a theoretical benefit over lower-frequency probes, yet no comparison of image quality was performed during this case. While our probe was rated up to 70 Mhz frequency, a frequency of 50 Mhz was used in order to achieve appropriate ultrasound penetration depth of 5.5mm for epicoronary scanning. In our case, the UFHUS allowed for real-time evaluation of the extensive native coronary calcification during cardiopulmonary bypass. It can often be challenging to assess this in an arrested heart, and inadvertent selection of a distal graft site with heavy calcification requiring endarterectomy may lead to lower long-term patency. In addition to serving as an imaging aid for selection of acceptable graft target sites, other potential applications of UFHUS epicoronary scanning include confirming cardioplegia flow in the setting of low coronary sinus pressures and appraising distal coronary flow post-revascularization.
To our knowledge, this is the first report of the use of UFHUS for epicoronary scanning in CABG surgery. Further study is necessary to compare the efficacy of UFHUS versus high frequency ultrasound for use in epicoronary scanning during CABG surgery.