VANCOUVER, BC — New research lends support for the use of multiple arterial grafting in a broad spectrum of patients undergoing CABG, including many higher-risk subgroups[1].
The observational study of more than 20,000 patients showed a 21% decrease in 15-year mortality with multiple arterial grafting (MAG) compared with standard CABG using the left internal thoracic artery (LITA) supplemented by saphenous vein grafts (SVGs) (adjusted cumulative incidence 27% vs 32.1%; adjusted hazard ratio [HR] 0.79; 95% CI 0.72–0.87).
This association remained significant regardless of whether patients had diabetes, obesity, renal disease, or a moderately impaired ejection fraction (35%–50%).
Mortality also trended lower among patients with peripheral vascular disease, chronic obstructive pulmonary disease, or advanced age (>70 years), although no survival benefit was seen for those with an ejection fraction of less than 35%, according to the study, published online in JAMA Cardiology.
“If you look at the mortality curves in the low-ejection-fraction group at 15 years, it’s pretty substantial, at about 60%, so death is a competing risk, and the same is true for those 70 years and older,” senior author Dr James G Abel (St Paul’s Hospital, Vancouver, BC) told theheart.org | Medscape Cardiology.
MAG using either the right internal thoracic artery (RITA) or radial artery (RA) in addition to the LITA was also associated with a 26% reduction in repeat revascularization at 15 years (adjusted cumulative incidence 14.7% vs 19.6%; adjusted HR 0.74; 95% CI 0.66–0.84). The association was significant in all subgroups, except for those with an ejection fraction below 35% or aged at least 70 years.
“I think this gives surgeons a lot of information that patients actually do benefit in these subgroups and the question is at what risk,” Abel said.
The recent randomized ART trial surprised many when it reported no 5-year mortality benefit from bilateral vs single internal-mammary-artery grafting and a threefold higher need for sternal wound reconstruction with bilateral grafting (1.9% vs 0.6%).
Among short-term adverse outcomes in the present study, only sternal reconstruction within 180 days was higher with the MAG strategy (1.9% vs 1.1%; P=0.02), and this was predominantly when using the RITA rather than RA (2.5% vs 0.6%; P<0.001).
Short-term Outcomes*
<
| Outcome | MAG LITA+SVG (%) | MAG (%) | Relative risk (95% CI) |
|---|---|---|---|
| 30-d mortality | 0.6 | 0.6 | 0.99 (0.61–1.62) |
| 30-d repeat revascularization | 0.4 | 0.4 | 1.13 (0.62–2.06) |
| 30-d MI | 1.0 | 0.8 | 0.80 (0.45–1.42) |
| 30-d stroke | 0.8 | 0.6 | 0.76 (0.40–1.47) |
| 30-d heart failure | 2.3 | 2.4 | 1.04 (0.73–1.49) |
| 30-d reoperation for bleeding | 2.2 | 2.0 | 0.90 (0.69–1.16) |
| In-hospital post-op dialysis | 0.5 | 0.3 | 0.64 (0.35–1.18) |
| 30-d sternal reconstruction | 1.0 | 1.2 | 1.24 (0.72–2.13) |
| 180-d sternal reconstruction | 1.1 | 1.9 | 1.76 (1.10–2.81) |
|
*Adjusted cumulative incidences and relative risks with 7 years follow-up. LITA=left internal thoracic artery SVG=saphenous vein graft MAG=Multiple arterial grafting |
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“Again, this gives the surgeon information that if he or she wants a long-term strategy for a morality benefit, they can use the radial artery as a secondary conduit without the increased risk, maybe double the risk, of a sternal complication,” Abel said. “But that risk is still absolutely low if you took down both internal thoracic arteries.”
Commenting to theheart.org | Medscape Cardiology, ART lead investigator Prof David Taggart (University of Oxford, UK) said, “If you have a population with a high proportion of diabetes and obesity, then of course you have to be very careful taking both ITA grafts because of the risk of sternal wound problems, but technically there’s absolutely no difference in harvesting the right ITA and the left ITA.”
He added that “I’ve never really quite understood the profound reluctance to use two ITA grafts,” particularly in light of years of observational data showing a survival benefit over vein grafts and very strong angiographic evidence of superior patency at 10, even 20, years of follow-up.
“So we still think with long-term follow-up there may still be a benefit of ITA grafts, and that’s perhaps what the Canadian group is showing because of the long-term follow-up,” said Taggart, who noted that 10-year data from ART will be reported in early to mid-2018.
Abel observed that the broad use of MAG in Canada, which ranged from 23% to 36% during the study vs about 10% of CABG patients in the US, provided a unique opportunity to examine real-world MAG use in specific subgroups and rarely reported outcomes like repeat revascularization or sternal reconstruction out to 180 days.
The cohort included 20,076 patients with triple-vessel or left-main coronary disease who underwent isolated CABG in British Columbia between January 2000 and December 2014, with follow-up through December 2015. Of these, 5580 patients received MAG (n=3056 RITA; n=2524 RA) and 14,496 patients received LITA plus SVG.
Among the RITA-MAG patients, 40.5% received an RA in addition to the bilateral internal thoracic arteries. None of the LITA-SVG group received a supplemental RA graft. Median follow-up was 9.1 years for the MAG group and 8.1 for the LITA/SVT group.
The primary outcomes were all-cause mortality and repeat revascularization. Hospitalization data were available from April 2007 to March 2015 for 10,545 patients in the cohort and used for secondary outcomes analyses.
Patients receiving MAG rather than LITA-SVG were younger (mean age 60 years vs 68 years), more likely to be male (89.5% vs 80.7%), and less likely to have an ejection fraction <35% (5% vs 9.5%) or comorbidities such as renal disease, COPD, and diabetes.
To minimize the effect of potential confounders and treatment selection bias, the investigators, led by Aihua Pu MSc (Cardiac Services BC, Vancouver) performed propensity-score analyses by weighting and matching and multivariable Cox regression analyses.
The potential for residual confounding is the main limitation of the study, but a lack of an association between MAG and falsification end points suggests patients who received MAG were not systematically healthier after adjustment, and therefore the observed MAG benefit is less likely to be due to residual confounding, Abel said.
“It’s always of course a criticism of an observation study, but a criticism of a randomized trial is that they’re not generalizable because of the specific entry requirements,” he added. “For instance, in ART, both internal thoracic arteries had to go to the left-sided arteries in the heart, and that isn’t the case in our study. The surgeon could put them anywhere that was best for reach or the specific coronary anatomy.”
Still, many US surgeons are hesitant to use MAG, so should they wait for the 10-year data from ART before adopting MAG?
“No,” Abel said. “I think the hope with ART was that it was going to be positive and people are still hoping it will be, but there’s a substantial base of observational evidence that surgeons are doing their patients a favor by using a second arterial graft. And, now there’s more evidence that the radial artery is a very excellent second arterial graft as well as the second internal thoracic artery.”
Taggart said that there was a trend toward a survival benefit at 5 years in ART in patients under the age of 70 that almost reached statistical significance, “and if that shows a benefit at 10 years, I think that will be an important game changer.”
The study was supported by Cardiac Services, British Columbia. The authors and Taggart reported no relevant financial relationships.
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