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.