PDA to RIMA Graft: Definition and Clinical Context
A PDA to RIMA graft is a coronary artery bypass configuration where the right internal mammary artery (RIMA) is used as a conduit to bypass the posterior descending artery (PDA), typically a branch of the right coronary artery system. This represents an arterial revascularization strategy that leverages the superior long-term patency of internal mammary arteries compared to saphenous vein grafts 1.
Anatomical and Technical Considerations
The posterior descending artery (PDA) supplies the inferior wall of the left ventricle and is most commonly a branch of the right coronary artery (in right-dominant systems). 2, 3
The RIMA can be used to graft the PDA through several technical approaches:
- In situ RIMA routing: The RIMA can be brought through the transverse sinus in a retroaortic course to reach the PDA and right coronary territory 1, 4
- Composite grafting: The RIMA can be used as a free graft connected to the left internal mammary artery (LIMA) in a Y-configuration, extending the reach to distal targets including the PDA 2, 3, 5
- Sequential grafting: The RIMA can be anastomosed to multiple targets including the PDA and posterolateral branches 3
Clinical Appropriateness and Guidelines
Arterial grafting of the right coronary artery territory (including the PDA) is only reasonable when critical stenosis (>90%) is present, as arterial grafts are prone to competitive flow-related failure in less severe stenoses. 1, 6
The ACC/AHA guidelines provide specific recommendations:
- Class IIb recommendation: Arterial grafting of the right coronary artery may be reasonable when a critical (>90%) stenosis is present 1
- Class III: HARM recommendation: An arterial graft should NOT be used to bypass the right coronary artery with less than critical stenosis (<90%) 1, 6
Rationale for Arterial Grafting to PDA
When anatomically and clinically suitable, use of a second internal mammary artery (such as RIMA to PDA) to graft critically stenosed vessels perfusing left ventricular myocardium is reasonable to improve survival and decrease reintervention. 1
The advantages include:
- Superior long-term patency: Internal mammary arteries maintain >90% patency at 10 years, compared to only 50-60% for saphenous vein grafts 1, 7
- Resistance to atherosclerosis: Only 4% of IMAs develop atherosclerosis versus the progressive deterioration seen in vein grafts 1
- Improved clinical outcomes: Bilateral internal mammary artery grafting demonstrates higher freedom from cardiac-related events compared to single IMA use 7, 4
Critical Technical Pitfalls to Avoid
The most important consideration is ensuring adequate target vessel stenosis severity—the PDA must have ≥90% stenosis to justify arterial grafting, otherwise competitive flow will cause graft failure through vasospasm and atrophy. 1, 6
Additional technical considerations:
- Graft length: The PDA location may require composite grafting techniques or use of the RIMA as a free graft to achieve adequate length 2, 3, 5
- Flow assessment: Intraoperative graft-free flow measurements can confirm adequate flow through composite configurations (mean flows of 98 mL/min have been reported for RIMA-radial artery composites) 3
- Sternal blood supply: When using RIMA, consider preserving the distal two-thirds to maintain sternal perfusion and reduce wound complications, particularly in diabetic, elderly, or obese patients 3
Alternative Conduit Considerations
If the PDA stenosis is <90%, saphenous vein grafting should be strongly considered over arterial grafting to avoid competitive flow-related graft failure. 1, 6
When RIMA is unavailable or unsuitable for PDA grafting:
- Saphenous vein grafts remain appropriate for moderately stenotic vessels or when arterial conduits are contraindicated 1
- Radial artery grafts can be used for right-sided vessels with critical stenoses (>90%) perfusing left ventricular myocardium, though they also require severe stenosis to prevent string sign 1