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HOUSTON -- Volume matters for short-term outcomes of multiple arterial coronary artery grafts, national registry data suggested.

Bilateral internal thoracic artery (BITA) use was associated with 14% elevated perioperative mortality risk and 2.09-fold higher risk of deep sternal wound infections after adjustment for other factors compared with the more common strategy of a single arterial graft with saphenous veins for the rest (P=0.050 and P<0.001, respectively).

Multiple grafts using the radial artery were not more risky for these outcomes in the adjusted analyses than using saphenous vein along with the left internal thoracic artery, , of the University of Toledo Medical Center in Ohio, reported here at the Society of Thoracic Surgeons meeting.

In both cases, getting the multi-arterial grafts at a center where these accounted for fewer than 5% of their procedures was associated with significantly elevated perioperative mortality.

Considered by institutional experience level, deep sternal wound infections were more common across the board of BITA use, whereas multi-arterial grafting with radial arteries was actually significantly protective at centers doing at least 20% of their procedures that way.

The researchers cautioned against overinterpreting the "marginally significant" and "modest" increased risk of mortality with BITA multi-arterial bypass grafting.

It "should in no way discourage BITA use and discount the long-term BITA survival advantage, especially if surgeons' familiarity with MABG [multi-arterial bypass graft] techniques and patient selection can be optimized," Schwann concluded.

"These grafting strategies should not be viewed as competitive," he added, "they should be viewed as complementary, because I think that we will be in the near future moving away from a one-size-fits-all approach, as we try to tailor the available specific grafting strategies that are becoming increasingly frequent and increasingly familiar to us, to specific patient subcohorts based on their specific demographics."

He noted it was "equally safe in appropriately selected CABG subcohorts," which according to the sensitivity analysis of subgroups included centers that did at least 20% of their procedures and more than 50 cases annually with BITA, off-pump cases, elective cases, mild or no chronic lung disease, no diabetes, no smoking, and age under 70.

But session moderator , of the Oregon Health and Sciences University in Portland, pointed out that in the radial versus single arterial graft comparison, the one significant variable "was not a patient factor but more or less a surgeon factor favoring off-pump. To me this suggests that, in addition to how old the patient is, whether or not they have diabetes, and so forth when you're selecting a grafting strategy that who you are, what your familiarity is with complex arterial grafting is as or more important."

He questioned whether that association was just a surrogate for very experienced surgeons.

Schwann agreed that such surgeons might have a greater case volume making them experts in both but noted that patient demographics could be at play as well, so the results pose questions that require further probing for mechanism.

"Importantly, we did not look at things like the incidence of MI, the incidence of stroke, the incidence of blood transfusions, the incidence of potential reoperations, et cetera, et cetera, that might give us a hint as to what the mechanisms might be behind these observations we identified," Schwann said.

The study included 1.49 million patients in the STS National Database for adult cardiac procedures from 2004 through 2015 who received primary, non-emergent, non-salvage, isolated CABG with the left internal thoracic artery and at least one other graft.

"Given the association of worse outcomes in low MABG use centers, there may be a quality improvement opportunity in optimizing surgeons' MABG learning curve and perhaps surgeons should choose coronary surgery as an area of further sub-specialization," Schwann suggested.

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