Coronary Artery Bypass Grafting to Acute Marginal Branch: Forgotten Coronary Artery

Abstract

Background

Current practice for coronary artery bypass grafting focuses on left ventricular function, whereas there is increasing recognition right ventricular dysfunction is associated with a higher risk of mortality and morbidity. We evaluated the impact of acute marginal branch (AMB) bypass on right ventricular function.

Methods

We reviewed 134 patients who underwent AMB bypass, comparing pre- and postoperative right heart catheter data. The surgical indication for AMB revascularization was multiple significant stenosis in right coronary artery across AMB or significant stenosis in AMB with lumen size of >1.5 mm.

Results

The median age was 63 years, and 97 were male. The median preoperative left ventricular ejection fraction was 55%, and 22% of patients had right ventricular dysfunction by echocardiography. One hundred twenty-one (90%) cases were done by off-pump. The median number of anastomoses was 5. Saphenous vein graft was used in most cases (96%) and mainly done in sequential fashion (84%). There was a significant reduction in right atrial pressure, and diastolic and mean pulmonary artery pressure. Conversely, there was a notable increase in pulmonary artery pulsatility index and cardiac index. Preoperative mean pulmonary artery pressure and preoperative pulmonary artery pulsatility index were identified as significant independent predictors of improved post-operative pulmonary artery pulsatility index.

Conclusions

Our initial investigation indicated coronary artery bypass grafting to AMB enhanced right ventricular function. This approach appeared to be advantageous for patients with preoperative pulmonary hypertension and right ventricular dysfunction. Additional research comparing coronary artery bypass grafting with and without AMB bypass is necessary to elucidate the true impact of this surgical intervention on right ventricular function and long-term survival.

Visual Abstract

In Short.

• ▪Coronary artery bypass grafting to acute marginal branch improved right ventricular function evaluated by right heart catheter.
• ▪This approach was more beneficial to patients with preoperative pulmonary hypertension and right ventricular dysfunction.

Historically, structures on the right side of the heart have tended to be ignored or forgotten, as the tricuspid valve has finally received attention compared to the mitral valve.¹ The same holds true for coronary artery bypass grafting (CABG) where current practice focuses on left ventricular function, while there is increasing recognition the presence of right ventricular (RV) dysfunction is associated with a higher risk of mortality and morbidity.²

Acute marginal branch (AMB) arises from the mid part of the right coronary artery (RCA) and provides the main blood supply to the RV free wall. Inferior wall myocardial infarction due to RCA occlusion proximal to AMB may be complicated by RV myocardial infarction resulting in severe hemodynamic compromise. It has been reported that complete revascularization of the RCA, including the major RV branch, was associated with a higher rate of RV function recovery and improved mortality.³

From these standpoints, it is reasonable to bypass AMB for the sake of better RV function; however, it is rarely performed in common practice, and data regarding the CABG to AMB remain sparse, which we sought to determine in this study.^4,5

Patients and Methods

Between 2012 and 2022, we bypassed 134 total AMBs. The right heart catheter (RHC) data were compared between pre- and postoperatively to evaluate the effect of bypassing AMB on RV function. Preoperative RHC data were obtained from the operating room after anesthesia induction. Postoperative data were gathered before Swan-Ganz catheter removal when inotrope support became no longer necessary. This study was approved by the Temple University institutional review board (protocol number: 32027; approved on November 15, 2024). Patient consent requirements were waived due to the minimal risk of the study.

Indications and Surgical Techniques

The surgical indication for AMB revascularization was multiple significant stenosis in the RCA across AMB or significant stenosis in the AMB with a lumen size of >1.5 mm (Figure 1).

Figure 1.

Different angle of the images of the right coronary artery angiogram shows diffuse significant stenosis across acute marginal branch (yellow arrow).

All cases were performed through median sternotomy. Graft configuration was decided depending on other coronary targets and the length of the free graft available. For AMB bypass, the Urchin Evo Heart Positioner (Medtronic) and Octopus Tissue Stabilizer (Medtronic) were used to expose and stabilize AMB.

Statistical Analysis

Categorical variables are shown as counts (percentages). Continuous variables are shown as the median (interquartile range). A paired t test was used for the comparison of pre- and postoperative RHC data. Predictors of having a better pulmonary artery pulsatility index (PAPi) postoperatively were assessed using univariate and multivariable logistic regression analysis. Variables with a P value <.10 in univariate analysis were incorporated into the multivariable analysis. A P value of less than .05 was considered significant. All statistical analyses were conducted with JMP Pro 15 software and SAS 9.4 (SAS Institute).

Results

Patient Characteristics

The baseline characteristics are shown in Supplemental Table 1. The median age was 63 years, and 97 (72%) were male. Seventy-six (57%) patients had acute coronary syndrome. The median preoperative left ventricle ejection fraction was 55%, and 26 patients (22%) had RV dysfunction by echocardiography.

Operative Findings

Intraoperative findings are summarized in Table 1. One hundred twenty-one (90%) cases were performed off-pump, and the remaining 13 cases (10%) were done by on-pump beating. The median number of distal anastomoses was 5 (range, 2-8). For AMB, saphenous vein graft was used in most cases (n = 129, 96%), and the rest of the cases were done with radial artery (n = 2), right internal mammary artery (n = 1), and left internal mammary artery (n = 1). AMB bypass was done in sequential fashion in 112 cases (84%) and isolated fashion in 22 cases (16%).

Table 1.

Intraoperative Findings

Variable	Value (N = 134)
Cardiopulmonary bypass
Off-pump	121 (90)
On-pump beating	13 (10)
Number of distal anastomosis	5 (4-6); range, 2-8
Graft conduit
Saphenous vein graft	129 (96)
Radial artery	2 (1.5)
Right internal mammary artery	2 (1.5)
Left internal mammary artery	1 (1)
Graft design	5 (20)
Sequential	112 (84)
Isolated	22 (16)
Size of shunt tube, mm	1.5 (1.25-1.5); range, 1-2.5

Data are presented as n (%) or median (interquartile range).

Right Heart Catheter Data

Pre- and postoperative RHC data are summarized in Table 2. Right atrial pressure (13.5 mm Hg to 9.9 mm Hg, P < .001), diastolic pulmonary artery pressure (PAP, 20.3 mm Hg to 16.2 mm Hg, P < .001), and mean PAP (25.5 mm Hg to 22.4 mm Hg, P < .001) were significantly decreased after the surgery. PAPi (1.39 to 3.01, P < .001) and cardiac index (2.21 L/min/m² to 2.87 L/min/m², P < .001) were significantly increased. The right ventricular stroke work index was not changed.

Table 2.

Right Heart Catheter Data

Variable	Preoperative	Postoperative	P Value
RAP, mm Hg	13.5	9.9	<.001
Systolic PAP, mm Hg	36.2	34.8	.175
Diastolic PAP, mm Hg	20.3	16.2	<.001
Mean PAP, mm Hg	25.6	22.4	<.001
PAPi	1.39	3.00	<.001
CO, L/min	4.3	5.61	<.001
CI, L/min/m2	2.2	2.9	<.001
RVSWI, g∗m/m2	5.59	5.65	.824

CI, cardiac index; CO, cardiac output, PAP, pulmonary artery pressure; PAPi, pulmonary artery pulsatility index; RAP, right atrium pressure; RVSWI, right ventricular stroke work index.

Factors Associated With Having Better Postoperative PAPi

Preoperative mean PAP (odds ratio, 1.32; P < .001) and preoperative PAPi (odds ratio, 0.30; P < .001) were the significant independent factors for better postoperative PAPi (Table 3).

Table 3.

Factors Associated With Improved PAPi

Factor	Univariate Analysis		Multivariable Analysis
	Odds Ratio (95% CI)	P Value	Odds Ratio (95% CI)	P Value
Age	1.01 (0.96-1.06)	.690
Male	1.20 (0.45-3.24)	.718
Number of anastomoses	0.82 (0.54-1.25)	.360
Off-pump	0.82 (0.17-4.07)	.809
Preop ejection fraction	0.99 (0.96-1.02)	.376
RV dysfunction by echocardiography	2.04 (0.55-7.63)	.288
Preop mPAP	1.34 (1.17-1.52)	<.001	1.32 (1.15-1.52)	<.001
Preop PAPi	0.31 (0.17-0.57)	<.001	0.30 (0.14-0.64)	.002
Preop CI	0.88 (0.37-2.08)	.770
Preop RVSWI	1.17 (0.94-1.44)	.154

CI, cardiac index; mPAP, mean pulmonary arterial pressure; PAPi, pulmonary artery pulsatility index; Preop, preoperative; RV, right ventricular; RVSWI, right ventricular stroke work index.

Comment

This study of 134 AMB bypasses demonstrated that CABG to AMB improved RV function evaluated by RHC. Multivariate analysis suggests that it is more beneficial for patients who have preoperative pulmonary hypertension and RV dysfunction. While more attention has been drawn to RV function in CABG, this strategy might shed light on better postoperative outcomes.

Historically, it has been reported that RV function declines after CABG, however, most of the causes examined were not specifically related to CABG, such as cardiopulmonary bypass, cardioplegia, and pericardial disruption/adhesion.6, 7, 8 Recently, it has begun attracting more attention that the presence of RV dysfunction is not uncommon, and it is also independently associated with a higher risk of morbidities and mortalities. A post hoc analysis of the STICH (Surgical Treatment for Ischemic Heart Failure) trial showed RV dysfunction was associated with a worse prognosis in patients with ischemic cardiomyopathy, and interestingly, CABG provided no additional survival benefits to patients with moderate-to-severe RV dysfunction.² CABG to AMB has been studied by the Turkish groups led by Ozerdem⁴ and Sahin.⁵ Sahin and colleauges⁵ compared RV function with echocardiogram between patients with single distal RCA bypass and patients with distal RCA and additional bypass on AMB. They concluded that an additional graft on the RV branch prevented severe RV dysfunction after surgery and allowed for rapid recovery of RV dysfunction. Our results were concordant with theirs and demonstrated that RV function even improved after CABG with AMB bypass. Further studies are warranted regarding the long-term benefits of this surgery.

Identifying patients best suited for AMB revascularization is necessary as additional grafts may increase operative time and the associated sequelae of CABG surgery. We found that preoperative RV function by PAPi as well as preoperative pulmonary hypertension by mean PAP were both independent predictors of improved RV function after AMB. As the AMB provides proximal RV blood flow, it seems logical that those with preoperative impaired RV function would benefit the most from revascularization. This is supported by our finding that the number of anastomoses performed did not correlate with improved post-CABG RV function, suggesting that it is likely that the AMB was the graft responsible for postoperative RV improvement. Interestingly, in our study, neither LV nor RV function by echocardiography helped to identify those best suited for AMB revascularization, highlighting the utility of preoperative RHC. While additional work is needed to assess the long-term benefit of AMB, at least in the immediate postoperative period, pulmonary hypertension and RV dysfunction seem to be strong indicators to consider AMB when feasible.

On-pump vs off-pump is the neverending discussion. It is a well-known fact that the original ROOBY (Randomized On/Off Bypass) trial reported the number of bypasses performed in the off-pump group was considerably lower than that of the on-pump group.⁹ Although 90% of our cases were performed by off-pump, the median number of distal anastomosis was 5, and it was much higher than in the ROOBY trial (around 3). If AMB bypass was done by on-pump arrest CABG, adding 1 more distal anastomosis will make aortic cross-clamp time longer, which may attribute to worsening RV dysfunction. In case patients don’t tolerate off-pump CABG, we use CPB but do not arrest the heart to avoid ischemic time. To achieve better RV function, surgeons need to be experts in off-pump CABG.

The present study has several limitations. First, this was a single-center, retrospective observational study, which confers an inherent selection bias. Second, we did not have a control group of patients who had multiple stenosis in RCA or severe stenosis in AMB but did not undergo AMB bypass. Thus, it is uncertain whether this improved RV function was because of AMB bypass. In addition, we did not have a postoperative coronary angiogram. Graft patency was unknown. Third, preoperative RHC data were obtained under general anesthesia and postoperative RHC data were obtained prior to Swan-Ganz catheter removal (most patients were already extubated). While comparison under same condition would be ideal, there was controversy of whether positive airway pressure leads to a decrease RV function.¹⁰ And last, we did not have other granular data sets for RV function, such as echocardiogram or cardiac magnetic resonance imaging. While we highlighted the importance of RHC in this study, the use of echocardiogram should not be undervalued since our data was not thorough. All of these are well considered to be included for future comparative study.

In conclusion, our preliminary study showed CABG to AMB improved RV function. It seemed more beneficial for preoperative pulmonary hypertension and RV dysfunction. Further studies comparing CABG with and without AMB are planned and warranted to clarify the real effect of this surgery on RV function and long-term survival.