Effect of Using Bilateral Internal Mammary Artery on Long-Term Survival　– Reply –

We appreciate the insightful comments of Dr Gokalp and his colleagues regarding our report concerning the efficacy of bilateral internal mammary artery (BIMA) grafting in elderly patients aged 75 years or older.¹ At the time of our study, we were aware that the groups of elderly patients treated with a single internal mammary artery (SIMA) graft and those treated with a BIMA graft were not homogeneous with respect to important clinical factors, including age, sex ratio, the presence of hypertension, and the incidence of urgent surgery. As noted in our paper, we applied propensity scores to account for potential confounding variables and then compared late survival and freedom from major cardiac and cerebrovascular events (MACCEs) between the 2 matched groups. Furthermore, Cox proportional hazard modeling was performed to identify predictors of late mortality and MACCE. Any selection bias should have been adequately controlled for by these approaches.

Regarding surgical techniques, we began off-pump coronary artery bypass grafting (OPCAB) for multi-arterial grafting, including BIMA grafting, in 2001. Therefore, most of the BIMA grafting in the study patients was performed by off-pump technique. OPCAB was performed in 45.4% (133/293) of patients in the Elderly SIMA group and in 86.9% (93/107) of patients in the Elderly BIMA group (P<0.01). The 30-day mortality was 1.5% (2/133) for patients who underwent OPCAB in the Elderly SIMA group and 1.9% (3/160) for those who underwent on-pump CABG (P=0.82). In the Elderly BIMA group, the respective 30-day mortality rates were 0% (0/93) and 0% (0/14) (P=1.0). Early outcomes (30-day mortality and complication rates) of OPCAB and on-pump CABG were similar between the Elderly SIMA group and Elderly BIMA group. The 8-year survival of patients in the Elderly SIMA group who underwent OPCAB was 58.8±5.7%, and for patients who underwent on-pump CABG it was 49.1±4.2% (P=0.28). The 8-year survival in the Elderly BIMA group was 57.1±9.0% and 57.5±14.6%, respectively (P=0.78). As with the early outcomes, late outcomes (survival and MACCE-free survival) of OPCABG and on-pump CABG were comparable between the Elderly SIMA group and Elderly BIMA group.

As Dr Gokalp and colleagues suggested, MACCE-free survival was not shown to differ significantly in either the non-risk adjusted (P=0.085) or propensity score-matched elderly patients (P=0.051), despite the fact that 10-year survival differed.¹ We believe this discrepancy was due mainly to the relatively small total patient group (n=400). Cox proportional hazards analysis showed that use of a SIMA graft (non-use of a BIMA graft) increased the risk of late mortality. We believe that BIMA grafting can provide a survival benefit in elderly patients by reducing the risk of a fatal cardiac event.

• Satoshi Itoh, MD, PhD
• Naoyuki Kimura, MD, PhD
• Hideo Adachi, MD, PhD
• Atsushi Yamaguchi, MD, PhD
• Department of Cardiovascular Surgery, Saitama Medical Center, Jichi Medical University, Saitama, Japan

(Released online October 14, 2016)

Reference

• 1.    Itoh  S,  Kimura  N,  Adachi  H,  Yamaguchi  A. Is bilateral internal mammary arterial grafting beneficial for patients aged 75 years or older? Circ J 2016; 80: 1756–1763.